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Lothmann K, Deitersen J, Zilles K, Amunts K, Herold C. New boundaries and dissociation of the mouse hippocampus along the dorsal-ventral axis based on glutamatergic, GABAergic and catecholaminergic receptor densities. Hippocampus 2020; 31:56-78. [PMID: 32986281 DOI: 10.1002/hipo.23262] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Revised: 08/31/2020] [Accepted: 09/05/2020] [Indexed: 02/01/2023]
Abstract
In rodents, gene-expression, neuronal tuning, connectivity and neurogenesis studies have postulated that the dorsal, the intermediate and the ventral hippocampal formation (HF) are distinct entities. These findings are underpinned by behavioral studies showing a dissociable role of dorsal and ventral HF in learning, memory, stress and emotional processing. However, up to now, the molecular basis of such differences in relation to discrete boundaries is largely unknown. Therefore, we analyzed binding site densities for glutamatergic AMPA, NMDA, kainate and mGluR2/3 , GABAergic GABAA (including benzodiazepine binding sites), GABAB , dopaminergic D1/5 and noradrenergic α1 and α2 receptors as key modulators for signal transmission in hippocampal functions, using quantitative in vitro receptor autoradiography along the dorsal-ventral axis of the mouse HF. Beside general different receptor profiles of the dentate gyrus (DG) and Cornu Ammonis fields (CA1, CA2, CA3, CA4/hilus), we detected substantial differences between dorsal, intermediate and ventral subdivisions and individual layers for all investigated receptor types, except GABAB . For example, striking higher densities of α2 receptors were detected in the ventral DG, while the dorsal DG possesses higher numbers of kainate, NMDA, GABAA and D1/5 receptors. CA1 dorsal and intermediate subdivisions showed higher AMPA, NMDA, mGluR2/3 , GABAA , D1/5 receptors, while kainate receptors are higher expressed in ventral CA1, and noradrenergic α1 and α2 receptors in the intermediate region of CA1. CA2 dorsal was distinguished by higher kainate, α1 and α2 receptors in the intermediate region, while CA3 showed a more complex dissociation. Our findings resulted not only in a clear segmentation of the mouse hippocampus along the dorsal-ventral axis, but also provides insights into the neurochemical basis and likely associated physiological processes in hippocampal functions. Therein, the presented data has a high impact for future studies modeling and investigating dorsal, intermediate and ventral hippocampal dysfunction in relation to neurodegenerative diseases or psychiatric disorders.
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Affiliation(s)
- Kimberley Lothmann
- C. & O. Vogt-Institute for Brain Research, Medical Faculty, University Clinic Düsseldof, Heinrich Heine University of Düsseldorf, Düsseldorf, Germany
| | - Jana Deitersen
- C. & O. Vogt-Institute for Brain Research, Medical Faculty, University Clinic Düsseldof, Heinrich Heine University of Düsseldorf, Düsseldorf, Germany
| | - Karl Zilles
- Institute of Neuroscience and Medicine INM-1, Research Centre Jülich, 52425, Jülich, Germany
| | - Katrin Amunts
- C. & O. Vogt-Institute for Brain Research, Medical Faculty, University Clinic Düsseldof, Heinrich Heine University of Düsseldorf, Düsseldorf, Germany.,Institute of Neuroscience and Medicine INM-1, Research Centre Jülich, 52425, Jülich, Germany
| | - Christina Herold
- C. & O. Vogt-Institute for Brain Research, Medical Faculty, University Clinic Düsseldof, Heinrich Heine University of Düsseldorf, Düsseldorf, Germany
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2
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Hackett MJ, Hollings A, Caine S, Bewer BE, Alaverdashvili M, Takechi R, Mamo JCL, Jones MWM, de Jonge MD, Paterson PG, Pickering IJ, George GN. Elemental characterisation of the pyramidal neuron layer within the rat and mouse hippocampus. Metallomics 2020; 11:151-165. [PMID: 30398510 DOI: 10.1039/c8mt00230d] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
A unique combination of sensitivity, resolution, and penetration make X-ray fluorescence imaging (XFI) ideally suited to investigate trace elemental distributions in the biological context. XFI has gained widespread use as an analytical technique in the biological sciences, and in particular enables exciting new avenues of research in the field of neuroscience. In this study, elemental mapping by XFI was applied to characterise the elemental content within neuronal cell layers of hippocampal sub-regions of mice and rats. Although classical histochemical methods for metal detection exist, such approaches are typically limited to qualitative analysis. Specifically, histochemical methods are not uniformly sensitive to all chemical forms of a metal, often displaying variable sensitivity to specific "pools" or chemical forms of a metal. In addition, histochemical methods require fixation and extensive chemical treatment of samples, creating the strong likelihood for metal redistribution, leaching, or contamination. Direct quantitative elemental mapping of total elemental pools, in situ within ex vivo tissue sections, without the need for chemical fixation or addition of staining reagents is not possible with traditional histochemical methods; however, such a capability, which is provided by XFI, can offer an enormous analytical advantage. The results we report herein demonstrate the analytical advantage of XFI elemental mapping for direct, label-free metal quantification, in situ within ex vivo brain tissue sections. Specifically, we definitively characterise for the first time, the abundance of Fe within the pyramidal cell layers of the hippocampus. Localisation of Fe to this cell layer is not reproducibly achieved with classical Perls histochemical Fe stains. The ability of XFI to directly quantify neuronal elemental (P, S, Cl, K, Ca, Fe, Cu, Zn) distributions, revealed unique profiles of Fe and Zn within anatomical sub-regions of the hippocampus i.e., cornu ammonis 1, 2 or 3 (CA1, CA2 or CA3) sub-regions. Interestingly, our study reveals a unique Fe gradient across neuron populations within the non-degenerating and pathology free rat hippocampus, which curiously mirrors the pattern of region-specific vulnerability of the hippocampus that has previously been established to occur in various neurodegenerative diseases.
