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Feng Y, Diego KS, Dong Z, Wick ZC, Page-Harley L, Page-Harley V, Schnipper J, Lamsifer SI, Pennington ZT, Vetere LM, Philipsberg PA, Soler I, Jurkowski A, Rosado CJ, Khan NN, Cai DJ, Shuman T. Distinct changes to hippocampal and medial entorhinal circuits emerge across the progression of cognitive deficits in epilepsy. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.12.584697. [PMID: 38559224 PMCID: PMC10979962 DOI: 10.1101/2024.03.12.584697] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
Temporal lobe epilepsy (TLE) causes pervasive and progressive memory impairments, yet the specific circuit changes that drive these deficits remain unclear. To investigate how hippocampal-entorhinal dysfunction contributes to progressive memory deficits in epilepsy, we performed simultaneous in vivo electrophysiology in hippocampus (HPC) and medial entorhinal cortex (MEC) of control and epileptic mice 3 or 8 weeks after pilocarpine-induced status epilepticus (Pilo-SE). We found that HPC synchronization deficits (including reduced theta power, coherence, and altered interneuron spike timing) emerged within 3 weeks of Pilo-SE, aligning with early-onset, relatively subtle memory deficits. In contrast, abnormal synchronization within MEC and between HPC-MEC emerged later, by 8 weeks after Pilo-SE, when spatial memory impairment was more severe. Furthermore, a distinct subpopulation of MEC layer 3 excitatory neurons (active at theta troughs) was specifically impaired in epileptic mice. Together, these findings suggest that hippocampal-entorhinal circuit dysfunction accumulates and shifts as cognitive impairment progresses in TLE.
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Affiliation(s)
- Yu Feng
- Icahn School of Medicine at Mount Sinai, New York, NY
| | | | - Zhe Dong
- Icahn School of Medicine at Mount Sinai, New York, NY
| | | | | | | | | | | | | | | | | | - Ivan Soler
- Icahn School of Medicine at Mount Sinai, New York, NY
| | | | | | - Nadia N Khan
- Icahn School of Medicine at Mount Sinai, New York, NY
| | - Denise J Cai
- Icahn School of Medicine at Mount Sinai, New York, NY
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2
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Chen X, Tang SJ. Neural Circuitry Polarization in the Spinal Dorsal Horn (SDH): A Novel Form of Dysregulated Circuitry Plasticity during Pain Pathogenesis. Cells 2024; 13:398. [PMID: 38474361 PMCID: PMC10930392 DOI: 10.3390/cells13050398] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2024] [Revised: 02/20/2024] [Accepted: 02/23/2024] [Indexed: 03/14/2024] Open
Abstract
Pathological pain emerges from nociceptive system dysfunction, resulting in heightened pain circuit activity. Various forms of circuitry plasticity, such as central sensitization, synaptic plasticity, homeostatic plasticity, and excitation/inhibition balance, contribute to the malfunction of neural circuits during pain pathogenesis. Recently, a new form of plasticity in the spinal dorsal horn (SDH), named neural circuit polarization (NCP), was discovered in pain models induced by HIV-1 gp120 and chronic morphine administration. NCP manifests as an increase in excitatory postsynaptic currents (EPSCs) in excitatory neurons and a decrease in EPSCs in inhibitory neurons, presumably facilitating hyperactivation of pain circuits. The expression of NCP is associated with astrogliosis. Ablation of reactive astrocytes or suppression of astrogliosis blocks NCP and, concomitantly, the development of gp120- or morphine-induced pain. In this review, we aim to compare and integrate NCP with other forms of plasticity in pain circuits to improve the understanding of the pathogenic contribution of NCP and its cooperation with other forms of circuitry plasticity during the development of pathological pain.
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Affiliation(s)
| | - Shao-Jun Tang
- Stony Brook University Pain and Anesthesia Research Center (SPARC), Department of Anesthesiology, Stony Brook University, Stony Brook, NY 11794, USA;
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3
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Xu Z, Mo F, Yang G, Fan P, Lu B, Liang W, Kong F, Jing L, Xu W, Liu J, Wang M, Wu Y, Cai X. Impaired Spatial Firing Representations of Neurons in the Medial Entorhinal Cortex of the Epileptic Rat Using Microelectrode Arrays. RESEARCH (WASHINGTON, D.C.) 2023; 6:0229. [PMID: 37719050 PMCID: PMC10503993 DOI: 10.34133/research.0229] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Accepted: 08/28/2023] [Indexed: 09/19/2023]
Abstract
Epilepsy severely impairs the cognitive behavior of patients. It remains unclear whether epilepsy-induced cognitive impairment is associated with neuronal activities in the medial entorhinal cortex (MEC), a region known for its involvement in spatial cognition. To explore this neural mechanism, we recorded the spikes and local field potentials from MEC neurons in lithium-pilocarpine-induced epileptic rats using self-designed microelectrode arrays. Through the open field test, we identified spatial cells exhibiting spatially selective firing properties and assessed their spatial representations in relation to the progression of epilepsy. Meanwhile, we analyzed theta oscillations and theta modulation in both excitatory and inhibitory neurons. Furthermore, we used a novel object recognition test to evaluate changes in spatial cognitive ability of epileptic rats. After the epilepsy modeling, the spatial tuning of various types of spatial cells had suffered a rapid and pronounced damage during the latent period (1 to 5 d). Subsequently, the firing characteristics and theta oscillations were impaired. In the chronic period (>10 d), the performance in the novel object experiment deteriorated. In conclusion, our study demonstrates the detrimental effect on spatial representations and electrophysiological properties of MEC neurons in the epileptic latency, suggesting the potential use of these changes as a "functional biomarker" for predicting cognitive impairment caused by epilepsy.
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Affiliation(s)
- Zhaojie Xu
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute,
Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Fan Mo
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute,
Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Gucheng Yang
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute,
Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Penghui Fan
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute,
Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Botao Lu
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute,
Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Wei Liang
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute,
Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Fanli Kong
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute,
Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Luyi Jing
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute,
Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Wei Xu
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute,
Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Juntao Liu
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute,
Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Mixia Wang
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute,
Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yirong Wu
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute,
Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xinxia Cai
- State Key Laboratory of Transducer Technology, Aerospace Information Research Institute,
Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
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4
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Wu B, Xu W. Case report: Neonatal diabetes mellitus caused by KCNJ11 mutation presenting with intracranial hemorrhage. Front Neurol 2023; 14:1072078. [PMID: 36937531 PMCID: PMC10022729 DOI: 10.3389/fneur.2023.1072078] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2022] [Accepted: 02/06/2023] [Indexed: 03/06/2023] Open
Abstract
Neonatal diabetes mellitus (NDM) is a rare type of monogenic diabetes. At present, most published studies have focused on the types of gene mutations associated with NDM and the therapeutic effect of sulfonylureas (SUs) on the disease; few studies on NDM-associated intracranial hemorrhage (ICH) exist. In addition, p.V59M mutations generally lead to intermediate DEND (iDEND: intermediate developmental delay and neonatal diabetes) syndrome without epilepsy. Here, we present a case of a 1-month-old male infant who was diagnosed with NDM caused by a KCNJ11 missense mutation (p.V59M), presenting with cerebral injury. In the early stage of the disease, continuous insulin dose adjustment did not achieve an ideal level of blood glucose. Although blood glucose was subsequently controlled by oral SUs, which were administered after the genetic test result, the patient still displayed epilepsy and developmental delay. In this case report, we present our experience in the treatment of the infant, switching from insulin to oral SUs and we thought that SUs have limited effects on improving the prognosis of neurodevelopmental disturbances in NDM with foci of encephalomalacia. In addition, there may be a relationship between KCNJ11 missense mutations and cerebral injury, and further research must be carried out to confirm these points.
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Tukker JJ, Beed P, Brecht M, Kempter R, Moser EI, Schmitz D. Microcircuits for spatial coding in the medial entorhinal cortex. Physiol Rev 2022; 102:653-688. [PMID: 34254836 PMCID: PMC8759973 DOI: 10.1152/physrev.00042.2020] [Citation(s) in RCA: 23] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The hippocampal formation is critically involved in learning and memory and contains a large proportion of neurons encoding aspects of the organism's spatial surroundings. In the medial entorhinal cortex (MEC), this includes grid cells with their distinctive hexagonal firing fields as well as a host of other functionally defined cell types including head direction cells, speed cells, border cells, and object-vector cells. Such spatial coding emerges from the processing of external inputs by local microcircuits. However, it remains unclear exactly how local microcircuits and their dynamics within the MEC contribute to spatial discharge patterns. In this review we focus on recent investigations of intrinsic MEC connectivity, which have started to describe and quantify both excitatory and inhibitory wiring in the superficial layers of the MEC. Although the picture is far from complete, it appears that these layers contain robust recurrent connectivity that could sustain the attractor dynamics posited to underlie grid pattern formation. These findings pave the way to a deeper understanding of the mechanisms underlying spatial navigation and memory.
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Affiliation(s)
- John J Tukker
- German Center for Neurodegenerative Diseases (DZNE) Berlin, Berlin, Germany
| | - Prateep Beed
- Neuroscience Research Center, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humbold-Universität zu Berlin, Berlin, Germany
- Berlin Institute of Health at Charité-Universitätsmedizin Berlin, Berlin, Germany
| | - Michael Brecht
- Bernstein Center for Computational Neuroscience, Humboldt-Universität zu Berlin, Berlin, Germany
- Neurocure Cluster of Excellence, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany
- Einstein Center for Neurosciences Berlin, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany
| | - Richard Kempter
- Institute for Theoretical Biology, Humboldt-Universität zu Berlin, Berlin, Germany
- Bernstein Center for Computational Neuroscience, Humboldt-Universität zu Berlin, Berlin, Germany
- Einstein Center for Neurosciences Berlin, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany
| | - Edvard I Moser
- Einstein Center for Neurosciences Berlin, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany
- Kavli Institute for Systems Neuroscience and Centre for Neural Computation, Norwegian University of Science and Technology, Trondheim, Norway
| | - Dietmar Schmitz
- German Center for Neurodegenerative Diseases (DZNE) Berlin, Berlin, Germany
- Neuroscience Research Center, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humbold-Universität zu Berlin, Berlin, Germany
- Berlin Institute of Health at Charité-Universitätsmedizin Berlin, Berlin, Germany
- Neurocure Cluster of Excellence, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany
- Einstein Center for Neurosciences Berlin, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany
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6
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Quattrocolo G, Dunville K, Nigro MJ. Resurgent Sodium Current in Neurons of the Cerebral Cortex. Front Cell Neurosci 2021; 15:760610. [PMID: 34658797 PMCID: PMC8517112 DOI: 10.3389/fncel.2021.760610] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Accepted: 09/13/2021] [Indexed: 11/29/2022] Open
Abstract
In the late ’90, Dr. Indira Raman, at the time a postdoctoral fellow with Dr. Bruce Bean, at Harvard University, identified a new type of sodium current, flowing through the channels that reopens when the membrane is repolarized. This current, called “resurgent Sodium current,” was originally identified in cerebellar Purkinje neurons and has now been confirmed in around 20 different neuronal types. Since moving to Northwestern University in 1999 to establish her own research group, Dr. Raman has dedicated great efforts in identifying the mechanisms supporting the resurgent Sodium current and how its biophysical properties shape the firing of the different cell types. Her work has impacted greatly the field of cellular neurophysiology, from basic research to translation neuroscience. In fact, alterations in the resurgent sodium currents have been observed in several neuropathologies, from Huntington’s disease to epilepsy. In this Perspective we will focus on the current knowledge on the expression and function of the resurgent Sodium current in neurons of the cerebral cortex and hippocampus. We will also briefly highlight the role of Dr. Raman’s as teacher and mentor, not only for her pupils, but for the whole scientific community.
