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Jain S, LaFrancois JJ, Gerencer K, Botterill JJ, Kennedy M, Criscuolo C, Scharfman HE. Increasing adult neurogenesis protects mice from epilepsy. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.07.08.548217. [PMID: 37502909 PMCID: PMC10369878 DOI: 10.1101/2023.07.08.548217] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/29/2023]
Abstract
Neurogenesis occurs in the adult brain in the hippocampal dentate gyrus, an area that contains neurons which are vulnerable to insults and injury, such as severe seizures. Previous studies showed that increasing adult neurogenesis reduced neuronal damage after these seizures. Because the damage typically is followed by chronic life-long seizures (epilepsy), we asked if increasing adult neurogenesis would prevent epilepsy. Adult neurogenesis was selectively increased by deleting the pro-apoptotic gene Bax from Nestin-expressing progenitors. Tamoxifen was administered at 6 weeks of age to conditionally delete Bax in Nestin-CreERT2 Bax fl/fl mice. Six weeks after tamoxifen administration, severe seizures (status epilepticus; SE) were induced by injection of the convulsant pilocarpine. After mice developed epilepsy, seizure frequency was quantified for 3 weeks. Mice with increased adult neurogenesis exhibited fewer chronic seizures. Postictal depression was reduced also. These results were primarily in female mice, possibly because they were the more affected by Bax deletion than males, consistent with sex differences in Bax. The female mice with enhanced adult neurogenesis also showed less neuronal loss of hilar mossy cells and hilar somatostatin-expressing neurons than wild type females or males, which is notable because these two hilar cell types are implicated in epileptogenesis. The results suggest that selective Bax deletion to increase adult neurogenesis can reduce experimental epilepsy, and the effect shows a striking sex difference. The results are surprising in light of past studies showing that suppressing adult-born neurons can also reduce chronic seizures.
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Affiliation(s)
- Swati Jain
- Center for Dementia Research, The Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY 10962
| | - John J. LaFrancois
- Center for Dementia Research, The Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY 10962
| | - Kasey Gerencer
- Center for Dementia Research, The Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY 10962
- Current address: Department of Psychology, The University of Maine, Orono, ME 04469
| | - Justin J. Botterill
- Department of Anatomy, Physiology, & Pharmacology, College of Medicine, Saskatoon, SK S7N 5E5
| | - Meghan Kennedy
- Center for Dementia Research, The Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY 10962
| | - Chiara Criscuolo
- Center for Dementia Research, The Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY 10962
- Departments of Child and Adolescent Psychiatry, New York University Grossman School of Medicine, New York, NY 10016
| | - Helen E. Scharfman
- Center for Dementia Research, The Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY 10962
- Departments of Child and Adolescent Psychiatry, New York University Grossman School of Medicine, New York, NY 10016
- Departments of Neuroscience & Physiology, Psychiatry, and the New York University Neuroscience Institute, New York University Grossman School of Medicine, New York, NY 10016
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2
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Kaufhold D, Maristany de Las Casas E, Ocaña-Fernández MDÁ, Cazala A, Yuan M, Kulik A, Cholvin T, Steup S, Sauer JF, Eyre MD, Elgueta C, Strüber M, Bartos M. Spine plasticity of dentate gyrus parvalbumin-positive interneurons is regulated by experience. Cell Rep 2024; 43:113806. [PMID: 38377001 DOI: 10.1016/j.celrep.2024.113806] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2023] [Revised: 12/21/2023] [Accepted: 01/31/2024] [Indexed: 02/22/2024] Open
Abstract
Experience-driven alterations in neuronal activity are followed by structural-functional modifications allowing cells to adapt to these activity changes. Structural plasticity has been observed for cortical principal cells. However, how GABAergic interneurons respond to experience-dependent network activity changes is not well understood. We show that parvalbumin-expressing interneurons (PVIs) of the dentate gyrus (DG) possess dendritic spines, which undergo behaviorally induced structural dynamics. Glutamatergic inputs at PVI spines evoke signals with high spatial compartmentalization defined by neck length. Mice experiencing novel contexts form more PVI spines with elongated necks and exhibit enhanced network and PVI activity and cFOS expression. Enhanced green fluorescent protein reconstitution across synaptic partner-mediated synapse labeling shows that experience-driven PVI spine growth boosts targeting of PVI spines over shafts by glutamatergic synapses. Our findings propose a role for PVI spine dynamics in regulating PVI excitation by their inputs, which may allow PVIs to dynamically adjust their functional integration in the DG microcircuitry in relation to network computational demands.
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Affiliation(s)
- Dorthe Kaufhold
- Institute of Physiology I, Faculty of Medicine, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany; Faculty of Biology, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany
| | | | | | - Aurore Cazala
- Institute of Physiology I, Faculty of Medicine, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany
| | - Mei Yuan
- Institute of Physiology I, Faculty of Medicine, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany
| | - Akos Kulik
- Institute of Physiology II, Faculty of Medicine, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany; BIOSS Centre for Biological Signaling Studies, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany
| | - Thibault Cholvin
- Institute of Physiology I, Faculty of Medicine, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany
| | - Stefanie Steup
- Institute of Physiology I, Faculty of Medicine, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany
| | - Jonas-Frederic Sauer
- Institute of Physiology I, Faculty of Medicine, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany
| | - Mark D Eyre
- Institute of Physiology I, Faculty of Medicine, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany
| | - Claudio Elgueta
- Institute of Physiology I, Faculty of Medicine, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany
| | - Michael Strüber
- Epilepsy Center Frankfurt Rhine-Main, Center of Neurology and Neurosurgery, Goethe University, 60528 Frankfurt am Main, Germany
| | - Marlene Bartos
- Institute of Physiology I, Faculty of Medicine, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany.
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Kapur J, Long L, Dixon-Salazar T. Consequences: Bench to home. Epilepsia 2022; 63 Suppl 1:S14-S24. [PMID: 35999173 DOI: 10.1111/epi.17342] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 06/08/2022] [Accepted: 06/08/2022] [Indexed: 01/02/2023]
Abstract
Seizure clusters (also referred to as acute repetitive seizures) consist of several seizures interspersed with brief interictal periods. Seizure clusters can break down γ-aminobutyric acidergic (GABAergic) inhibition of dentate granule cells, leading to hyperactivation. Functional changes to GABAA receptors, which play a vital neuroinhibitory role, can include altered GABAA receptor subunit trafficking and cellular localization, intracellular chloride accumulation, and dysregulation of proteins critical to chloride homeostasis. A reduction in neuroinhibition and potentiation of excitatory neurotransmission in CA1 pyramidal neurons represent pathological mechanisms that underlie seizure clusters. Benzodiazepines are well-established treatments for seizure clusters; however, there remain barriers to appropriate care. At the clinical level, there is variability in seizure cluster definitions, such as the number and/or type of seizures associated with a cluster as well as the interictal duration between seizures. This can lead to delays in diagnosis and timely treatment. There are gaps in understanding between clinicians, their patients, and caregivers regarding acute treatment for seizure clusters, such as the use of rescue medications and emergency services. This lack of consensus to define seizure clusters in addition to a lack of education for appropriate treatment can affect quality of life for patients and place a greater burden on patient families and caregivers. For patients with seizure clusters, the sense of unpredictability can lead to continuous traumatic stress, during which patients and families live with a heightened level of anxiety. Clinicians can affect patient quality of life and clinical outcomes through improved seizure cluster education and treatment, such as the development and implementation of a personalized seizure action plan as well as prescriptions for suitable rescue medications indicated for seizure clusters and instructions for their proper use. In all, the combination of targeted therapy along with patient education and support can improve quality of life.
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Affiliation(s)
- Jaideep Kapur
- Department of Neurology, University of Virginia, Charlottesville, Virginia, USA
| | - Lucretia Long
- Wexner Medical Center, The Ohio State University, Columbus, Ohio, USA
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Perrenoud Q, Leclerc C, Geoffroy H, Vitalis T, Richetin K, Rampon C, Gallopin T. Molecular and electrophysiological features of GABAergic neurons in the dentate gyrus reveal limited homology with cortical interneurons. PLoS One 2022; 17:e0270981. [PMID: 35802727 PMCID: PMC9269967 DOI: 10.1371/journal.pone.0270981] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Accepted: 06/21/2022] [Indexed: 11/18/2022] Open
Abstract
GABAergic interneurons tend to diversify into similar classes across telencephalic regions. However, it remains unclear whether the electrophysiological and molecular properties commonly used to define these classes are discriminant in the hilus of the dentate gyrus. Here, using patch-clamp combined with single cell RT-PCR, we compare the relevance of commonly used electrophysiological and molecular features for the clustering of GABAergic interneurons sampled from the mouse hilus and primary sensory cortex. While unsupervised clustering groups cortical interneurons into well-established classes, it fails to provide a convincing partition of hilar interneurons. Statistical analysis based on resampling indicates that hilar and cortical GABAergic interneurons share limited homology. While our results do not invalidate the use of classical molecular marker in the hilus, they indicate that classes of hilar interneurons defined by the expression of molecular markers do not exhibit strongly discriminating electrophysiological properties.
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Affiliation(s)
- Quentin Perrenoud
- Brain Plasticity Unit, CNRS, ESPCI Paris, PSL Research University, Paris, France
| | - Clémence Leclerc
- Brain Plasticity Unit, CNRS, ESPCI Paris, PSL Research University, Paris, France
- Centre de Recherches sur la Cognition Animale (CRCA), Centre de Biologie Intégrative (CBI), Université de Toulouse; CNRS, UPS, France
| | - Hélène Geoffroy
- Brain Plasticity Unit, CNRS, ESPCI Paris, PSL Research University, Paris, France
| | - Tania Vitalis
- Brain Plasticity Unit, CNRS, ESPCI Paris, PSL Research University, Paris, France
| | - Kevin Richetin
- Centre de Recherches sur la Cognition Animale (CRCA), Centre de Biologie Intégrative (CBI), Université de Toulouse; CNRS, UPS, France
| | - Claire Rampon
- Centre de Recherches sur la Cognition Animale (CRCA), Centre de Biologie Intégrative (CBI), Université de Toulouse; CNRS, UPS, France
| | - Thierry Gallopin
- Brain Plasticity Unit, CNRS, ESPCI Paris, PSL Research University, Paris, France
- * E-mail:
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Urrutia-Piñones J, Morales-Moraga C, Sanguinetti-González N, Escobar AP, Chiu CQ. Long-Range GABAergic Projections of Cortical Origin in Brain Function. Front Syst Neurosci 2022; 16:841869. [PMID: 35392440 PMCID: PMC8981584 DOI: 10.3389/fnsys.2022.841869] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Accepted: 02/10/2022] [Indexed: 12/12/2022] Open
Abstract
The study of long-range GABAergic projections has traditionally been focused on those with subcortical origin. In the last few years, cortical GABAergic neurons have been shown to not only mediate local inhibition, but also extend long-range axons to remote cortical and subcortical areas. In this review, we delineate the different types of long-range GABAergic neurons (LRGNs) that have been reported to arise from the hippocampus and neocortex, paying attention to the anatomical and functional circuits they form to understand their role in behavior. Although cortical LRGNs are similar to their interneuron and subcortical counterparts, they comprise distinct populations that show specific patterns of cortico-cortical and cortico-fugal connectivity. Functionally, cortical LRGNs likely induce timed disinhibition in target regions to synchronize network activity. Thus, LRGNs are emerging as a new element of cortical output, acting in concert with long-range excitatory projections to shape brain function in health and disease.
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Affiliation(s)
- Jocelyn Urrutia-Piñones
- Ph.D. Program in Neuroscience, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
- Facultad de Ciencias, Instituto de Neurociencia, Universidad de Valparaíso, Valparaíso, Chile
| | - Camila Morales-Moraga
- Facultad de Ciencias, Instituto de Neurociencia, Universidad de Valparaíso, Valparaíso, Chile
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
| | - Nicole Sanguinetti-González
- Ph.D. Program in Neuroscience, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
- Facultad de Ciencias, Instituto de Neurociencia, Universidad de Valparaíso, Valparaíso, Chile
| | - Angelica P. Escobar
- Instituto de Fisiología, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
- Centro de Neurobiología y Fisiopatología Integrativa, Universidad de Valparaíso, Valparaíso, Chile
| | - Chiayu Q. Chiu
- Facultad de Ciencias, Instituto de Neurociencia, Universidad de Valparaíso, Valparaíso, Chile
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
- *Correspondence: Chiayu Q. Chiu,
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6
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Degro CE, Bolduan F, Vida I, Booker SA. Interneuron diversity in the rat dentate gyrus: An unbiased in vitro classification. Hippocampus 2022; 32:310-331. [PMID: 35171512 PMCID: PMC9306941 DOI: 10.1002/hipo.23408] [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: 06/22/2021] [Revised: 01/24/2022] [Accepted: 01/29/2022] [Indexed: 11/08/2022]
Abstract
Information processing in cortical circuits, including the hippocampus, relies on the dynamic control of neuronal activity by GABAergic interneurons (INs). INs form a heterogenous population with defined types displaying distinct morphological, molecular, and physiological characteristics. In the major input region of the hippocampus, the dentate gyrus (DG), a number of IN types have been described which provide synaptic inhibition to distinct compartments of excitatory principal cells (PrCs) and other INs. In this study, we perform an unbiased classification of GABAergic INs in the DG by combining in vitro whole-cell patch-clamp recordings, intracellular labeling, morphological analysis, and supervised cluster analysis to better define IN type diversity in this region. This analysis reveals that DG INs divide into at least 13 distinct morpho-physiological types which reflect the complexity of the local IN network and serve as a basis for further network analyses.
