1
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Rahimi S, Salami P, Matulewicz P, Schmuck A, Bukovac A, Ramos-Prats A, Tasan RO, Drexel M. The role of subicular VIP-expressing interneurons on seizure dynamics in the intrahippocampal kainic acid model of temporal lobe epilepsy. Exp Neurol 2023; 370:114580. [PMID: 37884187 DOI: 10.1016/j.expneurol.2023.114580] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2023] [Revised: 10/10/2023] [Accepted: 10/21/2023] [Indexed: 10/28/2023]
Abstract
The subiculum, a key output region of the hippocampus, is increasingly recognized as playing a crucial role in seizure initiation and spread. The subiculum consists of glutamatergic pyramidal cells, which show alterations in intrinsic excitability in the course of epilepsy, and multiple types of GABAergic interneurons, which exhibit varying characteristics in epilepsy. In this study, we aimed to assess the role of the vasoactive intestinal peptide interneurons (VIP-INs) of the ventral subiculum in the pathophysiology of temporal lobe epilepsy. We observed that an anatomically restricted inhibition of VIP-INs of the ventral subiculum was sufficient to reduce seizures in the intrahippocampal kainic acid model of epilepsy, changing the circadian rhythm of seizures, emphasizing the critical role of this small cell population in modulating TLE. As we expected, permanent unilateral or bilateral silencing of VIP-INs of the ventral subiculum in non-epileptic animals did not induce seizures or epileptiform activity. Interestingly, transient activation of VIP-INs of the ventral subiculum was enough to increase the frequency of seizures in the acute seizure model. Our results offer new perspectives on the crucial involvement of VIP-INs of the ventral subiculum in the pathophysiology of TLE. Given the observed predominant disinhibitory role of the VIP-INs input in subicular microcircuits, modifications of this input could be considered in the development of therapeutic strategies to improve seizure control.
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Affiliation(s)
- Sadegh Rahimi
- Department of Pharmacology, Medical University of Innsbruck, Innsbruck, Austria
| | - Pariya Salami
- Department of Neurology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
| | - Pawel Matulewicz
- Department of Pharmacology, Medical University of Innsbruck, Innsbruck, Austria
| | - Armin Schmuck
- Department of Pharmacology, Medical University of Innsbruck, Innsbruck, Austria
| | - Anneliese Bukovac
- Department of Pharmacology, Medical University of Innsbruck, Innsbruck, Austria
| | - Arnau Ramos-Prats
- Department of Pharmacology, Medical University of Innsbruck, Innsbruck, Austria
| | - Ramon Osman Tasan
- Department of Pharmacology, Medical University of Innsbruck, Innsbruck, Austria
| | - Meinrad Drexel
- Department of Pharmacology, Medical University of Innsbruck, Innsbruck, Austria.
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2
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Samalens L, Courivaud C, Adam JF, Barbier EL, Serduc R, Depaulis A. Innovative minimally invasive options to treat drug-resistant epilepsies. Rev Neurol (Paris) 2023:S0035-3787(23)01038-X. [PMID: 37798162 DOI: 10.1016/j.neurol.2023.05.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2023] [Revised: 03/20/2023] [Accepted: 05/14/2023] [Indexed: 10/07/2023]
Abstract
Despite the regular discovery of new molecules, one-third of epileptic patients are resistant to antiepileptic drugs. Only a few can benefit from resective surgery, the current gold standard. Although effective in 50-70% of cases, this therapy remains risky, costly, and can be associated with long-term cognitive or neurological side effects. In addition, patients are increasingly reluctant to have a craniotomy, emphasizing the need for new less invasive therapies for focal drug-resistant epilepsies. Here, we review different minimally invasive approaches already in use in the clinic or under preclinical development to treat drug-resistant epilepsies. Localized thermolesion of the epileptogenic zone has been developed in the clinic using high-frequency thermo-coagulations or magnetic resonance imaging-guided laser or ultrasounds. Although less invasive, they have not yet significantly improved the outcomes when compared with resective surgery. Radiosurgery techniques have been used in the clinic for the last 20years and have proven efficiency. However, their efficacy is not better than resective surgery, and various side effects have been reported as well as the potential risk of sudden unexpected death associated with epilepsy. Recently, a new strategy of radiosurgery has emerged using synchrotron-generated X-ray microbeams: microbeam radiation therapy (MRT). The low divergence and high-flux of the synchrotron beams and the unique tolerance to MRT by healthy brain tissues, allows a precise targeting of specific brain regions with minimal invasiveness and limited behavioral or functional consequences in animals. Antiepileptic effects over several months have been recorded in animal models, and histological and synaptic tracing analysis suggest a reduction of neuronal connectivity as a mechanism of action. The possibility of transferring this approach to epileptic patients is discussed in this review.
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Affiliation(s)
- L Samalens
- Université Grenoble-Alpes, Inserm, U1216, Grenoble Institut Neurosciences, 38000 Grenoble, France; Université Grenoble-Alpes, Inserm, UA7, STROBE, 38000 Grenoble, France
| | - C Courivaud
- Université Grenoble-Alpes, Inserm, U1216, Grenoble Institut Neurosciences, 38000 Grenoble, France
| | - J-F Adam
- Université Grenoble-Alpes, Inserm, UA7, STROBE, 38000 Grenoble, France; Centre Hospitalier Universitaire Grenoble-Alpes, 38700 La Tronche, France
| | - E L Barbier
- Université Grenoble-Alpes, Inserm, U1216, Grenoble Institut Neurosciences, 38000 Grenoble, France
| | - R Serduc
- Université Grenoble-Alpes, Inserm, UA7, STROBE, 38000 Grenoble, France
| | - A Depaulis
- Université Grenoble-Alpes, Inserm, U1216, Grenoble Institut Neurosciences, 38000 Grenoble, France.
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3
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Bod R, Tóth K, Essam N, Tóth EZ, Erõss L, Entz L, Bagó AG, Fabó D, Ulbert I, Wittner L. Synaptic alterations and neuronal firing in human epileptic neocortical excitatory networks. Front Synaptic Neurosci 2023; 15:1233569. [PMID: 37635750 PMCID: PMC10450510 DOI: 10.3389/fnsyn.2023.1233569] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2023] [Accepted: 07/25/2023] [Indexed: 08/29/2023] Open
Abstract
Epilepsy is a prevalent neurological condition, with underlying neuronal mechanisms involving hyperexcitability and hypersynchrony. Imbalance between excitatory and inhibitory circuits, as well as histological reorganization are relatively well-documented in animal models or even in the human hippocampus, but less is known about human neocortical epileptic activity. Our knowledge about changes in the excitatory signaling is especially scarce, compared to that about the inhibitory cell population. This study investigated the firing properties of single neurons in the human neocortex in vitro, during pharmacological blockade of glutamate receptors, and additionally evaluated anatomical changes in the excitatory circuit in tissue samples from epileptic and non-epileptic patients. Both epileptic and non-epileptic tissues exhibited spontaneous population activity (SPA), NMDA receptor antagonization reduced SPA recurrence only in epileptic tissue, whereas further blockade of AMPA/kainate receptors reversibly abolished SPA emergence regardless of epilepsy. Firing rates did not significantly change in excitatory principal cells and inhibitory interneurons during pharmacological experiments. Granular layer (L4) neurons showed an increased firing rate in epileptic compared to non-epileptic tissue. The burstiness of neurons remained unchanged, except for that of inhibitory cells in epileptic recordings, which decreased during blockade of glutamate receptors. Crosscorrelograms computed from single neuron discharge revealed both mono- and polysynaptic connections, particularly involving intrinsically bursting principal cells. Histological investigations found similar densities of SMI-32-immunopositive long-range projecting pyramidal cells in both groups, and shorter excitatory synaptic active zones with a higher proportion of perforated synapses in the epileptic group. These findings provide insights into epileptic modifications from the perspective of the excitatory system and highlight discrete alterations in firing patterns and synaptic structure. Our data suggest that NMDA-dependent glutamatergic signaling, as well as the excitatory synaptic machinery are perturbed in epilepsy, which might contribute to epileptic activity in the human neocortex.
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Affiliation(s)
- Réka Bod
- Institute of Cognitive Neuroscience and Psychology, Research Centre for Natural Sciences, Eötvös Loránd Research Network, Budapest, Hungary
- Semmelweis University Doctoral School, Budapest, Hungary
| | - Kinga Tóth
- Institute of Cognitive Neuroscience and Psychology, Research Centre for Natural Sciences, Eötvös Loránd Research Network, Budapest, Hungary
| | - Nour Essam
- Institute of Cognitive Neuroscience and Psychology, Research Centre for Natural Sciences, Eötvös Loránd Research Network, Budapest, Hungary
| | - Estilla Zsófia Tóth
- Institute of Cognitive Neuroscience and Psychology, Research Centre for Natural Sciences, Eötvös Loránd Research Network, Budapest, Hungary
- Semmelweis University Doctoral School, Budapest, Hungary
| | - Loránd Erõss
- National Institute of Mental Health, Neurology and Neurosurgery, Budapest, Hungary
| | - László Entz
- National Institute of Mental Health, Neurology and Neurosurgery, Budapest, Hungary
| | - Attila G. Bagó
- National Institute of Mental Health, Neurology and Neurosurgery, Budapest, Hungary
| | - Dániel Fabó
- National Institute of Mental Health, Neurology and Neurosurgery, Budapest, Hungary
| | - István Ulbert
- Institute of Cognitive Neuroscience and Psychology, Research Centre for Natural Sciences, Eötvös Loránd Research Network, Budapest, Hungary
- Semmelweis University Doctoral School, Budapest, Hungary
- National Institute of Mental Health, Neurology and Neurosurgery, Budapest, Hungary
- Faculty of Information Technology and Bionics, Pázmány Péter Catholic University, Budapest, Hungary
| | - Lucia Wittner
- Institute of Cognitive Neuroscience and Psychology, Research Centre for Natural Sciences, Eötvös Loránd Research Network, Budapest, Hungary
- Semmelweis University Doctoral School, Budapest, Hungary
- National Institute of Mental Health, Neurology and Neurosurgery, Budapest, Hungary
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4
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Franz J, Barheier N, Wilms H, Tulke S, Haas CA, Häussler U. Differential vulnerability of neuronal subpopulations of the subiculum in a mouse model for mesial temporal lobe epilepsy. Front Cell Neurosci 2023; 17:1142507. [PMID: 37066079 PMCID: PMC10090355 DOI: 10.3389/fncel.2023.1142507] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2023] [Accepted: 03/06/2023] [Indexed: 03/30/2023] Open
Abstract
Selective loss of inhibitory interneurons (INs) that promotes a shift toward an excitatory predominance may have a critical impact on the generation of epileptic activity. While research on mesial temporal lobe epilepsy (MTLE) has mostly focused on hippocampal changes, including IN loss, the subiculum as the major output region of the hippocampal formation has received less attention. The subiculum has been shown to occupy a key position in the epileptic network, but data on cellular alterations are controversial. Using the intrahippocampal kainate (KA) mouse model for MTLE, which recapitulates main features of human MTLE such as unilateral hippocampal sclerosis and granule cell dispersion, we identified cell loss in the subiculum and quantified changes in specific IN subpopulations along its dorso-ventral axis. We performed intrahippocampal recordings, FluoroJade C-staining for degenerating neurons shortly after status epilepticus (SE), fluorescence in situ hybridization for glutamic acid decarboxylase (Gad) 67 mRNA and immunohistochemistry for neuronal nuclei (NeuN), parvalbumin (PV), calretinin (CR) and neuropeptide Y (NPY) at 21 days after KA. We observed remarkable cell loss in the ipsilateral subiculum shortly after SE, reflected in lowered density of NeuN+ cells in the chronic stage when epileptic activity occurred in the subiculum concomitantly with the hippocampus. In addition, we show a position-dependent reduction of Gad67-expressing INs by ∼50% (along the dorso-ventral as well as transverse axis of the subiculum). This particularly affected the PV- and to a lesser extent CR-expressing INs. The density of NPY-positive neurons was increased, but the double-labeling for Gad67 mRNA expression revealed that an upregulation or de novo expression of NPY in non-GABAergic cells with a concomitant reduction of NPY-positive INs underlies this observation. Our data suggest a position- and cell type-specific vulnerability of subicular INs in MTLE, which might contribute to hyperexcitability of the subiculum, reflected in epileptic activity.
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Affiliation(s)
- Julia Franz
- Experimental Epilepsy Research, Department of Neurosurgery, Faculty of Medicine, Medical Center-University of Freiburg, Freiburg, Germany
| | - Nicole Barheier
- Experimental Epilepsy Research, Department of Neurosurgery, Faculty of Medicine, Medical Center-University of Freiburg, Freiburg, Germany
- Faculty of Biology, University of Freiburg, Freiburg, Germany
| | - Henrike Wilms
- Experimental Epilepsy Research, Department of Neurosurgery, Faculty of Medicine, Medical Center-University of Freiburg, Freiburg, Germany
| | - Susanne Tulke
- Experimental Epilepsy Research, Department of Neurosurgery, Faculty of Medicine, Medical Center-University of Freiburg, Freiburg, Germany
| | - Carola A. Haas
- Experimental Epilepsy Research, Department of Neurosurgery, Faculty of Medicine, Medical Center-University of Freiburg, Freiburg, Germany
- Center for Basics in NeuroModulation, Faculty of Medicine, University of Freiburg, Freiburg, Germany
- BrainLinks-BrainTools, University of Freiburg, Freiburg, Germany
| | - Ute Häussler
- Experimental Epilepsy Research, Department of Neurosurgery, Faculty of Medicine, Medical Center-University of Freiburg, Freiburg, Germany
- BrainLinks-BrainTools, University of Freiburg, Freiburg, Germany
- *Correspondence: Ute Häussler,
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5
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Fei F, Wang X, Xu C, Shi J, Gong Y, Cheng H, Lai N, Ruan Y, Ding Y, Wang S, Chen Z, Wang Y. Discrete subicular circuits control generalization of hippocampal seizures. Nat Commun 2022; 13:5010. [PMID: 36008421 PMCID: PMC9411516 DOI: 10.1038/s41467-022-32742-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Accepted: 08/15/2022] [Indexed: 11/09/2022] Open
Abstract
Epilepsy is considered a circuit-level dysfunction associated with imbalanced excitation-inhibition, it is therapeutically necessary to identify key brain regions and related circuits in epilepsy. The subiculum is an essential participant in epileptic seizures, but the circuit mechanism underlying its role remains largely elusive. Here we deconstruct the diversity of subicular circuits in a mouse model of epilepsy. We find that excitatory subicular pyramidal neurons heterogeneously control the generalization of hippocampal seizures by projecting to different downstream regions. Notably, anterior thalamus-projecting subicular neurons bidirectionally mediate seizures, while entorhinal cortex-projecting subicular neurons act oppositely in seizure modulation. These two subpopulations are structurally and functionally dissociable. An intrinsically enhanced hyperpolarization-activated current and robust bursting intensity in anterior thalamus-projecting neurons facilitate synaptic transmission, thus contributing to the generalization of hippocampal seizures. These results demonstrate that subicular circuits have diverse roles in epilepsy, suggesting the necessity to precisely target specific subicular circuits for effective treatment of epilepsy.
