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Romero-Barragán MT, Gruart A, Delgado-García JM. Transsynaptic Long-Term Potentiation in the Hippocampus of Behaving Mice. Front Synaptic Neurosci 2022; 13:811806. [PMID: 35126083 PMCID: PMC8810508 DOI: 10.3389/fnsyn.2021.811806] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Accepted: 12/31/2021] [Indexed: 11/17/2022] Open
Abstract
Long-term potentiation (LTP) is an experimental procedure that shares certain mechanisms with neuronal learning and memory processes and represents a well-known example of synaptic plasticity. LTP consists of an increase of the synaptic response to a control stimulus following the presentation of a high-frequency stimulation (HFS) train to an afferent pathway. This technique is studied mostly in the hippocampus due to the latter’s high susceptibility and its laminar nature which facilitates the location of defined synapses. Although most preceding studies have been performed in vitro, we have developed an experimental approach to carry out these experiments in alert behaving animals. The main goal of this study was to confirm the existence of synaptic changes in strength in synapses that are post-synaptic to the one presented with the HFS. We recorded field excitatory post-synaptic potentials (fEPSPs) evoked in five hippocampal synapses, from both hemispheres, of adult male mice. HFS was presented to the perforant pathway (PP). We characterized input/output curves, paired-pulse stimulation, and LTP of these synapses. We also performed depth-profile recordings to determine differences in fEPSP latencies. Collected data indicate that the five selected synapses have similar basic electrophysiological properties, a fact that enables an easier comparison of LTP characteristics. Importantly, we observed the presence of significant LTP in the contralateral CA1 (cCA1) area following the control stimulation of non-HFS-activated pathways. These results indicate that LTP appears as a physiological process present in synapses located far away from the HFS-stimulated afferent pathway.
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Remme MWH, Bergmann U, Alevi D, Schreiber S, Sprekeler H, Kempter R. Hebbian plasticity in parallel synaptic pathways: A circuit mechanism for systems memory consolidation. PLoS Comput Biol 2021; 17:e1009681. [PMID: 34874938 PMCID: PMC8683039 DOI: 10.1371/journal.pcbi.1009681] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2021] [Revised: 12/17/2021] [Accepted: 11/24/2021] [Indexed: 12/03/2022] Open
Abstract
Systems memory consolidation involves the transfer of memories across brain regions and the transformation of memory content. For example, declarative memories that transiently depend on the hippocampal formation are transformed into long-term memory traces in neocortical networks, and procedural memories are transformed within cortico-striatal networks. These consolidation processes are thought to rely on replay and repetition of recently acquired memories, but the cellular and network mechanisms that mediate the changes of memories are poorly understood. Here, we suggest that systems memory consolidation could arise from Hebbian plasticity in networks with parallel synaptic pathways-two ubiquitous features of neural circuits in the brain. We explore this hypothesis in the context of hippocampus-dependent memories. Using computational models and mathematical analyses, we illustrate how memories are transferred across circuits and discuss why their representations could change. The analyses suggest that Hebbian plasticity mediates consolidation by transferring a linear approximation of a previously acquired memory into a parallel pathway. Our modelling results are further in quantitative agreement with lesion studies in rodents. Moreover, a hierarchical iteration of the mechanism yields power-law forgetting-as observed in psychophysical studies in humans. The predicted circuit mechanism thus bridges spatial scales from single cells to cortical areas and time scales from milliseconds to years.
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Affiliation(s)
- Michiel W. H. Remme
- Department of Biology, Institute for Theoretical Biology, Humboldt-Universität zu Berlin, Berlin, Germany
| | - Urs Bergmann
- Department of Biology, Institute for Theoretical Biology, Humboldt-Universität zu Berlin, Berlin, Germany
| | - Denis Alevi
- Department for Electrical Engineering and Computer Science, Technische Universität Berlin, Berlin, Germany
- Bernstein Center for Computational Neuroscience Berlin, Berlin, Germany
| | - Susanne Schreiber
- Department of Biology, Institute for Theoretical Biology, Humboldt-Universität zu Berlin, Berlin, Germany
- Bernstein Center for Computational Neuroscience Berlin, Berlin, Germany
- Einstein Center for Neurosciences Berlin, Berlin, Germany
| | - Henning Sprekeler
- Department for Electrical Engineering and Computer Science, Technische Universität Berlin, Berlin, Germany
- Bernstein Center for Computational Neuroscience Berlin, Berlin, Germany
- Einstein Center for Neurosciences Berlin, Berlin, Germany
- Excellence Cluster Science of Intelligence, Berlin, Germany
| | - Richard Kempter
- Department of Biology, Institute for Theoretical Biology, Humboldt-Universität zu Berlin, Berlin, Germany
- Bernstein Center for Computational Neuroscience Berlin, Berlin, Germany
- Einstein Center for Neurosciences Berlin, Berlin, Germany
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Long-term potentiation of the nucleus reuniens and entorhinal cortex to CA1 distal dendritic synapses in mice. Brain Struct Funct 2020; 225:1817-1838. [DOI: 10.1007/s00429-020-02095-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Accepted: 05/31/2020] [Indexed: 02/07/2023]
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Wu B, Liu J, Zhao R, Li Y, Peer J, Braun AL, Zhao L, Wang Y, Tong Z, Huang Y, Zheng JC. Glutaminase 1 regulates the release of extracellular vesicles during neuroinflammation through key metabolic intermediate alpha-ketoglutarate. J Neuroinflammation 2018. [PMID: 29540215 PMCID: PMC5853116 DOI: 10.1186/s12974-018-1120-x] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Background Extracellular vesicles (EVs) are important in the intercellular communication of the central nervous system, and their release is increased during neuroinflammation. Our previous data demonstrated an increased release of EVs during HIV-1 infection and immune activation in glial cells. However, the molecular mechanism by which infection and inflammation increase EV release remains unknown. In the current study, we investigated the role of glutaminase 1 (GLS1)-mediated glutaminolysis and the production of a key metabolic intermediate α-ketoglutarate on EV release. Methods Human monocyte-derived macrophage primary cultures and a BV2 microglia cell line were used to represent the innate immune cells in the CNS. Transmission electron microscopy, nanoparticle tracking analysis, and Western blots were used to determine the EV regulation. GLS1 overexpression was performed using an adenovirus vector in vitro and transgenic mouse models in vivo. Data were evaluated statistically by ANOVA, followed by the Bonferroni post-test for paired observations. Results Our data revealed an increased release of EVs in GLS1-overexpressing HeLa cells. In HIV-1-infected macrophages and immune-activated microglia BV2 cells, treatment with bis-2-(5-phenylacetamido-1,2,4-thiadiazol-2-yl)ethyl sulfide (BPTES) or CB839, two specific GLS inhibitors, significantly decreased EV release, suggesting a critical role of GLS1 in EV release. Furthermore, addition of α-ketoglutarate or ceramide rescued EV release during BPTES treatment, implicating α-ketoglutarate and ceramide as critical downstream effectors for GLS inhibitors. These findings were further corroborated with the investigation of brain tissues in GLS1-transgenic mice. The EV levels were significantly higher in GLS1 transgenic mice than those in control mice, suggesting that GLS1 increases EV release in vivo. Conclusions These findings suggest that GLS1-mediated glutaminolysis and its downstream production of α-ketoglutarate are essential in regulating EV release during HIV-1 infection and immune activation. These new mechanistic regulations may help understand how glutamine metabolism shapes EV biogenesis and release during neuroinflammation. Electronic supplementary material The online version of this article (10.1186/s12974-018-1120-x) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Beiqing Wu
- Center for Translational Neurodegeneration and Regenerative Therapy, Shanghai Tenth People's Hospital affiliated to Tongji University School of Medicine, Shanghai, China.,Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Jianhui Liu
- Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Runze Zhao
- Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Yuju Li
- Center for Translational Neurodegeneration and Regenerative Therapy, Shanghai Tenth People's Hospital affiliated to Tongji University School of Medicine, Shanghai, China.,Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Justin Peer
- Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Alexander L Braun
- Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Lixia Zhao
- Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Yi Wang
- Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Zenghan Tong
- Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Yunlong Huang
- Center for Translational Neurodegeneration and Regenerative Therapy, Shanghai Tenth People's Hospital affiliated to Tongji University School of Medicine, Shanghai, China. .,Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA.
| | - Jialin C Zheng
- Center for Translational Neurodegeneration and Regenerative Therapy, Shanghai Tenth People's Hospital affiliated to Tongji University School of Medicine, Shanghai, China. .,Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA. .,Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE, 68198-5930, USA.
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Glutaminase C overexpression in the brain induces learning deficits, synaptic dysfunctions, and neuroinflammation in mice. Brain Behav Immun 2017. [PMID: 28624534 PMCID: PMC5650935 DOI: 10.1016/j.bbi.2017.06.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Glutaminolysis, a metabolic process that converts glutamine to glutamate, is particularly important for the central nervous system since glutamate is the major transmitter of excitatory synapses. Glutaminase is the mitochondrial enzyme that catalyzes the first step of glutaminolysis. Two genes encode at least four isoforms of glutaminase in humans. Gls1 gene encodes isoforms kidney-type glutaminase (KGA) and glutaminase C (GAC) through alternative splicing, whereas Gls2 gene encodes liver-type glutaminase isoforms. KGA and GAC have been associated with several neurological diseases. However, it remains unclear whether changes in their expressions can directly cause brain abnormalities. Using a transgenic approach, we generated mice that overexpressed GAC in the brain. The resulting transgenic mice had severe impairments in spatial and fear learning compared with littermate controls. The learning deficits were consistent with diminished hippocampal long-term potentiation in the hippocampal slices of the GAC transgenic mice. Furthermore, we found increases in astrocyte and microglia markers, inflammatory factors, and a decrease in synapse marker synaptophysin, suggesting neuroinflammation and synaptic changes in the GAC transgenic mouse brains. In conclusion, these findings provide the first evidence that GAC overexpression in the brain has deleterious effects on learning and synaptic integrity in vivo.