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Affiliation(s)
- Claudius E Degro
- Institute for Integrative Neuroanatomy, Charité - Universitätmedizin Berlin, Berlin, Germany
| | - Felix Bolduan
- Institute for Integrative Neuroanatomy, Charité - Universitätmedizin Berlin, Berlin, Germany
| | - Imre Vida
- Institute for Integrative Neuroanatomy, Charité - Universitätmedizin Berlin, Berlin, Germany
| | - Sam A Booker
- Institute for Integrative Neuroanatomy, Charité - Universitätmedizin Berlin, Berlin, Germany.,Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, UK.,Simons Initiative for the Developing Brain, University of Edinburgh, Edinburgh, UK
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7
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Abstract
Temporal lobe epilepsy is considered to be one of the most common and severe forms of focal epilepsies. Patients frequently develop cognitive deficits and emotional blunting along progression of the disease. The high incidence of refractoriness to antiepileptic drugs and a frequent lack of admissibility to surgery pose an unmet medical challenge. In the urgent quest for novel treatment strategies, neuropeptides and their receptors are interesting candidates. However, their therapeutic potential has not yet been fully exploited. This chapter focuses on the functional role of the dynorphins (Dyns) and the kappa opioid receptor (KOR) system in temporal lobe epilepsy and the hippocampus.Genetic polymorphisms in the prepro-dynorphin (pDyn) gene causing lower levels of Dyns in humans and pDyn gene knockout in mice increase the risk to develop epilepsy. This suggests a role of Dyns and KOR as modulators of neuronal excitability. Indeed, KOR agonists induce inhibition of presynaptic neurotransmitter release, as well as postsynaptic hyperpolarization in glutamatergic neurons, both producing anticonvulsant effects.The development of new approaches to modulate the complex KOR signalling cascade (e.g. biased agonism and gene therapy) opens up new exciting therapeutic opportunities with regard to seizure control and epilepsy. Potential adverse side effects of KOR agonists may be minimized through functional selectivity or locally restricted treatment. Preclinical data suggest a high potential of such approaches to control seizures.
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Affiliation(s)
- Luca Zangrandi
- Institute of Virology, Campus Benjamin Franklin, Charité - Universitätsmedizin Berlin, Berlin, Germany
- Freie Universität Berlin, Berlin, Germany
- Humboldt-Universität zu Berlin, Berlin, Germany
- Berlin Institute of Health, Berlin, Germany
| | - Christoph Schwarzer
- Department of Pharmacology, Medical University of Innsbruck, Innsbruck, Austria.
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8
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Guzman SJ, Schlögl A, Espinoza C, Zhang X, Suter BA, Jonas P. How connectivity rules and synaptic properties shape the efficacy of pattern separation in the entorhinal cortex-dentate gyrus-CA3 network. NATURE COMPUTATIONAL SCIENCE 2021; 1:830-842. [PMID: 38217181 DOI: 10.1038/s43588-021-00157-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Accepted: 10/12/2021] [Indexed: 01/15/2024]
Abstract
Pattern separation is a fundamental brain computation that converts small differences in input patterns into large differences in output patterns. Several synaptic mechanisms of pattern separation have been proposed, including code expansion, inhibition and plasticity; however, which of these mechanisms play a role in the entorhinal cortex (EC)-dentate gyrus (DG)-CA3 circuit, a classical pattern separation circuit, remains unclear. Here we show that a biologically realistic, full-scale EC-DG-CA3 circuit model, including granule cells (GCs) and parvalbumin-positive inhibitory interneurons (PV+-INs) in the DG, is an efficient pattern separator. Both external gamma-modulated inhibition and internal lateral inhibition mediated by PV+-INs substantially contributed to pattern separation. Both local connectivity and fast signaling at GC-PV+-IN synapses were important for maximum effectiveness. Similarly, mossy fiber synapses with conditional detonator properties contributed to pattern separation. By contrast, perforant path synapses with Hebbian synaptic plasticity and direct EC-CA3 connection shifted the network towards pattern completion. Our results demonstrate that the specific properties of cells and synapses optimize higher-order computations in biological networks and might be useful to improve the deep learning capabilities of technical networks.
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Affiliation(s)
- S Jose Guzman
- IST Austria, Klosterneuburg, Austria
- Institute of Molecular Biotechnology, Vienna, Austria
| | | | - Claudia Espinoza
- IST Austria, Klosterneuburg, Austria
- Medical University of Austria, Division of Cognitive Neurobiology, Vienna, Austria
| | - Xiaomin Zhang
- IST Austria, Klosterneuburg, Austria
- Brain Research Institute, University of Zürich, Zurich, Switzerland
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9
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Cheng Q, Lamb P, Stevanovic K, Bernstein BJ, Fry SA, Cushman JD, Yakel JL. Differential signalling induced by α7 nicotinic acetylcholine receptors in hippocampal dentate gyrus in vitro and in vivo. J Physiol 2021; 599:4687-4704. [PMID: 34487349 DOI: 10.1113/jp280505] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Accepted: 09/03/2021] [Indexed: 11/08/2022] Open
Abstract
The activation of α7 nicotinic acetylcholine receptors (nAChRs) has been shown to improve hippocampus-dependent learning and memory. α7 nAChRs are densely expressed among several different cell types in the hippocampus, with high Ca2+ permeability, although it is unclear if α7 nAChRs mobilize differential signalling mechanisms among distinct neuronal populations. To address this question, we compared α7 nAChR agonist-induced responses (i.e. calcium and cAMP changes) between granule cells and GABAergic neurons in the hippocampal dentate gyrus both in vitro and in vivo. In cultured organotypic hippocampal slices, we observed robust intracellular calcium and cAMP increases in dentate granule cells upon activation of α7 nAChRs. In contrast, GABAergic interneurons displayed little change in either calcium or cAMP concentration after α7 nAChR activation, even though they displayed much larger α7 nAChR current responses than those of dentate granule cells. We found that this was due to smaller α7 nAChR-induced Ca2+ rises in GABAergic interneurons. Thus, the regulation of the Ca2+ transients in different cell types resulted in differential subsequent intracellular signalling cascades and likely the ultimate outcome of α7 nAChR activation. Furthermore, we monitored neuronal activities of dentate granule cells and GABAergic interneurons in vivo via optic fibre photometry. We observed enhancement of neuronal activities after nicotine administration in dentate granule cells, but not in GABAergic neurons, which was absent in α7 nAChR-deficient granule cells. In summary, we reveal a mechanism for α7 nAChR-mediated increase of neuronal activity via cell type-specific intracellular signalling pathways. KEY POINTS: α7 nicotinic acetylcholine receptors (nAChRs) are widely distributed throughout the central nervous system and regulate a variety of brain functions including learning and memory. Understanding the cellular signalling mechanisms of their activations among different neuronal populations is important for delineating their actions in cognitive function, and developing effective treatment strategies for cognitive deficits. We report that α7 nAChR activation leads to Ca2+ and cAMP increases in granule cells (but not in GABAergic interneurons) in hippocampal dentate gyrus in vitro, a key region for pattern separation during learning. We also found that nicotine enhanced granule cell (but not in GABAergic interneurons) activity in an α7 nAChR-dependent manner via in vivo fibre photometry recording. Based on our findings, we propose that differential responses to α7 nAChR activation between granule cells and GABAergic interneurons is responsible for the increase of excitation by α7 nAChR agonists in hippocampal circuits synergistically.
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Affiliation(s)
- Qing Cheng
- Neurobiology Laboratory, The National Institute of Environmental Health Sciences/National Institutes of Health, Durham, NC, USA.,Biological/Biomedical Research Institute, North Carolina Central University, Durham, NC, USA
| | - Patricia Lamb
- Neurobiology Laboratory, The National Institute of Environmental Health Sciences/National Institutes of Health, Durham, NC, USA
| | - Korey Stevanovic
- Neurobiology Laboratory, The National Institute of Environmental Health Sciences/National Institutes of Health, Durham, NC, USA
| | - Briana J Bernstein
- Neurobiology Laboratory, The National Institute of Environmental Health Sciences/National Institutes of Health, Durham, NC, USA
| | - Sydney A Fry
- Neurobiology Laboratory, The National Institute of Environmental Health Sciences/National Institutes of Health, Durham, NC, USA
| | - Jesse D Cushman
- Neurobiology Laboratory, The National Institute of Environmental Health Sciences/National Institutes of Health, Durham, NC, USA
| | - Jerrel L Yakel
- Neurobiology Laboratory, The National Institute of Environmental Health Sciences/National Institutes of Health, Durham, NC, USA
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10
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Honoré E, Khlaifia A, Bosson A, Lacaille JC. Hippocampal Somatostatin Interneurons, Long-Term Synaptic Plasticity and Memory. Front Neural Circuits 2021; 15:687558. [PMID: 34149368 PMCID: PMC8206813 DOI: 10.3389/fncir.2021.687558] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Accepted: 04/30/2021] [Indexed: 12/13/2022] Open
Abstract
A distinctive feature of the hippocampal structure is the diversity of inhibitory interneurons. These complex inhibitory interconnections largely contribute to the tight modulation of hippocampal circuitry, as well as to the formation and coordination of neuronal assemblies underlying learning and memory. Inhibitory interneurons provide more than a simple transitory inhibition of hippocampal principal cells (PCs). The synaptic plasticity of inhibitory neurons provides long-lasting changes in the hippocampal network and is a key component of memory formation. The dendrite targeting interneurons expressing the peptide somatostatin (SOM) are particularly interesting in this regard because they display unique long-lasting synaptic changes leading to metaplastic regulation of hippocampal networks. In this article, we examine the actions of the neuropeptide SOM on hippocampal cells, synaptic plasticity, learning, and memory. We address the different subtypes of hippocampal SOM interneurons. We describe the long-term synaptic plasticity that takes place at the excitatory synapses of SOM interneurons, its singular induction and expression mechanisms, as well as the consequences of these changes on the hippocampal network, learning, and memory. We also review evidence that astrocytes provide cell-specific dynamic regulation of inhibition of PC dendrites by SOM interneurons. Finally, we cover how, in mouse models of Alzheimer’s disease (AD), dysfunction of plasticity of SOM interneuron excitatory synapses may also contribute to cognitive impairments in brain disorders.
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Affiliation(s)
- Eve Honoré
- Department of Neurosciences, Centre for Interdisciplinary Research on Brain and Learning, Research Group on the Central Nervous System, Université de Montréal, Montreal, QC, Canada
| | - Abdessattar Khlaifia
- Department of Neurosciences, Centre for Interdisciplinary Research on Brain and Learning, Research Group on the Central Nervous System, Université de Montréal, Montreal, QC, Canada
| | - Anthony Bosson
- Department of Neurosciences, Centre for Interdisciplinary Research on Brain and Learning, Research Group on the Central Nervous System, Université de Montréal, Montreal, QC, Canada
| | - Jean-Claude Lacaille
- Department of Neurosciences, Centre for Interdisciplinary Research on Brain and Learning, Research Group on the Central Nervous System, Université de Montréal, Montreal, QC, Canada
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11
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Sabet N, Soltani Z, Khaksari M. Multipotential and systemic effects of traumatic brain injury. J Neuroimmunol 2021; 357:577619. [PMID: 34058510 DOI: 10.1016/j.jneuroim.2021.577619] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2021] [Revised: 05/07/2021] [Accepted: 05/24/2021] [Indexed: 02/06/2023]
Abstract
Traumatic brain injury (TBI) is one of the leading causes of disability and mortality of people at all ages. Biochemical, cellular and physiological events that occur during primary injury lead to a delayed and long-term secondary damage that can last from hours to years. Secondary brain injury causes tissue damage in the central nervous system and a subsequent strong and rapid inflammatory response that may lead to persistent inflammation. However, this inflammatory response is not limited to the brain. Inflammatory mediators are transferred from damaged brain tissue to the bloodstream and produce a systemic inflammatory response in peripheral organs, including the cardiovascular, pulmonary, gastrointestinal, renal and endocrine systems. Complications of TBI are associated with its multiple and systemic effects that should be considered in the treatment of TBI patients. Therefore, in this review, an attempt was made to examine the systemic effects of TBI in detail. It is hoped that this review will identify the mechanisms of injury and complications of TBI, and open a window for promising treatment in TBI complications.
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Affiliation(s)
- Nazanin Sabet
- Endocrinology and Metabolism Research Center, Institute of Basic and Clinical Physiology Sciences, Faculty of Medicine, Kerman University of Medical Sciences, Kerman, Iran; Department of Physiology and Pharmacology, Afzalipour Faculty of Medicine, Kerman University of Medical Sciences, Kerman, Iran
| | - Zahra Soltani
- Endocrinology and Metabolism Research Center, Institute of Basic and Clinical Physiology Sciences, Faculty of Medicine, Kerman University of Medical Sciences, Kerman, Iran; Department of Physiology and Pharmacology, Afzalipour Faculty of Medicine, Kerman University of Medical Sciences, Kerman, Iran.
| | - Mohammad Khaksari
- Physiology Research Center, Institute of Neuropharmacology, Kerman University of Medical Sciences, Kerman, Iran
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Botterill JJ, Gerencer KJ, Vinod KY, Alcantara‐Gonzalez D, Scharfman HE. Dorsal and ventral mossy cells differ in their axonal projections throughout the dentate gyrus of the mouse hippocampus. Hippocampus 2021; 31:522-539. [PMID: 33600026 PMCID: PMC8247909 DOI: 10.1002/hipo.23314] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2020] [Revised: 01/24/2021] [Accepted: 01/30/2021] [Indexed: 11/14/2022]
Abstract
Glutamatergic hilar mossy cells (MCs) have axons that terminate both near and far from their cell body but stay within the DG, making synapses primarily in the molecular layer. The long-range axons are considered the primary projection, and extend throughout the DG ipsilateral to the soma, and project to the contralateral DG. The specificity of MC axons for the inner molecular layer (IML) has been considered to be a key characteristic of the DG. In the present study, we made the surprising finding that dorsal MC axons are an exception to this rule. We used two mouse lines that allow for Cre-dependent viral labeling of MCs and their axons: dopamine receptor D2 (Drd2-Cre) and calcitonin receptor-like receptor (Crlr-Cre). A single viral injection into the dorsal DG to label dorsal MCs resulted in labeling of MC axons in both the IML and middle molecular layer (MML). Interestingly, this broad termination of dorsal MC axons occurred throughout the septotemporal DG. In contrast, long-range axons of ventral MCs terminated in the IML, consistent with the literature. Taken together, these results suggest that dorsal and ventral MCs differ significantly in their axonal projections. Since MC projections in the ML are thought to terminate primarily on GCs, the results suggest a dorsal-ventral difference in MC activation of GCs. The surprising difference in dorsal and ventral MC projections should therefore be considered when evaluating dorsal-ventral differences in DG function.
