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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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52
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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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53
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Bird CW, Taylor DH, Pinkowski NJ, Chavez GJ, Valenzuela CF. Long-term Reductions in the Population of GABAergic Interneurons in the Mouse Hippocampus following Developmental Ethanol Exposure. Neuroscience 2018; 383:60-73. [PMID: 29753864 PMCID: PMC5994377 DOI: 10.1016/j.neuroscience.2018.05.003] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2017] [Revised: 04/27/2018] [Accepted: 05/02/2018] [Indexed: 02/07/2023]
Abstract
Developmental exposure to ethanol leads to a constellation of cognitive and behavioral abnormalities known as Fetal Alcohol Spectrum Disorders (FASDs). Many cell types throughout the central nervous system are negatively impacted by gestational alcohol exposure, including inhibitory, GABAergic interneurons. Little evidence exists, however, describing the long-term impact of fetal alcohol exposure on survival of interneurons within the hippocampal formation, which is critical for learning and memory processes that are impaired in individuals with FASDs. Mice expressing Venus yellow fluorescent protein in inhibitory interneurons were exposed to vaporized ethanol during the third trimester equivalent of human gestation (postnatal days 2-9), and the long-term effects on interneuron numbers were measured using unbiased stereology at P90. In adulthood, interneuron populations were reduced in every hippocampal region examined. Moreover, we found that a single exposure to ethanol at P7 caused robust activation of apoptotic neurodegeneration of interneurons in the hilus, granule cell layer, CA1 and CA3 regions of the hippocampus. These studies demonstrate that developmental ethanol exposure has a long-term impact on hippocampal interneuron survivability, and may provide a mechanism partially explaining deficits in hippocampal function and hippocampus-dependent behaviors in those afflicted with FASDs.
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Affiliation(s)
- Clark W Bird
- Department of Neurosciences, School of Medicine, University of New Mexico Health Sciences Center, Albuquerque, NM, USA
| | - Devin H Taylor
- Department of Neurosciences, School of Medicine, University of New Mexico Health Sciences Center, Albuquerque, NM, USA
| | - Natalie J Pinkowski
- Department of Neurosciences, School of Medicine, University of New Mexico Health Sciences Center, Albuquerque, NM, USA
| | - G Jill Chavez
- Department of Neurosciences, School of Medicine, University of New Mexico Health Sciences Center, Albuquerque, NM, USA
| | - C Fernando Valenzuela
- Department of Neurosciences, School of Medicine, University of New Mexico Health Sciences Center, Albuquerque, NM, USA.
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54
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Tran T, Gallagher M, Kirkwood A. Enhanced postsynaptic inhibitory strength in hippocampal principal cells in high-performing aged rats. Neurobiol Aging 2018; 70:92-101. [PMID: 30007169 DOI: 10.1016/j.neurobiolaging.2018.06.008] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2018] [Revised: 05/28/2018] [Accepted: 06/03/2018] [Indexed: 11/20/2022]
Abstract
Hyperactivity within the hippocampal formation, frequently observed in aged individuals, is thought to be a potential contributing mechanism to the memory decline often associated with aging. Consequently, we evaluated the postsynaptic strength of excitatory and inhibitory synapses in the granule cells of the dentate gyrus and CA1 pyramidal cells of a rat model of aging, in which each individual was behaviorally characterized as aged impaired (AI) or aged unimpaired (AU, with performance comparable to young (Y) individuals). In hippocampal slices of these 3 aged groups (Y, AI, AU), we found that compared to the young, the miniature excitatory and inhibitory currents (mEPSCs and mIPSCs) were larger in amplitude in the granule cells of the AU group and smaller in the AI group. In contrast, in CA1 cells, neither the mEPSCs nor the mIPSCs were affected by age, whereas the extrasynaptic conductance responsible for tonic inhibition was selectively enhanced in CA1 cells of AU individuals. Tonic inhibition conductance was not affected by age in the granule cells. These results support the notion that upregulation of synaptic inhibition could be a necessary condition for the maintenance of performance during aging. These findings also underscore the notions that successful aging requires adaptive upregulation, not merely the preservation of youthful functionality, and that age effects are not homogeneous across hippocampal subfields.
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Affiliation(s)
- Trinh Tran
- Mind/Brain Institute and Department of Neurosciences, Johns Hopkins University, 3400 N. Charles St, Baltimore, MD 21218, USA
| | - Michela Gallagher
- Department of Psychological and Brain Sciences, Johns Hopkins University, 3400 N. Charles St, Baltimore, MD 21218, USA.
| | - Alfredo Kirkwood
- Mind/Brain Institute and Department of Neurosciences, Johns Hopkins University, 3400 N. Charles St, Baltimore, MD 21218, USA.
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55
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Kassab R, Alexandre F. Pattern separation in the hippocampus: distinct circuits under different conditions. Brain Struct Funct 2018; 223:2785-2808. [PMID: 29637298 DOI: 10.1007/s00429-018-1659-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Accepted: 03/26/2018] [Indexed: 10/17/2022]
Abstract
Pattern separation is a fundamental hippocampal process thought to be critical for distinguishing similar episodic memories, and has long been recognized as a natural function of the dentate gyrus (DG), supporting autoassociative learning in CA3. Understanding how neural circuits within the DG-CA3 network mediate this process has received much interest, yet the exact mechanisms behind remain elusive. Here, we argue for the case that sparse coding is necessary but not sufficient to ensure efficient separation and, alternatively, propose a possible interaction of distinct circuits which, nevertheless, act in synergy to produce a unitary function of pattern separation. The proposed circuits involve different functional granule-cell populations, a primary population mediates sparsification and provides recurrent excitation to the other populations which are related to additional pattern separation mechanisms with higher degrees of robustness against interference in CA3. A variety of top-down and bottom-up factors, such as motivation, emotion, and pattern similarity, control the selection of circuitry depending on circumstances. According to this framework, a computational model is implemented and tested against model variants in a series of numerical simulations and biological experiments. The results demonstrate that the model combines fast learning, robust pattern separation and high storage capacity. It also accounts for the controversy around the involvement of the DG during memory recall, explains other puzzling findings, and makes predictions that can inform future investigations.
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Affiliation(s)
- Randa Kassab
- INRIA, Bordeaux Sud-Ouest, Talence, France. .,Institut des Maladies Neurodégénératives, University of Bordeaux, CNRS UMR 5293-Case 28, Centre Broca Nouvelle-Aquitaine, 146 rue Léo Saignat, 33076, Bordeaux, France. .,LaBRI, UMR 5800, CNRS, Bordeaux INP, University of Bordeaux, Talence, France.
| | - Frédéric Alexandre
- INRIA, Bordeaux Sud-Ouest, Talence, France.,Institut des Maladies Neurodégénératives, University of Bordeaux, CNRS UMR 5293-Case 28, Centre Broca Nouvelle-Aquitaine, 146 rue Léo Saignat, 33076, Bordeaux, France.,LaBRI, UMR 5800, CNRS, Bordeaux INP, University of Bordeaux, Talence, France
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56
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Poli D, Wheeler BC, DeMarse TB, Brewer GJ. Pattern separation and completion of distinct axonal inputs transmitted via micro-tunnels between co-cultured hippocampal dentate, CA3, CA1 and entorhinal cortex networks. J Neural Eng 2018; 15:046009. [PMID: 29623900 DOI: 10.1088/1741-2552/aabc20] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
OBJECTIVE Functions ascribed to the hippocampal sub-regions for encoding episodic memories include the separation of activity patterns propagated from the entorhinal cortex (EC) into the dentate gyrus (DG) and pattern completion in CA3 region. Since a direct assessment of these functions is lacking at the level of specific axonal inputs, our goal is to directly measure the separation and completion of distinct axonal inputs in engineered pairs of hippocampal sub-regional circuits. APPROACH We co-cultured EC-DG, DG-CA3, CA3-CA1 or CA1-EC neurons in a two-chamber PDMS device over a micro-electrode array (MEA60), inter-connected via distinct axons that grow through the micro-tunnels between the compartments. Taking advantage of the axonal accessibility, we quantified pattern separation and completion of the evoked activity transmitted through the tunnels from source into target well. Since pattern separation can be inferred when inputs are more correlated than outputs, we first compared the correlations among axonal inputs with those of target somata outputs. We then compared, in an analog approach, the distributions of correlation distances between rate patterns of the axonal inputs inside the tunnels with those of the somata outputs evoked in the target well. Finally, in a digital approach, we measured the spatial population distances between binary patterns of the same axonal inputs and somata outputs. MAIN RESULTS We found the strongest separation of the propagated axonal inputs when EC was axonally connected to DG, with a decline in separation to CA3 and to CA1 for both rate and digital approaches. Furthermore, the digital approach showed stronger pattern completion in CA3, then CA1 and EC. SIGNIFICANCE To the best of our knowledge, these are the first direct measures of pattern separation and completion for axonal transmission to the somata target outputs at the rate and digital population levels in each of four stages of the EC-DG-CA3-CA1 circuit.