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Affiliation(s)
- Fan Fei
- Institute of Pharmacology and Toxicology, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China
| | - Xia Wang
- Institute of Pharmacology and Toxicology, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China
| | - Cenglin Xu
- Key Laboratory of Neuropharmacology and Translational Medicine of Zhejiang Province, School of Pharmaceutical Sciences, Zhejiang Chinese Medical University, Hangzhou, China.
| | - Jiaying Shi
- Institute of Pharmacology and Toxicology, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China
| | - Yiwei Gong
- Institute of Pharmacology and Toxicology, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China.,Key Laboratory of Neuropharmacology and Translational Medicine of Zhejiang Province, School of Pharmaceutical Sciences, Zhejiang Chinese Medical University, Hangzhou, China
| | - Heming Cheng
- Key Laboratory of Neuropharmacology and Translational Medicine of Zhejiang Province, School of Pharmaceutical Sciences, Zhejiang Chinese Medical University, Hangzhou, China
| | - Nanxi Lai
- Institute of Pharmacology and Toxicology, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China
| | - Yeping Ruan
- Key Laboratory of Neuropharmacology and Translational Medicine of Zhejiang Province, School of Pharmaceutical Sciences, Zhejiang Chinese Medical University, Hangzhou, China
| | - Yao Ding
- Epilepsy Center, Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, China
| | - Shuang Wang
- Epilepsy Center, Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, China
| | - Zhong Chen
- Institute of Pharmacology and Toxicology, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China. .,Key Laboratory of Neuropharmacology and Translational Medicine of Zhejiang Province, School of Pharmaceutical Sciences, Zhejiang Chinese Medical University, Hangzhou, China. .,Epilepsy Center, Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, China.
| | - Yi Wang
- Institute of Pharmacology and Toxicology, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China. .,Key Laboratory of Neuropharmacology and Translational Medicine of Zhejiang Province, School of Pharmaceutical Sciences, Zhejiang Chinese Medical University, Hangzhou, China. .,Epilepsy Center, Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, China.
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6
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Ciolac D, Gonzalez-Escamilla G, Winter Y, Melzer N, Luessi F, Radetz A, Fleischer V, Groppa SA, Kirsch M, Bittner S, Zipp F, Muthuraman M, Meuth SG, Grothe M, Groppa S. Altered grey matter integrity and network vulnerability relate to epilepsy occurrence in patients with multiple sclerosis. Eur J Neurol 2022; 29:2309-2320. [PMID: 35582936 DOI: 10.1111/ene.15405] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Revised: 03/22/2022] [Accepted: 05/13/2022] [Indexed: 11/29/2022]
Abstract
BACKGROUND To investigate the relevance of compartmentalized grey matter (GM) pathology and network reorganization in MS patients with concomitant epilepsy. METHODS From 3T MRI scans of 30 MS patients with epilepsy (MSE; age 41±15 years, 21 females, disease duration 8±6 years, median Expanded Disability Status Scale (EDSS) 3), 60 MS patients without epilepsy (MS; age 41±12 years, 35 females, disease duration 6±4 years, EDSS 2), and 60 healthy subjects (HS; age 40±13 years, 27 females) regional volumes of GM lesions and of cortical, subcortical, and hippocampal structures were quantified. Network topology and vulnerability were modeled within the graph theoretical framework. The receiver operating characteristic (ROC) analysis was applied to assess the accuracy of GM pathology measures to discriminate between MSE and MS patients. RESULTS Higher lesion volumes within the hippocampus, mesiotemporal cortex, and amygdala were detected in MSE compared to MS (all p<0.05). MSE displayed lower cortical volumes mainly in temporal and parietal areas compared to MS and HS (all p<0.05). Lower volumes of hippocampal tail and presubiculum were identified in both MSE and MS patients compared to HS (all p<0.05). Network topology in MSE was characterized by higher transitivity and assortativity, and higher vulnerability compared to MS and HS (all p<0.05). Hippocampal lesion volume yielded the highest accuracy (area under the ROC curve 0.80 [0.67-0.91]) in discriminating between MSE and MS patients. CONCLUSIONS High lesion load, altered integrity of mesiotemporal GM structures, and network reorganization are associated with a greater propensity of epilepsy occurrence in MS.
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Affiliation(s)
- Dumitru Ciolac
- Department of Neurology, Focus Program Translational Neuroscience (FTN), Rhine-Main Neuroscience Network (rmn2), University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany.,Nicolae Testemitanu State University of Medicine and Pharmacy, Chisinau, Republic of Moldova.,Department of Neurology, Institute of Emergency Medicine, Chisinau, Republic of Moldova
| | - Gabriel Gonzalez-Escamilla
- Department of Neurology, Focus Program Translational Neuroscience (FTN), Rhine-Main Neuroscience Network (rmn2), University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Yaroslav Winter
- Mainz Comprehensive Epilepsy and Sleep Medicine Center, Department of Neurology, Johannes Gutenberg University Mainz, Mainz, Germany.,Department of Neurology, Philipps-University, Marburg, Germany
| | - Nico Melzer
- Department of Neurology, Heinrich Heine University, Düsseldorf, Germany
| | - Felix Luessi
- Department of Neurology, Focus Program Translational Neuroscience (FTN), Rhine-Main Neuroscience Network (rmn2), University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Angela Radetz
- Department of Neurology, Focus Program Translational Neuroscience (FTN), Rhine-Main Neuroscience Network (rmn2), University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Vinzenz Fleischer
- Department of Neurology, Focus Program Translational Neuroscience (FTN), Rhine-Main Neuroscience Network (rmn2), University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Stanislav A Groppa
- Nicolae Testemitanu State University of Medicine and Pharmacy, Chisinau, Republic of Moldova.,Department of Neurology, Institute of Emergency Medicine, Chisinau, Republic of Moldova
| | - Michael Kirsch
- Institute for Diagnostic Radiology and Neuroradiology, University Medicine of Greifswald, Germany
| | - Stefan Bittner
- Department of Neurology, Focus Program Translational Neuroscience (FTN), Rhine-Main Neuroscience Network (rmn2), University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Frauke Zipp
- Department of Neurology, Focus Program Translational Neuroscience (FTN), Rhine-Main Neuroscience Network (rmn2), University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Muthuraman Muthuraman
- Department of Neurology, Focus Program Translational Neuroscience (FTN), Rhine-Main Neuroscience Network (rmn2), University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Sven G Meuth
- Department of Neurology, Heinrich Heine University, Düsseldorf, Germany
| | - Matthias Grothe
- Department of Neurology, University Medicine of Greifswald, Greifswald, Germany
| | - Sergiu Groppa
- Department of Neurology, Focus Program Translational Neuroscience (FTN), Rhine-Main Neuroscience Network (rmn2), University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany
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7
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Lin X, Amalraj M, Blanton C, Avila B, Holmes TC, Nitz DA, Xu X. Noncanonical projections to the hippocampal CA3 regulate spatial learning and memory by modulating the feedforward hippocampal trisynaptic pathway. PLoS Biol 2021; 19:e3001127. [PMID: 34928938 PMCID: PMC8741299 DOI: 10.1371/journal.pbio.3001127] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Revised: 01/07/2022] [Accepted: 11/24/2021] [Indexed: 12/27/2022] Open
Abstract
The hippocampal formation (HF) is well documented as having a feedforward, unidirectional circuit organization termed the trisynaptic pathway. This circuit organization exists along the septotemporal axis of the HF, but the circuit connectivity across septal to temporal regions is less well described. The emergence of viral genetic mapping techniques enhances our ability to determine the detailed complexity of HF circuitry. In earlier work, we mapped a subiculum (SUB) back projection to CA1 prompted by the discovery of theta wave back propagation from the SUB to CA1 and CA3. We reason that this circuitry may represent multiple extended noncanonical pathways involving the subicular complex and hippocampal subregions CA1 and CA3. In the present study, multiple retrograde viral tracing approaches produced robust mapping results, which supports this prediction. We find significant noncanonical synaptic inputs to dorsal hippocampal CA3 from ventral CA1 (vCA1), perirhinal cortex (Prh), and the subicular complex. Thus, CA1 inputs to CA3 run opposite the trisynaptic pathway and in a temporal to septal direction. Our retrograde viral tracing results are confirmed by anterograde-directed viral mapping of projections from input mapped regions to hippocampal dorsal CA3 (dCA3). We find that genetic inactivation of the projection of vCA1 to dCA3 impairs object-related spatial learning and memory but does not modulate anxiety-related behaviors. Our data provide a circuit foundation to explore novel functional roles contributed by these noncanonical hippocampal circuit connections to hippocampal circuit dynamics and learning and memory behaviors.
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Affiliation(s)
- Xiaoxiao Lin
- Department Anatomy & Neurobiology, School of Medicine, University of California, Irvine, California, United States of America
| | - Michelle Amalraj
- Department Anatomy & Neurobiology, School of Medicine, University of California, Irvine, California, United States of America
| | - Crisylle Blanton
- Department Anatomy & Neurobiology, School of Medicine, University of California, Irvine, California, United States of America
| | - Brenda Avila
- Department Anatomy & Neurobiology, School of Medicine, University of California, Irvine, California, United States of America
| | - Todd C. Holmes
- Department Physiology & Biophysics, School of Medicine, University of California, Irvine, California, United States of America
- The Center for Neural Circuit Mapping, University of California, Irvine, Irvine, California, United States of America
| | - Douglas A. Nitz
- The Center for Neural Circuit Mapping, University of California, Irvine, Irvine, California, United States of America
- Department of Cognitive Science, University of California San Diego, La Jolla, California, United States of America
| | - Xiangmin Xu
- Department Anatomy & Neurobiology, School of Medicine, University of California, Irvine, California, United States of America
- The Center for Neural Circuit Mapping, University of California, Irvine, Irvine, California, United States of America
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8
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Anstötz M, Fiske MP, Maccaferri G. Impaired KCC2 Function Triggers Interictal-Like Activity Driven by Parvalbumin-Expressing Interneurons in the Isolated Subiculum In Vitro. Cereb Cortex 2021; 31:4681-4698. [PMID: 33987649 PMCID: PMC8408463 DOI: 10.1093/cercor/bhab115] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2021] [Revised: 04/07/2021] [Accepted: 04/10/2021] [Indexed: 12/30/2022] Open
Abstract
The decreased expression of the KCC2 membrane transporter in subicular neurons has been proposed to be a key epileptogenic event in temporal lobe epilepsy (TLE). Here, we have addressed this question in a reduced model in vitro and have studied the properties and mechanistic involvement of a major class of interneurons, that is, parvalbumin-expressing cells (PVs). When exposed to the KCC2 blocker VU0463271, mouse subicular slices generated hypersynchronous discharges that could be recorded electrophysiologically and visualized as clusters of co-active neurons with calcium imaging. The pharmacological profile of these events resembled interictal-like discharges in human epileptic tissue because of their dependence on GABAA and AMPA receptors. On average, PVs fired before pyramidal cells (PCs) and the area of co-active clusters was comparable to the individual axonal spread of PVs, suggesting their mechanistic involvement. Optogenetic experiments confirmed this hypothesis, as the flash-stimulation of PVs in the presence of VU0463271 initiated interictal-like discharges, whereas their optogenetic silencing suppressed network hyper-excitability. We conclude that reduced KCC2 activity in subicular networks in vitro is sufficient to induce interictal-like activity via altered GABAergic signaling from PVs without other epilepsy-related changes. This conclusion supports an epileptogenic role for impaired subicular KCC2 function during the progression of TLE.
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Affiliation(s)
- Max Anstötz
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
| | - Michael Patrick Fiske
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
| | - Gianmaria Maccaferri
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
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9
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Núñez-Ochoa MA, Chiprés-Tinajero GA, González-Domínguez NP, Medina-Ceja L. Causal relationship of CA3 back-projection to the dentate gyrus and its role in CA1 fast ripple generation. BMC Neurosci 2021; 22:37. [PMID: 34001031 PMCID: PMC8130286 DOI: 10.1186/s12868-021-00641-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Accepted: 05/07/2021] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Pathophysiological evidence from temporal lobe epilepsy models highlights the hippocampus as the most affected structure due to its high degree of neuroplasticity and control of the dynamics of limbic structures, which are necessary to encode information, conferring to it an intrinsic epileptogenicity. A loss in this control results in observable oscillatory perturbations called fast ripples, in epileptic rats those events are found in CA1, CA3, and the dentate gyrus (DG), which are the principal regions of the trisynaptic circuit of the hippocampus. The present work used Granger causality to address which relationships among these three regions of the trisynaptic circuit are needed to cause fast ripples in CA1 in an in vivo model. For these purposes, male Wistar rats (210-300 g) were injected with a single dose of pilocarpine hydrochloride (2.4 mg/2 µl) into the right lateral ventricle and video-monitored 24 h/day to detect spontaneous and recurrent seizures. Once detected, rats were implanted with microelectrodes in these regions (fixed-recording tungsten wire electrodes, 60-μm outer diameter) ipsilateral to the pilocarpine injection. A total of 336 fast ripples were recorded and probabilistically characterized, from those fast ripples we made a subset of all the fast ripple events associated with sharp-waves in CA1 region (n = 40) to analyze them with Granger Causality. RESULTS Our results support existing evidence in vitro in which fast ripple events in CA1 are initiated by CA3 multiunit activity and describe a general synchronization in the theta band across the three regions analyzed DG, CA3, and CA1, just before the fast ripple event in CA1 have begun. CONCLUSION This in vivo study highlights the causal participation of the CA3 back-projection to the DG, a connection commonly overlooked in the trisynaptic circuit, as a facilitator of a closed-loop among these regions that prolongs the excitatory activity of CA3. We speculate that the loss of inhibitory drive of DG and the mechanisms of ripple-related memory consolidation in which also the CA3 back-projection to DG has a fundamental role might be underlying processes of the fast ripples generation in CA1.
