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Piskorowski RA, Chevaleyre V. Synaptic integration by different dendritic compartments of hippocampal CA1 and CA2 pyramidal neurons. Cell Mol Life Sci 2012; 69:75-88. [PMID: 21796451 PMCID: PMC11115016 DOI: 10.1007/s00018-011-0769-4] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2011] [Revised: 06/13/2011] [Accepted: 07/05/2011] [Indexed: 01/18/2023]
Abstract
Pyramidal neurons have a complex dendritic arbor containing tens of thousands of synapses. In order for the somatic/axonal membrane potential to reach action potential threshold, concurrent activation of multiple excitatory synapses is required. Frequently, instead of a simple algebraic summation of synaptic potentials in the soma, different dendritic compartments contribute to the integration of multiple inputs, thus endowing the neuron with a powerful computational ability. Most pyramidal neurons share common functional properties. However, different and sometimes contrasting dendritic integration rules are also observed. In this review, we focus on the dendritic integration of two neighboring pyramidal neurons in the hippocampus: the well-characterized CA1 and the much less understood CA2. The available data reveal that the dendritic integration of these neurons is markedly different even though they are targeted by common inputs at similar locations along their dendrites. This contrasting dendritic integration results in different routing of information flow and generates different corticohippocampal loops.
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Affiliation(s)
- Rebecca A. Piskorowski
- Université Paris Descartes, Sorbonne Paris Cité, IFR 95, CNRS UMR8118, Equipe ATIP, 45 rue des Saints-Pères, 75006 Paris, France
| | - Vivien Chevaleyre
- Université Paris Descartes, Sorbonne Paris Cité, IFR 95, CNRS UMR8118, Equipe ATIP, 45 rue des Saints-Pères, 75006 Paris, France
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52
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Hsiao MC, Yu PN, Song D, Liu CY, Heck CN, Millett D, Berger TW. Spatio-temporal inter-ictal activity recorded from human epileptic hippocampal slices. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2012; 2012:5166-9. [PMID: 23367092 DOI: 10.1109/embc.2012.6347157] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Epilepsy is a medical syndrome that produces seizures affecting a variety of mental and physical functions. The actual mechanisms of the onset and termination of the seizure are still unclear. While medical therapies can suppress the symptoms of seizures, 30% of patients do not respond well. Temporal lobectomy is a common surgical treatment for medically refractory epilepsy. Part of the hippocampus is removed from the patient. In this study, we have developed an in vitro epileptic model in human hippocampal slices resected from patients suffering from intractable mesial temporal lobe epilepsy. Using a planar multielectrode array system, spatio-temporal inter-ictal activity can be consistently recorded in high-potassium (8 mM), low-magnesium (0.25 mM) aCSF with additional 100 µM 4-aminopyridine. The induced inter-ictal activity can be recorded in different regions including dentate, CA1 and Subiculum. We hope the experimental model built in this study will help us understand more about seizure generation, as well as providing insights into prevention and novel therapeutics.
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Affiliation(s)
- Min-Chi Hsiao
- Department of Biomedical Engineering at University of Southern California USC, Los Angeles, CA 90089, USA.
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53
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Khalilov I, Chazal G, Chudotvorova I, Pellegrino C, Corby S, Ferrand N, Gubkina O, Nardou R, Tyzio R, Yamamoto S, Jentsch TJ, Hübner CA, Gaiarsa JL, Ben-Ari Y, Medina I. Enhanced Synaptic Activity and Epileptiform Events in the Embryonic KCC2 Deficient Hippocampus. Front Cell Neurosci 2011; 5:23. [PMID: 22065950 PMCID: PMC3206525 DOI: 10.3389/fncel.2011.00023] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Accepted: 10/13/2011] [Indexed: 11/13/2022] Open
Abstract
The neuronal potassium-chloride co-transporter 2 [indicated thereafter as KCC2 (for protein) and Kcc2 (for gene)] is thought to play an important role in the post natal excitatory to inhibitory switch of GABA actions in the rodent hippocampus. Here, by studying hippocampi of wild-type (Kcc2(+/+)) and Kcc2 deficient (Kcc2(-/-)) mouse embryos, we unexpectedly found increased spontaneous neuronal network activity at E18.5, a developmental stage when KCC2 is thought not to be functional in the hippocampus. Embryonic Kcc2(-/-) hippocampi have also an augmented synapse density and a higher frequency of spontaneous glutamatergic and GABA-ergic postsynaptic currents than naïve age matched neurons. However, intracellular chloride concentration ([Cl(-)](i)) and the reversal potential of GABA-mediated currents (E(GABA)) were similar in embryonic Kcc2(+/+) and Kcc2(-/-) CA3 neurons. In addition, KCC2 immunolabeling was cytoplasmic in the majority of neurons suggesting that the molecule is not functional as a plasma membrane chloride co-transporter. Collectively, our results show that already at an embryonic stage, KCC2 controls the formation of synapses and, when deleted, the hippocampus has a higher density of GABA-ergic and glutamatergic synapses and generates spontaneous and evoked epileptiform activities. These results may be explained either by a small population of orchestrating neurons in which KCC2 operates early as a chloride exporter or by transporter independent actions of KCC2 that are instrumental in synapse formation and networks construction.