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Hosseini N, Alaei H, Reisi P, Radahmadi M. The effects of NBM- lesion on synaptic plasticity in rats. Brain Res 2017; 1655:122-127. [DOI: 10.1016/j.brainres.2016.11.013] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Revised: 10/20/2016] [Accepted: 11/11/2016] [Indexed: 01/01/2023]
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Gonzalez J, Villarreal DM, Morales IS, Derrick BE. Long-term Potentiation at Temporoammonic Path-CA1 Synapses in Freely Moving Rats. Front Neural Circuits 2016; 10:2. [PMID: 26903815 PMCID: PMC4748048 DOI: 10.3389/fncir.2016.00002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Accepted: 01/12/2016] [Indexed: 11/23/2022] Open
Abstract
Hippocampal area CA1 receives direct entorhinal layer III input via the temporoammonic path (TAP) and recent studies implicate TAP-CA1 synapses are important for some aspects of hippocampal memory function. Nonetheless, as few studies have examined TAP-CA1 synaptic plasticity in vivo, the induction and longevity of TAP-CA1 long-term potentiation (LTP) has not been fully characterized. We analyzed CA1 responses following stimulation of the medial aspect of the angular bundle and investigated LTP at medial temporoammonic path (mTAP)-CA1 synapses in freely moving rats. We demonstrate monosynaptic mTAP-CA1 responses can be isolated in vivo as evidenced by observations of independent current sinks in the stratum lacunosum moleculare of both areas CA1 and CA3 following angular bundle stimulation. Contrasting prior indications that TAP input rarely elicits CA1 discharge, we observed mTAP-CA1 responses that appeared to contain putative population spikes in 40% of our behaving animals. Theta burst high frequency stimulation of mTAP afferents resulted in an input specific and N-methyl-D-aspartate (NMDA) receptor-dependent LTP of mTAP-CA1 responses in behaving animals. LTP of mTAP-CA1 responses decayed as a function of two exponential decay curves with time constants (τ) of 2.7 and 148 days to decay 63.2% of maximal LTP. In contrast, mTAP-CA1 population spike potentiation longevity demonstrated a τ of 9.6 days. To our knowledge, these studies provide the first description of mTAP-CA1 LTP longevity in vivo. These data indicate TAP input to area CA1 is a physiologically relevant afferent system that displays robust synaptic plasticity.
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Affiliation(s)
- Jossina Gonzalez
- Department of Biology, University of Texas at San Antonio San Antonio, TX, USA
| | | | - Isaiah S Morales
- Department of Biology, University of Texas at San Antonio San Antonio, TX, USA
| | - Brian E Derrick
- Department of Biology, University of Texas at San AntonioSan Antonio, TX, USA; UTSA Neurosciences Institute, University of Texas at San AntonioSan Antonio, TX, USA
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Hendrickson PJ, Yu GJ, Song D, Berger TW. Interactions between Inhibitory Interneurons and Excitatory Associational Circuitry in Determining Spatio-Temporal Dynamics of Hippocampal Dentate Granule Cells: A Large-Scale Computational Study. Front Syst Neurosci 2015; 9:155. [PMID: 26635545 PMCID: PMC4647071 DOI: 10.3389/fnsys.2015.00155] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Accepted: 10/27/2015] [Indexed: 11/16/2022] Open
Abstract
This paper reports on findings from a million-cell granule cell model of the rat dentate gyrus that was used to explore the contributions of local interneuronal and associational circuits to network-level activity. The model contains experimentally derived morphological parameters for granule cells, which each contain approximately 200 compartments, and biophysical parameters for granule cells, basket cells, and mossy cells that were based both on electrophysiological data and previously published models. Synaptic input to cells in the model consisted of glutamatergic AMPA-like EPSPs and GABAergic-like IPSPs from excitatory and inhibitory neurons, respectively. The main source of input to the model was from layer II entorhinal cortical neurons. Network connectivity was constrained by the topography of the system, and was derived from axonal transport studies, which provided details about the spatial spread of axonal terminal fields, as well as how subregions of the medial and lateral entorhinal cortices project to subregions of the dentate gyrus. Results of this study show that strong feedback inhibition from the basket cell population can cause high-frequency rhythmicity in granule cells, while the strength of feedforward inhibition serves to scale the total amount of granule cell activity. Results furthermore show that the topography of local interneuronal circuits can have just as strong an impact on the development of spatio-temporal clusters in the granule cell population as the perforant path topography does, both sharpening existing clusters and introducing new ones with a greater spatial extent. Finally, results show that the interactions between the inhibitory and associational loops can cause high frequency oscillations that are modulated by a low-frequency oscillatory signal. These results serve to further illustrate the importance of topographical constraints on a global signal processing feature of a neural network, while also illustrating how rich spatio-temporal and oscillatory dynamics can evolve from a relatively small number of interacting local circuits.
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Affiliation(s)
- Phillip J Hendrickson
- Department of Biomedical Engineering, University of Southern California Los Angeles, CA, USA
| | - Gene J Yu
- Department of Biomedical Engineering, University of Southern California Los Angeles, CA, USA
| | - Dong Song
- Department of Biomedical Engineering, University of Southern California Los Angeles, CA, USA
| | - Theodore W Berger
- Department of Biomedical Engineering, University of Southern California Los Angeles, CA, USA
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Abstract
This review covers the spatial and temporal rules governing induction of hippocampal long-term potentiation (LTP) by theta-burst stimulation. Induction of LTP in field CA1 by high frequency stimulation bursts that resemble the burst discharges (complex-spikes) of hippocampal pyramidal neurons involves a multiple-step mechanism. A single burst is insufficient for LTP induction because it evokes both excitatory and inhibitory currents that partially cancel and limit postsynaptic depolarization. Bursts repeated at the frequency (~5 Hz) of the endogenous theta rhythm induce maximal LTP, primarily because this frequency disables feed-forward inhibition and allows sufficient postsynaptic depolarization to activate voltage-sensitive NMDA receptors. The disinhibitory process, referred to as "priming", involves presynaptic GABA autoreceptors that inhibit GABA release. Activation of NMDA receptors allows a calcium flux into dendritic spines that serves as the proximal trigger for LTP. We include new data showing that theta-burst stimulation is more efficient than other forms of stimulation for LTP induction. In addition, we demonstrate that associative interactions between synapses activated during theta-bursts are limited to major dendritic domains since such interactions occur within apical or basal dendritic trees but not between them. We review evidence that recordings of electrophysiological responses during theta burst stimulation can help to determine if experimental manipulations that affect LTP do so by affecting events antecedent to the induction process, such as NMDA receptor activation, or downstream signaling cascades that result from postsynaptic calcium fluxes. Finally, we argue that theta-burst LTP represents a minimal model for stable, non-decremental LTP that is more sensitive to a variety of experimental manipulations than is LTP induced by other stimulation paradigms. This article is part of a Special Issue entitled SI: Brain and Memory.
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Affiliation(s)
- John Larson
- Psychiatric Institute, Department of Psychiatry, University of Illinois College of Medicine, Chicago, IL 60612, United States.
| | - Erin Munkácsy
- Barshop Institute for Longevity and Aging Studies, Department of Cell and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78245, United States
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Moreno A, Morris RGM, Canals S. Frequency-Dependent Gating of Hippocampal-Neocortical Interactions. Cereb Cortex 2015; 26:2105-2114. [PMID: 25761637 DOI: 10.1093/cercor/bhv033] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
How and where hippocampal-neocortical interactions required for memory formation take place is a major issue of current research. Using a combined in vivo functional magnetic resonance imaging/electrophysiology approach, we have investigated whether specific frequencies of CA3 neuronal activation, inducing different forms of short-term plasticity at CA1 synapses, contribute to differential activity propagation in brain-wide networks connected to the hippocampus. We report that localized activation of CA3 neurons in dorsal hippocampus produced activity propagation within the hippocampal formation, including the subiculum and entorhinal cortex, which increased monotonically with frequency to a maximum at 20-40 Hz. However, robust extrahippocampal propagation was seen specifically at theta-beta frequencies (10-20 Hz), reaching a network of midline neocortical and mesolimbic structures. Activation in those regions correlated with a frequency-dependent facilitation of spiking activity recorded in CA1. These results provide a mechanistic link between the dynamic properties of short-term plasticity in the efferent synapses of CA3 neurons in CA1 and activity propagation in brain-wide networks, and identify polysynaptic information channels segregated in the frequency domain.
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Affiliation(s)
- Andrea Moreno
- Centre for Cognitive and Neural Systems, Edinburgh Neuroscience, University of Edinburgh, Edinburgh EH8 9JZ, UK.,Instituto de Neurociencias, Consejo Superior de Investigaciones Científicas, Universidad Miguel Hernández, Sant Joan d'Alacant 03550, Spain
| | - Richard G M Morris
- Centre for Cognitive and Neural Systems, Edinburgh Neuroscience, University of Edinburgh, Edinburgh EH8 9JZ, UK
| | - Santiago Canals
- Instituto de Neurociencias, Consejo Superior de Investigaciones Científicas, Universidad Miguel Hernández, Sant Joan d'Alacant 03550, Spain
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Psarrou M, Stefanou SS, Papoutsi A, Tzilivaki A, Cutsuridis V, Poirazi P. A simulation study on the effects of dendritic morphology on layer V prefrontal pyramidal cell firing behavior. Front Cell Neurosci 2014; 8:287. [PMID: 25278837 PMCID: PMC4165233 DOI: 10.3389/fncel.2014.00287] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Accepted: 08/29/2014] [Indexed: 11/13/2022] Open
Abstract
Pyramidal cells, the most abundant neurons in neocortex, exhibit significant structural variability across different brain areas and layers in different species. Moreover, in response to a somatic step current, these cells display a range of firing behaviors, the most common being (1) repetitive action potentials (Regular Spiking-RS), and (2) an initial cluster of 2-5 action potentials with short interspike interval (ISIs) followed by single spikes (Intrinsic Bursting-IB). A correlation between firing behavior and dendritic morphology has recently been reported. In this work we use computational modeling to investigate quantitatively the effects of the basal dendritic tree morphology on the firing behavior of 112 three-dimensional reconstructions of layer V PFC rat pyramidal cells. Particularly, we focus on how different morphological (diameter, total length, volume, and branch number) and passive [Mean Electrotonic Path length (MEP)] features of basal dendritic trees shape somatic firing when the spatial distribution of ionic mechanisms in the basal dendritic trees is uniform or non-uniform. Our results suggest that total length, volume and branch number are the best morphological parameters to discriminate the cells as RS or IB, regardless of the distribution of ionic mechanisms in basal trees. The discriminatory power of total length, volume, and branch number remains high in the presence of different apical dendrites. These results suggest that morphological variations in the basal dendritic trees of layer V pyramidal neurons in the PFC influence their firing patterns in a predictive manner and may in turn influence the information processing capabilities of these neurons.