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Affiliation(s)
- Daniele Poli
- Department of Biomedical Engineering, University of California, Irvine, CA, United States of America. Research Center 'Enrico Piaggio', University of Pisa, Pisa, Italy
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57
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Unfolding the cognitive map: The role of hippocampal and extra-hippocampal substrates based on a systems analysis of spatial processing. Neurobiol Learn Mem 2018; 147:90-119. [DOI: 10.1016/j.nlm.2017.11.012] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2017] [Revised: 11/17/2017] [Accepted: 11/21/2017] [Indexed: 01/03/2023]
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58
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Excitatory Synaptic Input to Hilar Mossy Cells under Basal and Hyperexcitable Conditions. eNeuro 2017; 4:eN-NWR-0364-17. [PMID: 29214210 PMCID: PMC5714709 DOI: 10.1523/eneuro.0364-17.2017] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2017] [Revised: 11/06/2017] [Accepted: 11/10/2017] [Indexed: 11/21/2022] Open
Abstract
Hilar mossy cells (HMCs) in the hippocampus receive glutamatergic input from dentate granule cells (DGCs) via mossy fibers (MFs) and back-projections from CA3 pyramidal neuron collateral axons. Many fundamental features of these excitatory synapses have not been characterized in detail despite their potential relevance to hippocampal cognitive processing and epilepsy-induced adaptations in circuit excitability. In this study, we compared pre- and postsynaptic parameters between MF and CA3 inputs to HMCs in young and adult mice of either sex and determined the relative contributions of the respective excitatory inputs during in vitro and in vivo models of hippocampal hyperexcitability. The two types of excitatory synapses both exhibited a modest degree of short-term plasticity, with MF inputs to HMCs exhibiting lower paired-pulse (PP) and frequency facilitation than was described previously for MF–CA3 pyramidal cell synapses. MF–HMC synapses exhibited unitary excitatory synaptic currents (EPSCs) of larger amplitude, contained postsynaptic kainate receptors, and had a lower NMDA/AMPA receptor ratio compared to CA3–HMC synapses. Pharmacological induction of hippocampal hyperexcitability in vitro transformed the abundant but relatively weak CA3–HMC connections to very large amplitude spontaneous bursts of compound EPSCs (cEPSCs) in young mice (∼P20) and, to a lesser degree, in adult mice (∼P70). CA3–HMC cEPSCs were also observed in slices prepared from mice with spontaneous seizures several weeks after intrahippocampal kainate injection. Strong excitation of HMCs during synchronous CA3 activity represents an avenue of significant excitatory network generation back to DGCs and might be important in generating epileptic networks.
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59
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Linking neuronal structure to function in rodent hippocampus: a methodological prospective. Cell Tissue Res 2017; 373:605-618. [PMID: 29181629 DOI: 10.1007/s00441-017-2732-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Accepted: 10/27/2017] [Indexed: 10/18/2022]
Abstract
Since the discovery of place cells, hippocampus-dependent spatial navigation has proven to be an ideal model system for resolving the relationship between neural coding and behavior. Electrical recordings from the hippocampal formation in freely moving animals have revealed a rich repertoire of spatial firing patterns and have enormously advanced our understanding of the neural principles of spatial representation. However, limited progress has been achieved in resolving the underlying cellular mechanisms. This is partially attributable to the inability of standard recording techniques to link neuronal structure to function directly. In this review, we summarize recent efforts aimed at filling this gap. We also highlight the development of methodologies that allow functional measurements from identified neuronal elements in behaving rodents. Recent progress in the dentate gyrus serves as a showcase to reveal the potential of such methodologies and the necessity of resolving structure-function relationships in order to access the cellular mechanisms of hippocampal circuit computations.
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60
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Scharfman HE, MacLusky NJ. Sex differences in hippocampal area CA3 pyramidal cells. J Neurosci Res 2017; 95:563-575. [PMID: 27870399 DOI: 10.1002/jnr.23927] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2016] [Revised: 08/14/2016] [Accepted: 08/24/2016] [Indexed: 11/07/2022]
Abstract
Numerous studies have demonstrated differences between males and females in hippocampal structure, function, and plasticity. There also are many studies about the different predisposition of a males and females for disorders where the hippocampus plays an important role. Many of these reports focus on area CA1, but other subfields are also very important, and unlikely to be the same as area CA1 based on what is known. Here we review basic studies of male and female structure, function, and plasticity of area CA3 pyramidal cells of adult rats. The data suggest that the CA3 pyramidal cells of males and females are distinct in structure, function, and plasticity. These sex differences cannot be simply explained by the effects of circulating gonadal hormones. This view agrees with previous studies showing that there are substantial sex differences in the brain that cannot be normalized by removing the gonads and depleting peripheral gonadal hormones. Implications of these comparisons for understanding sex differences in hippocampal function and dysfunction are discussed. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Helen E Scharfman
- Department of Child and Adolescent Psychiatry, Physiology and Neuroscience, and Psychiatry, New York University Langone Medical Center, New York, New York.,Department of Nathan S. Kline Institute for Psychiatric Research, Orangeburg, New York
| | - Neil J MacLusky
- Department of Biomedical Sciences, University of Guelph, Guelph, Ontario, Canada
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61
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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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62
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Hashimotodani Y, Nasrallah K, Jensen KR, Chávez AE, Carrera D, Castillo PE. LTP at Hilar Mossy Cell-Dentate Granule Cell Synapses Modulates Dentate Gyrus Output by Increasing Excitation/Inhibition Balance. Neuron 2017; 95:928-943.e3. [PMID: 28817805 PMCID: PMC5609819 DOI: 10.1016/j.neuron.2017.07.028] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Revised: 06/23/2017] [Accepted: 07/25/2017] [Indexed: 01/20/2023]
Abstract
Excitatory hilar mossy cells (MCs) in the dentate gyrus receive inputs from dentate granule cells (GCs) and project back to GCs locally, contralaterally, and along the longitudinal axis of the hippocampus, thereby establishing an associative positive-feedback loop and connecting functionally diverse hippocampal areas. MCs also synapse with GABAergic interneurons that mediate feed-forward inhibition onto GCs. Surprisingly, although these circuits have been implicated in both memory formation (e.g., pattern separation) and temporal lobe epilepsy, little is known about activity-dependent plasticity of their synaptic connections. Here, we report that MC-GC synapses undergo a presynaptic, NMDA-receptor-independent form of long-term potentiation (LTP) that requires postsynaptic brain-derived neurotrophic factor (BDNF)/TrkB and presynaptic cyclic AMP (cAMP)/PKA signaling. This LTP is input specific and selectively expressed at MC-GC synapses, but not at the disynaptic inhibitory loop. By increasing the excitation/inhibition balance, MC-GC LTP enhances GC output at the associative MC-GC recurrent circuit and may contribute to dentate-dependent forms of learning and epilepsy.
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Affiliation(s)
- Yuki Hashimotodani
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Kaoutsar Nasrallah
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Kyle R Jensen
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Andrés E Chávez
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Daniel Carrera
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Pablo E Castillo
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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63
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HIPP neurons in the dentate gyrus mediate the cholinergic modulation of background context memory salience. Nat Commun 2017; 8:189. [PMID: 28775269 PMCID: PMC5543060 DOI: 10.1038/s41467-017-00205-3] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2016] [Accepted: 06/11/2017] [Indexed: 12/24/2022] Open
Abstract
Cholinergic neuromodulation in the hippocampus controls the salience of background context memory acquired in the presence of elemental stimuli predicting an aversive reinforcement. With pharmacogenetic inhibition we here demonstrate that hilar perforant path-associated (HIPP) cells of the dentate gyrus mediate the devaluation of background context memory during Pavlovian fear conditioning. The salience adjustment is sensitive to reduction of hilar neuropeptide Y (NPY) expression via dominant negative CREB expression in HIPP cells and to acute blockage of NPY-Y1 receptors in the dentate gyrus during conditioning. We show that NPY transmission and HIPP cell activity contribute to inhibitory effects of acetylcholine in the dentate gyrus and that M1 muscarinic receptors mediate the cholinergic activation of HIPP cells as well as their control of background context salience. Our data provide evidence for a peptidergic local circuit in the dentate gyrus that mediates the cholinergic encoding of background context salience during fear memory acquisition. Intra-hippocampal circuits are essential for associating a background context with behaviorally salient stimuli and involve cholinergic modulation at SST+ interneurons. Here the authors show that the salience of the background context memory is modulated through muscarinic activation of NPY+ hilar perforant path associated interneurons and NPY signaling in the dentate gyrus.
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64
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Chavlis S, Poirazi P. Pattern separation in the hippocampus through the eyes of computational modeling. Synapse 2017; 71. [PMID: 28316111 DOI: 10.1002/syn.21972] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2016] [Revised: 03/02/2017] [Accepted: 03/14/2017] [Indexed: 12/24/2022]
Abstract
Pattern separation is a mnemonic process that has been extensively studied over the years. It entails the ability -of primarily hippocampal circuits- to distinguish between highly similar inputs, via generating different neuronal activity (output) patterns. The dentate gyrus (DG) in particular has long been hypothesized to implement pattern separation by detecting and storing similar inputs as distinct representations. The ways in which these distinct representations can be generated have been explored in a number of theoretical and computational modeling studies. Here, we review two categories of pattern separation models: those that address the phenomenon in an abstract mathematical fashion and those that delve into the underlying biological mechanisms by taking into account the anatomy and/or physiology of hippocampal circuits. We summarize the strategies, findings and limitations of these modeling approaches in the light of new experimental findings and propose a unifying framework whereby different network, cellular and sub-cellular mechanisms converge to a common goal: controlling sparsity, the key determinant of pattern separation in the DG.
