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Leontiadis LJ, Trompoukis G, Felemegkas P, Tsotsokou G, Miliou A, Papatheodoropoulos C. Increased Inhibition May Contribute to Maintaining Normal Network Function in the Ventral Hippocampus of a Fmr1-Targeted Transgenic Rat Model of Fragile X Syndrome. Brain Sci 2023; 13:1598. [PMID: 38002556 PMCID: PMC10669536 DOI: 10.3390/brainsci13111598] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Revised: 11/10/2023] [Accepted: 11/13/2023] [Indexed: 11/26/2023] Open
Abstract
A common neurobiological mechanism in several neurodevelopmental disorders, including fragile X syndrome (FXS), is alterations in the balance between excitation and inhibition in the brain. It is thought that in the hippocampus, as in other brain regions, FXS is associated with increased excitability and reduced inhibition. However, it is still not known whether these changes apply to both the dorsal and ventral hippocampus, which appear to be differently involved in neurodegenerative disorders. Using a Fmr1 knock-out (KO) rat model of FXS, we found increased neuronal excitability in both the dorsal and ventral KO hippocampus and increased excitatory synaptic transmission in the dorsal hippocampus. Interestingly, synaptic inhibition is significantly increased in the ventral but not the dorsal KO hippocampus. Furthermore, the ventral KO hippocampus displays increased expression of the α1GABAA receptor subtype and a remarkably reduced rate of epileptiform discharges induced by magnesium-free medium. In contrast, the dorsal KO hippocampus displays an increased rate of epileptiform discharges and similar expression of α1GABAA receptors compared with the dorsal WT hippocampus. Blockade of α5GABAA receptors by L-655,708 did not affect epileptiform discharges in any genotype or hippocampal segment, and the expression of α5GABAA receptors did not differ between WT and KO hippocampus. These results suggest that the increased excitability of the dorsal KO hippocampus contributes to its heightened tendency to epileptiform discharges, while the increased phasic inhibition in the Fmr1-KO ventral hippocampus may represent a homeostatic mechanism that compensates for the increased excitability reducing its vulnerability to epileptic activity.
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Affiliation(s)
| | | | | | | | | | - Costas Papatheodoropoulos
- Laboratory of Neurophysiology, Department of Medicine, University of Patras, 26504 Rion, Greece; (L.J.L.); (G.T. (George Trompoukis)); (P.F.); (G.T. (Giota Tsotsokou)); (A.M.)
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2
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Jami SA, Wilkinson BJ, Guglietta R, Hartel N, Babiec WE, Graham NA, Coba MP, O'Dell TJ. Functional and phosphoproteomic analysis of β-adrenergic receptor signaling at excitatory synapses in the CA1 region of the ventral hippocampus. Sci Rep 2023; 13:7493. [PMID: 37161045 PMCID: PMC10170123 DOI: 10.1038/s41598-023-34401-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2022] [Accepted: 04/28/2023] [Indexed: 05/11/2023] Open
Abstract
Activation of β-adrenergic receptors (β-ARs) not only enhances learning and memory but also facilitates the induction of long-term potentiation (LTP), a form of synaptic plasticity involved in memory formation. To identify the mechanisms underlying β-AR-dependent forms of LTP we examined the effects of the β-AR agonist isoproterenol on LTP induction at excitatory synapses onto CA1 pyramidal cells in the ventral hippocampus. LTP induction at these synapses is inhibited by activation of SK-type K+ channels, suggesting that β-AR activation might facilitate LTP induction by inhibiting SK channels. However, although the SK channel blocker apamin enhanced LTP induction, it did not fully mimic the effects of isoproterenol. We therefore searched for potential alternative mechanisms using liquid chromatography-tandem mass spectrometry to determine how β-AR activation regulates phosphorylation of postsynaptic density (PSD) proteins. Strikingly, β-AR activation regulated hundreds of phosphorylation sites in PSD proteins that have diverse roles in dendritic spine structure and function. Moreover, within the core scaffold machinery of the PSD, β-AR activation increased phosphorylation at several sites previously shown to be phosphorylated after LTP induction. Together, our results suggest that β-AR activation recruits a diverse set of signaling pathways that likely act in a concerted fashion to regulate LTP induction.