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Affiliation(s)
- Maria Psarrou
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas Heraklion, Greece ; Centre for Computer Science and Informatics Research, Science and Technology Institute, University of Hertfordshire Hatfield, UK ; School of Computer Science, University of Hertfordshire Hatfield, UK
| | - Stefanos S Stefanou
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas Heraklion, Greece ; Department of Biology, University of Crete Heraklion, Greece
| | - Athanasia Papoutsi
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas Heraklion, Greece
| | - Alexandra Tzilivaki
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas Heraklion, Greece ; Department of Biology, University of Crete Heraklion, Greece
| | - Vassilis Cutsuridis
- 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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Kato R, Tachibana K, Nishimoto N, Hashimoto T, Uchida Y, Ito R, Tsuruga K, Takita K, Morimoto Y. Neonatal exposure to sevoflurane causes significant suppression of hippocampal long-term potentiation in postgrowth rats. Anesth Analg 2014; 117:1429-35. [PMID: 24132013 DOI: 10.1213/ane.0b013e3182a8c709] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
BACKGROUND The inhaled anesthetic sevoflurane is commonly used for neonates in the clinical setting. Recent studies have indicated that exposure of neonatal rodents to sevoflurane causes acute widespread neurodegeneration and long-lasting neurocognitive dysfunction. Although acute toxic effects of sevoflurane on cellular viability in the hippocampus have been reported in some studies, little is known about the effects of neonatal sevoflurane exposure on long-term hippocampal synaptic plasticity, which has been implicated in the processes of learning and memory formation. Our study is the first to examine the long-term electrophysiological impact of neonatal exposure to a clinically relevant concentration of sevoflurane. METHODS On postnatal day 7, rats were exposed to sevoflurane (1% or 2% for 2 hours) with oxygen. To eliminate the influence of blood gas abnormalities caused by sevoflurane-induced respiratory suppression, a group of rats were exposed to a high concentration of carbon dioxide (8% for 2 hours) to duplicate respiratory disturbances caused by 2% sevoflurane exposure. RESULTS Exposure of neonatal rats to 2% sevoflurane for 2 hours caused significant suppression of long-term potentiation (LTP) induction in the postgrowth period. There was no significant difference between the control group and the CO2-exposed group in LTP induction, indicating that sevoflurane-induced LTP suppression was not caused by blood gas abnormalities. CONCLUSION Our present findings indicate that neonatal exposure to sevoflurane at a higher concentration can cause alterations in the hippocampal synaptic plasticity that persists into adulthood.
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Affiliation(s)
- Rui Kato
- From the *Department of Anesthesiology and Critical Care Medicine and †Division of Clinical Trial Management, Center for Translational Research, Hokkaido University Graduate School of Medicine, Sapporo, Japan
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Tachibana K, Hashimoto T, Kato R, Uchida Y, Ito R, Takita K, Morimoto Y. Neonatal administration with dexmedetomidine does not impair the rat hippocampal synaptic plasticity later in adulthood. Paediatr Anaesth 2012; 22:713-9. [PMID: 22309594 DOI: 10.1111/j.1460-9592.2012.03810.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
BACKGROUND AND OBJECTIVE The use of dexmedetomidine (DEX), a selective alpha-2 agonist, in pediatric practice is expanding as a result of its desirable properties. To clarify the long-term neurological consequences of neonatal administration of DEX, we investigated the long-term effects of neonatal administration of DEX on hippocampal synaptic activity. METHODS The rat pups received a bolus intraperitoneal injection of either 5 or 10 μg·kg(-1) DEX, or an equivalent volume of vehicle on postnatal day 7 (P7). Nine weeks after administration, evoked potentials (population spike, PS) and long-term potentiation (LTP) in the hippocampal CA1 region of rats were studied in vivo. RESULTS Dexmedetomidine had a considerable sedative effect at these doses with little respiratory depression on P7. Nine weeks after administration of DEX, the amplitude of PS in the two treated groups was similar to that in the control group. DEX-treated rats showed no impairment in the induction of LTP. Furthermore, the response in PS to the paired stimuli was not impaired by neonatal administration of DEX. CONCLUSION These findings demonstrate that a single administration of DEX to rats on P7 preserves hippocampal synaptic plasticity as well as synaptic transmission later in life. In view of the some evidence that have demonstrated the permanent detrimental impact of commonly used anesthetics on neurological outcomes after neonatal exposure, our findings may suggest the relative safety of DEX administered as a sedative agent to neonatal animals with regard to the development of hippocampal synaptic functions.
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Affiliation(s)
- Kaori Tachibana
- Department of Anesthesiology and Critical Care Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
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Fung TK, Peloquin P, Wu K, Leung LS. Differential long-term depression in CA3 but not in dentate gyrus following low-frequency stimulation of the medial perforant path. Synapse 2011; 65:677-86. [PMID: 21190218 DOI: 10.1002/syn.20901] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2010] [Accepted: 12/02/2010] [Indexed: 11/05/2022]
Abstract
Synaptic plasticity may depend not only on the afferent fibers but also on the recipient structure. The medial perforant path (MPP) from the entorhinalcortex projects to both the dentate gyrus (DG) and CA3, resulting in excitatory postsynaptic potentials (EPSPs) in both areas. In this study, we showed that long-term depression (LTD) following low-frequency stimulation of MPP was found only in CA3a, a CA3 subfield, but not in DG. Field potentials were recorded and current source density (CSD) analyzed in CA3a and DG following stimulation of MPP in urethane-anesthetized rats. MPP evoked a short-latency population spike (PS) and EPSP in CA3a, <2.5 ms delayed from the respective events in DG. A small electrolytic lesion of CA3a abolished the locally recorded PS in CA3a but did not affect the responses in the DG. Low-frequency stimulation of the MPP for 600 pulses at 5 Hz, but not at 1 Hz, resulted in LTD of up to 2 h in CA3a but not in DG. High-frequency stimulation (400 Hz bursts) of the MPP resulted in long-term potentiation (LTP) in both CA3a and DG. LTD at CA3a was blocked by a prior intracerebroventricular administration of an N-methyl-D-aspartate receptor (NMDAR) antagonist DL-2-amino-5-phosphonovaleric acid or a nonselective group I/II metabotropic glutamate receptor (mGluR) antagonist (RS)-α-methyl-4-carboxyphenylglycine. We conclude that an NMDAR and mGluR sensitive LTD is induced in CA3 but not in the DG following low-frequency MPP stimulation in vivo, and the bi-directional synaptic plasticity in CA3 may be responsible for its behavioral functions.
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Affiliation(s)
- Thomas K Fung
- Department Physiology and Pharmacology, University of Western Ontario, London, ON N6A5C1, Canada
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15
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Theta oscillations during holeboard training in rats: different learning strategies entail different context-dependent modulations in the hippocampus. Neuroscience 2009; 165:642-53. [PMID: 19896522 DOI: 10.1016/j.neuroscience.2009.11.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2009] [Accepted: 11/02/2009] [Indexed: 11/24/2022]
Abstract
A functional connection between theta rhythms, information processing, learning and memory formation is well documented by studies focusing on the impact of theta waves on motor activity, global context or phase coding in spatial learning. In the present study we analyzed theta oscillations during a spatial learning task and assessed which specific behavioral contexts were connected to changes in theta power and to the formation of memory. Therefore, we measured hippocampal dentate gyrus theta modulations in male rats that were allowed to establish a long-term spatial reference memory in a holeboard (fixed pattern of baited holes) in comparison to rats that underwent similar training conditions but could not form a reference memory (randomly baited holes). The first group established a pattern specific learning strategy, while the second developed an arbitrary search strategy, visiting increasingly more holes during training. Theta power was equally influenced during the training course in both groups, but was significantly higher when compared to untrained controls. A detailed behavioral analysis, however, revealed behavior- and context-specific differences within the experimental groups. In spatially trained animals theta power correlated with the amounts of reference memory errors in the context of the inspection of unbaited holes and exploration in which, as suggested by time frequency analyses, also slow wave (delta) power was increased. In contrast, in randomly trained animals positive correlations with working memory errors were found in the context of rearing behavior. These findings indicate a contribution of theta/delta to long-lasting memory formation in spatially trained animals, whereas in pseudo trained animals theta seems to be related to attention in order to establish trial specific short-term working memory. Implications for differences in neuronal plasticity found in earlier studies are discussed.
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16
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Young CK, Eggermont JJ. Coupling of mesoscopic brain oscillations: recent advances in analytical and theoretical perspectives. Prog Neurobiol 2009; 89:61-78. [PMID: 19549556 DOI: 10.1016/j.pneurobio.2009.06.002] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2009] [Revised: 04/27/2009] [Accepted: 06/15/2009] [Indexed: 01/12/2023]
Abstract
Oscillatory brain activities have been traditionally studied in the context of how oscillations at a single frequency recorded from a single area could reveal functional insights. Recent advances in methodology used in signal analysis have revealed that cross-frequency coupling, within or between functional related areas, is more informative in determining the possible roles played by brain oscillations. In this review, we begin by describing the cellular basis of oscillatory field potentials and its theorized as well as demonstrated role in brain function. The recent development of mathematical tools that allow the investigation of cross-frequency and cross-area oscillation coupling will be presented and discussed in the context of recent advances in oscillation research based on animal data. Particularly, some pitfalls and caveats of methods currently available are discussed. Data generated from the application of examined techniques are integrated back into the theoretical framework regarding the functional role of brain oscillations. We suggest that the coupling of oscillatory activities at different frequencies between brain regions is crucial for understanding the brain from a functional ensemble perspective. Effort should be directed to elucidate how cross-frequency and area coupling are modulated and controlled. To achieve this, only the correct application of analytical tools may shed light on the intricacies of information representation, generation, binding, encoding, storage and retrieval in the brain.
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Affiliation(s)
- Calvin K Young
- Behavioural Neuroscience Group, Department of Psychology, University of Calgary, Calgary, AB, Canada
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17
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Kim DS, Kim JE, Kwak SE, Choi KC, Kim DW, Kwon OS, Choi SY, Kang TC. Spatiotemporal characteristics of astroglial death in the rat hippocampo-entorhinal complex following pilocarpine-induced status epilepticus. J Comp Neurol 2009; 511:581-98. [PMID: 18853423 DOI: 10.1002/cne.21851] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Recently we reported that astroglial loss and subsequent gliogenesis in the dentate gyrus play a role in epileptogenesis following pilocarpine-induced status epilepticus (SE). In the present study we investigated whether astroglial damages in the hippocampo-entorhinal complex following SE are relevant to pathological or electrophysiological properties of temporal lobe epilepsy. Astroglial loss/damage was observed in the entorhinal cortex and the CA1 region at 4 weeks and 8 weeks after SE, respectively. These astroglial responses in the hippocampo-entorhinal cortex were accompanied by hyperexcitability of the CA1 region (impairment of paired-pulse inhibition and increase in excitability ratio). Unlike the dentate gyrus and the entorhinal cortex, CA1 astroglial damage was protected by conventional anti-epileptic drugs. alpha-Aminoadipic acid (a specific astroglial toxin) infusion into the entorhinal cortex induced astroglial damage and changed the electrophysiological properties in the CA1 region. Astroglial regeneration in the dentate gyrus and the stratum oriens of the CA1 region was found to originate from gliogenesis, while that in the entorhinal cortex and stratum radiatum of the CA1 region originated from in situ proliferation. These findings suggest that regional specific astroglial death/regeneration patterns may play an important role in the pathogenesis of temporal lobe epilepsy.
