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Seljeset S, Liebowitz S, Bright DP, Smart TG. Pre- and postsynaptic modulation of hippocampal inhibitory synaptic transmission by pregnenolone sulphate. Neuropharmacology 2023; 233:109530. [PMID: 37037282 DOI: 10.1016/j.neuropharm.2023.109530] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Revised: 03/28/2023] [Accepted: 03/31/2023] [Indexed: 04/12/2023]
Abstract
Neurosteroids are important endogenous modulators of GABAA receptor-mediated neurotransmission within the CNS and play a vital role in maintaining normal healthy brain function. Research has mainly focussed on neurosteroids such as allopregnanolone and tetrahydro-deoxycorticosterone (THDOC) which are allosteric potentiators of GABAA receptors, whilst the sulphated steroids, including pregnenolone sulphate (PS), which inhibit GABAA receptor function, have been relatively neglected. Importantly, a full description of PS effects on inhibitory synaptic transmission, at concentrations that are expected to inhibit postsynaptic GABAA receptors, is lacking. Here, we address this deficit by recording inhibitory postsynaptic currents (IPSCs) from rat hippocampal neurons both in culture and in acute brain slices and explore the impact of PS at micromolar concentrations. We reveal that PS inhibits postsynaptic GABAA receptors, evident from reductions in IPSC amplitude and decay time. Concurrently, PS also causes an increase in synaptic GABA release which we discover is due to the activation of presynaptic TRPM3 receptors located close to presynaptic GABA release sites. Pharmacological blockade of TRPM3 receptors uncovers a PS-evoked reduction in IPSC frequency. This second presynaptic effect is caused by PS activation of inwardly-rectifying Kir2.3 channels on interneurons, which act to depress synaptic GABA release. Overall, we provide a comprehensive characterisation of pre- and postsynaptic modulation by PS of inhibitory synaptic transmission onto hippocampal neurons which elucidates the diverse mechanisms by which this understudied neurosteroid can modulate brain function.
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Affiliation(s)
- Sandra Seljeset
- Department of Neuroscience, Physiology & Pharmacology, UCL, Gower Street, London, WC1E 6BT, UK
| | - Seth Liebowitz
- Department of Neuroscience, Physiology & Pharmacology, UCL, Gower Street, London, WC1E 6BT, UK
| | - Damian P Bright
- Department of Neuroscience, Physiology & Pharmacology, UCL, Gower Street, London, WC1E 6BT, UK.
| | - Trevor G Smart
- Department of Neuroscience, Physiology & Pharmacology, UCL, Gower Street, London, WC1E 6BT, UK.
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2
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Whalen TC, Parker JE, Gittis AH, Rubin JE. Transmission of delta band (0.5-4 Hz) oscillations from the globus pallidus to the substantia nigra pars reticulata in dopamine depletion. J Comput Neurosci 2022; 51:361-380. [PMID: 37266768 PMCID: PMC10527635 DOI: 10.1007/s10827-023-00853-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Revised: 01/20/2023] [Accepted: 04/28/2023] [Indexed: 06/03/2023]
Abstract
Parkinson's disease (PD) and animal models of PD feature enhanced oscillations in several frequency bands in the basal ganglia (BG). Past research has emphasized the enhancement of 13-30 Hz beta oscillations. Recently, however, oscillations in the delta band (0.5-4 Hz) have been identified as a robust predictor of dopamine loss and motor dysfunction in several BG regions in mouse models of PD. In particular, delta oscillations in the substantia nigra pars reticulata (SNr) were shown to lead oscillations in motor cortex (M1) and persist under M1 lesion, but it is not clear where these oscillations are initially generated. In this paper, we use a computational model to study how delta oscillations may arise in the SNr due to projections from the globus pallidus externa (GPe). We propose a network architecture that incorporates inhibition in SNr from oscillating GPe neurons and other SNr neurons. In our simulations, this configuration yields firing patterns in model SNr neurons that match those measured in vivo. In particular, we see the spontaneous emergence of near-antiphase active-predicting and inactive-predicting neural populations in the SNr, which persist under the inclusion of STN inputs based on experimental recordings. These results demonstrate how delta oscillations can propagate through BG nuclei despite imperfect oscillatory synchrony in the source site, narrowing down potential targets for the source of delta oscillations in PD models and giving new insight into the dynamics of SNr oscillations.