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Affiliation(s)
- Spyridon Chavlis
- Institute of Molecular Biology & Biotechnology (IMBB), Foundation for Research and Technology - Hellas (FORTH), N. Plastira 100, Heraklion, Crete, 70013, Greece.,Department of Biology, University of Crete, Vasilika Vouton, P.O. Box 2208, Heraklion, Crete, 71409, Greece
| | - Panayiota Poirazi
- Institute of Molecular Biology & Biotechnology (IMBB), Foundation for Research and Technology - Hellas (FORTH), N. Plastira 100, Heraklion, Crete, 70013, Greece
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65
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Lee JW, Jung MW. Separation or binding? Role of the dentate gyrus in hippocampal mnemonic processing. Neurosci Biobehav Rev 2017; 75:183-194. [PMID: 28174077 DOI: 10.1016/j.neubiorev.2017.01.049] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2016] [Revised: 11/26/2016] [Accepted: 01/05/2017] [Indexed: 01/15/2023]
Abstract
As a major component of the hippocampal trisynaptic circuit, the dentate gyrus (DG) relays inputs from the entorhinal cortex to the CA3 subregion. Although the anatomy of the DG is well characterized, its contribution to hippocampal mnemonic processing is still unclear. A currently popular theory proposes that the primary function of the DG is to orthogonalize incoming input patterns into non-overlapping patterns (pattern separation). We critically review the available data and conclude that the theoretical support and empirical evidence for this theory are not strong. We then review an alternative theory that posits a role for the DG in binding together different types of incoming sensory information. We conclude that 'binding' better captures the contribution of the DG to memory encoding than 'pattern separation'.
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Affiliation(s)
- Jong Won Lee
- Center for Synaptic Brain Dysfunctions, Institute for Basic Science, Daejeon 34141, Republic of Korea
| | - Min Whan Jung
- Center for Synaptic Brain Dysfunctions, Institute for Basic Science, Daejeon 34141, Republic of Korea; Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea.
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66
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Physiological Properties and Behavioral Correlates of Hippocampal Granule Cells and Mossy Cells. Neuron 2017; 93:691-704.e5. [PMID: 28132824 DOI: 10.1016/j.neuron.2016.12.011] [Citation(s) in RCA: 185] [Impact Index Per Article: 26.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Revised: 10/31/2016] [Accepted: 12/07/2016] [Indexed: 02/04/2023]
Abstract
The hippocampal dentate gyrus is often viewed as a segregator of upstream information. Physiological support for such function has been hampered by a lack of well-defined characteristics that can identify granule cells and mossy cells. We developed an electrophysiology-based classification of dentate granule cells and mossy cells in mice that we validated by optogenetic tagging of mossy cells. Granule cells exhibited sparse firing, had a single place field, and showed only modest changes when the mouse was tested in different mazes in the same room. In contrast, mossy cells were more active, had multiple place fields and showed stronger remapping of place fields under the same conditions. Although the granule cell-mossy cell synapse was strong and facilitating, mossy cells rarely "inherited" place fields from single granule cells. Our findings suggest that the granule cells and mossy cells could be modulated separately and their joint action may be critical for pattern separation.
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67
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GoodSmith D, Chen X, Wang C, Kim SH, Song H, Burgalossi A, Christian KM, Knierim JJ. Spatial Representations of Granule Cells and Mossy Cells of the Dentate Gyrus. Neuron 2017; 93:677-690.e5. [PMID: 28132828 DOI: 10.1016/j.neuron.2016.12.026] [Citation(s) in RCA: 165] [Impact Index Per Article: 23.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Revised: 11/01/2016] [Accepted: 12/12/2016] [Indexed: 01/12/2023]
Abstract
Granule cells in the dentate gyrus of the hippocampus are thought to be essential to memory function by decorrelating overlapping input patterns (pattern separation). A second excitatory cell type in the dentate gyrus, the mossy cell, forms an intricate circuit with granule cells, CA3c pyramidal cells, and local interneurons, but the influence of mossy cells on dentate function is often overlooked. Multiple tetrode recordings, supported by juxtacellular recording techniques, showed that granule cells fired very sparsely, whereas mossy cells in the hilus fired promiscuously in multiple locations and in multiple environments. The activity patterns of these cell types thus represent different environments through distinct computational mechanisms: sparse coding in granule cells and changes in firing field locations in mossy cells.
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Affiliation(s)
- Douglas GoodSmith
- Krieger Mind/Brain Institute, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Xiaojing Chen
- Krieger Mind/Brain Institute, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Cheng Wang
- Krieger Mind/Brain Institute, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Sang Hoon Kim
- Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore MD 21205 USA; Department of Neurology, Johns Hopkins University School of Medicine, Baltimore MD 21205 USA
| | - Hongjun Song
- Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore MD 21205 USA; Department of Neurology, Johns Hopkins University School of Medicine, Baltimore MD 21205 USA; Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore MD 21205 USA
| | - Andrea Burgalossi
- Werner-Reichardt Centre for Integrative Neuroscience, 72076 Tübingen, Germany
| | - Kimberly M Christian
- Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore MD 21205 USA; Department of Neurology, Johns Hopkins University School of Medicine, Baltimore MD 21205 USA
| | - James J Knierim
- Krieger Mind/Brain Institute, Johns Hopkins University, Baltimore, MD 21218, USA; Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore MD 21205 USA.
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68
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Danielson NB, Turi GF, Ladow M, Chavlis S, Petrantonakis PC, Poirazi P, Losonczy A. In Vivo Imaging of Dentate Gyrus Mossy Cells in Behaving Mice. Neuron 2017; 93:552-559.e4. [PMID: 28132825 DOI: 10.1016/j.neuron.2016.12.019] [Citation(s) in RCA: 108] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2016] [Revised: 10/20/2016] [Accepted: 11/26/2016] [Indexed: 12/01/2022]
Abstract
Mossy cells in the hilus of the dentate gyrus constitute a major excitatory principal cell type in the mammalian hippocampus; however, it remains unknown how these cells behave in vivo. Here, we have used two-photon Ca2+ imaging to monitor the activity of mossy cells in awake, behaving mice. We find that mossy cells are significantly more active than dentate granule cells in vivo, exhibit spatial tuning during head-fixed spatial navigation, and undergo robust remapping of their spatial representations in response to contextual manipulation. Our results provide a functional characterization of mossy cells in the behaving animal and demonstrate their active participation in spatial coding and contextual representation.
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Affiliation(s)
- Nathan B Danielson
- Department of Neuroscience, Columbia University, New York, NY 10032, USA; Doctoral Program in Neurobiology and Behavior, Columbia University, New York, NY 10032, USA
| | - Gergely F Turi
- Department of Neuroscience, Columbia University, New York, NY 10032, USA
| | - Max Ladow
- Department of Neuroscience, Columbia University, New York, NY 10032, USA
| | - Spyridon Chavlis
- Institute of Molecular Biology and Biotechnology (IMBB), Foundation for Research and Technology - Hellas (FORTH), 700 13 Heraklion, Crete, Greece; Department of Biology, School of Sciences and Engineering, University of Crete, 741 00 Heraklion, Crete, Greece, Columbia University, New York, NY 10032, USA
| | - Panagiotis C Petrantonakis
- Institute of Molecular Biology and Biotechnology (IMBB), Foundation for Research and Technology - Hellas (FORTH), 700 13 Heraklion, Crete, Greece
| | - Panayiota Poirazi
- Institute of Molecular Biology and Biotechnology (IMBB), Foundation for Research and Technology - Hellas (FORTH), 700 13 Heraklion, Crete, Greece.
| | - Attila Losonczy
- Department of Neuroscience, Columbia University, New York, NY 10032, USA; Kavli Institute for Brain Science, Columbia University, New York, NY 10032, USA; Mortimer B. Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10032, USA.
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69
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Chavlis S, Petrantonakis PC, Poirazi P. Dendrites of dentate gyrus granule cells contribute to pattern separation by controlling sparsity. Hippocampus 2017; 27:89-110. [PMID: 27784124 PMCID: PMC5217096 DOI: 10.1002/hipo.22675] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2016] [Accepted: 10/25/2016] [Indexed: 12/24/2022]
Abstract
The hippocampus plays a key role in pattern separation, the process of transforming similar incoming information to highly dissimilar, nonverlapping representations. Sparse firing granule cells (GCs) in the dentate gyrus (DG) have been proposed to undertake this computation, but little is known about which of their properties influence pattern separation. Dendritic atrophy has been reported in diseases associated with pattern separation deficits, suggesting a possible role for dendrites in this phenomenon. To investigate whether and how the dendrites of GCs contribute to pattern separation, we build a simplified, biologically relevant, computational model of the DG. Our model suggests that the presence of GC dendrites is associated with high pattern separation efficiency while their atrophy leads to increased excitability and performance impairments. These impairments can be rescued by restoring GC sparsity to control levels through various manipulations. We predict that dendrites contribute to pattern separation as a mechanism for controlling sparsity. © 2016 The Authors Hippocampus Published by Wiley Periodicals, Inc.
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Affiliation(s)
- Spyridon Chavlis
- Institute of Molecular Biology and Biotechnology (IMBB), Foundation for Research and Technology, Hellas (FORTH)HeraklionCreteGreece
- Department of Biology, School of Sciences and EngineeringUniversity of CreteHeraklionCreteGreece
| | - Panagiotis C. Petrantonakis
- Institute of Molecular Biology and Biotechnology (IMBB), Foundation for Research and Technology, Hellas (FORTH)HeraklionCreteGreece
| | - Panayiota Poirazi
- Institute of Molecular Biology and Biotechnology (IMBB), Foundation for Research and Technology, Hellas (FORTH)HeraklionCreteGreece
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70
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Becker S. Neurogenesis and pattern separation: time for a divorce. WILEY INTERDISCIPLINARY REVIEWS. COGNITIVE SCIENCE 2016; 8. [PMID: 28026915 DOI: 10.1002/wcs.1427] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Revised: 09/09/2016] [Accepted: 09/30/2016] [Indexed: 01/08/2023]
Abstract
The generation of new neurons in the adult mammalian brain has led to numerous theories as to their functional significance. One of the most widely held views is that adult neurogenesis promotes pattern separation, a process by which overlapping patterns of neural activation are mapped to less overlapping representations. While a large body of evidence supports a role for neurogenesis in high interference memory tasks, it does not support the proposed function of neurogenesis in mediating pattern separation. Instead, the adult-generated neurons seem to generate highly overlapping and yet distinct distributed representations for similar events. One way in which these immature, highly plastic, hyperactive neurons may contribute to novel memory formation while avoiding interference is by virtue of their extremely sparse connectivity with incoming perforant path fibers. Another intriguing proposal, awaiting empirical confirmation, is that the young neurons' recruitment into memory formation is gated by a novelty/mismatch mechanism mediated by CA3 or hilar back-projections. Ongoing research into the intriguing link between neurogenesis, stress-related mood disorders, and age-related neurodegeneration may lead to promising neurogenesis-based treatments for this wide range of clinical disorders. WIREs Cogn Sci 2017, 8:e1427. doi: 10.1002/wcs.1427 For further resources related to this article, please visit the WIREs website.