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Affiliation(s)
- Duk-Soo Kim
- Department of Anatomy and Neurobiology, College of Medicine, Hallym University, Chunchon 200-702, South Korea
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18
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Middleton S, Jalics J, Kispersky T, LeBeau FEN, Roopun AK, Kopell NJ, Whittington MA, Cunningham MO. NMDA receptor-dependent switching between different gamma rhythm-generating microcircuits in entorhinal cortex. Proc Natl Acad Sci U S A 2008; 105:18572-7. [PMID: 18997013 PMCID: PMC2587538 DOI: 10.1073/pnas.0809302105] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2008] [Indexed: 12/20/2022] Open
Abstract
Local circuits in the medial entorhinal cortex (mEC) and hippocampus generate gamma frequency population rhythms independently. Temporal interaction between these areas at gamma frequencies is implicated in memory-a phenomenon linked to activity of NMDA-subtype glutamate receptors. While blockade of NMDA receptors does not affect frequency of gamma rhythms in hippocampus, it exposes a second, lower frequency (25-35 Hz) gamma rhythm in mEC. In experiment and model, NMDA receptor-dependent mEC gamma rhythms were mediated by basket interneurons, but NMDA receptor-independent gamma rhythms were mediated by a novel interneuron subtype-the goblet cell. This cell was distinct from basket cells in morphology, intrinsic membrane properties and synaptic inputs. The two different gamma frequencies matched the different intrinsic frequencies in hippocampal areas CA3 and CA1, suggesting that NMDA receptor activation may control the nature of temporal interactions between mEC and hippocampus, thus influencing the pathway for information transfer between the two regions.
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Affiliation(s)
- Steven Middleton
- Institute of Neuroscience, Newcastle University, Newcastle NE2 4HH, United Kingdom
| | - Jozsi Jalics
- Department of Mathematics and Statistics, Youngstown State University, One University Plaza, Youngstown, OH 44555
| | - Tilman Kispersky
- Program in Neuroscience, Center for BioDynamics, Boston University, Boston, MA 02215; and
| | - Fiona E. N. LeBeau
- Institute of Neuroscience, Newcastle University, Newcastle NE2 4HH, United Kingdom
| | - Anita K. Roopun
- Institute of Neuroscience, Newcastle University, Newcastle NE2 4HH, United Kingdom
| | - Nancy J. Kopell
- Department of Mathematics and Statistics, Center for BioDynamics, 111 Cummington Street, Boston University, Boston, MA 02215
| | - Miles A. Whittington
- Institute of Neuroscience, Newcastle University, Newcastle NE2 4HH, United Kingdom
| | - Mark O. Cunningham
- Institute of Neuroscience, Newcastle University, Newcastle NE2 4HH, United Kingdom
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19
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Gant JC, Thibault O. Action potential throughput in aged rat hippocampal neurons: regulation by selective forms of hyperpolarization. Neurobiol Aging 2008; 30:2053-64. [PMID: 18367293 DOI: 10.1016/j.neurobiolaging.2008.02.006] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2007] [Revised: 02/07/2008] [Accepted: 02/14/2008] [Indexed: 01/23/2023]
Abstract
At hippocampal synapses, repetitive synaptic stimulation (RSS) in the theta frequency range (3-12Hz) is associated with robust EPSP frequency facilitation (FF) and consequently, enhanced action potential (spike) generation and throughput. A complex, synaptically induced hyperpolarization (SIHP) is also triggered by synaptic activation, and a Ca(2+)-dependent afterhyperpolarization (AHP) is triggered above spike threshold. With aging, the AHP is increased and impairs intracellular spike generation, at least in accommodation protocols. However, little is known about how these aging changes interact to affect spike generation at physiological frequencies of RSS, or if the SIHP also is modified in aging. Here we performed the first tests of the net impact of these excitatory and inhibitory aging changes on spike generation during RSS. We report that during RSS at spike threshold (1) spike throughput is well sustained at theta frequencies in young and aged neurons; (2) an interposed AHP dampens spike generation, particularly in aged neurons and at higher frequencies; (3) compared to the AHP, the SIHP does not exert an equivalent inhibitory effect on spike throughput; and (4) in contrast to the AHP, the SIHP is reduced with aging. Together, these results are consistent with a model in which the source of the hyperpolarization is important in determining hippocampal spike throughput within the theta frequency range.
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Affiliation(s)
- John C Gant
- Department of Molecular and Biomedical Pharmacology, University of Kentucky Medical Center (UKMC), MS320, Lexington, KY 40503, United States.
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20
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Angenstein F, Kammerer E, Niessen HG, Frey JU, Scheich H, Frey S. Frequency-dependent activation pattern in the rat hippocampus, a simultaneous electrophysiological and fMRI study. Neuroimage 2007; 38:150-63. [PMID: 17728153 DOI: 10.1016/j.neuroimage.2007.07.022] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2007] [Revised: 07/12/2007] [Accepted: 07/20/2007] [Indexed: 10/23/2022] Open
Abstract
Frequency-dependent hippocampal activation during electrical perforant pathway stimulation was analyzed simultaneously by electrophysiological recordings in dentate gyrus and functional magnetic resonance imaging (fMRI). Pulse trains at low-frequency stimulation (2.5 Hz) did not influence electrophysiological responses within stimulation trains in the dentate gyrus and triggered no detectable BOLD responses. Increased stimulation frequencies (5.0-20 Hz) generated a roughly linear enhancement of the BOLD response. The BOLD signal within the dentate gyrus correlated more closely with stimulus pattern than with generated action potentials of the granular cells. However, the BOLD signal was strongly influenced by additional local signal processing activated by repetitive stimulus trains. fMRI visualized a frequency-specific spatial activation pattern of the hippocampus; spatially restricted activation in the dentate gyrus during 5-Hz stimulation, activation of the entire hippocampus and subiculum at 10 Hz and activation of the contralateral hippocampus during 20-Hz stimulation.
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Affiliation(s)
- Frank Angenstein
- Leibniz Institute for Neurobiology, Special Lab Non-Invasive Brain Imaging, Magdeburg, Germany.
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21
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Yu Z, McKnight TE, Ericson MN, Melechko AV, Simpson ML, Morrison B. Vertically aligned carbon nanofiber arrays record electrophysiological signals from hippocampal slices. NANO LETTERS 2007; 7:2188-95. [PMID: 17604402 DOI: 10.1021/nl070291a] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Vertically aligned carbon nanofiber (VACNF) electrode arrays were tested for their potential application in recording neuro-electrophysiological activity. We report, for the first time, stimulation and extracellular recording of spontaneous and evoked neuroelectrical activity in organotypic hippocampal slice cultures with ultramicroelectrode VACNF arrays. Because the electrodes are carbon-based, these arrays have potential advantages over metal electrodes and could enable a variety of future applications as precise, informative, and biocompatible neural interfaces.
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Affiliation(s)
- Zhe Yu
- Department of Biomedical Engineering, Columbia University, 1210 Amsterdam Avenue, 351 Engineering Terrace, New York, New York 10027, USA
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22
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Gureviciene I, Gurevicius K, Tanila H. Role of alpha-synuclein in synaptic glutamate release. Neurobiol Dis 2007; 28:83-9. [PMID: 17689254 DOI: 10.1016/j.nbd.2007.06.016] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2006] [Revised: 06/07/2007] [Accepted: 06/17/2007] [Indexed: 11/23/2022] Open
Abstract
Defective mobilization of dopamine from the reserve pool has been reported in both alpha-synuclein knockout mice (KO) and pPrp-A30P transgenic mice. The present study extends these findings to glutamate release. Standard hippocampal slices were prepared from KO, pPrp-A30P, and C57BL/6J wild type (WT1) mice, as well as from mice with transgenic overexpression of wild type human alpha-synuclein (pSyn-hASY) and their negative littermates (WT2), and field responses were measured in CA3 in response to mossy fiber stimulation. The input/output curves indicated no differences in basal synaptic transmission between groups. Paired-pulse facilitation was significantly weaker in both transgenic alpha-synuclein lines and KO mice compared to their controls. High-frequency stimulation induced LTP only in transgenic mice. Frequency-facilitation was absent in KO mice and different from other mouse lines. These findings support the idea that lack of alpha-synuclein impairs mobilization of glutamate from the reserve pool. However, transgenic expression of A30P mutated or wild type alpha-synuclein does not appear to prevent endogenous mouse alpha-synuclein to carry out this function.
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Affiliation(s)
- Irina Gureviciene
- Department Neurobiology, A. I. Virtanen Institute for Molecular Science, University of Kuopio, P.O. Box 1627/Neulaniementie 2, FIN-70211 Kuopio, Finland.
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23
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Hamam BN, Sinai M, Poirier G, Chapman CA. Cholinergic suppression of excitatory synaptic responses in layer II of the medial entorhinal cortex. Hippocampus 2007; 17:103-13. [PMID: 17146776 DOI: 10.1002/hipo.20249] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Theta-frequency (4-12 Hz) electroencephalographic activity is thought to play a role in mechanisms mediating sensory and mnemonic processing in the entorhinal cortex and hippocampus, but the effects of acetylcholine on excitatory synaptic inputs to the entorhinal cortex are not well understood. Field excitatory postsynaptic potentials (fEPSPs) evoked by stimulation of the piriform (olfactory) cortex were recorded in the medial entorhinal cortex during behaviors associated with theta activity (active mobility) and were compared with those recorded during nontheta behaviors (awake immobility and slow wave sleep). Synaptic responses were smaller during behavioral activity than during awake immobility and sleep, and responses recorded during movement were largest during the negative phase of the theta rhythm. Systemic administration of cholinergic agonists reduced the amplitude of fEPSPs, and the muscarinic receptor blocker scopolamine strongly enhanced fEPSPs, suggesting that the theta-related suppression of fEPSPs is mediated in part by cholinergic inputs. The reduction in fEPSPs was investigated using in vitro intracellular recordings of EPSPs in Layer II neurons evoked by stimulation of Layer I afferents. Constant bath application of the muscarinic agonist carbachol depolarized membrane potential and suppressed EPSP amplitude in Layer II neurons. The suppression of EPSPs was not associated with a substantial change in input resistance, and could not be accounted for by a depolarization-induced reduction in driving force on the EPSP. The GABA(A) receptor-blocker bicuculline (50 microM) did not prevent the cholinergic suppression of EPSPs, suggesting that the suppression is not dependent on inhibitory mechanisms. Paired-pulse facilitation of field and intracellular EPSPs were enhanced by carbachol, indicating that the suppression is likely due to inhibition of presynaptic glutamate release. These results indicate that, in addition to well known effects on postsynaptic conductances that increase cellular excitability, cholinergic activation in the entorhinal cortex results in a strong reduction in strength of excitatory synaptic inputs from the piriform cortex.
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Affiliation(s)
- Bassam N Hamam
- Department of Psychology, Concordia University, Montréal, Québec, Canada
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24
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Marrone DF. Ultrastructural plasticity associated with hippocampal-dependent learning: A meta-analysis. Neurobiol Learn Mem 2007; 87:361-71. [PMID: 17174119 DOI: 10.1016/j.nlm.2006.10.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2006] [Revised: 10/01/2006] [Accepted: 10/02/2006] [Indexed: 11/24/2022]
Abstract
In order to develop a profile of how individual synapses in the hippocampal formation alter their structure following learning experience, a meta-analysis synthesized the available literature on morphological change following hippocampal-dependent learning. Analysis of the 132 calculated effect sizes suggest a consistent profile of morphological change in the hippocampus following learning experience. Across the hippocampal formation, dendritic complexity, spine density, and the size of perforated postsynaptic densities showed consistent increases following training. Both the density of synapses in general and perforated synapses in particular showed unique responses to training, depending on the duration of training and/or different cell layers of the hippocampal formation. Most importantly, it seems that this profile, while consistent, is small and specific--only a select few of the morphological parameters typically measured in anatomical studies of plasticity showed significant change following training. Collectively, these data suggest that the distinct electrophysiological properties of neocortical versus hippocampal synapses may be at least partially mediated by distinct morphological cascades. That is, on the basis of theory, and with the support of the current data, it seems that synaptogenesis correlates with enduring neocortical plasticity, while structural changes correlate with more transient hippocampal plasticity. To be able to state these conclusions with conviction, however, more data are needed in several key areas for continued pursuit of the morphological correlates of hippocampal-dependent learning.