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Affiliation(s)
- Giulia Quattrocolo
- Center for Neural Computation, Egil and Pauline Braathen and Fred Kavli Center for Cortical Microcircuits, Kavli Institute for Systems Neuroscience, Norwegian University of Science and Technology, Trondheim, Norway
| | - Keagan Dunville
- Center for Neural Computation, Egil and Pauline Braathen and Fred Kavli Center for Cortical Microcircuits, Kavli Institute for Systems Neuroscience, Norwegian University of Science and Technology, Trondheim, Norway
| | - Maximiliano José Nigro
- Center for Neural Computation, Egil and Pauline Braathen and Fred Kavli Center for Cortical Microcircuits, Kavli Institute for Systems Neuroscience, Norwegian University of Science and Technology, Trondheim, Norway
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7
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Lenck-Santini PP, Sakkaki S. Alterations of Neuronal Dynamics as a Mechanism for Cognitive Impairment in Epilepsy. Curr Top Behav Neurosci 2021; 55:65-106. [PMID: 33454922 DOI: 10.1007/7854_2020_193] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Epilepsy is commonly associated with cognitive and behavioral deficits that dramatically affect the quality of life of patients. In order to identify novel therapeutic strategies aimed at reducing these deficits, it is critical first to understand the mechanisms leading to cognitive impairments in epilepsy. Traditionally, seizures and epileptiform activity in addition to neuronal injury have been considered to be the most significant contributors to cognitive dysfunction. In this review we however highlight the role of a new mechanism: alterations of neuronal dynamics, i.e. the timing at which neurons and networks receive and process neural information. These alterations, caused by the underlying etiologies of epilepsy syndromes, are observed in both animal models and patients in the form of abnormal oscillation patterns in unit firing, local field potentials, and electroencephalogram (EEG). Evidence suggests that such mechanisms significantly contribute to cognitive impairment in epilepsy, independently of seizures and interictal epileptiform activity. Therefore, therapeutic strategies directly targeting neuronal dynamics rather than seizure reduction may significantly benefit the quality of life of patients.
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Affiliation(s)
- Pierre-Pascal Lenck-Santini
- Aix-Marseille Université, INSERM, INMED, Marseille, France. .,Department of Neurological sciences, University of Vermont, Burlington, VT, USA.
| | - Sophie Sakkaki
- Department of Neurological sciences, University of Vermont, Burlington, VT, USA.,Université de. Montpellier, CNRS, INSERM, IGF, Montpellier, France
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8
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Beesley S, Sullenberger T, Ailani R, D'Orio C, Crockett MS, Kumar SS. d-Serine Intervention In The Medial Entorhinal Area Alters TLE-Related Pathology In CA1 Hippocampus Via The Temporoammonic Pathway. Neuroscience 2021; 453:168-186. [PMID: 33197499 PMCID: PMC7796904 DOI: 10.1016/j.neuroscience.2020.10.025] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Revised: 10/20/2020] [Accepted: 10/22/2020] [Indexed: 01/15/2023]
Abstract
Entrainment of the hippocampus by the medial entorhinal area (MEA) in Temporal Lobe Epilepsy (TLE), the most common type of drug-resistant epilepsy in adults, is believed to be mediated primarily through the perforant pathway (PP), which connects stellate cells in layer (L) II of the MEA with granule cells of the dentate gyrus (DG) to drive the hippocampal tri-synaptic circuit. Using immunohistochemistry, high-resolution confocal microscopy and the rat pilocarpine model of TLE, we show here that the lesser known temporoammonic pathway (TAP) plays a significant role in transferring MEA pathology to the CA1 region of the hippocampus independently of the PP. The pathology observed was region-specific and restricted primarily to the CA1c subfield of the hippocampus. As shown previously, daily intracranial infusion of d-serine (100 μm), an antagonist of GluN3-containing triheteromeric N-Methyl d-aspartate receptors (t-NMDARs), into the MEA prevented loss of LIII neurons and epileptogenesis. This intervention in the MEA led to the rescue of hippocampal CA1 neurons that would have otherwise perished in the epileptic animals, and down regulation of the expression of astrocytes and microglia thereby mitigating the effects of neuroinflammation. Interestingly, these changes were not observed to a similar extent in other regions of vulnerability like the hilus, DG or CA3, suggesting that the pathology manifest in CA1 is driven predominantly through the TAP. This work highlights TAP's role in the entrainment of the hippocampus and identifies specific areas for therapeutic intervention in dealing with TLE.
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Affiliation(s)
- Stephen Beesley
- Department of Biomedical Sciences, College of Medicine & Program in Neuroscience, Florida State University, 1115 W. Call Street, Tallahassee, FL 32306-4300, United States
| | - Thomas Sullenberger
- Department of Biomedical Sciences, College of Medicine & Program in Neuroscience, Florida State University, 1115 W. Call Street, Tallahassee, FL 32306-4300, United States
| | - Roshan Ailani
- Department of Biomedical Sciences, College of Medicine & Program in Neuroscience, Florida State University, 1115 W. Call Street, Tallahassee, FL 32306-4300, United States
| | - Cameron D'Orio
- Department of Biomedical Sciences, College of Medicine & Program in Neuroscience, Florida State University, 1115 W. Call Street, Tallahassee, FL 32306-4300, United States
| | - Mathew S Crockett
- Department of Biomedical Sciences, College of Medicine & Program in Neuroscience, Florida State University, 1115 W. Call Street, Tallahassee, FL 32306-4300, United States
| | - Sanjay S Kumar
- Department of Biomedical Sciences, College of Medicine & Program in Neuroscience, Florida State University, 1115 W. Call Street, Tallahassee, FL 32306-4300, United States.
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Sullenberger T, Don H, Kumar SS. Functional Connectivity of the Parasubiculum and Its Role in Temporal Lobe Epilepsy. Neuroscience 2019; 410:217-238. [PMID: 31121261 DOI: 10.1016/j.neuroscience.2019.05.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2019] [Revised: 04/22/2019] [Accepted: 05/05/2019] [Indexed: 10/26/2022]
Abstract
Temporal lobe epilepsy (TLE) is the commonest of adult epilepsies, often refractory to antiepileptic medications, whose prevention and treatment rely on understanding basic pathophysiological mechanisms in interlinked structures of the temporal lobe. The medial entorhinal area (MEA) is affected in TLE but mechanisms underlying hyperexcitability of MEA neurons require further elucidation. Previous studies have examined the role of the presubiculum (PrS) in mediating MEA pathophysiology but not the juxtaposed parasubiculum (Par). Here, we report on an electrophysiological assessment of the cells and circuits of the Par, their excitability under normal and epileptic conditions, and alterations in functional connectivity with neighboring PrS and MEA using the rat pilocarpine model of TLE. We show that Par, unlike the cell heterogeneous PrS, has a single dominant neuronal population whose excitability under epileptic conditions is altered by changes in both intrinsic properties and synaptic drive. These neurons experience significant reductions in synaptic inhibition and perish under chronic epileptic conditions. Connectivity between brain regions was deduced through changes in excitatory and inhibitory synaptic drive to neurons recorded in one region upon focal application of glutamate followed by NBQX to neurons in another using a microfluidic technique called CESOP and TLE-related circuit reorganization was assessed using data from normal and epileptic animals. The region-specific changes in Par and neighboring PrS and MEA together with their unexpected interactions are of significance in identifying ictogenic cells and circuits within the parahippocampal region and in unraveling pathophysiological mechanisms underlying TLE.
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Affiliation(s)
- Thomas Sullenberger
- Department of Biomedical Sciences, College of Medicine & Program in Neuroscience, Florida State University, 1115 W. Call Street, Tallahassee, FL 32306-4300, United States of America
| | - Hershel Don
- Department of Biomedical Sciences, College of Medicine & Program in Neuroscience, Florida State University, 1115 W. Call Street, Tallahassee, FL 32306-4300, United States of America
| | - Sanjay S Kumar
- Department of Biomedical Sciences, College of Medicine & Program in Neuroscience, Florida State University, 1115 W. Call Street, Tallahassee, FL 32306-4300, United States of America.
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10
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Moxon KA, Shahlaie K, Girgis F, Saez I, Kennedy J, Gurkoff GG. From adagio to allegretto: The changing tempo of theta frequencies in epilepsy and its relation to interneuron function. Neurobiol Dis 2019; 129:169-181. [PMID: 30798003 DOI: 10.1016/j.nbd.2019.02.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2018] [Revised: 02/06/2019] [Accepted: 02/20/2019] [Indexed: 12/29/2022] Open
Abstract
Despite decades of research, our understanding of epilepsy, including how seizures are generated and propagate, is incomplete. However, there is growing recognition that epilepsy is more than just the occurrence of seizures, with patients often experiencing comorbid deficits in cognition that are poorly understood. In addition, the available therapies for treatment of epilepsy, from pharmaceutical treatment to surgical resection and seizure prevention devices, often exacerbate deficits in cognitive function. In this review, we discuss the hypothesis that seizure generation and cognitive deficits have a similar pathological source characterized by, but not limited to, deficits in theta oscillations and their influence on interneurons. We present a new framework that describes oscillatory states in epilepsy as alternating between hyper- and hypo-synchrony rather than solely the spontaneous transition to hyper-excitability characterized by the seizures. This framework suggests that as neural oscillations, specifically in the theta range, vary their tempo from a slowed almost adagio tempo during interictal periods to faster, more rhythmic allegretto tempo preictally, they impact the function of interneurons, modulating their ability to control seizures and their role in cognitive processing. This slow wave oscillatory framework may help explain why current therapies that work to reduce hyper-excitability do not completely eliminate seizures and often lead to exacerbated cognitive deficits.