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Affiliation(s)
- Timothy C Whalen
- Department of Mathematics, University of Pittsburgh, Pittsburgh, PA, United States
- Neuroscience Institute, Carnegie Mellon University, Pittsburgh, PA, United States
- Center for the Neural Basis of Cognition, Pittsburgh, PA, United States
- Design Interactive, Inc., Orlando, FL, United States
| | - John E Parker
- Department of Mathematics, University of Pittsburgh, Pittsburgh, PA, United States
- Center for the Neural Basis of Cognition, Pittsburgh, PA, United States
| | - Aryn H Gittis
- Neuroscience Institute, Carnegie Mellon University, Pittsburgh, PA, United States
- Center for the Neural Basis of Cognition, Pittsburgh, PA, United States
| | - Jonathan E Rubin
- Department of Mathematics, University of Pittsburgh, Pittsburgh, PA, United States.
- Center for the Neural Basis of Cognition, Pittsburgh, PA, United States.
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3
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Wiera G, Lebida K, Lech AM, Brzdąk P, Van Hove I, De Groef L, Moons L, Petrini EM, Barberis A, Mozrzymas JW. Long-term plasticity of inhibitory synapses in the hippocampus and spatial learning depends on matrix metalloproteinase 3. Cell Mol Life Sci 2021; 78:2279-2298. [PMID: 32959071 PMCID: PMC7966195 DOI: 10.1007/s00018-020-03640-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Revised: 08/19/2020] [Accepted: 09/03/2020] [Indexed: 12/16/2022]
Abstract
Learning and memory are known to depend on synaptic plasticity. Whereas the involvement of plastic changes at excitatory synapses is well established, plasticity mechanisms at inhibitory synapses only start to be discovered. Extracellular proteolysis is known to be a key factor in glutamatergic plasticity but nothing is known about its role at GABAergic synapses. We reveal that pharmacological inhibition of MMP3 activity or genetic knockout of the Mmp3 gene abolishes induction of postsynaptic iLTP. Moreover, the application of exogenous active MMP3 mimics major iLTP manifestations: increased mIPSCs amplitude, enlargement of synaptic gephyrin clusters, and a decrease in the diffusion coefficient of synaptic GABAA receptors that favors their entrapment within the synapse. Finally, we found that MMP3 deficient mice show faster spatial learning in Morris water maze and enhanced contextual fear conditioning. We conclude that MMP3 plays a key role in iLTP mechanisms and in the behaviors that presumably in part depend on GABAergic plasticity.
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Affiliation(s)
- Grzegorz Wiera
- Laboratory of Neuroscience, Department of Biophysics, Wroclaw Medical University, 50-367, Wroclaw, Poland.
| | - Katarzyna Lebida
- Laboratory of Neuroscience, Department of Biophysics, Wroclaw Medical University, 50-367, Wroclaw, Poland.
| | - Anna Maria Lech
- Laboratory of Neuroscience, Department of Biophysics, Wroclaw Medical University, 50-367, Wroclaw, Poland
- Laboratory of Cellular Neurobiology, Department of Physiology and Molecular Neurobiology, Wroclaw University, 50-205, Wroclaw, Poland
| | - Patrycja Brzdąk
- Laboratory of Neuroscience, Department of Biophysics, Wroclaw Medical University, 50-367, Wroclaw, Poland
- Laboratory of Cellular Neurobiology, Department of Physiology and Molecular Neurobiology, Wroclaw University, 50-205, Wroclaw, Poland
| | - Inge Van Hove
- Neural Circuit Development and Regeneration Research Group, Department of Biology, University of Leuven (KU Leuven), 3000, Leuven, Belgium
| | - Lies De Groef
- Neural Circuit Development and Regeneration Research Group, Department of Biology, University of Leuven (KU Leuven), 3000, Leuven, Belgium
- Leuven Brain Institute (LBI), KU Leuven, Leuven, Belgium
| | - Lieve Moons
- Neural Circuit Development and Regeneration Research Group, Department of Biology, University of Leuven (KU Leuven), 3000, Leuven, Belgium
- Leuven Brain Institute (LBI), KU Leuven, Leuven, Belgium
| | - Enrica Maria Petrini
- Laboratory of Synaptic Plasticity of Inhibitory Networks, Fondazione Istituto Italiano Di Tecnologia, 16163, Genoa, Italy
| | - Andrea Barberis
- Laboratory of Synaptic Plasticity of Inhibitory Networks, Fondazione Istituto Italiano Di Tecnologia, 16163, Genoa, Italy
| | - Jerzy W Mozrzymas
- Laboratory of Neuroscience, Department of Biophysics, Wroclaw Medical University, 50-367, Wroclaw, Poland
