1
|
Singh S, Becker S, Trappenberg T, Nunes A. Granule cells perform frequency-dependent pattern separation in a computational model of the dentate gyrus. Hippocampus 2024; 34:14-28. [PMID: 37950569 DOI: 10.1002/hipo.23585] [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: 05/14/2023] [Revised: 09/28/2023] [Accepted: 10/23/2023] [Indexed: 11/12/2023]
Abstract
Mnemonic discrimination (MD) may be dependent on oscillatory perforant path input frequencies to the hippocampus in a "U"-shaped fashion, where some studies show that slow and fast input frequencies support MD, while other studies show that intermediate frequencies disrupt MD. We hypothesize that pattern separation (PS) underlies frequency-dependent MD performance. We aim to study, in a computational model of the hippocampal dentate gyrus (DG), the network and cellular mechanisms governing this putative "U"-shaped PS relationship. We implemented a biophysical model of the DG that produces the hypothesized "U"-shaped input frequency-PS relationship, and its associated oscillatory electrophysiological signatures. We subsequently evaluated the network's PS ability using an adapted spatiotemporal task. We undertook systematic lesion studies to identify the network-level mechanisms driving the "U"-shaped input frequency-PS relationship. A minimal circuit of a single granule cell (GC) stimulated with oscillatory inputs was also used to study potential cellular-level mechanisms. Lesioning synapses onto GCs did not impact the "U"-shaped input frequency-PS relationship. Furthermore, GC inhibition limits PS performance for fast frequency inputs, while enhancing PS for slow frequency inputs. GC interspike interval was found to be input frequency dependent in a "U"-shaped fashion, paralleling frequency-dependent PS observed at the network level. Additionally, GCs showed an attenuated firing response for fast frequency inputs. We conclude that independent of network-level inhibition, GCs may intrinsically be capable of producing a "U"-shaped input frequency-PS relationship. GCs may preferentially decorrelate slow and fast inputs via spike timing reorganization and high frequency filtering.
Collapse
Affiliation(s)
- Selena Singh
- Department of Psychology, Neuroscience and Behaviour, McMaster University, Hamilton, Ontario, Canada
| | - Suzanna Becker
- Department of Psychology, Neuroscience and Behaviour, McMaster University, Hamilton, Ontario, Canada
| | - Thomas Trappenberg
- Faculty of Computer Science, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Abraham Nunes
- Faculty of Computer Science, Dalhousie University, Halifax, Nova Scotia, Canada
- Department of Psychiatry, Dalhousie University, Halifax, Nova Scotia, Canada
| |
Collapse
|
2
|
Pelkey KA, Vargish GA, Pellegrini LV, Calvigioni D, Chapeton J, Yuan X, Hunt S, Cummins AC, Eldridge MAG, Pickel J, Chittajallu R, Averbeck BB, Tóth K, Zaghloul K, McBain CJ. Evolutionary conservation of hippocampal mossy fiber synapse properties. Neuron 2023; 111:3802-3818.e5. [PMID: 37776852 PMCID: PMC10841147 DOI: 10.1016/j.neuron.2023.09.005] [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: 02/07/2023] [Revised: 07/03/2023] [Accepted: 09/06/2023] [Indexed: 10/02/2023]
Abstract
Various specialized structural/functional properties are considered essential for contextual memory encoding by hippocampal mossy fiber (MF) synapses. Although investigated to exquisite detail in model organisms, synapses, including MFs, have undergone minimal functional interrogation in humans. To determine the translational relevance of rodent findings, we evaluated MF properties within human tissue resected to treat epilepsy. Human MFs exhibit remarkably similar hallmark features to rodents, including AMPA receptor-dominated synapses with small contributions from NMDA and kainate receptors, large dynamic range with strong frequency facilitation, NMDA receptor-independent presynaptic long-term potentiation, and strong cyclic AMP (cAMP) sensitivity of release. Array tomography confirmed the evolutionary conservation of MF ultrastructure. The astonishing congruence of rodent and human MF core features argues that the basic MF properties delineated in animal models remain critical to human MF function. Finally, a selective deficit in GABAergic inhibitory tone onto human MF postsynaptic targets suggests that unrestrained detonator excitatory drive contributes to epileptic circuit hyperexcitability.
Collapse
Affiliation(s)
- Kenneth A Pelkey
- Eunice Kennedy Shriver National Institute of Child Health and Human Development Intramural Research Program, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Geoffrey A Vargish
- Eunice Kennedy Shriver National Institute of Child Health and Human Development Intramural Research Program, National Institutes of Health, Bethesda, MD 20892, USA
| | - Leonardo V Pellegrini
- Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Brain and Mind Research Institute, Ottawa, ON K1H 8M5, Canada
| | - Daniela Calvigioni
- Eunice Kennedy Shriver National Institute of Child Health and Human Development Intramural Research Program, National Institutes of Health, Bethesda, MD 20892, USA
| | - Julio Chapeton
- National Institute of Neurological Disorders and Stroke Intramural Research Program, National Institutes of Health, Bethesda, MD 20892, USA
| | - Xiaoqing Yuan
- Eunice Kennedy Shriver National Institute of Child Health and Human Development Intramural Research Program, National Institutes of Health, Bethesda, MD 20892, USA
| | - Steven Hunt
- Eunice Kennedy Shriver National Institute of Child Health and Human Development Intramural Research Program, National Institutes of Health, Bethesda, MD 20892, USA
| | - Alex C Cummins
- National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA
| | - Mark A G Eldridge
- National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA
| | - James Pickel
- National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA
| | - Ramesh Chittajallu
- Eunice Kennedy Shriver National Institute of Child Health and Human Development Intramural Research Program, National Institutes of Health, Bethesda, MD 20892, USA
| | - Bruno B Averbeck
- National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA
| | - Katalin Tóth
- Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Brain and Mind Research Institute, Ottawa, ON K1H 8M5, Canada
| | - Kareem Zaghloul
- National Institute of Neurological Disorders and Stroke Intramural Research Program, National Institutes of Health, Bethesda, MD 20892, USA
| | - Chris J McBain
- Eunice Kennedy Shriver National Institute of Child Health and Human Development Intramural Research Program, National Institutes of Health, Bethesda, MD 20892, USA.
| |
Collapse
|
3
|
Bosque-Cordero KY, Vazquez-Torres R, Calo-Guadalupe C, Consuegra-Garcia D, Fois GR, Georges F, Jimenez-Rivera CA. I h blockade reduces cocaine-induced firing patterns of putative dopaminergic neurons of the ventral tegmental area in the anesthetized rat. Prog Neuropsychopharmacol Biol Psychiatry 2022; 112:110431. [PMID: 34454991 PMCID: PMC8489561 DOI: 10.1016/j.pnpbp.2021.110431] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Revised: 08/23/2021] [Accepted: 08/23/2021] [Indexed: 01/12/2023]
Abstract
The hyperpolarization-activated cation current (Ih) is a determinant of intrinsic excitability in various cells, including dopaminergic neurons (DA) of the ventral tegmental area (VTA). In contrast to other cellular conductances, Ih is activated by hyperpolarization negative to -55 mV and activating Ih produces a time-dependent depolarizing current. Our laboratory demonstrated that cocaine sensitization, a chronic cocaine behavioral model, significantly reduces Ih amplitude in VTA DA neurons. Despite this reduction in Ih, the spontaneous firing of VTA DA cells after cocaine sensitization remained similar to control groups. Although the role of Ih in controlling VTA DA excitability is still poorly understood, our hypothesis is that Ih reduction could play a role of a homeostatic controller compensating for cocaine-induced change in excitability. Using in vivo single-unit extracellular electrophysiology in isoflurane anesthetized rats, we explored the contribution of Ih on spontaneous firing patterns of VTA DA neurons. A key feature of spontaneous excitability is bursting activity; bursting is defined as trains of two or more spikes occurring within a short interval and followed by a prolonged period of inactivity. Burst activity increases the reliability of information transfer. To elucidate the contribution of Ih to spontaneous firing patterns of VTA DA neurons, we locally infused an Ih blocker (ZD 7288, 8.3 μM) and evaluated its effect. Ih blockade significantly reduced firing rate, bursting frequency, and percent of spikes within a burst. In addition, Ih blockade significantly reduced acute cocaine-induced spontaneous firing rate, bursting frequency, and percent of spikes within a burst. Using whole-cell patch-clamp, we determine the progressive reduction of Ih after acute and chronic cocaine administration (15 mg/k.g intraperitoneally). Our data show a significant reduction (~25%) in Ih amplitude after 24 but not 2 h of acute cocaine administration. These results suggest that a progressive reduction of Ih could serve as a homeostatic regulator of cocaine-induced spontaneous firing patterns related to VTA DA excitability.
Collapse
Affiliation(s)
| | | | | | | | - Giulia R Fois
- University of Bordeaux, Neurodegeneratives Diseases Institute, IMN-UMR-CNRS 5293, 146 rue Léo Saignat, 33076 Bordeaux, France; CNRS, Neurodegeneratives Diseases Institute, IMN-UMR-CNRS 5293, 146 rue Léo Saignat, 33076 Bordeaux, France
| | - François Georges
- University of Bordeaux, Neurodegeneratives Diseases Institute, IMN-UMR-CNRS 5293, 146 rue Léo Saignat, 33076 Bordeaux, France; CNRS, Neurodegeneratives Diseases Institute, IMN-UMR-CNRS 5293, 146 rue Léo Saignat, 33076 Bordeaux, France
| | | |
Collapse
|
4
|
Traumatic Brain Injury Diminishes Feedforward Activation of Parvalbumin-Expressing Interneurons in the Dentate Gyrus. eNeuro 2020; 7:ENEURO.0195-19.2020. [PMID: 33106385 PMCID: PMC7675145 DOI: 10.1523/eneuro.0195-19.2020] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 09/14/2020] [Accepted: 09/20/2020] [Indexed: 12/18/2022] Open
Abstract
Traumatic brain injury (TBI) is associated with aberrant network hyperexcitability in the dentate gyrus (DG). GABAAergic parvalbumin-expressing interneurons (PV-INs) in the DG regulate network excitability with strong, perisomatic inhibition, although the posttraumatic effects on PV-IN function after TBI are not well understood. In this study, we investigated physiological alterations in PV-INs one week after mild lateral fluid percussion injury (LFPI) in mice. PV-IN cell loss was observed in the dentate hilus after LFPI, with surviving PV-INs showing no change in intrinsic membrane properties. Whole-cell voltage clamp recordings in PV-INs revealed alterations in both EPSCs and IPSCs (EPSCs/IPSCs). Evoked EPSCs (eEPSCs) in PV-INs from perforant path electrical stimulation were diminished after injury but could be recovered with application of a GABAA-receptor antagonist. Furthermore, current-clamp recordings using minimal perforant path stimulation demonstrated a decrease in evoked PV-IN action potentials (APs) after LFPI, which could be restored by blocking GABAAergic inhibition. Together, these findings suggest that injury alters synaptic input onto PV-INs, resulting in a net inhibitory effect that reduces feedforward PV-IN activation in the DG. Decreased PV-IN activation suggests a potential mechanism of DG network hyperexcitability contributing to hippocampal dysfunction after TBI.