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Affiliation(s)
- Karen A Moxon
- Department of Biomedical Engineering, University of California Davis, Davis, CA 95616, United States of America.
| | - Kiarash Shahlaie
- Department of Neurological Surgery, University of California Davis, Sacramento, CA 95817, United States of America; Center for Neuroscience, University of California Davis, Davis, CA 95618, United States of America
| | - Fady Girgis
- Department of Neurological Surgery, University of California Davis, Sacramento, CA 95817, United States of America
| | - Ignacio Saez
- Department of Neurological Surgery, University of California Davis, Sacramento, CA 95817, United States of America; Center for Neuroscience, University of California Davis, Davis, CA 95618, United States of America
| | - Jeffrey Kennedy
- Department of Neurology, University of California Davis, Sacramento, CA 95817, United States of America
| | - Gene G Gurkoff
- Department of Neurological Surgery, University of California Davis, Sacramento, CA 95817, United States of America; Center for Neuroscience, University of California Davis, Davis, CA 95618, United States of America
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11
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Trigeminal Nerve Transection-Induced Neuroplastic Changes in the Somatosensory and Insular Cortices in a Rat Ectopic Pain Model. eNeuro 2019; 6:eN-NWR-0462-18. [PMID: 30693315 PMCID: PMC6348450 DOI: 10.1523/eneuro.0462-18.2019] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2018] [Revised: 12/21/2018] [Accepted: 01/03/2019] [Indexed: 11/21/2022] Open
Abstract
The primary sensory cortex processes competitive sensory inputs. Ablation of these competitive inputs induces neuroplastic changes in local cortical circuits. However, information concerning cortical plasticity induced by a disturbance of competitive nociceptive inputs is limited. Nociceptive information from the maxillary and mandibular molar pulps converges at the border between the ventral secondary somatosensory cortex (S2) and insular oral region (IOR); therefore, S2/IOR is a suitable target for examining the cortical changes induced by a disturbance of noxious inputs, which often causes neuropathic pain and allodynia. We focused on the plastic changes in S2/IOR excitation in a model of rats subjected to inferior alveolar nerve transection (IANX). Our optical imaging using a voltage-sensitive dye (VSD) revealed that the maxillary molar pulp stimulation-induced excitatory propagation was expanded one to two weeks after IANX at the macroscopic level. At the cellular level, based on Ca2+ imaging using two-photon microscopy, the amplitude of the Ca2+ responses and the number of responding neurons in S2/IOR increased in both excitatory and inhibitory neurons. The in vitro laser scanning photostimulation (LSPS) revealed that Layer II/III pyramidal and GABAergic fast-spiking neurons in S2/IOR received larger excitatory inputs from Layer IV in the IANX models, which supports the findings obtained by the macroscopic and microscopic optical imaging. Furthermore, the inhibitory postsynaptic inputs to the pyramidal neurons were decreased in the IANX models, suggesting suppression of inhibitory synaptic transmission onto excitatory neurons. These results suggest that IANX induces plastic changes in S2/IOR by changing the local excitatory and inhibitory circuits.
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12
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Zhang J, Chen X, Kårbø M, Zhao Y, An L, Wang R, Wang K, Huang Z. Anticonvulsant effect of dipropofol by enhancing native GABA currents in cortical neurons in mice. J Neurophysiol 2018; 120:1404-1414. [DOI: 10.1152/jn.00241.2018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Temporal lobe epilepsy (TLE), the most common pharmacoresistant focal epilepsy disorder, remains a major unmet medical need. Propofol is used as a short-acting medication for general anesthesia and refractory status epilepticus with issues of decreased consciousness and memory loss. Dipropofol, a derivative of propofol, has been reported to exert antioxidative and antibacterial activities. Here we report that dipropofol exerted anticonvulsant activity in a mouse model of kainic acid-induced seizures. Whole cell patch-clamp recordings of brain slices from the medial entorhinal cortex (mEC) revealed that dipropofol hyperpolarized the resting membrane potential and reduced the number of action potential firings, resulting in suppression of cortical neuronal excitability. Furthermore, dipropofol activated native tonic GABAA currents of mEC layer II stellate neurons in a dose-dependent manner with an EC50 value of 9.3 ± 1.6 μM (mean ± SE). Taken together, our findings show that dipropofol activated GABAA currents and exerted anticonvulsant activities in mice, thus possessing developmental potential for new anticonvulsant therapy. NEW & NOTEWORTHY The anticonvulsant effect of dipropofol was shown in a mouse model of kainic acid-induced seizures. Whole cell patch-clamp recordings of brain slices showed suppression of cortical neuronal excitability by dipropofol. Dipropofol activated the native tonic GABAA currents in a dose-dependent manner.
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Affiliation(s)
- Jingliang Zhang
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking University Health Science Center, Beijing, China
| | - Xiaoling Chen
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking University Health Science Center, Beijing, China
| | - Matti Kårbø
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking University Health Science Center, Beijing, China
| | - Yi Zhao
- Tech-Development Department, Xi’an Libang Pharmaceutical Company, Xi’an, China
| | - Long An
- Tech-Development Department, Xi’an Libang Pharmaceutical Company, Xi’an, China
| | - Rutao Wang
- Tech-Development Department, Xi’an Libang Pharmaceutical Company, Xi’an, China
| | - KeWei Wang
- Department of Pharmacology, Qingdao University School of Pharmacy, Qingdao, China
| | - Zhuo Huang
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking University Health Science Center, Beijing, China
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Takahashi DK, Jin S, Prince DA. Gabapentin Prevents Progressive Increases in Excitatory Connectivity and Epileptogenesis Following Neocortical Trauma. Cereb Cortex 2018; 28:2725-2740. [PMID: 28981586 PMCID: PMC6041890 DOI: 10.1093/cercor/bhx152] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Revised: 05/30/2017] [Accepted: 06/01/2017] [Indexed: 11/12/2022] Open
Abstract
Neocortical injury initiates a cascade of events, some of which result in maladaptive epileptogenic reorganization of surviving neural circuits. Research focused on molecular and organizational changes that occur following trauma may reveal processes that underlie human post-traumatic epilepsy (PTE), a common and unfortunate consequence of traumatic brain injury. The latency between injury and development of PTE provides an opportunity for prophylactic intervention, once the key underlying mechanisms are understood. In rodent neocortex, injury to pyramidal neurons promotes axonal sprouting, resulting in increased excitatory circuitry that is one important factor promoting epileptogenesis. We used laser-scanning photostimulation of caged glutamate and whole-cell recordings in in vitro slices from injured neocortex to assess formation of new excitatory synapses, a process known to rely on astrocyte-secreted thrombospondins (TSPs), and to map the distribution of maladaptive circuit reorganization. We show that this reorganization is centered principally in layer V and associated with development of epileptiform activity. Short-term blockade of the synaptogenic effects of astrocyte-secreted TSPs with gabapentin (GBP) after injury suppresses the new excitatory connectivity and epileptogenesis for at least 2 weeks. Results reveal that aberrant circuit rewiring is progressive in vivo and provide further rationale for prophylactic anti-epileptogenic use of gabapentinoids following cortical trauma.
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Affiliation(s)
- D K Takahashi
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA, USA
| | - Sha Jin
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA, USA
| | - D A Prince
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA, USA
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Karunakaran S, Grasse DW, Moxon KA. Role of CA3 theta-modulated interneurons during the transition to spontaneous seizures. Exp Neurol 2016; 283:341-52. [DOI: 10.1016/j.expneurol.2016.06.027] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Revised: 05/27/2016] [Accepted: 06/24/2016] [Indexed: 10/21/2022]
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15
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Armstrong C, Wang J, Yeun Lee S, Broderick J, Bezaire MJ, Lee SH, Soltesz I. Target-selectivity of parvalbumin-positive interneurons in layer II of medial entorhinal cortex in normal and epileptic animals. Hippocampus 2016; 26:779-93. [PMID: 26663222 DOI: 10.1002/hipo.22559] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/10/2015] [Indexed: 11/12/2022]
Abstract
The medial entorhinal cortex layer II (MEClayerII ) is a brain region critical for spatial navigation and memory, and it also demonstrates a number of changes in patients with, and animal models of, temporal lobe epilepsy (TLE). Prior studies of GABAergic microcircuitry in MEClayerII revealed that cholecystokinin-containing basket cells (CCKBCs) select their targets on the basis of the long-range projection pattern of the postsynaptic principal cell. Specifically, CCKBCs largely avoid reelin-containing principal cells that form the perforant path to the ipsilateral dentate gyrus and preferentially innervate non-perforant path forming calbindin-containing principal cells. We investigated whether parvalbumin containing basket cells (PVBCs), the other major perisomatic targeting GABAergic cell population, demonstrate similar postsynaptic target selectivity as well. In addition, we tested the hypothesis that the functional or anatomic arrangement of circuit selectivity is disrupted in MEClayerII in chronic TLE, using the repeated low-dose kainate model in rats. In control animals, we found that PVBCs innervated both principal cell populations, but also had significant selectivity for calbindin-containing principal cells in MEClayerII . However, the magnitude of this preference was smaller than for CCKBCs. In addition, axonal tracing and paired recordings showed that individual PVBCs were capable of contacting both calbindin and reelin-containing principal cells. In chronically epileptic animals, we found that the intrinsic properties of the two principal cell populations, the GABAergic perisomatic bouton numbers, and selectivity of the CCKBCs and PVBCs remained remarkably constant in MEClayerII . However, miniature IPSC frequency was decreased in epilepsy, and paired recordings revealed the presence of direct excitatory connections between principal cells in the MEClayerII in epilepsy, which is unusual in normal adult MEClayerII . Taken together, these findings advance our knowledge about the organization of perisomatic inhibition both in control and in epileptic animals. © 2015 Wiley Periodicals, Inc.
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Affiliation(s)
- Caren Armstrong
- Irvine Department of Anatomy & Neurobiology, University of California, Irvine, California
| | - Jessica Wang
- Irvine Department of Anatomy & Neurobiology, University of California, Irvine, California
| | - Soo Yeun Lee
- Irvine Department of Anatomy & Neurobiology, University of California, Irvine, California
| | - John Broderick
- Irvine Department of Anatomy & Neurobiology, University of California, Irvine, California
| | - Marianne J Bezaire
- Irvine Department of Anatomy & Neurobiology, University of California, Irvine, California
| | - Sang-Hun Lee
- Irvine Department of Anatomy & Neurobiology, University of California, Irvine, California
| | - Ivan Soltesz
- Irvine Department of Anatomy & Neurobiology, University of California, Irvine, California.,Department of Neurosurgery, Stanford University, Palo Alto, CA
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Gao F, Song X, Zhu D, Wang X, Hao A, Nadler JV, Zhan RZ. Dendritic morphology, synaptic transmission, and activity of mature granule cells born following pilocarpine-induced status epilepticus in the rat. Front Cell Neurosci 2015; 9:384. [PMID: 26500490 PMCID: PMC4596052 DOI: 10.3389/fncel.2015.00384] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2015] [Accepted: 09/14/2015] [Indexed: 01/23/2023] Open
Abstract
To understand the potential role of enhanced hippocampal neurogenesis after pilocarpine-induced status epilepticus (SE) in the development of epilepsy, we quantitatively analyzed the geometry of apical dendrites, synaptic transmission, and activation levels of normotopically distributed mature newborn granule cells in the rat. SE in male Sprague-Dawley rats (between 6 and 7 weeks old) lasting for more than 2 h was induced by an intraperitoneal injection of pilocarpine. The complexity, spine density, miniature post-synaptic currents, and activity-regulated cytoskeleton-associated protein (Arc) expression of granule cells born 5 days after SE were studied between 10 and 17 weeks after CAG-GFP retroviral vector-mediated labeling. Mature granule cells born after SE had dendritic complexity similar to that of granule cells born naturally, but with denser mushroom-like spines in dendritic segments located in the outer molecular layer. Miniature inhibitory post-synaptic currents (mIPSCs) were similar between the controls and rats subjected to SE; however, smaller miniature excitatory post-synaptic current (mEPSC) amplitude with a trend toward less frequent was found in mature granule cells born after SE. After maturation, granule cells born after SE did not show denser Arc expression in the resting condition or 2 h after being activated by pentylenetetrazol-induced transient seizure activity than vicinal GFP-unlabeled granule cells. Thus our results suggest that normotopic granule cells born after pilocarpine-induced SE are no more active when mature than age-matched, naturally born granule cells.