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Affiliation(s)
- Suzanna Becker
- Department of Psychology Neuroscience and Behaviour, McMaster University, Hamilton, Canada
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71
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Zhuo JM, Tseng HA, Desai M, Bucklin ME, Mohammed AI, Robinson NT, Boyden ES, Rangel LM, Jasanoff AP, Gritton HJ, Han X. Young adult born neurons enhance hippocampal dependent performance via influences on bilateral networks. eLife 2016; 5. [PMID: 27914197 PMCID: PMC5156524 DOI: 10.7554/elife.22429] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2016] [Accepted: 11/16/2016] [Indexed: 02/06/2023] Open
Abstract
Adult neurogenesis supports performance in many hippocampal dependent tasks. Considering the small number of adult-born neurons generated at any given time, it is surprising that this sparse population of cells can substantially influence behavior. Recent studies have demonstrated that heightened excitability and plasticity may be critical for the contribution of young adult-born cells for certain tasks. What is not well understood is how these unique biophysical and synaptic properties may translate to networks that support behavioral function. Here we employed a location discrimination task in mice while using optogenetics to transiently silence adult-born neurons at different ages. We discovered that adult-born neurons promote location discrimination during early stages of development but only if they undergo maturation during task acquisition. Silencing of young adult-born neurons also produced changes extending to the contralateral hippocampus, detectable by both electrophysiology and fMRI measurements, suggesting young neurons may modulate location discrimination through influences on bilateral hippocampal networks. DOI:http://dx.doi.org/10.7554/eLife.22429.001
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Affiliation(s)
- Jia-Min Zhuo
- Biomedical Engineering Department, Boston University, Boston, United States
| | - Hua-An Tseng
- Biomedical Engineering Department, Boston University, Boston, United States
| | - Mitul Desai
- Department of Bioengineering, McGovern Institute, Cambridge, United States
| | - Mark E Bucklin
- Biomedical Engineering Department, Boston University, Boston, United States
| | - Ali I Mohammed
- Biomedical Engineering Department, Boston University, Boston, United States
| | - Nick Tm Robinson
- Department of Psychology, Boston University, Boston, United States
| | - Edward S Boyden
- Department of Bioengineering, McGovern Institute, Cambridge, United States.,Media Lab, Massachusetts Institute of Technology, Cambridge, United States
| | - Lara M Rangel
- Department of Psychology, Boston University, Boston, United States
| | - Alan P Jasanoff
- Department of Bioengineering, McGovern Institute, Cambridge, United States
| | - Howard J Gritton
- Biomedical Engineering Department, Boston University, Boston, United States
| | - Xue Han
- Biomedical Engineering Department, Boston University, Boston, United States
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72
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Diamantaki M, Frey M, Berens P, Preston-Ferrer P, Burgalossi A. Sparse activity of identified dentate granule cells during spatial exploration. eLife 2016; 5. [PMID: 27692065 PMCID: PMC5077296 DOI: 10.7554/elife.20252] [Citation(s) in RCA: 96] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Accepted: 10/01/2016] [Indexed: 01/20/2023] Open
Abstract
In the dentate gyrus - a key component of spatial memory circuits - granule cells (GCs) are known to be morphologically diverse and to display heterogeneous activity profiles during behavior. To resolve structure-function relationships, we juxtacellularly recorded and labeled single GCs in freely moving rats. We found that the vast majority of neurons were silent during exploration. Most active GCs displayed a characteristic spike waveform, fired at low rates and showed spatial activity. Primary dendritic parameters were sufficient for classifying neurons as active or silent with high accuracy. Our data thus support a sparse coding scheme in the dentate gyrus and provide a possible link between structural and functional heterogeneity among the GC population.
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Affiliation(s)
- Maria Diamantaki
- Werner-Reichardt Centre for Integrative Neuroscience, University of Tübingen, Tübingen, Germany.,Graduate Training Centre of Neuroscience - IMPRS, University of Tübingen, Tübingen, Germany
| | - Markus Frey
- Werner-Reichardt Centre for Integrative Neuroscience, University of Tübingen, Tübingen, Germany
| | - Philipp Berens
- Werner-Reichardt Centre for Integrative Neuroscience, University of Tübingen, Tübingen, Germany.,Institute for Ophthalmic Research, University of Tübingen, Tübingen, Germany.,Bernstein Centre for Computational Neuroscience, University of Tübingen, Tübingen, Germany
| | - Patricia Preston-Ferrer
- Werner-Reichardt Centre for Integrative Neuroscience, University of Tübingen, Tübingen, Germany
| | - Andrea Burgalossi
- Werner-Reichardt Centre for Integrative Neuroscience, University of Tübingen, Tübingen, Germany
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73
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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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74
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Abstract
The restriction of adult neurogenesis to only a handful of regions of the brain is suggestive of some shared requirement for this dramatic form of structural plasticity. However, a common driver across neurogenic regions has not yet been identified. Computational studies have been invaluable in providing insight into the functional role of new neurons; however, researchers have typically focused on specific scales ranging from abstract neural networks to specific neural systems, most commonly the dentate gyrus area of the hippocampus. These studies have yielded a number of diverse potential functions for new neurons, ranging from an impact on pattern separation to the incorporation of time into episodic memories to enabling the forgetting of old information. This review will summarize these past computational efforts and discuss whether these proposed theoretical functions can be unified into a common rationale for why neurogenesis is required in these unique neural circuits.
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Affiliation(s)
- James B Aimone
- Data Driven and Neural Computing Group, Center for Computing Research, Sandia National Laboratories, Albuquerque, New Mexico 87185-1327
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75
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van Dijk RM, Huang SH, Slomianka L, Amrein I. Taxonomic Separation of Hippocampal Networks: Principal Cell Populations and Adult Neurogenesis. Front Neuroanat 2016; 10:22. [PMID: 27013984 PMCID: PMC4783399 DOI: 10.3389/fnana.2016.00022] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2015] [Accepted: 02/23/2016] [Indexed: 11/13/2022] Open
Abstract
While many differences in hippocampal anatomy have been described between species, it is typically not clear if they are specific to a particular species and related to functional requirements or if they are shared by species of larger taxonomic units. Without such information, it is difficult to infer how anatomical differences may impact on hippocampal function, because multiple taxonomic levels need to be considered to associate behavioral and anatomical changes. To provide information on anatomical changes within and across taxonomic ranks, we present a quantitative assessment of hippocampal principal cell populations in 20 species or strain groups, with emphasis on rodents, the taxonomic group that provides most animals used in laboratory research. Of special interest is the importance of adult hippocampal neurogenesis (AHN) in species-specific adaptations relative to other cell populations. Correspondence analysis of cell numbers shows that across taxonomic units, phylogenetically related species cluster together, sharing similar proportions of principal cell populations. CA3 and hilus are strong separators that place rodent species into a tight cluster based on their relatively large CA3 and small hilus while non-rodent species (including humans and non-human primates) are placed on the opposite side of the spectrum. Hilus and CA3 are also separators within rodents, with a very large CA3 and rather small hilar cell populations separating mole-rats from other rodents that, in turn, are separated from each other by smaller changes in the proportions of CA1 and granule cells. When adult neurogenesis is included, the relatively small populations of young neurons, proliferating cells and hilar neurons become main drivers of taxonomic separation within rodents. The observations provide challenges to the computational modeling of hippocampal function, suggest differences in the organization of hippocampal information streams in rodent and non-rodent species, and support emerging concepts of functional and structural interactions between CA3 and the dentate gyrus.