Collapse
|
5
|
Karimi SA, Hosseinmardi N, Sayyah M, Hajisoltani R, Janahmadi M. Enhancement of intrinsic neuronal excitability-mediated by a reduction in hyperpolarization-activated cation current (I h ) in hippocampal CA1 neurons in a rat model of traumatic brain injury. Hippocampus 2020; 31:156-169. [PMID: 33107111 DOI: 10.1002/hipo.23270] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2020] [Revised: 09/28/2020] [Accepted: 10/04/2020] [Indexed: 01/13/2023]
Abstract
Traumatic brain injury (TBI) is associated with epileptiform activity in the hippocampus; however, the underlying mechanisms have not been fully determined. The goal was to understand what changes take place in intrinsic neuronal physiology in the hippocampus after blunt force trauma to the cortex. In this context, hyperpolarization-activated cation current (Ih ) currents may have a critical role in modulating the neuronal intrinsic membrane excitability; therefore, its contribution to the TBI-induced hyperexcitability was assessed. In a model of TBI caused by controlled cortical impact (CCI), the intrinsic electrophysiological properties of pyramidal neurons were examined 1 week after TBI induction in rats. Whole-cell patch-clamp recordings were performed under current- and voltage-clamp conditions following ionotropic receptors blockade. Induction of TBI caused changes in the intrinsic excitability of pyramidal neurons, as shown by a significant increase and decrease in firing frequency and in the rheobase current, respectively (p < .05). The evoked firing rate and the action potential time to peak were also significantly increased and decreased, respectively (p < .05). In the TBI group, the amplitude of instantaneous and steady-state Ih currents was both significantly smaller than those in the control group (p < .05). The Ih current density was also significantly decreased (p < .001). Findings indicated that TBI led to an increase in the intrinsic excitability in CA1 pyramidal neurons and changes in Ih current could be, in part, one of the underlying mechanisms involved in this hyperexcitability.
Collapse
Affiliation(s)
- Seyed Asaad Karimi
- Neuroscience Research Center, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran.,Department of Physiology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran.,Neurophysiology Research Center, Hamadan University of Medical Sciences, Hamadan, Iran.,Department of Neuroscience, School of Science and Advanced Technologies in Medicine, Hamadan University of Medical Sciences, Hamadan, Iran
| | - Narges Hosseinmardi
- Department of Physiology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Mohammad Sayyah
- Department of Physiology and Pharmacology, Pasteur Institute of Iran, Tehran, Iran
| | - Razieh Hajisoltani
- Department of Physiology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Mahyar Janahmadi
- Neuroscience Research Center, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran.,Department of Physiology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| |
Collapse
|
6
|
Traumatic Brain Injury Preserves Firing Rates But Disrupts Laminar Oscillatory Coupling and Neuronal Entrainment in Hippocampal CA1. eNeuro 2020; 7:ENEURO.0495-19.2020. [PMID: 32737188 PMCID: PMC7477953 DOI: 10.1523/eneuro.0495-19.2020] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2019] [Revised: 07/15/2020] [Accepted: 07/19/2020] [Indexed: 11/21/2022] Open
Abstract
While hippocampal-dependent learning and memory are particularly vulnerable to traumatic brain injury (TBI), the functional status of individual hippocampal neurons and their interactions with oscillations are unknown following injury. Using the most common rodent TBI model and laminar recordings in CA1, we found a significant reduction in oscillatory input into the radiatum layer of CA1 after TBI. Surprisingly, CA1 neurons maintained normal firing rates despite attenuated input, but did not maintain appropriate synchronization with this oscillatory input or with local high-frequency oscillations. Normal synchronization between these coordinating oscillations was also impaired. Simultaneous recordings of medial septal neurons known to participate in theta oscillations revealed increased GABAergic/glutamatergic firing rates postinjury under anesthesia, potentially because of a loss of modulating feedback from the hippocampus. These results suggest that TBI leads to a profound disruption of connectivity and oscillatory interactions, potentially disrupting the timing of CA1 neuronal ensembles that underlie aspects of learning and memory.
Collapse
|
7
|
Sun J, Harrington MA. The Alteration of Intrinsic Excitability and Synaptic Transmission in Lumbar Spinal Motor Neurons and Interneurons of Severe Spinal Muscular Atrophy Mice. Front Cell Neurosci 2019; 13:15. [PMID: 30792629 PMCID: PMC6374350 DOI: 10.3389/fncel.2019.00015] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Accepted: 01/16/2019] [Indexed: 01/22/2023] Open
Abstract
Spinal muscular atrophy (SMA) is the leading genetic cause of death in infants. Studies with mouse models have demonstrated increased excitability and loss of afferent proprioceptive synapses on motor neurons (MNs). To further understand functional changes in the motor neural network occurring in SMA, we studied the intrinsic excitability and synaptic transmission of both MNs and interneurons (INs) from ventral horn in the lumbar spinal cord in the survival motor neuron (SMN)Δ7 mouse model. We found significant differences in the membrane properties of MNs in SMA mice compared to littermate controls, including hyperpolarized resting membrane potential, increased input resistance and decreased membrane capacitance. Action potential (AP) properties in MNs from SMA mice were also different from controls, including decreased rheobase current, increased amplitude and an increased afterdepolarization (ADP) potential. The relationship between AP firing frequency and injected current was reduced in MNs, as was the threshold current, while the percentage of MNs showing long-lasting potentiation (LLP) in the intrinsic excitability was higher in SMA mice. INs showed a high rate of spontaneous firing, and those from SMA mice fired at higher frequency. INs from SMA mice showed little difference in their input-output relationship, threshold current, and plasticity in intrinsic excitability. The changes observed in both passive membrane and AP properties suggest greater overall excitability in both MNs and INs in SMA mice, with MNs showing more differences. There were also changes of synaptic currents in SMA mice. The average charge transfer per post-synaptic current of spontaneous excitatory and inhibitory synaptic currents (sEPSCs/sIPSCs) were lower in SMA MNs, while in INs sIPSC frequency was higher. Strikingly in light of the known loss of excitatory synapses on MNs, there was no difference in sEPSC frequency in MNs from SMA mice compared to controls. For miniature synaptic currents, mEPSC frequency was higher in SMA MNs, while for SMA INs, both mEPSC and mIPSC frequencies were higher. In SMA-affected mice we observed alterations of intrinsic and synaptic properties in both MNs and INs in the spinal motor network that may contribute to the pathophysiology, or alternatively, may be a compensatory response to preserve network function.
Collapse
Affiliation(s)
- Jianli Sun
- Delaware Center for Neuroscience Research, Delaware State University, Dover, DE, United States.,Department of Biological Science, Delaware State University, Dover, DE, United States
| | - Melissa A Harrington
- Delaware Center for Neuroscience Research, Delaware State University, Dover, DE, United States.,Department of Biological Science, Delaware State University, Dover, DE, United States
| |
Collapse
|
8
|
A Network Model Reveals That the Experimentally Observed Switch of the Granule Cell Phenotype During Epilepsy Can Maintain the Pattern Separation Function of the Dentate Gyrus. ACTA ACUST UNITED AC 2019. [DOI: 10.1007/978-3-319-99103-0_23] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
|
9
|
Kuhn T, Gullett JM, Boutzoukas AE, Bohsali A, Mareci TH, FitzGerald DB, Carney PR, Bauer RM. Temporal lobe epilepsy affects spatial organization of entorhinal cortex connectivity. Epilepsy Behav 2018; 88:87-95. [PMID: 30243111 PMCID: PMC6294293 DOI: 10.1016/j.yebeh.2018.06.038] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2018] [Revised: 06/18/2018] [Accepted: 06/20/2018] [Indexed: 12/15/2022]
Abstract
Evidence for structural connectivity patterns within the medial temporal lobe derives primarily from postmortem histological studies. In humans and nonhuman primates, the parahippocampal gyrus (PHg) is subdivided into parahippocampal (PHc) and perirhinal (PRc) cortices, which receive input from distinct cortical networks. Likewise, their efferent projections to the entorhinal cortex (ERc) are distinct. The PHc projects primarily to the medial ERc (M-ERc). The PRc projects primarily to the lateral portion of the ERc (L-ERc). Both M-ERc and L-ERc, via the perforant pathway, project to the dentate gyrus and hippocampal (HC) subfields. Until recently, these neural circuits could not be visualized in vivo. Diffusion tensor imaging algorithms have been developed to segment gray matter structures based on probabilistic connectivity patterns. However, these algorithms have not yet been applied to investigate connectivity in the temporal lobe or changes in connectivity architecture related to disease processes. In this study, this segmentation procedure was used to classify ERc gray matter based on PRc, ERc, and HC connectivity patterns in 7 patients with temporal lobe epilepsy (TLE) without hippocampal sclerosis (mean age, 14.86 ± 3.34 years) and 7 healthy controls (mean age, 23.86 ± 2.97 years). Within samples paired t-tests allowed for comparison of ERc connectivity between epileptogenic and contralateral hemispheres. In healthy controls, there were no significant within-group differences in surface area, volume, or cluster number of ERc connectivity-defined regions (CDR). Likewise, in line with histology results, ERc CDR in the control group were well-organized, uniform, and segregated via PRc/PHc afferent and HC efferent connections. Conversely, in TLE, there were significantly more PRc and HC CDR clusters in the epileptogenic than the contralateral hemisphere. The surface area of the PRc CDR was greater, and that of the HC CDRs was smaller, in the epileptogenic hemisphere as well. Further, there was no clear delineation between M-ERc and L-ERc connectivity with PRc, PHc or HC in TLE. These results suggest a breakdown of the spatial organization of PHg-ERc-HC connectivity in TLE. Whether this breakdown is the cause or result of epileptic activity remains an exciting research question.