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Affiliation(s)
- Diano F Marrone
- Department of Psychology, University of Toronto, 1265 Military Trail, Toronto, Ont., Canada.
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25
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Gipson KE, Yeckel MF. Coincident glutamatergic and cholinergic inputs transiently depress glutamate release at rat schaffer collateral synapses. J Neurophysiol 2007; 97:4108-19. [PMID: 17303811 PMCID: PMC2878610 DOI: 10.1152/jn.01051.2006] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The mammalian hippocampus, together with subcortical and cortical areas, is responsible for some forms of learning and memory. Proper hippocampal function depends on the highly dynamic nature of its circuitry, including the ability of synapses to change their strength for brief to long periods of time. In this study, we focused on a transient depression of glutamatergic synaptic transmission at Schaffer collateral synapses in acute hippocampal slices. The depression of evoked excitatory postsynaptic current (EPSC) amplitudes, herein called transient depression, follows brief trains of synaptic stimulation in stratum radiatum of CA1 and lasts for 2-3 min. Depression results from a decrease in presynaptic glutamate release, as NMDA-receptor-mediated EPSCs and composite EPSCs are depressed similarly and depression is accompanied by an increase in the paired-pulse ratio. Transient depression is prevented by blockade of metabotropic glutamate and acetylcholine receptors, presumably located presynaptically. These two receptor types--acting together--cause depression. Blockade of a single receptor type necessitates significantly stronger conditioning trains for triggering depression. Addition of an acetylcholinesterase inhibitor enables depression from previously insufficient conditioning trains. Furthermore, a strong coincident, but not causal, relationship existed between presynaptic depression and postsynaptic internal Ca(2+) release, emphasizing the potential importance of functional interactions between presynaptic and postsynaptic effects of convergent cholinergic and glutamatergic inputs to CA1. These convergent afferents, one intrinsic to the hippocampus and the other likely originating in the medial septum, may regulate CA1 network activity, the induction of long-term synaptic plasticity, and ultimately hippocampal function.
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Affiliation(s)
- Keith E Gipson
- Department of Neurobiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06510, USA
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26
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Derrick BE. Plastic processes in the dentate gyrus: a computational perspective. PROGRESS IN BRAIN RESEARCH 2007; 163:417-51. [PMID: 17765732 DOI: 10.1016/s0079-6123(07)63024-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The dentate gyrus has the capacity for numerous types of synaptic plasticity that use diverse mechanisms and are thought essential for the storage of information in the hippocampus. Here we review the various forms of synaptic plasticity that involve afferents and efferents of the dentate gyrus, and, from a computational perspective, relate how these plastic processes might contribute to sparse, orthogonal encoding, and the selective recall of information within the hippocampus.
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Affiliation(s)
- Brian E Derrick
- Department of Biology, The Cajal Neuroscience Research Institute, The University of Texas at San Antonio, TX 78249-0662, USA.
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27
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Kim MT, Soussou W, Gholmieh G, Ahuja A, Tanguay A, Berger TW, Brinton RD. 17beta-Estradiol potentiates field excitatory postsynaptic potentials within each subfield of the hippocampus with greatest potentiation of the associational/commissural afferents of CA3. Neuroscience 2006; 141:391-406. [PMID: 16725270 DOI: 10.1016/j.neuroscience.2006.03.075] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2005] [Revised: 03/22/2006] [Accepted: 03/26/2006] [Indexed: 11/26/2022]
Abstract
We sought to determine the impact of 17beta-estradiol throughout the hippocampal trisynaptic pathway and to investigate the afferent fiber systems within CA1 and CA3 in detail. To achieve this objective, we utilized multielectrode arrays to simultaneously record the field excitatory postsynaptic potentials from the CA1, dentate gyrus, and CA3 of rat hippocampal slices in the presence or absence of 100 pM 17beta-estradiol. We confirmed our earlier findings in CA1, where 17beta-estradiol significantly increased field excitatory postsynaptic potentials amplitude (20%+/-3%) and slope (22%+/-7%). 17beta-Estradiol significantly potentiated the field excitatory postsynaptic potentials in dentate gyrus, amplitude (15%+/-4%) and slope (17%+/-5), and in CA3, amplitude (15%+/-4%) and slope (19%+/-5%). Using a high-density multielectrode array, we sought to determine the source of potentiation in CA1 and CA3 by determining the impact of 17beta-estradiol on the apical afferents and the basal afferents within CA1 and on the mossy fibers and the associational/commissural fibers within CA3. In CA1, 17beta-estradiol induced a modest increase in the amplitude (7%+/-2%) and slope (9%+/-3%) following apical stimulation with similar magnitude of increase following basal stimulation amplitude (10%+/-2%) and slope (12%+/-3%). In CA3, 17beta-estradiol augmented the mossy fiber amplitude (15%+/-3%) and slope (18%+/-6%) and the associational/commissural fiber amplitude (31%+/-13%) and slope (40%+/-15%). These results indicate that 17beta-estradiol potentiated synaptic transmission in each subfield of the hippocampal slice, with the greatest magnitude of potentiation at the associational/commissural fibers in CA3. 17beta-Estradiol regulation of CA3 responses provides a novel site of 17beta-estradiol action that corresponds to the density of estrogen receptors within the hippocampus. The implications of 17beta-estradiol potentiation of the field potential in each of the hippocampal subfields and in particular CA3 associational/commissural fibers for memory function and clinical assessment are discussed.
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Affiliation(s)
- M T Kim
- Neuroscience Program, University of Southern California, Los Angeles, CA 90089-2520, USA
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28
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Zhong WX, Dong ZF, Tian M, Cao J, Xu L, Luo JH. N-methyl-d-aspartate receptor-dependent long-term potentiation in CA1 region affects synaptic expression of glutamate receptor subunits and associated proteins in the whole hippocampus. Neuroscience 2006; 141:1399-413. [PMID: 16766131 DOI: 10.1016/j.neuroscience.2006.04.070] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2006] [Revised: 03/12/2006] [Accepted: 04/28/2006] [Indexed: 11/29/2022]
Abstract
Long term potentiation in hippocampus, evoked by high-frequency stimulation, is mediated by two major glutamate receptor subtypes, alpha-amino-3-hydroxyl-5-methyl-4-isoxazole propionate receptors and N-methyl-D-aspartate receptors. Receptor subunit composition and its interaction with cytoplasmic proteins constitute different pathways regulating synaptic plasticity. Here, we provide further evidence that N-methyl-D-aspartate receptor-mediated long term potentiation evoked at hippocampal CA1 region of rats induced by high-frequency stimulation of the Schaffer collateral-commissural pathway in vivo is not dependent on N-methyl-D-aspartate receptor subunit NR2B. Applying semi-quantitative immunoblotting, we found that in the whole tetanized hippocampus, synaptic expression of the N-methyl-D-aspartate and alpha-amino-3-hydroxyl-5-methyl-4-isoxazole propionate receptor subunits (NR1, NR2A, glutamate receptor 1) and their associated partners, e.g. synaptic associated protein 97, postsynaptic density protein 95, alpha subunit of Ca2+/calmodulin-dependent protein kinase II, neuronal nitricoxide synthase, increased 180 min post-high-frequency stimulation. Moreover, phosphorylation of Ca2+/calmodulin-dependent protein kinase II at thr286 and glutamate receptor 1 at ser831 was increased 30 min post-high-frequency stimulation and blocked by N-methyl-D-aspartate receptor antagonists (AP-5 and MK-801). In sham group and controls, these changes were not observed. The expression of several other synaptic proteins (NR2B, glutamate receptors 2/3, N-ethylmaleimide sensitive factor) was not affected by long term potentiation induction. In hippocampal homogenates, the level of these proteins remained unchanged. These data indicate that N-methyl-D-aspartate receptor-dependent long term potentiation in CA1 region in vivo mainly affects the synaptic expression of glutamate receptor subunits and associated proteins in the whole hippocampus. The alteration of molecular aspects can play a role in regulating the long-lasting synaptic modification in hippocampal long term potentiation in vivo.
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Affiliation(s)
- W X Zhong
- Department of Neurobiology, Zhejiang University School of Medicine, 353 Yanan Road, Hangzhou 310006, PR China
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29
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Kim M, Yu ZX, Fredholm BB, Rivkees SA. Susceptibility of the developing brain to acute hypoglycemia involving A1 adenosine receptor activation. Am J Physiol Endocrinol Metab 2005; 289:E562-9. [PMID: 16150954 DOI: 10.1152/ajpendo.00112.2005] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It has been suggested that the developing brain is less vulnerable to the adverse effects of hypoglycemia than the mature brain; however, this issue remains controversial. We also do not know the magnitude or duration of hypoglycemia needed to trigger hypoglycemic brain injury during development. To address this issue a series of in vivo and in vitro studies were performed. First, we established an acute model of insulin-induced hypoglycemia in mice by administering 3 U/kg of neutral-protamine Hagadorn insulin subcutaneously. When we examined degenerating neurons in hippocampus and striatum by TUNEL labeling, injury was observed after 4 h of hypoglycemia in postnatal day (P)7 mice, and we observed more cell injury in animals rendered hypoglycemic at P7 than at P21. Studies of hippocampal slice cultures revealed that reduction in glucose concentration induced more neuronal injury in slices prepared from P3 and P7 than from P14 and P21 mice. Treatment of slices with an adenosine A(1) receptor (A(1)AR) antagonist reduced the hypoglycemic damage, whereas agonists increased damage, particularly in slices prepared from very young pups. This suggests a critically important role for A(1)ARs, which was further demonstrated by the reduction of hypoglycemic damage in hippocampal slices prepared from A(1)AR(-/-) mice. Furthermore, insulin-induced hypoglycemia in P7 A(1)AR(-/-) mice did not increase TUNEL-positive cells, but a major increase was seen in A(1)AR(+/-) mice. These observations show that the developing nervous system is indeed sensitive to acute hypoglycemic injury and that A(1)AR activation contributes to damage induced by hypoglycemia, particularly in immature mouse brain.