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Affiliation(s)
- Justin J. Botterill
- Center for Dementia ResearchThe Nathan Kline Institute for Psychiatric ResearchOrangeburgNew YorkUSA
| | - Kathleen J. Gerencer
- Center for Dementia ResearchThe Nathan Kline Institute for Psychiatric ResearchOrangeburgNew YorkUSA
| | - K. Yaragudri Vinod
- Department of Analytical PsychopharmacologyThe Nathan Kline Institute for Psychiatric ResearchOrangeburgNew YorkUSA
- Emotional Brain InstituteThe Nathan Kline Institute for Psychiatric ResearchOrangeburgNew YorkUSA
- Department of Child & Adolescent Psychiatry, Neuroscience & Physiology and Psychiatry and the New York University Neuroscience InstituteNew York University Langone HealthNew YorkNew YorkUSA
| | - David Alcantara‐Gonzalez
- Center for Dementia ResearchThe Nathan Kline Institute for Psychiatric ResearchOrangeburgNew YorkUSA
| | - Helen E. Scharfman
- Center for Dementia ResearchThe Nathan Kline Institute for Psychiatric ResearchOrangeburgNew YorkUSA
- Department of Child & Adolescent Psychiatry, Neuroscience & Physiology and Psychiatry and the New York University Neuroscience InstituteNew York University Langone HealthNew YorkNew YorkUSA
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Fernández-Ruiz A, Oliva A, Soula M, Rocha-Almeida F, Nagy GA, Martin-Vazquez G, Buzsáki G. Gamma rhythm communication between entorhinal cortex and dentate gyrus neuronal assemblies. Science 2021; 372:eabf3119. [PMID: 33795429 PMCID: PMC8285088 DOI: 10.1126/science.abf3119] [Citation(s) in RCA: 105] [Impact Index Per Article: 35.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2020] [Accepted: 01/29/2021] [Indexed: 01/02/2023]
Abstract
Gamma oscillations are thought to coordinate the spike timing of functionally specialized neuronal ensembles across brain regions. To test this hypothesis, we optogenetically perturbed gamma spike timing in the rat medial (MEC) and lateral (LEC) entorhinal cortices and found impairments in spatial and object learning tasks, respectively. MEC and LEC were synchronized with the hippocampal dentate gyrus through high- and low-gamma-frequency rhythms, respectively, and engaged either granule cells or mossy cells and CA3 pyramidal cells in a task-dependent manner. Gamma perturbation disrupted the learning-induced assembly organization of target neurons. Our findings imply that pathway-specific gamma oscillations route task-relevant information between distinct neuronal subpopulations in the entorhinal-hippocampal circuit. We hypothesize that interregional gamma-time-scale spike coordination is a mechanism of neuronal communication.
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Affiliation(s)
- Antonio Fernández-Ruiz
- New York University Neuroscience Institute, New York University, New York, NY 10016, USA.
| | - Azahara Oliva
- New York University Neuroscience Institute, New York University, New York, NY 10016, USA
- Department of Neuroscience, Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA
| | - Marisol Soula
- New York University Neuroscience Institute, New York University, New York, NY 10016, USA
| | - Florbela Rocha-Almeida
- New York University Neuroscience Institute, New York University, New York, NY 10016, USA
- Division of Neurosciences, University Pablo de Olavide, 41013 Seville, Spain
| | - Gergo A Nagy
- New York University Neuroscience Institute, New York University, New York, NY 10016, USA
- Institute of Experimental Medicine, Hungarian Academy of Sciences, H-1083 Budapest, Szigony utca 43, Hungary
- János Szentágothai Doctoral School of Neurosciences, Semmelweis University, H-1085 Budapest, Üllői út 26, Hungary
| | - Gonzalo Martin-Vazquez
- Department of Theoretical Physics, Complutense University, 28040 Madrid, Spain
- School of Experimental Sciences, University Francisco de Vitoria, 28223 Pozuelo de Alarcón, Madrid, Spain
| | - György Buzsáki
- New York University Neuroscience Institute, New York University, New York, NY 10016, USA.
- Center for Neural Science, New York University, New York, NY 10016, USA
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Comprehensive Estimates of Potential Synaptic Connections in Local Circuits of the Rodent Hippocampal Formation by Axonal-Dendritic Overlap. J Neurosci 2020; 41:1665-1683. [PMID: 33361464 DOI: 10.1523/jneurosci.1193-20.2020] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2020] [Revised: 10/19/2020] [Accepted: 12/13/2020] [Indexed: 12/12/2022] Open
Abstract
A quantitative description of the hippocampal formation synaptic architecture is essential for understanding the neural mechanisms of episodic memory. Yet the existing knowledge of connectivity statistics between different neuron types in the rodent hippocampus only captures a mere 5% of this circuitry. We present a systematic pipeline to produce first-approximation estimates for most of the missing information. Leveraging the www.Hippocampome.org knowledge base, we derive local connection parameters between distinct pairs of morphologically identified neuron types based on their axonal-dendritic overlap within every layer and subregion of the hippocampal formation. Specifically, we adapt modern image analysis technology to determine the parcel-specific neurite lengths of every neuron type from representative morphologic reconstructions obtained from either sex. We then compute the average number of synapses per neuron pair using relevant anatomic volumes from the mouse brain atlas and ultrastructurally established interaction distances. Hence, we estimate connection probabilities and number of contacts for >1900 neuron type pairs, increasing the available quantitative assessments more than 11-fold. Connectivity statistics thus remain unknown for only a minority of potential synapses in the hippocampal formation, including those involving long-range (23%) or perisomatic (6%) connections and neuron types without morphologic tracings (7%). The described approach also yields approximate measurements of synaptic distances from the soma along the dendritic and axonal paths, which may affect signal attenuation and delay. Overall, this dataset fills a substantial gap in quantitatively describing hippocampal circuits and provides useful model specifications for biologically realistic neural network simulations, until further direct experimental data become available.SIGNIFICANCE STATEMENT The hippocampal formation is a crucial functional substrate for episodic memory and spatial representation. Characterizing the complex neuron type circuit of this brain region is thus important to understand the cellular mechanisms of learning and navigation. Here we present the first numerical estimates of connection probabilities, numbers of contacts per connected pair, and synaptic distances from the soma along the axonal and dendritic paths, for more than 1900 distinct neuron type pairs throughout the dentate gyrus, CA3, CA2, CA1, subiculum, and entorhinal cortex. This comprehensive dataset, publicly released online at www.Hippocampome.org, constitutes an unprecedented quantification of the majority of the local synaptic circuit for a prominent mammalian neural system and provides an essential foundation for data-driven, anatomically realistic neural network models.
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Silkis IG, Markevich VA. Possible Mechanisms of the Influence of the Supramillary Nucleus on the Functioning of the Dentate Gyrus and the CA2 Field of the Hippocamsus (Role of Disinhibition). NEUROCHEM J+ 2020. [DOI: 10.1134/s181971242004011x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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16
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Enhanced LTP of population spikes in the dentate gyrus of mice haploinsufficient for neurobeachin. Sci Rep 2020; 10:16058. [PMID: 32994505 PMCID: PMC7524738 DOI: 10.1038/s41598-020-72925-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Accepted: 09/07/2020] [Indexed: 12/16/2022] Open
Abstract
Deletion of the autism candidate molecule neurobeachin (Nbea), a large PH-BEACH-domain containing neuronal protein, has been shown to affect synaptic function by interfering with neurotransmitter receptor targeting and dendritic spine formation. Previous analysis of mice lacking one allele of the Nbea gene identified impaired spatial learning and memory in addition to altered autism-related behaviours. However, no functional data from living heterozygous Nbea mice (Nbea+/−) are available to corroborate the behavioural phenotype. Here, we explored the consequences of Nbea haploinsufficiency on excitation/inhibition balance and synaptic plasticity in the intact hippocampal dentate gyrus of Nbea+/− animals in vivo by electrophysiological recordings. Based on field potential recordings, we show that Nbea+/− mice display enhanced LTP of the granule cell population spike, but no differences in basal synaptic transmission, synapse numbers, short-term plasticity, or network inhibition. These data indicate that Nbea haploinsufficiency causes remarkably specific alterations to granule cell excitability in vivo, which may contribute to the behavioural abnormalities in Nbea+/− mice and to related symptoms in patients.
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Semilunar Granule Cells Are the Primary Source of the Perisomatic Excitatory Innervation onto Parvalbumin-Expressing Interneurons in the Dentate Gyrus. eNeuro 2020; 7:ENEURO.0323-19.2020. [PMID: 32571963 PMCID: PMC7340841 DOI: 10.1523/eneuro.0323-19.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Revised: 05/29/2020] [Accepted: 06/02/2020] [Indexed: 11/21/2022] Open
Abstract
We analyzed the origin and relevance of the perisomatic excitatory inputs on the parvalbumin interneurons of the granule cell layer in mouse. Confocal analysis of the glutamatergic innervation showed that it represents ∼50% of the perisomatic synapses that parvalbumin cells receive. This excitatory input may originate from granule cell collaterals, the mossy cells, or even supramammillary nucleus. First, we assessed the input from the mossy cells on parvalbumin interneurons. Axon terminals of mossy cells were visualized by their calretinin content. Using multicolor confocal microscopy, we observed that less than 10% of perisomatic excitatory innervation of parvalbumin cells could originate from mossy cells. Correlative light and electron microscopy revealed that innervation from mossy cells, although present, was indeed infrequent, except for those parvalbumin cells whose somata were located in the inner molecular layer. Second, we investigated the potential input from supramammillary nucleus on parvalbumin cell somata using anterograde tracing or immunocytochemistry against vesicular glutamate transporter 2 (VGLUT2) and found only occasional contacts. Third, we intracellularly filled dentate granule cells in acute slice preparations using whole-cell recording and examined whether their axon collaterals target parvalbumin interneurons. We found that typical granule cells do not innervate the perisomatic region of these GABAergic cells. In sharp contrast, semilunar granule cells (SGCs), a scarce granule cell subtype often contacted the parvalbumin cell soma and proximal dendrites. Our data, therefore, show that perisomatic excitatory drive of parvalbumin interneurons in the granular layer of the dentate gyrus is abundant and originates primarily from SGCs.
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18
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Komendantov AO, Venkadesh S, Rees CL, Wheeler DW, Hamilton DJ, Ascoli GA. Quantitative firing pattern phenotyping of hippocampal neuron types. Sci Rep 2019; 9:17915. [PMID: 31784578 PMCID: PMC6884469 DOI: 10.1038/s41598-019-52611-w] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Accepted: 09/20/2019] [Indexed: 01/19/2023] Open
Abstract
Systematically organizing the anatomical, molecular, and physiological properties of cortical neurons is important for understanding their computational functions. Hippocampome.org defines 122 neuron types in the rodent hippocampal formation based on their somatic, axonal, and dendritic locations, putative excitatory/inhibitory outputs, molecular marker expression, and biophysical properties. We augmented the electrophysiological data of this knowledge base by collecting, quantifying, and analyzing the firing responses to depolarizing current injections for every hippocampal neuron type from published experiments. We designed and implemented objective protocols to classify firing patterns based on 5 transients (delay, adapting spiking, rapidly adapting spiking, transient stuttering, and transient slow-wave bursting) and 4 steady states (non-adapting spiking, persistent stuttering, persistent slow-wave bursting, and silence). This automated approach revealed 9 unique (plus one spurious) families of firing pattern phenotypes while distinguishing potential new neuronal subtypes. Novel statistical associations emerged between firing responses and other electrophysiological properties, morphological features, and molecular marker expression. The firing pattern parameters, experimental conditions, spike times, references to the original empirical evidences, and analysis scripts are released open-source through Hippocampome.org for all neuron types, greatly enhancing the existing search and browse capabilities. This information, collated online in human- and machine-accessible form, will help design and interpret both experiments and model simulations.
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Affiliation(s)
- Alexander O Komendantov
- Krasnow Institute for Advanced Study, George Mason University, 4400 University Drive, MS 2A1, Fairfax, Virginia, 2230, USA.
| | - Siva Venkadesh
- Krasnow Institute for Advanced Study, George Mason University, 4400 University Drive, MS 2A1, Fairfax, Virginia, 2230, USA
| | - Christopher L Rees
- Krasnow Institute for Advanced Study, George Mason University, 4400 University Drive, MS 2A1, Fairfax, Virginia, 2230, USA
| | - Diek W Wheeler
- Krasnow Institute for Advanced Study, George Mason University, 4400 University Drive, MS 2A1, Fairfax, Virginia, 2230, USA
| | - David J Hamilton
- Krasnow Institute for Advanced Study, George Mason University, 4400 University Drive, MS 2A1, Fairfax, Virginia, 2230, USA
| | - Giorgio A Ascoli
- Krasnow Institute for Advanced Study, George Mason University, 4400 University Drive, MS 2A1, Fairfax, Virginia, 2230, USA.