Collapse
Affiliation(s)
- Taylor Kuhn
- Department of Clinical and Health Psychology, University of Florida, Gainesville, FL, United States of America; Department of Physical Therapy, University of Florida, Gainesville, FL, United States of America.
| | - Joseph M Gullett
- Department of Clinical and Health Psychology, University of Florida, Gainesville, FL, United States of America; Department of VA Brain Rehabilitation Research Center, Malcolm Randall VA Center Gainesville, FL, United States of America
| | - Angelique E Boutzoukas
- Department of Clinical and Health Psychology, University of Florida, Gainesville, FL, United States of America
| | - Anastasia Bohsali
- Department of Neurology, University of Florida, Gainesville, FL, United States of America
| | - Thomas H Mareci
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL, United States of America
| | - David B FitzGerald
- Department of VA Brain Rehabilitation Research Center, Malcolm Randall VA Center Gainesville, FL, United States of America
| | - Paul R Carney
- Department of Pediatrics, University of Florida, Gainesville, FL, United States of America; Department of Neurology, University of Florida, Gainesville, FL, United States of America; Department of Neuroscience, University of Florida, Gainesville, FL, United States of America; J. Crayton Pruitt Department of Biomedical Engineering, University of Florida, Gainesville, FL, United States of America; B.J. and Eve Wilder Epilepsy Center Excellence, University of Florida, Gainesville, FL, United States of America
| | - Russell M Bauer
- Department of Clinical and Health Psychology, University of Florida, Gainesville, FL, United States of America; Department of VA Brain Rehabilitation Research Center, Malcolm Randall VA Center Gainesville, FL, United States of America
| |
Collapse
|
10
|
Folweiler KA, Samuel S, Metheny HE, Cohen AS. Diminished Dentate Gyrus Filtering of Cortical Input Leads to Enhanced Area Ca3 Excitability after Mild Traumatic Brain Injury. J Neurotrauma 2018; 35:1304-1317. [PMID: 29338620 PMCID: PMC5962932 DOI: 10.1089/neu.2017.5350] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Mild traumatic brain injury (mTBI) disrupts hippocampal function and can lead to long-lasting episodic memory impairments. The encoding of episodic memories relies on spatial information processing within the hippocampus. As the primary entry point for spatial information into the hippocampus, the dentate gyrus is thought to function as a physiological gate, or filter, of afferent excitation before reaching downstream area Cornu Ammonis (CA3). Although injury has previously been shown to alter dentate gyrus network excitability, it is unknown whether mTBI affects dentate gyrus output to area CA3. In this study, we assessed hippocampal function, specifically the interaction between the dentate gyrus and CA3, using behavioral and electrophysiological techniques in ex vivo brain slices 1 week following mild lateral fluid percussion injury (LFPI). Behaviorally, LFPI mice were found to be impaired in an object-place recognition task, indicating that spatial information processing in the hippocampus is disrupted. Extracellular recordings and voltage-sensitive dye imaging demonstrated that perforant path activation leads to the aberrant spread of excitation from the dentate gyrus into area CA3 along the mossy fiber pathway. These results suggest that after mTBI, the dentate gyrus has a diminished capacity to regulate cortical input into the hippocampus, leading to increased CA3 network excitability. The loss of the dentate filtering efficacy reveals a potential mechanism by which hippocampal-dependent spatial information processing is disrupted, and may contribute to memory dysfunction after mTBI.
Collapse
Affiliation(s)
- Kaitlin A. Folweiler
- Department of Anesthesiology and Critical Care Medicine, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania
- Department of Anesthesiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
- Neuroscience Graduate Group, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Sandy Samuel
- Department of Anesthesiology and Critical Care Medicine, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania
- Department of Anesthesiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Hannah E. Metheny
- Department of Anesthesiology and Critical Care Medicine, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania
- Department of Anesthesiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Akiva S. Cohen
- Department of Anesthesiology and Critical Care Medicine, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania
- Department of Anesthesiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
- Neuroscience Graduate Group, University of Pennsylvania, Philadelphia, Pennsylvania
| |
Collapse
|
11
|
Smirnova EY, Amakhin DV, Malkin SL, Chizhov AV, Zaitsev AV. Acute Changes in Electrophysiological Properties of Cortical Regular-Spiking Cells Following Seizures in a Rat Lithium–Pilocarpine Model. Neuroscience 2018; 379:202-215. [DOI: 10.1016/j.neuroscience.2018.03.020] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2017] [Revised: 03/14/2018] [Accepted: 03/15/2018] [Indexed: 11/26/2022]
|
12
|
Neuberger EJ, Gupta A, Subramanian D, Korgaonkar AA, Santhakumar V. Converging early responses to brain injury pave the road to epileptogenesis. J Neurosci Res 2017; 97:1335-1344. [PMID: 29193309 DOI: 10.1002/jnr.24202] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Revised: 11/06/2017] [Accepted: 11/09/2017] [Indexed: 12/19/2022]
Abstract
Epilepsy, characterized by recurrent seizures and abnormal electrical activity in the brain, is one of the most prevalent brain disorders. Over two million people in the United States have been diagnosed with epilepsy and 3% of the general population will be diagnosed with it at some point in their lives. While most developmental epilepsies occur due to genetic predisposition, a class of "acquired" epilepsies results from a variety of brain insults. A leading etiological factor for epilepsy that is currently on the rise is traumatic brain injury (TBI), which accounts for up to 20% of all symptomatic epilepsies. Remarkably, the presence of an identified early insult that constitutes a risk for development of epilepsy provides a therapeutic window in which the pathological processes associated with brain injury can be manipulated to limit the subsequent development of recurrent seizure activity and epilepsy. Recent studies have revealed diverse pathologies, including enhanced excitability, activated immune signaling, cell death, and enhanced neurogenesis within a week after injury, suggesting a period of heightened adaptive and maladaptive plasticity. An integrated understanding of these processes and their cellular and molecular underpinnings could lead to novel targets to arrest epileptogenesis after trauma. This review attempts to highlight and relate the diverse early changes after trauma and their role in development of epilepsy and suggests potential strategies to limit neurological complications in the injured brain.
Collapse
Affiliation(s)
- Eric J Neuberger
- Department of Pharmacology, Physiology & Neuroscience, Rutgers New Jersey Medical School, Newark, NJ
| | - Akshay Gupta
- Department of Pharmacology, Physiology & Neuroscience, Rutgers New Jersey Medical School, Newark, NJ
| | - Deepak Subramanian
- Department of Pharmacology, Physiology & Neuroscience, Rutgers New Jersey Medical School, Newark, NJ
| | - Akshata A Korgaonkar
- Department of Pharmacology, Physiology & Neuroscience, Rutgers New Jersey Medical School, Newark, NJ
| | - Vijayalakshmi Santhakumar
- Department of Pharmacology, Physiology & Neuroscience, Rutgers New Jersey Medical School, Newark, NJ
| |
Collapse
|
13
|
Paterno R, Folweiler KA, Cohen AS. Pathophysiology and Treatment of Memory Dysfunction After Traumatic Brain Injury. Curr Neurol Neurosci Rep 2017; 17:52. [PMID: 28500417 PMCID: PMC5861722 DOI: 10.1007/s11910-017-0762-x] [Citation(s) in RCA: 63] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Memory is fundamental to everyday life, and cognitive impairments resulting from traumatic brain injury (TBI) have devastating effects on TBI survivors. A contributing component to memory impairments caused by TBI is alteration in the neural circuits associated with memory function. In this review, we aim to bring together experimental findings that characterize behavioral memory deficits and the underlying pathophysiology of memory-involved circuits after TBI. While there is little doubt that TBI causes memory and cognitive dysfunction, it is difficult to conclude which memory phase, i.e., encoding, maintenance, or retrieval, is specifically altered by TBI. This is most likely due to variation in behavioral protocols and experimental models. Additionally, we review a selection of experimental treatments that hold translational potential to mitigate memory dysfunction following injury.
Collapse
Affiliation(s)
- Rosalia Paterno
- Center for Sleep and Circadian Neurobiology, Perelman School of Medicine, University of Pennsylvania, 3615 Civic Center Boulevard, Abramson Research Center, Rm. 816-h, Philadelphia, PA, 19104, USA.
| | - Kaitlin A Folweiler
- Department of Anesthesiology and Critical Care Medicine, Joseph Stokes, Jr. Research Institute, Children's Hospital of Philadelphia, 3615 Civic Center Boulevard, Abramson Research Center, Rm. 816-h, Philadelphia, PA, 19104, USA
| | - Akiva S Cohen
- Department of Anesthesiology and Critical Care Medicine, Joseph Stokes, Jr. Research Institute, Children's Hospital of Philadelphia, 3615 Civic Center Boulevard, Abramson Research Center, Rm. 816-h, Philadelphia, PA, 19104, USA
- Department of Anesthesiology and Critical Care Medicine, Perelman School of Medicine, University of Pennsylvania, 3615 Civic Center Boulevard, Abramson Research Center, Rm. 816-h, Philadelphia, PA, 19104, USA
| |
Collapse
|
14
|
Alexander A, Maroso M, Soltesz I. Organization and control of epileptic circuits in temporal lobe epilepsy. PROGRESS IN BRAIN RESEARCH 2016; 226:127-54. [PMID: 27323941 PMCID: PMC5140277 DOI: 10.1016/bs.pbr.2016.04.007] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
When studying the pathological mechanisms of epilepsy, there are a seemingly endless number of approaches from the ultrastructural level-receptor expression by EM-to the behavioral level-comorbid depression in behaving animals. Epilepsy is characterized as a disorder of recurrent seizures, which are defined as "a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain" (Fisher et al., 2005). Such abnormal activity typically does not occur in a single isolated neuron; rather, it results from pathological activity in large groups-or circuits-of neurons. Here we choose to focus on two aspects of aberrant circuits in temporal lobe epilepsy: their organization and potential mechanisms to control these pathological circuits. We also look at two scales: microcircuits, ie, the relationship between individual neurons or small groups of similar neurons, and macrocircuits, ie, the organization of large-scale brain regions. We begin by summarizing the large body of literature that describes the stereotypical anatomical changes in the temporal lobe-ie, the anatomical basis of alterations in microcircuitry. We then offer a brief introduction to graph theory and describe how this type of mathematical analysis, in combination with computational neuroscience techniques and using parameters obtained from experimental data, can be used to postulate how microcircuit alterations may lead to seizures. We then zoom out and look at the changes which are seen over large whole-brain networks in patients and animal models, and finally we look to the future.
Collapse
Affiliation(s)
- A Alexander
- Stanford University, Stanford, CA, United States
| | - M Maroso
- Stanford University, Stanford, CA, United States
| | - I Soltesz
- Stanford University, Stanford, CA, United States.
| |
Collapse
|
15
|
Beamer M, Tummala SR, Gullotti D, Kopil C, Gorka S, Bass CRD, Morrison B, Cohen AS, Meaney DF. Primary blast injury causes cognitive impairments and hippocampal circuit alterations. Exp Neurol 2016; 283:16-28. [PMID: 27246999 DOI: 10.1016/j.expneurol.2016.05.025] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Revised: 05/14/2016] [Accepted: 05/20/2016] [Indexed: 11/17/2022]
Abstract
Blast-induced traumatic brain injury (bTBI) and its long term consequences are a major health concern among veterans. Despite recent work enhancing our knowledge about bTBI, very little is known about the contribution of the blast wave alone to the observed sequelae. Herein, we isolated its contribution in a mouse model by constraining the animals' heads during exposure to a shockwave (primary blast). Our results show that exposure to primary blast alone results in changes in hippocampus-dependent behaviors that correspond with electrophysiological changes in area CA1 and are accompanied by reactive gliosis. Specifically, five days after exposure, behavior in an open field and performance in a spatial object recognition (SOR) task were significantly different from sham. Network electrophysiology, also performed five days after injury, demonstrated a significant decrease in excitability and increase in inhibitory tone. Immunohistochemistry for GFAP and Iba1 performed ten days after injury showed a significant increase in staining. Interestingly, a threefold increase in the impulse of the primary blast wave did not exacerbate these measures. However, we observed a significant reduction in the contribution of the NMDA receptors to the field EPSP at the highest blast exposure level. Our results emphasize the need to account for the effects of primary blast loading when studying the sequelae of bTBI.