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Affiliation(s)
- Mina Kim
- Section of Developmental Endocrinology and Biology, Yale Child Health Research Center, New Haven, CT 06520, USA
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30
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Safiulina VF, Kas'yanov AM, Markevich VA, Bogdanova OG, Dvorzhak AY, Zosimovskii VA, Ezrokhi VL. Studies of the synaptic plasticity of field CA3 of the hippocampus during tetanization of the perforant path. NEUROSCIENCE AND BEHAVIORAL PHYSIOLOGY 2005; 35:693-8. [PMID: 16433064 DOI: 10.1007/s11055-005-0112-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Studies on living slices of hippocampus-entorhinal cortex formation from adult rats were performed to investigate changes in responses in field CA3 to stimulation of mossy fibers in conditions of perforant path tetanization with different parameters. Tetanization of the perforant path at frequencies of 10 and 100 Hz induced depression of responses in CA3 on testing of this same path. Tetanization of the perforant path at a frequency of 10 Hz and an amplitude subthreshold for potentiating mossy fiber synapses in CA3 became threshold if preceded by tetanization of the perforant path at a frequency of 100 Hz. Tetanization of mossy fibers at 10 Hz resulted in potentiation of the input to CA3, while tetanization at 100 Hz induced depression. High-frequency tetanization of the perforant path (100 Hz) delivered in trains following at the frequency of the theta rhythm, led mainly to depression of field CA3 responses to stimulation of mossy fibers.
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Affiliation(s)
- V F Safiulina
- Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences, Moscow
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31
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Leung LS, Canning KJ, Shen B. Hippocampal afterdischarges after GABA(B)-receptor blockade in the freely moving rat. Epilepsia 2005; 46:203-16. [PMID: 15679501 DOI: 10.1111/j.0013-9580.2005.35804.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
PURPOSE To determine whether hippocampal afterdischarges (ADs) and excitability changes were induced by gamma-aminobutyric acid (GABA)(B)-receptor blockade in adult, freely moving rats. METHODS A specific GABA(B)-receptor antagonist CGP35348, CGP55845A, or CGP55699A was injected intracerebroventricularly (i.c.v.), and EEGs and behaviors of rats were analyzed. RESULTS CGP35348 (56-110 microg, i.c.v.) induced afterdischarges (ADs) approximately 60% of the time, starting at the hippocampus or neocortex. Neocortical-onset ADs began with sporadic discharges and were <3 mV. Hippocampal-onset ADs were bilateral, >5 mV, and spread to the entorhinal cortex and amygdala, often ending in a rebound AD and accompanied with stereotypic jumping, forelimb clonus, and wet-dog shakes. The CGP35348-induced hippocampal AD had an onset frequency (5-9 Hz) that was higher than the electrically evoked AD (2-4 Hz). CGP35348 i.c.v. also increased the mean starting frequency of an electrically evoked hippocampal AD from 3.6 Hz to 5.3 Hz. Hippocampal gamma activity (25-80 Hz) increased up to twofold for 30 min after a hippocampal but not a neocortical AD. A single dose of CGP35348 induced repeated ADs of increasing duration. Paired-pulse inhibition of the evoked potentials in CA1, at interpulse interval of <100 ms, was decreased after but not before a hippocampal AD. CGP56999A (i.c.v.) gave results similar to those with CGP35348, whereas CGP55845A (i.c.v.) rarely induced ADs. CONCLUSIONS GABA(B)-receptor blockade increases seizure susceptibility by reducing AD threshold and increasing the frequency and spread of a hippocampal AD. Hippocampal excitability (based on paired-pulse test) and gamma activity increased after but not before a hippocampal AD.
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Affiliation(s)
- L Stan Leung
- Department of Physiology-Pharmacology, University of Western Ontario, London, Ontario, Canada.
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32
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Prendergast MA, Harris BR, Mullholland PJ, Blanchard JA, Gibson DA, Holley RC, Littleton JM. Hippocampal CA1 region neurodegeneration produced by ethanol withdrawal requires activation of intrinsic polysynaptic hippocampal pathways and function of N-methyl-D-aspartate receptors. Neuroscience 2004; 124:869-77. [PMID: 15026127 DOI: 10.1016/j.neuroscience.2003.12.013] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/10/2003] [Indexed: 10/26/2022]
Abstract
Long-term intake of ethanol produces adaptive alterations in multiple transmitter systems in the hippocampal formation that likely contribute to ethanol withdrawal-induced seizure and excitotoxicity. The present studies were designed to examine the role of N-methyl-d-aspartate receptor activation and cytosolic Ca(2+) accumulation in the neurotoxic effects of ethanol withdrawal. Further, these studies investigated the role of hippocampal network excitation in promoting both Ca(2+) accumulation and neurotoxicity during ethanol withdrawal. Chronic, continuous (11 day) exposure to ethanol (91 mM starting concentration) did not produce neurotoxicity in any region of organotypic hippocampal explants, as measured by uptake of the non-vital fluorescent marker propidium iodide. Withdrawal from chronic (10 day) ethanol exposure was associated with rapid (30 min) and significant increases in intracellular Ca(2+), assessed by visualization of Calcium-Orange fluorescence, in each region of hippocampal explants. However, neurotoxicity was observed 24 h after initiation of withdrawal and was only seen in the cornu ammonis 1 (CA1) region. Exposure to MK-801 (20 microM) at the start of ethanol withdrawal markedly attenuated Ca(2+) entry in all regions, as well as, CA1 region neurodegeneration. Further, treatment of explants with tetrodotoxin (500 nM) as well as surgical transection of mossy fiber or Schaffer collateral projections immediately prior to ethanol withdrawal blocked both regional increases in Ca(2+) accumulation and CA1 neurotoxicity. These data suggest that neurodegeneration observed during ethanol withdrawal is dependent upon polysynaptic propagation of action potentials ("network excitation") and whole-hippocampal excitation of glutamatergic systems.
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Affiliation(s)
- M A Prendergast
- Department of Psychology, University of Kentucky, 115 Kastle Hall, Lexington, KY 40506-0044, USA.
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33
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Dieguez D, Barea-Rodriguez EJ. Aging impairs the late phase of long-term potentiation at the medial perforant path-CA3 synapse in awake rats. Synapse 2004; 52:53-61. [PMID: 14755632 PMCID: PMC1913478 DOI: 10.1002/syn.20004] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The effects of aging on long-term potentiation (LTP) in the dentate gyrus (DG) and CA1 are well documented, but LTP at the medial perforant path (MPP)-CA3 synapse of aged animals has remained unexplored. Because the MPP-DG and Schaffer-collateral-CA1 synapses account for only about 20% of total hippocampal synapses, global understanding of how aging affects hippocampal plasticity has remained limited. Much is known about LTP induction in the hippocampal formation, whereas the mechanisms that regulate LTP maintenance are less understood, especially during aging. We investigated the effects of aging on MPP-CA3 LTP induction and maintenance in awake rats. As is the case in the DG and CA1, high-frequency stimulation-induced LTP at the MPP-CA3 synapse is normal in aged rats. These data indicate that N-methyl-D-aspartate (NMDA) receptor-mediated processes are intact at the MPP-CA3 synapse in aged rats. In contrast, aging impaired the magnitude and duration of MPP-CA3 LTP over a period of days. Also, these data are consistent with reports that area CA3 is especially susceptible to age-related changes. Our data suggest that aging impairs mechanisms that regulate the late phase of MPP-CA3 LTP and contribute to a more global understanding of how aging affects hippocampal plasticity.
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Affiliation(s)
- Dario Dieguez
- Neurobiology of Aging Laboratory, Department of Biology, The University of Texas, San Antonio, Texas 78249-0662
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34
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Yorns WR, Blaise JH, Bronzino JD. Frequency-dependent changes in the paired-pulse index in the hippocampus of the freely moving adult male rat. Exp Neurol 2004; 186:104-8. [PMID: 14980815 DOI: 10.1016/j.expneurol.2003.09.022] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2002] [Revised: 06/16/2003] [Accepted: 09/25/2003] [Indexed: 10/26/2022]
Abstract
The paired-pulse index (PPI) has been widely used as a measure of modulation of cellular excitability in the hippocampal trisynaptic circuit. This paper presents a quantification of the changes in this measure of neuronal modulation as a result of the application of pulse trains having six different train frequencies (0.1, 1, 5, 8, 15, and 30 Hz) to one of the major efferent pathways to the dentate gyrus, the medial perforant path (MPP). Our findings indicate that the modulation of the first leg of the hippocampal trisynaptic circuit is dependent on the frequency of the "burst train" applied to the perforant pathway. This methodological finding is of importance to all investigators studying hippocampal plasticity via LTP or LTD approaches. The different synaptic mechanisms implicated in being responsible for the changes in the PPI are also discussed.
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Affiliation(s)
- W R Yorns
- Department of Engineering, Trinity College, Hartford, CT 006106-3100, USA.
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35
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Lee I, Kesner RP. Encoding versus retrieval of spatial memory: Double dissociation between the dentate gyrus and the perforant path inputs into CA3 in the dorsal hippocampus. Hippocampus 2004; 14:66-76. [PMID: 15058484 DOI: 10.1002/hipo.10167] [Citation(s) in RCA: 183] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The hippocampus is an essential neural structure for spatial memory. Computational models suggest that the CA3 subregion of the hippocampus plays an essential role in encoding and retrieval of spatial memory. The perforant path (PPCA3) and dentate gyrus (DG)-mediated mossy fibers (MFs) compose major afferent inputs into CA3. A possible functional dissociation between these afferent inputs was attempted using a simple navigation test (i.e., the modified Hebb-Williams maze). Behavioral testing was combined with electrolytic lesions of PPCA3 or neurotoxic lesions of the DG, to eliminate each afferent input into CA3. Lesions in either afferent input into CA3 affected learning of an effective navigational path on the maze. The contributions of the two CA3 afferent inputs, however, were different regarding encoding and retrieval of memory measured based on indices operationally defined for the behavioral paradigm (i.e., encoding, the number of errors reduced within a day; retrieval, the number of errors reduced between days). The DG-lesioned animals exhibited deficits regarding the encoding index, but not the retrieval index, whereas the PPCA3-lesioned rats displayed deficits regarding the retrieval index, but not the encoding index. The results suggest that the two major afferent inputs of CA3 may contribute differentially to encoding and retrieval of spatial memory.
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Affiliation(s)
- Inah Lee
- Department of Neurobiology and Anatomy, University of Texas Houston Medical School, Houston, Texas, USA
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36
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O'Boyle MP, Do V, Derrick BE, Claiborne BJ. In vivo recordings of long-term potentiation and long-term depression in the dentate gyrus of the neonatal rat. J Neurophysiol 2003; 91:613-22. [PMID: 14645375 DOI: 10.1152/jn.00307.2003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Previous in vitro studies demonstrated that long-term potentiation (LTP) could be elicited at medial perforant path (MPP) synapses onto hippocampal granule cells in slices from 7-day-old rats. In contrast, in vivo studies suggested that LTP at perforant path synapses could not be induced until at least days 9 or 10 and then in only a small percentage of animals. Because several characteristics of the oldest granule cells are adult-like on day 7, we re-examined the possibility of eliciting LTP in 7-day-old rats in vivo. We also recorded from 8- and 9-day-old rats to further elucidate the occurrence and magnitude of LTP in neonates. With halothane anesthesia, all animals in each age group exhibited synaptic plasticity of the excitatory postsynaptic potential following high-frequency stimulation of the MPP. In 7-day-old rats, LTP was elicited in 40% of the animals and had an average magnitude of 143%. Long-term depression (LTD) alone (magnitude of 84%) was induced in 40% of the animals, while short-term potentiation (STP) alone (magnitude of 123%) was induced in 10%. STP followed by LTD was elicited in the remaining 10%. Data were similar for all ages combined. In addition, the N-methyl-d-aspartate (NMDA) antagonist (R,S)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) blocked the occurrence of LTP at each age and doubled the percentage of animals expressing LTD alone for all ages combined. These results demonstrate that tetanic stimulation can elicit LTP or LTD at MPP synapses in 7-day-old rats, supporting our premise that at least a portion of the dentate gyrus is functional at this early age.