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Affiliation(s)
- Miguel A Núñez-Ochoa
- Laboratory of Neurophysiology, Department of Cellular and Molecular Biology, CUCBA, University of Guadalajara, Camino Ing. R. Padilla Sánchez 2100, Las Agujas, Nextipac, CP 45110, Zapopan, Jalisco, Mexico
- Biomedical Sciences, CUCS, University of Guadalajara, Sierra Mojada 950, Colonia Independencia, CP 44340, Guadalajara, Jalisco, Mexico
| | - Gustavo A Chiprés-Tinajero
- Laboratory of Neurophysiology, Department of Cellular and Molecular Biology, CUCBA, University of Guadalajara, Camino Ing. R. Padilla Sánchez 2100, Las Agujas, Nextipac, CP 45110, Zapopan, Jalisco, Mexico
- Biomedical Sciences, CUCS, University of Guadalajara, Sierra Mojada 950, Colonia Independencia, CP 44340, Guadalajara, Jalisco, Mexico
| | - Nadia P González-Domínguez
- Laboratory of Neurophysiology, Department of Cellular and Molecular Biology, CUCBA, University of Guadalajara, Camino Ing. R. Padilla Sánchez 2100, Las Agujas, Nextipac, CP 45110, Zapopan, Jalisco, Mexico
| | - Laura Medina-Ceja
- Laboratory of Neurophysiology, Department of Cellular and Molecular Biology, CUCBA, University of Guadalajara, Camino Ing. R. Padilla Sánchez 2100, Las Agujas, Nextipac, CP 45110, Zapopan, Jalisco, Mexico.
- Biomedical Sciences, CUCS, University of Guadalajara, Sierra Mojada 950, Colonia Independencia, CP 44340, Guadalajara, Jalisco, Mexico.
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10
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Lei S, Hu B, Rezagholizadeh N. Activation of V 1a vasopressin receptors excite subicular pyramidal neurons by activating TRPV1 and depressing GIRK channels. Neuropharmacology 2021; 190:108565. [PMID: 33891950 DOI: 10.1016/j.neuropharm.2021.108565] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 03/04/2021] [Accepted: 04/06/2021] [Indexed: 11/25/2022]
Abstract
Arginine vasopressin (AVP) is a nonapeptide that serves as a neuromodulator in the brain and a hormone in the periphery that regulates water homeostasis and vasoconstriction. The subiculum is the major output region of the hippocampus and an integral component in the networks that processes sensory and motor cues to form a cognitive map encoding spatial, contextual, and emotional information. Whereas the subiculum expresses high densities of AVP-binding sites and AVP has been shown to increase the synaptic excitability of subicular pyramidal neurons, the underlying cellular and molecular mechanisms have not been determined. We found that activation of V1a receptors increased the excitability of subicular pyramidal neurons via activation of TRPV1 channels and depression of the GIRK channels. V1a receptor-induced excitation of subicular pyramidal neurons required the function of phospholipase Cβ, but was independent of intracellular Ca2+ release. Protein kinase C was responsible for AVP-mediated depression of GIRK channels, whereas degradation of phosphatidylinositol 4,5-bisphosphate was involved in V1a receptor-elicited activation of TRPV1 channels. Our results may provide one of the cellular and molecular mechanisms to explain the physiological functions of AVP in the brain.
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Affiliation(s)
- Saobo Lei
- Department of Biomedical Sciences, School of Medicine and Health Sciences, University of North Dakota, Grand Forks, ND, 58203, USA.
| | - Binqi Hu
- Department of Biomedical Sciences, School of Medicine and Health Sciences, University of North Dakota, Grand Forks, ND, 58203, USA
| | - Neda Rezagholizadeh
- Department of Biomedical Sciences, School of Medicine and Health Sciences, University of North Dakota, Grand Forks, ND, 58203, USA
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11
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Rasia-Filho AA, Guerra KTK, Vásquez CE, Dall’Oglio A, Reberger R, Jung CR, Calcagnotto ME. The Subcortical-Allocortical- Neocortical continuum for the Emergence and Morphological Heterogeneity of Pyramidal Neurons in the Human Brain. Front Synaptic Neurosci 2021; 13:616607. [PMID: 33776739 PMCID: PMC7991104 DOI: 10.3389/fnsyn.2021.616607] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Accepted: 02/01/2021] [Indexed: 11/13/2022] Open
Abstract
Human cortical and subcortical areas integrate emotion, memory, and cognition when interpreting various environmental stimuli for the elaboration of complex, evolved social behaviors. Pyramidal neurons occur in developed phylogenetic areas advancing along with the allocortex to represent 70-85% of the neocortical gray matter. Here, we illustrate and discuss morphological features of heterogeneous spiny pyramidal neurons emerging from specific amygdaloid nuclei, in CA3 and CA1 hippocampal regions, and in neocortical layers II/III and V of the anterolateral temporal lobe in humans. Three-dimensional images of Golgi-impregnated neurons were obtained using an algorithm for the visualization of the cell body, dendritic length, branching pattern, and pleomorphic dendritic spines, which are specialized plastic postsynaptic units for most excitatory inputs. We demonstrate the emergence and development of human pyramidal neurons in the cortical and basomedial (but not the medial, MeA) nuclei of the amygdala with cells showing a triangular cell body shape, basal branched dendrites, and a short apical shaft with proximal ramifications as "pyramidal-like" neurons. Basomedial neurons also have a long and distally ramified apical dendrite not oriented to the pial surface. These neurons are at the beginning of the allocortex and the limbic lobe. "Pyramidal-like" to "classic" pyramidal neurons with laminar organization advance from the CA3 to the CA1 hippocampal regions. These cells have basal and apical dendrites with specific receptive synaptic domains and several spines. Neocortical pyramidal neurons in layers II/III and V display heterogeneous dendritic branching patterns adapted to the space available and the afferent inputs of each brain area. Dendritic spines vary in their distribution, density, shapes, and sizes (classified as stubby/wide, thin, mushroom-like, ramified, transitional forms, "atypical" or complex forms, such as thorny excrescences in the MeA and CA3 hippocampal region). Spines were found isolated or intermingled, with evident particularities (e.g., an extraordinary density in long, deep CA1 pyramidal neurons), and some showing a spinule. We describe spiny pyramidal neurons considerably improving the connectional and processing complexity of the brain circuits. On the other hand, these cells have some vulnerabilities, as found in neurodegenerative Alzheimer's disease and in temporal lobe epilepsy.
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Affiliation(s)
- Alberto A. Rasia-Filho
- Department of Basic Sciences/Physiology and Graduate Program in Biosciences, Universidade Federal de Ciências da Saúde de Porto Alegre, Porto Alegre, Brazil
- Graduate Program in Neuroscience, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil
| | - Kétlyn T. Knak Guerra
- Graduate Program in Neuroscience, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil
| | - Carlos Escobar Vásquez
- Graduate Program in Neuroscience, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil
| | - Aline Dall’Oglio
- Department of Basic Sciences/Physiology and Graduate Program in Biosciences, Universidade Federal de Ciências da Saúde de Porto Alegre, Porto Alegre, Brazil
| | - Roman Reberger
- Medical Engineering Program, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Cláudio R. Jung
- Institute of Informatics, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil
| | - Maria Elisa Calcagnotto
- Graduate Program in Neuroscience, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil
- Neurophysiology and Neurochemistry of Neuronal Excitability and Synaptic Plasticity Laboratory, Department of Biochemistry and Biochemistry Graduate Program, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil
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12
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Fei F, Wang X, Wang Y, Chen Z. Dissecting the role of subiculum in epilepsy: Research update and translational potential. Prog Neurobiol 2021; 201:102029. [PMID: 33636224 DOI: 10.1016/j.pneurobio.2021.102029] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2020] [Revised: 01/12/2021] [Accepted: 02/21/2021] [Indexed: 11/25/2022]
Abstract
The subiculum serves as the strategic core output of the hippocampus, through which neural activity exits the hippocampal proper and targets the entorhinal cortex and other more distant subcortical and cortical areas. The past decade has witnessed a growing interest in the subiculum, owing to discoveries revealing its critical role in regulating many physiological and pathophysiological processes. Notably, accumulating evidence from both clinical and experimental studies suggests that the subiculum plays a vital role in seizure initiation and propagation, in epilepsy. In this review, we briefly describe the structure and connectivity of the subiculum and then summarize the molecular and cellular mechanisms in the subiculum underlying the epileptic brain, in both epilepsy patients and animal models. Next, we review some translational approaches targeting the malfunctioned subiculum to treat epilepsy. Finally, we pose open questions for future research in the subiculum and their clinical translation challenges.
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Affiliation(s)
- Fan Fei
- Institute of Pharmacology & Toxicology, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China
| | - Xia Wang
- Institute of Pharmacology & Toxicology, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China
| | - Yi Wang
- Institute of Pharmacology & Toxicology, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China; Key Laboratory of Neuropharmacology and Translational Medicine of Zhejiang Province, College of Pharmaceutical Science, Zhejiang Chinese Medical University, Hangzhou, China
| | - Zhong Chen
- Institute of Pharmacology & Toxicology, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China; Key Laboratory of Neuropharmacology and Translational Medicine of Zhejiang Province, College of Pharmaceutical Science, Zhejiang Chinese Medical University, Hangzhou, China; Epilepsy Center, Department of Neurology, Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China.
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13
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Hu B, Boyle CA, Lei S. Activation of Oxytocin Receptors Excites Subicular Neurons by Multiple Signaling and Ionic Mechanisms. Cereb Cortex 2020; 31:2402-2415. [PMID: 33341872 DOI: 10.1093/cercor/bhaa363] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2020] [Revised: 11/01/2020] [Accepted: 11/02/2020] [Indexed: 12/14/2022] Open
Abstract
Oxytocin (OXT) is a nonapeptide that serves as a neuromodulator in the brain and a hormone participating in parturition and lactation in the periphery. The subiculum is the major output region of the hippocampus and an integral component in the networks that process sensory and motor cues to form a cognitive map encoding spatial, contextual, and emotional information. Whilst the subiculum expresses the highest OXT-binding sites and is the first brain region to be activated by peripheral application of OXT, the precise actions of OXT in the subiculum have not been determined. Our results demonstrate that application of the selective OXT receptor (OXTR) agonist, [Thr4,Gly7]-oxytocin (TGOT), excited subicular neurons via activation of TRPV1 channels, and depression of K+ channels. The OXTR-mediated excitation of subicular neurons required the functions of phospholipase Cβ, protein kinase C, and degradation of phosphatidylinositol 4,5-bisphosphate (PIP2). OXTR-elicited excitation of subicular neurons enhanced long-term potentiation via activation of TRPV1 channels. Our results provide a cellular and molecular mechanism to explain the physiological functions of OXT in the brain.
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Affiliation(s)
- Binqi Hu
- Department of Biomedical Sciences, School of Medicine and Health Sciences, University of North Dakota, Grand Forks, ND 58203, USA
| | - Cody A Boyle
- Department of Biomedical Sciences, School of Medicine and Health Sciences, University of North Dakota, Grand Forks, ND 58203, USA
| | - Saobo Lei
- Department of Biomedical Sciences, School of Medicine and Health Sciences, University of North Dakota, Grand Forks, ND 58203, USA
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14
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Lévesque M, Avoli M. The subiculum and its role in focal epileptic disorders. Rev Neurosci 2020; 32:249-273. [PMID: 33661586 DOI: 10.1515/revneuro-2020-0091] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Accepted: 09/29/2020] [Indexed: 01/07/2023]
Abstract
The subicular complex (hereafter referred as subiculum), which is reciprocally connected with the hippocampus and rhinal cortices, exerts a major control on hippocampal outputs. Over the last three decades, several studies have revealed that the subiculum plays a pivotal role in learning and memory but also in pathological conditions such as mesial temporal lobe epilepsy (MTLE). Indeed, subicular networks actively contribute to seizure generation and this structure is relatively spared from the cell loss encountered in this focal epileptic disorder. In this review, we will address: (i) the functional properties of subicular principal cells under normal and pathological conditions; (ii) the subiculum role in sustaining seizures in in vivo models of MTLE and in in vitro models of epileptiform synchronization; (iii) its presumptive role in human MTLE; and (iv) evidence underscoring the relationship between subiculum and antiepileptic drug effects. The studies reviewed here reinforce the view that the subiculum represents a limbic area with relevant, as yet unexplored, roles in focal epilepsy.
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Affiliation(s)
- Maxime Lévesque
- Departments of Neurology and Neurosurgery, Montreal Neurological Institute-Hospital, McGill University, 3801 University Street, Montreal, H3A 2B4Québec, Canada
| | - Massimo Avoli
- Departments of Neurology, Neurosurgery, and Physiology, Montreal Neurological Institute-Hospital, McGill University, 3801 University Street, Montreal, H3A 2B4Québec, Canada
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15
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Tóth E, Bokodi V, Somogyvári Z, Maglóczky Z, Wittner L, Ulbert I, Erőss L, Fabó D. Laminar distribution of electrically evoked hippocampal short latency ripple activity highlights the importance of the subiculum in vivo in human epilepsy, an intraoperative study. Epilepsy Res 2020; 169:106509. [PMID: 33310654 DOI: 10.1016/j.eplepsyres.2020.106509] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Revised: 11/04/2020] [Accepted: 11/21/2020] [Indexed: 10/22/2022]
Abstract
OBJECTIVE The goal of this study was to define the pathology and anesthesia dependency of single pulse electrical stimulation (SPES) dependent high-frequency oscillations (HFOs, ripples, fast ripples) in the hippocampal formation. METHODS Laminar profile of electrically evoked short latency (<100 ms) high-frequency oscillations (80-500 Hz) was examined in the hippocampus of therapy-resistant epileptic patients (6 female, 2 male) in vivo, under general anesthesia. RESULTS Parahippocampal SPES evoked HFOs in all recorded hippocampal subregions (Cornu Ammonis 2-3, dentate gyrus, and subiculum) were not uniform, rather the combination of ripples, fast ripples, sharp transients, and multiple unit activities. Mild and severe hippocampal sclerosis (HS) differed in the probability to evoke fast ripples: it decreased with the severity of sclerosis in CA2-3 but increased in the subiculum. Modulation in the ripple spectrum was observed only in the subiculum with increased fast HFO rate and frequency in severe HS. Inhalational anesthetics (isoflurane) suppressed the chance to evoke HFOs compared to propofol. CONCLUSION The presence of early HFOs in the dentate gyrus and early fast HFOs (>250 Hz) in the other subregions indicate the pathological nature of these evoked oscillations. Subiculum was found to be active producing HFOs in parallel with the cell loss in the hippocampus proper, which emphasize the role of this region in the generation of epileptic activity.