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Mortensen M, Huckvale R, Pandurangan AP, Baker JR, Smart TG. Optopharmacology reveals a differential contribution of native GABA A receptors to dendritic and somatic inhibition using azogabazine. Neuropharmacology 2020; 176:108135. [PMID: 32445639 PMCID: PMC7482436 DOI: 10.1016/j.neuropharm.2020.108135] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2020] [Revised: 04/20/2020] [Accepted: 05/09/2020] [Indexed: 12/13/2022]
Abstract
γ-aminobutyric acid type-A receptors (GABAARs) are inhibitory ligand-gated ion channels in the brain that are crucial for controlling neuronal excitation. To explore their physiological roles in cellular and neural network activity, it is important to understand why specific GABAAR isoforms are distributed not only to various brain regions and cell types, but also to specific areas of the membrane in individual neurons. To address this aim we have developed a novel photosensitive compound, azogabazine, that targets and reversibly inhibits GABAARs. The receptor selectivity of the compound is based on the competitive antagonist, gabazine, and photosensitivity is conferred by a photoisomerisable azobenzene group. Azogabazine can exist in either cis or trans conformations that are controlled by UV and blue light respectively, to affect receptor inhibition. We report that the trans-isomer preferentially binds and inhibits GABAAR function, whilst promotion of the cis-isomer caused unbinding of azogabazine from GABAARs. Using cultured cerebellar granule cells, azogabazine in conjunction with UV light applied to defined membrane domains, revealed higher densities of GABAARs at somatic inhibitory synapses compared to those populating proximal dendritic zones, even though the latter displayed a higher number of synapses per unit area of membrane. Azogabazine also revealed more pronounced GABA-mediated inhibition of action potential firing in proximal dendrites compared to the soma. Overall, azogabazine is a valuable addition to the photochemical toolkit that can be used to interrogate GABAAR function and inhibition.
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Affiliation(s)
- Martin Mortensen
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK
| | - Rosemary Huckvale
- The Institute of Cancer Research, 123 Old Brompton Road, London, SW7 3RP, UK
| | - Arun P Pandurangan
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge, CB2 0QH, UK
| | - James R Baker
- Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK
| | - Trevor G Smart
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK.
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Lu Y. Subtle differences in synaptic transmission in medial nucleus of trapezoid body neurons between wild-type and Fmr1 knockout mice. Brain Res 2019; 1717:95-103. [PMID: 31004576 DOI: 10.1016/j.brainres.2019.04.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Revised: 03/27/2019] [Accepted: 04/11/2019] [Indexed: 12/21/2022]
Abstract
In animal models for fragile X syndrome where the gene for fragile X mental retardation protein is knocked out (Fmr1 KO), neurotransmission in multiple brain regions shifts excitation/inhibition balance, resulting in hyperexcitability in neural circuits. Here, using whole-cell recordings from brainstem slices, we investigated synaptic transmission at the medial nucleus of trapezoid body (MNTB, a critical nucleus in the brainstem sound localization circuit), in Fmr1 KO and wild-type (WT) mice 2-3 weeks of age in both sexes. Surprisingly, neither synaptic excitation nor inhibition in KO neurons was significantly changed. The synaptic strength, kinetics, and short-term plasticity of synaptic excitation remained largely unaltered. Subtle differences were observed in response patterns, with KO neurons displaying less all-or-none eEPSCs. Similarly, synaptic inhibition mediated by glycine and GABA remains largely unchanged, except for a slower kinetics of mixed sIPSCs. In pharmacologically isolated glycinergic and GABAergic inhibition, no significant differences in synaptic strength and kinetics were detected between the two genotypes. These results demonstrate that at the cellular level synaptic transmission at MNTB is largely unaffected in Fmr1 KO mice by 2-3 weeks after birth, suggesting the existence of compensatory mechanisms that maintain the inhibitory output of MNTB to its targets in the auditory brainstem.