Collapse
Affiliation(s)
- Matthew Beamer
- Department of Bioengineering(1), University of Pennsylvania, Philadelphia, PA, USA
| | - Shanti R Tummala
- Department of Bioengineering(1), University of Pennsylvania, Philadelphia, PA, USA
| | - David Gullotti
- Department of Bioengineering(1), University of Pennsylvania, Philadelphia, PA, USA
| | - Catherine Kopil
- Department of Bioengineering(1), University of Pennsylvania, Philadelphia, PA, USA
| | - Samuel Gorka
- Department of Bioengineering(1), University of Pennsylvania, Philadelphia, PA, USA
| | | | - Barclay Morrison
- Department of Biomedical Engineering, Columbia University, New York, NY, USA
| | - Akiva S Cohen
- Department of Anesthesiology and Critical Care Medicine, University of Pennsylvania, Philadelphia, PA, USA; Division of Critical Care Medicine, Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - David F Meaney
- Department of Bioengineering(1), University of Pennsylvania, Philadelphia, PA, USA; Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA, USA.
| |
Collapse
|
16
|
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.
Collapse
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
| |
Collapse
|
17
|
Smith CJ, Xiong G, Elkind JA, Putnam B, Cohen AS. Brain Injury Impairs Working Memory and Prefrontal Circuit Function. Front Neurol 2015; 6:240. [PMID: 26617569 PMCID: PMC4643141 DOI: 10.3389/fneur.2015.00240] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Accepted: 10/30/2015] [Indexed: 12/13/2022] Open
Abstract
More than 2.5 million Americans suffer a traumatic brain injury (TBI) each year. Even mild to moderate TBI causes long-lasting neurological effects. Despite its prevalence, no therapy currently exists to treat the underlying cause of cognitive impairment suffered by TBI patients. Following lateral fluid percussion injury (LFPI), the most widely used experimental model of TBI, we investigated alterations in working memory and excitatory/inhibitory synaptic balance in the prefrontal cortex. LFPI impaired working memory as assessed with a T-maze behavioral task. Field excitatory postsynaptic potentials recorded in the prefrontal cortex were reduced in slices derived from brain-injured mice. Spontaneous and miniature excitatory postsynaptic currents onto layer 2/3 neurons were more frequent in slices derived from LFPI mice, while inhibitory currents onto layer 2/3 neurons were smaller after LFPI. Additionally, an increase in action potential threshold and concomitant decrease in firing rate was observed in layer 2/3 neurons in slices from injured animals. Conversely, no differences in excitatory or inhibitory synaptic transmission onto layer 5 neurons were observed; however, layer 5 neurons demonstrated a decrease in input resistance and action potential duration after LFPI. These results demonstrate synaptic and intrinsic alterations in prefrontal circuitry that may underlie working memory impairment caused by TBI.
Collapse
Affiliation(s)
- Colin J. Smith
- Research Institute of Children’s Hospital of Philadelphia, Philadelphia, PA, USA
- Neuroscience Graduate Group, University of Pennsylvania School of Medicine, Philadelphia, PA, USA
| | - Guoxiang Xiong
- Research Institute of Children’s Hospital of Philadelphia, Philadelphia, PA, USA
| | - Jaclynn A. Elkind
- Research Institute of Children’s Hospital of Philadelphia, Philadelphia, PA, USA
| | - Brendan Putnam
- Research Institute of Children’s Hospital of Philadelphia, Philadelphia, PA, USA
| | - Akiva S. Cohen
- Research Institute of Children’s Hospital of Philadelphia, Philadelphia, PA, USA
- Department of Anesthesiology and Critical Care Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| |
Collapse
|
18
|
Bui A, Kim HK, Maroso M, Soltesz I. Microcircuits in Epilepsy: Heterogeneity and Hub Cells in Network Synchronization. Cold Spring Harb Perspect Med 2015; 5:5/11/a022855. [PMID: 26525454 DOI: 10.1101/cshperspect.a022855] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Epilepsy is a complex disorder involving neurological alterations that lead to the pathological development of spontaneous, recurrent seizures. For decades, seizures were thought to be largely repetitive, and had been examined at the macrocircuit level using electrophysiological recordings. However, research mapping the dynamics of large neuronal populations has revealed that seizures are not simply recurrent bursts of hypersynchrony. Instead, it is becoming clear that seizures involve a complex interplay of different neurons and circuits. Herein, we will review studies examining microcircuit changes that may underlie network hyperexcitability, discussing observations from network theory, computational modeling, and optogenetics. We will delve into the idea of hub cells as pathological centers for seizure activity, and will explore optogenetics as a novel avenue to target and treat pathological circuits. Finally, we will conclude with a discussion on future directions in the field.
Collapse
Affiliation(s)
- Anh Bui
- Department of Anatomy and Neurobiology, University of California, Irvine, California 92697
| | - Hannah K Kim
- Department of Anatomy and Neurobiology, University of California, Irvine, California 92697
| | - Mattia Maroso
- Department of Anatomy and Neurobiology, University of California, Irvine, California 92697
| | - Ivan Soltesz
- Department of Anatomy and Neurobiology, University of California, Irvine, California 92697
| |
Collapse
|
19
|
Nagaraj V, Lee S, Krook-Magnuson E, Soltesz I, Benquet P, Irazoqui P, Netoff T. Future of seizure prediction and intervention: closing the loop. J Clin Neurophysiol 2015; 32:194-206. [PMID: 26035672 PMCID: PMC4455045 DOI: 10.1097/wnp.0000000000000139] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The ultimate goal of epilepsy therapies is to provide seizure control for all patients while eliminating side effects. Improved specificity of intervention through on-demand approaches may overcome many of the limitations of current intervention strategies. This article reviews the progress in seizure prediction and detection, potential new therapies to provide improved specificity, and devices to achieve these ends. Specifically, we discuss (1) potential signal modalities and algorithms for seizure detection and prediction, (2) closed-loop intervention approaches, and (3) hardware for implementing these algorithms and interventions. Seizure prediction and therapies maximize efficacy, whereas minimizing side effects through improved specificity may represent the future of epilepsy treatments.
Collapse
Affiliation(s)
- Vivek Nagaraj
- Graduate Program in Neuroscience, University of Minnesota
| | - Steven Lee
- Weldon School of Biomedical Engineering, Purdue University
| | | | - Ivan Soltesz
- Department of Anatomy & Neurobiology, University of California, Irvine
| | | | - Pedro Irazoqui
- Weldon School of Biomedical Engineering, Purdue University
| | - Theoden Netoff
- Graduate Program in Neuroscience, University of Minnesota
- Department of Biomedical Engineering, University of Minnesota
| |
Collapse
|
20
|
Sokolova IV, Schneider CJ, Bezaire M, Soltesz I, Vlkolinsky R, Nelson GA. Proton Radiation Alters Intrinsic and Synaptic Properties of CA1 Pyramidal Neurons of the Mouse Hippocampus. Radiat Res 2015; 183:208-18. [DOI: 10.1667/rr13785.1] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
- Irina V. Sokolova
- Department of Basic Sciences, Division of Radiation Research, School of Medicine, Loma Linda University, Loma Linda, California
| | - Calvin J. Schneider
- Department of Anatomy and Neurobiology, University of California, Irvine, Irvine, California
| | - Marianne Bezaire
- Department of Anatomy and Neurobiology, University of California, Irvine, Irvine, California
| | - Ivan Soltesz
- Department of Anatomy and Neurobiology, University of California, Irvine, Irvine, California
| | - Roman Vlkolinsky
- Department of Basic Sciences, Division of Radiation Research, School of Medicine, Loma Linda University, Loma Linda, California
| | - Gregory A. Nelson
- Department of Basic Sciences, Division of Radiation Research, School of Medicine, Loma Linda University, Loma Linda, California
| |
Collapse
|
21
|
Zhang W, Thamattoor AK, LeRoy C, Buckmaster PS. Surviving mossy cells enlarge and receive more excitatory synaptic input in a mouse model of temporal lobe epilepsy. Hippocampus 2014; 25:594-604. [PMID: 25488607 DOI: 10.1002/hipo.22396] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/24/2014] [Indexed: 11/07/2022]
Abstract
Numerous hypotheses of temporal lobe epileptogenesis have been proposed, and several involve hippocampal mossy cells. Building on previous hypotheses we sought to test the possibility that after epileptogenic injuries surviving mossy cells develop into super-connected seizure-generating hub cells. If so, they might require more cellular machinery and consequently have larger somata, elongate their dendrites to receive more synaptic input, and display higher frequencies of miniature excitatory synaptic currents (mEPSCs). To test these possibilities pilocarpine-treated mice were evaluated using GluR2-immunocytochemistry, whole-cell recording, and biocytin-labeling. Epileptic pilocarpine-treated mice displayed substantial loss of GluR2-positive hilar neurons. Somata of surviving neurons were 1.4-times larger than in controls. Biocytin-labeled mossy cells also were larger in epileptic mice, but dendritic length per cell was not significantly different. The average frequency of mEPSCs of mossy cells recorded in the presence of tetrodotoxin and bicuculline was 3.2-times higher in epileptic pilocarpine-treated mice as compared to controls. Other parameters of mEPSCs were similar in both groups. Average input resistance of mossy cells in epileptic mice was reduced to 63% of controls, which is consistent with larger somata and would tend to make surviving mossy cells less excitable. Other intrinsic physiological characteristics examined were similar in both groups. Increased excitatory synaptic input is consistent with the hypothesis that surviving mossy cells develop into aberrantly super-connected seizure-generating hub cells, and soma hypertrophy is indirectly consistent with the possibility of axon sprouting. However, no obvious evidence of hyperexcitable intrinsic physiology was found. Furthermore, similar hypertrophy and hyper-connectivity has been reported for other neuron types in the dentate gyrus, suggesting mossy cells are not unique in this regard. Thus, findings of the present study reveal epilepsy-related changes in mossy cell anatomy and synaptic input but do not strongly support the hypothesis that mossy cells develop into seizure-generating hub cells.
Collapse
Affiliation(s)
- Wei Zhang
- Department of Comparative Medicine, Stanford University, Stanford, California
| | | | | | | |
Collapse
|
22
|
Johnson BN, Palmer CP, Bourgeois EB, Elkind JA, Putnam BJ, Cohen AS. Augmented Inhibition from Cannabinoid-Sensitive Interneurons Diminishes CA1 Output after Traumatic Brain Injury. Front Cell Neurosci 2014; 8:435. [PMID: 25565968 PMCID: PMC4271495 DOI: 10.3389/fncel.2014.00435] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Accepted: 12/02/2014] [Indexed: 11/15/2022] Open
Abstract
The neurological impairments associated with traumatic brain injury include learning and memory deficits and increased risk of seizures. The hippocampus is critically involved in both of these phenomena and highly susceptible to damage by traumatic brain injury. To examine network activity in the hippocampal CA1 region after lateral fluid percussion injury, we used a combination of voltage-sensitive dye, field potential, and patch clamp recording in mouse hippocampal brain slices. When the stratum radiatum (SR) was stimulated in slices from injured mice, we found decreased depolarization in SR and increased hyperpolarization in stratum oriens (SO), together with a decrease in the percentage of pyramidal neurons firing stimulus-evoked action potentials. Increased hyperpolarization in SO persisted when glutamatergic transmission was blocked. However, we found no changes in SO responses when the alveus was stimulated to directly activate SO. These results suggest that the increased SO hyperpolarization evoked by SR stimulation was mediated by interneurons that have cell bodies and/or axons in SR, and form synapses in stratum pyramidale and SO. A low concentration (100 nM) of the synthetic cannabinoid WIN55,212-2, restored CA1 output in slices from injured animals. These findings support the hypothesis that increased GABAergic signaling by cannabinoid-sensitive interneurons contributes to the reduced CA1 output following traumatic brain injury.