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54
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Drexel M, Preidt AP, Kirchmair E, Sperk G. Parvalbumin interneurons and calretinin fibers arising from the thalamic nucleus reuniens degenerate in the subiculum after kainic acid-induced seizures. Neuroscience 2011; 189:316-29. [PMID: 21616128 PMCID: PMC3152681 DOI: 10.1016/j.neuroscience.2011.05.021] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2011] [Revised: 05/03/2011] [Accepted: 05/11/2011] [Indexed: 12/20/2022]
Abstract
The subiculum is the major output area of the hippocampus. It is closely interconnected with the entorhinal cortex and other parahippocampal areas. In animal models of temporal lobe epilepsy (TLE) and in TLE patients it exerts increased network excitability and may crucially contribute to the propagation of limbic seizures. Using immunohistochemistry and in situ-hybridization we now investigated neuropathological changes affecting parvalbumin and calretinin containing neurons in the subiculum and other parahippocampal areas after kainic acid-induced status epilepticus. We observed prominent losses in parvalbumin containing interneurons in the subiculum and entorhinal cortex, and in the principal cell layers of the pre- and parasubiculum. Degeneration of parvalbumin-positive neurons was associated with significant precipitation of parvalbumin-immunoreactive debris 24 h after kainic acid injection. In the subiculum the superficial portion of the pyramidal cell layer was more severely affected than its deep part. In the entorhinal cortex, the deep layers were more severely affected than the superficial ones. The decrease in number of parvalbumin-positive neurons in the subiculum and entorhinal cortex correlated with the number of spontaneous seizures subsequently experienced by the rats. The loss of parvalbumin neurons thus may contribute to the development of spontaneous seizures. On the other hand, surviving parvalbumin neurons revealed markedly increased expression of parvalbumin mRNA notably in the pyramidal cell layer of the subiculum and in all layers of the entorhinal cortex. This indicates increased activity of these neurons aiming to compensate for the partial loss of this functionally important neuron population. Furthermore, calretinin-positive fibers terminating in the molecular layer of the subiculum, in sector CA1 of the hippocampus proper and in the entorhinal cortex degenerated together with their presumed perikarya in the thalamic nucleus reuniens. In addition, a significant loss of calretinin containing interneurons was observed in the subiculum. Notably, the loss in parvalbumin positive neurons in the subiculum equaled that in human TLE. It may result in marked impairment of feed-forward inhibition of the temporo-ammonic pathway and may significantly contribute to epileptogenesis. Similarly, the loss of calretinin-positive fiber tracts originating from the nucleus reuniens thalami significantly contributes to the rearrangement of neuronal circuitries in the subiculum and entorhinal cortex during epileptogenesis.
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Affiliation(s)
- M Drexel
- Department of Pharmacology, Innsbruck Medical University, Peter-Mayr-Str. 1a, 6020 Innsbruck, Austria.
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55
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Cunningham MO, Chinnery PF. Mitochondria and cortical gamma oscillations: food for thought? Brain 2011; 134:330-2. [PMID: 21278404 DOI: 10.1093/brain/awq382] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Mark O Cunningham
- Institute of Neuroscience, The Medical School, Framlington Place, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK.
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56
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Alonso-Nanclares L, Kastanauskaite A, Rodriguez JR, Gonzalez-Soriano J, Defelipe J. A stereological study of synapse number in the epileptic human hippocampus. Front Neuroanat 2011; 5:8. [PMID: 21390290 PMCID: PMC3046382 DOI: 10.3389/fnana.2011.00008] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2010] [Accepted: 02/11/2011] [Indexed: 11/13/2022] Open
Abstract
Hippocampal sclerosis is the most frequent pathology encountered in resected mesial temporal structures from patients with intractable temporal lobe epilepsy (TLE). Here, we have used stereological methods to compare the overall density of synapses and neurons between non-sclerotic and sclerotic hippocampal tissue obtained by surgical resection from patients with TLE. Specifically, we examined the possible changes in the subiculum and CA1, regions that seem to be critical for the development and/or maintenance of seizures in these patients. We found a remarkable decrease in synaptic and neuronal density in the sclerotic CA1, and while the subiculum from the sclerotic hippocampus did not display changes in synaptic density, the neuronal density was higher. Since the subiculum from the sclerotic hippocampus displays a significant increase in neuronal density, as well as a various other neurochemical changes, we propose that the apparently normal subiculum from the sclerotic hippocampus suffers profound alterations in neuronal circuits at both the molecular and synaptic level that are likely to be critical for the development or maintenance of seizure activity.