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Affiliation(s)
- Yong Lu
- Department of Anatomy and Neurobiology, College of Medicine, Northeast Ohio Medical University, Rootstown, OH 44272, USA.
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6
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Tran T, Gallagher M, Kirkwood A. Enhanced postsynaptic inhibitory strength in hippocampal principal cells in high-performing aged rats. Neurobiol Aging 2018; 70:92-101. [PMID: 30007169 DOI: 10.1016/j.neurobiolaging.2018.06.008] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2018] [Revised: 05/28/2018] [Accepted: 06/03/2018] [Indexed: 11/20/2022]
Abstract
Hyperactivity within the hippocampal formation, frequently observed in aged individuals, is thought to be a potential contributing mechanism to the memory decline often associated with aging. Consequently, we evaluated the postsynaptic strength of excitatory and inhibitory synapses in the granule cells of the dentate gyrus and CA1 pyramidal cells of a rat model of aging, in which each individual was behaviorally characterized as aged impaired (AI) or aged unimpaired (AU, with performance comparable to young (Y) individuals). In hippocampal slices of these 3 aged groups (Y, AI, AU), we found that compared to the young, the miniature excitatory and inhibitory currents (mEPSCs and mIPSCs) were larger in amplitude in the granule cells of the AU group and smaller in the AI group. In contrast, in CA1 cells, neither the mEPSCs nor the mIPSCs were affected by age, whereas the extrasynaptic conductance responsible for tonic inhibition was selectively enhanced in CA1 cells of AU individuals. Tonic inhibition conductance was not affected by age in the granule cells. These results support the notion that upregulation of synaptic inhibition could be a necessary condition for the maintenance of performance during aging. These findings also underscore the notions that successful aging requires adaptive upregulation, not merely the preservation of youthful functionality, and that age effects are not homogeneous across hippocampal subfields.
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Affiliation(s)
- Trinh Tran
- Mind/Brain Institute and Department of Neurosciences, Johns Hopkins University, 3400 N. Charles St, Baltimore, MD 21218, USA
| | - Michela Gallagher
- Department of Psychological and Brain Sciences, Johns Hopkins University, 3400 N. Charles St, Baltimore, MD 21218, USA.
| | - Alfredo Kirkwood
- Mind/Brain Institute and Department of Neurosciences, Johns Hopkins University, 3400 N. Charles St, Baltimore, MD 21218, USA.
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7
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Chen X, Durisic N, Lynch JW, Keramidas A. Inhibitory synapse deficits caused by familial α1 GABA A receptor mutations in epilepsy. Neurobiol Dis 2017; 108:213-24. [PMID: 28870844 DOI: 10.1016/j.nbd.2017.08.020] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2017] [Revised: 08/17/2017] [Accepted: 08/24/2017] [Indexed: 11/20/2022] Open
Abstract
Epilepsy is a spectrum of neurological disorders with many causal factors. The GABA type-A receptor (GABAAR) is a major genetic target for heritable human epilepsies. Here we examine the functional effects of three epilepsy-causing mutations to the α1 subunit (α1T10'I, α1D192N and α1A295D) on inhibitory postsynaptic currents (IPSCs) mediated by the major synaptic GABAAR isoform, α1β2γ2L. We employed a neuron - HEK293 cell heterosynapse preparation to record IPSCs mediated by mutant-containing GABAARs in isolation from other GABAAR isoforms. IPSCs were recorded in the presence of the anticonvulsant drugs, carbamazepine and midazolam, and at elevated temperatures (22, 37 and 40°C) to gain insight into mechanisms of febrile seizures. The mutant subunits were also transfected into cultured cortical neurons to investigate changes in synapse formation and neuronal morphology using fluorescence microscopy. We found that IPSCs mediated by α1T10'Iβ2γ2L, α1D192Nβ2γ2L GABAARs decayed faster than those mediated by α1β2γ2L receptors. IPSCs mediated by α1D192Nβ2γ2L and α1A295Dβ2γ2L receptors also exhibited a heightened temperature sensitivity. In addition, the α1T10'Iβ2γ2L GABAARs were refractory to modulation by carbamazepine or midazolam. In agreement with previous studies, we found that α1A295Dβ2γ2L GABAARs were retained intracellularly in HEK293 cells and neurons. However, pre-incubation with 100nM suberanilohydroxamic acid (SAHA) induced α1A295Dβ2γ2L GABAARs to mediate IPSCs that were indistinguishable in magnitude and waveform from those mediated by α1β2γ2L receptors. Finally, mutation-specific changes to synaptic bouton size, synapse number and neurite branching were also observed. These results provide new insights into the mechanisms of epileptogenesis of α1 epilepsy mutations and suggest possible leads for improving treatments for patients harbouring these mutations.