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Affiliation(s)
- M J Hackett
- Curtin Institute for Functional Molecules and Interfaces, School of Molecular and Life Sciences, Curtin University, GPOBox U1987, Bentley, WA 6845, Australia.
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3
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Cacciaguerra L, Pagani E, Mesaros S, Dackovic J, Dujmovic-Basuroski I, Drulovic J, Valsasina P, Filippi M, Rocca MA. Dynamic volumetric changes of hippocampal subfields in clinically isolated syndrome patients: A 2-year MRI study. Mult Scler 2018; 25:1232-1242. [DOI: 10.1177/1352458518787347] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Background:Different subregional patterns of hippocampal involvement have been observed in diverse multiple sclerosis (MS) phenotypes.Objective:To evaluate the occurrence of regional hippocampal variations in clinically isolated syndrome (CIS) patients, their relationships with focal white matter (WM) lesions, and their prognostic implications.Methods:Brain dual-echo and three-dimensional (3D) T1-weighted scans were acquired from 14 healthy controls and 36 CIS patients within 2 months from clinical onset and after 3, 12, and 24 months. Radial distance distribution was assessed using 3D parametric surface mesh models. A cognitive screening was also performed.Results:Patients showed clusters of reduced radial distance in the Cornu Ammonis 1 from month 3, progressively extending to the subiculum, negatively correlated with ipsilateral T2 and T1 lesion volume. Increased radial distance appeared in the right dentate gyrus after 3 ( p < 0.05), 12, and 24 ( p < 0.001) months, and in the left one after 3 and 24 months ( p < 0.001), positively correlated with lesional measures. Hippocampal volume variations were more pronounced in patients converting to MS after 24 months and did not correlate with cognitive performance.Conclusion:Regional hippocampal changes occur in CIS, are more pronounced in patients converting to MS, and are modulated by focal WM lesions.
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Affiliation(s)
- Laura Cacciaguerra
- Neuroimaging Research Unit, Institute of Experimental Neurology, Division of Neuroscience, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy/Department of Neurology, Institute of Experimental Neurology, Division of Neuroscience, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy
| | - Elisabetta Pagani
- Neuroimaging Research Unit, Institute of Experimental Neurology, Division of Neuroscience, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy
| | - Sharlota Mesaros
- Clinic of Neurology, Faculty of Medicine, University of Belgrade, Belgrade, Serbia
| | - Jelena Dackovic
- Clinic of Neurology, Faculty of Medicine, University of Belgrade, Belgrade, Serbia
| | | | - Jelena Drulovic
- Clinic of Neurology, Faculty of Medicine, University of Belgrade, Belgrade, Serbia
| | - Paola Valsasina
- Neuroimaging Research Unit, Institute of Experimental Neurology, Division of Neuroscience, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy
| | - Massimo Filippi
- Neuroimaging Research Unit, Institute of Experimental Neurology, Division of Neuroscience, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy/Department of Neurology, Institute of Experimental Neurology, Division of Neuroscience, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy
| | - Maria Assunta Rocca
- Neuroimaging Research Unit, Institute of Experimental Neurology, Division of Neuroscience, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy/Department of Neurology, Institute of Experimental Neurology, Division of Neuroscience, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy
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4
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Li Y, Chen H, Jiang X, Li X, Lv J, Li M, Peng H, Tsien JZ, Liu T. Transcriptome Architecture of Adult Mouse Brain Revealed by Sparse Coding of Genome-Wide In Situ Hybridization Images. Neuroinformatics 2018; 15:285-295. [PMID: 28608010 DOI: 10.1007/s12021-017-9333-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Highly differentiated brain structures with distinctly different phenotypes are closely correlated with the unique combination of gene expression patterns. Using a genome-wide in situ hybridization image dataset released by Allen Mouse Brain Atlas, we present a data-driven method of dictionary learning and sparse coding. Our results show that sparse coding can elucidate patterns of transcriptome organization of mouse brain. A collection of components obtained from sparse coding display robust region-specific molecular signatures corresponding to the canonical neuroanatomical subdivisions including fiber tracts and ventricular systems. Other components revealed finer anatomical delineation of domains previously considered homogeneous. We also build an open-access informatics portal that contains the detail of each component along with its ontology and expressed genes. This portal allows intuitive visualization, interpretation and explorations of the transcriptome architecture of a mouse brain.
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Affiliation(s)
- Yujie Li
- Cortical Architecture Imaging and Discovery Lab, Department of Computer Science and Bioimaging Research Center, The University of Georgia, Athens, GA, USA
| | - Hanbo Chen
- Cortical Architecture Imaging and Discovery Lab, Department of Computer Science and Bioimaging Research Center, The University of Georgia, Athens, GA, USA
| | - Xi Jiang
- Cortical Architecture Imaging and Discovery Lab, Department of Computer Science and Bioimaging Research Center, The University of Georgia, Athens, GA, USA
| | - Xiang Li
- Cortical Architecture Imaging and Discovery Lab, Department of Computer Science and Bioimaging Research Center, The University of Georgia, Athens, GA, USA
| | - Jinglei Lv
- Cortical Architecture Imaging and Discovery Lab, Department of Computer Science and Bioimaging Research Center, The University of Georgia, Athens, GA, USA.,School of Automation, Northwestern Polytechnical University, Xi'an, China
| | - Meng Li
- Brain and Behavior Discovery Institute, Medical College of Georgia at Augusta University, Augusta, GA, USA
| | | | - Joe Z Tsien
- Brain and Behavior Discovery Institute, Medical College of Georgia at Augusta University, Augusta, GA, USA
| | - Tianming Liu
- Cortical Architecture Imaging and Discovery Lab, Department of Computer Science and Bioimaging Research Center, The University of Georgia, Athens, GA, USA.