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19
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Eyre MD, Bartos M. Somatostatin-Expressing Interneurons Form Axonal Projections to the Contralateral Hippocampus. Front Neural Circuits 2019; 13:56. [PMID: 31507383 PMCID: PMC6716454 DOI: 10.3389/fncir.2019.00056] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Accepted: 08/08/2019] [Indexed: 12/31/2022] Open
Abstract
Conscious memories are critically dependent upon bilateral hippocampal formation, and interhemispheric commissural projections made by mossy cells and CA3 pyramidal cells. GABAergic interneurons also make long-range axonal projections, but little is known regarding their commissural, inter-hippocampal connections. We used retrograde and adeno-associated viral tracing, immunofluorescence and electron microscopy, and in vitro optogenetics to assess contralateral projections of neurochemically defined interneuron classes. We found that contralateral-projecting interneurons were 24-fold less common compared to hilar mossy cells, and mostly consisted of somatostatin- and parvalbumin-expressing types. Somatostatin-expressing cells made denser contralateral axonal projections than parvalbumin-expressing cells, although this was typically 10-fold less than the ipsilateral projection density. Somatostatin-expressing cells displayed a topographic-like innervation according to the location of their somata, whereas parvalbumin-expressing cells mostly innervated CA1. In the dentate gyrus molecular layer, commissural interneuron post-synaptic targets were predominantly putative granule cell apical dendrites. In the hilus, varicosities in close vicinity to various interneuron subtypes, as well as mossy cells, were observed, but most contralateral axon varicosities had no adjacent immunolabeled structure. Due to the relative sparsity of the connection and the likely distal dendritic location of their synapses, commissural projections made by interneurons were found to be weak. We postulate that these projections may become functionally active upon intense network activity during tasks requiring increased memory processing.
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Affiliation(s)
- Mark D Eyre
- Medical Faculty, Institute for Physiology I, Systemic and Cellular Neurophysiology, University of Freiburg, Freiburg, Germany
| | - Marlene Bartos
- Medical Faculty, Institute for Physiology I, Systemic and Cellular Neurophysiology, University of Freiburg, Freiburg, Germany
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20
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Abstract
This review describes developments in epilepsy research during the last 3 to 4 decades that focused on the dentate gyrus (DG) and its role in temporal lobe epilepsy (TLE). The emphasis is on basic research in laboratory animals and is chronological, starting with hypotheses that attracted a lot of attention in the 1980s. Then experiments are described that addressed the questions, as well as new methods that often made the experiments possible. In addition, where new questions arose and the implications for clinical epilepsy are discussed.
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Affiliation(s)
- Helen E. Scharfman
- Departments of Child & Adolescent Psychiatry, Neuroscience &
Physiology, and Psychiatry, New York University Langone Health, New York, NY, USA
- Center for Dementia Research, The Nathan Kline Institute for Psychiatric
Research, Orangeburg, NY, USA
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21
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Interplay of Entorhinal Input and Local Inhibitory Network in the Hippocampus at the Origin of Slow Inhibition in Granule Cells. J Neurosci 2019; 39:6399-6413. [PMID: 31182636 DOI: 10.1523/jneurosci.2976-18.2019] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2018] [Revised: 05/17/2019] [Accepted: 05/21/2019] [Indexed: 11/21/2022] Open
Abstract
Neuronal activity from the entorhinal cortex propagates through the perforant path (PP) to the molecular layer of the dentate gyrus (DG) where information is filtered and converted into sparse hippocampal code. Nearly simultaneous signaling to both granule cells (GC) and local interneurons (INs) engages network interactions that will modulate input integration and output generation. When triggered, GABA release from interneurons counteracts the glutamatergic signals of PP terminals, scaling down the overall DG activation. Inhibition occurs at fast or slow timescales depending on the activation of ionotropic GABAA-R or metabotropic GABAB-R. Although postsynaptic GABAA and GABAB-R differ in their location at the synapse, mixed GABAA/B-R IPSPs can also occur. Here we describe a slow inhibition mechanism in mouse GCs recorded from either sex, mediated by GABAA/B-R in combination with metabotropic glutamate receptors. Short burst PP stimulation in the gamma frequency range lead to a long-lasting hyperpolarization (LLH) of the GCs with a duration that exceeds GABAB-R IPSPs. As a result, LLH alters GC firing patterns and the responses to concomitant excitatory signals are also affected. Synaptic recruitment of feedforward inhibition and subsequent GABA release from interneurons, also successfully trigger mixed GABA responses in GCs. Together these results suggest that slow inhibition through LLH leads to reduced excitability of GCs during entorhinal input integration. The implication of LLH in regulation of neuronal excitability suggests it also contributes to the sparse population coding in DG.SIGNIFICANCE STATEMENT Our study describes a long-lasting hyperpolarization (LLH) in hippocampal granule cells. We used whole-cell patch-clamp recordings and an optogenetic approach to characterize this event. LLH is a slow inhibitory mechanism that occurs following the stimulation of the perforant pathway in the molecular layer of the dentate gyrus. We found that it is mediated via postsynaptic ionotropic and metabotropic GABA and metabotropic glutamate receptors. The duration of LLH exceeds previously described IPSPs mediated by any of these receptors. The activation of LLH requires presynaptic gamma frequency bursts and recruitment of the local feedforward inhibition. LLH defines prolonged periods of low excitability of GCs and a restrained neuronal discharge. Our results suggest that LLH can contribute to sparse activation of GCs.
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GABAergic Medial Septal Neurons with Low-Rhythmic Firing Innervating the Dentate Gyrus and Hippocampal Area CA3. J Neurosci 2019; 39:4527-4549. [PMID: 30926750 PMCID: PMC6554630 DOI: 10.1523/jneurosci.3024-18.2019] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Revised: 03/08/2019] [Accepted: 03/15/2019] [Indexed: 02/06/2023] Open
Abstract
The medial septum implements cortical theta oscillations, a 5–12 Hz rhythm associated with locomotion and paradoxical sleep reflecting synchronization of neuronal assemblies such as place cell sequence coding. Highly rhythmic burst-firing parvalbumin-positive GABAergic medial septal neurons are strongly coupled to theta oscillations and target cortical GABAergic interneurons, contributing to coordination within one or several cortical regions. However, a large population of medial septal neurons of unidentified neurotransmitter phenotype and with unknown axonal target areas fire with a low degree of rhythmicity. We investigated whether low-rhythmic-firing neurons (LRNs) innervated similar or different cortical regions to high-rhythmic-firing neurons (HRNs) and assessed their temporal dynamics in awake male mice. The majority of LRNs were GABAergic and parvalbumin-immunonegative, some expressing calbindin; they innervated interneurons mostly in the dentate gyrus (DG) and CA3. Individual LRNs showed several distinct firing patterns during immobility and locomotion, forming a parallel inhibitory stream for the modulation of cortical interneurons. Despite their fluctuating firing rates, the preferred firing phase of LRNs during theta oscillations matched the highest firing probability phase of principal cells in the DG and CA3. In addition, as a population, LRNs were markedly suppressed during hippocampal sharp-wave ripples, had a low burst incidence, and several of them did not fire on all theta cycles. Therefore, CA3 receives GABAergic input from both HRNs and LRNs, but the DG receives mainly LRN input. We propose that distinct GABAergic LRNs contribute to changing the excitability of the DG and CA3 during memory discrimination via transient disinhibition of principal cells. SIGNIFICANCE STATEMENT For the encoding and recall of episodic memories, nerve cells in the cerebral cortex are activated in precisely timed sequences. Rhythmicity facilitates the coordination of neuronal activity and these rhythms are detected as oscillations of different frequencies such as 5–12 Hz theta oscillations. Degradation of these rhythms, such as through neurodegeneration, causes memory deficits. The medial septum, a part of the basal forebrain that innervates the hippocampal formation, contains high- and low-rhythmic-firing neurons (HRNs and LRNs, respectively), which may contribute differentially to cortical neuronal coordination. We discovered that GABAergic LRNs preferentially innervate the dentate gyrus and the CA3 area of the hippocampus, regions important for episodic memory. These neurons act in parallel with the HRNs mostly via transient inhibition of inhibitory neurons.
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23
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Cayco-Gajic NA, Silver RA. Re-evaluating Circuit Mechanisms Underlying Pattern Separation. Neuron 2019; 101:584-602. [PMID: 30790539 PMCID: PMC7028396 DOI: 10.1016/j.neuron.2019.01.044] [Citation(s) in RCA: 123] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Revised: 01/07/2019] [Accepted: 01/18/2019] [Indexed: 11/22/2022]
Abstract
When animals interact with complex environments, their neural circuits must separate overlapping patterns of activity that represent sensory and motor information. Pattern separation is thought to be a key function of several brain regions, including the cerebellar cortex, insect mushroom body, and dentate gyrus. However, recent findings have questioned long-held ideas on how these circuits perform this fundamental computation. Here, we re-evaluate the functional and structural mechanisms underlying pattern separation. We argue that the dimensionality of the space available for population codes representing sensory and motor information provides a common framework for understanding pattern separation. We then discuss how these three circuits use different strategies to separate activity patterns and facilitate associative learning in the presence of trial-to-trial variability.
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Affiliation(s)
- N Alex Cayco-Gajic
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, UK
| | - R Angus Silver
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, UK.
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24
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Function of local circuits in the hippocampal dentate gyrus-CA3 system. Neurosci Res 2018; 140:43-52. [PMID: 30408501 DOI: 10.1016/j.neures.2018.11.003] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2018] [Revised: 09/27/2018] [Accepted: 10/15/2018] [Indexed: 11/20/2022]
Abstract
Anatomical observations, theoretical work and lesioning experiments have supported the idea that the CA3 in the hippocampus is important for encoding, storage and retrieval of memory while the dentate gyrus (DG) is important for the pattern separation of the incoming inputs from the entorhinal cortex. Study of the presumed function of the dentate gyrus in pattern separation has been hampered by the lack of reliable methods to identify different excitatory cell types in the DG. Recent papers have identified different cell types in the DG, in awake behaving animals, with more reliable methods. These studies have revealed each cell type's spatial representation as well as their involvement in pattern separation. Moreover, chronic electrophysiological recording from sleeping and waking animals also provided more insights into the operation of the DG-CA3 system for memory encoding and retrieval. This article will review the local circuit architectures and physiological properties of the DG-CA3 system and discuss how the local circuit in the DG-CA3 may function, incorporating recent physiological findings in the DG-CA3 system.
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25
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Espinoza C, Guzman SJ, Zhang X, Jonas P. Parvalbumin + interneurons obey unique connectivity rules and establish a powerful lateral-inhibition microcircuit in dentate gyrus. Nat Commun 2018; 9:4605. [PMID: 30389916 PMCID: PMC6214995 DOI: 10.1038/s41467-018-06899-3] [Citation(s) in RCA: 91] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2018] [Accepted: 10/02/2018] [Indexed: 12/31/2022] Open
Abstract
Parvalbumin-positive (PV+) GABAergic interneurons in hippocampal microcircuits are thought to play a key role in several higher network functions, such as feedforward and feedback inhibition, network oscillations, and pattern separation. Fast lateral inhibition mediated by GABAergic interneurons may implement a winner-takes-all mechanism in the hippocampal input layer. However, it is not clear whether the functional connectivity rules of granule cells (GCs) and interneurons in the dentate gyrus are consistent with such a mechanism. Using simultaneous patch-clamp recordings from up to seven GCs and up to four PV+ interneurons in the dentate gyrus, we find that connectivity is structured in space, synapse-specific, and enriched in specific disynaptic motifs. In contrast to the neocortex, lateral inhibition in the dentate gyrus (in which a GC inhibits neighboring GCs via a PV+ interneuron) is ~ 10-times more abundant than recurrent inhibition (in which a GC inhibits itself). Thus, unique connectivity rules may enable the dentate gyrus to perform specific higher-order computations. GABAergic interneurons are known to provide inhibition to allow computational function of neuronal network. Here, Espinoza and colleagues show that connectivity of granule cells and interneurons in the dentate gyrus of mouse hippocampus are consistent with the circuit architecture capable of performing a winners-take-all mechanism.
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Affiliation(s)
- Claudia Espinoza
- IST Austria (Institute of Science and Technology Austria), Am Campus 1, 3400, Klosterneuburg, Austria
| | - Segundo Jose Guzman
- Institute for Molecular Biotechnology (IMBA), Dr. Bohr-Gasse 3, 1030, Wien, Austria
| | - Xiaomin Zhang
- IST Austria (Institute of Science and Technology Austria), Am Campus 1, 3400, Klosterneuburg, Austria
| | - Peter Jonas
- IST Austria (Institute of Science and Technology Austria), Am Campus 1, 3400, Klosterneuburg, Austria.
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26
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Newell AJ, Lalitsasivimol D, Willing J, Gonzales K, Waters EM, Milner TA, McEwen BS, Wagner CK. Progesterone receptor expression in cajal-retzius cells of the developing rat dentate gyrus: Potential role in hippocampus-dependent memory. J Comp Neurol 2018; 526:2285-2300. [PMID: 30069875 PMCID: PMC6193812 DOI: 10.1002/cne.24485] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Revised: 05/03/2018] [Accepted: 05/23/2018] [Indexed: 12/16/2022]
Abstract
The development of medial temporal lobe circuits is critical for subsequent learning and memory functions later in life. The present study reports the expression of progesterone receptor (PR), a powerful transcription factor of the nuclear steroid receptor superfamily, in Cajal-Retzius cells of the molecular layer of the dentate gyrus of rats. PR was transiently expressed from the day of birth through postnatal day 21, but was absent thereafter. Although PR immunoreactive (PR-ir) cells did not clearly express typical markers of mature neurons, they possessed an ultrastructural morphology consistent with neurons. PRir cells did not express markers for GABAergic neurons, neuronal precursor cells, nor radial glia. However, virtually all PR cells co-expressed the calcium binding protein, calretinin, and the glycoprotein, reelin, both reliable markers for Cajal-Retzius neurons, a transient population of developmentally critical pioneer neurons that guide synaptogenesis of perforant path afferents and histogenesis of the dentate gyrus. Indeed, inhibition of PR activity during the first two weeks of life impaired adult performance on both the novel object recognition and object placement memory tasks, two behavioral tasks hypothesized to describe facets of episodic-like memory in rodents. These findings suggest that PR plays an unexplored and important role in the development of hippocampal circuitry and adult memory function.