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Affiliation(s)
- Fei Gao
- Department of Physiology, Shandong University School of Medicine Jinan, China
| | - Xueying Song
- Department of Physiology, Shandong University School of Medicine Jinan, China
| | - Dexiao Zhu
- Department of Physiology, Shandong University School of Medicine Jinan, China
| | - Xiaochen Wang
- Department of Physiology, Shandong University School of Medicine Jinan, China
| | - Aijun Hao
- Department of Histology and Embryology, Shandong University School of Medicine Jinan, China
| | - J Victor Nadler
- Departments of Pharmacology and Neurobiology, Duke University Medical Center Durham, NC, USA
| | - Ren-Zhi Zhan
- Department of Physiology, Shandong University School of Medicine Jinan, China
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Abbasi S, Kumar SS. Layer-specific modulation of entorhinal cortical excitability by presubiculum in a rat model of temporal lobe epilepsy. J Neurophysiol 2015; 114:2854-66. [PMID: 26378210 DOI: 10.1152/jn.00823.2015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2015] [Accepted: 09/09/2015] [Indexed: 11/22/2022] Open
Abstract
Temporal lobe epilepsy (TLE) is the most common form of epilepsy in adults and is often refractory to antiepileptic medications. The medial entorhinal area (MEA) is affected in TLE but mechanisms underlying hyperexcitability of MEA neurons require further elucidation. Previous studies suggest that inputs from the presubiculum (PrS) contribute to MEA pathophysiology. We assessed electrophysiologically how PrS influences MEA excitability using the rat pilocarpine model of TLE. PrS-MEA connectivity was confirmed by electrically stimulating PrS afferents while recording from neurons within superficial layers of MEA. Assessment of alterations in PrS-mediated synaptic drive to MEA neurons was made following focal application of either glutamate or NBQX to the PrS in control and epileptic animals. Here, we report that monosynaptic inputs to MEA from PrS neurons are conserved in epileptic rats, and that PrS modulation of MEA excitability is layer-specific. PrS contributes more to synaptic inhibition of LII stellate cells than excitation. Under epileptic conditions, stellate cell inhibition is significantly reduced while excitatory synaptic drive is maintained at levels similar to control. PrS contributes to both synaptic excitation and inhibition of LIII pyramidal cells in control animals. Under epileptic conditions, overall excitatory synaptic drive to these neurons is enhanced while inhibitory synaptic drive is maintained at control levels. Additionally, neither glutamate nor NBQX applied focally to PrS now affected EPSC and IPSC frequency of LIII pyramidal neurons. These layer-specific changes in PrS-MEA interactions are unexpected and of significance in unraveling pathophysiological mechanisms underlying TLE.
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Affiliation(s)
- Saad Abbasi
- Department of Biomedical Sciences, College of Medicine and Program in Neuroscience, Florida State University, Tallahassee, Florida
| | - Sanjay S Kumar
- Department of Biomedical Sciences, College of Medicine and Program in Neuroscience, Florida State University, Tallahassee, Florida
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18
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Laurent F, Brotons-Mas JR, Cid E, Lopez-Pigozzi D, Valero M, Gal B, de la Prida LM. Proximodistal structure of theta coordination in the dorsal hippocampus of epileptic rats. J Neurosci 2015; 35:4760-75. [PMID: 25788692 PMCID: PMC6605134 DOI: 10.1523/jneurosci.4297-14.2015] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2014] [Revised: 01/16/2015] [Accepted: 02/10/2015] [Indexed: 01/10/2023] Open
Abstract
Coherent neuronal activity in the hippocampal-entorhinal circuit is a critical mechanism for episodic memory function, which is typically impaired in temporal lobe epilepsy. To better understand how this mechanism is implemented and degraded in this condition, we used normal and epileptic rats to examine theta activity accompanying active exploration. Assisted by multisite recordings of local field potentials (LFPs) and layer-specific profiling of input pathways, we provide detailed quantification of the proximodistal coherence of theta activity in the dorsal hippocampus of these animals. Normal rats showed stronger coordination between the temporoammonic and perforant entorhinal inputs (measured from lamina-specific current source density signals) at proximal locations, i.e., closer to CA3; while epileptic rats exhibited stronger interactions at distal locations, i.e., closer to subiculum. This opposing trend in epileptic rats was associated with the reorganization of the temporoammonic and perforant pathways that accompany hippocampal sclerosis, the pathological hallmark of this disease. In addition to this connectivity constraint, we discovered that the appropriate timing between entorhinal inputs arriving over several theta cycles at the proximal and distal ends of the dorsal hippocampus was impaired in epileptic rats. Computational reconstruction of LFP signals predicted that restoring timing variability has a major impact on repairing theta coherence. This manipulation, when tested pharmacologically via systemic administration of group III mGluR antagonists, successfully re-established theta coordination of LFPs in epileptic rats. Thus, proximodistal organization of entorhinal inputs is instrumental in temporal lobe physiology and a candidate mechanism to study cognitive comorbidities of temporal lobe epilepsy.
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Affiliation(s)
| | | | - Elena Cid
- Instituto Cajal, CSIC, Madrid 28002, Spain and
| | | | | | - Beatriz Gal
- Instituto Cajal, CSIC, Madrid 28002, Spain and Universidad Europea de Madrid, Villaviciosa de Odón, Madrid 28670, Spain
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19
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Long LL, Bunce JG, Chrobak JJ. Theta variation and spatiotemporal scaling along the septotemporal axis of the hippocampus. Front Syst Neurosci 2015; 9:37. [PMID: 25852496 PMCID: PMC4360780 DOI: 10.3389/fnsys.2015.00037] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2014] [Accepted: 02/23/2015] [Indexed: 01/03/2023] Open
Abstract
Hippocampal theta has been related to locomotor speed, attention, anxiety, sensorimotor integration and memory among other emergent phenomena. One difficulty in understanding the function of theta is that the hippocampus (HPC) modulates voluntary behavior at the same time that it processes sensory input. Both functions are correlated with characteristic changes in theta indices. The current review highlights a series of studies examining theta local field potential (LFP) signals across the septotemporal or longitudinal axis of the HPC. While the theta signal is coherent throughout the entirety of the HPC, the amplitude, but not the frequency, of theta varies significantly across its three-dimensional expanse. We suggest that the theta signal offers a rich vein of information about how distributed neuronal ensembles support emergent function. Further, we speculate that emergent function across the long axis varies with respect to spatiotemporal scale. Thus, septal HPC processes details of the proximal spatiotemporal environment while more temporal aspects process larger spaces and wider time-scales. The degree to which emergent functions are supported by the synchronization of theta across the septotemporal axis is an open question. Our working model is that theta synchrony serves to bind ensembles representing varying resolutions of spatiotemporal information at interdependent septotemporal areas of the HPC. Such synchrony and cooperative interactions along the septotemporal axis likely support memory formation and subsequent consolidation and retrieval.
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Affiliation(s)
- Lauren L Long
- Behavioral Neuroscience Division, Department of Psychology, University of Connecticut Storrs, CT, USA
| | - Jamie G Bunce
- Neural Systems Lab, Department of Health Sciences, Boston University Boston, MA, USA
| | - James J Chrobak
- Behavioral Neuroscience Division, Department of Psychology, University of Connecticut Storrs, CT, USA
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20
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Abbasi S, Kumar SS. Regular-spiking cells in the presubiculum are hyperexcitable in a rat model of temporal lobe epilepsy. J Neurophysiol 2014; 112:2888-900. [PMID: 25210155 DOI: 10.1152/jn.00406.2014] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Temporal lobe epilepsy (TLE) is the most common form of adult epilepsy, characterized by recurrent seizures originating in the temporal lobes. Here, we examine TLE-related changes in the presubiculum (PrS), a less-studied parahippocampal structure that both receives inputs from and projects to regions affected by TLE. We assessed the state of PrS neurons in TLE electrophysiologically to determine which of the previously identified cell types were rendered hyperexcitable in epileptic rats and whether their intrinsic and/or synaptic properties were altered. Cell types were characterized based on action potential discharge profiles followed by unsupervised hierarchical clustering. PrS neurons in epileptic animals could be divided into three major groups comprising of regular-spiking (RS), irregular-spiking (IR), and fast-adapting (FA) cells. RS cells, the predominant cell type encountered in PrS, were the only cells that were hyperexcitable in TLE. These neurons were previously identified as sending long-range axonal projections to neighboring structures including medial entorhinal area (MEA), and alterations in intrinsic properties increased their propensity for sustained firing of action potentials. Frequency and amplitude of both spontaneous excitatory and inhibitory synaptic events were reduced. Further analysis of nonaction potential-dependent miniature currents (in tetrodotoxin) indicated that reduction in excitatory drive to these neurons was mediated by decreased activity of excitatory neurons that synapse with RS cells concomitant with reduced activity of inhibitory neurons. Alterations in physiological properties of PrS neurons and their ensuing hyperexcitability could entrain parahippocampal structures downstream of PrS, including the MEA, contributing to temporal lobe epileptogenesis.
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Affiliation(s)
- Saad Abbasi
- Department of Biomedical Sciences, College of Medicine and Program in Neuroscience, Florida State University, Tallahassee, Florida
| | - Sanjay S Kumar
- Department of Biomedical Sciences, College of Medicine and Program in Neuroscience, Florida State University, Tallahassee, Florida
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21
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Jin X, Jiang K, Prince DA. Excitatory and inhibitory synaptic connectivity to layer V fast-spiking interneurons in the freeze lesion model of cortical microgyria. J Neurophysiol 2014; 112:1703-13. [PMID: 24990567 DOI: 10.1152/jn.00854.2013] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A variety of major developmental cortical malformations are closely associated with clinically intractable epilepsy. Pathophysiological aspects of one such disorder, human polymicrogyria, can be modeled by making neocortical freeze lesions (FL) in neonatal rodents, resulting in the formation of microgyri. Previous studies showed enhanced excitatory and inhibitory synaptic transmission and connectivity in cortical layer V pyramidal neurons in the paramicrogyral cortex. In young adult transgenic mice that express green fluorescent protein (GFP) specifically in parvalbumin positive fast-spiking (FS) interneurons, we used laser scanning photostimulation (LSPS) of caged glutamate to map excitatory and inhibitory synaptic connectivity onto FS interneurons in layer V of paramicrogyral cortex in control and FL groups. The proportion of uncaging sites from which excitatory postsynaptic currents (EPSCs) could be evoked (hotspot ratio) increased slightly but significantly in FS cells of the FL vs. control cortex, while the mean amplitude of LSPS-evoked EPSCs at hotspots did not change. In contrast, the hotspot ratio of inhibitory postsynaptic currents (IPSCs) was significantly decreased in FS neurons of the FL cortex. These alterations in synaptic inputs onto FS interneurons may result in an enhanced inhibitory output. We conclude that alterations in synaptic connectivity to cortical layer V FS interneurons do not contribute to hyperexcitability of the FL model. Instead, the enhanced inhibitory output from these neurons may partially offset an earlier demonstrated increase in synaptic excitation of pyramidal cells and thereby maintain a relative balance between excitation and inhibition in the affected cortical circuitry.