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5
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Oliva A, Fernández-Ruiz A, Buzsáki G, Berényi A. Role of Hippocampal CA2 Region in Triggering Sharp-Wave Ripples. Neuron 2016; 91:1342-1355. [PMID: 27593179 DOI: 10.1016/j.neuron.2016.08.008] [Citation(s) in RCA: 133] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Revised: 05/17/2016] [Accepted: 07/29/2016] [Indexed: 12/20/2022]
Abstract
Sharp-wave ripples (SPW-Rs) in the hippocampus are implied in memory consolidation, as shown by observational and interventional experiments. However, the mechanism of their generation remains unclear. Using two-dimensional silicon probe arrays, we investigated the propagation of SPW-Rs across the hippocampal CA1, CA2, and CA3 subregions. Synchronous activation of CA2 ensembles preceded SPW-R-related population activity in CA3 and CA1 regions. Deep CA2 neurons gradually increased their activity prior to ripples and were suppressed during the population bursts of CA3-CA1 neurons (ramping cells). Activity of superficial CA2 cells preceded the activity surge in CA3-CA1 (phasic cells). The trigger role of the CA2 region in SPW-R was more pronounced during waking than sleeping. These results point to the CA2 region as an initiation zone for SPW-Rs.
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Affiliation(s)
- Azahara Oliva
- MTA-SZTE "Momentum" Oscillatory Neuronal Networks Research Group, Department of Physiology, University of Szeged, Szeged 6720, Hungary
| | - Antonio Fernández-Ruiz
- MTA-SZTE "Momentum" Oscillatory Neuronal Networks Research Group, Department of Physiology, University of Szeged, Szeged 6720, Hungary; School of Physics, Complutense University, 28040 Madrid, Spain
| | - György Buzsáki
- New York University Neuroscience Institute and Center for Neural Science, New York University, New York, NY 10016, USA.
| | - Antal Berényi
- MTA-SZTE "Momentum" Oscillatory Neuronal Networks Research Group, Department of Physiology, University of Szeged, Szeged 6720, Hungary; New York University Neuroscience Institute and Center for Neural Science, New York University, New York, NY 10016, USA.
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6
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Smith AS, Williams Avram SK, Cymerblit-Sabba A, Song J, Young WS. Targeted activation of the hippocampal CA2 area strongly enhances social memory. Mol Psychiatry 2016; 21:1137-44. [PMID: 26728562 PMCID: PMC4935650 DOI: 10.1038/mp.2015.189] [Citation(s) in RCA: 142] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Revised: 10/10/2015] [Accepted: 11/05/2015] [Indexed: 12/28/2022]
Abstract
Social cognition enables individuals to understand others' intentions. Social memory is a necessary component of this process, for without it, subsequent encounters are devoid of any historical information. The CA2 area of the hippocampus, particularly the vasopressin 1b receptor (Avpr1b) expressed there, is necessary for memory formation. We used optogenetics to excite vasopressin terminals, originating from the hypothalamic paraventricular nucleus, in the CA2 of mice. This markedly enhanced their social memory if the stimulation occurred during memory acquisition, but not retrieval. This effect was blocked by an Avpr1b antagonist. Finally, this enhanced memory is resistant to the social distraction of an introduced second mouse, important for socially navigating populations of individuals. Our results indicate the CA2 can increase the salience of social signals. Targeted pharmacotherapy with Avpr1b agonists or deep brain stimulation of the CA2 are potential avenues of treatment for those with declining social memory as in various dementias.
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Affiliation(s)
- Adam S. Smith
- Section on Neural Gene Expression, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA
| | - Sarah K. Williams Avram
- Section on Neural Gene Expression, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA
| | - Adi Cymerblit-Sabba
- Section on Neural Gene Expression, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA
| | - June Song
- Section on Neural Gene Expression, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA
| | - W. Scott Young
- Section on Neural Gene Expression, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA
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7
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Abstract
Hippocampal area CA2 has several features that distinguish it from CA1 and CA3, including a unique gene expression profile, failure to display long-term potentiation and relative resistance to cell death. A recent increase in interest in the CA2 region, combined with the development of new methods to define and manipulate its neurons, has led to some exciting new discoveries on the properties of CA2 neurons and their role in behaviour. Here, we review these findings and call attention to the idea that the definition of area CA2 ought to be revised in light of gene expression data.