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Affiliation(s)
- Shekib A Jami
- Molecular, Cellular, and Integrative Physiology Interdepartmental PhD Program, University of California, Los Angeles, Los Angeles, CA, USA
| | | | - Ryan Guglietta
- Interdepartmental PhD Program for Neuroscience, University of California, Los Angeles, Los Angeles, CA, USA
| | - Nicolas Hartel
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, CA, USA
| | - Walter E Babiec
- Undergraduate Interdepartmental Program for Neuroscience, University of California, Los Angeles, Los Angeles, CA, USA
| | - Nicholas A Graham
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, CA, USA
| | - Marcelo P Coba
- Zilkha Neurogenetic Institute, Los Angeles, CA, USA
- Department of Psychiatry and Behavioral Sciences, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
- Department of Physiology and Neuroscience, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Thomas J O'Dell
- Integrative Center for Learning and Memory, Brain Research Institute, University of California, Los Angeles, Los Angeles, CA, USA.
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA.
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Recognition Memory Induces Natural LTP-like Hippocampal Synaptic Excitation and Inhibition. Int J Mol Sci 2022; 23:ijms231810806. [PMID: 36142727 PMCID: PMC9501019 DOI: 10.3390/ijms231810806] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Revised: 09/09/2022] [Accepted: 09/12/2022] [Indexed: 11/29/2022] Open
Abstract
Synaptic plasticity is a cellular process involved in learning and memory by which specific patterns of neural activity adapt the synaptic strength and efficacy of the synaptic transmission. Its induction is governed by fine tuning between excitatory/inhibitory synaptic transmission. In experimental conditions, synaptic plasticity can be artificially evoked at hippocampal CA1 pyramidal neurons by repeated stimulation of Schaffer collaterals. However, long-lasting synaptic modifications studies during memory formation in physiological conditions in freely moving animals are very scarce. Here, to study synaptic plasticity phenomena during recognition memory in the dorsal hippocampus, field postsynaptic potentials (fPSPs) evoked at the CA3–CA1 synapse were recorded in freely moving mice during object-recognition task performance. Paired pulse stimuli were applied to Schaffer collaterals at the moment that the animal explored a new or a familiar object along different phases of the test. Stimulation evoked a complex synaptic response composed of an ionotropic excitatory glutamatergic fEPSP, followed by two inhibitory responses, an ionotropic, GABAA-mediated fIPSP and a metabotropic, G-protein-gated inwardly rectifying potassium (GirK) channel-mediated fIPSP. Our data showed the induction of LTP-like enhancements for both the glutamatergic and GirK-dependent components of the dorsal hippocampal CA3–CA1 synapse during the exploration of novel but not familiar objects. These results support the contention that synaptic plasticity processes that underlie hippocampal-dependent memory are sustained by fine tuning mechanisms that control excitatory and inhibitory neurotransmission balance.
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A. Samara M, Oikonomou GD, Trompoukis G, Madarou G, Adamopoulou M, Papatheodoropoulos C. Septotemporal variation in modulation of synaptic transmission, paired-pulse ratio and frequency facilitation/depression by adenosine and GABA B receptors in the rat hippocampus. Brain Neurosci Adv 2022; 6:23982128221106315. [PMID: 35782711 PMCID: PMC9240614 DOI: 10.1177/23982128221106315] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2021] [Accepted: 05/19/2022] [Indexed: 11/26/2022] Open
Abstract
Short-term synaptic plasticity represents a fundamental mechanism in
neural information processing and is regulated by neuromodulators.
Here, using field recordings from the CA1 region of adult rat
hippocampal slices, we show that excitatory synaptic transmission is
suppressed by strong but not moderate activation of adenosine
A1 receptors by
2-Chloro-N6-cyclopentyladenosine (CCPA) more in the dorsal
than the ventral hippocampus; in contrast, both mild and strong
activation of GABAB receptors by baclofen (1 μM, 10 μM)
suppress synaptic transmission more in the ventral than the dorsal
hippocampus. Using a 10-pulse stimulation train of variable frequency,
we found that CCPA modulates short-term synaptic plasticity
independently of the suppression of synaptic transmission in both
segments of the hippocampus and at stimulation frequencies greater
than 10 Hz. However, specifically regarding the paired-pulse ratio
(PPR) and frequency facilitation/depression (FF/D) we found
significant drug action before but not after adjusting conditioning
responses to control levels. Activation of GABABRs by
baclofen suppressed synaptic transmission more in the ventral than the
dorsal hippocampus. Furthermore, relatively high (10 μM) but not low
(1 μM) baclofen concentration enhanced both PPR and FF in both
hippocampal segments at stimulation frequencies greater than 1 Hz,
independently of the suppression of synaptic transmission by baclofen.
These results show that A1Rs and GABABRs control
synaptic transmission more effectively in the dorsal and the ventral
hippocampus, respectively, and suggest that these receptors modulate
PPR and FF/D at different frequency bands of afferent input, in both
segments of the hippocampus.