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Affiliation(s)
- Xiaoming Jin
- Stark Neurosciences Research Institute, Indiana Spinal Cord and Brain Injury Research Group, Indiana University School of Medicine, Indianapolis, Indiana; Departments of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, Indiana; Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, California
| | - Kewen Jiang
- Stark Neurosciences Research Institute, Indiana Spinal Cord and Brain Injury Research Group, Indiana University School of Medicine, Indianapolis, Indiana; Department of Neurology, Children's Hospital of the Zhejiang University School of Medicine, Hangzhou, Zhejiang, China; and
| | - David A Prince
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, California
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Ren H, Shi YJ, Lu QC, Liang PJ, Zhang PM. The role of the entorhinal cortex in epileptiform activities of the hippocampus. Theor Biol Med Model 2014; 11:14. [PMID: 24656055 PMCID: PMC3994397 DOI: 10.1186/1742-4682-11-14] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2014] [Accepted: 03/17/2014] [Indexed: 01/24/2023] Open
Abstract
BACKGROUND Temporal lobe epilepsy (TLE) is the commonest type of epilepsy in adults, and the hippocampus is indicated to have a close relationship with TLE. Recent researches also indicate that the entorhinal cortex (EC) is involved in epilepsy. To explore the essential role that the EC may play in epilepsy, a computational model of the hippocampal CA3 region was built, which consisted of pyramidal cells and two types of interneurons. By changing the input signals from the EC, the effects of EC on epileptiform activities of the hippocampus were investigated. Additionally, recent studies have found that the antiepileptic drug valproate (VPA) can block ictal discharges but cannot block interictal discharges in vitro, and the mechanism under this phenomenon is still confusing. In our model, the effects of VPA on epileptiform activities were simulated and some mechanisms were explored. RESULTS Interictal discharges were induced in the model without the input signals from the EC, whereas the model with the EC input produced ictal discharges when the EC input contained ictal discharges. The GABA-ergic connection strength was enhanced and the NMDA-ergic connection strength was reduced to simulate the effects of VPA, and the simulation results showed that the disappearance of ictal discharges in the model mainly due to the disappearance of ictal discharges in the input signals from the EC. CONCLUSIONS Simulation results showed that ictal discharges in the EC were necessary for the hippocampus to generate ictal discharges, and VPA might block the ictal discharges in the EC, which led to the disappearance of ictal discharges in the hippocampus.
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Affiliation(s)
| | | | | | | | - Pu-Ming Zhang
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
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Gorter JA, Iyer A, White I, Colzi A, van Vliet EA, Sisodiya S, Aronica E. Hippocampal subregion-specific microRNA expression during epileptogenesis in experimental temporal lobe epilepsy. Neurobiol Dis 2014; 62:508-20. [DOI: 10.1016/j.nbd.2013.10.026] [Citation(s) in RCA: 141] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2013] [Revised: 10/11/2013] [Accepted: 10/24/2013] [Indexed: 11/25/2022] Open
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Cellular, columnar and modular organization of spatial representations in medial entorhinal cortex. Curr Opin Neurobiol 2014; 24:47-54. [DOI: 10.1016/j.conb.2013.08.011] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2013] [Revised: 08/14/2013] [Accepted: 08/15/2013] [Indexed: 11/20/2022]
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Brecht M, Ray S, Burgalossi A, Tang Q, Schmidt H, Naumann R. An isomorphic mapping hypothesis of the grid representation. Philos Trans R Soc Lond B Biol Sci 2013; 369:20120521. [PMID: 24366133 PMCID: PMC3866443 DOI: 10.1098/rstb.2012.0521] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
We introduce a grid cell microcircuit hypothesis. We propose the ‘grid in the world’ (evident in grid cell discharges) is generated by a ‘grid in the cortex’. This cortical grid is formed by patches of calbindin-positive pyramidal neurons in layer 2 of medial entorhinal cortex (MEC). Our isomorphic mapping hypothesis assumes three types of isomorphism: (i) metric correspondence of neural space (the two-dimensional cortical sheet) and the external two-dimensional space within patches; (ii) isomorphism between cellular connectivity matrix and firing field; (iii) isomorphism between single cell and population activity. Each patch is a grid cell lattice arranged in a two-dimensional map of space with a neural : external scale of approximately 1 : 2000 in the dorsal part of rat MEC. The lattice behaves like an excitable medium with neighbouring grid cells exciting each other. Spatial scale is implemented as an intrinsic scaling factor for neural propagation speed. This factor varies along the dorsoventral cortical axis. A connectivity scheme of the grid system is described. Head direction input specifies the direction of activity propagation. We extend the theory to neurons between grid patches and predict a rare discharge pattern (inverted grid cells) and the relative location and proportion of grid cells and spatial band cells.
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Affiliation(s)
- Michael Brecht
- Bernstein Center for Computational Neuroscience, Humboldt University of Berlin, , Philippstrasse 13 Haus 6, 10115 Berlin, Germany
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Rotstein HG. Abrupt and gradual transitions between low and hyperexcited firing frequencies in neuronal models with fast synaptic excitation: a comparative study. CHAOS (WOODBURY, N.Y.) 2013; 23:046104. [PMID: 24387583 DOI: 10.1063/1.4824320] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Hyperexcitability of neuronal networks is one of the hallmarks of epileptic brain seizure generation, and results from a net imbalance between excitation and inhibition that promotes excessive abnormal firing frequencies. The transition between low and high firing frequencies as the levels of recurrent AMPA excitation change can occur either gradually or abruptly. We used modeling, numerical simulations, and dynamical systems tools to investigate the biophysical and dynamic mechanisms that underlie these two identified modes of transition in recurrently connected neurons via AMPA excitation. We compare our results and demonstrate that these two modes of transition are qualitatively different and can be linked to different intrinsic properties of the participating neurons.
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Affiliation(s)
- Horacio G Rotstein
- Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, New Jersey 07102, USA
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Inhibitory Gradient along the Dorsoventral Axis in the Medial Entorhinal Cortex. Neuron 2013; 79:1197-207. [PMID: 24050405 DOI: 10.1016/j.neuron.2013.06.038] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/23/2013] [Indexed: 11/23/2022]
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Hargus NJ, Nigam A, Bertram EH, Patel MK. Evidence for a role of Nav1.6 in facilitating increases in neuronal hyperexcitability during epileptogenesis. J Neurophysiol 2013; 110:1144-57. [PMID: 23741036 DOI: 10.1152/jn.00383.2013] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
During epileptogenesis a series of molecular and cellular events occur, culminating in an increase in neuronal excitability, leading to seizure initiation. The entorhinal cortex has been implicated in the generation of epileptic seizures in both humans and animal models of temporal lobe epilepsy. This hyperexcitability is due, in part, to proexcitatory changes in ion channel activity. Sodium channels play an important role in controlling neuronal excitability, and alterations in their activity could facilitate seizure initiation. We sought to investigate whether medial entorhinal cortex (mEC) layer II neurons become hyperexcitable and display proexcitatory behavior of Na channels during epileptogenesis. Experiments were conducted 7 days after electrical induction of status epilepticus (SE), a time point during the latent period of epileptogenesis and before the onset of seizures. mEC layer II stellate neurons from post-SE animals were hyperexcitable, eliciting action potentials at higher frequencies compared with control neurons. Na channel currents recorded from post-SE neurons revealed increases in Na current amplitudes, particularly persistent and resurgent currents, as well as depolarized shifts in inactivation parameters. Immunocytochemical studies revealed increases in voltage-gated Na (Nav) 1.6 isoform levels. The toxin 4,9-anhydro-tetrodotoxin, which has greater selectivity for Nav1.6 over other Na channel isoforms, suppressed neuronal hyperexcitability, reduced macroscopic Na currents, persistent and resurgent Na current densities, and abolished depolarized shifts in inactivation parameters in post-SE neurons. These studies support a potential role for Nav1.6 in facilitating the hyperexcitability of mEC layer II neurons during epileptogenesis.
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Affiliation(s)
- Nicholas J Hargus
- Department of Anesthesiology, University of Virginia Health System, Charlottesville, VA 22908-0710, USA
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Abstract
Cortical circuits are thought to multiplex firing rate codes with temporal codes that rely on oscillatory network activity, but the circuit mechanisms that combine these coding schemes are unclear. We establish with optogenetic activation of layer II of the medial entorhinal cortex that theta frequency drive to this circuit is sufficient to generate nested gamma frequency oscillations in synaptic activity. These nested gamma oscillations closely resemble activity during spatial exploration, are generated by local feedback inhibition without recurrent excitation, and have clock-like features suitable as reference signals for multiplexing temporal codes within rate-coded grid firing fields. In network models deduced from our data, feedback inhibition supports coexistence of theta-nested gamma oscillations with attractor states that generate grid firing fields. These results indicate that grid cells communicate primarily via inhibitory interneurons. This circuit mechanism enables multiplexing of oscillation-based temporal codes with rate-coded attractor states.
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Recurrent inhibitory circuitry as a mechanism for grid formation. Nat Neurosci 2013; 16:318-24. [PMID: 23334580 DOI: 10.1038/nn.3310] [Citation(s) in RCA: 270] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2012] [Accepted: 12/17/2012] [Indexed: 11/08/2022]
Abstract
Grid cells in layer II of the medial entorhinal cortex form a principal component of the mammalian neural representation of space. The firing pattern of a single grid cell has been hypothesized to be generated through attractor dynamics in a network with a specific local connectivity including both excitatory and inhibitory connections. However, experimental evidence supporting the presence of such connectivity among grid cells in layer II is limited. Here we report recordings from more than 600 neuron pairs in rat entorhinal slices, demonstrating that stellate cells, the principal cell type in the layer II grid network, are mainly interconnected via inhibitory interneurons. Using a model attractor network, we demonstrate that stable grid firing can emerge from a simple recurrent inhibitory network. Our findings thus suggest that the observed inhibitory microcircuitry between stellate cells is sufficient to generate grid-cell firing patterns in layer II of the medial entorhinal cortex.
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Yan XX, Cai Y, Shelton J, Deng SH, Luo XG, Oddo S, LaFerla FM, Cai H, Rose GM, Patrylo PR. Chronic temporal lobe epilepsy is associated with enhanced Alzheimer-like neuropathology in 3×Tg-AD mice. PLoS One 2012; 7:e48782. [PMID: 23155407 PMCID: PMC3498246 DOI: 10.1371/journal.pone.0048782] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2012] [Accepted: 10/01/2012] [Indexed: 11/18/2022] Open
Abstract
The comorbidity between epilepsy and Alzheimer's disease (AD) is a topic of growing interest. Senile plaques and tauopathy are found in epileptic human temporal lobe structures, and individuals with AD have an increased incidence of spontaneous seizures. However, why and how epilepsy is associated with enhanced AD-like pathology remains unknown. We have recently shown β-secretase-1 (BACE1) elevation associated with aberrant limbic axonal sprouting in epileptic CD1 mice. Here we sought to explore whether BACE1 upregulation affected the development of Alzheimer-type neuropathology in mice expressing mutant human APP, presenilin and tau proteins, the triple transgenic model of AD (3×Tg-AD). 3×Tg-AD mice were treated with pilocarpine or saline (i.p.) at 6-8 months of age. Immunoreactivity (IR) for BACE1, β-amyloid (Aβ) and phosphorylated tau (p-tau) was subsequently examined at 9, 11 or 14 months of age. Recurrent convulsive seizures, as well as mossy fiber sprouting and neuronal death in the hippocampus and limbic cortex, were observed in all epileptic mice. Neuritic plaques composed of BACE1-labeled swollen/sprouting axons and extracellular AβIR were seen in the hippocampal formation, amygdala and piriform cortices of 9 month-old epileptic, but not control, 3×Tg-AD mice. Densities of plaque-associated BACE1 and AβIR were elevated in epileptic versus control mice at 11 and 14 months of age. p-Tau IR was increased in dentate granule cells and mossy fibers in epileptic mice relative to controls at all time points examined. Thus, pilocarpine-induced chronic epilepsy was associated with accelerated and enhanced neuritic plaque formation and altered intraneuronal p-tau expression in temporal lobe structures in 3×Tg-AD mice, with these pathologies occurring in regions showing neuronal death and axonal dystrophy.