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8
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Kay K, Sosa M, Chung JE, Karlsson MP, Larkin MC, Frank LM. A hippocampal network for spatial coding during immobility and sleep. Nature 2016; 531:185-90. [PMID: 26934224 PMCID: PMC5037107 DOI: 10.1038/nature17144] [Citation(s) in RCA: 132] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2015] [Accepted: 01/13/2016] [Indexed: 12/11/2022]
Abstract
How does an animal know where it is when it stops moving? Hippocampal place cells fire at discrete locations as subjects traverse space, thereby providing an explicit neural code for current location during locomotion. In contrast, during awake immobility, the hippocampus is thought to be dominated by neural firing representing past and possible future experience. The question of whether and how the hippocampus constructs a representation of current location in the absence of locomotion has stood unresolved. Here we report that a distinct population of hippocampal neurons, located in the CA2 subregion, signals current location during immobility, and furthermore does so in association with a previously unidentified hippocampus-wide network pattern. In addition, signaling of location persists into brief periods of desynchronization prevalent in slow-wave sleep. The hippocampus thus generates a distinct representation of current location during immobility, pointing to mnemonic processing specific to experience occurring in the absence of locomotion.
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Affiliation(s)
- Kenneth Kay
- UCSF Center for Integrative Neuroscience and Department of Physiology, University of California San Francisco, California 94158, USA
| | - Marielena Sosa
- UCSF Center for Integrative Neuroscience and Department of Physiology, University of California San Francisco, California 94158, USA
| | - Jason E Chung
- UCSF Center for Integrative Neuroscience and Department of Physiology, University of California San Francisco, California 94158, USA
| | - Mattias P Karlsson
- UCSF Center for Integrative Neuroscience and Department of Physiology, University of California San Francisco, California 94158, USA
| | - Margaret C Larkin
- UCSF Center for Integrative Neuroscience and Department of Physiology, University of California San Francisco, California 94158, USA
| | - Loren M Frank
- UCSF Center for Integrative Neuroscience and Department of Physiology, University of California San Francisco, California 94158, USA.,Howard Hughes Medical Institute, University of California San Francisco, California 94158, USA
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9
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Rocca MA, Morelli ME, Amato MP, Moiola L, Ghezzi A, Veggiotti P, Capra R, Pagani E, Portaccio E, Fiorino A, Pippolo L, Pera MC, Comi G, Falini A, Filippi M. Regional hippocampal involvement and cognitive impairment in pediatric multiple sclerosis. Mult Scler 2015; 22:628-40. [DOI: 10.1177/1352458515598569] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2015] [Accepted: 07/09/2015] [Indexed: 11/17/2022]
Abstract
Objectives: We assessed global and regional hippocampal volume abnormalities in pediatric multiple sclerosis (MS) patients and their correlations with clinical, neuropsychological and magnetic resonance imaging metrics. Methods: From 53 pediatric MS patients and 18 healthy controls, global hippocampal volume was computed using a manual tracing procedure. Regional hippocampal volume modifications were assessed using a radial mapping analysis. MS patients with abnormal performance in three or more tests of a neuropsychological battery for children were classified as cognitively impaired. Results: Global hippocampal volume was reduced in MS patients compared with controls, but did not correlate with clinical, neuropsychological and magnetic resonance imaging measures. Compared to controls, MS patients experienced bilateral radial atrophy of the cornu ammonis, subiculum and dentate gyrus subfields as well as radial hypertrophy of the dentate gyrus subfield. Regional hippocampal volume modifications correlated with brain T2 lesion volume as well as attention and language abilities. Global hippocampal volume did not differ between cognitively impaired ( n=12) and cognitively preserved MS patients. Compared to cognitively preserved, cognitively impaired MS patients had atrophy of the subiculum and dentate gyrus subfields of the right hippocampus. Conclusions: Hippocampal subregions have different vulnerability to damage in pediatric MS. Regional rather than global hippocampal involvement contributes to global cognitive impairment as well as to deficits of selected cognitive tests.
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Affiliation(s)
- Maria A Rocca
- Neuroimaging Research Unit, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Italy/Department of Neurology, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Italy
| | - Maria E Morelli
- Neuroimaging Research Unit, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Italy/Department of Neurology, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Italy
| | - Maria P Amato
- Department of Neurology, University of Florence, Italy
| | - Lucia Moiola
- Department of Neurology, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Italy
| | - Angelo Ghezzi
- Multiple Sclerosis Center, Ospedale di Gallarate, Italy
| | - Pierangelo Veggiotti
- Department of Child Neurology and Psychiatry, C. Mondino National Neurological Institute, Pavia, Italy and Brain and Behaviour Department, University of Pavia, Pavia, Italy
| | - Ruggero Capra
- Multiple Sclerosis Center, Spedali Civili of Brescia, Italy
| | - Elisabetta Pagani
- Neuroimaging Research Unit, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Italy
| | | | - Agnese Fiorino
- Department of Neurology, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Italy
| | | | - Maria C Pera
- Department of Child Neurology and Psychiatry, C. Mondino National Neurological Institute, Pavia, Italy and Brain and Behaviour Department, University of Pavia, Pavia, Italy
| | - Giancarlo Comi
- Department of Neurology, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Italy
| | - Andrea Falini
- Department of Neuroradiology, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Italy
| | - Massimo Filippi
- Neuroimaging Research Unit, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Italy/Department of Neurology, San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Italy
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10
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Mankin EA, Diehl GW, Sparks FT, Leutgeb S, Leutgeb JK. Hippocampal CA2 activity patterns change over time to a larger extent than between spatial contexts. Neuron 2015; 85:190-201. [PMID: 25569350 DOI: 10.1016/j.neuron.2014.12.001] [Citation(s) in RCA: 189] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/21/2014] [Indexed: 11/24/2022]
Abstract
The hippocampal CA2 subregion has a different anatomical connectivity pattern within the entorhino-hippocampal circuit than either the CA1 or CA3 subregion. Yet major differences in the neuronal activity patterns of CA2 compared with the other CA subregions have not been reported. We show that standard spatial and temporal firing patterns of individual hippocampal principal neurons in behaving rats, such as place fields, theta modulation, and phase precession, are also present in CA2, but that the CA2 subregion differs substantially from the other CA subregions in its population coding. CA2 ensembles do not show a persistent code for space or for differences in context. Rather, CA2 activity patterns become progressively dissimilar over time periods of hours to days. The weak coding for a particular context is consistent with recent behavioral evidence that CA2 circuits preferentially support social, emotional, and temporal rather than spatial aspects of memory.