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Affiliation(s)
- Lidia Alonso-Nanclares
- Department of Functional and Systems Neurobiology, Instituto Cajal (Consejo Superior de Investigaciones Cientificas) Madrid, Spain
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57
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Mercer A, Eastlake K, Trigg HL, Thomson AM. Local circuitry involving parvalbumin-positive basket cells in the CA2 region of the hippocampus. Hippocampus 2010; 22:43-56. [PMID: 20882544 DOI: 10.1002/hipo.20841] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/10/2010] [Indexed: 11/07/2022]
Abstract
There is a growing recognition that the CA2 region of the hippocampus has its own distinctive properties, inputs, and pathologies. The dendritic and axonal patterns of some interneurons in this region are also strikingly different from those described previously in CA1 and CA3. The local circuitry in this region, however, had yet to be studied in detail. Accordingly, using dual intracellular recordings and biocytin-filling, excitatory and inhibitory connections involving CA2 parvalbumin-positive basket cells were characterized for the first time. CA2 basket cells targeted neighboring pyramidal cells and received excitatory inputs from them. CA2 basket cells that resembled those in CA1 with a fast spiking behavior and dendritic tree confined to the region of origin received depressing excitatory postsynaptic potentials (EPSPs). In contrast, unlike CA1 basket cells but like CA1 Oriens-Lacunosum Moleculare (OLM) cells, the majority of CA2 basket cells had horizontally oriented dendrites in Stratum Oriens (SO), which extended into all three CA subfields, had an adapting firing pattern, presented a "sag" in their voltage responses to hyperpolarizing current injection, and received facilitating EPSPs. The expression of I(h) did not influence the EPSP time courses and paired pulse ratios (PPR). Estimates of the probability of release (p) for the depressing and facilitating EPSPs were correlated with the PPR. Connections with low probabilities of release had higher PPR. Quantal amplitude (q) for the facilitating connections was larger than q at depressing inputs onto fast spiking basket cells.
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Affiliation(s)
- Audrey Mercer
- Department of Pharmacology, School of Pharmacy, University of London, London WC1N 1AX, United Kingdom.
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58
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Csercsa R, Dombovári B, Fabó D, Wittner L, Eross L, Entz L, Sólyom A, Rásonyi G, Szucs A, Kelemen A, Jakus R, Juhos V, Grand L, Magony A, Halász P, Freund TF, Maglóczky Z, Cash SS, Papp L, Karmos G, Halgren E, Ulbert I. Laminar analysis of slow wave activity in humans. ACTA ACUST UNITED AC 2010; 133:2814-29. [PMID: 20656697 DOI: 10.1093/brain/awq169] [Citation(s) in RCA: 153] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Brain electrical activity is largely composed of oscillations at characteristic frequencies. These rhythms are hierarchically organized and are thought to perform important pathological and physiological functions. The slow wave is a fundamental cortical rhythm that emerges in deep non-rapid eye movement sleep. In animals, the slow wave modulates delta, theta, spindle, alpha, beta, gamma and ripple oscillations, thus orchestrating brain electrical rhythms in sleep. While slow wave activity can enhance epileptic manifestations, it is also thought to underlie essential restorative processes and facilitate the consolidation of declarative memories. Animal studies show that slow wave activity is composed of rhythmically recurring phases of widespread, increased cortical cellular and synaptic activity, referred to as active- or up-state, followed by cellular and synaptic inactivation, referred to as silent- or down-state. However, its neural mechanisms in humans are poorly understood, since the traditional intracellular techniques used in animals are inappropriate for investigating the cellular and synaptic/transmembrane events in humans. To elucidate the intracortical neuronal mechanisms of slow wave activity in humans, novel, laminar multichannel microelectrodes were chronically implanted into the cortex of patients with drug-resistant focal epilepsy undergoing cortical mapping for seizure focus localization. Intracortical laminar local field potential gradient, multiple-unit and single-unit activities were recorded during slow wave sleep, related to simultaneous electrocorticography, and analysed with current source density and spectral methods. We found that slow wave activity in humans reflects a rhythmic oscillation between widespread cortical activation and silence. Cortical activation was demonstrated as increased wideband (0.3-200 Hz) spectral power including virtually all bands of cortical oscillations, increased multiple- and single-unit activity and powerful inward transmembrane currents, mainly localized to the supragranular layers. Neuronal firing in the up-state was sparse and the average discharge rate of single cells was less than expected from animal studies. Action potentials at up-state onset were synchronized within +/-10 ms across all cortical layers, suggesting that any layer could initiate firing at up-state onset. These findings provide strong direct experimental evidence that slow wave activity in humans is characterized by hyperpolarizing currents associated with suppressed cell firing, alternating with high levels of oscillatory synaptic/transmembrane activity associated with increased cell firing. Our results emphasize the major involvement of supragranular layers in the genesis of slow wave activity.