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Affiliation(s)
- Andrew J. Newell
- Department of Psychology, Center for Neuroscience Research’, 1400 Washington Ave., University at Albany, Albany, NY 12222
| | - Diana Lalitsasivimol
- Department of Psychology, Center for Neuroscience Research’, 1400 Washington Ave., University at Albany, Albany, NY 12222
| | - Jari Willing
- Department of Psychology, Behavioral Neuroscience Program, 603 E Daniel St., University of Illinois at Urbana-Champaign, Champaign, IL 61820
| | - Keith Gonzales
- Department of Psychology, Center for Neuroscience Research’, 1400 Washington Ave., University at Albany, Albany, NY 12222
| | - Elizabeth M. Waters
- Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology, The Rockefeller University, 1230 York Avenue, New York, NY 10065
| | - Teresa A. Milner
- Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology, The Rockefeller University, 1230 York Avenue, New York, NY 10065
- Feil Family Brain and Mind Research Institute, Weill Cornell Medicine, 407 East 61, St New York, NY 1006521
| | - Bruce S. McEwen
- Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology, The Rockefeller University, 1230 York Avenue, New York, NY 10065
| | - Christine K. Wagner
- Department of Psychology, Center for Neuroscience Research’, 1400 Washington Ave., University at Albany, Albany, NY 12222
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27
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Scharfman HE. Advances in understanding hilar mossy cells of the dentate gyrus. Cell Tissue Res 2018; 373:643-652. [PMID: 29222692 PMCID: PMC5993616 DOI: 10.1007/s00441-017-2750-5] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Accepted: 11/21/2017] [Indexed: 02/01/2023]
Abstract
Hilar mossy cells (MCs) of the dentate gyrus (DG) distinguish the DG from other hippocampal subfields (CA1-3) because there are two glutamatergic cell types in the DG rather than one. Thus, in the DG, the main cell types include glutamatergic granule cells (GCs) and MCs, whereas in CA1-3, the only glutamatergic cell type is the pyramidal cell. In contrast to GCs, MCs are different in morphology, intrinsic electrophysiological properties, afferent input and axonal projections, so their function is likely to be very different from GCs. Why are MCs necessary to the DG? In past studies, the answer has been unclear because MCs not only excite GCs directly but also inhibit them disynaptically, by exciting GABAergic neurons that project to GCs. Results of new studies are discussed that shed light on this issue. These studies take advantage of recently available transgenic mice with Cre recombinase expression mostly in MCs and techniques such as optogenetics and DREADDs (designer receptors exclusively activated by designer drugs). The recent studies also address in vivo behavioral functions of MCs. Some of the results support past hypotheses whereas others suggest new conceptualizations of how the MCs contribute to DG circuitry and function. While substantial progess has been made, additional research is still needed to clarify the characteristics and functions of these unique cells.
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Affiliation(s)
- Helen E Scharfman
- Departments of Child & Adolescent Psychiatry, Neuroscience & Physiology, Psychiatry, and the New York University Neuroscience Institute, New York University Langone Medical Center, One Park Avenue, 7th floor, New York, NY, 10016, USA.
- Center for Dementia Research, The Nathan Kline Institute for Psychiatric Research, 140 Old Orangeburg Road, Building 39, Orangeburg, NY, 10962, USA.
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28
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Booker SA, Vida I. Morphological diversity and connectivity of hippocampal interneurons. Cell Tissue Res 2018; 373:619-641. [PMID: 30084021 PMCID: PMC6132631 DOI: 10.1007/s00441-018-2882-2] [Citation(s) in RCA: 105] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Accepted: 07/03/2018] [Indexed: 12/21/2022]
Abstract
The mammalian forebrain is constructed from ensembles of neurons that form local microcircuits giving rise to the exquisite cognitive tasks the mammalian brain can perform. Hippocampal neuronal circuits comprise populations of relatively homogenous excitatory neurons, principal cells and exceedingly heterogeneous inhibitory neurons, the interneurons. Interneurons release GABA from their axon terminals and are capable of controlling excitability in every cellular compartment of principal cells and interneurons alike; thus, they provide a brake on excess activity, control the timing of neuronal discharge and provide modulation of synaptic transmission. The dendritic and axonal morphology of interneurons, as well as their afferent and efferent connections within hippocampal circuits, is central to their ability to differentially control excitability, in a cell-type- and compartment-specific manner. This review aims to provide an up-to-date compendium of described hippocampal interneuron subtypes, with respect to their morphology, connectivity, neurochemistry and physiology, a full understanding of which will in time help to explain the rich diversity of neuronal function.
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Affiliation(s)
- Sam A Booker
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH8 9XD, UK.
- Simons Initiative for the Developing Brain, University of Edinburgh, Edinburgh, EH8 9XD, UK.
| | - Imre Vida
- Institute for Integrative Neuroanatomy, Charité - Universitätmedizin Berlin, Berlin, Germany.
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29
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Le Maître TW, Dhanabalan G, Bogdanovic N, Alkass K, Druid H. Effects of Alcohol Abuse on Proliferating Cells, Stem/Progenitor Cells, and Immature Neurons in the Adult Human Hippocampus. Neuropsychopharmacology 2018; 43:690-699. [PMID: 29052615 PMCID: PMC5809795 DOI: 10.1038/npp.2017.251] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/21/2017] [Revised: 10/12/2017] [Accepted: 10/16/2017] [Indexed: 02/02/2023]
Abstract
In animal studies, impaired adult hippocampal neurogenesis is associated with behavioral pathologies including addiction to alcohol. We hypothesize that alcohol abuse may have a detrimental effect on the neurogenic pool of the dentate gyrus in the human hippocampus. In this study we investigate whether alcohol abuse affects the number of proliferating cells, stem/progenitor cells, and immature neurons in samples from postmortem human hippocampus. The specimens were isolated from deceased donors with an on-going alcohol abuse, and from controls with no alcohol overconsumption. Mid-hippocampal sections were immunostained for Ki67, a marker for cell proliferation, Sox2, a stem/progenitor cell marker, and DCX, a marker for immature neurons. Immunoreactivity was counted in alcoholic subjects and compared with controls. Counting was performed in the three layers of dentate gyrus: the subgranular zone, the granular cell layer, and the molecular layer. Our data showed reduced numbers of all three markers in the dentate gyrus in subjects with an on-going alcohol abuse. This reduction was most prominent in the subgranular zone, and uniformly distributed across the distances from the granular cell layer. Furthermore, alcohol abusers showed a more pronounced reduction of Sox2-IR cells than DCX-IR cells, suggesting that alcohol primarily causes a depletion of the stem/progenitor cell pool and that immature neurons are secondarily affected. These results are in agreement with observations of impaired adult hippocampal neurogenesis in animal studies and lend further support for the association between hippocampal dysfunction and alcohol abuse.
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Affiliation(s)
- Tara Wardi Le Maître
- Forensic Medicine Laboratory, Department of Oncology-Pathology, Stockholm, Sweden
| | | | - Nenad Bogdanovic
- Neurogeriatric Clinic, Theme Aging, Karolinska University Hospital, Stockholm Sweden
| | - Kanar Alkass
- Forensic Medicine Laboratory, Department of Oncology-Pathology, Stockholm, Sweden
| | - Henrik Druid
- Forensic Medicine Laboratory, Department of Oncology-Pathology, Stockholm, Sweden,Forensic Medicine Laboratory, Department of Oncology-Pathology, Retzius väg 3, SE-171 77, Stockholm, Sweden, Tel: +46 (0)8 425 877 70, E-mail:
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30
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Zhang BL, Fan YS, Wang JW, Zhou ZW, Wu YG, Yang MC, Sun DD, Zhang JN. Cognitive impairment after traumatic brain injury is associated with reduced long-term depression of excitatory postsynaptic potential in the rat hippocampal dentate gyrus. Neural Regen Res 2018; 13:1753-1758. [PMID: 30136690 PMCID: PMC6128047 DOI: 10.4103/1673-5374.238618] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Traumatic brain injury can cause loss of neuronal tissue, remote symptomatic epilepsy, and cognitive deficits. However, the mechanisms underlying the effects of traumatic brain injury are not yet clear. Hippocampal excitability is strongly correlated with cognitive dysfunction and remote symptomatic epilepsy. In this study, we examined the relationship between traumatic brain injury-induced neuronal loss and subsequent hippocampal regional excitability. We used hydraulic percussion to generate a rat model of traumatic brain injury. At 7 days after injury, the mean modified neurological severity score was 9.5, suggesting that the neurological function of the rats was remarkably impaired. Electrophysiology and immunocytochemical staining revealed increases in the slope of excitatory postsynaptic potentials and long-term depression (indicating weakened long-term inhibition), and the numbers of cholecystokinin and parvalbumin immunoreactive cells were clearly reduced in the rat hippocampal dentate gyrus. These results indicate that interneuronal loss and changes in excitability occurred in the hippocampal dentate gyrus. Thus, traumatic brain injury-induced loss of interneurons appears to be associated with reduced long-term depression in the hippocampal dentate gyrus.
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Affiliation(s)
- Bao-Liang Zhang
- Department of Neurosurgery, Tianjin Medical University General Hospital; Tianjin Neurological Institute; Key Laboratory of Post-trauma Neuro-repair and Regeneration in Central Nervous System, Ministry of Education; Tianjin Key Laboratory of Injuries, Variations and Regeneration of Nervous System, Tianjin, China
| | - Yue-Shan Fan
- Department of Neurosurgery, Tianjin Medical University General Hospital; Tianjin Neurological Institute; Key Laboratory of Post-trauma Neuro-repair and Regeneration in Central Nervous System, Ministry of Education; Tianjin Key Laboratory of Injuries, Variations and Regeneration of Nervous System, Tianjin, China
| | - Ji-Wei Wang
- Department of Neurosurgery, Tianjin Medical University General Hospital; Tianjin Neurological Institute; Key Laboratory of Post-trauma Neuro-repair and Regeneration in Central Nervous System, Ministry of Education; Tianjin Key Laboratory of Injuries, Variations and Regeneration of Nervous System, Tianjin, China
| | - Zi-Wei Zhou
- Department of Neurosurgery, Tianjin Medical University General Hospital; Tianjin Neurological Institute; Key Laboratory of Post-trauma Neuro-repair and Regeneration in Central Nervous System, Ministry of Education; Tianjin Key Laboratory of Injuries, Variations and Regeneration of Nervous System, Tianjin, China
| | - Yin-Gang Wu
- Department of Neurosurgery, Tianjin Medical University General Hospital; Tianjin Neurological Institute; Key Laboratory of Post-trauma Neuro-repair and Regeneration in Central Nervous System, Ministry of Education; Tianjin Key Laboratory of Injuries, Variations and Regeneration of Nervous System, Tianjin, China
| | - Meng-Chen Yang
- Department of Neurosurgery, Tianjin Medical University General Hospital; Tianjin Neurological Institute; Key Laboratory of Post-trauma Neuro-repair and Regeneration in Central Nervous System, Ministry of Education; Tianjin Key Laboratory of Injuries, Variations and Regeneration of Nervous System, Tianjin, China
| | - Dong-Dong Sun
- Department of Neurosurgery, Tianjin Medical University General Hospital; Tianjin Neurological Institute; Key Laboratory of Post-trauma Neuro-repair and Regeneration in Central Nervous System, Ministry of Education; Tianjin Key Laboratory of Injuries, Variations and Regeneration of Nervous System, Tianjin, China
| | - Jian-Ning Zhang
- Department of Neurosurgery, Tianjin Medical University General Hospital; Tianjin Neurological Institute; Key Laboratory of Post-trauma Neuro-repair and Regeneration in Central Nervous System, Ministry of Education; Tianjin Key Laboratory of Injuries, Variations and Regeneration of Nervous System, Tianjin, China
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31
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Gilbride CJ. The hyperexcitability of dentate granule neurons in organotypic hippocampal slice cultures is due to reorganization of synaptic inputs in vitro. Physiol Rep 2017; 4:4/19/e12889. [PMID: 27707779 PMCID: PMC5064129 DOI: 10.14814/phy2.12889] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2016] [Accepted: 07/15/2016] [Indexed: 11/24/2022] Open
Abstract
Organotypic hippocampal slice cultures (OHSCs) provide the experimental flexibility of cell culture while leaving much of the natural neuronal connectivity intact. Previously, it was shown that the functional and morphological features of CA1 pyramidal neurons in OHSCs resemble, to a surprising extent, those of CA1 neurons in the acute brain slice preparation. However, the extent to which the characteristics of other principle hippocampal neurons change or are preserved in cultured slices remains to be determined. In the present study, I initially sought to understand whether and how the synaptic inputs and morphology of cultured dentate granule neurons (GCs) differ from GCs that have developed in vivo. To this end, I compared GCs in OHSCs and GCs in acute slices at two equivalent developmental time points (P14 vs. DIV7 and P21 vs. DIV21). The findings suggest that there is considerable reorganization of synaptic input to the organotypic GCs, such that these cells are more susceptible to hyperexcitation than GCs in acute slices after 3 weeks. It appears that this hyperexcitability emerges through an increase in the proportion of mature synapses at proximal dendritic sites and is accompanied by an increase in inhibitory neuron activity. These alterations appear to arise in a coordinated manner such that the substantial increase in excitatory synaptic drive received by the DIV21 GCs in OHSCs remains local and is not translated into excessive output possibly leading to damage or major morphological alterations of downstream pyramidal neurons.
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Affiliation(s)
- Charlie J Gilbride
- Depatment of Neuroscience, Physiology and Pharmacology, University College London, London, UK
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32
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Pelkey KA, Chittajallu R, Craig MT, Tricoire L, Wester JC, McBain CJ. Hippocampal GABAergic Inhibitory Interneurons. Physiol Rev 2017; 97:1619-1747. [PMID: 28954853 DOI: 10.1152/physrev.00007.2017] [Citation(s) in RCA: 495] [Impact Index Per Article: 70.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Revised: 05/16/2017] [Accepted: 05/26/2017] [Indexed: 12/11/2022] Open
Abstract
In the hippocampus GABAergic local circuit inhibitory interneurons represent only ~10-15% of the total neuronal population; however, their remarkable anatomical and physiological diversity allows them to regulate virtually all aspects of cellular and circuit function. Here we provide an overview of the current state of the field of interneuron research, focusing largely on the hippocampus. We discuss recent advances related to the various cell types, including their development and maturation, expression of subtype-specific voltage- and ligand-gated channels, and their roles in network oscillations. We also discuss recent technological advances and approaches that have permitted high-resolution, subtype-specific examination of their roles in numerous neural circuit disorders and the emerging therapeutic strategies to ameliorate such pathophysiological conditions. The ultimate goal of this review is not only to provide a touchstone for the current state of the field, but to help pave the way for future research by highlighting where gaps in our knowledge exist and how a complete appreciation of their roles will aid in future therapeutic strategies.