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Affiliation(s)
- Emily A Mankin
- Neurobiology Section and Center for Neural Circuits and Behavior, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA
| | - Geoffrey W Diehl
- Neurobiology Section and Center for Neural Circuits and Behavior, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA
| | - Fraser T Sparks
- Canadian Centre for Behavioural Neuroscience, Department of Neuroscience, University of Lethbridge, Lethbridge, AB T1K 3M4, Canada
| | - Stefan Leutgeb
- Neurobiology Section and Center for Neural Circuits and Behavior, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA; Kavli Institute for Brain and Mind, University of California, San Diego, La Jolla, CA 92093, USA
| | - Jill K Leutgeb
- Neurobiology Section and Center for Neural Circuits and Behavior, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA.
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11
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Longoni G, Rocca MA, Pagani E, Riccitelli GC, Colombo B, Rodegher M, Falini A, Comi G, Filippi M. Deficits in memory and visuospatial learning correlate with regional hippocampal atrophy in MS. Brain Struct Funct 2013; 220:435-44. [DOI: 10.1007/s00429-013-0665-9] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2013] [Accepted: 10/19/2013] [Indexed: 01/18/2023]
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12
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Caruana DA, Alexander GM, Dudek SM. New insights into the regulation of synaptic plasticity from an unexpected place: hippocampal area CA2. Learn Mem 2012; 19:391-400. [PMID: 22904370 DOI: 10.1101/lm.025304.111] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The search for molecules that restrict synaptic plasticity in the brain has focused primarily on sensory systems during early postnatal development, as critical periods for inducing plasticity in sensory regions are easily defined. The recent discovery that Schaffer collateral inputs to hippocampal area CA2 do not readily support canonical activity-dependent long-term potentiation (LTP) serves as a reminder that the capacity for synaptic modification is also regulated anatomically across different brain regions. Hippocampal CA2 shares features with other similarly "LTP-resistant" brain areas in that many of the genes linked to synaptic function and the associated proteins known to restrict synaptic plasticity are expressed there. Add to this a rich complement of receptors and signaling molecules permissive for induction of atypical forms of synaptic potentiation, and area CA2 becomes an ideal model system for studying specific modulators of brain plasticity. Additionally, recent evidence suggests that hippocampal CA2 is instrumental for certain forms of learning, memory, and social behavior, but the links between CA2-enriched molecules and putative CA2-dependent behaviors are only just beginning to be made. In this review, we offer a detailed look at what is currently known about the synaptic plasticity in this important, yet largely overlooked component of the hippocampus and consider how the study of CA2 may provide clues to understanding the molecular signals critical to the modulation of synaptic function in different brain regions and across different stages of development.
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Affiliation(s)
- Douglas A Caruana
- Laboratory of Neurobiology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA
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RGS14 is a natural suppressor of both synaptic plasticity in CA2 neurons and hippocampal-based learning and memory. Proc Natl Acad Sci U S A 2010; 107:16994-8. [PMID: 20837545 DOI: 10.1073/pnas.1005362107] [Citation(s) in RCA: 140] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Learning and memory have been closely linked to strengthening of synaptic connections between neurons (i.e., synaptic plasticity) within the dentate gyrus (DG)-CA3-CA1 trisynaptic circuit of the hippocampus. Conspicuously absent from this circuit is area CA2, an intervening hippocampal region that is poorly understood. Schaffer collateral synapses on CA2 neurons are distinct from those on other hippocampal neurons in that they exhibit a perplexing lack of synaptic long-term potentiation (LTP). Here we demonstrate that the signaling protein RGS14 is highly enriched in CA2 pyramidal neurons and plays a role in suppression of both synaptic plasticity at these synapses and hippocampal-based learning and memory. RGS14 is a scaffolding protein that integrates G protein and H-Ras/ERK/MAP kinase signaling pathways, thereby making it well positioned to suppress plasticity in CA2 neurons. Supporting this idea, deletion of exons 2-7 of the RGS14 gene yields mice that lack RGS14 (RGS14-KO) and now express robust LTP at glutamatergic synapses in CA2 neurons with no impact on synaptic plasticity in CA1 neurons. Treatment of RGS14-deficient CA2 neurons with a specific MEK inhibitor blocked this LTP, suggesting a role for ERK/MAP kinase signaling pathways in this process. When tested behaviorally, RGS14-KO mice exhibited marked enhancement in spatial learning and in object recognition memory compared with their wild-type littermates, but showed no differences in their performance on tests of nonhippocampal-dependent behaviors. These results demonstrate that RGS14 is a key regulator of signaling pathways linking synaptic plasticity in CA2 pyramidal neurons to hippocampal-based learning and memory but distinct from the canonical DG-CA3-CA1 circuit.