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Affiliation(s)
- Emília Tóth
- Epilepsy Centrum, Dept of Neurology, National Institute of Clinical Neurosciences, Budapest, 1145, Hungary; Department of Neurology, The University of Texas Health Science Center at Houston, Houston, Texas, 77030, USA (present affiliation)
| | - Virág Bokodi
- Epilepsy Centrum, Dept of Neurology, National Institute of Clinical Neurosciences, Budapest, 1145, Hungary; Pázmány Péter Catholic University, Faculty of Information Technology and Bionics, Budapest, 1083, Hungary
| | - Zoltán Somogyvári
- Department of Computational Sciences, Wigner Research Centre, Eötvös Loránd Research Network, Budapest, 1121, Hungary
| | - Zsófia Maglóczky
- Department of Cellular and Network Neurobiology, Institute of Experimental Medicine, Eötvös Loránd Research Network, Budapest, 1083, Hungary; Human Brain Research Laboratory, Institute of Experimental Medicine, Eötvös Loránd Research Network, Budapest, 1083, Hungary
| | - Lucia Wittner
- Epilepsy Centrum, Dept of Neurology, National Institute of Clinical Neurosciences, Budapest, 1145, Hungary; Pázmány Péter Catholic University, Faculty of Information Technology and Bionics, Budapest, 1083, Hungary; Institute of Cognitive Neuroscience and Psychology, Research Center for Natural Sciences, Eötvös Loránd Research Network, Budapest, 1117, Hungary
| | - István Ulbert
- Epilepsy Centrum, Dept of Neurology, National Institute of Clinical Neurosciences, Budapest, 1145, Hungary; Pázmány Péter Catholic University, Faculty of Information Technology and Bionics, Budapest, 1083, Hungary; Institute of Cognitive Neuroscience and Psychology, Research Center for Natural Sciences, Eötvös Loránd Research Network, Budapest, 1117, Hungary
| | - Loránd Erőss
- Pázmány Péter Catholic University, Faculty of Information Technology and Bionics, Budapest, 1083, Hungary; Department of Functional Neurosurgery, National Institute of Clinical Neurosciences, Budapest, 1145, Hungary
| | - Dániel Fabó
- Epilepsy Centrum, Dept of Neurology, National Institute of Clinical Neurosciences, Budapest, 1145, Hungary.
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16
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Fiske MP, Anstötz M, Welty LJ, Maccaferri G. The intrinsic cell type-specific excitatory connectivity of the developing mouse subiculum is sufficient to generate synchronous epileptiform activity. J Physiol 2020; 598:1965-1985. [PMID: 32119127 DOI: 10.1113/jp279561] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Accepted: 02/18/2020] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The activity of local excitatory circuits of the subiculum has been suggested to be involved in the initiation of pathological activity in epileptic patients and experimental animal models of temporal lobe epilepsy. We have taken advantage of multimodal techniques to classify subicular cells in distinct subclasses and have investigated their morphofunctional properties and connectivity in vitro. Our results indicate that local subicular excitatory circuits are connected in a cell type-specific fashion and that synapses are preferentially established on basal vs. apical dendrites. We show that local excitatory circuits, isolated from extrasubicular inputs and pharmacologically disinhibited, are sufficient to initiate synchronous epileptiform activity in vitro. In conclusion, this work provides a high-resolution description of local excitatory circuits of the subiculum and highlights their mechanistic involvement in the generation of pathological activity. ABSTRACT The subiculum has been suggested to be involved in the initiation of pathological discharges in human patients and animal models of temporal lobe epilepsy. Although converging evidence has revealed the existence of functional diversity within its principal neurons, much less attention has been devoted to its intrinsic connectivity and whether its local excitatory circuits are sufficient to generate epileptiform activity. Here, we have directly addressed these two key points in mouse subicular slices. First, using multivariate techniques, we have distinguished two groups of principal cells, which we have termed type 1 and type 2. These subgroups roughly overlap with what were classically indicated as regular and bursting cells, and showed differences in the extension and complexity of their apical dendrites. Functional connectivity was found both between similar (homotypic) and different (heterotypic) types of cells, with a marked asymmetry within heterotypic pairs. Unitary excitatory postsynaptic potentials (uEPSPs) revealed a high degree of variability both in amplitude, failure rate, rise time and half-width. Post hoc analysis of functionally connected pairs suggested that the observed uEPSPs were mediated by few contact sites, predominantly located on the basal dendrites. When surgically isolated from extrasubicular excitatory afferents, pharmacologically disinhibited subicular slices generated hyper-synchronous discharges. Thus, we conclude that local subicular excitatory circuits, connected according to cell type-specific rules, are sufficient to promote epileptiform activity. This conclusion fits well with a previous suggestion that local subicular events, purely mediated by excitatory connections, may underlie the pre-ictal discharges that govern interictal-ictal transitions.
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Affiliation(s)
- Michael Patrick Fiske
- Northwestern University Interdepartmental PhD Program & Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, 60611, USA
| | - Max Anstötz
- Northwestern University Interdepartmental PhD Program & Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, 60611, USA
| | - Leah J Welty
- Biostatistics Collaboration Center, Feinberg School of Medicine, Northwestern University, Chicago, IL, 60611, USA
| | - Gianmaria Maccaferri
- Northwestern University Interdepartmental PhD Program & Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, 60611, USA
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17
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Matsumoto N, Kitanishi T, Mizuseki K. The subiculum: Unique hippocampal hub and more. Neurosci Res 2019; 143:1-12. [DOI: 10.1016/j.neures.2018.08.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2018] [Revised: 07/10/2018] [Accepted: 08/03/2018] [Indexed: 01/09/2023]
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18
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Reyes-Garcia SZ, Scorza CA, Araújo NS, Ortiz-Villatoro NN, Jardim AP, Centeno R, Yacubian EMT, Faber J, Cavalheiro EA. Different patterns of epileptiform-like activity are generated in the sclerotic hippocampus from patients with drug-resistant temporal lobe epilepsy. Sci Rep 2018; 8:7116. [PMID: 29740014 PMCID: PMC5940759 DOI: 10.1038/s41598-018-25378-9] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2018] [Accepted: 04/19/2018] [Indexed: 12/26/2022] Open
Abstract
Human hippocampal slice preparations from patients with temporal lobe epilepsy (TLE) associated with hippocampal sclerosis (HS) are excellent material for the characterization of epileptiform-like activity. However, it is still unknown if hippocampal regions as cornu Ammonis (CA) 1, CA3 and CA4, generate population epileptiform-like activity. Here, we investigated epileptiform activities of the subiculum, CA1, CA2, CA3, CA4 (induced by elevation of extracellular potassium concentration) and the dentate gyrus (induced with hilar stimulation and elevation of potassium concentration) from sclerotic hippocampi of patients with drug-resistant TLE. Five types of epileptiform-like activity were observed: interictal-like events; periodic ictal spiking; seizure-like events; spreading depression-like events; tonic seizure-like events and no activity. Different susceptibilities to generate epileptiform activity among hippocampal regions were observed; the dentate gyrus was the most susceptible region followed by the subiculum, CA4, CA1, CA2 and CA3. The incidence of epileptiform activity pattern was associated with specific regions of the hippocampal formation. Moreover, it was observed that each region of the hippocampal formation exhibits frequency-specific ranges in each subfield of the sclerotic human tissue. In conclusion, this study demonstrates that epileptiform-like activity may be induced in different regions of the hippocampal formation, including regions that are severely affected by neuronal loss.
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Affiliation(s)
- Selvin Z Reyes-Garcia
- Departamento de Neurologia e Neurocirurgia, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil. .,Departamento de Ciencias Morfológicas, Facultad de Ciencias Médicas, Universidad Nacional Autónoma de Honduras, Tegucigalpa, Honduras.
| | - Carla A Scorza
- Departamento de Neurologia e Neurocirurgia, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Noemi S Araújo
- Departamento de Neurologia e Neurocirurgia, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Nancy N Ortiz-Villatoro
- Departamento de Neurologia e Neurocirurgia, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Anaclara Prada Jardim
- Departamento de Neurologia e Neurocirurgia, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Ricardo Centeno
- Departamento de Neurologia e Neurocirurgia, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Elza Márcia Targas Yacubian
- Departamento de Neurologia e Neurocirurgia, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Jean Faber
- Departamento de Neurologia e Neurocirurgia, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Esper A Cavalheiro
- Departamento de Neurologia e Neurocirurgia, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil
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Tóth K, Hofer KT, Kandrács Á, Entz L, Bagó A, Erőss L, Jordán Z, Nagy G, Sólyom A, Fabó D, Ulbert I, Wittner L. Hyperexcitability of the network contributes to synchronization processes in the human epileptic neocortex. J Physiol 2017; 596:317-342. [PMID: 29178354 DOI: 10.1113/jp275413] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Accepted: 11/15/2017] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Hyperexcitability and hypersynchrony of neuronal networks are thought to be linked to the generation of epileptic activity in both humans and animal models. Here we show that human epileptic postoperative neocortical tissue is able to generate two different types of synchronies in vitro. Epileptiform bursts occurred only in slices derived from epileptic patients and were hypersynchronous events characterized by high levels of excitability. Spontaneous population activity emerged in both epileptic and non-epileptic tissue, with a significantly lower degree of excitability and synchrony, and could not be linked to epilepsy. These results help us to understand better the role of excitatory and inhibitory neuronal circuits in the generation of population events, and to define the subtle border between physiological and pathological synchronies. ABSTRACT Interictal activity is a hallmark of epilepsy diagnostics and is linked to neuronal hypersynchrony. Little is known about perturbations in human epileptic neocortical microcircuits, and their role in generating pathological synchronies. To explore hyperexcitability of the human epileptic network, and its contribution to convulsive activity, we investigated an in vitro model of synchronous burst activity spontaneously occurring in postoperative tissue slices derived from patients with or without preoperative clinical and electrographic manifestations of epileptic activity. Human neocortical slices generated two types of synchronies. Interictal-like discharges (classified as epileptiform events) emerged only in epileptic samples, and were hypersynchronous bursts characterized by considerably elevated levels of excitation. Synchronous population activity was initiated in both epileptic and non-epileptic tissue, with a significantly lower degree of excitability and synchrony, and could not be linked to epilepsy. However, in pharmacoresistant epileptic tissue, a higher percentage of slices exhibited population activity, with higher local field potential gradient amplitudes. More intracellularly recorded neurons received depolarizing synaptic potentials, discharging more reliably during the events. Light and electron microscopic examinations showed slightly lower neuron densities and higher densities of excitatory synapses in the human epileptic neocortex. Our data suggest that human neocortical microcircuits retain their functionality and plasticity in vitro, and can generate two significantly different synchronies. We propose that population bursts might not be pathological events while interictal-like discharges may reflect the epileptogenicity of the human cortex. Our results show that hyperexcitability characterizes the human epileptic neocortical network, and that it is closely related to the emergence of synchronies.
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Affiliation(s)
- Kinga Tóth
- Institute of Cognitive Neuroscience and Psychology, Research Center for Natural Sciences, Hungarian Academy of Sciences, 1117, Budapest, Hungary.,Institute of Experimental Medicine, Hungarian Academy of Sciences, 1083, Budapest, Hungary
| | - Katharina T Hofer
- Institute of Cognitive Neuroscience and Psychology, Research Center for Natural Sciences, Hungarian Academy of Sciences, 1117, Budapest, Hungary.,Department of Information Technology, Pázmány Péter Catholic University, 1083, Budapest, Hungary
| | - Ágnes Kandrács
- Institute of Cognitive Neuroscience and Psychology, Research Center for Natural Sciences, Hungarian Academy of Sciences, 1117, Budapest, Hungary.,Department of Information Technology, Pázmány Péter Catholic University, 1083, Budapest, Hungary
| | - László Entz
- National Institute of Clinical Neuroscience, 1145, Budapest, Hungary
| | - Attila Bagó
- National Institute of Clinical Neuroscience, 1145, Budapest, Hungary
| | - Loránd Erőss
- National Institute of Clinical Neuroscience, 1145, Budapest, Hungary
| | - Zsófia Jordán
- National Institute of Clinical Neuroscience, 1145, Budapest, Hungary
| | - Gábor Nagy
- National Institute of Clinical Neuroscience, 1145, Budapest, Hungary
| | - András Sólyom
- National Institute of Clinical Neuroscience, 1145, Budapest, Hungary
| | - Dániel Fabó
- National Institute of Clinical Neuroscience, 1145, Budapest, Hungary
| | - István Ulbert
- Institute of Cognitive Neuroscience and Psychology, Research Center for Natural Sciences, Hungarian Academy of Sciences, 1117, Budapest, Hungary.,Department of Information Technology, Pázmány Péter Catholic University, 1083, Budapest, Hungary.,National Institute of Clinical Neuroscience, 1145, Budapest, Hungary
| | - Lucia Wittner
- Institute of Cognitive Neuroscience and Psychology, Research Center for Natural Sciences, Hungarian Academy of Sciences, 1117, Budapest, Hungary.,Institute of Experimental Medicine, Hungarian Academy of Sciences, 1083, Budapest, Hungary.,National Institute of Clinical Neuroscience, 1145, Budapest, Hungary
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20
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Voets NL, Hodgetts CJ, Sen A, Adcock JE, Emir U. Hippocampal MRS and subfield volumetry at 7T detects dysfunction not specific to seizure focus. Sci Rep 2017; 7:16138. [PMID: 29170537 PMCID: PMC5700920 DOI: 10.1038/s41598-017-16046-5] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Accepted: 11/03/2017] [Indexed: 01/06/2023] Open
Abstract
Ultra high-field 7T MRI offers sensitivity to localize hippocampal pathology in temporal lobe epilepsy (TLE), but has rarely been evaluated in patients with normal-appearing clinical MRI. We applied multimodal 7T MRI to assess if focal subfield atrophy and deviations in brain metabolites characterize epileptic hippocampi. Twelve pre-surgical TLE patients (7 MRI-negative) and age-matched healthy volunteers were scanned at 7T. Hippocampal subfields were manually segmented from 600μm isotropic resolution susceptibility-weighted images. Hippocampal metabolite spectra were acquired to determine absolute concentrations of glutamate, glutamine, myo-inositol, NAA, creatine and choline. We performed case-controls analyses, using permutation testing, to identify abnormalities in hippocampal imaging measures in individual patients, for evaluation against clinical evidence of seizure lateralisation and neuropsychological memory test scores. Volume analyses identified hippocampal subfield atrophy in 9/12 patients (75%), commonly affecting CA3. 7/8 patients had altered metabolite concentrations, most showing reduced glutamine levels (62.5%). However, neither volume nor metabolite deviations consistently lateralized the epileptogenic hippocampus. Rather, lower subiculum volumes and glutamine concentrations correlated with impaired verbal memory performance. Hippocampal subfield and metabolic abnormalities detected at 7T appear to reflect pathophysiological processes beyond epileptogenesis. Despite limited diagnostic contributions, these markers show promise to help elucidate mnemonic processing in TLE.