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8
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Chen X, Keramidas A, Lynch JW. Physiological and pharmacological properties of inhibitory postsynaptic currents mediated by α5β1γ2, α5β2γ2 and α5β3γ2 GABA A receptors. Neuropharmacology 2017; 125:243-253. [PMID: 28757051 DOI: 10.1016/j.neuropharm.2017.07.027] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2017] [Revised: 07/18/2017] [Accepted: 07/26/2017] [Indexed: 02/07/2023]
Abstract
α5-containing GABAARs are potential therapeutic targets for clinical conditions including age-related dementia, stroke, schizophrenia, Down syndrome, anaesthetic-induced amnesia, anxiety and pain. α5-containing GABAARs are expressed in layer 5 cortical neurons and hippocampal pyramidal neurons where they mediate both tonic currents and slow inhibitory postsynaptic currents (IPSCs). A range of drugs has been developed to specifically modulate these receptors. The main α5-containing GABAARs that are likely to exist in vivo are the α5β1γ2, α5β2γ2 and α5β3γ2 isoforms. We currently have few clues as to how these isoforms are distributed between synaptic and extrasynaptic compartments or their relative roles in controlling neuronal excitability. Accordingly, the aim of this study was to define the basic biophysical and pharmacological properties of IPSCs mediated by the three isoforms in a hippocampal neuron-HEK293 cell co-culture assay. The IPSC decay time constants were slow (α5β1γ2L: 45 ms; α5β1γ2L: 80 ms; α5β3γ2L: 184 ms) and were largely dominated by the intrinsic channel deactivation rates. By comparing IPSC rise times, we inferred that α5β1γ2L GABAARs are located postsynaptically whereas the other two are predominantly perisynaptic. α5β3γ2L GABAARs alone mediated tonic currents. We quantified the effects of four α5-specific inverse agonists (TB-21007, MRK-016, α5IA and L-655708) on IPSCs mediated by the three isoforms. All compounds selectively inhibited IPSC amplitudes and accelerated IPSC decay rates, albeit with distinct isoform specificities. MRK-016 also significantly accelerated IPSC rise times. These results provide a reference for future studies seeking to identify and characterize the properties of IPSCs mediated by α5-containing GABAAR isoforms in neurons.
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Affiliation(s)
- Xiumin Chen
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Angelo Keramidas
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Joseph W Lynch
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia.
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Copeland CS, Wall TM, Sims RE, Neale SA, Nisenbaum E, Parri HR, Salt TE. Astrocytes modulate thalamic sensory processing via mGlu2 receptor activation. Neuropharmacology 2017; 121:100-110. [PMID: 28416443 PMCID: PMC5480778 DOI: 10.1016/j.neuropharm.2017.04.019] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2016] [Revised: 03/27/2017] [Accepted: 04/13/2017] [Indexed: 11/27/2022]
Abstract
Astrocytes possess many of the same signalling molecules as neurons. However, the role of astrocytes in information processing, if any, is unknown. Using electrophysiological and imaging methods, we report the first evidence that astrocytes modulate neuronal sensory inhibition in the rodent thalamus. We found that mGlu2 receptor activity reduces inhibitory transmission from the thalamic reticular nucleus to the somatosensory ventrobasal thalamus (VB): mIPSC frequencies in VB slices were reduced by the Group II mGlu receptor agonist LY354740, an effect potentiated by mGlu2 positive allosteric modulator (PAM) LY487379 co-application (30 nM LY354740: 10.0 ± 1.6% reduction; 30 nM LY354740 & 30 μM LY487379: 34.6 ± 5.2% reduction). We then showed activation of mGlu2 receptors on astrocytes: astrocytic intracellular calcium levels were elevated by the Group II agonist, which were further potentiated upon mGlu2 PAM co-application (300 nM LY354740: ratio amplitude 0.016 ± 0.002; 300 nM LY354740 & 30 μM LY487379: ratio amplitude 0.035 ± 0.003). We then demonstrated mGlu2-dependent astrocytic disinhibition of VB neurons in vivo: VB neuronal responses to vibrissae stimulation trains were disinhibited by the Group II agonist and the mGlu2 PAM (LY354740: 156 ± 12% of control; LY487379: 144 ± 10% of control). Presence of the glial inhibitor fluorocitrate abolished the mGlu2 PAM effect (91 ± 5% of control), suggesting the mGlu2 component to the Group II effect can be attributed to activation of mGlu2 receptors localised on astrocytic processes within