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Brinn L, Pereira Leite J, Larson R, Martins A. Differential patterns of myosin Va expression during the ontogenesis of the rat hippocampus. Braz J Med Biol Res 2010; 43:890-8. [DOI: 10.1590/s0100-879x2010007500080] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2010] [Accepted: 08/05/2010] [Indexed: 11/22/2022] Open
Affiliation(s)
- L.S. Brinn
- Universidade de São Paulo, Brasil; Universidade de São Paulo, Brasil
| | | | | | - A.R. Martins
- Universidade de São Paulo, Brasil; Universidade de São Paulo, Brasil
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15
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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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16
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Woźnicka A, Malinowska M, Kosmal A. Cytoarchitectonic organization of the entorhinal cortex of the canine brain. ACTA ACUST UNITED AC 2006; 52:346-67. [PMID: 16787665 DOI: 10.1016/j.brainresrev.2006.04.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2005] [Revised: 04/26/2006] [Accepted: 04/28/2006] [Indexed: 11/26/2022]
Abstract
The present study describes the cytoarchitectonic and chemoarchitectonic organization of the canine entorhinal cortex (EC). We distinguished medial, laterodorsal, and latero-intermediate subdivisions based on the organization of cortical layers using Nissl and Timm staining and AChE histochemistry. The medial subdivision is located at the border of the parasubiculum and is characterized by a narrow cortex, wide layer II, and densely packed cells in layer V. At its caudal extent, distinct spherical groups of small cells are situated at the border of layer I/II. The laterodorsal subdivision is located along the rhinal sulcus and borders area 35 of the perirhinal cortex. Its cortex is wide and layers tend to merge. Layer II of the laterodorsal subdivision contains scattered "stellate" cells, which are not organized into islands. The latero-intermediate subdivision displays a complex layer organization. The most easily distinguished is layer II, which is comprised of two main cell populations; "stellate" neurons arranged into "islands" and small, round cells distributed within and below the stellate cells. Layer III contains sparse cells that are arranged into vertical clusters, whereas layer IV (lamina dissecans) is especially wide. Nine fields, named according to their rostral to caudal position, were distinguished based on further analyses of layer differentiation. The main features of the rostrocaudal differentiation are a gradual disappearance of "island" organization in layer II, increasing cortical thickness, and wider layers containing small and more densely packed cells. Cytoarchitectonic differentiation was determined by observation of specific histochemical patterns of AChE- and Timm-stained sections.
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Affiliation(s)
- Agnieszka Woźnicka
- Department of Neurophysiology, Nencki Institute of Experimental Biology, 3 Pasteur Str., 02-093 Warsaw, Poland
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17
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Bjarkam CR, Sørensen JC, Geneser FA. Distribution and morphology of serotonin-immunoreactive axons in the retrohippocampal areas of the New Zealand white rabbit. ACTA ACUST UNITED AC 2005; 210:199-207. [PMID: 16170538 DOI: 10.1007/s00429-005-0004-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/08/2005] [Indexed: 12/19/2022]
Abstract
This study provides a detailed light microscopic description of the morphology and distribution of serotonin-immunoreactive axons in the paleocortical retrohippocampal areas, viz. the subiculum, presubiculum, parasubiculum and entorhinal area, and the adjoining neocortical perirhinal and retrosplenial cortices of the New Zealand white rabbit. Serotonergic axons could be segregated into three different fiber types named fine fibers, beaded fibers and stem-axons. Fine fibers were evenly distributed thin axons with small fusiform/granular varicosities. Beaded fibers were thin axons with large varicosities, predominantly located in the retrohippocampal supragranular layers, where they often formed pericellular arrays. Stem-axons were thick straight, nonvaricose axons seen in the white matter of psalterium dorsale, alveus and the plexiform layer. The paleocortical retrohippocampal areas had a dense supragranular innervation with numerous tortuous fine and beaded fibers, intermingled in conglomerates with conspicuous varicosities forming pericellular arrays. In contrast, the neocortical area 17 and the lateral part of the perirhinal cortex (area 36) were innervated by evenly distributed fine fibers with a moderate number of small varicosities and few ramifications, whereas, the retrosplenial cortex (areas 29e, 29ab and 29cd), and the medial part of the perirhinal cortex (area 35) displayed an intermediate innervation pattern, probably reflecting the transitional nature of these areas being located between the paleo- and the neocortex. The described dualistic innervation pattern may functionally enable the serotonergic system to exert a strong influence on the supragranular layers of the retrohippocampal areas and thus on the neural input entering these areas from the perirhinal and neighboring polymodal association neocortices, whereas the innervation pattern in the adjoining neocortical areas points towards a more diffuse and general modulation of neural activity herein.
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Affiliation(s)
- Carsten R Bjarkam
- Department of Neurobiology, Institute of Anatomy, University of Aarhus, 8000 Aarhus C, Denmark.