Collapse
Affiliation(s)
- Brian N Johnson
- Children's Hospital of Philadelphia Research Institute, Children's Hospital of Philadelphia , Philadelphia, PA , USA
| | - Chris P Palmer
- Department of Neuroscience, University of Pennsylvania School of Medicine , Philadelphia, PA , USA
| | - Elliot B Bourgeois
- Department of Pathology, Brigham and Women's Hospital, Harvard Medical School , Boston, MA , USA
| | - Jaclynn A Elkind
- Children's Hospital of Philadelphia Research Institute, Children's Hospital of Philadelphia , Philadelphia, PA , USA
| | - Brendan J Putnam
- Children's Hospital of Philadelphia Research Institute, Children's Hospital of Philadelphia , Philadelphia, PA , USA
| | - Akiva S Cohen
- Children's Hospital of Philadelphia Research Institute, Children's Hospital of Philadelphia , Philadelphia, PA , USA ; Department of Pediatrics, University of Pennsylvania School of Medicine , Philadelphia, PA , USA
| |
Collapse
|
23
|
Li Y, Korgaonkar AA, Swietek B, Wang J, Elgammal FS, Elkabes S, Santhakumar V. Toll-like receptor 4 enhancement of non-NMDA synaptic currents increases dentate excitability after brain injury. Neurobiol Dis 2014; 74:240-53. [PMID: 25497689 DOI: 10.1016/j.nbd.2014.11.021] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2014] [Revised: 11/21/2014] [Accepted: 11/26/2014] [Indexed: 11/18/2022] Open
Abstract
Concussive brain injury results in neuronal degeneration, microglial activation and enhanced excitability in the hippocampal dentate gyrus, increasing the risk for epilepsy and memory dysfunction. Endogenous molecules released during injury can activate innate immune responses including toll-like receptor 4 (TLR4). Recent studies indicate that immune mediators can modulate neuronal excitability. Since non-specific agents that reduce TLR4 signaling can limit post-traumatic neuropathology, we examined whether TLR4 signaling contributes to early changes in dentate excitability after brain injury. Concussive brain injury caused a transient increase in hippocampal TLR4 expression within 4h, which peaked at 24h. Post-injury increase in TLR4 expression in the dentate gyrus was primarily neuronal and persisted for one week. Acute, in vitro treatment with TLR4 ligands caused bidirectional modulation of dentate excitability in control and brain-injured rats, with a reversal in the direction of modulation after brain injury. TLR4 antagonists decreased, and agonist increased, afferent-evoked dentate excitability one week after brain injury. NMDA receptor antagonist did not occlude the ability of LPS-RS, a TLR4 antagonist, to decrease post-traumatic dentate excitability. LPS-RS failed to modulate granule cell NMDA EPSCs but decreased perforant path-evoked non-NMDA EPSC peak amplitude and charge transfer in both granule cells and mossy cells. Our findings indicate an active role for TLR4 signaling in early post-traumatic dentate hyperexcitability. The novel TLR4 modulation of non-NMDA glutamatergic currents, identified herein, could represent a general mechanism by which immune activation influences neuronal excitability in neurological disorders that recruit sterile inflammatory responses.
Collapse
Affiliation(s)
- Ying Li
- Department of Neurology and Neurosciences, Rutgers New Jersey Medical School, Newark, NJ 07103, USA
| | - Akshata A Korgaonkar
- Department of Neurology and Neurosciences, Rutgers New Jersey Medical School, Newark, NJ 07103, USA; Graduate School of Biomedical Sciences, Rutgers New Jersey Medical School, Newark, NJ 07103, USA
| | - Bogumila Swietek
- Department of Neurology and Neurosciences, Rutgers New Jersey Medical School, Newark, NJ 07103, USA
| | - Jianfeng Wang
- Department of Neurology and Neurosciences, Rutgers New Jersey Medical School, Newark, NJ 07103, USA
| | - Fatima S Elgammal
- Department of Neurology and Neurosciences, Rutgers New Jersey Medical School, Newark, NJ 07103, USA
| | - Stella Elkabes
- Graduate School of Biomedical Sciences, Rutgers New Jersey Medical School, Newark, NJ 07103, USA; Department of Neurological Surgery, Rutgers New Jersey Medical School, Newark, NJ 07103, USA
| | - Vijayalakshmi Santhakumar
- Department of Neurology and Neurosciences, Rutgers New Jersey Medical School, Newark, NJ 07103, USA; Graduate School of Biomedical Sciences, Rutgers New Jersey Medical School, Newark, NJ 07103, USA; Department of Pharmacology and Physiology, Rutgers New Jersey Medical School, Newark, NJ 07103, USA.
| |
Collapse
|
24
|
Yim MY, Hanuschkin A, Wolfart J. Intrinsic rescaling of granule cells restores pattern separation ability of a dentate gyrus network model during epileptic hyperexcitability. Hippocampus 2014; 25:297-308. [DOI: 10.1002/hipo.22373] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2014] [Revised: 09/29/2014] [Accepted: 09/29/2014] [Indexed: 01/12/2023]
Affiliation(s)
- Man Yi Yim
- Department of Mathematics; University of Hong Kong; Hong Kong
| | - Alexander Hanuschkin
- Institute of Neuroinformatics, University of Zurich and ETH Zurich; Zurich Switzerland
| | - Jakob Wolfart
- Oscar Langendorff Institute of Physiology, University of Rostock; Rostock Germany
| |
Collapse
|
25
|
Ahmed Z. Trans-spinal direct current stimulation modifies spinal cord excitability through synaptic and axonal mechanisms. Physiol Rep 2014; 2:2/9/e12157. [PMID: 25263206 PMCID: PMC4270225 DOI: 10.14814/phy2.12157] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The spinal cord is extremely complex. Therefore, trans‐spinal direct current stimulation (tsDCS) is expected to produce a multitude of neurophysiological changes. Here, we asked how tsDCS differentially affects synaptic and nonsynaptic transmission. We investigated the effects of tsDCS on synaptically mediated responses by stimulating the medullary longitudinal fascicle and recording responses in the sciatic nerve and triceps and tibialis anterior muscles. Response amplitude was increased during cathodal‐tsDCS (c‐tsDCS), but reduced during anodal‐tsDCS (a‐tsDCS). After‐effects were dependent on the frequency of the test stimulation. c‐tsDCS‐reduced responses evoked by low‐frequency (0.5 Hz) test stimulation and increased responses evoked by high‐frequency (400 Hz) test stimulation. a‐tsDCS had opposite effects. During and after c‐tsDCS, excitability of the lateral funiculus tract (LFT) and dorsal root fibers was increased. However, a‐tsDCS caused a complex response, reducing the excitability of LFT and increasing dorsal root fiber responses. Local DC application on the sciatic nerve showed that the effects of DC on axonal excitability were dependent on polarity, duration of stimulation, temporal profile (during vs. after stimulation), orientation of the current direction relative to the axon and relative to the direction of action potential propagation, distance from the DC electrode, and the local environment of the nervous tissue. Collectively, these results indicate that synaptic as well as axonal mechanisms might play a role in tsDCS‐induced effects. Therefore, this study identified many factors that should be considered in interpreting results of DCS and in designing tsDCS‐based interventions. There are two plastic mechanisms operating in different regions in the nervous system: synaptic‐mediated mechanisms and intrinsic excitability mechanisms. This study indicates that direct current stimulation affects both synaptic and intrinsic mechanisms of plasticity.
Collapse
Affiliation(s)
- Zaghloul Ahmed
- Department of Physical Therapy, College of Staten Island for Developmental Neuroscience, the College of Staten Island, Staten IslandNew York, New York Graduate Center/The City University of New York, New York, New York
| |
Collapse
|
26
|
Golowasch J. Ionic Current Variability and Functional Stability in the Nervous System. Bioscience 2014; 64:570-580. [PMID: 26069342 DOI: 10.1093/biosci/biu070] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Identified neurons in different animals express ionic currents at highly variable levels (population variability). If neuronal identity is associated with stereotypical function, as is the case in genetically identical neurons or in unambiguously identified individual neurons, this variability poses a conundrum: How is activity the same if the components that generate it-ionic current levels-are different? In some cases, ionic current variability across similar neurons generates an output gradient. However, many neurons produce very similar output activity, despite substantial variability in ionic conductances. It appears that, in many such cells, conductance levels of one ionic current vary in proportion to the conductance levels of another current. As a result, in a population of neurons, these conductances appear to be correlated. Here, I review theoretical and experimental work that suggests that neuronal ionic current correlation can reduce the global ionic current variability and can contribute to functional stability.
Collapse
Affiliation(s)
- Jorge Golowasch
- Federated Department of Biological Sciences, at the New Jersey Institute of Technology and Rutgers University, in Newark
| |
Collapse
|
27
|
Ratté S, Zhu Y, Lee KY, Prescott SA. Criticality and degeneracy in injury-induced changes in primary afferent excitability and the implications for neuropathic pain. eLife 2014; 3:e02370. [PMID: 24692450 PMCID: PMC3970756 DOI: 10.7554/elife.02370] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Neuropathic pain remains notoriously difficult to treat despite numerous drug targets. Here, we offer a novel explanation for this intractability. Computer simulations predicted that qualitative changes in primary afferent excitability linked to neuropathic pain arise through a switch in spike initiation dynamics when molecular pathologies reach a tipping point (criticality), and that this tipping point can be reached via several different molecular pathologies (degeneracy). We experimentally tested these predictions by pharmacologically blocking native conductances and/or electrophysiologically inserting virtual conductances. Multiple different manipulations successfully reproduced or reversed neuropathic changes in primary afferents from naïve or nerve-injured rats, respectively, thus confirming the predicted criticality and its degenerate basis. Degeneracy means that several different molecular pathologies are individually sufficient to cause hyperexcitability, and because several such pathologies co-occur after nerve injury, that no single pathology is uniquely necessary. Consequently, single-target-drugs can be circumvented by maladaptive plasticity in any one of several ion channels. DOI:http://dx.doi.org/10.7554/eLife.02370.001 Although the pain associated with an injury is unpleasant, it normally serves an important purpose: to make you avoid its source. However, some pain appears to arise from nowhere. Frustratingly, this type of pain, known as neuropathic pain, does not respond to common painkillers and is thus very difficult to treat. The neurons that transmit pain and other sensory information do so using electrical signals. In response to a stimulus, ions travel through channels in the membrane of a neuron, which leads to a change in the electrical potential of the membrane. When this change is large enough, a voltage spike is produced: this signal is ultimately transmitted to the brain. When certain neurons fire too easily or too often, neuropathic pain can arise. This hyperexcitability can make something painful feel even worse, or it can make things hurt that shouldn’t. To prevent this, extensive research has been devoted to identify drugs that target particular types of ion channels and block them. However, despite the discovery of many promising drugs, those drugs have been frustratingly ineffective in clinical trials. Using simulations and experiments, Ratté et al. have examined the behavior of a type of neuron that normally conducts information about touch, but the brain sometimes misinterprets this information as pain. Increasing the flow of ions through the cell membrane in these simulations eventually causes a ‘tipping point’ to be crossed, which triggers a dramatic, discontinuous change in spiking pattern. However, as several different types of ion channels contribute to the current, there are several different ways in which the tipping point can be crossed. This ability to produce the same result by multiple means is a common feature of complex systems. Known as degeneracy, it makes systems more robust, as a given result can still be achieved if one particular attempt to achieve this result fails. The work of Ratté et al. helps to explain why drugs that target just one type of ion channel may fail to relieve neuropathic pain: maladaptive changes in any one of several other ion channels may circumvent the therapeutic effect. DOI:http://dx.doi.org/10.7554/eLife.02370.002
Collapse
Affiliation(s)
- Stéphanie Ratté
- Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Canada
| | | | | | | |
Collapse
|
28
|
Bidirectional homeostatic plasticity induced by interneuron cell death and transplantation in vivo. Proc Natl Acad Sci U S A 2013; 111:492-7. [PMID: 24344303 DOI: 10.1073/pnas.1307784111] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Chronic changes in excitability and activity can induce homeostatic plasticity. These perturbations may be associated with neurological disorders, particularly those involving loss or dysfunction of GABA interneurons. In distal-less homeobox 1 (Dlx1(-/-)) mice with late-onset interneuron loss and reduced inhibition, we observed both excitatory synaptic silencing and decreased intrinsic neuronal excitability. These homeostatic changes do not fully restore normal circuit function, because synaptic silencing results in enhanced potential for long-term potentiation and abnormal gamma oscillations. Transplanting medial ganglionic eminence interneuron progenitors to introduce new GABAergic interneurons, we demonstrate restoration of hippocampal function. Specifically, miniature excitatory postsynaptic currents, input resistance, hippocampal long-term potentiation, and gamma oscillations are all normalized. Thus, in vivo homeostatic plasticity is a highly dynamic and bidirectional process that responds to changes in inhibition.