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Affiliation(s)
- R Maarten van Dijk
- Functional Neuroanatomy, Institute of Anatomy, University of ZürichZurich, Switzerland; Neuroscience Center Zurich, University of Zurich and ETH ZurichZürich, Switzerland; Department of Health Sciences and Technology, Institute of Human Movement Sciences and Sport, ETH ZurichZürich, Switzerland
| | - Shih-Hui Huang
- Functional Neuroanatomy, Institute of Anatomy, University of ZürichZurich, Switzerland; Neuroscience Center Zurich, University of Zurich and ETH ZurichZürich, Switzerland; Department of Health Sciences and Technology, Institute of Human Movement Sciences and Sport, ETH ZurichZürich, Switzerland
| | - Lutz Slomianka
- Functional Neuroanatomy, Institute of Anatomy, University of Zürich Zurich, Switzerland
| | - Irmgard Amrein
- Functional Neuroanatomy, Institute of Anatomy, University of ZürichZurich, Switzerland; Neuroscience Center Zurich, University of Zurich and ETH ZurichZürich, Switzerland
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76
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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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77
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Priming Spatial Activity by Single-Cell Stimulation in the Dentate Gyrus of Freely Moving Rats. Curr Biol 2016; 26:536-41. [PMID: 26853363 DOI: 10.1016/j.cub.2015.12.053] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Revised: 12/07/2015] [Accepted: 12/21/2015] [Indexed: 11/21/2022]
Abstract
An essential requirement for hippocampal circuits to function in episodic memory is the ability to rapidly disambiguate and store incoming sensory information. This "pattern separation" function has been classically associated to the dentate gyrus, where spatial learning is accompanied by rapid and persistent modifications of place-cell representation. How these rapid modifications are implemented at the cellular level has remained largely unresolved. Here, we tested whether plasticity-inducing stimuli--spike trains--evoked in postsynaptic neurons are sufficient for the rapid induction of place-field activity in the dentate gyrus. We juxtacellularly stimulated 67 silent granule cells while rats explored a maze for the first time. Spike trains with different characteristics (e.g., number of spikes, frequency, and theta-rhythmicity) were evoked at randomly selected spatial locations. We found that, under novelty, ∼30% (10/33) of the stimulated neurons fired selectively at the "primed" spatial location on subsequent laps. Induced place fields were either transient or persisted for multiple laps. The "priming" effect was experience dependent, as it was less frequently observed in habituated animals (3/34 neurons), and it correlated with the number of spikes and theta-rhythmicity of the stimulus trains. These data indicate that, albeit with low efficiency, evoked theta-rhythmic spike trains can be sufficient for priming spatial activity in the dentate gyrus and thus recruiting silent granule cells into the coding population.
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78
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Zylberberg J, Hyde RA, Strowbridge BW. Dynamics of robust pattern separability in the hippocampal dentate gyrus. Hippocampus 2015; 26:623-32. [PMID: 26482936 DOI: 10.1002/hipo.22546] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2015] [Revised: 10/05/2015] [Accepted: 10/09/2015] [Indexed: 11/05/2022]
Abstract
The dentate gyrus (DG) is thought to perform pattern separation on inputs received from the entorhinal cortex, such that the DG forms distinct representations of different input patterns. Neuronal responses, however, are known to be variable, and that variability has the potential to confuse the representations of different inputs, thereby hindering the pattern separation function. This variability can be especially problematic for tissues such as the DG, in which the responses can persist for tens of seconds following stimulation: the long response duration allows for variability from many different sources to accumulate. To understand how the DG can robustly encode different input patterns, we investigated a recently developed in vitro hippocampal DG preparation that generates persistent responses to transient electrical stimulation. For 10-20 s after stimulation, the responses are indicative of the pattern of stimulation that was applied, even though the responses exhibit significant trial-to-trial variability. Analyzing the dynamical trajectories of the evoked responses, we found that, following stimulation, the neural responses follow distinct paths through the space of possible neural activations, with a different path associated with each stimulation pattern. The neural responses' trial-to-trial variability shifts the responses along these paths rather than between them, maintaining the separability of the input patterns. Manipulations that redistributed the variability more isotropically over the space of possible neural activations impeded the pattern separation function. Consequently, we conclude that the confinement of neuronal variability to these one-dimensional paths mitigates the impacts of variability on pattern encoding and, thus, may be an important aspect of the DG's ability to robustly encode input patterns.
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Affiliation(s)
- Joel Zylberberg
- Department of Applied Mathematics, University of Washington, Seattle, Washington.,Department of Physiology and Biophysics, University of Colorado School of Medicine, Aurora, Colorado
| | - Robert A Hyde
- Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio
| | - Ben W Strowbridge
- Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio
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79
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Knierim JJ, Neunuebel JP. Tracking the flow of hippocampal computation: Pattern separation, pattern completion, and attractor dynamics. Neurobiol Learn Mem 2015; 129:38-49. [PMID: 26514299 DOI: 10.1016/j.nlm.2015.10.008] [Citation(s) in RCA: 160] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2015] [Revised: 10/04/2015] [Accepted: 10/21/2015] [Indexed: 10/22/2022]
Abstract
Classic computational theories of the mnemonic functions of the hippocampus ascribe the processes of pattern separation to the dentate gyrus (DG) and pattern completion to the CA3 region. Until the last decade, the large majority of single-unit studies of the hippocampus in behaving animals were from the CA1 region. The lack of data from the DG, CA3, and the entorhinal inputs to the hippocampus severely hampered the ability to test these theories with neurophysiological techniques. The past ten years have seen a major increase in the recordings from the CA3 region and the medial entorhinal cortex (MEC), with an increasing (but still limited) number of experiments from the lateral entorhinal cortex (LEC) and DG. This paper reviews a series of studies in a local-global cue mismatch (double-rotation) experiment in which recordings were made from cells in the anterior thalamus, MEC, LEC, DG, CA3, and CA1 regions. Compared to the standard cue environment, the change in the DG representation of the cue-mismatch environment was greater than the changes in its entorhinal inputs, providing support for the theory of pattern separation in the DG. In contrast, the change in the CA3 representation of the cue-mismatch environment was less than the changes in its entorhinal and DG inputs, providing support for a pattern completion/error correction function of CA3. The results are interpreted in terms of continuous attractor network models of the hippocampus and the relationship of these models to pattern separation and pattern completion theories. Whereas DG may perform an automatic pattern separation function, the attractor dynamics of CA3 allow it to perform a pattern separation or pattern completion function, depending on the nature of its inputs and the relative strength of the internal attractor dynamics.
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Affiliation(s)
- James J Knierim
- Krieger Mind/Brain Institute and Solomon H. Snyder Department of Neuroscience, Johns Hopkins University, United States.
| | - Joshua P Neunuebel
- Dept. of Psychological and Brain Sciences, University of Delaware, United States
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80
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Finnegan R, Becker S. Neurogenesis paradoxically decreases both pattern separation and memory interference. Front Syst Neurosci 2015; 9:136. [PMID: 26500511 PMCID: PMC4593858 DOI: 10.3389/fnsys.2015.00136] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2015] [Accepted: 09/18/2015] [Indexed: 01/01/2023] Open
Abstract
The hippocampus has been the focus of memory research for decades. While the functional role of this structure is not fully understood, it is widely recognized as being vital for rapid yet accurate encoding and retrieval of associative memories. Since the discovery of adult hippocampal neurogenesis in the dentate gyrus by Altman and Das in the 1960's, many theories and models have been put forward to explain the functional role it plays in learning and memory. These models postulate different ways in which new neurons are introduced into the dentate gyrus and their functional importance for learning and memory. Few if any previous models have incorporated the unique properties of young adult-born dentate granule cells and the developmental trajectory. In this paper, we propose a novel computational model of the dentate gyrus that incorporates the developmental trajectory of the adult-born dentate granule cells, including changes in synaptic plasticity, connectivity, excitability and lateral inhibition, using a modified version of the Restricted Boltzmann machine. Our results show superior performance on memory reconstruction tasks for both recent and distally learned items, when the unique characteristics of young dentate granule cells are taken into account. Even though the hyperexcitability of the young neurons generates more overlapping neural codes, reducing pattern separation, the unique properties of the young neurons nonetheless contribute to reducing retroactive and proactive interference, at both short and long time scales. The sparse connectivity is particularly important for generating distinct memory traces for highly overlapping patterns that are learned within the same context.
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Affiliation(s)
- Rory Finnegan
- Neurotechnology and Neuroplasticity Lab, McMaster Integrative Neuroscience Discovery & Study, McMaster University Hamilton, ON, Canada
| | - Suzanna Becker
- Neurotechnology and Neuroplasticity Lab, Department of Psychology, Neuroscience and Behaviour, McMaster University Hamilton, ON, Canada
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81
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Blackstad JS, Osen KK, Scharfman HE, Storm-Mathisen J, Blackstad TW, Leergaard TB. Observations on hippocampal mossy cells in mink (Neovison vison) with special reference to dendrites ascending to the granular and molecular layers. Hippocampus 2015; 26:229-45. [PMID: 26286893 DOI: 10.1002/hipo.22518] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Revised: 08/10/2015] [Accepted: 08/11/2015] [Indexed: 12/25/2022]
Abstract
Detailed knowledge about the neural circuitry connecting the hippocampus and entorhinal cortex is necessary to understand how this system contributes to spatial navigation and episodic memory. The two principal cell types of the dentate gyrus, mossy cells and granule cells, are interconnected in a positive feedback loop, by which mossy cells can influence information passing from the entorhinal cortex via granule cells to hippocampal pyramidal cells. Mossy cells, like CA3 pyramidal cells, are characterized by thorny excrescences on their proximal dendrites, postsynaptic to giant terminals of granule cell axons. In addition to disynaptic input from the entorhinal cortex and perforant path via granule cells, mossy cells may also receive monosynaptic input from the perforant path via special dendrites ascending to the molecular layer. We here report qualitative and quantitative descriptions of Golgi-stained hippocampal mossy cells in mink, based on light microscopic observations and three-dimensional reconstructions. The main focus is on the location, branching pattern, and length of dendrites, particularly those ascending to the granular and molecular layers. In mink, the latter dendrites are more numerous than in rat, but fewer than in primates. They form on average 12% (and up to 29%) of the total dendritic length, and appear to cover the terminal fields of both the lateral and medial perforant paths. In further contrast to rat, the main mossy cell dendrites in mink branch more extensively with distal dendrites encroaching upon the CA3 field. The dendritic arbors extend both along and across the septotemporal axis of the dentate gyrus, not conforming to the lamellar pattern of the hippocampus. The findings suggest that the afferent input to the mossy cells becomes more complex in species closer to primates.