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Affiliation(s)
- Xiao-Xin Yan
- Department of Anatomy and Neurobiology, Central South University Xiangya School of Medicine, Changsha, Hunan, China
- * E-mail: (XXY); (GMR); (PRP)
| | - Yan Cai
- Department of Anatomy and Neurobiology, Central South University Xiangya School of Medicine, Changsha, Hunan, China
- Center for Integrated Research in Cognitive and Neural Sciences, Southern Illinois University Carbondale, Illinois, United States of America
- Department of Physiology, Southern Illinois University School of Medicine, Carbondale, Illinois, United States of America
| | - Jarod Shelton
- Department of Physiology, Southern Illinois University School of Medicine, Carbondale, Illinois, United States of America
| | - Si-Hao Deng
- Department of Anatomy and Neurobiology, Central South University Xiangya School of Medicine, Changsha, Hunan, China
| | - Xue-Gang Luo
- Department of Anatomy and Neurobiology, Central South University Xiangya School of Medicine, Changsha, Hunan, China
| | - Salvatore Oddo
- Department of Physiology and The Barshop Institute for Longevity and Aging Studies, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Frank M. LaFerla
- Department of Neurobiology and Behavior, University of California Irvine, Irvine, California, United States of America
| | - Huaibin Cai
- Laboratory of Neurogenetics, National Institute on Aging, Bethesda, Maryland, United States of America
| | - Gregory M. Rose
- Center for Integrated Research in Cognitive and Neural Sciences, Southern Illinois University Carbondale, Illinois, United States of America
- Department of Physiology, Southern Illinois University School of Medicine, Carbondale, Illinois, United States of America
- * E-mail: (XXY); (GMR); (PRP)
| | - Peter R. Patrylo
- Center for Integrated Research in Cognitive and Neural Sciences, Southern Illinois University Carbondale, Illinois, United States of America
- Department of Physiology, Southern Illinois University School of Medicine, Carbondale, Illinois, United States of America
- * E-mail: (XXY); (GMR); (PRP)
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Pilli J, Abbasi S, Richardson M, Kumar SS. Diversity and excitability of deep-layer entorhinal cortical neurons in a model of temporal lobe epilepsy. J Neurophysiol 2012; 108:1724-38. [PMID: 22745466 DOI: 10.1152/jn.00364.2012] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The entorhinal cortex (ERC) is critically implicated in temporal lobe epileptogenesis--the most common type of adult epilepsy. Previous studies have suggested that epileptiform discharges likely initiate in seizure-sensitive deep layers (V-VI) of the medial entorhinal area (MEA) and propagate into seizure-resistant superficial layers (II-III) and hippocampus, establishing a lamina-specific distinction between activities of deep- versus superficial-layer neurons and their seizure susceptibilities. While layer II stellate cells in MEA have been shown to be hyperexcitable and hypersynchronous in patients and animal models of temporal lobe epilepsy (TLE), the fate of neurons in the deep layers under epileptic conditions and their overall contribution to epileptogenicity of this region have remained unclear. We used whole cell recordings from slices of the ERC in normal and pilocarpine-treated epileptic rats to characterize the electrophysiological properties of neurons in this region and directly assess changes in their excitatory and inhibitory synaptic drive under epileptic conditions. We found a surprising heterogeneity with at least three major types and two subtypes of functionally distinct excitatory neurons. However, contrary to expectation, none of the major neuron types characterized showed any significant changes in their excitability, barring loss of excitatory and inhibitory inputs in a subtype of neurons whose dendrite extended into layer III, where neurons are preferentially lost during TLE. We confirmed hyperexcitability of layer II neurons in the same slices, suggesting minimal influence of deep-layer input on superficial-layer neuron excitability under epileptic conditions. These data show that deep layers of ERC contain a more diverse population of excitatory neurons than previously envisaged that appear to belie their seizure-sensitive reputation.
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Affiliation(s)
- Jyotsna Pilli
- Dept. of Biomedical Sciences, College of Medicine, Florida State Univ., 1115 West Call St., Tallahassee, FL 32306-4300, USA
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Pastoll H, Ramsden HL, Nolan MF. Intrinsic electrophysiological properties of entorhinal cortex stellate cells and their contribution to grid cell firing fields. Front Neural Circuits 2012; 6:17. [PMID: 22536175 PMCID: PMC3334835 DOI: 10.3389/fncir.2012.00017] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2011] [Accepted: 03/25/2012] [Indexed: 11/21/2022] Open
Abstract
The medial entorhinal cortex (MEC) is an increasingly important focus for investigation of mechanisms for spatial representation. Grid cells found in layer II of the MEC are likely to be stellate cells, which form a major projection to the dentate gyrus. Entorhinal stellate cells are distinguished by distinct intrinsic electrophysiological properties, but how these properties contribute to representation of space is not yet clear. Here, we review the ionic conductances, synaptic, and excitable properties of stellate cells, and examine their implications for models of grid firing fields. We discuss why existing data are inconsistent with models of grid fields that require stellate cells to generate periodic oscillations. An alternative possibility is that the intrinsic electrophysiological properties of stellate cells are tuned specifically to control integration of synaptic input. We highlight recent evidence that the dorsal-ventral organization of synaptic integration by stellate cells, through differences in currents mediated by HCN and leak potassium channels, influences the corresponding organization of grid fields. Because accurate cellular data will be important for distinguishing mechanisms for generation of grid fields, we introduce new data comparing properties measured with whole-cell and perforated patch-clamp recordings. We find that clustered patterns of action potential firing and the action potential after-hyperpolarization (AHP) are particularly sensitive to recording condition. Nevertheless, with both methods, these properties, resting membrane properties and resonance follow a dorsal-ventral organization. Further investigation of the molecular basis for synaptic integration by stellate cells will be important for understanding mechanisms for generation of grid fields.
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Affiliation(s)
- Hugh Pastoll
- Neuroinformatics Doctoral Training Centre, University of Edinburgh Edinburgh, UK
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Yoshida M, Knauer B, Jochems A. Cholinergic modulation of the CAN current may adjust neural dynamics for active memory maintenance, spatial navigation and time-compressed replay. Front Neural Circuits 2012; 6:10. [PMID: 22435051 PMCID: PMC3304506 DOI: 10.3389/fncir.2012.00010] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Accepted: 02/24/2012] [Indexed: 11/13/2022] Open
Abstract
Suppression of cholinergic receptors and inactivation of the septum impair short-term memory, and disrupt place cell and grid cell activity in the medial temporal lobe (MTL). Location-dependent hippocampal place cell firing during active waking, when the acetylcholine level is high, switches to time-compressed replay activity during quiet waking and slow-wave-sleep (SWS), when the acetylcholine level is low. However, it remains largely unknown how acetylcholine supports short-term memory, spatial navigation, and the functional switch to replay mode in the MTL. In this paper, we focus on the role of the calcium-activated non-specific cationic (CAN) current which is activated by acetylcholine. The CAN current is known to underlie persistent firing, which could serve as a memory trace in many neurons in the MTL. Here, we review the CAN current and discuss possible roles of the CAN current in short-term memory and spatial navigation. We further propose a novel theoretical model where the CAN current switches the hippocampal place cell activity between real-time and time-compressed sequential activity during encoding and consolidation, respectively.
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Affiliation(s)
- Motoharu Yoshida
- Faculty of Psychology, Mercator Research Group - Structure of Memory, Ruhr-University Bochum Bochum, Germany
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35
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Increased excitatory synaptic input to granule cells from hilar and CA3 regions in a rat model of temporal lobe epilepsy. J Neurosci 2012; 32:1183-96. [PMID: 22279204 DOI: 10.1523/jneurosci.5342-11.2012] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
One potential mechanism of temporal lobe epilepsy is recurrent excitation of dentate granule cells through aberrant sprouting of their axons (mossy fibers), which is found in many patients and animal models. However, correlations between the extent of mossy fiber sprouting and seizure frequency are weak. Additional potential sources of granule cell recurrent excitation that would not have been detected by markers of mossy fiber sprouting in previous studies include surviving mossy cells and proximal CA3 pyramidal cells. To test those possibilities in hippocampal slices from epileptic pilocarpine-treated rats, laser-scanning glutamate uncaging was used to randomly and focally activate neurons in the granule cell layer, hilus, and proximal CA3 pyramidal cell layer while measuring evoked EPSCs in normotopic granule cells. Consistent with mossy fiber sprouting, a higher proportion of glutamate-uncaging spots in the granule cell layer evoked EPSCs in epileptic rats compared with controls. In addition, stimulation spots in the hilus and proximal CA3 pyramidal cell layer were more likely to evoke EPSCs in epileptic rats, despite significant neuron loss in those regions. Furthermore, synaptic strength of recurrent excitatory inputs to granule cells from CA3 pyramidal cells and other granule cells was increased in epileptic rats. These findings reveal substantial levels of excessive, recurrent, excitatory synaptic input to granule cells from neurons in the hilus and proximal CA3 field. The aberrant development of these additional positive-feedback circuits might contribute to epileptogenesis in temporal lobe epilepsy.
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36
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Wang S, Chandrasekaran L, Fernandez FR, White JA, Canavier CC. Short conduction delays cause inhibition rather than excitation to favor synchrony in hybrid neuronal networks of the entorhinal cortex. PLoS Comput Biol 2012; 8:e1002306. [PMID: 22241969 PMCID: PMC3252263 DOI: 10.1371/journal.pcbi.1002306] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2011] [Accepted: 10/31/2011] [Indexed: 12/02/2022] Open
Abstract
How stable synchrony in neuronal networks is sustained in the presence of conduction delays is an open question. The Dynamic Clamp was used to measure phase resetting curves (PRCs) for entorhinal cortical cells, and then to construct networks of two such neurons. PRCs were in general Type I (all advances or all delays) or weakly type II with a small region at early phases with the opposite type of resetting. We used previously developed theoretical methods based on PRCs under the assumption of pulsatile coupling to predict the delays that synchronize these hybrid circuits. For excitatory coupling, synchrony was predicted and observed only with no delay and for delays greater than half a network period that cause each neuron to receive an input late in its firing cycle and almost immediately fire an action potential. Synchronization for these long delays was surprisingly tight and robust to the noise and heterogeneity inherent in a biological system. In contrast to excitatory coupling, inhibitory coupling led to antiphase for no delay, very short delays and delays close to a network period, but to near-synchrony for a wide range of relatively short delays. PRC-based methods show that conduction delays can stabilize synchrony in several ways, including neutralizing a discontinuity introduced by strong inhibition, favoring synchrony in the case of noisy bistability, and avoiding an initial destabilizing region of a weakly type II PRC. PRCs can identify optimal conduction delays favoring synchronization at a given frequency, and also predict robustness to noise and heterogeneity. Individual oscillators, such as pendulum-based clocks and fireflies, can spontaneously organize into a coherent, synchronized entity with a common frequency. Neurons can oscillate under some circumstances, and can synchronize their firing both within and across brain regions. Synchronized assemblies of neurons are thought to underlie cognitive functions such as recognition, recall, perception and attention. Pathological synchrony can lead to epilepsy, tremor and other dynamical diseases, and synchronization is altered in most mental disorders. Biological neurons synchronize despite conduction delays, heterogeneous circuit composition, and noise. In biological experiments, we built simple networks in which two living neurons could interact via a computer in real time. The computer precisely controlled the nature of the connectivity and the length of the communication delays. We characterized the synchronization tendencies of individual, isolated oscillators by measuring how much a single input delivered by the computer transiently shortened or lengthened the cycle period of the oscillation. We then used this information to correctly predict the strong dependence of the coordination pattern of the firing of the component neurons on the length of the communication delays. Upon this foundation, we can begin to build a theory of the basic principles of synchronization in more complex brain circuits.