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Affiliation(s)
- Kenneth A Pelkey
- Porter Neuroscience Center, Eunice Kennedy-Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland; Institute of Biomedical and Clinical Sciences, University of Exeter Medical School, Hatherly Laboratories, University of Exeter, Exeter, United Kingdom; and Sorbonne Universités, UPMC University of Paris, INSERM, CNRS, Neurosciences Paris Seine-Institut de Biologie Paris Seine, Paris, France
| | - Ramesh Chittajallu
- Porter Neuroscience Center, Eunice Kennedy-Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland; Institute of Biomedical and Clinical Sciences, University of Exeter Medical School, Hatherly Laboratories, University of Exeter, Exeter, United Kingdom; and Sorbonne Universités, UPMC University of Paris, INSERM, CNRS, Neurosciences Paris Seine-Institut de Biologie Paris Seine, Paris, France
| | - Michael T Craig
- Porter Neuroscience Center, Eunice Kennedy-Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland; Institute of Biomedical and Clinical Sciences, University of Exeter Medical School, Hatherly Laboratories, University of Exeter, Exeter, United Kingdom; and Sorbonne Universités, UPMC University of Paris, INSERM, CNRS, Neurosciences Paris Seine-Institut de Biologie Paris Seine, Paris, France
| | - Ludovic Tricoire
- Porter Neuroscience Center, Eunice Kennedy-Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland; Institute of Biomedical and Clinical Sciences, University of Exeter Medical School, Hatherly Laboratories, University of Exeter, Exeter, United Kingdom; and Sorbonne Universités, UPMC University of Paris, INSERM, CNRS, Neurosciences Paris Seine-Institut de Biologie Paris Seine, Paris, France
| | - Jason C Wester
- Porter Neuroscience Center, Eunice Kennedy-Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland; Institute of Biomedical and Clinical Sciences, University of Exeter Medical School, Hatherly Laboratories, University of Exeter, Exeter, United Kingdom; and Sorbonne Universités, UPMC University of Paris, INSERM, CNRS, Neurosciences Paris Seine-Institut de Biologie Paris Seine, Paris, France
| | - Chris J McBain
- Porter Neuroscience Center, Eunice Kennedy-Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland; Institute of Biomedical and Clinical Sciences, University of Exeter Medical School, Hatherly Laboratories, University of Exeter, Exeter, United Kingdom; and Sorbonne Universités, UPMC University of Paris, INSERM, CNRS, Neurosciences Paris Seine-Institut de Biologie Paris Seine, Paris, France
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33
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Neural mechanisms underlying GABAergic regulation of adult hippocampal neurogenesis. Cell Tissue Res 2017; 371:33-46. [PMID: 28948349 DOI: 10.1007/s00441-017-2668-y] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2017] [Accepted: 07/01/2017] [Indexed: 12/25/2022]
Abstract
Within the dentate gyrus of the adult hippocampus is the subgranular zone, which contains a neurogenic niche for radial-glia like cells, the most primitive neural stem cells in the adult brain. The quiescence of neural stem cells is maintained by tonic gamma-aminobutyric acid (GABA) released from local interneurons. Once these cells differentiate into neural progenitor cells, GABA continues to regulate their development into mature granule cells, the principal cell type of the dentate gyrus. Here, we review the role of GABA circuits, signaling, and receptors in regulating development of adult-born cells, as well as the molecular players that modulate GABA signaling. Furthermore, we review recent findings linking dysregulation of adult hippocampal neurogenesis to the altered GABAergic circuitry and signaling under various pathological conditions.
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34
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Vidal V, García-Cerro S, Martínez P, Corrales A, Lantigua S, Vidal R, Rueda N, Ozmen L, Hernández MC, Martínez-Cué C. Decreasing the Expression of GABA A α5 Subunit-Containing Receptors Partially Improves Cognitive, Electrophysiological, and Morphological Hippocampal Defects in the Ts65Dn Model of Down Syndrome. Mol Neurobiol 2017; 55:4745-4762. [PMID: 28717969 DOI: 10.1007/s12035-017-0675-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Accepted: 06/27/2017] [Indexed: 12/31/2022]
Abstract
Trisomy 21 or Down syndrome (DS) is the most common cause of intellectual disability of a genetic origin. The Ts65Dn (TS) mouse, which is the most commonly used and best-characterized mouse model of DS, displays many of the cognitive, neuromorphological, and biochemical anomalies that are found in the human condition. One of the mechanisms that have been proposed to be responsible for the cognitive deficits in this mouse model is impaired GABA-mediated inhibition. Because of the well-known modulatory role of GABAA α5 subunit-containing receptors in cognitive processes, these receptors are considered to be potential targets for improving the intellectual disability in DS. The chronic administration of GABAA α5-negative allosteric modulators has been shown to be procognitive without anxiogenic or proconvulsant side effects. In the present study, we use a genetic approach to evaluate the contribution of GABAA α5 subunit-containing receptors to the cognitive, electrophysiological, and neuromorphological deficits in TS mice. We show that reducing the expression of GABAA α5 receptors by deleting one or two copies of the Gabra5 gene in TS mice partially ameliorated the cognitive impairments, improved long-term potentiation, enhanced neural differentiation and maturation, and normalized the density of the GABAergic synapse markers. Reducing the gene dosage of Gabra5 in TS mice did not induce motor alterations and anxiety or affect the viability of the mice. Our results provide further evidence of the role of GABAA α5 receptor-mediated inhibition in cognitive impairment in the TS mouse model of DS.
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Affiliation(s)
- Verónica Vidal
- Departamento de Fisiología y Farmacología, Facultad de Medicina, Universidad deCantabria, Santander, Spain
| | - Susana García-Cerro
- Departamento de Fundamentos Clínicos, Unidad de Farmacología, Universitat de Barcelona, Barcelona, Spain
| | - Paula Martínez
- Departamento de Fisiología y Farmacología, Facultad de Medicina, Universidad deCantabria, Santander, Spain
| | - Andrea Corrales
- Departamento de Fisiología y Farmacología, Facultad de Medicina, Universidad deCantabria, Santander, Spain
| | - Sara Lantigua
- Departamento de Fisiología y Farmacología, Facultad de Medicina, Universidad deCantabria, Santander, Spain
| | - Rebeca Vidal
- Departamento de Fisiología y Farmacología, Facultad de Medicina, Universidad deCantabria, Santander, Spain.,Instituto de Biomedicina y Biotecnología de Cantabria, IBBTEC (Universidad de Cantabria, CSIC, SODERCAN), Santander, Spain.,Centro de Investigacion Biomédica en Red de Salud Mental (CIBERSAM), Instituto de Salud Carlos III, Madrid, Spain
| | - Noemí Rueda
- Departamento de Fisiología y Farmacología, Facultad de Medicina, Universidad deCantabria, Santander, Spain
| | - Laurence Ozmen
- Pharma Research and Early Development, Hoffman-La Roche Ltd., Basel, Switzerland
| | | | - Carmen Martínez-Cué
- Departamento de Fisiología y Farmacología, Facultad de Medicina, Universidad deCantabria, Santander, Spain.
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35
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Paterno R, Folweiler KA, Cohen AS. Pathophysiology and Treatment of Memory Dysfunction After Traumatic Brain Injury. Curr Neurol Neurosci Rep 2017; 17:52. [PMID: 28500417 PMCID: PMC5861722 DOI: 10.1007/s11910-017-0762-x] [Citation(s) in RCA: 63] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Memory is fundamental to everyday life, and cognitive impairments resulting from traumatic brain injury (TBI) have devastating effects on TBI survivors. A contributing component to memory impairments caused by TBI is alteration in the neural circuits associated with memory function. In this review, we aim to bring together experimental findings that characterize behavioral memory deficits and the underlying pathophysiology of memory-involved circuits after TBI. While there is little doubt that TBI causes memory and cognitive dysfunction, it is difficult to conclude which memory phase, i.e., encoding, maintenance, or retrieval, is specifically altered by TBI. This is most likely due to variation in behavioral protocols and experimental models. Additionally, we review a selection of experimental treatments that hold translational potential to mitigate memory dysfunction following injury.
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Affiliation(s)
- Rosalia Paterno
- Center for Sleep and Circadian Neurobiology, Perelman School of Medicine, University of Pennsylvania, 3615 Civic Center Boulevard, Abramson Research Center, Rm. 816-h, Philadelphia, PA, 19104, USA.
| | - Kaitlin A Folweiler
- Department of Anesthesiology and Critical Care Medicine, Joseph Stokes, Jr. Research Institute, Children's Hospital of Philadelphia, 3615 Civic Center Boulevard, Abramson Research Center, Rm. 816-h, Philadelphia, PA, 19104, USA
| | - Akiva S Cohen
- Department of Anesthesiology and Critical Care Medicine, Joseph Stokes, Jr. Research Institute, Children's Hospital of Philadelphia, 3615 Civic Center Boulevard, Abramson Research Center, Rm. 816-h, Philadelphia, PA, 19104, USA
- Department of Anesthesiology and Critical Care Medicine, Perelman School of Medicine, University of Pennsylvania, 3615 Civic Center Boulevard, Abramson Research Center, Rm. 816-h, Philadelphia, PA, 19104, USA
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36
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Yuan M, Meyer T, Benkowitz C, Savanthrapadian S, Ansel-Bollepalli L, Foggetti A, Wulff P, Alcami P, Elgueta C, Bartos M. Somatostatin-positive interneurons in the dentate gyrus of mice provide local- and long-range septal synaptic inhibition. eLife 2017; 6. [PMID: 28368242 PMCID: PMC5395294 DOI: 10.7554/elife.21105] [Citation(s) in RCA: 58] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Accepted: 04/01/2017] [Indexed: 01/16/2023] Open
Abstract
Somatostatin-expressing-interneurons (SOMIs) in the dentate gyrus (DG) control formation of granule cell (GC) assemblies during memory acquisition. Hilar-perforant-path-associated interneurons (HIPP cells) have been considered to be synonymous for DG-SOMIs. Deviating from this assumption, we show two functionally contrasting DG-SOMI-types. The classical feedback-inhibitory HIPPs distribute axon fibers in the molecular layer. They are engaged by converging GC-inputs and provide dendritic inhibition to the DG circuitry. In contrast, SOMIs with axon in the hilus, termed hilar interneurons (HILs), provide perisomatic inhibition onto GABAergic cells in the DG and project to the medial septum. Repetitive activation of glutamatergic inputs onto HIPP cells induces long-lasting-depression (LTD) of synaptic transmission but long-term-potentiation (LTP) of synaptic signals in HIL cells. Thus, LTD in HIPPs may assist flow of spatial information from the entorhinal cortex to the DG, whereas LTP in HILs may facilitate the temporal coordination of GCs with activity patterns governed by the medial septum. DOI:http://dx.doi.org/10.7554/eLife.21105.001
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Affiliation(s)
- Mei Yuan
- Systemic and Cellular Neurophysiology, Institute for Physiology I, University of Freiburg, Freiburg, Germany.,Faculty for Biology, University of Freiburg, Freiburg, Germany
| | - Thomas Meyer
- Systemic and Cellular Neurophysiology, Institute for Physiology I, University of Freiburg, Freiburg, Germany
| | - Christoph Benkowitz
- Systemic and Cellular Neurophysiology, Institute for Physiology I, University of Freiburg, Freiburg, Germany
| | - Shakuntala Savanthrapadian
- Systemic and Cellular Neurophysiology, Institute for Physiology I, University of Freiburg, Freiburg, Germany
| | | | | | - Peer Wulff
- Institute for Physiology, University of Kiel, Kiel, Germany
| | - Pepe Alcami
- Systemic and Cellular Neurophysiology, Institute for Physiology I, University of Freiburg, Freiburg, Germany
| | - Claudio Elgueta
- Systemic and Cellular Neurophysiology, Institute for Physiology I, University of Freiburg, Freiburg, Germany
| | - Marlene Bartos
- Systemic and Cellular Neurophysiology, Institute for Physiology I, University of Freiburg, Freiburg, Germany
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Akgül G, McBain CJ. Diverse roles for ionotropic glutamate receptors on inhibitory interneurons in developing and adult brain. J Physiol 2016; 594:5471-90. [PMID: 26918438 PMCID: PMC5043048 DOI: 10.1113/jp271764] [Citation(s) in RCA: 58] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2015] [Accepted: 02/10/2016] [Indexed: 01/07/2023] Open
Abstract
Glutamate receptor-mediated recruitment of GABAergic inhibitory interneurons is a critical determinant of network processing. Early studies observed that many, but not all, interneuron glutamatergic synapses contain AMPA receptors that are GluA2-subunit lacking and Ca(2+) permeable, making them distinct from AMPA receptors at most principal cell synapses. Subsequent studies demonstrated considerable alignment of synaptic AMPA and NMDA receptor subunit composition within specific subtypes of interneurons, suggesting that both receptor expression profiles are developmentally and functionally linked. Indeed glutamate receptor expression profiles are largely predicted by the embryonic origins of cortical interneurons within the medial and caudal ganglionic eminences of the developing telencephalon. Distinct complements of AMPA and NMDA receptors within different interneuron subpopulations contribute to the differential recruitment of functionally divergent interneuron subtypes by common afferent inputs for appropriate feed-forward and feedback inhibitory drive and network entrainment. In contrast, the lesser-studied kainate receptors, which are often present at both pre- and postsynaptic sites, appear to follow an independent developmental expression profile. Loss of specific ionotropic glutamate receptor (iGluR) subunits during interneuron development has dramatic consequences for both cellular and network function, often precipitating circuit inhibition-excitation imbalances and in some cases lethality. Here we briefly review recent findings highlighting the roles of iGluRs in interneuron development.