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Affiliation(s)
- Natalie L Voets
- Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, Oxford, OX3 9DU, UK. .,Oxford Epilepsy Research Group, Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, Oxford, OX3 9DU, UK.
| | - Carl J Hodgetts
- Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, Oxford, OX3 9DU, UK.,Cardiff University Brain Research Imaging Centre, School of Psychology, Cardiff University, Cardiff, CF24 4HQ, UK
| | - Arjune Sen
- Oxford Epilepsy Research Group, Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, Oxford, OX3 9DU, UK
| | - Jane E Adcock
- Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, Oxford, OX3 9DU, UK.,Oxford Epilepsy Research Group, Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, Oxford, OX3 9DU, UK
| | - Uzay Emir
- Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, Oxford, OX3 9DU, UK
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21
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Pro-excitatory alterations in sodium channel activity facilitate subiculum neuron hyperexcitability in temporal lobe epilepsy. Neurobiol Dis 2017; 108:183-194. [PMID: 28860087 DOI: 10.1016/j.nbd.2017.08.018] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2017] [Revised: 08/07/2017] [Accepted: 08/26/2017] [Indexed: 11/23/2022] Open
Abstract
Temporal lobe epilepsy (TLE) is a common form of adult epilepsy involving the limbic structures of the temporal lobe. Subiculum neurons act to provide a major output from the hippocampus and consist of a large population of endogenously bursting excitatory neurons. In TLE, subiculum neurons are largely spared, become hyperexcitable and show spontaneous epileptiform activity. The basis for this hyperexcitability is unclear, but is likely to involve alterations in the expression levels and function of various ion channels. In this study, we sought to determine the importance of sodium channel currents in facilitating neuronal hyperexcitability of subiculum neurons in the continuous hippocampal stimulation (CHS) rat model of TLE. Subiculum neurons from TLE rats were hyperexcitable, firing a higher frequency of action potentials after somatic current injection and action potential (AP) bursts after synaptic stimulation. Voltage clamp recordings revealed increases in resurgent (INaR) and persistent (INaP) sodium channel currents and pro-excitatory shifts in sodium channel activation and inactivation parameters that would facilitate increases in AP generation. Attenuation of INaR and INaP currents with 4,9-anhydro-tetrodotoxin (4,9-ah TTX; 100nM), a toxin with increased potency against Nav1.6 channels, suppressed neuronal firing frequency and inhibited AP bursting induced by synaptic stimulation in TLE neurons. These findings support an important role of sodium channels, particularly Nav1.6, in facilitating subiculum neuron hyperexcitability in TLE and provide further support for the importance of INaR and INaP currents in establishing epileptiform activity of subiculum neurons.
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22
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Jozwiak S, Becker A, Cepeda C, Engel J, Gnatkovsky V, Huberfeld G, Kaya M, Kobow K, Simonato M, Loeb JA. WONOEP appraisal: Development of epilepsy biomarkers-What we can learn from our patients? Epilepsia 2017; 58:951-961. [PMID: 28387933 PMCID: PMC5806696 DOI: 10.1111/epi.13728] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/20/2017] [Indexed: 12/13/2022]
Abstract
OBJECTIVE Current medications for patients with epilepsy work in only two of three patients. For those medications that do work, they only suppress seizures. They treat the symptoms, but do not modify the underlying disease, forcing patients to take these drugs with significant side effects, often for the rest of their lives. A major limitation in our ability to advance new therapeutics that permanently prevent, reduce the frequency of, or cure epilepsy comes from a lack of understanding of the disease coupled with a lack of reliable biomarkers that can predict who has or who will get epilepsy. METHODS The main goal of this report is to present a number of approaches for identifying reliable biomarkers from observing patients with brain disorders that have a high probability of producing epilepsy. RESULTS A given biomarker, or more likely a profile of biomarkers, will have both a quantity and a time course during epileptogenesis that can be used to predict who will get the disease, to confirm epilepsy as a diagnosis, to identify coexisting pathologies, and to monitor the course of treatments. SIGNIFICANCE Additional studies in patients and animal models could identify common and clinically valuable biomarkers to successfully translate animal studies into new and effective clinical trials.
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Affiliation(s)
- Sergiusz Jozwiak
- Department of Child Neurology, Medical University of Warsaw, Poland
- Department of Child Neurology, The Children’s Memorial Health Institute, Warsaw, Poland
| | - Albert Becker
- Section for Translational Epilepsy Research, Department of Neuropathology, University of Bonn Medical Center, Bonn, Germany
| | - Carlos Cepeda
- IDDRC, Semel Institute for Neuroscience & Human Behavior, University of California Los Angeles, Los Angeles, CA, USA
| | - Jerome Engel
- Departments of Neurology, Neurobiology, and Psychiatry & Biobehavioral Sciences and the Brain Research Institute, David Geffen School of Medicine at UCLA, Los Angeles, CA
| | - Vadym Gnatkovsky
- Unit of Epilepsy and Experimental Neurophysiology, Fondazione Istituto Neurologico Carlo Besta, Milan, Italy
| | - Gilles Huberfeld
- Sorbonne and UPMC University, AP-HP, Department of Neurophysiology, UPMC and La Pitié-Salpêtrière Hospital, Paris, France
- INSERM U1129, Paris Descartes University, PRES Sorbonne Paris, Cité, Paris, CEA, France
| | - Mehmet Kaya
- Department of Physiology, Koc University School of Medicine, Rumelifeneri Yolu, Sariver, Istanbul, Turkey
| | - Katja Kobow
- Department of Neuropathology, University Hospital Erlangen, Erlangen, Germany
| | - Michele Simonato
- Department of Medical Sciences, University of Ferrara and Division of Neuroscience, University Vita-Salute San Raffaele, Milan, Italy
| | - Jeffrey A. Loeb
- Department of Neurology and Rehabilitation, The University of Illinois at Chicago, Chicago, IL
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23
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Wang XX, Li YH, Gong HQ, Liang PJ, Zhang PM, Lu QC. The Subiculum: A Potential Site of Ictogenesis in a Neonatal Seizure Model. Front Neurol 2017; 8:147. [PMID: 28473802 PMCID: PMC5397469 DOI: 10.3389/fneur.2017.00147] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2016] [Accepted: 03/31/2017] [Indexed: 01/03/2023] Open
Abstract
Studies have reported that the subiculum is one origin of interictal-like discharges in adult patients with temporal lobe epilepsy; however, whether the subiculum represents a site of ictogenesis for neonatal seizures remains unclear. In this study, multi-electrode recording techniques were used to record epileptiform discharges induced by low-Mg2+ or high-K+ artificial cerebrospinal fluid in neonatal mouse hippocampal slices, and the spatiotemporal dynamics of the epileptiform discharges were analyzed. The Na+–K+–2Cl− cotransporter 1 (NKCC1) blocker, bumetanide, was applied to test its effect upon epileptiform discharges in low-Mg2+ model. The effect of N-methyl-d-aspartate receptors (NMDARs) antagonist, d-AP5, upon the epileptiform discharges in high-K+ model was examined. We found that the neonatal subiculum not only relayed epileptiform discharges emanating from the hippocampus proper (HP) but also initiated epileptiform discharges (interictal- and ictal-like discharges) independently. The latency to onset of the first epileptiform discharge initiated in the subiculum was similar to that initiated in the HP. Bumetanide efficiently blocked seizures in the neonatal HP, but was less effectively in suppressing seizures initiated in the subiculum. In high-K+ model, d-AP5 was more effective in blocking seizures initiated in the subiculum than that initiated in the HP. Furthermore, Western blotting analysis showed that NKCC1 expression was lower in the subiculum than that in the HP, whereas the expression of NMDAR subunits, NR2A and NR2B, was higher in the subiculum than that in the HP. Our results revealed that the subiculum was a potential site of ictogenesis in neonatal seizures and possessed similar seizure susceptibility to the HP. GABAergic excitation resulting from NKCC1 may play a less dominant role during ictogenesis in the subiculum than that in the HP. The subicular ictogenesis may be related to the glutamatergic excitation mediated by NMDARs.
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Affiliation(s)
- Xin-Xin Wang
- Department of Neurology, Ren Ji Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
| | - Yong-Hua Li
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China
| | - Hai-Qing Gong
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China
| | - Pei-Ji Liang
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China
| | - Pu-Ming Zhang
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China
| | - Qin-Chi Lu
- Department of Neurology, Ren Ji Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
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24
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Petersen AV, Jensen CS, Crépel V, Falkerslev M, Perrier JF. Serotonin Regulates the Firing of Principal Cells of the Subiculum by Inhibiting a T-type Ca 2+ Current. Front Cell Neurosci 2017; 11:60. [PMID: 28326015 PMCID: PMC5339341 DOI: 10.3389/fncel.2017.00060] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Accepted: 02/20/2017] [Indexed: 11/13/2022] Open
Abstract
The subiculum is the main output of the hippocampal formation. A high proportion of its principal neurons fire action potentials in bursts triggered by the activation of low threshold calcium currents. This firing pattern promotes synaptic release and regulates spike-timing-dependent plasticity. The subiculum receives a high density of fibers originating from the raphe nuclei, suggesting that serotonin (5-HT) modulates subicular neurons. Here we investigated if and how 5-HT modulates the firing pattern of bursting neurons. By combining electrophysiological analysis with pharmacology, optogenetics and calcium imaging, we demonstrate that 5-HT2C receptors reduce bursting activity by inhibiting a low-threshold calcium current mediated by T-type Ca2+ channels in principal cells of the subiculum. In addition, we show that the activation of this novel pathway decreases bursting activity and the occurrence of epileptiform discharges induced in in vitro models for temporal lobe epilepsy (TLE).
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Affiliation(s)
- Anders V Petersen
- Department of Neuroscience and Pharmacology, University of Copenhagen Copenhagen, Denmark
| | - Camilla S Jensen
- Department of Biomedical Sciences, University of Copenhagen Copenhagen, Denmark
| | - Valérie Crépel
- Institut de Neurobiologie de la Méditerranée (INMED), Institut National de la Santé et de la Recherche Médicale (INSERM) U901, Aix-Marseille Université Marseille, France
| | - Mathias Falkerslev
- Department of Neuroscience and Pharmacology, University of Copenhagen Copenhagen, Denmark
| | - Jean-François Perrier
- Department of Neuroscience and Pharmacology, University of Copenhagen Copenhagen, Denmark
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25
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Chung S, Spruston N, Koh S. Age-dependent changes in intrinsic neuronal excitability in subiculum after status epilepticus. PLoS One 2015; 10:e0119411. [PMID: 25775210 PMCID: PMC4361192 DOI: 10.1371/journal.pone.0119411] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2012] [Accepted: 01/30/2015] [Indexed: 12/03/2022] Open
Abstract
Kainic acid-induced status epilepticus (KA-SE) in mature rats results in the development of spontaneous recurrent seizures and a pattern of cell death resembling hippocampal sclerosis in patients with temporal lobe epilepsy. In contrast, KA-SE in young animals before postnatal day (P) 18 is less likely to cause cell death or epilepsy. To investigate whether changes in neuronal excitability occur in the subiculum after KA-SE, we examined the age-dependent effects of SE on the bursting neurons of subiculum, the major output region of the hippocampus. Patch-clamp recordings were used to monitor bursting in pyramidal neurons in the subiculum of rat hippocampal slices. Neurons were studied either one or 2-3 weeks following injection of KA or saline (control) in immature (P15) or more mature (P30) rats, which differ in their sensitivity to KA as well as the long-term sequelae of the KA-SE. A significantly greater proportion of subicular pyramidal neurons from P15 rats were strong-bursting neurons and showed increased frequency-dependent bursting compared to P30 animals. Frequency-dependent burst firing was enhanced in P30, but not in P15 rats following KA-SE. The enhancement of bursting induced by KA-SE in more mature rats suggests that the frequency-dependent limitation of repetitive burst firing, which normally occurs in the subiculum, is compromised following SE. These changes could facilitate the initiation of spontaneous recurrent seizures or their spread from the hippocampus to other parts of the brain.