Collapse
|
29
|
Neurons within the same network independently achieve conserved output by differentially balancing variable conductance magnitudes. J Neurosci 2013; 33:9950-6. [PMID: 23761890 DOI: 10.1523/jneurosci.1095-13.2013] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Biological and theoretical evidence suggest that individual neurons may achieve similar outputs by differentially balancing variable underlying ionic conductances. Despite the substantial amount of data consistent with this idea, a direct biological demonstration that cells with conserved output, particularly within the same network, achieve these outputs via different solutions has been difficult to achieve. Here we demonstrate definitively that neurons from native neural networks with highly similar output achieve this conserved output by differentially tuning underlying conductance magnitudes. Multiple motor neurons of the crab (Cancer borealis) cardiac ganglion have highly conserved output within a preparation, despite showing a 2-4-fold range of conductance magnitudes. By blocking subsets of these currents, we demonstrate that the remaining conductances become unbalanced, causing disparate output as a result. Therefore, as strategies to understand neuronal excitability become increasingly sophisticated, it is important that such variability in excitability of neurons, even among those within the same individual, is taken into account.
Collapse
|
30
|
Thomas EA, Petrou S. Network-specific mechanisms may explain the paradoxical effects of carbamazepine and phenytoin. Epilepsia 2013; 54:1195-202. [PMID: 23566163 DOI: 10.1111/epi.12172] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/05/2013] [Indexed: 11/29/2022]
Abstract
PURPOSE A common notion of the mechanism by which the antiepileptic drugs (AEDs) carbamazepine and phenytoin act is that they block sodium channels by binding preferentially to the inactivated state, thereby allowing normal neuronal firing while blocking ictal activity. However, these drugs have unpredictable efficacy and, in some cases, may exacerbate seizures. Previous studies have suggested that reducing sodium channel availability in the dentate gyrus (DG) paradoxically increases excitability. We used a biophysically detailed computer model of the DG to test the hypothesis that AEDs increase excitability by disproportionately reducing negative feedback mechanisms. METHODS We built a Markov model of sodium channel gating that reproduces responses to voltage clamp experiments in the presence of carbamazepine and phenytoin. We incorporated this validated Markov model into a biophysically realistic computer model of DG neurons and networks. Simulated drug concentrations were similar to those measured in cerebral spinal fluid in medicated patients. Single neuron models were stimulated with current injections, and networks were stimulated with perforant path synaptic input. In the network model, environmental effects were studied by introducing mossy fiber sprouting. KEY FINDINGS As expected, drugs reduced sodium channel availability, which in turn reduced action potential amplitude. This had only a small effect on action potential (AP) firing rate during brief (100 msec) current injections. Paradoxically, long current injections (2,500 msec) increased AP firing rates. This was caused by reduced calcium entry and consequently reduced activation of calcium activated potassium channels. It is important to note that the main determinant of drug effect was resting membrane potential (RMP) and not action potential firing rate. Binding of phenytoin and carbamazepine is slow and, thus drug effects are largely determined by the long term state of the RMP. This paradoxical AP firing increase was dependent on the unusually large calcium-activated potassium conductances expressed by DG granule cells. This predicts that drug efficacy in a given network will depend on the precise makeup of conductances in the network. RMP is expected to vary with the level of activity in the network. We simulated the effects of drugs on single shot stimulus responses in networks with mossy fiber sprouting and varied the RMP in all neurons as a model for network activity. For an RMP of -50 mV, representing an active network, drugs had no effect, or in some cases, increased excitability. Drugs had an increasingly larger inhibitory effect on network responses as RMP decreased. An important prediction is that drugs will be unable to block ictal activity invading an active network. SIGNIFICANCE Our key findings are that drug effects depend on both intrinsic properties of the network and its behavioral state. This may explain the paradoxical and unpredictable effects of some AEDs on seizure control in some patients.
Collapse
Affiliation(s)
- Evan A Thomas
- Florey Neuroscience Institutes, Parkville, Victoria, Australia.
| | | |
Collapse
|
31
|
Yu J, Proddutur A, Elgammal FS, Ito T, Santhakumar V. Status epilepticus enhances tonic GABA currents and depolarizes GABA reversal potential in dentate fast-spiking basket cells. J Neurophysiol 2013; 109:1746-63. [PMID: 23324316 DOI: 10.1152/jn.00891.2012] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Temporal lobe epilepsy is associated with loss of interneurons and inhibitory dysfunction in the dentate gyrus. While status epilepticus (SE) leads to changes in granule cell inhibition, whether dentate basket cells critical for regulating granule cell feedforward and feedback inhibition express tonic GABA currents (I(GABA)) and undergo changes in inhibition after SE is not known. We find that interneurons immunoreactive for parvalbumin in the hilar-subgranular region express GABAA receptor (GABA(A)R) δ-subunits, which are known to underlie tonic I(GABA). Dentate fast-spiking basket cells (FS-BCs) demonstrate baseline tonic I(GABA) blocked by GABA(A)R antagonists. In morphologically and physiologically identified FS-BCs, tonic I(GABA) is enhanced 1 wk after pilocarpine-induced SE, despite simultaneous reduction in spontaneous inhibitory postsynaptic current (sIPSC) frequency. Amplitude of tonic I(GABA) in control and post-SE FS-BCs is enhanced by 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP), demonstrating the contribution of GABA(A)R δ-subunits. Whereas FS-BC resting membrane potential is unchanged after SE, perforated-patch recordings from FS-BCs show that the reversal potential for GABA currents (E(GABA)) is depolarized after SE. In model FS-BCs, increasing tonic GABA conductance decreased excitability when E(GABA) was shunting and increased excitability when E(GABA) was depolarizing. Although simulated focal afferent activation evoked seizurelike activity in model dentate networks with FS-BC tonic GABA conductance and shunting E(GABA), excitability of identical networks with depolarizing FS-BC E(GABA) showed lower activity levels. Thus, together, post-SE changes in tonic I(GABA) and E(GABA) maintain homeostasis of FS-BC activity and limit increases in dentate excitability. These findings have implications for normal FS-BC function and can inform studies examining comorbidities and therapeutics following SE.
Collapse
Affiliation(s)
- Jiandong Yu
- Department of Neurology and Neurosciences, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ, USA
| | | | | | | | | |
Collapse
|
32
|
The presynaptic active zone protein RIM1α controls epileptogenesis following status epilepticus. J Neurosci 2012; 32:12384-95. [PMID: 22956829 DOI: 10.1523/jneurosci.0223-12.2012] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
To ensure operation of synaptic transmission within an appropriate dynamic range, neurons have evolved mechanisms of activity-dependent plasticity, including changes in presynaptic efficacy. The multidomain protein RIM1α is an integral component of the cytomatrix at the presynaptic active zone and has emerged as key mediator of presynaptically expressed forms of synaptic plasticity. We have therefore addressed the role of RIM1α in aberrant cellular plasticity and structural reorganization after an episode of synchronous neuronal activity pharmacologically induced in vivo [status epilepticus (SE)]. Post-SE, all animals developed spontaneous seizure events, but their frequency was dramatically increased in RIM1α-deficient mice (RIM1α(-/-)). We found that in wild-type mice (RIM1α(+/+)) SE caused an increase in paired-pulse facilitation in the CA1 region of the hippocampus to the level observed in RIM1α(-/-) mice before SE. In contrast, this form of short-term plasticity was not further enhanced in RIM1α-deficient mice after SE. Intriguingly, RIM1α(-/-) mice showed a unique pattern of selective hilar cell loss (i.e., endfolium sclerosis), which so far has not been observed in a genetic epilepsy animal model, as well as less severe astrogliosis and attenuated mossy fiber sprouting. These findings indicate that the decrease in release probability and altered short- and long-term plasticity as present in RIM1α(-/-) mice result in the formation of a hyperexcitable network but act in part neuroprotectively with regard to neuropathological alterations associated with epileptogenesis. In summary, our results suggest that presynaptic plasticity and proper function of RIM1α play an important part in a neuron's adaptive response to aberrant electrical activity.
Collapse
|
33
|
Decrease in tonic inhibition contributes to increase in dentate semilunar granule cell excitability after brain injury. J Neurosci 2012; 32:2523-37. [PMID: 22396425 DOI: 10.1523/jneurosci.4141-11.2012] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Brain injury is an etiological factor for temporal lobe epilepsy and can lead to memory and cognitive impairments. A recently characterized excitatory neuronal class in the dentate molecular layer, semilunar granule cell (SGC), has been proposed to regulate dentate network activity patterns and working memory formation. Although SGCs, like granule cells, project to CA3, their typical sustained firing and associational axon collaterals suggest that they are functionally distinct from granule cells. We find that brain injury results in an enhancement of SGC excitability associated with an increase in input resistance 1 week after trauma. In addition to prolonging miniature and spontaneous IPSC interevent intervals, brain injury significantly reduces the amplitude of tonic GABA currents in SGCs. The postinjury decrease in SGC tonic GABA currents is in direct contrast to the increase observed in granule cells after trauma. Although our observation that SGCs express Prox1 indicates a shared lineage with granule cells, data from control rats show that SGC tonic GABA currents are larger and sIPSC interevent intervals shorter than in granule cells, demonstrating inherent differences in inhibition between these cell types. GABA(A) receptor antagonists selectively augmented SGC input resistance in controls but not in head-injured rats. Moreover, post-traumatic differences in SGC firing were abolished in GABA(A) receptor blockers. Our data show that cell-type-specific post-traumatic decreases in tonic GABA currents boost SGC excitability after brain injury. Hyperexcitable SGCs could augment dentate throughput to CA3 and contribute substantively to the enhanced risk for epilepsy and memory dysfunction after traumatic brain injury.