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Affiliation(s)
- Shuoguo Wang
- Neuroscience Center, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA.
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37
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Anderson WS, Azhar F, Kudela P, Bergey GK, Franaszczuk PJ. Epileptic seizures from abnormal networks: why some seizures defy predictability. Epilepsy Res 2011; 99:202-13. [PMID: 22169211 DOI: 10.1016/j.eplepsyres.2011.11.006] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2011] [Revised: 10/19/2011] [Accepted: 11/18/2011] [Indexed: 11/17/2022]
Abstract
Seizure prediction has proven to be difficult in clinically realistic environments. Is it possible that fluctuations in cortical firing could influence the onset of seizures in an ictal zone? To test this, we have now used neural network simulations in a computational model of cortex having a total of 65,536 neurons with intercellular wiring patterned after histological data. A spatially distributed Poisson driven background input representing the activity of neighboring cortex affected 1% of the neurons. Gamma distributions were fit to the interbursting phase intervals, a non-parametric test for randomness was applied, and a dynamical systems analysis was performed to search for period-1 orbits in the intervals. The non-parametric analysis suggests that intervals are being drawn at random from their underlying joint distribution and the dynamical systems analysis is consistent with a nondeterministic dynamical interpretation of the generation of bursting phases. These results imply that in a region of cortex with abnormal connectivity analogous to a seizure focus, it is possible to initiate seizure activity with fluctuations of input from the surrounding cortical regions. These findings suggest one possibility for ictal generation from abnormal focal epileptic networks. This mechanism additionally could help explain the difficulty in predicting partial seizures in some patients.
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Affiliation(s)
- William S Anderson
- The Johns Hopkins University School of Medicine, Department of Neurosurgery, 600 North Wolfe Street, Baltimore, MD 21287, USA.
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38
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Canto CB, Witter MP. Cellular properties of principal neurons in the rat entorhinal cortex. II. The medial entorhinal cortex. Hippocampus 2011; 22:1277-99. [PMID: 22161956 DOI: 10.1002/hipo.20993] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/08/2011] [Indexed: 11/05/2022]
Abstract
Principal neurons in different medial entorhinal cortex (MEC) layers show variations in spatial modulation that stabilize between 15 and 30 days postnatally. These in vivo variations are likely due to differences in intrinsic membrane properties and integrative capacities of neurons. The latter depends on inputs and thus potentially on the morphology of principal neurons. In this comprehensive study, we systematically compared the morphological and physiological characteristics of principal neurons in all MEC layers of newborn rats before and after weaning. We recorded simultaneously from up to four post-hoc morphologically identified MEC principal neurons in vitro. Neurons in L(ayer) I-LIII have dendritic and axonal arbors mainly in superficial layers, and LVI neurons mainly in deep layers. The dendritic and axonal trees of part of LV neurons diverge throughout all layers. Physiological properties of principal neurons differ between layers. In LII, most neurons have a prominent sag potential, resonance and membrane oscillations. Neurons in LIII and LVI fire relatively regular, and lack sag potentials and membrane oscillations. LV neurons show the most prominent spike-frequency adaptation and highest input resistance. The data indicate that adult-like principal neuron types can be differentiated early on during postnatal development. The results of the accompanying paper, in which principal neurons in the lateral entorhinal cortex (LEC) were described (Canto and Witter,2011), revealed that significant differences between LEC and MEC exist mainly in LII neurons. We therefore systematically analyzed changes in LII biophysical properties along the mediolateral axis of MEC and LEC. There is a gradient in properties typical for MEC LII neurons. These properties are most pronounced in medially located neurons and become less apparent in more laterally positioned ones. This gradient continues into LEC, such that in LEC medially positioned neurons share some properties with adjacent MEC cells.
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Affiliation(s)
- Cathrin B Canto
- Kavli Institute for Systems Neuroscience and Centre for the Biology of Memory, Norwegian University of Science and Technology, Trondheim, Norway
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39
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Sebe JY, Baraban SC. The promise of an interneuron-based cell therapy for epilepsy. Dev Neurobiol 2011; 71:107-17. [PMID: 21154914 DOI: 10.1002/dneu.20813] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Of the nearly 3 million Americans diagnosed with epilepsy, approximately 30% are unresponsive to current medications. Recent data has shown that early postnatal transplantation of interneuronal precursor cells increases GABAergic inhibition in the host brain and dramatically suppresses seizure activity in epileptic mice. In this review, we will highlight findings from seizure-prone mice and humans that demonstrate the link between dysfunctional GABAergic inhibition and hyperexcitability. In particular, we will focus on rodent models of temporal lobe epilepsy, the most common and difficult to treat form of the disease, and interneuronopathies, an emerging classification. A wealth of literature showing a causal link between reduced GABA-mediated inhibition and seizures has directed our efforts to recover the loss of inhibition via transplantation of interneuronal precursors. Numerous related studies have explored the anticonvulsant potential of cell grafts derived from a variety of brain regions, yet the mechanism underlying the effect of such heterogeneous cell transplants is unknown. In discussing our recent findings and placing them in context with what is known about epilepsy, and how related transplant approaches have progressed, we hope to initiate a frank discussion of the best path toward the translation of this approach to patients with intractable forms of epilepsy.
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Affiliation(s)
- Joy Y Sebe
- Epilepsy Research Laboratory, Department of Neurological Surgery, University of California, San Francisco, California, USA.
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40
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Abstract
Grid cells are space-modulated neurons with periodic firing fields. In moving animals, the multiple firing fields of an individual grid cell form a triangular pattern tiling the entire space available to the animal. Collectively, grid cells are thought to provide a context-independent metric representation of the local environment. Since the discovery of grid cells in 2005, a number of models have been proposed to explain the formation of spatially repetitive firing patterns as well as the conversion of these signals to place signals one synapse downstream in the hippocampus. The present article reviews the most recent developments in our understanding of how grid patterns are generated, maintained, and transformed, with particular emphasis on second-generation computational models that have emerged during the past 2-3 years in response to criticism and new data.
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Affiliation(s)
- Lisa M Giocomo
- Kavli Institute for Systems Neuroscience and Centre for the Biology of Memory, Medical Technical Research Centre, Norwegian University of Science and Technology, 7030 Trondheim, Norway.
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Chronic dietary intake of α-linolenic acid does not replicate the effects of DHA on passive properties of entorhinal cortex neurons. Br J Nutr 2011; 107:1099-111. [PMID: 21851757 DOI: 10.1017/s0007114511004089] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
n-3 PUFA are receiving growing attention for their therapeutic potential in central nervous system (CNS) disorders. We have recently shown that long-term treatment with DHA alters the physiology of entorhinal cortex (EC) neurons. In the present study, we investigated by patch-clamp the effect of another major dietary n-3 PUFA, α-linolenic acid (LNA), on the intrinsic properties of EC neurons. Mice were chronically exposed to isoenergetic diets deficient in n-3 PUFA or enriched in either DHA or LNA on an equimolar basis. GC analyses revealed an increase in DHA (34%) and a decrease in arachidonic acid (AA, - 23%) in brain fatty acid concentrations after consumption of the DHA-enriched diet. Dietary intake of LNA similarly affected brain fatty acid profiles, but at a lower magnitude (DHA: 23%, AA: - 13%). Compared to the n-3 PUFA-deficient diet, consumption of DHA, but not LNA, induced membrane hyperpolarisation ( -60 to -70 mV), increased cellular capacitance (32%) and spontaneous excitatory postsynaptic current frequency (50%). We propose that the inefficiency of LNA to modulate cellular capacitance was related to its inability to increase the brain DHA:AA ratio over the threshold necessary to up-regulate syntaxin-3 (46%) and translocate drebrin (40% membrane:cytosol ratio). In summary, our present study shows that the increase in brain DHA content following chronic administration of LNA was not sufficient to alter the passive and synaptic properties of EC neurons, compared to direct dietary intake of DHA. These diverging results have important implications for the therapeutic use of n-3 PUFA in CNS disease, favouring the use of preformed DHA.
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Navratilova Z, Giocomo LM, Fellous JM, Hasselmo ME, McNaughton BL. Phase precession and variable spatial scaling in a periodic attractor map model of medial entorhinal grid cells with realistic after-spike dynamics. Hippocampus 2011; 22:772-89. [PMID: 21484936 DOI: 10.1002/hipo.20939] [Citation(s) in RCA: 126] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/19/2010] [Indexed: 11/06/2022]
Abstract
We present a model that describes the generation of the spatial (grid fields) and temporal (phase precession) properties of medial entorhinal cortical (MEC) neurons by combining network and intrinsic cellular properties. The model incorporates network architecture derived from earlier attractor map models, and is implemented in 1D for simplicity. Periodic driving of conjunctive (position × head-direction) layer-III MEC cells at theta frequency with intensity proportional to the rat's speed, moves an 'activity bump' forward in network space at a corresponding speed. The addition of prolonged excitatory currents and simple after-spike dynamics resembling those observed in MEC stellate cells (for which new data are presented) accounts for both phase precession and the change in scale of grid fields along the dorso-ventral axis of MEC. Phase precession in the model depends on both synaptic connectivity and intrinsic currents, each of which drive neural spiking either during entry into, or during exit out of a grid field. Thus, the model predicts that the slope of phase precession changes between entry into and exit out of the field. The model also exhibits independent variation in grid spatial period and grid field size, which suggests possible experimental tests of the model.
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Affiliation(s)
- Zaneta Navratilova
- Department of Neuroscience, Canadian Centre for Behavioural Neuroscience, University of Lethbridge, Alberta, Canada
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43
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Beed P, Bendels MHK, Wiegand HF, Leibold C, Johenning FW, Schmitz D. Analysis of excitatory microcircuitry in the medial entorhinal cortex reveals cell-type-specific differences. Neuron 2011; 68:1059-66. [PMID: 21172609 DOI: 10.1016/j.neuron.2010.12.009] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/29/2010] [Indexed: 11/28/2022]
Abstract
Medial entorhinal cortex (MEC) plays an important role in physiological processes underlying navigation, learning, and memory. Excitatory cells in the different MEC layers project in a region-specific manner to the hippocampus. However, the intrinsic microcircuitry of the main excitatory cells in the superficial MEC layers is largely unknown. Using scanning photostimulation, we investigated the functional microcircuitry of two such cell types, stellate and pyramidal cells. We found cell-type-specific intralaminar and ascending interlaminar feedback inputs. The ascending interlaminar inputs display distinct organizational principles depending on the cell-type and its position within the superficial lamina: the spatial spread of inputs for stellate cells is narrower than for pyramidal cells, while inputs to pyramidal cells in layer 3, but not in layer 2, exhibit an asymmetric offset to the medial side of the cell's main axis. Differential laminar sources of excitatory inputs might contribute to the functional diversity of stellate and pyramidal cells.