the VB. Gating of thalamocortical function via astrocyte activation represents a novel sensory processing mechanism. As this thalamocortical circuitry is important in discriminative processes, this demonstrates the importance of astrocytes in synaptic processes underlying attention and cognition. Thalamic inhibition is mediated by both neuronal and astrocytic mechanisms. Group II mGlu receptor (mGlu2/3) activation can modulate this thalamic inhibition. Thalamic astrocytes can be activated upon mGlu2 receptor stimulation. This process may enable relevant activity to be discerned from background noise. Targeting astrocytic mGlu2 receptors may therefore affect attention and cognition.
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Affiliation(s)
- C S Copeland
- Institute of Ophthalmology, University College London, 11-43 Bath Street, London, EC1V 9EL, UK; St George's, University of London, Cranmer Terrace, London, SW17 0RE, UK.
| | - T M Wall
- Eli Lilly and Company, 893 S Delaware Street, Indianapolis, IN 46285, USA.
| | - R E Sims
- School of Life and Health Sciences, Aston University, Birmingham, B4 7ET, UK.
| | - S A Neale
- Neurexpert Limited, Kemp House, 152-160 City Road, London, EC1V 2NX, UK.
| | - E Nisenbaum
- Eli Lilly and Company, 893 S Delaware Street, Indianapolis, IN 46285, USA.
| | - H R Parri
- School of Life and Health Sciences, Aston University, Birmingham, B4 7ET, UK.
| | - T E Salt
- Institute of Ophthalmology, University College London, 11-43 Bath Street, London, EC1V 9EL, UK.
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Abstract
This review centers on the discoveries made during more than six decades of neuroscience research on the role of gamma-amino-butyric acid (GABA) as neurotransmitter. In doing so, special emphasis is directed to the significant involvement of Canadian scientists in these advances. Starting with the early studies that established GABA as an inhibitory neurotransmitter at central synapses, we summarize the results pointing at the GABA receptor as a drug target as well as more recent evidence showing that GABAA receptor signaling plays a surprisingly active role in neuronal network synchronization, both during development and in the adult brain. Finally, we briefly address the involvement of GABA in neurological conditions that encompass epileptic disorders and mental retardation.
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11
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Kann O. The interneuron energy hypothesis: Implications for brain disease. Neurobiol Dis 2015; 90:75-85. [PMID: 26284893 DOI: 10.1016/j.nbd.2015.08.005] [Citation(s) in RCA: 150] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2015] [Revised: 07/22/2015] [Accepted: 08/12/2015] [Indexed: 12/12/2022] Open
Abstract
Fast-spiking, inhibitory interneurons - prototype is the parvalbumin-positive (PV+) basket cell - generate action potentials at high frequency and synchronize the activity of numerous excitatory principal neurons, such as pyramidal cells, during fast network oscillations by rhythmic inhibition. For this purpose, fast-spiking, PV+ interneurons have unique electrophysiological characteristics regarding action potential kinetics and ion conductances, which are associated with high energy expenditure. This is reflected in the neural ultrastructure by enrichment with mitochondria and cytochrome c oxidase, indicating the dependence on oxidative phosphorylation for adenosine-5'-triphosphate (ATP) generation. The high energy expenditure is most likely required for membrane ion transport in dendrites and the extensive axon arbor as well as for presynaptic release of neurotransmitter, gamma-aminobutyric acid (GABA). Fast-spiking, PV+ interneurons are central for the emergence of gamma oscillations (30-100Hz) that provide a fundamental mechanism of complex information processing during sensory perception, motor behavior and memory formation in networks of the hippocampus and the neocortex. Conversely, shortage in glucose and oxygen supply (metabolic stress) and/or excessive formation of reactive oxygen and nitrogen species (oxidative stress) may render these interneurons to be a vulnerable target. Dysfunction in fast-spiking, PV+ interneurons might set a low threshold for impairment of fast network oscillations and thus higher brain functions. This pathophysiological mechanism might be highly relevant for cerebral aging as well as various acute and chronic brain diseases, such as stroke, vascular cognitive impairment, epilepsy, Alzheimer's disease and schizophrenia.