Collapse
|
34
|
Hofmann ME, Frazier CJ. Marijuana, endocannabinoids, and epilepsy: potential and challenges for improved therapeutic intervention. Exp Neurol 2011; 244:43-50. [PMID: 22178327 DOI: 10.1016/j.expneurol.2011.11.047] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2011] [Revised: 11/25/2011] [Accepted: 11/29/2011] [Indexed: 10/14/2022]
Abstract
Phytocannabinoids isolated from the cannabis plant have broad potential in medicine that has been well recognized for many centuries. It is presumed that these lipid soluble signaling molecules exert their effects in both the central and peripheral nervous system in large part through direct interaction with metabotropic cannabinoid receptors. These same receptors are also targeted by a variety of endogenous cannabinoids including 2-arachidonoyl glycerol and anandamide. Significant effort over the last decade has produced an enormous advance in our understanding of both the cellular and the synaptic physiology of endogenous lipid signaling systems. This increase in knowledge has left us better prepared to carefully evaluate the potential for both natural and synthetic cannabinoids in the treatment of a variety of neurological disorders. In the case of epilepsy, long standing interest in therapeutic approaches that target endogenous cannabinoid signaling systems are, for the most part, not well justified by available clinical data from human epileptics. Nevertheless, basic science experiments have clearly indicated a key role for endogenous cannabinoid signaling systems in moment to moment regulation of neuronal excitability. Further it has become clear that these systems can both alter and be altered by epileptiform activity in a wide range of in vitro and in vivo models of epilepsy. Collectively these observations suggest clear potential for effective therapeutic modulation of endogenous cannabinoid signaling systems in the treatment of human epilepsy, and in fact, further highlight key obstacles that would need to be addressed to reach that goal.
Collapse
Affiliation(s)
- Mackenzie E Hofmann
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, USA
| | | |
Collapse
|
35
|
Wijesinghe R, Camp AJ. Intrinsic neuronal excitability: implications for health and disease. Biomol Concepts 2011; 2:247-59. [PMID: 25962033 DOI: 10.1515/bmc.2011.026] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2011] [Accepted: 05/30/2011] [Indexed: 11/15/2022] Open
Abstract
The output of a single neuron depends on both synaptic connectivity and intrinsic membrane properties. Changes in both synaptic and intrinsic membrane properties have been observed during homeostatic processes (e.g., vestibular compensation) as well as in several central nervous system (CNS) disorders. Although changes in synaptic properties have been extensively studied, particularly with regard to learning and memory, the contribution of intrinsic membrane properties to either physiological or pathological processes is much less clear. Recent research, however, has shown that alterations in the number, location or properties of voltage- and ligand-gated ion channels can underlie both normal and abnormal physiology, and that these changes arise via a diverse suite of molecular substrates. The literature reviewed here shows that changes in intrinsic neuronal excitability (presumably in concert with synaptic plasticity) can fundamentally modify the output of neurons, and that these modifications can subserve both homeostatic mechanisms and the pathogenesis of CNS disorders including epilepsy, migraine, and chronic pain.
Collapse
|
36
|
Deng P, Xu ZC. Contribution of Ih to Neuronal Damage in the Hippocampus after Traumatic Brain Injury in Rats. J Neurotrauma 2011; 28:1173-83. [DOI: 10.1089/neu.2010.1683] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Affiliation(s)
- Ping Deng
- Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, Indiana
| | - Zao C. Xu
- Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, Indiana
| |
Collapse
|
37
|
Hofmann ME, Bhatia C, Frazier CJ. Cannabinoid receptor agonists potentiate action potential-independent release of GABA in the dentate gyrus through a CB1 receptor-independent mechanism. J Physiol 2011; 589:3801-21. [PMID: 21646412 DOI: 10.1113/jphysiol.2011.211482] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
We report a novel excitatory effect of cannabinoid agonists on action potential-independent GABAergic transmission in the rat dentate gyrus. Specifically, we find that both WIN55,212-2 and anandamide increase the frequency of miniature IPSCs (mIPSCs)recorded from hilar mossy cells without altering event amplitude, area, rise time, or decay. The effect of WIN55,212-2 on mIPSCs is insensitive to AM251 and preserved in CB1 −/− animals,indicating that it does not depend on activation of CB1 receptors. It is also insensitive to AM630 and unaffected by capsazepine suggesting that neither CB2 nor TRPV1 receptors are involved. Further, it is blocked by pre-incubation in suramin and by a selective protein kinase A inhibitor (H-89), and is mimicked (and occluded) by bath application of forskolin. Similar CB1 receptor-independent facilitation of exocytosis is not apparent when recording evoked IPSCs in the presence of AM251, suggesting that the exocytotic mechanism that produces WIN55,212-2 sensitive mIPSCs is distinct from that which produces CB1 sensitive and action potential-dependent release. Despite clear independence from action potentials, WIN55,212-2 mediated facilitation of mIPSCs requires calcium, and yet is insensitive to chelation of calcium in the postsynaptic cell. Finally, we demonstrate that both bath application of 2-arachidonoylglycerol(2-AG) and depolarization-induced release of endogenous cannabinoids have minimal effect on mIPSC frequency. Cumulatively, our results indicate that cannabinoid ligands can selectively facilitate action potential-independent exocytosis of GABA in the rat dentate gyrus, and further emphasize that this new cannabinoid sensitive signalling system is distinct from previously described CB1 receptor-dependent systems in numerous respects.
Collapse
Affiliation(s)
- Mackenzie E Hofmann
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, FL, USA
| | | | | |
Collapse
|
38
|
Lindsly C, Frazier CJ. Two distinct and activity-dependent mechanisms contribute to autoreceptor-mediated inhibition of GABAergic afferents to hilar mossy cells. J Physiol 2010; 588:2801-22. [PMID: 20547680 DOI: 10.1113/jphysiol.2009.184648] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
We report that bath application of 3 mum carbachol (CCh), a muscarinic acetylcholine receptor agonist, reduces evoked IPSC amplitude recorded from hilar mossy cells in the rat dentate gyrus through a presynaptic mechanism. While CCh has been shown to inhibit evoked IPSCs in other systems, this effect is intriguing in that it does not require inhibitory action of either presynaptic muscarinic receptors or presynaptic cannabinoid receptors. Previous work from our lab has shown that identical application of CCh produces an action potential-dependent increase in ambient GABA in this system; however, inhibition of evoked IPSCs produced by both 3 and 10 mum CCh is insensitive to the GABA(B) antagonist CGP52432. Therefore we hypothesized that CCh-mediated inhibition of evoked IPSCs might be produced by activity-dependent increases in ambient GABA and subsequent activation of presynaptic GABA(A) receptors. Consistent with that hypothesis, we report that CCh-mediated inhibition of evoked IPSCs appears to be well correlated with CCh-mediated facilitation of spontaneous IPSCs and that CCh does not affect GABA(B)-mediated IPSCs recorded in the presence of the GABA(A) receptor antagonist picrotoxin. Intriguingly, however, we found that bath application of the GAT-1 transport blocker NO-711 (1 mum) produces inhibition of evoked IPSCs that is reversed by CGP52432, and that lower doses of CCh produce inhibition with greater CGP52432 sensitivity. These observations, combined with subsequent work on multiple pulse depression, reveal that feedback inhibition of GABAergic afferents to hilar mossy cells is governed by a complex relationship between two distinct and activity-dependent mechanisms.
Collapse
Affiliation(s)
- Casie Lindsly
- Department of Neuroscience, College of Medicine, University of Florida,1600 S.W. Archer Road, Gainesville, FL 32610, USA
| | | |
Collapse
|
39
|
Hofmann ME, Frazier CJ. Muscarinic receptor activation modulates the excitability of hilar mossy cells through the induction of an afterdepolarization. Brain Res 2010; 1318:42-51. [PMID: 20079344 DOI: 10.1016/j.brainres.2010.01.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2009] [Revised: 01/05/2010] [Accepted: 01/06/2010] [Indexed: 11/19/2022]
Abstract
In the present study we used electrophysiological techniques in an in vitro preparation of the rat dentate gyrus to examine the effect of muscarinic acetylcholine receptor activation on the intrinsic excitability of hilar neurons. We found that bath application of muscarine caused a direct depolarization in approximately 80% of mossy cells tested, and also produced a clear afterdepolarization (ADP) in nearly 100% of trials. The ADP observed in hilar mossy cells is produced by the opening of a Na(+) permeant and yet largely TTX insensitive ion channel. It requires an increase in postsynaptic calcium for activation, and is blocked by flufenamic acid, an antagonist of a previously identified calcium activated non-selective cation channel (I(CAN)). Further, we demonstrate that induction of an ADP in current clamp causes release of cannabinoids, and subsequent depression of GABAergic transmission that is comparable to that produced in the same cells by a more conventional 5s depolarization in voltage clamp. By contrast, other types of hilar neurons were less strongly depolarized by bath application of muscarinic agonists, and uniformly lacked a similar muscarinic ADP. Overall, the data presented here extend our understanding of the specific mechanisms through which muscarinic agonists are likely to modulate neuronal excitability in the hilar network, and further reveal a mechanism that could plausibly promote endocannabinoid mediated signaling in vivo.
Collapse
Affiliation(s)
- Mackenzie E Hofmann
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, USA; Department of Neuroscience, College of Medicine, University of Florida, USA
| | | |
Collapse
|
40
|
Nahir B, Lindsly C, Frazier CJ. mGluR-mediated and endocannabinoid-dependent long-term depression in the hilar region of the rat dentate gyrus. Neuropharmacology 2010; 58:712-21. [PMID: 20045707 DOI: 10.1016/j.neuropharm.2009.12.022] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2009] [Revised: 12/08/2009] [Accepted: 12/22/2009] [Indexed: 01/29/2023]
Abstract
We report that bath application of the group I mGluR agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) causes acute inhibition of evoked IPSCs recorded from hilar mossy cells, and that significant long-term depression (LTD) of synaptic transmission remains following washout of DHPG. Subsequent experiments using minimal stimulation techniques revealed that expression of both acute and long-term effects of DHPG are restricted to a subset of GABAergic afferents that are also sensitive to depolarization-induced suppression of inhibition (DSI). Experiments with a selective CB1 antagonist and with transgenic animals lacking CB1 receptors indicate that all effects of DHPG, like DSI, depend on activation of CB1 receptors. Further work with selective mGluR antagonists suggests a direct involvement of mGluR1 receptors. Interestingly, we also report that induction of LTD under our experimental conditions does not require prior direct somatic depolarization via the patch pipette and does not appear to depend critically on the level of activity in incoming GABAergic afferents. Collectively, these results represent the first characterization of mGluR-mediated and endocannabinoid-dependent LTD in the hilar region of the dentate gyrus. The dentate gyrus is thus one of relatively few areas where this mechanism has clearly been demonstrated to induce long-term modulation of inhibitory synaptic transmission.