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Affiliation(s)
- Prateep Beed
- Neuroscience Research Center, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany
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Kispersky T, White JA, Rotstein HG. The mechanism of abrupt transition between theta and hyper-excitable spiking activity in medial entorhinal cortex layer II stellate cells. PLoS One 2010; 5:e13697. [PMID: 21079802 PMCID: PMC2973955 DOI: 10.1371/journal.pone.0013697] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2010] [Accepted: 09/04/2010] [Indexed: 11/18/2022] Open
Abstract
Recent studies have shown that stellate cells (SCs) of the medial entorhinal cortex become hyper-excitable in animal models of temporal lobe epilepsy. These studies have also demonstrated the existence of recurrent connections among SCs, reduced levels of recurrent inhibition in epileptic networks as compared to control ones, and comparable levels of recurrent excitation among SCs in both network types. In this work, we investigate the biophysical and dynamic mechanism of generation of the fast time scale corresponding to hyper-excitable firing and the transition between theta and fast firing frequency activity in SCs. We show that recurrently connected minimal networks of SCs exhibit abrupt, threshold-like transition between theta and hyper-excitable firing frequencies as the result of small changes in the maximal synaptic (AMPAergic) conductance. The threshold required for this transition is modulated by synaptic inhibition. Similar abrupt transition between firing frequency regimes can be observed in single, self-coupled SCs, which represent a network of recurrently coupled neurons synchronized in phase, but not in synaptically isolated SCs as the result of changes in the levels of the tonic drive. Using dynamical systems tools (phase-space analysis), we explain the dynamic mechanism underlying the genesis of the fast time scale and the abrupt transition between firing frequency regimes, their dependence on the intrinsic SC's currents and synaptic excitation. This abrupt transition is mechanistically different from others observed in similar networks with different cell types. Most notably, there is no bistability involved. 'In vitro' experiments using single SCs self-coupled with dynamic clamp show the abrupt transition between firing frequency regimes, and demonstrate that our theoretical predictions are not an artifact of the model. In addition, these experiments show that high-frequency firing is burst-like with a duration modulated by an M-current.
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Affiliation(s)
- Tilman Kispersky
- Program in Neuroscience and Center for BioDynamics, Boston University, Boston, Massachusetts, United States of America
| | - John A. White
- Department of Bioengineering, University of Utah, Salt Lake City, Utah, United States of America
| | - Horacio G. Rotstein
- Department of Mathematical Sciences and Center for Applied Mathematics and Statistics, New Jersey Institute of Technology, Newark, New Jersey, United States of America
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Hargus NJ, Merrick EC, Nigam A, Kalmar CL, Baheti AR, Bertram EH, Patel MK. Temporal lobe epilepsy induces intrinsic alterations in Na channel gating in layer II medial entorhinal cortex neurons. Neurobiol Dis 2010; 41:361-76. [PMID: 20946956 DOI: 10.1016/j.nbd.2010.10.004] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2010] [Revised: 09/22/2010] [Accepted: 10/04/2010] [Indexed: 11/18/2022] Open
Abstract
Temporal lobe epilepsy (TLE) is the most common form of adult epilepsy involving the limbic structures of the temporal lobe. Layer II neurons of the entorhinal cortex (EC) form the major excitatory input into the hippocampus via the perforant path and consist of non-stellate and stellate neurons. These neurons are spared and hyper-excitable in TLE. The basis for the hyper-excitability is likely multifactorial and may include alterations in intrinsic properties. In a rat model of TLE, medial EC (mEC) non-stellate and stellate neurons had significantly higher action potential (AP) firing frequencies than in control. The increase remained in the presence of synaptic blockers, suggesting intrinsic mechanisms. Since sodium (Na) channels play a critical role in AP generation and conduction we sought to determine if Na channel gating parameters and expression levels were altered in TLE. Na channel currents recorded from isolated mEC TLE neurons revealed increased Na channel conductances, depolarizing shifts in inactivation parameters and larger persistent (I(NaP)) and resurgent (I(NaR)) Na currents. Immunofluorescence experiments revealed increased staining of Na(v)1.6 within the axon initial segment and Na(v)1.2 within the cell bodies of mEC TLE neurons. These studies provide support for additional intrinsic alterations within mEC layer II neurons in TLE and implicate alterations in Na channel activity and expression, in part, for establishing the profound increase in intrinsic membrane excitability of mEC layer II neurons in TLE. These intrinsic changes, together with changes in the synaptic network, could support seizure activity in TLE.
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Affiliation(s)
- Nicholas J Hargus
- Department of Anesthesiology, University of Virginia Health System, Charlottesville, VA 22908, USA
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Jin X, Huguenard JR, Prince DA. Reorganization of inhibitory synaptic circuits in rodent chronically injured epileptogenic neocortex. Cereb Cortex 2010; 21:1094-104. [PMID: 20855494 DOI: 10.1093/cercor/bhq181] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Reduced synaptic inhibition is an important factor contributing to posttraumatic epileptogenesis. Axonal sprouting and enhanced excitatory synaptic connectivity onto rodent layer V pyramidal (Pyr) neurons occur in epileptogenic partially isolated (undercut) neocortex. To determine if enhanced excitation also affects inhibitory circuits, we used laser scanning photostimulation of caged glutamate and whole-cell recordings from GAD67-GFP-expressing mouse fast spiking (FS) interneurons and Pyr cells in control and undercut in vitro slices to map excitatory and inhibitory synaptic inputs. Results are 1) the region-normalized excitatory postsynaptic current (EPSC) amplitudes and proportion of uncaging sites from which EPSCs could be evoked (hotspot ratio) "increased" significantly in FS cells of undercut slices; 2) in contrast, these parameters were significantly "decreased" for inhibitory postsynaptic currents (IPSCs) in undercut FS cells; and 3) in rat layer V Pyr neurons, we found significant decreases in IPSCs in undercut versus control Pyr neurons. The decreases were mainly located in layers II and IV, suggesting a reduction in the efficacy of interlaminar synaptic inhibition. Results suggest that there is significant synaptic reorganization in this model of posttraumatic epilepsy, resulting in increased excitatory drive and reduced inhibitory input to FS interneurons that should enhance their inhibitory output and, in part, offset similar alterations in innervation of Pyr cells.
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Affiliation(s)
- Xiaoming Jin
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA 94305, USA
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Bendels MHK, Beed P, Schmitz D, Johenning FW, Leibold C. Detection of input sites in scanning photostimulation data based on spatial correlations. J Neurosci Methods 2010; 192:286-95. [PMID: 20705098 DOI: 10.1016/j.jneumeth.2010.08.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2009] [Revised: 08/03/2010] [Accepted: 08/04/2010] [Indexed: 01/16/2023]
Abstract
Scanning photostimulation is a well-established method for studying the functional microcircuitry in brain slices. Light-evoked responses are thereby taken as an indicator for a connected presynaptic partner. Such an approach thus requires a clear distinction between the photo-evoked and the spontaneous responses. Here we show that, for a data set from entorhinal cortex layer II with high spontaneous synaptic rates of up to 10Hz, it is possible to identify presynaptic sites. The underlying detection algorithm is based on the finding that a presynaptic cell has several neighboring activation sites, resulting in the clustered appearance of specific photo-evoked inputs. The main idea behind this approach is to identify "hit" locations at which the number of intracellularly recorded synaptic events is significantly larger as expected from the hypothesis of statistical independence. The algorithm works without making use of EPSC amplitude information and for single trials, i.e., each site is stimulated only once. The hit maps are tested upon reliability by repeated stimulations and by blocking synaptically mediated responses via TTX. Furthermore, based on the hit density of surrogate data, we devise a Bayesian formalism to estimate the number of presynaptic partners. In these simulations we find good agreement between estimated and real number of input cells, which shows that the hit density can be used as a reliable measure for afferent connectivity.
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Affiliation(s)
- Michael H K Bendels
- Division of Neurobiology, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
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48
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Grid cells in pre- and parasubiculum. Nat Neurosci 2010; 13:987-94. [PMID: 20657591 DOI: 10.1038/nn.2602] [Citation(s) in RCA: 345] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2010] [Accepted: 06/25/2010] [Indexed: 01/23/2023]
Abstract
Allocentric space is mapped by a widespread brain circuit of functionally specialized cell types located in interconnected subregions of the hippocampal-parahippocampal cortices. Little is known about the neural architectures required to express this variety of firing patterns. In rats, we found that one of the cell types, the grid cell, was abundant not only in medial entorhinal cortex (MEC), where it was first reported, but also in pre- and parasubiculum. The proportion of grid cells in pre- and parasubiculum was comparable to deep layers of MEC. The symmetry of the grid pattern and its relationship to the theta rhythm were weaker, especially in presubiculum. Pre- and parasubicular grid cells intermingled with head-direction cells and border cells, as in deep MEC layers. The characterization of a common pool of space-responsive cells in architecturally diverse subdivisions of parahippocampal cortex constrains the range of mechanisms that might give rise to their unique functional discharge phenotypes.
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Hasselmo ME, Brandon MP, Yoshida M, Giocomo LM, Heys JG, Fransen E, Newman EL, Zilli EA. A phase code for memory could arise from circuit mechanisms in entorhinal cortex. Neural Netw 2009; 22:1129-38. [PMID: 19656654 PMCID: PMC2825042 DOI: 10.1016/j.neunet.2009.07.012] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2009] [Revised: 06/24/2009] [Accepted: 07/14/2009] [Indexed: 10/20/2022]
Abstract
Neurophysiological data reveals intrinsic cellular properties that suggest how entorhinal cortical neurons could code memory by the phase of their firing. Potential cellular mechanisms for this phase coding in models of entorhinal function are reviewed. This mechanism for phase coding provides a substrate for modeling the responses of entorhinal grid cells, as well as the replay of neural spiking activity during waking and sleep. Efforts to implement these abstract models in more detailed biophysical compartmental simulations raise specific issues that could be addressed in larger scale population models incorporating mechanisms of inhibition.
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Affiliation(s)
- Michael E Hasselmo
- Center for Memory and Brain, Department of Psychology and Program in Neuroscience, Boston University, 2 Cummington Street, Boston, MA 02215, USA.
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Scharfman HE, Malthankar-Phatak GH, Friedman D, Pearce P, McCloskey DP, Harden CL, Maclusky NJ. A rat model of epilepsy in women: a tool to study physiological interactions between endocrine systems and seizures. Endocrinology 2009; 150:4437-42. [PMID: 19443573 PMCID: PMC2736077 DOI: 10.1210/en.2009-0135] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Epilepsy in women is influenced by endocrine status and antiepileptic drugs, but without an animal model, the effects of endocrine variables and antiepileptic drugs cannot be easily dissociated from the influence of epilepsy itself. Animal models have had limited utility because experimentally induced seizures typically result in reproductive failure. This study was conducted to develop an improved animal model. The muscarinic convulsant pilocarpine was used to elicit status epilepticus (SE) in adult female Sprague Dawley rats. The selective estrogen receptor modulator raloxifene was administered 30 min before pilocarpine. An anticonvulsant barbiturate, pentobarbital, was injected 5-10 min after the onset of SE and at least once thereafter to minimize acute convulsions. Mortality, morbidity, estrous cyclicity, and the ultimate success of the procedure (i.e. induction of recurrent, spontaneous seizures) were monitored. The combination of raloxifene and pentobarbital led to significantly improved estrous cyclicity compared with previous methods. Animals treated with raloxifene and pentobarbital became epileptic, as defined by the recurrence of spontaneous convulsions in the weeks after SE. The results of this study provide an improved animal model to examine the interactions between seizures and ovarian hormone secretion. The results also suggest that treatment of SE with raloxifene may benefit women with SE.
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