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Affiliation(s)
- Michael P O'Boyle
- Department of Biology, The University of Texas at San Antonio, San Antonio, Texas 78249, USA
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37
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Huang CC, You JL, Lee CC, Hsu KS. Insulin induces a novel form of postsynaptic mossy fiber long-term depression in the hippocampus. Mol Cell Neurosci 2003; 24:831-41. [PMID: 14664829 DOI: 10.1016/s1044-7431(03)00238-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The mechanisms of induction and the site of expression of long-term depression (LTD) at the hippocampal mossy fiber-CA3 synapses are not clear. Here, we show that a brief bath application of insulin induces a novel form of mossy fiber LTD. This insulin-LTD is (1) induced and expressed postsynaptically, (2) entirely independent of synaptic stimulation during insulin application, (3) involving a rise in postsynaptic [Ca(2+)](i) and L-type voltage-activated Ca(2+) channel activation, (4) mechanistically distinct from low-frequency stimulation-induced LTD, (5) dependent on phosphatidylinositol 3-kinase signaling, and (6) associated with a clathrin-mediated endocytotic removal of surface 3-hydroxy-5-methylisoxazole-4-propionic acid receptors from the postsynaptic neurons. Moreover, insulin-LTD is specific to mossy fibers to CA3 pyramidal cell synapses, and is not present at associational commissural synapses. These findings not only support a postsynaptic locus of mossy fiber LTD, but also provide a further link between the AMPA receptor trafficking and the bidirectional expression of long-term synaptic plasticity.
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Affiliation(s)
- Chiung-Chun Huang
- Department of Pharmacology, College of Medicine, National Cheng Kung University, Tainan City 701, Taiwan
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38
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Mulholland PJ, Prendergast MA. Transection of intrinsic polysynaptic pathways reduces N-methyl-D-aspartate neurotoxicity in hippocampal slice cultures. Neurosci Res 2003; 46:369-76. [PMID: 12804798 DOI: 10.1016/s0168-0102(03)00102-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Hippocampal CA1 neurons have been shown to be highly susceptible to excitotoxicity produced by various forms of insult. CA1 neurotoxicity is partly dependent on over activity of N-methyl-D-aspartate (NMDA) receptors. It is unclear, however, if sensitivity of this region to excitotoxicity is related to inherent properties of CA1 neurons and/or network activation of polysynaptic pathways. The present studies examined the role of mossy fiber and Schaffer collateral function in promoting NMDA-induced neurodegeneration. Organotypic hippocampal cultures were subjected to transection of mossy fibers, Schaffer collaterals, or CA1 efferent fibers and then exposed to NMDA (20 microM) for 1 h. Hippocampal damage was assessed 24 h later via fluorescent microscopy. NMDA exposure produced significant excitotoxicity in all regions (160-500% of control), particularly in the CA1. In each region, toxicity was reduced by co-exposure to NMDA with MK-801 (20 microM), to near-control levels. Surgical transection of mossy fibers and Schaffer collaterals significantly reduced NMDA-induced neurotoxicity in the CA1 ( approximately 20%), and to a lesser extent, the CA3 and dentate regions. Conversely, transection of CA1 efferent fibers did not reduce the neurotoxicity in these regions. These data indicate that CA1 neurotoxicity caused by excitotoxic insult depends, in part, on 'network activation' of intrinsic polysynaptic pathways.
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Affiliation(s)
- Patrick J Mulholland
- Department of Psychology, University of Kentucky, 115 Kastle Hall, Lexington, KY 40506-0044, USA
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39
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40
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Wu K, Leung LS. Increased dendritic excitability in hippocampal ca1 in vivo in the kainic acid model of temporal lobe epilepsy: a study using current source density analysis. Neuroscience 2003; 116:599-616. [PMID: 12559115 DOI: 10.1016/s0306-4522(02)00567-5] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We used kainic acid in rats as an animal model of temporal lobe epilepsy, and studied the synaptic transmission in hippocampal subfield CA1 of urethane-anesthetized rats in vivo. Dendritic currents were revealed by field potential mapping, using a single micropipette or a 16-channel silicon probe, followed by current source density analysis. We found that the population excitatory postsynaptic potentials in the basal dendrites and distal apical dendrites of CA1 were increased in kainate-treated as compared with control rats following paired-pulse, but not single-pulse, stimulation of CA3b or medial perforant path. In contrast, the trisynaptic midapical dendritic response in CA1 following medial perforant path stimulation was decreased in kainate-treated as compared with control rats. Increased coupling between excitatory postsynaptic potential and the population spike in CA1 was found after kainate seizures. Short-latency, presumably monosynaptic CA1 population spikes following medial perforant path stimulation was found in kainate-treated but not control rats. An enhancement of dendritic excitability was evidenced by population spikes that invaded into or originated from the distal apical dendrites of CA1 in kainate-treated but not control rats. Reverberation of hippocampo-entorhinal activity was evidenced by recurrent excitation of CA1 following CA3b stimulation in kainate-treated but not control rats. Blockade of inhibition by intraventricularly administered bicuculline induced excitatory potentials in CA1 that were stronger and more prolonged in kainate-treated than control rats. The bicuculline-induced excitation was mainly blocked by non-N-methyl-D-aspartate receptor antagonists. We conclude that kainate seizures induced disinhibition in CA1 that unveiled excitation at the basal and distal apical dendrites, resulting in enhancement of the direct entorhinal cortex to CA1 input and reverberations via the hippocampo-entorhinal loop. These changes in the output of the hippocampus from CA1 are likely detrimental to the behavioral functions of the hippocampus and they may contribute to increased seizure susceptibility after kainate seizures.
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Affiliation(s)
- K Wu
- Department of Clinical Neurological Sciences, University of Western Ontario, London, ON, Canada N6A 5A5
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41
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von Bohlen und Halbach O, Albrecht D. Reciprocal connections of the hippocampal area CA1, the lateral nucleus of the amygdala and cortical areas in a combined horizontal slice preparation. Neurosci Res 2002; 44:91-100. [PMID: 12204297 DOI: 10.1016/s0168-0102(02)00092-5] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The entorhinal and perirhinal cortices, the hippocampus and the amygdala are heavily interconnected limbic structures that are implicated in memory, and under pathological conditions, in seizure generation and propagation of temporal lobe epilepsy. In-vitro coronal preparations have been limited by the anatomical disposition of these structures. Here we describe a modified horizontal slice preparation that includes all these structures in the same plane. To evaluate whether axonal connectivities are preserved, fluorescent tracers were used. Most of the connections known from in-vivo studies within and between the entorhinal and perirhinal cortices, the amygdala (basolateral nucleus, lateral nucleus, and amygdalopiriform transition area) and the hippocampus were preserved in the 400 microm-thick horizontal slices employed.
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Affiliation(s)
- Oliver von Bohlen und Halbach
- Interdisciplinary Center for Neurosciences, Institute of Anatomy, Ruprecht-Karls University Heidelberg, Im Neuenheimer Feld 307, D-69120 Heidelberg, Germany
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42
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Krichmar JL, Nasuto SJ, Scorcioni R, Washington SD, Ascoli GA. Effects of dendritic morphology on CA3 pyramidal cell electrophysiology: a simulation study. Brain Res 2002; 941:11-28. [PMID: 12031543 DOI: 10.1016/s0006-8993(02)02488-5] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We investigated the effect of morphological differences on neuronal firing behavior within the hippocampal CA3 pyramidal cell family by using three-dimensional reconstructions of dendritic morphology in computational simulations of electrophysiology. In this paper, we report for the first time that differences in dendritic structure within the same morphological class can have a dramatic influence on the firing rate and firing mode (spiking versus bursting and type of bursting). Our method consisted of converting morphological measurements from three-dimensional neuroanatomical data of CA3 pyramidal cells into a computational simulator format. In the simulation, active channels were distributed evenly across the cells so that the electrophysiological differences observed in the neurons would only be due to morphological differences. We found that differences in the size of the dendritic tree of CA3 pyramidal cells had a significant qualitative and quantitative effect on the electrophysiological response. Cells with larger dendritic trees: (1) had a lower burst rate, but a higher spike rate within a burst, (2) had higher thresholds for transitions from quiescent to bursting and from bursting to regular spiking and (3) tended to burst with a plateau. Dendritic tree size alone did not account for all the differences in electrophysiological responses. Differences in apical branching, such as the distribution of branch points and terminations per branch order, appear to effect the duration of a burst. These results highlight the importance of considering the contribution of morphology in electrophysiological and simulation studies.
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Affiliation(s)
- Jeffrey L Krichmar
- Krasnow Institute for Advanced Study at George Mason University, MS 2A1, Fairfax, VA 22030, USA.
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43
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Krug M, Brödemann R, Wagner M. Simultaneous activation and opioid modulation of long-term potentiation in the dentate gyrus and the hippocampal CA3 region after stimulation of the perforant pathway in freely moving rats. Brain Res 2001; 913:68-77. [PMID: 11532248 DOI: 10.1016/s0006-8993(01)02401-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Recent investigations indicate monosynaptic activation by the perforant pathway (pp) of the dentate gyrus and the CA3 region. While short-term potentiation and long-term potentiation (LTP) and its opioid modulation are frequently described for the dentate gyrus, data for the CA3 region are rare. Therefore, evoked potentials and opioid modulation of LTP were directly compared in both target regions of the pp. Male Wistar rats were chronically implanted with a bipolar stimulation electrode in the pp (angular bundle) and two recording electrodes in the dorsal dentate gyrus and the CA3 region. Stimulation of the pp in the freely behaving animals induced short-latency evoked potentials in both target structures which were compared with respect to waveform, latency, amplitude and signs of short- and long-term neuronal plasticity. The short-latency potential in the CA3 region seemed to be a monosynaptic potential which displayed LTP sensitive to the N-methyl-D-aspartate receptor antagonist, MK 801, and depotentiating stimulation. After application of specific opioid antagonists at the mu-, delta- and kappa-opioid receptor subtypes, naloxone, funaltrexamine, naltrindole and binaltorphimine, different effects on induction and maintenance of LTP of the population spike were found both within the dentate gyrus and between the dentate gyrus and the CA3 region. The results show marked diminution of LTP in the dentate gyrus only for naloxone and naltrindole and only small, if any, effects of naloxone on LTP in the CA3 region. Thus, neuronal plasticity in the direct perforant pathway input to the CA3 region seems not to be under such substantial opioidergic control. LTP would be inducible in that region even when LTP in the input formation, the dentate gyrus, and transsynaptic LTP via the mossy fibres are blocked.