Collapse
Affiliation(s)
- Ben Nahir
- Department of Neuroscience, College of Medicine, University of Florida, USA
| | | | | |
Collapse
|
41
|
Thomas EA, Reid CA, Petrou S. Mossy fiber sprouting interacts with sodium channel mutations to increase dentate gyrus excitability. Epilepsia 2010; 51:136-45. [DOI: 10.1111/j.1528-1167.2009.02202.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
42
|
O'Leary T, van Rossum MCW, Wyllie DJA. Homeostasis of intrinsic excitability in hippocampal neurones: dynamics and mechanism of the response to chronic depolarization. J Physiol 2009; 588:157-70. [PMID: 19917565 DOI: 10.1113/jphysiol.2009.181024] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
In order to maintain stable functionality in the face of continually changing input, neurones in the CNS must dynamically modulate their electrical characteristics. It has been hypothesized that in order to retain stable network function, neurones possess homeostatic mechanisms which integrate activity levels and alter network and cellular properties in such a way as to counter long-term perturbations. Here we describe a simple model system where we investigate the effects of sustained neuronal depolarization, lasting up to several days, by exposing cultures of primary hippocampal pyramidal neurones to elevated concentrations (10-30 mm) of KCl. Following exposure to KCl, neurones exhibit lower input resistances and resting potentials, and require more current to be injected to evoke action potentials. This results in a rightward shift in the frequency-input current (FI) curve which is explained by a simple linear model of the subthreshold I-V relationship. No changes are observed in action potential profiles, nor in the membrane potential at which action potentials are evoked. Furthermore, following depolarization, an increase in subthreshold potassium conductance is observed which is accounted for within a biophysical model of the subthreshold I-V characteristics of neuronal membranes. The FI curve shift was blocked by the presence of the L-type Ca(2+) channel blocker nifedipine, whilst antagonism of NMDA receptors did not interfere with the effect. Finally, changes in the intrinsic properties of neurones are reversible following removal of the depolarizing stimulus. We suggest that this experimental system provides a convenient model of homeostatic regulation of intrinsic excitability, and permits the study of temporal characteristics of homeostasis and its dependence on stimulus magnitude.
Collapse
Affiliation(s)
- Timothy O'Leary
- Doctoral Training Centre for Neuroinformatics and Computational Neuroscience, School of Informatics, University of Edinburgh, Edinburgh EH8 9XD, UK.
| | | | | |
Collapse
|
43
|
Armstrong C, Morgan RJ, Soltesz I. Pursuing paradoxical proconvulsant prophylaxis for epileptogenesis. Epilepsia 2009; 50:1657-69. [PMID: 19552655 DOI: 10.1111/j.1528-1167.2009.02173.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
There are essentially two potential treatment options for any acquired disorder: symptomatic or prophylactic. For acquired epilepsies that follow a variety of different brain insults, there remains a complete lack of prophylactic treatment options, whereas at the same time these epilepsies are notoriously resistant, once they have emerged, to symptomatic treatments with antiepileptic drugs. The development of prophylactic strategies is logistically challenging, both for basic researchers and clinicians. Nevertheless, cannabinoid-targeting drugs provide a very interesting example of a system within the central nervous system (CNS) that can have very different acute and long-term effects on hyperexcitability and seizures. In this review, we outline research on cannabinoids suggesting that although cannabinoid antagonists are acutely proconvulsant, they may have beneficial effects on long-term hyperexcitability following brain insults of multiple etiologies, making them promising candidates for further investigation as prophylactics against acquired epilepsy. We then discuss some of the implications of this finding on future attempts at prophylactic treatments, specifically, the very short window within which prevention may be possible, the possibility that traditional anticonvulsants may interfere with prophylactic strategies, and the importance of moving beyond anticonvulsants-even to proconvulsants-to find the ideal preventative strategy for acquired epilepsy.
Collapse
Affiliation(s)
- Caren Armstrong
- Department of Anatomy and Neurobiology, University of California, Irvine, California, USA.
| | | | | |
Collapse
|
44
|
Dyhrfjeld-Johnsen J, Morgan RJ, Soltesz I. Double Trouble? Potential for Hyperexcitability Following Both Channelopathic up- and Downregulation of I(h) in Epilepsy. Front Neurosci 2009; 3:25-33. [PMID: 19753094 PMCID: PMC2695388 DOI: 10.3389/neuro.01.005.2009] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2009] [Accepted: 03/04/2009] [Indexed: 11/13/2022] Open
Abstract
Studies of pathological ion channel regulation as an underlying mechanism of epilepsy have revealed alterations in the h-current in several animal models. While earlier reports indicate that downregulation of the h-current is pro-excitatory on the single neuron level, we found an upregulation of I(h) in hyperexcitable CA1 pyramidal neuron dendrites following experimental febrile seizures. In addition, in several CA1 pyramidal neuron computational models of different complexity, h-current upregulation has been shown to lead to pro-excitable effects. This focused review examines the complex impact of altered h-current on neuronal resting membrane potential (RMP) and input resistance (R(in)), as well as reported interactions with other ionic conductances.
Collapse
|
45
|
Echegoyen J, Armstrong C, Morgan RJ, Soltesz I. Single application of a CB1 receptor antagonist rapidly following head injury prevents long-term hyperexcitability in a rat model. Epilepsy Res 2009; 85:123-7. [PMID: 19369036 DOI: 10.1016/j.eplepsyres.2009.02.019] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2009] [Revised: 02/10/2009] [Accepted: 02/22/2009] [Indexed: 11/18/2022]
Abstract
Effective prophylaxis for post-traumatic epilepsy currently does not exist, and clinical trials using anticonvulsant drugs have yielded no long-term antiepileptogenic effects. We report that a single, rapid post-traumatic application of the proconvulsant cannabinoid type-1 (CB1) receptor antagonist SR141716A (Rimonabant-Acomplia) abolishes the long-term increase in seizure susceptibility caused by head injury in rats. These results indicate that, paradoxically, a seizure-enhancing drug may disrupt the epileptogenic process if applied within a short therapeutic time window.
Collapse
Affiliation(s)
- Julio Echegoyen
- Department of Anatomy and Neurobiology, University of California, Irvine, CA 92697-1280, United States
| | | | | | | |
Collapse
|
46
|
Beck H, Yaari Y. Plasticity of intrinsic neuronal properties in CNS disorders. Nat Rev Neurosci 2008; 9:357-69. [DOI: 10.1038/nrn2371] [Citation(s) in RCA: 192] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
|
47
|
Dyhrfjeld-Johnsen J, Morgan RJ, Földy C, Soltesz I. Upregulated H-current in hyperexcitable CA1 dendrites after febrile seizures. Front Cell Neurosci 2008; 2:2. [PMID: 18946517 PMCID: PMC2525926 DOI: 10.3389/neuro.03.002.2008] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2008] [Accepted: 04/01/2008] [Indexed: 01/28/2023] Open
Abstract
Somatic recordings from CA1 pyramidal cells indicated a persistent upregulation of the h-current (Ih) after experimental febrile seizures. Here, we examined febrile seizure-induced long-term changes in Ih and neuronal excitability in CA1 dendrites. Cell-attached recordings showed that dendritic Ih was significantly upregulated, with a depolarized half-activation potential and increased maximal current. Although enhanced Ih is typically thought to be associated with decreased dendritic excitability, whole-cell dendritic recordings revealed a robust increase in action potential firing after febrile seizures. We turned to computational simulations to understand how the experimentally observed changes in Ih influence dendritic excitability. Unexpectedly, the simulations, performed in three previously published CA1 pyramidal cell models, showed that the experimentally observed increases in Ih resulted in a general enhancement of dendritic excitability, primarily due to the increased Ih-induced depolarization of the resting membrane potential overcoming the excitability-depressing effects of decreased dendritic input resistance. Taken together, these experimental and modeling results reveal that, contrary to the exclusively anti-convulsive role often attributed to increased Ih in epilepsy, the enhanced Ih can co-exist with, and possibly even contribute to, persistent dendritic hyperexcitability following febrile seizures in the developing hippocampus.
Collapse
|
48
|
Echegoyen J, Neu A, Graber KD, Soltesz I. Homeostatic plasticity studied using in vivo hippocampal activity-blockade: synaptic scaling, intrinsic plasticity and age-dependence. PLoS One 2007; 2:e700. [PMID: 17684547 PMCID: PMC1933594 DOI: 10.1371/journal.pone.0000700] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2007] [Accepted: 07/05/2007] [Indexed: 11/18/2022] Open
Abstract
Homeostatic plasticity is thought to be important in preventing neuronal circuits from becoming hyper- or hypoactive. However, there is little information concerning homeostatic mechanisms following in vivo manipulations of activity levels. We investigated synaptic scaling and intrinsic plasticity in CA1 pyramidal cells following 2 days of activity-blockade in vivo in adult (postnatal day 30; P30) and juvenile (P15) rats. Chronic activity-blockade in vivo was achieved using the sustained release of the sodium channel blocker tetrodotoxin (TTX) from the plastic polymer Elvax 40W implanted directly above the hippocampus, followed by electrophysiological assessment in slices in vitro. Three sets of results were in general agreement with previous studies on homeostatic responses to in vitro manipulations of activity. First, Schaffer collateral stimulation-evoked field responses were enhanced after 2 days of in vivo TTX application. Second, miniature excitatory postsynaptic current (mEPSC) amplitudes were potentiated. However, the increase in mEPSC amplitudes occurred only in juveniles, and not in adults, indicating age-dependent effects. Third, intrinsic neuronal excitability increased. In contrast, three sets of results sharply differed from previous reports on homeostatic responses to in vitro manipulations of activity. First, miniature inhibitory postsynaptic current (mIPSC) amplitudes were invariably enhanced. Second, multiplicative scaling of mEPSC and mIPSC amplitudes was absent. Third, the frequencies of adult and juvenile mEPSCs and adult mIPSCs were increased, indicating presynaptic alterations. These results provide new insights into in vivo homeostatic plasticity mechanisms with relevance to memory storage, activity-dependent development and neurological diseases.
Collapse
Affiliation(s)
- Julio Echegoyen
- Department of Anatomy and Neurobiology, University of California at Irvine, California, United States of America.
| | | | | | | |
Collapse
|
49
|
Abstract
Computational modeling has become an increasingly useful tool for studying complex neuronal circuits such as the dentate gyrus. In order to effectively apply computational techniques and theories to answer pressing biological questions, however, it is necessary to develop detailed, data-driven models. Development of such models is a complicated process, akin to putting together a jigsaw puzzle with the pieces being such things as cell types, cell numbers, and specific connectivity. This chapter provides a walkthrough for the development of a very large-scale, biophysically realistic model of the dentate gyrus. Subsequently, it demonstrates the utility of a modeling approach in asking and answering questions about both healthy and pathological states involving the modeled brain region. Finally, this chapter discusses some predictions that come directly from the model that can be tested in future experimental approaches.
Collapse
Affiliation(s)
- Robert J Morgan
- Department of Anatomy and Neurobiology, 193 Irvine Hall, University of California, Irvine, CA 92697, USA.
| | | | | |
Collapse
|