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Affiliation(s)
- Maria A. Samara
- Laboratory of Neurophysiology, Department of Medicine, University of Patras, Rion, Greece
| | - George D. Oikonomou
- Laboratory of Neurophysiology, Department of Medicine, University of Patras, Rion, Greece
| | - George Trompoukis
- Laboratory of Neurophysiology, Department of Medicine, University of Patras, Rion, Greece
| | - Georgia Madarou
- Laboratory of Neurophysiology, Department of Medicine, University of Patras, Rion, Greece
| | - Maria Adamopoulou
- Laboratory of Neurophysiology, Department of Medicine, University of Patras, Rion, Greece
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Septotemporal variation in beta-adrenergic modulation of short-term dynamics in the hippocampus. IBRO Neurosci Rep 2021; 11:64-72. [PMID: 34409401 PMCID: PMC8363828 DOI: 10.1016/j.ibneur.2021.07.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Accepted: 07/31/2021] [Indexed: 12/15/2022] Open
Abstract
Recent evidence shows a greater facilitating effect of beta-adrenergic receptors (β-ARs) on long-term synaptic plasticity in the ventral versus the dorsal hippocampus. Here, using field potentials from the CA1 area and a ten-pulse stimulation train of varying frequency we show that activation of β-ARs by isoproterenol preferentially facilitates the output from the dorsal hippocampus at the frequency range of 3–40 Hz without affecting short-term synaptic plasticity. Furthermore, isoproterenol increases basal synaptic transmission in the dorsal hippocampus only and enhances basal neuronal excitation more in the dorsal than the ventral hippocampus. These results suggest that β-AR-modulation of short-term neuronal dynamics differs along the longitudinal axis of the hippocampus, thereby contributing to functional specialization along the same axis. We studied the effects of isoproterenol (ISO) in dorsal (DH) and ventral (VH) hippocampus. ISO increased synaptic transmission and population spike more in DH than VH. ISO modulated short-term changes of population spike in the dorsal hippocampus only. ISO did not affect short-term changes of synaptic transmission in DH or VH. β adrenergic receptors modulate short-term changes in excitation in DH only.
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Rodrigues NC, Silva-Cruz A, Caulino-Rocha A, Bento-Oliveira A, Alexandre Ribeiro J, Cunha-Reis D. Hippocampal CA1 theta burst-induced LTP from weaning to adulthood: Cellular and molecular mechanisms in young male rats revisited. Eur J Neurosci 2021; 54:5272-5292. [PMID: 34251729 DOI: 10.1111/ejn.15390] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 07/08/2021] [Accepted: 07/08/2021] [Indexed: 01/05/2023]
Abstract
Long-term potentiation (LTP) is a highly studied cellular process, yet determining the transduction and gamma aminobutyric acid (GABAergic) pathways that are the essential versus modulatory for LTP elicited by theta burst stimulation (TBS) in the hippocampal Cornu Ammonis 1 (CA1) area is still elusive, due to the use of different TBS intensities, patterns or different rodent/cellular models. We now characterised the developmental maturation and the transduction and GABAergic pathways required for mild TBS-induced LTP in hippocampal CA1 area in male rats. LTP induced by TBS (5x4) (five bursts of four pulses delivered at 100 Hz) lasted for up to 3 h and was increasingly larger from weaning to adulthood. Stronger TBS patterns - TBS (15x4) or three TBS (15x4) separated by 6 min induced nearly maximal LTP not being the best choice to study the value of LTP-enhancing drugs. LTP induced by TBS (5x4) in young adults was fully dependent on N-methyl D-aspartate (NMDA) receptor and calmodulin-dependent protein kinase II (CaMKII) activity but independent of protein kinase A (PKA) or protein kinase C (PKC) activity. Furthermore, it was partially dependent on GABAB receptor activation and was potentiated by GABAA receptor blockade and less by GAT-1 transporter blockade. AMPA GluA1 phosphorylation on Ser831 (CaMKII target) but not GluA1 Ser845 (PKA target) was essential for LTP expression. The phosphorylation of the Kv4.2 channel was observed at Ser438 (CaMKII target) but not at Thr602 or Thr607 (ERK/MAPK pathway target). This suggests that cellular kinases like PKA, PKC, or kinases of the ERK/MAPK family although important modulators of TBS (5x4)-induced LTP may not be essential for its expression in the CA1 area of the hippocampus.