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Affiliation(s)
- Jan Sigurd Blackstad
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
| | - Kirsten K Osen
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
| | - Helen E Scharfman
- Center for Dementia Research, The Nathan Kline Institute for Psychiatric Research, Orangeburg New York and Departments of Psychiatry, Physiology & Neuroscience, New York University Langone Medical Center, New York, New York
| | - Jon Storm-Mathisen
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
| | - Theodor W Blackstad
- Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
| | - Trygve B Leergaard
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
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82
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McAvoy K, Besnard A, Sahay A. Adult hippocampal neurogenesis and pattern separation in DG: a role for feedback inhibition in modulating sparseness to govern population-based coding. Front Syst Neurosci 2015; 9:120. [PMID: 26347621 PMCID: PMC4542503 DOI: 10.3389/fnsys.2015.00120] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2015] [Accepted: 08/07/2015] [Indexed: 12/17/2022] Open
Abstract
The dentate gyrus (DG) of mammals harbors neural stem cells that generate new dentate granule cells (DGCs) throughout life. Behavioral studies using the contextual fear discrimination paradigm have found that selectively augmenting or blocking adult hippocampal neurogenesis enhances or impairs discrimination under conditions of high, but not low, interference suggestive of a role in pattern separation. Although contextual discrimination engages population-based coding mechanisms underlying pattern separation such as global remapping in the DG and CA3, how adult hippocampal neurogenesis modulates pattern separation in the DG is poorly understood. Here, we propose a role for adult-born DGCs in re-activation coupled modulation of sparseness through feed-back inhibition to govern global remapping in the DG.
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Affiliation(s)
- Kathleen McAvoy
- Center for Regenerative Medicine, Massachusetts General Hospital, Harvard Medical School Boston, MA, USA
| | - Antoine Besnard
- Center for Regenerative Medicine, Massachusetts General Hospital, Harvard Medical School Boston, MA, USA
| | - Amar Sahay
- Center for Regenerative Medicine, Massachusetts General Hospital, Harvard Medical School Boston, MA, USA ; Harvard Stem Cell Institute, Harvard University Cambridge, MA, USA ; Department of Psychiatry, Massachusetts General Hospital, Harvard Medical School Boston, MA, USA
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83
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Kassab R, Alexandre F. Integration of exteroceptive and interoceptive information within the hippocampus: a computational study. Front Syst Neurosci 2015; 9:87. [PMID: 26097448 PMCID: PMC4456570 DOI: 10.3389/fnsys.2015.00087] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2015] [Accepted: 05/22/2015] [Indexed: 12/25/2022] Open
Abstract
Many episodic memory studies have critically implicated the hippocampus in the rapid binding of sensory information from the perception of the external environment, reported by exteroception. Other structures in the medial temporal lobe, especially the amygdala, have been more specifically linked with emotional dimension of episodic memories, reported by interoception. The hippocampal projection to the amygdala is proposed as a substrate important for the formation of extero-interoceptive associations, allowing adaptive behaviors based on past experiences. Recently growing evidence suggests that hippocampal activity observed in a wide range of behavioral tasks could reflect associations between exteroceptive patterns and their emotional valences. The hippocampal computational models, therefore, need to be updated to elaborate better interpretation of hippocampal-dependent behaviors. In earlier models, interoceptive features, if not neglected, are bound together with other exteroceptive features through autoassociative learning mechanisms. This way of binding integrates both kinds of features at the same level, which is not always suitable for example in the case of pattern completion. Based on the anatomical and functional heterogeneity along the septotemporal and transverse axes of the hippocampus, we suggest instead that distinct hippocampal subregions may be engaged in the representation of these different types of information, each stored apart in autoassociative memories but linked together in a heteroassociative way. The model is developed within the hard constraint of rapid, even single trial, learning of episodic memories. The performance of the model is assessed quantitatively and its resistance to interference is demonstrated through a series of numerical experiments. An experiment of reversal learning in patients with amnesic cognitive impairment is also reproduced.
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Affiliation(s)
- Randa Kassab
- INRIA Bordeaux Sud-Ouest Talence, France ; LaBRI, UMR 5800, Centre National de la Recherche Scientifique, Bordeaux INP, Université de Bordeaux Talence, France ; Institut des Maladies Neurodégénératives, UMR 5293, Centre National de la Recherche Scientifique, Université de Bordeaux Bordeaux, France
| | - Frédéric Alexandre
- INRIA Bordeaux Sud-Ouest Talence, France ; LaBRI, UMR 5800, Centre National de la Recherche Scientifique, Bordeaux INP, Université de Bordeaux Talence, France ; Institut des Maladies Neurodégénératives, UMR 5293, Centre National de la Recherche Scientifique, Université de Bordeaux Bordeaux, France
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84
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Faghihi F, Moustafa AA. A computational model of pattern separation efficiency in the dentate gyrus with implications in schizophrenia. Front Syst Neurosci 2015; 9:42. [PMID: 25859189 PMCID: PMC4373261 DOI: 10.3389/fnsys.2015.00042] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2014] [Accepted: 03/05/2015] [Indexed: 11/13/2022] Open
Abstract
Information processing in the hippocampus begins by transferring spiking activity of the entorhinal cortex (EC) into the dentate gyrus (DG). Activity pattern in the EC is separated by the DG such that it plays an important role in hippocampal functions including memory. The structural and physiological parameters of these neural networks enable the hippocampus to be efficient in encoding a large number of inputs that animals receive and process in their life time. The neural encoding capacity of the DG depends on its single neurons encoding and pattern separation efficiency. In this study, encoding by the DG is modeled such that single neurons and pattern separation efficiency are measured using simulations of different parameter values. For this purpose, a probabilistic model of single neurons efficiency is presented to study the role of structural and physiological parameters. Known neurons number of the EC and the DG is used to construct a neural network by electrophysiological features of granule cells of the DG. Separated inputs as activated neurons in the EC with different firing probabilities are presented into the DG. For different connectivity rates between the EC and DG, pattern separation efficiency of the DG is measured. The results show that in the absence of feedback inhibition on the DG neurons, the DG demonstrates low separation efficiency and high firing frequency. Feedback inhibition can increase separation efficiency while resulting in very low single neuron's encoding efficiency in the DG and very low firing frequency of neurons in the DG (sparse spiking). This work presents a mechanistic explanation for experimental observations in the hippocampus, in combination with theoretical measures. Moreover, the model predicts a critical role for impaired inhibitory neurons in schizophrenia where deficiency in pattern separation of the DG has been observed.
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Affiliation(s)
- Faramarz Faghihi
- Center for Neural Informatics, Structures, and Plasticity, Krasnow Institute for Advanced Study, George Mason University Fairfax, VA, USA
| | - Ahmed A Moustafa
- Department of Veterans Affairs, VA New Jersey Health Care System East Orange, NJ, USA ; School of Social Sciences and Psychology and Marcs Institute for Brain and Behaviour, University of Western Sydney Sydney NSW, Australia
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85
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Petrantonakis PC, Poirazi P. Dentate Gyrus circuitry features improve performance of sparse approximation algorithms. PLoS One 2015; 10:e0117023. [PMID: 25635776 PMCID: PMC4312091 DOI: 10.1371/journal.pone.0117023] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2014] [Accepted: 12/17/2014] [Indexed: 12/30/2022] Open
Abstract
Memory-related activity in the Dentate Gyrus (DG) is characterized by sparsity. Memory representations are seen as activated neuronal populations of granule cells, the main encoding cells in DG, which are estimated to engage 2–4% of the total population. This sparsity is assumed to enhance the ability of DG to perform pattern separation, one of the most valuable contributions of DG during memory formation. In this work, we investigate how features of the DG such as its excitatory and inhibitory connectivity diagram can be used to develop theoretical algorithms performing Sparse Approximation, a widely used strategy in the Signal Processing field. Sparse approximation stands for the algorithmic identification of few components from a dictionary that approximate a certain signal. The ability of DG to achieve pattern separation by sparsifing its representations is exploited here to improve the performance of the state of the art sparse approximation algorithm “Iterative Soft Thresholding” (IST) by adding new algorithmic features inspired by the DG circuitry. Lateral inhibition of granule cells, either direct or indirect, via mossy cells, is shown to enhance the performance of the IST. Apart from revealing the potential of DG-inspired theoretical algorithms, this work presents new insights regarding the function of particular cell types in the pattern separation task of the DG.