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Affiliation(s)
- Oliver Kann
- Institute of Physiology and Pathophysiology, University of Heidelberg, Heidelberg, Germany; Interdisciplinary Center for Neurosciences (IZN), University of Heidelberg, Heidelberg, Germany.
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12
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Titz S, Sammler EM, Hormuzdi SG. Could tuning of the inhibitory tone involve graded changes in neuronal chloride transport? Neuropharmacology 2015; 95:321-31. [PMID: 25843644 DOI: 10.1016/j.neuropharm.2015.03.026] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2014] [Revised: 03/17/2015] [Accepted: 03/24/2015] [Indexed: 11/15/2022]
Abstract
Hyperpolarizing synaptic inhibition through GABAA and glycine receptors depends on the presence of the neuronal cation-chloride-cotransporter protein, KCC2. Several transcriptional and post-transcriptional mechanisms have been shown to regulate KCC2 and thereby influence the polarity and efficacy of inhibitory synaptic transmission. It is unclear however whether regulation of KCC2 enables the transporter to attain different levels of activity thus allowing a neuron to modulate the strength of inhibitory synaptic transmission to its changing requirements. We therefore investigated whether phosphorylation can allow KCC2 to achieve distinct levels of [Cl(-)]i in neurons. We generated a variety of KCC2 alanine dephosphorylation mimics and used NH4(+)-induced pHi shifts in cultured hippocampal neurons to quantify the rate of KCC2 transport activity exhibited by these mutants. To explore the relationship between KCC2 transport and GABAA receptor-mediated current amplitudes we performed gramicidine perforated-patch recordings. The correlation between EGABA and NH4(+)-induced pHi shifts enabled an estimate of the range of chloride extrusion possible by kinase/phosphatase regulation of KCC2. Our results demonstrate that KCC2 transport can vary considerably in magnitude depending on the combination of alanine mutations present on the protein. Transport can be enhanced to sufficiently high levels that hyperpolarizing GABAA responses may be obtained even in neurons with an extremely negative resting membrane potential and at high extracellular K(+) concentrations. Our findings highlight the significant potential for regulating the inhibitory tone by KCC2-mediated chloride extrusion and suggest that cellular signaling pathways may act combinatorially to alter KCC2 phosphorylation/dephosphorylation and thereby tune the strength of synaptic inhibition.
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Affiliation(s)
- Stefan Titz
- Institute for Physiology und Pathophysiology, University of Heidelberg, Im Neuenheimer Feld 326, 69120 Heidelberg, Germany.
| | - Esther M Sammler
- Division of Neuroscience, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, UK
| | - Sheriar G Hormuzdi
- Division of Neuroscience, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, UK.