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Affiliation(s)
- Sungkwon Chung
- Department of Physiology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, South Korea
| | - Nelson Spruston
- Scientific Program, Janelia Research Campus, Ashburn, Virginia, United States of America
| | - Sookyong Koh
- Neurobiology Program, Stanley Manne Children’s Research Institute, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States of America
- * E-mail:
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26
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Huberfeld G, Blauwblomme T, Miles R. Hippocampus and epilepsy: Findings from human tissues. Rev Neurol (Paris) 2015; 171:236-51. [PMID: 25724711 PMCID: PMC4409112 DOI: 10.1016/j.neurol.2015.01.563] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Accepted: 01/20/2015] [Indexed: 11/18/2022]
Abstract
Surgical removal of the epileptogenic zone provides an effective therapy for several focal epileptic syndromes. This surgery offers the opportunity to study pathological activity in living human tissue for pharmacoresistant partial epilepsy syndromes including temporal lobe epilepsies with hippocampal sclerosis, cortical dysplasias, epilepsies associated with tumors and developmental malformations. Slices of tissue from patients with these syndromes retain functional neuronal networks and may generate epileptic activities. The properties of cells in this tissue may not be greatly changed, but excitatory synaptic transmission is often enhanced and GABAergic inhibition is preserved. Typically epileptic activity is not generated spontaneously by the neocortex, whether dysplastic or not, but can be induced by convulsants. The initiation of ictal discharges in the neocortex depends on both GABAergic signaling and increased extracellular potassium. In contrast, a spontaneous interictal-like activity is generated by tissues from patients with temporal lobe epilepsies associated with hippocampal sclerosis. This activity is initiated, not in the hippocampus but in the subiculum, an output region, which projects to the entorhinal cortex. Interictal events seem to be triggered by GABAergic cells, which paradoxically excite about 20% of subicular pyramidal cells while simultaneously inhibiting the majority. Interictal discharges thus depend on both GABAergic and glutamatergic signaling. The depolarizing effects of GABA depend on a pathological elevation in levels of chloride in some subicular cells, similar to those of developmentally immature cells. Such defect is caused by a perturbed expression of the cotransporters regulating intracellular chloride concentration, the importer NKCC1 and the extruder KCC2. Blockade of NKCC1 actions by the diuretic bumetanide restores intracellular chloride and thus hyperpolarizing GABAergic actions and consequently suppressing interictal activity.
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Affiliation(s)
- G Huberfeld
- Département de neurophysiologie, Sorbonne universités, UPMC - université Paris 06, UPMC, CHU de la Pitié-Salpêtrière, 47-83, boulevard de l'Hôpital, 75013 Paris, France; INSERM Unit U1129 Infantile Epilepsies and Brain Plasticity, University Paris Descartes, Sorbonne Paris Cité, CEA, 12, rue de l'École-de-Médecine, 75006 Paris, France.
| | - T Blauwblomme
- INSERM Unit U1129 Infantile Epilepsies and Brain Plasticity, University Paris Descartes, Sorbonne Paris Cité, CEA, 12, rue de l'École-de-Médecine, 75006 Paris, France; Neurosurgery Department, Necker-Enfants Malades Hospital, University Paris Descartes, PRES Sorbonne Paris Cité, 12, rue de l'École-de-Médecine, 75006 Paris, France
| | - R Miles
- Inserm U1127, CNRS UMR7225, Sorbonne universités, UPMC - université Paris 6 UMR S1127, Institut du cerveau et de la moelle épinière, 47, boulevard de l'Hôpital, 75013 Paris, France
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27
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Drexel M, Kirchmair E, Sperk G. Changes in the expression of GABAA receptor subunit mRNAs in parahippocampal areas after kainic acid induced seizures. Front Neural Circuits 2013; 7:142. [PMID: 24065890 PMCID: PMC3776158 DOI: 10.3389/fncir.2013.00142] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2013] [Accepted: 08/24/2013] [Indexed: 11/30/2022] Open
Abstract
The parahippocampal areas including the subiculum, pre- and parasubiculum, and notably the entorhinal cortex (EC) are intimately involved in the generation of limbic seizures in temporal lobe epilepsy. We investigated changes in the expression of 10 major GABAA receptor subunit mRNAs in subfields of the ventral hippocampus, ventral subiculum, EC, and perirhinal cortex (PRC) at different intervals (1, 8, 30, and 90 days) after kainic acid (KA)-induced status epilepticus priming epileptogenesis in the rat. The most pronounced and ubiquitous changes were a transient (24 h after KA only) down-regulation of γ2 mRNA and lasting decreases in subunit α5, β3, and δ mRNAs that were prominent in all hippocampal and parahippocampal areas. In the subiculum similarly as in sectors CA1 and CA3, levels of subunit α1, α2, α4, and γ2 mRNAs decreased transiently (1 day after KA-induced status epilepticus). They were followed by increased expression of subunit α1 and α3 mRNAs in the dentate gyrus (DG) and sectors CA1 and CA3, and subunit α1 also in the EC layer II (30 and 90 days after KA). We also observed sustained overexpression of subunits α4 and γ2 in the subiculum and in the Ammon’s horn. Subunit γ2 mRNA was also increased in sector CA1 at the late intervals after KA. Taken together, our results suggest distinct regulation of mRNA expression for individual GABAA receptor subunits. Especially striking was the wide-spread down-regulation of the often peri- or extrasynaptically located subunits α5 and δ. These subunits are often associated with tonic inhibition. Their decrease could be related to decreased tonic inhibition or may merely reflect compensatory changes. In contrast, expression of subunit α4 that may also mediate tonic inhibition when associated with the δ-subunit was significantly upregulated in the DG and in the proximal subiculum at late intervals. Thus, concomitant up-regulation of subunit γ2, α1 and α4 mRNAs (and loss in δ-subunits) ultimately indicates significant rearrangement of GABAA receptor composition after KA-induced seizures.
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Affiliation(s)
- Meinrad Drexel
- Department of Pharmacology, Innsbruck Medical University Innsbruck, Austria
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28
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Maslarova A, Salar S, Lapilover E, Friedman A, Veh RW, Heinemann U. Increased susceptibility to acetylcholine in the entorhinal cortex of pilocarpine-treated rats involves alterations in KCNQ channels. Neurobiol Dis 2013; 56:14-24. [DOI: 10.1016/j.nbd.2013.02.016] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Revised: 02/19/2013] [Accepted: 02/25/2013] [Indexed: 02/03/2023] Open
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29
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Kandratavicius L, Rosa-Neto P, Monteiro MR, Guiot MC, Assirati JA, Carlotti CG, Kobayashi E, Leite JP. Distinct increased metabotropic glutamate receptor type 5 (mGluR5) in temporal lobe epilepsy with and without hippocampal sclerosis. Hippocampus 2013; 23:1212-30. [PMID: 23804486 PMCID: PMC4165311 DOI: 10.1002/hipo.22160] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/31/2013] [Indexed: 12/04/2022]
Abstract
Metabotropic glutamate receptor type 5 (mGluR5) upregulation in temporal lobe epilepsy (TLE) and the correlation of its expression with features of hippocampal sclerosis (HS) remains unclear. Here we characterized mGluR5 immunoreactivity in hippocampus, entorhinal cortex (EC), and subiculum of TLE specimens with confirmed HS, with neocortical TLE (non-HS) and necropsy controls. We correlated mGluR5 immunoreactivity with neuronal density, mossy fiber sprouting, astrogliosis (GFAP), and dendritic alterations (MAP2). TLE specimens showed increased mGluR5 expression, which was most pronounced in the EC, subiculum, CA2, and dentate gyrus outer molecular layer. Increased mGluR5 expression was seen in hippocampal head and body segments and was independent of neuronal density, astrogliosis, or dendritic alterations. Positive correlation between mGluR5 expression with mossy fiber sprouting and with MAP2 in CA3 and CA1 was found only in HS specimens. Negative correlation between mGluR5 expression with seizure frequency and epilepsy duration was found only in non-HS cases. Specimens from HS patients without previous history of febrile seizure (FS) showed higher mGluR5 and MAP2 expression in CA2. Our study suggests that mGluR5 upregulation is part of a repertoire of post-synaptic adaptations that might control overexcitation and excessive glutamate release rather than a dysfunction that leads to seizure facilitation. That would explain why non-HS cases, on which seizures are likely to originate outside the hippocampal formation, also exhibit upregulated mGluR5. On the other hand, lower mGluR5 expression was related to increased seizure frequency. In addition to its role in hyperexcitability, mGluR5 upregulation could play a role in counterbalance mechanisms along the hyperexcitable circuitry uniquely altered in sclerotic hippocampal formation. Inefficient post-synaptic compensatory morphological (dendritic branching) and glutamatergic (mGluR5 expression) mechanisms in CA2 subfield could potentially underlie the association of FS with HS and TLE. © 2013 Wiley Periodicals, Inc.
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Affiliation(s)
- Ludmyla Kandratavicius
- Department of Neurosciences and Behavior, Ribeirao Preto Medical School, University of Sao PauloBrazil
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill UniversityMontreal, Canada
| | - Pedro Rosa-Neto
- Translational Neuroimaging Laboratory, Department of Neurology and Neurosurgery, Douglas Research Institute, McGill UniversityMontreal, Canada
| | - Mariana Raquel Monteiro
- Department of Neurosciences and Behavior, Ribeirao Preto Medical School, University of Sao PauloBrazil
| | - Marie-Christine Guiot
- Department of Pathology, Montreal Neurological Institute, McGill UniversityMontreal, Canada
| | | | | | - Eliane Kobayashi
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill UniversityMontreal, Canada
| | - Joao Pereira Leite
- Department of Neurosciences and Behavior, Ribeirao Preto Medical School, University of Sao PauloBrazil
- *Correspondence to: Joao Pereira Leite, Ribeirao Preto Medical School, Department of Neurosciences and Behavior, University of Sao Paulo, Av Bandeirantes 3900, 14049-900, Ribeirao Preto, SP, Brazil. E-mail:
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Sah N, Sikdar SK. Transition in subicular burst firing neurons from epileptiform activity to suppressed state by feedforward inhibition. Eur J Neurosci 2013; 38:2542-56. [DOI: 10.1111/ejn.12262] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2013] [Revised: 04/21/2013] [Accepted: 04/23/2013] [Indexed: 01/03/2023]
Affiliation(s)
- Nirnath Sah
- Molecular Biophysics Unit; Indian Institute of Science; Bangalore; India
| | - Sujit K. Sikdar
- Molecular Biophysics Unit; Indian Institute of Science; Bangalore; India
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Cell type-specific properties of subicular GABAergic currents shape hippocampal output firing mode. PLoS One 2012; 7:e50241. [PMID: 23251362 PMCID: PMC3519474 DOI: 10.1371/journal.pone.0050241] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2012] [Accepted: 10/22/2012] [Indexed: 11/19/2022] Open
Abstract
GABAergic function of the subiculum is central to the regulation of hippocampal output activity. Subicular neuronal networks are indeed under potent control by local inhibition. However, information about the properties of GABAergic currents generated by neurons of this parahippocampal area in normal tissue is still missing. Here, we describe GABAA receptor (GABAAR)-mediated phasic and tonic currents generated by principal cells (PCs) and interneurons (INs) of the rat subiculum. We show that in spite of similar synaptic current densities, INs generate spontaneous IPSCs (sIPSCs) that occur less frequently and exhibit smaller charge transfer, thus receiving less synaptic total current than PCs. Further distinction of PCs between intrinsically bursting (IB) and regular-spiking (RS) neurons suggested that sIPSCs generated by the two PC sub-types are likely to be similar. PCs and INs are also controlled by a similar tonic inhibition. However, whereas a comparable tonic current density is found in RS cells and INs, IB neurons are constrained by a greater inhibitory tone. Finally, pharmacological blockade of GABAAR did not promote functional switch of RS neurons to IB mode, but influenced the bursting propensity of IB cells and released fast spiking activity in INs. Our findings reveal differences in GABAergic currents between PCs and INs as well as within PC sub-types. We propose that GABAergic inhibition may shape hippocampal output activity by providing cell type-specific fine-tuning of subicular excitatory and inhibitory drives.
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Boido D, Jesuthasan N, de Curtis M, Uva L. Network dynamics during the progression of seizure-like events in the hippocampal-parahippocampal regions. ACTA ACUST UNITED AC 2012; 24:163-73. [PMID: 23048021 DOI: 10.1093/cercor/bhs298] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Seizure patterns in temporal lobe epilepsies have been described both in humans and in animal models. The involvement of specific hippocampal-parahippocampal subregions in the initiation and progression of temporal lobe seizures is not defined yet. We analyzed limbic network dynamics during seizures induced by 3-min arterial perfusion of 50 µM bicuculline in the in vitro isolated guinea pig brain preparation. As for human and animal temporal lobe epilepsies, 2 seizure types characterized at onset by either fast activity (FA) or hypersynchronous activity (HSA) were observed in our acute model. Simultaneous extracellular recordings were performed from ventral hippocampal-parahippocampal subregions with multichannel electrodes, and laminar analysis and propagation directions were computed to define reciprocal interactions during seizures. FA seizures started with fast oscillations generated in CA1-subiculum and entorhinal cortex, followed by irregular spikes and progressively regular bursts well defined in all subfields, with the exception of pre- and parasubiculum that do not participate in seizure activity. Dentate gyrus was not involved at FA seizure onset and became prominent during the transition to bursting in both FA and HSA patterns. HSA seizures were similar to FA events, but lacked initial FA. During seizures, reliable and steady propagation within the intra-hippocampal re-entrant loop was observed.