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Affiliation(s)
- Gülcan Akgül
- Porter Neuroscience Research Centre, Rm3C903, Lincoln Drive, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD, 20892, USA
| | - Chris J McBain
- Porter Neuroscience Research Centre, Rm3C903, Lincoln Drive, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD, 20892, USA.
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Song J, Olsen RHJ, Sun J, Ming GL, Song H. Neuronal Circuitry Mechanisms Regulating Adult Mammalian Neurogenesis. Cold Spring Harb Perspect Biol 2016; 8:cshperspect.a018937. [PMID: 27143698 DOI: 10.1101/cshperspect.a018937] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The adult mammalian brain is a dynamic structure, capable of remodeling in response to various physiological and pathological stimuli. One dramatic example of brain plasticity is the birth and subsequent integration of newborn neurons into the existing circuitry. This process, termed adult neurogenesis, recapitulates neural developmental events in two specialized adult brain regions: the lateral ventricles of the forebrain. Recent studies have begun to delineate how the existing neuronal circuits influence the dynamic process of adult neurogenesis, from activation of quiescent neural stem cells (NSCs) to the integration and survival of newborn neurons. Here, we review recent progress toward understanding the circuit-based regulation of adult neurogenesis in the hippocampus and olfactory bulb.
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Affiliation(s)
- Juan Song
- Department of Pharmacology and Pharmacology Training Program, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599 Neuroscience Center and Neurobiology Curriculum, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Reid H J Olsen
- Department of Pharmacology and Pharmacology Training Program, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Jiaqi Sun
- Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Guo-Li Ming
- Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 Adrienne Helis Malvin Medical Research Foundation, New Orleans, Louisiana 70130-2685
| | - Hongjun Song
- Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 Adrienne Helis Malvin Medical Research Foundation, New Orleans, Louisiana 70130-2685
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Abstract
Mossy cells comprise a large fraction of the cells in the hippocampal dentate gyrus, suggesting that their function in this region is important. They are vulnerable to ischaemia, traumatic brain injury and seizures, and their loss could contribute to dentate gyrus dysfunction in such conditions. Mossy cell function has been unclear because these cells innervate both glutamatergic and GABAergic neurons within the dentate gyrus, contributing to a complex circuitry. It has also been difficult to directly and selectively manipulate mossy cells to study their function. In light of the new data generated using methods to preferentially eliminate or activate mossy cells in mice, it is timely to ask whether mossy cells have become any less enigmatic than they were in the past.
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Affiliation(s)
- Helen E Scharfman
- Departments of Child and Adolescent Psychiatry, Physiology and Neuroscience, and Psychiatry, New York University Langone Medical Center, New York 10016, USA.,Center for Dementia Research, The Nathan Kline Institute for Psychiatric Research, Orangeburg, New York 10962, USA
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Wang X, Song X, Wu L, Nadler JV, Zhan RZ. Persistent Hyperactivity of Hippocampal Dentate Interneurons After a Silent Period in the Rat Pilocarpine Model of Epilepsy. Front Cell Neurosci 2016; 10:94. [PMID: 27092056 PMCID: PMC4824773 DOI: 10.3389/fncel.2016.00094] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Accepted: 03/24/2016] [Indexed: 12/15/2022] Open
Abstract
Profile of GABAergic interneuron activity after pilocarpine-induced status epilepticus (SE) was examined in the rat hippocampal dentate gyrus by analyzing immediate early gene expression and recording spontaneous firing at near resting membrane potential (REM). SE for exact 2 h or more than 2 h was induced in the male Sprague-Dawley rats by an intraperitoneal injection of pilocarpine. Expression of immediate early genes (IEGs) was examined at 1 h, 1 week, 2 weeks or more than 10 weeks after SE. For animals to be examined at 1 h after SE, SE lasted for exact 2 h was terminated by an intraperitoneal injection of diazepam. Spontaneous firing at near the REM was recorded in interneurons located along the border between the granule cell layer and the hilus more than 10 weeks after SE. Results showed that both c-fos and activity-regulated cytoskeleton associated protein (Arc) in hilar GABAergic interneurons were up-regulated after SE in a biphasic manner; they were increased at 1 h and more than 2 weeks, but not at 1 week after SE. Ten weeks after SE, nearly 60% of hilar GABAergic cells expressed c-fos. With the exception of calretinin (CR)-positive cells, percentages of hilar neuronal nitric oxide synthase (nNOS)-, neuropeptide Y (NPY)-, parvalbumin (PV)-, and somatostatin (SOM)-positive cells with c-fos expression are significantly higher than those of controls more than 10 weeks after SE. Without the REM to be more depolarizing and changed threshold potential level in SE-induced rats, cell-attached recording revealed that nearly 90% of hilar interneurons fired spontaneously at near the REM while only 22% of the same cell population did so in the controls. In conclusion, pilocarpine-induced SE eventually leads to a state in which surviving dentate GABAergic interneurons become hyperactive with a subtype-dependent manner; this implies that a fragile balance between excitation and inhibition exists in the dentate gyrus and in addition, the activity-dependent up-regulation of IEGs may underlie plastic changes seen in some types of GABAergic cells in the pilocarpine model of epilepsy.
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Affiliation(s)
- Xiaochen Wang
- Department of Physiology, Shandong University School of Medicine Jinan, China
| | - Xinyu Song
- Department of Respiratory Medicine, Affiliated Hospital of Binzhou Medical University Binzhou, Shandong, China
| | - Lin Wu
- Department of Physiology, Shandong University School of Medicine Jinan, China
| | - J Victor Nadler
- Department of Pharmacology and Cancer Biology, Duke University Medical Center Durham, NC, USA
| | - Ren-Zhi Zhan
- Department of Physiology, Shandong University School of Medicine Jinan, China
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Buckmaster PS, Yamawaki R, Thind K. More Docked Vesicles and Larger Active Zones at Basket Cell-to-Granule Cell Synapses in a Rat Model of Temporal Lobe Epilepsy. J Neurosci 2016; 36:3295-308. [PMID: 26985038 PMCID: PMC4792940 DOI: 10.1523/jneurosci.4049-15.2016] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Revised: 01/20/2016] [Accepted: 02/04/2016] [Indexed: 11/21/2022] Open
Abstract
Temporal lobe epilepsy is a common and challenging clinical problem, and its pathophysiological mechanisms remain unclear. One possibility is insufficient inhibition in the hippocampal formation where seizures tend to initiate. Normally, hippocampal basket cells provide strong and reliable synaptic inhibition at principal cell somata. In a rat model of temporal lobe epilepsy, basket cell-to-granule cell (BC→GC) synaptic transmission is more likely to fail, but the underlying cause is unknown. At some synapses, probability of release correlates with bouton size, active zone area, and number of docked vesicles. The present study tested the hypothesis that impaired GABAergic transmission at BC→GC synapses is attributable to ultrastructural changes. Boutons making axosomatic symmetric synapses in the granule cell layer were reconstructed from serial electron micrographs. BC→GC boutons were predicted to be smaller in volume, have fewer and smaller active zones, and contain fewer vesicles, including fewer docked vesicles. Results revealed the opposite. Compared with controls, epileptic pilocarpine-treated rats displayed boutons with over twice the average volume, active zone area, total vesicles, and docked vesicles and with more vesicles closer to active zones. Larger active zones in epileptic rats are consistent with previous reports of larger amplitude miniature IPSCs and larger BC→GC quantal size. Results of this study indicate that transmission failures at BC→GC synapses in epileptic pilocarpine-treated rats are not attributable to smaller boutons or fewer docked vesicles. Instead, processes following vesicle docking, including priming, Ca(2+) entry, or Ca(2+) coupling with exocytosis, might be responsible. SIGNIFICANCE STATEMENT One in 26 people develops epilepsy, and temporal lobe epilepsy is a common form. Up to one-third of patients are resistant to currently available treatments. This study tested a potential underlying mechanism for previously reported impaired inhibition in epileptic animals at basket cell-to-granule cell (BC→GC) synapses, which normally are reliable and strong. Electron microscopy was used to evaluate 3D ultrastructure of BC→GC synapses in a rat model of temporal lobe epilepsy. The hypothesis was that impaired synaptic transmission is attributable to smaller boutons, smaller synapses, and abnormally low numbers of synaptic vesicles. Results revealed the opposite. These findings suggest that impaired transmission at BC→GC synapses in epileptic rats is attributable to later steps in exocytosis following vesicle docking.
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Affiliation(s)
- Paul S Buckmaster
- Departments of Comparative Medicine and Neurology and Neurological Sciences, Stanford University, Stanford, California 94305
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Scharfman HE, Myers CE. Corruption of the dentate gyrus by "dominant" granule cells: Implications for dentate gyrus function in health and disease. Neurobiol Learn Mem 2016; 129:69-82. [PMID: 26391451 PMCID: PMC4792754 DOI: 10.1016/j.nlm.2015.09.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2015] [Revised: 09/02/2015] [Accepted: 09/06/2015] [Indexed: 12/31/2022]
Abstract
The dentate gyrus (DG) and area CA3 of the hippocampus are highly organized lamellar structures which have been implicated in specific cognitive functions such as pattern separation and pattern completion. Here we describe how the anatomical organization and physiology of the DG and CA3 are consistent with structures that perform pattern separation and completion. We then raise a new idea related to the complex circuitry of the DG and CA3 where CA3 pyramidal cell 'backprojections' play a potentially important role in the sparse firing of granule cells (GCs), considered important in pattern separation. We also propose that GC axons, the mossy fibers, already known for their highly specialized structure, have a dynamic function that imparts variance--'mossy fiber variance'--which is important to pattern separation and completion. Computational modeling is used to show that when a subset of GCs become 'dominant,' one consequence is loss of variance in the activity of mossy fiber axons and a reduction in pattern separation and completion in the model. Empirical data are then provided using an example of 'dominant' GCs--subsets of GCs that develop abnormally and have increased excitability. Notably, these abnormal GCs have been identified in animal models of disease where DG-dependent behaviors are impaired. Together these data provide insight into pattern separation and completion, and suggest that behavioral impairment could arise from dominance of a subset of GCs in the DG-CA3 network.
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Affiliation(s)
- Helen E Scharfman
- The Nathan S. Kline Institute for Psychiatric Research, 140 Old Orangeburg Rd., Orangeburg, NY 10962, United States; Departments of Child & Adolescent Psychiatry, Physiology & Neuroscience, and Psychiatry, New York University Langone Medical Center, United States.
| | - Catherine E Myers
- VA New Jersey Health Care System, VA Medical Center, NeuroBehavioral Research Lab (Mail Stop 15a), 385 Tremont Avenue, East Orange, NJ 07018, United States; Department of Pharmacology, Physiology & Neuroscience, Rutgers-New Jersey Medical School, United States
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43
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Dentate cannabinoid-sensitive interneurons undergo unique and selective strengthening of mutual synaptic inhibition in experimental epilepsy. Neurobiol Dis 2016; 89:23-35. [PMID: 26804027 DOI: 10.1016/j.nbd.2016.01.013] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2015] [Revised: 01/12/2016] [Accepted: 01/19/2016] [Indexed: 11/22/2022] Open
Abstract
Altered inhibition is a salient feature of hippocampal network reorganization in epilepsy. Hippocampal pyramidal cells and dentate granule cells show specific reduction in cannabinoid receptor type 1 (CB1R)-sensitive GABAergic inputs in experimental epilepsy. In the dentate gyrus, CB1Rs regulate synaptic release from accommodating interneurons (AC-INs) with adapting firing characteristics and axonal projections in the molecular layer, but not from fast-spiking basket cells (FS-BCs). However, it is not known whether the intrinsic physiology and synaptic inhibition of AC-INs responsible for CB1R-sensitive inhibition is altered in epilepsy. Using the pilocarpine-induced status epilepticus (SE) model of epilepsy, we find that the basic physiological characteristics of AC-INs in epileptic rats are not different from age-matched controls. In paired interneuronal recordings, the amplitude of unitary inhibitory synaptic currents (uIPSCs) between AC-INs doubled after SE. Non-stationary noise analysis revealed that the post-SE strengthening of synapses between AC-INs resulted from an increase in postsynaptic receptors. Baseline synaptic release and CB1R antagonist enhancement of release at synapses between AC-INs were not different between control and post-SE rats. Additionally, uIPSC amplitude in FS-BCs to AC-INs pairs was unchanged after SE indicating input-specific microcircuit alterations in inhibitory inputs to AC-INs. At the network level, AC-INs showed no reduction in spontaneous and miniature inhibitory synaptic current (sIPSC or mIPSC) frequency or amplitude after SE. However, AC-IN mIPSC amplitude was persistently enhanced in post-SE and epileptic rats. CB1R agonist reduced the amplitude and suppressed a greater proportion of sIPSCs in AC-INs from post-SE and epileptic rats demonstrating a novel, cell-type specific increase in CB1R-sensitive inhibition of AC-INs after SE. This unique post-SE strengthening of inhibition between AC-INs could lead to activity-dependent suppression of AC-IN firing and compromise dentate CB1R-sensitive inhibition in epilepsy.