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Affiliation(s)
| | - Armando Silva-Cruz
- Instituto de Medicina Molecular, Unidade de Neurociências, Lisbon, Portugal
| | - Ana Caulino-Rocha
- Departamento de Química e Bioquímica, Faculty of Sciences, Universidade de Lisboa, Lisbon, Portugal.,BioISI-Biosystems & Integrative Sciences Institute, Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal
| | - Andreia Bento-Oliveira
- Departamento de Química e Bioquímica, Faculty of Sciences, Universidade de Lisboa, Lisbon, Portugal.,BioISI-Biosystems & Integrative Sciences Institute, Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal
| | - Joaquim Alexandre Ribeiro
- Instituto de Medicina Molecular, Unidade de Neurociências, Lisbon, Portugal.,Instituto de Farmacologia e Neurociências, Faculdade de Medicina, Universidade de Lisboa, Lisbon, Portugal
| | - Diana Cunha-Reis
- Instituto de Medicina Molecular, Unidade de Neurociências, Lisbon, Portugal.,Departamento de Química e Bioquímica, Faculty of Sciences, Universidade de Lisboa, Lisbon, Portugal.,BioISI-Biosystems & Integrative Sciences Institute, Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal
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7
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Gholami M, Hosseinmardi N, Mirnajafi-Zadeh J, Javan M, Semnanian S, Naghdi N, Fathollahi Y. Long-term potentiation enhancing effect of epileptic insult in the CA1 area is dependent on prior-application of primed-burst stimulation. Exp Brain Res 2020; 238:897-903. [PMID: 32166345 DOI: 10.1007/s00221-020-05766-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2019] [Accepted: 03/01/2020] [Indexed: 12/13/2022]
Abstract
Herein field recordings were utilized to test the effects of a transient period of pentylenetetrazol (PTZ) treatment on theta-burst long-term potentiation (LTP) at the Schaffer collateral-CA1 synapses as well as RT-PCR was used to investigate the effects of the combination of the pharmacological treatment and the theta-burst LTP induction on the expression of NMDA subunit mRNA in hippocampal slices. The slope of field excitatory postsynaptic potential (fEPSP) was unaffected while the population spike amplitude and area were increased by a transient period of PTZ treatment (3 mM, 10 min). After a theta burst, a brief PTZ exposure can lead to an enhancement of LTP as documented by fEPSP recording. The effect can be blocked by a selective NMDA receptor antagonist DL-AP5. An increase in the expression of GluN2B and GluN2A subunit mRNAs was also shown due to the combined treatment. The results indicate that the combined treatment increases the degree of NMDA-dependent LTP and are in accord with literature data on the subunit alterations of the hippocampal NMDA receptors. Moreover, our experimental paradigm can be used as a new approach to study the relevance of LTP-like phenomena and epileptic mechanisms.
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Affiliation(s)
- Masoumeh Gholami
- Department of Physiology, Faculty of Medical Sciences, Tarbiat Modares University, P.O. Box: 14115-111, Tehran, Iran.,Department of Basic Sciences, Torbat Heydariyeh University of Medical Sciences, Torbat Heydariyeh, Iran
| | - Narges Hosseinmardi
- Department of Physiology, Medical School, Shaheed Beheshti University of Medical Sciences, Tehran, Iran.,Neurophysiology Research Center, Medical School, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Javad Mirnajafi-Zadeh
- Department of Physiology, Faculty of Medical Sciences, Tarbiat Modares University, P.O. Box: 14115-111, Tehran, Iran
| | - Mohamad Javan
- Department of Physiology, Faculty of Medical Sciences, Tarbiat Modares University, P.O. Box: 14115-111, Tehran, Iran
| | - Saeed Semnanian
- Department of Physiology, Faculty of Medical Sciences, Tarbiat Modares University, P.O. Box: 14115-111, Tehran, Iran
| | - Nasser Naghdi
- Department of Physiology and Pharmacology, Pasteur Institute of Iran, Tehran, Iran
| | - Yaghoub Fathollahi
- Department of Physiology, Faculty of Medical Sciences, Tarbiat Modares University, P.O. Box: 14115-111, Tehran, Iran.
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Neuromodulators and Long-Term Synaptic Plasticity in Learning and Memory: A Steered-Glutamatergic Perspective. Brain Sci 2019; 9:brainsci9110300. [PMID: 31683595 PMCID: PMC6896105 DOI: 10.3390/brainsci9110300] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2019] [Revised: 10/24/2019] [Accepted: 10/29/2019] [Indexed: 12/19/2022] Open
Abstract
The molecular pathways underlying the induction and maintenance of long-term synaptic plasticity have been extensively investigated revealing various mechanisms by which neurons control their synaptic strength. The dynamic nature of neuronal connections combined with plasticity-mediated long-lasting structural and functional alterations provide valuable insights into neuronal encoding processes as molecular substrates of not only learning and memory but potentially other sensory, motor and behavioural functions that reflect previous experience. However, one key element receiving little attention in the study of synaptic plasticity is the role of neuromodulators, which are known to orchestrate neuronal activity on brain-wide, network and synaptic scales. We aim to review current evidence on the mechanisms by which certain modulators, namely dopamine, acetylcholine, noradrenaline and serotonin, control synaptic plasticity induction through corresponding metabotropic receptors in a pathway-specific manner. Lastly, we propose that neuromodulators control plasticity outcomes through steering glutamatergic transmission, thereby gating its induction and maintenance.