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Affiliation(s)
- Panagiotis C Petrantonakis
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas, Heraklion, Greece
| | - Panayiota Poirazi
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas, Heraklion, Greece
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86
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A computational theory of hippocampal function, and tests of the theory: New developments. Neurosci Biobehav Rev 2015; 48:92-147. [DOI: 10.1016/j.neubiorev.2014.11.009] [Citation(s) in RCA: 226] [Impact Index Per Article: 25.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2014] [Revised: 10/24/2014] [Accepted: 11/12/2014] [Indexed: 01/01/2023]
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87
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Yim MY, Hanuschkin A, Wolfart J. Intrinsic rescaling of granule cells restores pattern separation ability of a dentate gyrus network model during epileptic hyperexcitability. Hippocampus 2014; 25:297-308. [DOI: 10.1002/hipo.22373] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2014] [Revised: 09/29/2014] [Accepted: 09/29/2014] [Indexed: 01/12/2023]
Affiliation(s)
- Man Yi Yim
- Department of Mathematics; University of Hong Kong; Hong Kong
| | - Alexander Hanuschkin
- Institute of Neuroinformatics, University of Zurich and ETH Zurich; Zurich Switzerland
| | - Jakob Wolfart
- Oscar Langendorff Institute of Physiology, University of Rostock; Rostock Germany
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88
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Dasgupta D, Sikdar SK. Calcium permeable AMPA receptor-dependent long lasting plasticity of intrinsic excitability in fast spiking interneurons of the dentate gyrus decreases inhibition in the granule cell layer. Hippocampus 2014; 25:269-85. [DOI: 10.1002/hipo.22371] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/19/2014] [Indexed: 02/01/2023]
Affiliation(s)
- Debanjan Dasgupta
- Molecular Biophysics Unit; Indian Institute of Science; Bangalore Karnataka India 560012
| | - Sujit Kumar Sikdar
- Molecular Biophysics Unit; Indian Institute of Science; Bangalore Karnataka India 560012
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89
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Petrantonakis PC, Poirazi P. A compressed sensing perspective of hippocampal function. Front Syst Neurosci 2014; 8:141. [PMID: 25152718 PMCID: PMC4126371 DOI: 10.3389/fnsys.2014.00141] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2014] [Accepted: 07/22/2014] [Indexed: 01/05/2023] Open
Abstract
Hippocampus is one of the most important information processing units in the brain. Input from the cortex passes through convergent axon pathways to the downstream hippocampal subregions and, after being appropriately processed, is fanned out back to the cortex. Here, we review evidence of the hypothesis that information flow and processing in the hippocampus complies with the principles of Compressed Sensing (CS). The CS theory comprises a mathematical framework that describes how and under which conditions, restricted sampling of information (data set) can lead to condensed, yet concise, forms of the initial, subsampled information entity (i.e., of the original data set). In this work, hippocampus related regions and their respective circuitry are presented as a CS-based system whose different components collaborate to realize efficient memory encoding and decoding processes. This proposition introduces a unifying mathematical framework for hippocampal function and opens new avenues for exploring coding and decoding strategies in the brain.
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Affiliation(s)
| | - Panayiota Poirazi
- Computational Biology Lab, Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-HellasHeraklion, Greece
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90
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Etter G, Krezel W. Dopamine D2 receptor controls hilar mossy cells excitability. Hippocampus 2014; 24:725-32. [PMID: 24753432 DOI: 10.1002/hipo.22280] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/01/2014] [Indexed: 12/12/2022]
Abstract
Hippocampal control of memory formation is regulated by dopaminergic signaling. Whereas the role of dopamine D1 receptors is well documented in such regulations, functions of dopamine D2 receptors (DRD2) are not fully understood. Using fluorescence in situ hybridization we demonstrate that Drd2 expression in the hippocampus of wild-type mice is limited to glutamatergic hilar mossy cells. Using whole cell electrophysiological recordings in hippocampal slice preparations, we provide evidence that unlike in basal ganglia, activation of DRD2 by the selective agonist, quinpirole, induces a long-lasting increase in excitability of hilar mossy cells, which can be blocked by the DRD2 antagonist raclopride. Such activity is mediated by the Akt/GSK pathway, as application of specific inhibitors such as A1070722 or SB216763 prevented quinpirole activity. Long-term effects of acute DRD2 activation in vitro suggest that volume transmission of dopamine may modulate mossy cell activities in vivo. This is supported by the presence of dense tyrosine hydroxylase positive varicosities in the hilus, which are rarely seen in the vicinity of mossy cell dendrites. From these data we discuss how dopamine could control mossy cell activity and thus dentate gyrus functions.
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Affiliation(s)
- Guillaume Etter
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, UMR 7104 CNRS, U 964 INSERM, Université de Strasbourg, B.P. 10142, 67404 Illkirch, Cedex, France
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91
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Spiegel AM, Koh MT, Vogt NM, Rapp PR, Gallagher M. Hilar interneuron vulnerability distinguishes aged rats with memory impairment. J Comp Neurol 2014; 521:3508-23. [PMID: 23749483 DOI: 10.1002/cne.23367] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Revised: 04/30/2013] [Accepted: 05/23/2013] [Indexed: 01/24/2023]
Abstract
Hippocampal interneuron populations are reportedly vulnerable to normal aging. The relationship between interneuron network integrity and age-related memory impairment, however, has not been tested directly. That question was addressed in the present study using a well-characterized model in which outbred, aged, male Long-Evans rats exhibit a spectrum of individual differences in hippocampal-dependent memory. Selected interneuron populations in the hippocampus were visualized for stereological quantification with a panel of immunocytochemical markers, including glutamic acid decarboxylase-67 (GAD67), somatostatin, and neuropeptide Y. The overall pattern of results was that, although the numbers of GAD67- and somatostatin-positive interneurons declined with age across multiple fields of the hippocampus, alterations specifically related to the cognitive outcome of aging were observed exclusively in the hilus of the dentate gyrus. Because the total number of NeuN-immunoreactive hilar neurons was unaffected, the decline observed with other markers likely reflects a loss of target protein rather than neuron death. In support of that interpretation, treatment with the atypical antiepileptic levetiracetam at a low dose shown previously to improve behavioral performance fully restored hilar SOM expression in aged, memory-impaired rats. Age-related decreases in GAD67- and somatostatin-immunoreactive neuron number beyond the hilus were regionally selective and spared the CA1 field of the hippocampus entirely. Together these findings confirm the vulnerability of hippocampal interneurons to normal aging and highlight that the integrity of a specific subpopulation in the hilus is coupled with age-related memory impairment.
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Affiliation(s)
- Amy M Spiegel
- Department of Psychological and Brain Sciences, Johns Hopkins University, Baltimore, Maryland, 21218
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92
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Álvarez-Salvado E, Pallarés V, Moreno A, Canals S. Functional MRI of long-term potentiation: imaging network plasticity. Philos Trans R Soc Lond B Biol Sci 2014; 369:20130152. [PMID: 24298154 PMCID: PMC3843884 DOI: 10.1098/rstb.2013.0152] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Neurons are able to express long-lasting and activity-dependent modulations of their synapses. This plastic property supports memory and conveys an extraordinary adaptive value, because it allows an individual to learn from, and respond to, changes in the environment. Molecular and physiological changes at the cellular level as well as network interactions are required in order to encode a pattern of synaptic activity into a long-term memory. While the cellular mechanisms linking synaptic plasticity to memory have been intensively studied, those regulating network interactions have received less attention. Combining high-resolution fMRI and in vivo electrophysiology in rats, we have previously reported a functional remodelling of long-range hippocampal networks induced by long-term potentiation (LTP) of synaptic plasticity in the perforant pathway. Here, we present new results demonstrating an increased bilateral coupling in the hippocampus specifically supported by the mossy cell commissural/associational pathway in response to LTP. This fMRI-measured increase in bilateral connectivity is accompanied by potentiation of the corresponding polysynaptically evoked commissural potential in the contralateral dentate gyrus and depression of the inactive convergent commissural pathway to the ipsilateral dentate. We review these and previous findings in the broader context of memory consolidation.
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Affiliation(s)
| | | | | | - Santiago Canals
- Instituto de Neurociencias, Consejo Superior de Investigaciones Científicas, Universidad Miguel Hernández, Sant Joan d'Alacant 03550, Spain
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93
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The influence of ectopic migration of granule cells into the hilus on dentate gyrus-CA3 function. PLoS One 2013; 8:e68208. [PMID: 23840835 PMCID: PMC3695928 DOI: 10.1371/journal.pone.0068208] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2013] [Accepted: 05/27/2013] [Indexed: 11/29/2022] Open
Abstract
Postnatal neurogenesis of granule cells (GCs) in the dentate gyrus (DG) produces GCs that normally migrate from the subgranular zone to the GC layer. However, GCs can mismigrate into the hilus, the opposite direction. Previous descriptions of these hilar ectopic GCs (hEGCs) suggest that they are rare unless there are severe seizures. However, it is not clear if severe seizures are required, and it also is unclear if severe seizures are responsible for the abnormalities of hEGCs, which include atypical dendrites and electrophysiological properties. Here we show that large numbers of hEGCs develop in a transgenic mouse without severe seizures. The mice have a deletion of BAX, which normally regulates apoptosis. Surprisingly, we show that hEGCs in the BAX-/- mouse have similar abnormalities as hEGCs that arise after severe seizures. We next asked if there are selective effects of hEGCs, i.e., whether a robust population of hEGCs would have any effect on the DG if they were induced without severe seizures. Indeed, this appears to be true, because it has been reported that BAX-/- mice have defects in a behavior that tests pattern separation, which depends on the DG. However, inferring functional effects of hEGCs is difficult in mice with a constitutive BAX deletion because there is decreased apoptosis in and outside the DG. Therefore, a computational model of the normal DG and hippocampal subfield CA3 was used. Adding a small population of hEGCs (5% of all GCs), with characteristics defined empirically, was sufficient to disrupt a simulation of pattern separation and completion. Modeling results also showed that effects of hEGCs were due primarily to “backprojections” of CA3 pyramidal cell axons to the hilus. The results suggest that hEGCs can develop for diverse reasons, do not depend on severe seizures, and a small population of hEGCs may impair DG-dependent function.
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94
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Holden HM, Toner C, Pirogovsky E, Kirwan CB, Gilbert PE. Visual object pattern separation varies in older adults. Learn Mem 2013; 20:358-62. [PMID: 23774765 PMCID: PMC3687255 DOI: 10.1101/lm.030171.112] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Young and nondemented older adults completed a visual object continuous recognition memory task in which some stimuli (lures) were similar but not identical to previously presented objects. The lures were hypothesized to result in increased interference and increased pattern separation demand. To examine variability in object pattern separation deficits, older adults were divided into impaired and unimpaired groups based on performance on a standardized serial list-learning task. Impaired older adults showed intact recognition memory, but were impaired relative to young and unimpaired older adults when identifying similar lure stimuli, demonstrating that object pattern separation varies in older adults.