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Affiliation(s)
- Davide Boido
- Unit of Experimental Epileptology and Neurophysiology, Fondazione Istituto Neurologico Carlo Besta, Milano, Italy
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33
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Drexel M, Preidt AP, Sperk G. Sequel of spontaneous seizures after kainic acid-induced status epilepticus and associated neuropathological changes in the subiculum and entorhinal cortex. Neuropharmacology 2012; 63:806-17. [PMID: 22722023 PMCID: PMC3409872 DOI: 10.1016/j.neuropharm.2012.06.009] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Revised: 05/15/2012] [Accepted: 06/08/2012] [Indexed: 12/31/2022]
Abstract
Injection of the seaweed toxin kainic acid (KA) in rats induces a severe status epilepticus initiating complex neuropathological changes in limbic brain areas and subsequently spontaneous recurrent seizures. Although neuropathological changes have been intensively investigated in the hippocampus proper and the dentate gyrus in various seizure models, much less is known about changes in parahippocampal areas. We now established telemetric EEG recordings combined with continuous video monitoring to characterize the development of spontaneous seizures after KA-induced status epilepticus, and investigated associated neurodegenerative changes, astrocyte and microglia proliferation in the subiculum and other parahippocampal brain areas. The onset of spontaneous seizures was heterogeneous, with an average latency of 15 ± 1.4 days (range 3–36 days) to the initial status epilepticus. The frequency of late spontaneous seizures was higher in rats in which the initial status epilepticus was recurrent after its interruption with diazepam compared to rats in which this treatment was more efficient. Seizure-induced neuropathological changes were assessed in the subiculum by losses in NeuN-positive neurons and by Fluoro-Jade C staining of degenerating neurons. Neuronal loss was already prominent 24 h after KA injection and only modestly progressed at the later intervals. It was most severe in the proximal subiculum and in layer III of the medial entorhinal cortex and distinct Fluoro-Jade C labeling was observed there in 75% of rats even after 3 months. Glutamatergic neurons, labeled by in situ hybridization for the vesicular glutamate transporter 1 followed a similar pattern of cell losses, except for the medial entorhinal cortex and the proximal subiculum that appeared more vulnerable. Glutamate decarboxylase65 (GAD65) mRNA expressing neurons were generally less vulnerable than glutamate neurons. Reactive astrocytes and microglia were present after 24 h, however, became prominent only after 8 days and remained high after 30 days. In the proximal subiculum, parasubiculum and entorhinal cortex the number of microglia cells was highest after 30 days. Although numbers of reactive astrocytes and microglia were reduced again after 3 months, they were still present in most rats. The time course of astrocyte and microglia proliferation parallels that of epileptogenesis.
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Affiliation(s)
- Meinrad Drexel
- Department of Pharmacology, Innsbruck Medical University, Peter-Mayr-Str. 1a, 6020 Innsbruck, Austria.
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Somatostatin and neuropeptide Y neurons undergo different plasticity in parahippocampal regions in kainic acid-induced epilepsy. J Neuropathol Exp Neurol 2012; 71:312-29. [PMID: 22437342 DOI: 10.1097/nen.0b013e31824d9882] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Parahippocampal brain areas including the subiculum, presubiculum and parasubiculum, and entorhinal cortex give rise to major input and output neurons of the hippocampus and exert increased excitability in animal models and human temporal lobe epilepsy. Using immunohistochemistry and in situ hybridization for somatostatin and neuropeptide Y, we investigated plastic morphologic and neurochemical changes in parahippocampal neurons in the kainic acid (KA) model of temporal lobe epilepsy. Although constitutively contained in similar subclasses of γ-aminobutyric acid (GABA)-ergic neurons, both neuropeptide systems undergo distinctly different changes in their expression. Somatostatin messenger RNA (mRNA) is rapidly but transiently expressed de novo in pyramidal neurons of the subiculum and entorhinal cortex 24 hours after KA. Surviving somatostatin interneurons display increased mRNA levels at late intervals (3 months) after KA and increased labeling of their terminals in the outer molecular layer of the subiculum; the labeling correlates with the number of spontaneous seizures, suggesting that the seizures may trigger somatostatin expression. In contrast, neuropeptide Y mRNA is consistently expressed in principal neurons of the proximal subiculum and the lateral entorhinal cortex and labeling for the peptide persistently increased in virtually all major excitatory pathways of the hippocampal formation. The pronounced plastic changes differentially involving both neuropeptide systems indicate marked rearrangement of parahippocampal areas, presumably aiming at endogenous seizure protection. Their receptors may be targets for anticonvulsive drug therapy.
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35
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Avoli M, de Curtis M. GABAergic synchronization in the limbic system and its role in the generation of epileptiform activity. Prog Neurobiol 2011; 95:104-32. [PMID: 21802488 PMCID: PMC4878907 DOI: 10.1016/j.pneurobio.2011.07.003] [Citation(s) in RCA: 193] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2011] [Revised: 07/14/2011] [Accepted: 07/15/2011] [Indexed: 11/30/2022]
Abstract
GABA is the main inhibitory neurotransmitter in the adult forebrain, where it activates ionotropic type A and metabotropic type B receptors. Early studies have shown that GABA(A) receptor-mediated inhibition controls neuronal excitability and thus the occurrence of seizures. However, more complex, and at times unexpected, mechanisms of GABAergic signaling have been identified during epileptiform discharges over the last few years. Here, we will review experimental data that point at the paradoxical role played by GABA(A) receptor-mediated mechanisms in synchronizing neuronal networks, and in particular those of limbic structures such as the hippocampus, the entorhinal and perirhinal cortices, or the amygdala. After having summarized the fundamental characteristics of GABA(A) receptor-mediated mechanisms, we will analyze their role in the generation of network oscillations and their contribution to epileptiform synchronization. Whether and how GABA(A) receptors influence the interaction between limbic networks leading to ictogenesis will be also reviewed. Finally, we will consider the role of altered inhibition in the human epileptic brain along with the ability of GABA(A) receptor-mediated conductances to generate synchronous depolarizing events that may lead to ictogenesis in human epileptic disorders as well.
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Affiliation(s)
- Massimo Avoli
- Montreal Neurological Institute and Departments of Neurology & Neurosurgery, and of Physiology, McGill University, Montreal H3A 2B4 Quebec, Canada.
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36
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Drexel M, Preidt AP, Kirchmair E, Sperk G. Parvalbumin interneurons and calretinin fibers arising from the thalamic nucleus reuniens degenerate in the subiculum after kainic acid-induced seizures. Neuroscience 2011; 189:316-29. [PMID: 21616128 PMCID: PMC3152681 DOI: 10.1016/j.neuroscience.2011.05.021] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2011] [Revised: 05/03/2011] [Accepted: 05/11/2011] [Indexed: 12/20/2022]
Abstract
The subiculum is the major output area of the hippocampus. It is closely interconnected with the entorhinal cortex and other parahippocampal areas. In animal models of temporal lobe epilepsy (TLE) and in TLE patients it exerts increased network excitability and may crucially contribute to the propagation of limbic seizures. Using immunohistochemistry and in situ-hybridization we now investigated neuropathological changes affecting parvalbumin and calretinin containing neurons in the subiculum and other parahippocampal areas after kainic acid-induced status epilepticus. We observed prominent losses in parvalbumin containing interneurons in the subiculum and entorhinal cortex, and in the principal cell layers of the pre- and parasubiculum. Degeneration of parvalbumin-positive neurons was associated with significant precipitation of parvalbumin-immunoreactive debris 24 h after kainic acid injection. In the subiculum the superficial portion of the pyramidal cell layer was more severely affected than its deep part. In the entorhinal cortex, the deep layers were more severely affected than the superficial ones. The decrease in number of parvalbumin-positive neurons in the subiculum and entorhinal cortex correlated with the number of spontaneous seizures subsequently experienced by the rats. The loss of parvalbumin neurons thus may contribute to the development of spontaneous seizures. On the other hand, surviving parvalbumin neurons revealed markedly increased expression of parvalbumin mRNA notably in the pyramidal cell layer of the subiculum and in all layers of the entorhinal cortex. This indicates increased activity of these neurons aiming to compensate for the partial loss of this functionally important neuron population. Furthermore, calretinin-positive fibers terminating in the molecular layer of the subiculum, in sector CA1 of the hippocampus proper and in the entorhinal cortex degenerated together with their presumed perikarya in the thalamic nucleus reuniens. In addition, a significant loss of calretinin containing interneurons was observed in the subiculum. Notably, the loss in parvalbumin positive neurons in the subiculum equaled that in human TLE. It may result in marked impairment of feed-forward inhibition of the temporo-ammonic pathway and may significantly contribute to epileptogenesis. Similarly, the loss of calretinin-positive fiber tracts originating from the nucleus reuniens thalami significantly contributes to the rearrangement of neuronal circuitries in the subiculum and entorhinal cortex during epileptogenesis.
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Affiliation(s)
- M Drexel
- Department of Pharmacology, Innsbruck Medical University, Peter-Mayr-Str. 1a, 6020 Innsbruck, Austria.
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37
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Panuccio G, D'Antuono M, de Guzman P, De Lannoy L, Biagini G, Avoli M. In vitro ictogenesis and parahippocampal networks in a rodent model of temporal lobe epilepsy. Neurobiol Dis 2010; 39:372-80. [PMID: 20452424 DOI: 10.1016/j.nbd.2010.05.003] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2010] [Revised: 04/14/2010] [Accepted: 05/01/2010] [Indexed: 12/29/2022] Open
Abstract
Temporal lobe epilepsy (TLE) is a chronic epileptic disorder involving the hippocampal formation. Details on the interactions between the hippocampus proper and parahippocampal networks during ictogenesis remain, however, unclear. In addition, recent findings have shown that epileptic limbic networks maintained in vitro are paradoxically less responsive than non-epileptic control (NEC) tissue to application of the convulsant drug 4-aminopyridine (4AP). Field potential recordings allowed us to establish here the effects of 4AP in brain slices obtained from NEC and pilocarpine-treated epileptic rats; these slices included the hippocampus and parahippocampal areas such as entorhinal and perirhinal cortices and the amygdala. First, we found that both types of tissue generate epileptiform discharges with similar electrographic characteristics. Further investigation showed that generation of robust ictal-like discharges in the epileptic rat tissue is (i) favored by decreased hippocampal output (ii) reinforced by EC-subiculum interactions and (iii) predominantly driven by amygdala networks. We propose that a functional switch to alternative synaptic routes may promote network hyperexcitability in the epileptic limbic system.
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Affiliation(s)
- G Panuccio
- Montreal Neurological Institute and Department of Neurology and Neurosurgery, McGill University, Montreal, QC, Canada
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38
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Wittner L, Huberfeld G, Clémenceau S, Eross L, Dezamis E, Entz L, Ulbert I, Baulac M, Freund TF, Maglóczky Z, Miles R. The epileptic human hippocampal cornu ammonis 2 region generates spontaneous interictal-like activity in vitro. Brain 2009; 132:3032-46. [PMID: 19767413 DOI: 10.1093/brain/awp238] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The dentate gyrus, the cornu ammonis 2 region and the subiculum of the human hippocampal formation are resistant to the cell loss associated with temporal lobe epilepsy. The subiculum, but not the dentate gyrus, generates interictal-like activity in tissue slices from epileptic patients. In this study, we asked whether a similar population activity is generated in the cornu ammonis 2 region and examined the electrophysiological and neuroanatomical characteristics of human epileptic cornu ammonis 2 neurons that may be involved. Hippocampal slices were prepared from postoperative temporal lobe tissue derived from epileptic patients. Field potentials and multi-unit activity were recorded in vitro using multiple extracellular microelectrodes. Pyramidal cells were characterized in intra-cellular records and were filled with biocytin for subsequent anatomy. Fluorescent immunostaining was made on fixed tissue against the chloride-cation cotransporters sodium-potassium-chloride cotransporter-1 and potassium-chloride cotransporter-2. Light and electron microscopy were used to examine the parvalbumin-positive perisomatic inhibitory network. In 15 of 20 slices, the hippocampal cornu ammonis 2 region generated a spontaneous interictal-like activity, independently of population events in the subiculum. Most cornu ammonis 2 pyramidal cells fired spontaneously. All cells fired single action potentials and burst firing was evoked in three cells. Spontaneous excitatory postsynaptic potentials were recorded in all cells, but hyperpolarizing inhibitory postsynaptic potentials were detected in only 27% of the cells. Two-thirds of cornu ammonis 2 neurons showed depolarizing responses during interictal-like events, while the others were inhibited, according to the current sink in the cell body layer. Two biocytin-filled cells both showed a pyramidal-like morphology with axons projecting to the cornu ammonis 2 and cornu ammonis 3 regions. Expression of sodium-potassium-chloride cotransporter-1 and potassium-chloride cotransporter-2 was reduced in some cells of the epileptic cornu ammonis 2 region, but not to an extent corresponding to the proportion of cells in which hyperpolarizing postsynaptic potentials were absent. Numbers of parvalbumin-positive inhibitory cells and axons were shown to be decreased in the epileptic tissue. Electron microscopy showed the preservation of somatic inhibitory input of cornu ammonis 2 cells, and confirmed the loss of parvalbumin from the interneurons rather than their death. An extra excitatory input (partly coming from sprouted mossy fibres) was demonstrated to innervate cornu ammonis 2 cell bodies. Our results show that the cornu ammonis 2 region of the sclerotic human hippocampus can generate an independent epileptiform activity. Inhibitory and excitatory signalling were functional but modified in epileptic cornu ammonis 2 pyramidal cells. Overexcitation and the altered functional properties of perisomatic inhibitory network, rather than a modified chloride homeostasis, may account for the perturbed gamma-aminobutyric acid-ergic signalling and the generation of interictal-like activity in the human epileptic cornu ammonis 2 region.
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Affiliation(s)
- Lucia Wittner
- INSERM U739, Faculté de Médecine Pitié-Salpêtrière, Paris, France.
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39
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Curia G, Papouin T, Séguéla P, Avoli M. Downregulation of tonic GABAergic inhibition in a mouse model of fragile X syndrome. Cereb Cortex 2009; 19:1515-20. [PMID: 18787232 PMCID: PMC4873279 DOI: 10.1093/cercor/bhn159] [Citation(s) in RCA: 176] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The absence of fragile X mental retardation protein results in the fragile X syndrome (FXS), a common form of mental retardation associated with attention deficit, autistic behavior, and epileptic seizures. The phenotype of FXS is reproduced in fragile X mental retardation 1 (fmr1) knockout (KO) mice that have region-specific altered expression of some gamma-aminobutyric acid (GABA(A)) receptor subunits. However, little is known about the characteristics of GABAergic inhibition in the subiculum of these animals. We employed patch-clamp recordings from subicular pyramidal cells in an in vitro slice preparation. In addition, semiquantitative polymerase chain reaction and western blot experiments were performed on subiculum obtained from wild-type (WT) and KO mice. We found that tonic GABA(A) currents were downregulated in fmr1 KO compared with WT neurons, whereas no significant differences were observed in phasic GABA(A) currents. Molecular biology analysis revealed that the tonic GABA(A) receptor subunits alpha5 and delta were underexpressed in the fmr1 KO mouse subiculum compared with WT. Because the subiculum plays a role in both cognitive functions and epileptic disorders, we propose that altered tonic inhibition in this structure contributes to the behavioral deficits and epileptic activity seen in FXS patients. This conclusion is in line with evidence implicating tonic GABA(A) inhibition in learning and memory.