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Koutsoumpa A, Papatheodoropoulos C. Short-term dynamics of input and output of CA1 network greatly differ between the dorsal and ventral rat hippocampus. BMC Neurosci 2019; 20:35. [PMID: 31331291 PMCID: PMC6647178 DOI: 10.1186/s12868-019-0517-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2018] [Accepted: 07/12/2019] [Indexed: 12/13/2022] Open
Abstract
Background The functional heterogeneity of the hippocampus along its longitudinal axis at the level of behavior is an established concept; however, the neurobiological mechanisms are still unknown. Diversifications in the functioning of intrinsic hippocampal circuitry including short-term dynamics of synaptic inputs and neuronal output, that are important determinants of information processing in the brain, may profoundly contribute to functional specializations along the hippocampus. The objectives of the present study were the examination of the role of the GABAA receptor-mediated inhibition, the μ-opioid receptors and the effect of stimulation intensity on the dynamics of both synaptic input and neuronal output of CA1 region in the dorsal and ventral hippocampus. We used recordings of field potentials from adult rat hippocampal slices evoked by brief repetitive activation of Schaffer collaterals. Results We find that the local CA1 circuit of the dorsal hippocampus presents a remarkably increased dynamic range of frequency-dependent short-term changes in both input and output, ranging from strong facilitation to intense depression at low and high stimulation frequencies respectively. Furthermore, the input–output relationship in the dorsal CA1 circuit is profoundly influenced by frequency and time of presynaptic activation. Strikingly, the ventral hippocampus responds mostly with depression, displaying a rather monotonous input–output relationship over frequency and time. Partial blockade of GABAA receptor-mediated transmission (by 5 μM picrotoxin) profoundly influences input and output dynamics in the dorsal hippocampus but affected only the neuronal output in the ventral hippocampus. M-opioid receptors control short-term dynamics of input and output in the dorsal hippocampus but they play no role in the ventral hippocampus. Conclusion The results demonstrate that information processing by CA1 local network is highly diversified between the dorsal and ventral hippocampus. Transient detection of incoming patterns of activity and frequency-dependent sustained signaling of amplified neuronal information may be assigned to the ventral and dorsal hippocampal circuitry respectively. This disparity should have profound implications for the functional roles ascribed to distinct segments along the long axis of the hippocampus. Electronic supplementary material The online version of this article (10.1186/s12868-019-0517-5) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Andriana Koutsoumpa
- Laboratory of Neurophysiology, Department of Medicine, University of Patras, 26504, Rion, Greece.,Molecular Systems Biology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands
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Functional Neurochemistry of the Ventral and Dorsal Hippocampus: Stress, Depression, Dementia and Remote Hippocampal Damage. Neurochem Res 2018; 44:1306-1322. [PMID: 30357653 DOI: 10.1007/s11064-018-2662-0] [Citation(s) in RCA: 83] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Revised: 09/15/2018] [Accepted: 10/15/2018] [Indexed: 12/15/2022]
Abstract
The hippocampus is not a homogeneous brain area, and the complex organization of this structure underlies its relevance and functional pleiotropism. The new data related to the involvement of the ventral hippocampus in the cognitive function, behavior, stress response and its association with brain pathology, in particular, depression, are analyzed with a focus on neuroplasticity, specializations of the intrinsic neuronal network, corticosteroid signaling through mineralocorticoid and glucocorticoid receptors and neuroinflammation in the hippocampus. The data on the septo-temporal hippicampal gradient are analyzed with particular emphasis on the ventral hippocampus, a region where most important alteration underlying depressive disorders occur. According to the recent data, the existing simple paradigm "learning (dorsal hippocampus) versus emotions (ventral hippocampus)" should be substantially revised and specified. A new hypothesis is suggested on the principal involvement of stress response mechanisms (including interaction of released glucocorticoids with hippocampal receptors and subsequent inflammatory events) in the remote hippocampal damage underlying delayed dementia and depression induced by focal brain damage (e.g. post-stroke and post-traumatic). The translational validity of this hypothesis comprising new approaches in preventing post-stroke and post-trauma depression and dementia can be confirmed in experimental and clinical studies.
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