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18
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Keuker JIH, Rochford CDP, Witter MP, Fuchs E. A cytoarchitectonic study of the hippocampal formation of the tree shrew (Tupaia belangeri). J Chem Neuroanat 2003; 26:1-15. [PMID: 12954527 DOI: 10.1016/s0891-0618(03)00030-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Tree shrews constitute an interesting animal model to study the impact of stress or aging on the hippocampal formation, a brain structure known to be affected under such environmental or internal influences. To perform detailed investigations of the hippocampal formation, adequate knowledge of its anatomy should be present. Until now, the hippocampal formation of the tree shrew has not yet been studied extensively. The main objective of this study, therefore, was to describe the subfield boundaries in various levels of the dorsoventral hippocampal axis of the tree shrew (Tupaia belangeri) in detail. The secondary aim was to clarify whether a separate CA2 field can actually be distinguished in the tree shrew hippocampus, a fact that was denied in former reports. In addition, we aimed at investigating whether or not a CA4 subfield can be identified in the tree shrew's hippocampus. The immunocytochemical distribution of microtubule-associated protein 2 and the calcium-binding proteins, parvalbumin and calbindin, and the characteristics of Nissl staining in adjacent sections were compared. Because of the rather dorsoventral orientation of the long hippocampal axis in tree shrews, staining patterns were analyzed mainly in horizontal sections. The subiculum and the hippocampal CA1 and CA3 areas were easily identified. Moreover, we were able to demonstrate the existence of a distinct CA2 subfield in the tree shrew's Ammon's horn, contrary to previous reports. However, our results indicate that a CA4 field in the tree shrew hippocampal formation cannot be identified with the methods that we used. Therefore, supposed CA4 pyramidal neurons should be included into the CA3 field.
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Affiliation(s)
- Jeanine I H Keuker
- Clinical Neurobiology Laboratory, German Primate Center, Kellnerweg 4, Göttingen 37077, Germany.
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19
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Tochitani S, Hashikawa T, Yamamori T. Occ1 mRNA expression reveals a characteristic feature in the hippocampal CA2 field of adult macaques. Neurosci Lett 2003; 346:105-8. [PMID: 12850559 DOI: 10.1016/s0304-3940(03)00595-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The gene occ1 is preferentially expressed in the primary visual cortex in an activity-dependent and developmentally regulated manner. In this report, we show the characteristic distribution of occ1 transcripts in the CA2 subfield of the hippocampal formation in adult monkeys. occ1 mRNA signals were observed selectively in the pyramidal cell layer of CA2. In addition to these signals, a relatively sparse distribution of occ1 was found in the stratum oriens and, occasionally, in the outermost regions of the pyramidal cell layers of both CA1 and CA2. A few labeled cells were detected in CA3. The elevated expression of occ1 in the CA2 subfield provides a new approach for investigating the function of this subregion, whose role has still not been well clarified.
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Affiliation(s)
- Shiro Tochitani
- Division of Speciation Mechanisms I, National Institute for Basic Biology, Okazaki, Aichi 444-8585, Japan
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20
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Künzle H, Radtke-Schuller S. Hippocampal fields in the hedgehog tenrec. Their architecture and major intrinsic connections. Neurosci Res 2001; 41:267-91. [PMID: 11672840 DOI: 10.1016/s0168-0102(01)00288-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The Madagascan lesser hedgehog tenrec was investigated to get insight into the areal evolution of the hippocampal formation in mammals with poorly differentiated brains. The hippocampal subdivisions were analyzed using cyto- and chemoarchitectural criteria; long associational and commissural connections were demonstrated with tracer techniques. The hedgehog tenrec shows a well differentiated dentate gyrus, CA3 and CA1. Their major intrinsic connections lie within the band of variations known from other species. The dentate hilar region shows calretinin-positive mossy cells with extensive projections to the molecular layer. The calbindin- and enkephalin-positive granule mossy fibers form a distinct endbulb and do not invade the CA1 as reported in the erinaceous hedgehog. Isolated granule cells with basal dendrites were also noted. A CA2 region is hard to identify architecturally; its presence is suggested due to its contralateral connections. Subicular and perisubicular regions are clearly present along the dorsal aspects of the hemisphere, but we failed to identify them unequivocally along the caudal and ventral tip of the hippocampus. A temporal portion of the subiculum, if present, differs in its chemoarchitecture from its dorsal counterpart. The perisubicular region, located medially adjacent to the dorsal subiculum may be equivalent to the rat's presubiculum; evidence for the presence of a parasubiculum was rather weak.
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Affiliation(s)
- H Künzle
- Institute of Anatomy, University of Munich, Pettenkoferstrasse 11, D-80336, Munich, Germany.
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21
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Blümcke I, Becker AJ, Klein C, Scheiwe C, Lie AA, Beck H, Waha A, Friedl MG, Kuhn R, Emson P, Elger C, Wiestler OD. Temporal lobe epilepsy associated up-regulation of metabotropic glutamate receptors: correlated changes in mGluR1 mRNA and protein expression in experimental animals and human patients. J Neuropathol Exp Neurol 2000; 59:1-10. [PMID: 10744030 DOI: 10.1093/jnen/59.1.1] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Aberrant axonal reorganization and altered distribution of neurotransmitter receptor subtypes have been proposed as major pathogenic mechanisms for hippocampal hyperexcitability in chronic temporal lobe epilepsies (TLE). Recent data point to excitatory class I metabotropic glutamate receptors (mGluR1 and mGluR5) as interesting candidates. Here, we have analyzed the hippocampal distribution and mRNA expression of mGluR1 and mGluR5 in two rat models of limbic seizures, i.e. electrical kindling and intraperitoneal kainate injections, as well as in human TLE. Quantitative RT-PCR analysis detected a significant increase of hippocampal mGluR1 gene transcript levels in kainate treated and kindled rats. In addition, microdissected hippocampal tissue samples localized this increase to the dentate gyrus. Using immunohistochemistry with mGluR1alpha subtype specific antibodies, increased labeling was observed within the dentate gyrus molecular layer (DG-ML). A similar pattern of increased mGluR1alpha neuropil staining was found within the DG-ML of epilepsy patients (n = 42) compared with peritumoral hippocampus specimens obtained from nonepileptic patients (biopsy controls, n = 3). This increase was detected in TLE patients with segmental hippocampal cell loss, as well as in TLE patients with focal lesions but no histopathological alterations of the hippocampus. In contrast, mGluR5 immunoreactivity and mRNA expression were not significantly altered in the DG-ML. Our data demonstrate a striking regional induction of mGluR1alpha in the hippocampal dentate gyrus of experimental animals with limbic seizures as well as in human patients with chronic, intractable TLE. This increase corresponds to functional alterations of class I mGluRs observed in seizure models and may significantly contribute to hippocampal hyperexcitability in focal human epilepsies.