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Copeland CS, Neale SA, Salt TE. Neuronal activity patterns in the mediodorsal thalamus and related cognitive circuits are modulated by metabotropic glutamate receptors. Neuropharmacology 2015; 92:16-24. [PMID: 25576798 PMCID: PMC4362770 DOI: 10.1016/j.neuropharm.2014.12.031] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2014] [Revised: 12/02/2014] [Accepted: 12/26/2014] [Indexed: 01/03/2023]
Abstract
The mediodorsal thalamus (MD) likely plays an important role in cognition as it receives abundant afferent connections from the amygdala and prefrontal cortex (PFC). Indeed, disturbed activity within the MD is thought to precipitate cognitive deficits associated with schizophrenia. As compounds acting at the Group II metabotropic glutamate (mGlu) receptors (subtypes mGlu2/mGlu3) have efficacy in animal models of schizophrenia, we investigated whether a Group II agonist and an mGlu2 positive allosteric modulator (PAM) could modulate MD activity. Extracellular single-unit recordings were made in vivo from MD neurones in anaesthetised rats. Responses were elicited by electrical stimulation of the PFC and/or amygdala, with Group II compounds locally applied as required. The Group II agonist reduced inhibition evoked in the MD: an effect manifested as an increase in short-latency responses, and a decrease in long-latency burst-firing. This disinhibitory action of the Group II receptors in the MD represents a mechanism of potential therapeutic importance as increased inhibition in the MD has been associated with cognitive deficit-onset. Furthermore, as co-application of the mGlu2 PAM did not potentiate the Group II agonist effects in the MD, we suggest that the Group II disinhibitory effect is majority-mediated via mGlu3. This heterogeneity in Group II receptor thalamic physiology bears consequence, as compounds active exclusively at the mGlu2 subtype are unlikely to perturb maladapted MD firing patterns associated with cognitive deficits, with activity at mGlu3 receptors possibly more appropriate. Indeed, polymorphisms in the mGlu3, but not the mGlu2, gene have been detected in patients with schizophrenia. There is heterogeneity in Group II receptor physiology across thalamic nuclei. This differential distribution may facilitate multimodal thalamic nuclei functions. Group II receptor activation reduced burst firing via reducing thalamic inhibition. Increased thalamic inhibition precipitates impairments in cognitive function. Activating the Group II receptors may therefore enhance cognitive function.
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Affiliation(s)
- C S Copeland
- Institute of Ophthalmology, University College London, 11-43 Bath Street, London, EC1V 9EL, UK.
| | - S A Neale
- Neurexpert Ltd, Kemp House, City Road, London, EC1V 2NX, UK.
| | - T E Salt
- Institute of Ophthalmology, University College London, 11-43 Bath Street, London, EC1V 9EL, UK.
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14
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Lévi S, Le Roux N, Eugène E, Poncer JC. Benzodiazepine ligands rapidly influence GABAA receptor diffusion and clustering at hippocampal inhibitory synapses. Neuropharmacology 2014; 88:199-208. [PMID: 24930360 DOI: 10.1016/j.neuropharm.2014.06.002] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2013] [Revised: 05/23/2014] [Accepted: 06/02/2014] [Indexed: 11/28/2022]
Abstract
Benzodiazepines (BZDs) are widely used in the treatment of a variety of neurological and psychiatric conditions including anxiety, insomnia and epilepsy. BZDs are thought to act predominantly by affecting the gating of GABAA receptor channels, resulting in enhanced GABA-mediated currents in neurons. However, mutations mimicking the effect of BZDs on GABAAR channel gating have been shown to also impact the membrane dynamics and synaptic anchoring of the receptors. Here, using single molecule tracking combined with electrophysiological recordings, we show that BZD ligands rapidly influence the dynamic behavior of GABAARs in hippocampal neurons. Application of the inverse BZD agonist DMCM rapidly increased the diffusion and reduced the clustering of GABAARs at synapses, resulting in reduced postsynaptic currents. Conversely, the BZD full agonist diazepam had little effect at rest but reduced lateral diffusion and increased synaptic stabilization and clustering of GABAARs upon sustained neuronal activity, resulting in enhanced potency of inhibitory synapses. These effects occurred in the absence of detectable changes in gephyrin clusters, suggesting they did not reflect a rapid dispersion of the synaptic scaffold. Thus, alterations of the diffusion and synaptic anchoring of GABAARs represent a novel, unsuspected mechanism through which BZDs rapidly modulate GABA signaling in central neurons.
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Affiliation(s)
- Sabine Lévi
- INSERM UMR-S 839, 75005, Paris, France; Université Pierre et Marie Curie, 75005, Paris, France; Institut du Fer a Moulin, 75005, Paris, France.
| | - Nicolas Le Roux
- INSERM UMR-S 839, 75005, Paris, France; Université Pierre et Marie Curie, 75005, Paris, France; Institut du Fer a Moulin, 75005, Paris, France
| | - Emmanuel Eugène
- INSERM UMR-S 839, 75005, Paris, France; Université Pierre et Marie Curie, 75005, Paris, France; Institut du Fer a Moulin, 75005, Paris, France
| | - Jean Christophe Poncer
- INSERM UMR-S 839, 75005, Paris, France; Université Pierre et Marie Curie, 75005, Paris, France; Institut du Fer a Moulin, 75005, Paris, France.
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