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Affiliation(s)
- Richárd Csercsa
- Institute for Psychology, Hungarian Academy of Sciences, Budapest, Hungary
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59
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Scorza CA, Araujo BHS, Arida RM, Scorza FA, Torres LB, Amorim HA, Cavalheiro EA. Distinctive hippocampal CA2 subfield of the Amazon rodent Proechimys. Neuroscience 2010; 169:965-73. [PMID: 20547211 DOI: 10.1016/j.neuroscience.2010.05.079] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2010] [Revised: 05/10/2010] [Accepted: 05/29/2010] [Indexed: 11/29/2022]
Abstract
Previous data of our laboratory have shown that the Amazonian rodents Proechimys do not present spontaneous seizures in different models of epilepsy, suggesting endogenous inhibitory mechanisms. Here, we describe a remarkably different Proechimy's cytoarchitecture organization of the hippocampal cornu Ammonis 2 (CA2) subfield. We identified a very distinctive Proechimy's CA2 sector exhibiting disorganized cell presentation of the pyramidal layer and atypical dispersion of the pyramidal-like cells to the stratum oriens, strongly contrasting to the densely packed CA2 cells in the Wistar rats. Studies showed that CA2 is the only cornu ammonis (CA) subfield resistant to the extensive pyramidal neural loss in mesial temporal lobe epilepsy (MTLE) associated to hippocampal sclerosis. Thus, in order to investigate this region, we used Nissl and Timm staining, stereological approach to count neurons and immunohistochemistry to neuronal nuclei (NeuN), parvalbumin (PV), calbindin (CB) and calretinin (CR). We did not notice statistically significant differences in the total number of neurons of the CA2 region between Proechimys and Wistar. However, Proechimys rodents presented higher CA2 volume than Wistar rats. Furthermore, no significant difference in the optical density of parvalbumin-immunoreactivity was found between subject groups. On the other hand, Proechimys presented significant higher density of calbindin and calretinin-immunoreactivity when compared to Wistar rats. In this context, this unique CA2 subfield seen in Proechimys opens up a new set of possibilities to explore the contribution of CA2 neurons in normal and pathological brain circuits.
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Affiliation(s)
- C A Scorza
- Disciplina de Neurologia Experimental, Universidade Federal de São Paulo/Escola Paulista de Medicina, Rua Botucatu 862, 04023-900 São Paulo, Brasil.
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60
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Sprouting in human temporal lobe epilepsy: excitatory pathways and axons of interneurons. Epilepsy Res 2010; 89:52-9. [PMID: 20149961 DOI: 10.1016/j.eplepsyres.2010.01.002] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2009] [Revised: 12/11/2009] [Accepted: 01/07/2010] [Indexed: 11/22/2022]
Abstract
Changes of hippocampal GABAergic interneuronal circuits are known to play a central role in epileptogenesis. Fate of functionally different hippocampal interneuron types has been investigated in surgically removed hippocampi of therapy resistant human TLE patients. Perisomatic inhibitory cells containing parvalbumin are responsible for controlling the output of principal cells. Electron microscopic examination revealed that perisomatic innervation of the principal cells was preserved in both sclerotic and non-sclerotic samples, and the ratio of the initial segment synapses increased among the postsynaptic targets, which might give rise to an increased synchrony of granule cell firing. Calbindin-containing dendritic inhibitory cells are well preserved, and they terminate on other interneurons in larger proportion than in the control both in sclerotic and non-sclerotic cases. Substance P receptor-immunopositive cells possessed significantly larger numbers of dendritic branches in the epileptic CA1 region, and the synaptic input of their dendrites has notably increased, whereas the ratio of inhibitory and excitatory synaptic inputs has not changed. Our results suggest that an intense synaptic reorganization takes place in the epileptic hippocampus, including axonal sprouting of certain interneuron types, both in sclerotic and non-sclerotic tissue. Thus, axonal sprouting is a more general phenomenon of TLE than cell loss.
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