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Affiliation(s)
- I Blümcke
- Department of Neuropathology, University of Bonn Medical Center, Germany
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22
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Psychobiological Models of Hippocampal Function in Learning and Memory. Neurobiol Learn Mem 1998. [DOI: 10.1016/b978-012475655-7/50012-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Tole S, Christian C, Grove EA. Early specification and autonomous development of cortical fields in the mouse hippocampus. Development 1997; 124:4959-70. [PMID: 9362459 DOI: 10.1242/dev.124.24.4959] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Studies of the specification of distinct areas in the developing cerebral cortex have until now focused mainly on neocortex. We demonstrate that the hippocampus, an archicortical structure, offers an elegant, alternative system in which to explore cortical area specification. Individual hippocampal areas, called CA fields, display striking molecular differences in maturity. We use these distinct patterns of gene expression as markers of CA field identity, and show that the two major hippocampal fields, CA1 and CA3, are specified early in hippocampal development, during the period of neurogenesis. Two field-specific markers display consistent patterns of expression from the embryo to the adult. Presumptive CA1 and CA3 fields (Pca1, Pca3) can therefore be identified between embryonic days 14.5 and 15.5 in the mouse, a week before the fields are morphologically distinct. No other individual cortical areas have been detected by gene expression as early in development. Indeed, other features that distinguish between the CA fields appear after birth, indicating that mature CA field identity is acquired over at least 3 weeks. To determine if Pca1 and Pca3 are already specified to acquire mature CA field identities, the embryonic fields were isolated from further potential specification cues by maintaining them in slice culture. CA field development proceeds in slices of the entire embryonic hippocampus. More strikingly, slices restricted to Pca1 or Pca3 alone also develop appropriate mature features of CA1 or CA3. Pca1 and Pca3 are therefore able to develop complex characteristics of mature CA field identity autonomously, that is, without contact or innervation from other fields or other parts of the brain. Because Pca1 and Pca3 can be identified before major afferents grow into the hippocampus, innervation may also be unnecessary for the initial division of the hippocampus into separate fields. Providing a clue to the source of the true specifying signals, the earliest field markers appear first at the poles of the hippocampus, then progress inwards. General hippocampal development does not follow this pronounced pattern. We suggest that the sources of signals that specify hippocampal field identity lie close to the hippocampal poles, and that the signals operate first on cells at the poles, then move inwards.
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Affiliation(s)
- S Tole
- Department of Pharmacological and Physiological Sciences, Pritzker School of Medicine, University of Chicago, IL 60637, USA
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Sekino Y, Obata K, Tanifuji M, Mizuno M, Murayama J. Delayed signal propagation via CA2 in rat hippocampal slices revealed by optical recording. J Neurophysiol 1997; 78:1662-8. [PMID: 9310451 DOI: 10.1152/jn.1997.78.3.1662] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Signal propagation from mossy fibers to CA1 neurons was investigated in rat hippocampal slices by a combination of electrical and optical recordings. The slices were prepared by oblique sectioning of the middle part of the hippocampus to preserve fiber connections. The mossy fibers were stimulated to induce population spikes (PSs) and excitatory postsynaptic potentials in the middle part of the CA1 region. Latencies of maximal PSs in CA1 varied widely among slices; they ranged from 7 to 13.5 ms, with two maxima at 9 and 11.5 ms. The fastest PSs probably are evoked by the Schaffer collaterals that connect the CA3 and CA1 regions in the well-known trisynaptic circuit. However, the slower PSs suggest the existence of additional delayed inputs. To determine the source of the delayed input, slices were stained with a voltage-sensitive dye, RH482, and the optical signals relevant to membrane potential changes were detected by a high-resolution optical imaging system. Optical recording of responses to mossy fiber stimulation indicated two distinct types of signal propagation from CA3 to CA1. In preparations evincing the fast type of propagation, signals spread to CA1 within 7.2 ms after the mossy fiber stimulation. During such propagation, activity flowed directly from CA3 to the stratum radiatum of CA1. Other preparations illustrated slow signal propagation, in which optical signals were generated in CA2 before spreading to CA1. During such slow signal transmission, activity persisted in CA2 and its surrounding area for 3 ms before propagating to the strata radiatum and oriens in CA1. In such cases, CA1 activity was detected within 10.8 ms of mossy fiber stimulation. In some slices, a mixture of the fast and slow propagation patterns was observed, indicating that these two transmission modes can coexist. Our data reveal that CA2 neurons can transmit delayed excitatory signals to CA1 neurons. We therefore conclude that consideration of electrical signal propagation through the hippocampus should include flow through the CA2 region in addition to the traditional dentate gyrus-CA3-CA1 trisynaptic circuit.
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Affiliation(s)
- Y Sekino
- Japan Science and Technology Corporation, Laboratory of Neurochemistry, National Institute for Physiological Sciences, Okazaki
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