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Affiliation(s)
- M Krug
- Institute of Pharmacology and Toxicology, Medical Faculty, Otto-von-Guericke-University, Leipziger Strasse 44, 39120 Magdeburg, Germany
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44
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Krug M, Brödemann R, Matthies R, Rüthrich H, Wagner M. Activation of the dentate gyrus by stimulation of the contralateral perforant pathway: evoked potentials and long-term potentiation after ipsi- and contralateral induction. Hippocampus 2001; 11:157-67. [PMID: 11345122 DOI: 10.1002/hipo.1033] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Rats were chronically implanted with stimulation electrodes in the perforant pathway (pp) bilaterally and a recording electrode in the dentate gyrus (DG) unilaterally. Evoked field potentials (EPs) were recorded upon alternating stimulation of the pp on both sides, and long-term potentiation (LTP) was induced. Besides the EP after ipsilateral stimulation, an EP with a latency of approximately 5.5-6.5 ms was also seen upon stimulation of the contralateral pp. This potential was reversibly abolished during pentobarbital anesthesia and irreversibly after lesioning of the ipsilateral angular bundle. Paired-pulse facilitation and paired-pulse depression, depending on interstimulus interval and intensity, were also observed. Therefore, this long-latency potential could be characterized as polysynaptic and induced perhaps by transsynaptic activation via the ipsilateral entorhinal cortex. Ipsilateral tetanization induced strong E/S potentiation of both the ipsilaterally and contralaterally evoked EP, but with different time courses. Tetanization of the contralateral pp did not induce LTP of the ipsilaterally induced EP in the first 4 h. But afterwards a late and slowly developing potentiation occurred. The contralaterally induced EP also showed potentiation of the population spike, which was not immediately detectable but developed slowly over time. The results can be interpreted such that, after stimulation of the pp, the DG on the opposite side cannot only be activated via the weak crossed entorhinal projection but also transsynaptically via an entorhino/entorhinal connection.
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Affiliation(s)
- M Krug
- Institute of Pharmacology and Toxicology, Medical Faculty, Otto-von-Guericke-University, Magdeburg, Germany.
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Gholmieh G, Soussou W, Courellis S, Marmarelis V, Berger T, Baudry M. A biosensor for detecting changes in cognitive processing based on nonlinear systems analysis. Biosens Bioelectron 2001; 16:491-501. [PMID: 11544043 DOI: 10.1016/s0956-5663(01)00163-4] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
A new type of biosensor, based on hippocampal slices cultured on multielectrode arrays, and using nonlinear systems analysis for the detection and classification of agents interfering with cognitive function is described. A new method for calculating first and second order kernel was applied for impulse input-spike output datasets and results are presented to show the reliability of the estimations of this parameter. We further decomposed second order kernels as a sum of nine exponentially decaying Laguerre base functions. The data indicate that the method also reliably estimates these nine parameters. Thus, the state of the system can now be described with a set of ten parameters (first order kernel plus nine coefficients of Laguerre base functions) that can be used for detection and classification purposes.
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Affiliation(s)
- G Gholmieh
- Department of Biomedical Engineering, University of Southern California, Los Angeles, CA 90089-1451, USA
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Striggow F, Riek-Burchardt M, Kiesel A, Schmidt W, Henrich-Noack P, Breder J, Krug M, Reymann KG, Reiser G. Four different types of protease-activated receptors are widely expressed in the brain and are up-regulated in hippocampus by severe ischemia. Eur J Neurosci 2001; 14:595-608. [PMID: 11556885 DOI: 10.1046/j.0953-816x.2001.01676.x] [Citation(s) in RCA: 165] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
A variety of extracellular serine proteases are expressed in the central nervous system or might permeate the blood-brain barrier under pathological conditions. However, their intracerebral targets and physiological functions are largely unknown. Here, we show that four distinct subtypes of protease-activated receptors (PARs) are abundantly expressed in the adult rat brain and in organotypic hippocampal slice cultures. PAR-1 expression was significant in the hippocampus, cortex and amygdala. Highest densities of PAR-2 and PAR-3 were observed in hippocampus, cortex, amygdala, thalamus, hypothalamus and striatum. Apart from the striatum, a similar localization was found for PAR-4. Within the hippocampal formation, each PAR subtype was predominantly localized in the pyramidal cell layers. Additionally, we identified PAR-2 in mossy fibers between dentate gyrus and CA3, PAR-3 in the subiculum and PAR-4 in CA3 and in mossy fibres as well as in the stratum lacunosum moleculare. After exposing hippocampal slice cultures to a severe experimental ischemia (oxygen-glucose deprivation), the expression of PARs 1-3 was up-regulated with subtype-specific kinetics. The localization of PARs in brain regions particularly vulnerable to ischemic insults as well as distinct alterations in the expression pattern after experimental ischemia support the notion of an important role of extracellular serine proteases and PARs in cerebral ischemia.
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Affiliation(s)
- F Striggow
- Institute for Neurobiochemistry, Otto-von-Guericke-University Magdeburg, Medical School, Leipziger Strasse 44, D-39120 Magdeburg, Germany
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Geiger JR, Jonas P. Dynamic control of presynaptic Ca(2+) inflow by fast-inactivating K(+) channels in hippocampal mossy fiber boutons. Neuron 2000; 28:927-39. [PMID: 11163277 DOI: 10.1016/s0896-6273(00)00164-1] [Citation(s) in RCA: 447] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
Analysis of presynaptic determinants of synaptic strength has been difficult at cortical synapses, mainly due to the lack of direct access to presynaptic elements. Here we report patch-clamp recordings from mossy fiber boutons (MFBs) in rat hippocampal slices. The presynaptic action potential is very short during low-frequency stimulation but is prolonged up to 3-fold during high-frequency stimulation. Voltage-gated K(+) channels in MFBs inactivate rapidly but recover from inactivation very slowly, suggesting that cumulative K(+) channel inactivation mediates activity-dependent spike broadening. Prolongation of the presynaptic voltage waveform leads to an increase in the number of Ca(2+) ions entering the terminal per action potential and to a consecutive potentiation of evoked excitatory postsynaptic currents at MFB-CA3 pyramidal cell synapses. Thus, inactivation of presynaptic K(+) channels contributes to the control of efficacy of a glutamatergic synapse in the cortex.
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Affiliation(s)
- J R Geiger
- Physiologisches Institut der Universität Freiburg, Hermann-Herder-Str. 7, D-79104, Freiburg, Germany
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Kimura A, Pavlides C. Long-term potentiation/depotentiation are accompanied by complex changes in spontaneous unit activity in the hippocampus. J Neurophysiol 2000; 84:1894-906. [PMID: 11024082 DOI: 10.1152/jn.2000.84.4.1894] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Typically, long-term potentiation (LTP) has been assessed as long-lasting changes in field potentials or intracellularly recorded postsynaptic potentials evoked by activation of a set of afferents. In the present experiment, we determined changes in spontaneous unit activity in the dentate gyrus (DG) following high-frequency (HFS) or low-frequency stimulation (LFS) of the medial perforant pathway. Experiments were performed in anesthetized rats. Field potentials and unit recordings were obtained alternatively from the same recording electrode. Of 39 single units isolated (from 25 independent sessions), the spontaneous discharges of 13 units (33%) increased, while 7 units (18%) decreased their discharges following HFS that induced significant LTP of the field potentials. Such opposing modulations of unit discharges following HFS were observed on simultaneously recorded units. LFS applied following HFS also induced bi-directional effects on unit discharges. Of 20 single units isolated from a subset of recordings (12 experiments) to which LFS was applied, 6 units increased and 4 units decreased their discharges. LFS produced a long-lasting (>20 min) depotentiation, to the baseline level, on field potentials in four recording cases. The autocorrelation functions indicated that the isolated unit discharges were comparable to those of the putative DG granule cells and interneurons, shown in previous studies. The results suggest that changes in synaptic efficacy following HFS or LFS produce rather dynamic changes in cell activity in the DG.
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Affiliation(s)
- A Kimura
- Department of Physiology, Wakayama Medical College, Wakayama 641-0012, Japan.
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Abstract
Changing the strength of connections between neurons is widely assumed to be the mechanism by which memory traces are encoded and stored in the central nervous system. In its most general form, the synaptic plasticity and memory hypothesis states that "activity-dependent synaptic plasticity is induced at appropriate synapses during memory formation and is both necessary and sufficient for the information storage underlying the type of memory mediated by the brain area in which that plasticity is observed." We outline a set of criteria by which this hypothesis can be judged and describe a range of experimental strategies used to investigate it. We review both classical and newly discovered properties of synaptic plasticity and stress the importance of the neural architecture and synaptic learning rules of the network in which it is embedded. The greater part of the article focuses on types of memory mediated by the hippocampus, amygdala, and cortex. We conclude that a wealth of data supports the notion that synaptic plasticity is necessary for learning and memory, but that little data currently supports the notion of sufficiency.
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Affiliation(s)
- S J Martin
- Department and Centre for Neuroscience, University of Edinburgh, United Kingdom.
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Davis S, Salin H, Helme-Guizon A, Dumas S, Stéphan A, Corbex M, Mallet J, Laroche S. Dysfunctional regulation of alphaCaMKII and syntaxin 1B transcription after induction of LTP in the aged rat. Eur J Neurosci 2000; 12:3276-82. [PMID: 10998111 DOI: 10.1046/j.1460-9568.2000.00193.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Syntaxin 1B and alphaCaMKII are two genes that are upregulated after the induction of LTP and appear to underlie different mechanisms of synaptic plasticity. alphaCaMKII is directly implicated in strengthening the synapses that have been modified, whereas syntaxin 1B has been implicated in a mechanism for the propagation of synaptic plasticity within neural circuits. In these experiments we have investigated whether the regulation of these genes is altered after the induction of LTP in aged rats. We found, three hours after the induction of LTP in the dentate gyrus, that aged rats could be subgrouped into those in which LTP was maintained and those in which LTP had decayed back to basal levels. Both genes were upregulated in young adult rats, whereas there was a differential pattern of LTP-induced expression in the aged rats. Dendritic alphaCaMKII was upregulated in aged rats only when LTP was maintained. In contrast, regulation of syntaxin 1B and alphaCaMKII was absent in the granule cell bodies of the aged rats regardless of whether LTP was maintained or not. These results suggest that molecular mechanisms implicated in two aspects of hippocampal synaptic plasticity malfunction during normal ageing and therefore may have some contributory role in the decline in memory function routinely observed in ageing.
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Affiliation(s)
- S Davis
- Laboratoire de Neurobiologie de l'Apprentissage, de la Mémoire et de la Communication, CNRS UMR 8620, Bât 446, Université Paris Sud, 91405 Orsay, France.
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