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Affiliation(s)
- Giulia Curia
- Montreal Neurological Institute and Department of Neurology and Neurosurgery, McGill University, Montreal, Canada H3A 2B4
| | - Thomas Papouin
- Montreal Neurological Institute and Department of Neurology and Neurosurgery, McGill University, Montreal, Canada H3A 2B4
- Department of Biology, Ecole Normale Superieure, 75005, Paris, France
| | - Philippe Séguéla
- Montreal Neurological Institute and Department of Neurology and Neurosurgery, McGill University, Montreal, Canada H3A 2B4
| | - Massimo Avoli
- Montreal Neurological Institute and Department of Neurology and Neurosurgery, McGill University, Montreal, Canada H3A 2B4
- Department of Experimental Medicine, Sapienza Universitàdi Roma, 00100, Rome, Italy
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Hargus NJ, Bertram EH, Patel MK. Adenosine A1 receptors presynaptically modulate excitatory synaptic input onto subiculum neurons. Brain Res 2009; 1280:60-8. [PMID: 19450566 DOI: 10.1016/j.brainres.2009.05.027] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2009] [Revised: 05/08/2009] [Accepted: 05/12/2009] [Indexed: 12/20/2022]
Abstract
Adenosine is an endogenous neuromodulator previously shown to suppress synaptic transmission and membrane excitability in the CNS. In this study we have determined the actions of adenosine on excitatory synaptic transmission in the subiculum, the main output area for the hippocampus. Adenosine (10 microM) reversibly inhibited excitatory post synaptic currents (EPSCs) recorded from subiculum neurons. These actions were mimicked by the A(1) receptor-specific agonist, N(6)-cyclopentyl-adenosine (CPA, 10 nM) and blocked by the A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 500 nM), but were unaffected by the A(2A) antagonist ZM 241385 (50 nM). In membrane excitability experiments, bath application of adenosine and CPA reversibly inhibited action potentials (AP) in subiculum neurons that were evoked by stimulation of the pyramidal cell layer of the CA1, but not by depolarizing current injection steps in subiculum neurons, suggesting a presynaptic mechanism of action. In support, adenosine and CPA application reduced mEPSC frequency without modulating mEPSC amplitude. These studies suggest that modulation of subiculum neuron excitability by adenosine is mediated via presynaptic A(1) receptors.
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Affiliation(s)
- Nicholas J Hargus
- Department of Anesthesiology, University of Virginia, Charlottesville, VA 22908, USA
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41
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Moore SJ, Cooper DC, Spruston N. Plasticity of burst firing induced by synergistic activation of metabotropic glutamate and acetylcholine receptors. Neuron 2009; 61:287-300. [PMID: 19186170 DOI: 10.1016/j.neuron.2008.12.013] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2007] [Revised: 04/14/2008] [Accepted: 12/09/2008] [Indexed: 11/25/2022]
Abstract
Subiculum, the primary efferent pathway of hippocampus, participates in memory for spatial tasks, relapse to drug abuse, and temporal lobe seizures. Subicular pyramidal neurons exhibit low-threshold burst firing driven by a spike afterdepolarization. Here we report that burst firing can be regulated by stimulation of afferent projections to subiculum. Unlike synaptic plasticity, burst plasticity did not require synaptic depolarization, activation of AMPA or NMDA receptors, or action potential firing. Rather, enhancement of burst firing required synergistic activation of group I, subtype 1 metabotropic glutamate receptors (mGluRs) and muscarinic acetylcholine receptors (mAChR). When either of these receptors was blocked, a suppression of bursting was revealed, which in turn was blocked by antagonists of group I, subtype 5 mGluRs. These results indicate that the output of subiculum can be strongly and bidirectionally regulated by activation of glutamatergic inputs within the hippocampus and cholinergic afferents from the medial septum.
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Affiliation(s)
- Shannon J Moore
- Department of Neurobiology and Physiology, Northwestern University, 2205 Tech Drive, Evanston, IL 60208, USA
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42
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Antagonism of glutamate receptors in the CA1 to perirhinal cortex projection prevents long-term potentiation and attenuates levels of brain-derived neurotrophic factor. Brain Res 2009; 1265:53-64. [PMID: 19232328 DOI: 10.1016/j.brainres.2009.01.067] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2008] [Revised: 01/30/2009] [Accepted: 01/31/2009] [Indexed: 12/30/2022]
Abstract
The CA1 to perirhinal cortex projection is one of multiple hippocampal-neocortical projections considered to be involved in memory consolidation. This projection has been shown to sustain long-term potentiation (LTP) following stimulation of CA1. Here we examined the pharmacological properties underpinning the plasticity observed in this projection. A stimulating electrode was inserted into the area CA1 and a recording electrode was inserted into the perirhinal cortex of urethane-anaesthetised Wistar rats. Rats (n=6 in each drug group) were administered with either saline (0.09%), MK-801 (NMDA antagonist; 0.1 mg/kg) or CNQX (AMPA/kainate antagonist; 1.5 mg/kg). Baseline recordings were made for 10 min by stimulating area CA1 (0.05 Hz stimulation protocol). High-frequency stimulation (HFS; 250 Hz) was performed and post-HFS fEPSP recordings were made for 1 h (0.05 Hz, as above). Baseline and post-HFS paired-pulse facilitation (PPF) recordings were performed across six different interpulse intervals. CA1 and perirhinal cortex tissue samples were taken from the stimulated and unstimulated hemispheres of each rat brain and analysed using a brain-derived neurotrophic factor (BDNF) ELISA. Results indicate that LTP was induced in the saline and MK-801 groups but not in the CNQX group; fEPSPs in the latter group rapidly returned to baseline levels following a short period of post-tetanic potentiation. Drug treatment and HFS had no effect on PPF levels. Drug treatment significantly reduced concentrations of both CA1 and perirhinal BDNF and prevented stimulation-induced increases in BDNF in CA1. This molecular and electrophysiological data suggests that LTP in the CA1-perirhinal cortex projection may require activation of postsynaptic AMPA/kainate receptors in order to sustain LTP.
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43
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Le Duigou C, Bouilleret V, Miles R. Epileptiform activities in slices of hippocampus from mice after intra-hippocampal injection of kainic acid. J Physiol 2008; 586:4891-904. [PMID: 18755752 DOI: 10.1113/jphysiol.2008.156281] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Intra-hippocampal kainate injection induces the emergence of recurrent seizures after a delay of 3-4 weeks. We examined the cellular and synaptic basis of this activity in vitro using extracellular and intracellular records from longitudinal hippocampal slices. These slices permitted recordings from the dentate gyrus, the CA3 and CA1 regions and the subiculum of both the injected and the contralateral non-injected hippocampus. A sclerotic zone was evident in dorsal regions of slices from the injected hippocampus, while ventral regions and tissue from the contralateral hippocampus were not sclerotic. Interictal field potentials of duration 50-200 ms were generated spontaneously in both ipsilateral and contralateral hippocampal slices, but not in the sclerotic region, at 3-12 months after injection. They were initiated in the CA1 and CA3 regions and the subiculum. They were blocked by antagonists at glutamatergic receptors and were transformed into prolonged epileptiform events by GABAergic receptor antagonists. The membrane potential and the reversal potential of GABAergic synaptic events were more depolarized in CA1 pyramidal cells from kainate-treated animals than in control animals. Ictal-like events of duration 8-80 s were induced by tetanic stimulation (50 Hz, 0.2-1 s) preferentially in dorsal contralateral and ventral ipsilateral slices. Similar events were initiated by focal application of a combination of high K(+) and GABA. These data show that both interictal and ictal-like activities can be induced in slices of both ipsilateral and contralateral hippocampus from kainate-treated animals and suggest that changes in cellular excitability and inhibitory synaptic signalling may contribute to their generation.
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Affiliation(s)
- Caroline Le Duigou
- INSERM U739, CHU Pitié-Salpêtrière, 105 boulevard de l'Hôpital, 75013 Paris, France
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Craig S, Commins S. Plastic and metaplastic changes in the CA1 and subicular projections to the entorhinal cortex. Brain Res 2007; 1147:124-39. [PMID: 17368431 DOI: 10.1016/j.brainres.2007.02.016] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2006] [Revised: 01/30/2007] [Accepted: 02/02/2007] [Indexed: 10/23/2022]
Abstract
The hippocampal formation (HF) is a brain structure critically involved in memory formation. Two major pathways have been identified in the rat; one projection targets the hippocampus via perirhinal cortex and lateral entorhinal cortex (LEC) while another targets the hippocampus via postrhinal cortex and medial entorhinal cortex (MEC). Areas CA1 and subiculum constitute major output structures of HF and target many cortical structures including EC. These return projections are also anatomically segregated with distinct regions of CA1 and subiculum projecting to either the LEC or MEC. We have previously demonstrated that the projections from CA1 and subiculum to the EC are capable of sustaining short- and long-term plastic changes. Here we detail a physiological topography that exists along the hippocampal output projections, equating well with the known anatomy. Specifically, field excitatory postsynaptic potential (fEPSP) responses in LEC are stronger following distal CA1 and proximal subiculum stimulation, compared to either proximal CA1 or distal subiculum stimulation. In addition, fEPSP responses in MEC are stronger following proximal CA1 stimulation compared to distal CA1. We also demonstrate that the distal CA1-LEC, proximal CA1-MEC and proximal subiculum-LEC projections are all capable of frequency-dependent plastic effects that shift the response from LTD to LTP. In addition, responses in distal CA1-LEC projection seem to show metaplastic capabilities. We discuss the possibility of dissociation between LEC and MEC projections, which may suggest two functional circuits from the HF to the cortex and may have implications in information processing, memory research and hippocampal seizure spread to the cortex.
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Affiliation(s)
- Sarah Craig
- Department of Psychology, National University of Ireland, Maynooth, Maynooth, Co. Kildare, Ireland
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Cavazos JE, Cross DJ. The role of synaptic reorganization in mesial temporal lobe epilepsy. Epilepsy Behav 2006; 8:483-93. [PMID: 16500154 PMCID: PMC2829602 DOI: 10.1016/j.yebeh.2006.01.011] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/30/2005] [Revised: 01/10/2006] [Accepted: 01/10/2006] [Indexed: 11/21/2022]
Abstract
The mechanisms underlying mesial temporal lobe epilepsy (MTLE) remain uncertain. Putative mechanisms should account for several features characteristic of the clinical presentation and the neurophysiological and neuropathological abnormalities observed in patients with intractable MTLE. Synaptic reorganization of the mossy fiber pathway has received considerable attention over the past two decades as a potential mechanism that increases the excitability of the hippocampal network through the formation of new recurrent excitatory collaterals. Morphological plasticity beyond the mossy fiber pathway has not been as thoroughly investigated. Recently, plasticity of the CA1 pyramidal axons has been demonstrated in acute and chronic experimental models of MTLE. As the hippocampal formation is topographically organized in stacks of slices (lamellae), synaptic reorganization of CA1 axons projecting to subiculum appears to increase the connectivity between lamellae, providing a mechanism for translamellar synchronization of cellular hyperexcitability, leading to pharmacologically intractable seizures.
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Affiliation(s)
- Jose E Cavazos
- South Texas Comprehensive Epilepsy Center and Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA.
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Siddiqui AH, Joseph SA. CA3 axonal sprouting in kainate-induced chronic epilepsy. Brain Res 2006; 1066:129-46. [PMID: 16359649 DOI: 10.1016/j.brainres.2005.10.066] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2005] [Revised: 10/17/2005] [Accepted: 10/20/2005] [Indexed: 11/25/2022]
Abstract
Latency between an early neurological insult and development of spontaneous recurrent seizures suggests aberrant chronological reorganization in patients with mesial temporal sclerosis associated epilepsy. Kainate-induced status similarly results in delayed development of spontaneous recurrent seizures. Mossy fiber sprouting by the dentate granule cells is a well-characterized manifestation of such temporal structural reorganization in both patients and animal models. However, alterations in other components of hippocampal circuitry have not been evaluated. We present results from studies using precise anterograde and retrograde tract tracing methodologies to evaluate the reorganization of outflow of the CA3 pyramidal cells. Although septotemporal relationships of the normal CA3 outflow tract through the Schaffer collaterals are well known, their aberrant reorganization following kainate-induced spontaneous recurrent seizures is not known. We provide the first definitive evidence of widespread CA3 structural reorganization in the form of sprouting of CA3 axons to widespread areas throughout the hippocampus and entorhinal cortex. This includes an apparent increase in the density of projection to areas that normally receive CA3 outflow such as CA1 and subiculum as well as novel projections beyond the confines of the hippocampus to the pre and parasubiculum and medial and lateral entorhinal cortex. We provide the first evidence of novel CA3 Schaffer collateral projection to the entorhinal cortex. The sprouting of CA3 outflow to widespread regions of the hippocampus and the entorhinal cortex may provide insight into how the injured hippocampus propagates unconventional impulse excitation to cortical fields which have a critical role in providing excitatory inputs into the hippocampus possibly setting up reverberating excitatory circuits as well as widespread connections throughout the cortical mantle. Sprouting-related mechanisms may also explain the latency associated with development of spontaneous recurrent seizures, the hallmark of temporal lobe epilepsy.
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Affiliation(s)
- Adnan H Siddiqui
- Department of Neurosurgery, Upstate Medical University, 750 East Adams Street, Syracuse, NY 13210, USA.
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Abstract
The subiculum has long been considered as a simple bidirectional relay region interposed between the hippocampus and the temporal cortex. Recent evidence, however, suggests that this region has specific roles in the cognitive functions and pathological deficits of the hippocampal formation. A group of 20 researchers participated in an ESF-sponsored meeting in Oxford in September, 2005 focusing on the neurobiology of the subiculum. Each brought a distinct expertise and approach to the anatomy, physiology, psychology, and pathologies of the subiculum. Here, we review the recent findings that were presented at the meeting.
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