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44
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Tong X, Peng Z, Zhang N, Cetina Y, Huang CS, Wallner M, Otis TS, Houser CR. Ectopic Expression of α6 and δ GABAA Receptor Subunits in Hilar Somatostatin Neurons Increases Tonic Inhibition and Alters Network Activity in the Dentate Gyrus. J Neurosci 2015; 35:16142-58. [PMID: 26658866 PMCID: PMC4682781 DOI: 10.1523/jneurosci.2853-15.2015] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Revised: 10/23/2015] [Accepted: 11/01/2015] [Indexed: 11/21/2022] Open
Abstract
The role of GABAA receptor (GABAAR)-mediated tonic inhibition in interneurons remains unclear and may vary among subgroups. Somatostatin (SOM) interneurons in the hilus of the dentate gyrus show negligible expression of nonsynaptic GABAAR subunits and very low tonic inhibition. To determine the effects of ectopic expression of tonic GABAAR subtypes in these neurons, Cre-dependent viral vectors were used to express GFP-tagged GABAAR subunits (α6 and δ) selectively in hilar SOM neurons in SOM-Cre mice. In single-transfected animals, immunohistochemistry demonstrated strong expression of either the α6 or δ subunit; in cotransfected animals, both subunits were consistently expressed in the same neurons. Electrophysiology revealed a robust increase of tonic current, with progressively larger increases following transfection of δ, α6, and α6/δ subunits, respectively, indicating formation of functional receptors in all conditions and likely coassembly of the subunits in the same receptor following cotransfection. An in vitro model of repetitive bursting was used to determine the effects of increased tonic inhibition in hilar SOM interneurons on circuit activity in the dentate gyrus. Upon cotransfection, the frequency of GABAAR-mediated bursting in granule cells was reduced, consistent with a reduction in synchronous firing among hilar SOM interneurons. Moreover, in vivo studies of Fos expression demonstrated reduced activation of α6/δ-cotransfected neurons following acute seizure induction by pentylenetetrazole. The findings demonstrate that increasing tonic inhibition in hilar SOM interneurons can alter dentate gyrus circuit activity during strong stimulation and suggest that tonic inhibition of interneurons could play a role in regulating excessive synchrony within the network. SIGNIFICANCE STATEMENT In contrast to many hippocampal interneurons, somatostatin (SOM) neurons in the hilus of the dentate gyrus have very low levels of nonsynaptic GABAARs and exhibit very little tonic inhibition. In an effort to increase tonic inhibition selectively in these interneurons, we used Cre-dependent viral vectors in SOM-Cre mice to achieve interneuron-specific expression of the nonsynaptic GABAAR subunits (α6 and δ) in vivo. We show, for the first time, that such recombinant GFP-tagged GABAAR subunits are expressed robustly, assemble to form functional receptors, substantially increase tonic inhibition in SOM interneurons, and alter circuit activity within the dentate gyrus.
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Affiliation(s)
- Xiaoping Tong
- Departments of Neurobiology and Department of Anatomy, Histology and Embryology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China, and
| | | | | | | | | | - Martin Wallner
- Molecular and Medical Pharmacology and Brain Research Institute, David Geffen School of Medicine at the University of California, Los Angeles, Los Angeles, California 90095
| | - Thomas S Otis
- Departments of Neurobiology and Brain Research Institute, David Geffen School of Medicine at the University of California, Los Angeles, Los Angeles, California 90095, Roche Pharmaceutical Research and Early Development, Neuroscience, Ophthalmology, and Rare Diseases Translational Area, Roche Innovation Center Basel, CH-4070, Basel, Switzerland
| | - Carolyn R Houser
- Departments of Neurobiology and Brain Research Institute, David Geffen School of Medicine at the University of California, Los Angeles, Los Angeles, California 90095,
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Toni N, Schinder AF. Maturation and Functional Integration of New Granule Cells into the Adult Hippocampus. Cold Spring Harb Perspect Biol 2015; 8:a018903. [PMID: 26637288 DOI: 10.1101/cshperspect.a018903] [Citation(s) in RCA: 115] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The adult hippocampus generates functional dentate granule cells (GCs) that release glutamate onto target cells in the hilus and cornus ammonis (CA)3 region, and receive glutamatergic and γ-aminobutyric acid (GABA)ergic inputs that tightly control their spiking activity. The slow and sequential development of their excitatory and inhibitory inputs makes them particularly relevant for information processing. Although they are still immature, new neurons are recruited by afferent activity and display increased excitability, enhanced activity-dependent plasticity of their input and output connections, and a high rate of synaptogenesis. Once fully mature, new GCs show all the hallmarks of neurons generated during development. In this review, we focus on how developing neurons remodel the adult dentate gyrus and discuss key aspects that illustrate the potential of neurogenesis as a mechanism for circuit plasticity and function.
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Affiliation(s)
- Nicolas Toni
- Department of Fundamental Neurosciences, University of Lausanne, CH-1005 Lausanne, Switzerland
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46
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Vivar C, Peterson BD, van Praag H. Running rewires the neuronal network of adult-born dentate granule cells. Neuroimage 2015; 131:29-41. [PMID: 26589333 DOI: 10.1016/j.neuroimage.2015.11.031] [Citation(s) in RCA: 104] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2015] [Revised: 11/11/2015] [Accepted: 11/12/2015] [Indexed: 01/06/2023] Open
Abstract
Exercise improves cognition in humans and animals. Running increases neurogenesis in the dentate gyrus of the hippocampus, a brain area important for learning and memory. It is unclear how running modifies the circuitry of new dentate gyrus neurons to support their role in memory function. Here we combine retroviral labeling with rabies virus mediated trans-synaptic retrograde tracing to define and quantify new neuron afferent inputs in young adult male C57Bl/6 mice, housed with or without a running wheel for one month. Exercise resulted in a shift in new neuron networks that may promote sparse encoding and pattern separation. Neurogenesis increased in the dorsal, but not the ventral, dentate gyrus by three-fold, whereas afferent traced cell labeling doubled in number. Regional analysis indicated that running differentially affected specific inputs. Within the hippocampus the ratio of innervation from inhibitory interneurons and glutamatergic mossy cells to new neurons was reduced. Distal traced cells were located in sub-cortical and cortical regions, including perirhinal, entorhinal and sensory cortices. Innervation from entorhinal cortex (EC) was augmented, in proportion to the running-induced enhancement of adult neurogenesis. Within EC afferent input and short-term synaptic plasticity from lateral entorhinal cortex, considered to convey contextual information to the hippocampus was increased. Furthermore, running upregulated innervation from regions important for spatial memory and theta rhythm generation, including caudo-medial entorhinal cortex and subcortical medial septum, supra- and medial mammillary nuclei. Altogether, running may facilitate contextual, spatial and temporal information encoding by increasing adult hippocampal neurogenesis and by reorganization of new neuron circuitry.
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Affiliation(s)
- Carmen Vivar
- Neuroplasticity and Behavior Unit, Laboratory of Neurosciences, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, United States
| | - Benjamin D Peterson
- Neuroplasticity and Behavior Unit, Laboratory of Neurosciences, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, United States
| | - Henriette van Praag
- Neuroplasticity and Behavior Unit, Laboratory of Neurosciences, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, United States.
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Yu J, Proddutur A, Swietek B, Elgammal FS, Santhakumar V. Functional Reduction in Cannabinoid-Sensitive Heterotypic Inhibition of Dentate Basket Cells in Epilepsy: Impact on Network Rhythms. Cereb Cortex 2015; 26:4229-4314. [PMID: 26400918 DOI: 10.1093/cercor/bhv199] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Strong perisomatic inhibition by fast-spiking basket cells (FS-BCs) regulates dentate throughput. Homotypic FS-BC interconnections that support gamma oscillations, and heterotypic inputs from diverse groups of interneurons that receive extensive neurochemical regulation, together, shape FS-BC activity patterns. However, whether seizures precipitate functional changes in inhibitory networks and contribute to abnormal network activity in epilepsy is not known. In the first recordings from dentate interneuronal pairs in a model of temporal lobe epilepsy, we demonstrate that status epilepticus (SE) selectively compromises GABA release at synapses from dentate accommodating interneurons (AC-INs) to FS-BCs, while efficacy of homotypic FS-BC synapses is unaltered. The functional decrease in heterotypic cannabinoid receptor type 1 (CB1R)-sensitive inhibition of FS-BCs resulted from enhanced baseline GABAB-mediated suppression of synaptic release after SE. The frequency of CB1R-sensitive inhibitory synaptic events in FS-BCs was depressed early after SE induction and remained reduced in epileptic rats. In biologically based simulations of heterogeneous inhibitory networks and excitatory-inhibitory cell networks, experimentally identified decrease in reliability of AC-IN to FS-BCs synaptic release reduced theta power and theta-gamma coupling and enhanced gamma coherence. Thus, the experimentally identified functional reduction in heterotypic inhibition of FS-BCs can contribute to compromised network oscillations in epilepsy and could precipitate memory and cognitive co-morbidities.
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Affiliation(s)
- Jiandong Yu
- Center for Neuropsychiatric Diseases, Institute of Life Science, Nanchang University, Nanchang 330031, China Department of Pharmacology, Physiology, and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ 07103, USA
| | - Archana Proddutur
- Department of Pharmacology, Physiology, and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ 07103, USA
| | - Bogumila Swietek
- Department of Pharmacology, Physiology, and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ 07103, USA
| | - Fatima S Elgammal
- Department of Pharmacology, Physiology, and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ 07103, USA
| | - Vijayalakshmi Santhakumar
- Department of Pharmacology, Physiology, and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ 07103, USA
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48
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Scharfman HE, Bernstein HL. Potential implications of a monosynaptic pathway from mossy cells to adult-born granule cells of the dentate gyrus. Front Syst Neurosci 2015; 9:112. [PMID: 26347618 PMCID: PMC4541026 DOI: 10.3389/fnsys.2015.00112] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2015] [Accepted: 07/20/2015] [Indexed: 11/13/2022] Open
Abstract
The dentate gyrus (DG) is important to many aspects of hippocampal function, but there are many aspects of the DG that are incompletely understood. One example is the role of mossy cells (MCs), a major DG cell type that is glutamatergic and innervates the primary output cells of the DG, the granule cells (GCs). MCs innervate the GCs as well as local circuit neurons that make GABAergic synapses on GCs, so the net effect of MCs on GCs – and therefore the output of the DG – is unclear. Here we first review fundamental information about MCs and the current hypotheses for their role in the normal DG and in diseases that involve the DG. Then we review previously published data which suggest that MCs are a source of input to a subset of GCs that are born in adulthood (adult-born GCs). In addition, we discuss the evidence that adult-born GCs may support the normal inhibitory ‘gate’ functions of the DG, where the GCs are a filter or gate for information from the entorhinal cortical input to area CA3. The implications are then discussed in the context of seizures and temporal lobe epilepsy (TLE). In TLE, it has been suggested that the DG inhibitory gate is weak or broken and MC loss leads to insufficient activation of inhibitory neurons, causing hyperexcitability. That idea was called the “dormant basket cell hypothesis.” Recent data suggest that loss of normal adult-born GCs may also cause disinhibition, and seizure susceptibility. Therefore, we propose a reconsideration of the dormant basket cell hypothesis with an intervening adult-born GC between the MC and basket cell and call this hypothesis the “dormant immature granule cell hypothesis.”
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Affiliation(s)
- Helen E Scharfman
- The Nathan Kline Institute for Psychiatric Research, Orangeburg NY, USA ; New York University Langone Medical Center, New York NY, USA
| | - Hannah L Bernstein
- The Nathan Kline Institute for Psychiatric Research, Orangeburg NY, USA ; New York University Langone Medical Center, New York NY, USA
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49
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Turkheimer FE, Leech R, Expert P, Lord LD, Vernon AC. The brain's code and its canonical computational motifs. From sensory cortex to the default mode network: A multi-scale model of brain function in health and disease. Neurosci Biobehav Rev 2015; 55:211-22. [PMID: 25956253 DOI: 10.1016/j.neubiorev.2015.04.014] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Revised: 04/01/2015] [Accepted: 04/25/2015] [Indexed: 12/21/2022]
Affiliation(s)
| | - Robert Leech
- Division of Brain Sciences, Imperial College London, London, UK
| | - Paul Expert
- Institute of Psychiatry, King's College London, London, UK
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50
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Foster JD, Kitchen I, Bettler B, Chen Y. GABAB receptor subtypes differentially modulate synaptic inhibition in the dentate gyrus to enhance granule cell output. Br J Pharmacol 2015. [PMID: 23186302 DOI: 10.1111/bph.12073] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
BACKGROUND AND PURPOSE Activation of GABAB receptors in the dentate gyrus (DG) enhances granule cell (GC) activity by reducing synaptic inhibition imposed by hilar interneurons. This disinhibitory action facilitates signal transfer from the perforant path to the hippocampus. However, as the two main molecular subtypes, GABA(B(1a,2)) and GABA(B(1b,2)) receptors, prefer axonal terminal and dendritic compartments, respectively, they may modulate the hilar pathways at different synaptic localizations. We examined their relative expression and functions in the DG. EXPERIMENTAL APPROACH The localization of GABAB subtypes was revealed immunohistochemically using subunit-selective antibodies in GABA(B1a)(-/-) and GABA(B1b)(-/-) mice. Effects of subtype activation by the GABAB receptor agonist, baclofen, were examined on the perforant path-stimulated GC population activities in brain slices. KEY RESULTS GABA(B(1a,2)) receptors were concentrated in the inner molecular layer, the neuropil of the hilus and hilar neurons at the border zone; while GABA(B(1b,2)) receptors dominated the outer molecular layer and hilar neurons in the deep layer, showing their differential localization on GC dendrite and in the hilus. Baclofen enhanced the GC population spike to a larger extent in the GABA(B1b)(-/-) mice, demonstrating exclusively disinhibitory roles of the GABA(B(1a,2)) receptors. Conversely, in the GABA(B1a)(-/-) mice baclofen not only enhanced but also inhibited the population spike during GABAA blockade, revealing both disinhibitory and inhibitory effects of GABA(B(1b,2)) receptors. CONCLUSIONS AND IMPLICATIONS The GABA(B(1a,2)) and GABA(B(1b,2)) receptor subtypes differentially modulate GC outputs via selective axonal terminal and dendritic locations in the hilar pathways. The GABA(B(1a,2)) receptors exclusively mediate disinhibition, thereby playing a greater role in gating signal transfer for hippocampal spatial and pattern learning.
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Affiliation(s)
- Joshua D Foster
- Department of Biochemistry and Physiology, Faculty of Health and Medical Sciences, University of Surrey, Guildford, UK
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