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Affiliation(s)
- Heather M Holden
- San Diego State University-University of California San Diego Joint Doctoral Program in Clinical Psychology, San Diego, California 92120, USA
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95
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Kesner RP. A process analysis of the CA3 subregion of the hippocampus. Front Cell Neurosci 2013; 7:78. [PMID: 23750126 PMCID: PMC3664330 DOI: 10.3389/fncel.2013.00078] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Accepted: 05/08/2013] [Indexed: 12/30/2022] Open
Abstract
From a behavioral perspective, the CA3a,b subregion of the hippocampus plays an important role in the encoding of new spatial information within short-term memory with a duration of seconds and minutes. This can easily be observed in tasks that require rapid encoding, novelty detection, one-trial short-term or working memory, and one-trial cued recall primarily for spatial information. These are tasks that have been assumed to reflect the operations of episodic memory and require interactions between CA3a,b and the dentate gyrus (DG) via mossy fiber inputs into the CA3a,b. The CA3a,b is also important for encoding of spatial information requiring the acquisition of arbitrary and relational associations. All these tasks are assumed to operate within an autoassociative network function of the CA3 region. The CA3a,b also supports retrieval of short-term memory information based on a spatial pattern completion process. Based on afferent inputs into CA3a,b from the DG via mossy fibers and afferents from the entorhinal cortex into CA3a,b as well as reciprocal connections with the septum, CA3a,b can bias the process of encoding utilizing the operation of spatial pattern separation and the process of retrieval utilizing the operation of pattern completion. The CA3a,b also supports sequential processing of information in cooperation with CA1 based on the Schaffer collateral output from CA3a,b to CA1. The CA3c function is in part based on modulation of the DG in supporting pattern separation processes.
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Affiliation(s)
- Raymond P Kesner
- Department of Psychology, University of Utah Salt Lake City, UT, USA
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96
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Piatti VC, Ewell LA, Leutgeb JK. Neurogenesis in the dentate gyrus: carrying the message or dictating the tone. Front Neurosci 2013; 7:50. [PMID: 23576950 PMCID: PMC3616253 DOI: 10.3389/fnins.2013.00050] [Citation(s) in RCA: 100] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Accepted: 03/15/2013] [Indexed: 12/12/2022] Open
Abstract
The dentate gyrus (DG) is a region in the mammalian brain critical for memory encoding with a neuronal architecture and function that deviates considerably from other cortical areas. One of the major differences of the DG compared to other brain regions is the finding that the dentate gyrus generates new principal neurons that are continuously integrated into a fully functional neural circuit throughout life. Another distinguishing characteristic of the dentate network is that the majority of principal neurons are held under strong inhibition and rarely fire action potentials. These two findings raise the question why a predominantly silent network would need to continually incorporate more functional units. The sparse nature of the neural code in the DG is thought to be fundamental to dentate network function, yet the relationship between neurogenesis and low activity levels in the network remains largely unknown. Clues to the functional role of new neurons come from inquiries at the cellular as well as the behavioral level. Few studies have bridged the gap between these levels of inquiry by considering the role of young neurons within the complex dentate network during distinct stages of memory processing. We will review and discuss from a network perspective, the functional role of immature neurons and how their unique cellular properties can modulate the dentate network in memory guided behaviors.
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Affiliation(s)
- Verónica C Piatti
- Neurobiology Section, Division of Biological Sciences, Center for Neural Circuits and Behavior, University of California San Diego, La Jolla, CA, USA
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97
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Jinde S, Zsiros V, Jiang Z, Nakao K, Pickel J, Kohno K, Belforte JE, Nakazawa K. Hilar mossy cell degeneration causes transient dentate granule cell hyperexcitability and impaired pattern separation. Neuron 2013; 76:1189-200. [PMID: 23259953 DOI: 10.1016/j.neuron.2012.10.036] [Citation(s) in RCA: 138] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/15/2012] [Indexed: 02/08/2023]
Abstract
Although excitatory mossy cells of the hippocampal hilar region are known to project both to dentate granule cells and to interneurons, it is as yet unclear whether mossy cell activity's net effect on granule cells is excitatory or inhibitory. To explore their influence on dentate excitability and hippocampal function, we generated a conditional transgenic mouse line, using the Cre/loxP system, in which diphtheria toxin receptor was selectively expressed in mossy cells. One week after injecting toxin into this line, mossy cells throughout the longitudinal axis were degenerated extensively, theta wave power of dentate local field potentials increased during exploration, and deficits occurred in contextual discrimination. By contrast, we detected no epileptiform activity, spontaneous behavioral seizures, or mossy-fiber sprouting 5-6 weeks after mossy cell degeneration. These results indicate that the net effect of mossy cell excitation is to inhibit granule cell activity and enable dentate pattern separation.
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Affiliation(s)
- Seiichiro Jinde
- Unit on Genetics of Cognition and Behavior, National Institute of Mental Health, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892, USA
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Vivar C, van Praag H. Functional circuits of new neurons in the dentate gyrus. Front Neural Circuits 2013; 7:15. [PMID: 23443839 PMCID: PMC3580993 DOI: 10.3389/fncir.2013.00015] [Citation(s) in RCA: 97] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2012] [Accepted: 01/23/2013] [Indexed: 01/17/2023] Open
Abstract
The hippocampus is crucial for memory formation. New neurons are added throughout life to the hippocampal dentate gyrus (DG), a brain area considered important for differential storage of similar experiences and contexts. To better understand the functional contribution of adult neurogenesis to pattern separation processes, we recently used a novel synapse specific trans-neuronal tracing approach to identify the (sub) cortical inputs to new dentate granule cells (GCs). It was observed that newly born neurons receive sequential innervation from structures important for memory function. Initially, septal-hippocampal cells provide input to new neurons, including transient innervation from mature GCs as well as direct feedback from area CA3 pyramidal neurons. After about 1 month perirhinal (PRH) and lateral entorhinal cortex (LEC), brain areas deemed relevant to integration of novel sensory and environmental information, become substantial input to new GCs. Here, we review the developmental time-course and proposed functional relevance of new neurons, within the context of their unique neural 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, USA
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99
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Jinde S, Zsiros V, Nakazawa K. Hilar mossy cell circuitry controlling dentate granule cell excitability. Front Neural Circuits 2013; 7:14. [PMID: 23407806 PMCID: PMC3569840 DOI: 10.3389/fncir.2013.00014] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2012] [Accepted: 01/23/2013] [Indexed: 12/27/2022] Open
Abstract
Glutamatergic hilar mossy cells of the dentate gyrus can either excite or inhibit distant granule cells, depending on whether their direct excitatory projections to granule cells or their projections to local inhibitory interneurons dominate. However, it remains controversial whether the net effect of mossy cell loss is granule cell excitation or inhibition. Clarifying this controversy has particular relevance to temporal lobe epilepsy, which is marked by dentate granule cell hyperexcitability and extensive loss of dentate hilar mossy cells. Two diametrically opposed hypotheses have been advanced to explain this granule cell hyperexcitability—the “dormant basket cell” and the “irritable mossy cell” hypotheses. The “dormant basket cell” hypothesis proposes that mossy cells normally exert a net inhibitory effect on granule cells and therefore their loss causes dentate granule cell hyperexcitability. The “irritable mossy cell” hypothesis takes the opposite view that mossy cells normally excite granule cells and that the surviving mossy cells in epilepsy increase their activity, causing granule cell excitation. The inability to eliminate mossy cells selectively has made it difficult to test these two opposing hypotheses. To this end, we developed a transgenic toxin-mediated, mossy cell-ablation mouse line. Using these mutants, we demonstrated that the extensive elimination of hilar mossy cells causes granule cell hyperexcitability, although the mossy cell loss observed appeared insufficient to cause clinical epilepsy. In this review, we focus on this topic and also suggest that different interneuron populations may mediate mossy cell-induced translamellar lateral inhibition and intralamellar recurrent inhibition. These unique local circuits in the dentate hilar region may be centrally involved in the functional organization of the dentate gyrus.
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Affiliation(s)
- Seiichiro Jinde
- Department of Neuropsychiatry, Graduate School of Medicine, The University of Tokyo Tokyo, Japan
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100
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Scharfman HE, Myers CE. Hilar mossy cells of the dentate gyrus: a historical perspective. Front Neural Circuits 2013; 6:106. [PMID: 23420672 PMCID: PMC3572871 DOI: 10.3389/fncir.2012.00106] [Citation(s) in RCA: 113] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2012] [Accepted: 12/02/2012] [Indexed: 11/24/2022] Open
Abstract
The circuitry of the dentate gyrus (DG) of the hippocampus is unique compared to other hippocampal subfields because there are two glutamatergic principal cells instead of one: granule cells, which are the vast majority of the cells in the DG, and the so-called “mossy cells.” The distinctive appearance of mossy cells, the extensive divergence of their axons, and their vulnerability to excitotoxicity relative to granule cells has led to a great deal of interest in mossy cells. Nevertheless, there is no consensus about the normal functions of mossy cells and the implications of their vulnerability. There even seems to be some ambiguity about exactly what mossy cells are. Here we review initial studies of mossy cells, characteristics that define them, and suggest a practical definition to allow investigators to distinguish mossy cells from other hilar neurons even if all morphological and physiological information is unavailable due to technical limitations of their experiments. In addition, hypotheses are discussed about the role of mossy cells in the DG network, reasons for their vulnerability and their implications for disease.
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Affiliation(s)
- Helen E Scharfman
- New York University Langone Medical Center New York, NY, USA ; Center for Dementia Research, The Nathan Kline Institute for Psychiatric Research Orangeburg, NY, USA
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