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Huang Y, Zelmann R, Hadar P, Dezha-Peralta J, Richardson RM, Williams ZM, Cash SS, Keller CJ, Paulk AC. Theta-burst direct electrical stimulation remodels human brain networks. Nat Commun 2024; 15:6982. [PMID: 39143083 PMCID: PMC11324911 DOI: 10.1038/s41467-024-51443-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2024] [Accepted: 08/07/2024] [Indexed: 08/16/2024] Open
Abstract
Theta-burst stimulation (TBS), a patterned brain stimulation technique that mimics rhythmic bursts of 3-8 Hz endogenous brain rhythms, has emerged as a promising therapeutic approach for treating a wide range of brain disorders, though the neural mechanism of TBS action remains poorly understood. We investigated the neural effects of TBS using intracranial EEG (iEEG) in 10 pre-surgical epilepsy participants undergoing intracranial monitoring. Here we show that individual bursts of direct electrical TBS at 29 frontal and temporal sites evoked strong neural responses spanning broad cortical regions. These responses exhibited dynamic local field potential voltage changes over the course of stimulation presentations, including either increasing or decreasing responses, suggestive of short-term plasticity. Stronger stimulation augmented the mean TBS response amplitude and spread with more recording sites demonstrating short-term plasticity. TBS responses were stimulation site-specific with stronger TBS responses observed in regions with strong baseline stimulation effective (cortico-cortical evoked potentials) and functional (low frequency phase locking) connectivity. Further, we could use these measures to predict stable and varying (e.g. short-term plasticity) TBS response locations. Future work may integrate pre-treatment connectivity alongside other biophysical factors to personalize stimulation parameters, thereby optimizing induction of neuroplasticity within disease-relevant brain networks.
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Affiliation(s)
- Yuhao Huang
- Department of Neurosurgery, Stanford University, Palo Alto, CA, USA
| | - Rina Zelmann
- Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
- Center for Neurotechnology and Neurorecovery, Department of Neurology, Massachusetts General Hospital, Boston, MA, USA
| | - Peter Hadar
- Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
| | - Jaquelin Dezha-Peralta
- Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
- Center for Neurotechnology and Neurorecovery, Department of Neurology, Massachusetts General Hospital, Boston, MA, USA
| | - R Mark Richardson
- Department of Neurosurgery, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
| | - Ziv M Williams
- Department of Neurosurgery, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
| | - Sydney S Cash
- Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
- Center for Neurotechnology and Neurorecovery, Department of Neurology, Massachusetts General Hospital, Boston, MA, USA
| | - Corey J Keller
- Department of Psychiatry and Behavioral Sciences, Stanford University, Palo Alto, CA, USA.
- Wu Tsai Neurosciences Institute, Stanford University, Palo Alto, CA, USA.
- Veterans Affairs Palo Alto Healthcare System, and the Sierra Pacific Mental Illness, Research, Education, and Clinical Center (MIRECC), Palo Alto, CA, USA.
| | - Angelique C Paulk
- Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
- Center for Neurotechnology and Neurorecovery, Department of Neurology, Massachusetts General Hospital, Boston, MA, USA.
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Extraoperative electrical stimulation mapping in epilepsy presurgical evaluation: a proposal and review of the literature. Clin Neurol Neurosurg 2022; 214:107170. [DOI: 10.1016/j.clineuro.2022.107170] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2022] [Revised: 02/07/2022] [Accepted: 02/08/2022] [Indexed: 11/18/2022]
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Kundu B, Davis TS, Philip B, Smith EH, Arain A, Peters A, Newman B, Butson CR, Rolston JD. A systematic exploration of parameters affecting evoked intracranial potentials in patients with epilepsy. Brain Stimul 2020; 13:1232-1244. [PMID: 32504827 PMCID: PMC7494632 DOI: 10.1016/j.brs.2020.06.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2019] [Revised: 05/27/2020] [Accepted: 06/01/2020] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND Brain activity is constrained by and evolves over a network of structural and functional connections. Corticocortical evoked potentials (CCEPs) have been used to measure this connectivity and to discern brain areas involved in both brain function and disease. However, how varying stimulation parameters influences the measured CCEP across brain areas has not been well characterized. OBJECTIVE To better understand the factors that influence the amplitude of the CCEPs as well as evoked gamma-band power (70-150 Hz) resulting from single-pulse stimulation via cortical surface and depth electrodes. METHODS CCEPs from 4370 stimulation-response channel pairs were recorded across a range of stimulation parameters and brain regions in 11 patients undergoing long-term monitoring for epilepsy. A generalized mixed-effects model was used to model cortical response amplitudes from 5 to 100 ms post-stimulation. RESULTS Stimulation levels <5.5 mA generated variable CCEPs with low amplitude and reduced spatial spread. Stimulation at ≥5.5 mA yielded a reliable and maximal CCEP across stimulation-response pairs over all regions. These findings were similar when examining the evoked gamma-band power. The amplitude of both measures was inversely correlated with distance. CCEPs and evoked gamma power were largest when measured in the hippocampus compared with other areas. Larger CCEP size and evoked gamma power were measured within the seizure onset zone compared with outside this zone. CONCLUSION These results will help guide future stimulation protocols directed at quantifying network connectivity across cognitive and disease states.
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Affiliation(s)
- Bornali Kundu
- Department of Neurosurgery, Clinical Neurosciences Center, University of Utah, Salt Lake City, UT, USA
| | - Tyler S Davis
- Department of Neurosurgery, Clinical Neurosciences Center, University of Utah, Salt Lake City, UT, USA
| | - Brian Philip
- Department of Biomedical Engineering, University of Utah, Salt Lake City, UT, USA
| | - Elliot H Smith
- Department of Neurosurgery, Clinical Neurosciences Center, University of Utah, Salt Lake City, UT, USA
| | - Amir Arain
- Department of Neurology, Clinical Neurosciences Center, University of Utah, Salt Lake City, UT, USA
| | - Angela Peters
- Department of Neurology, Clinical Neurosciences Center, University of Utah, Salt Lake City, UT, USA
| | - Blake Newman
- Department of Neurology, Clinical Neurosciences Center, University of Utah, Salt Lake City, UT, USA
| | - Christopher R Butson
- Department of Neurosurgery, Clinical Neurosciences Center, University of Utah, Salt Lake City, UT, USA; Department of Biomedical Engineering, University of Utah, Salt Lake City, UT, USA; Scientific Computing and Imaging Institute, University of Utah, Salt Lake City, UT, USA
| | - John D Rolston
- Department of Neurosurgery, Clinical Neurosciences Center, University of Utah, Salt Lake City, UT, USA; Department of Biomedical Engineering, University of Utah, Salt Lake City, UT, USA; Scientific Computing and Imaging Institute, University of Utah, Salt Lake City, UT, USA.
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Li L, Bragin A, Staba R, Engel J. Unit firing and oscillations at seizure onset in epileptic rodents. Neurobiol Dis 2019; 127:382-389. [PMID: 30928646 DOI: 10.1016/j.nbd.2019.03.027] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Revised: 03/04/2019] [Accepted: 03/26/2019] [Indexed: 01/27/2023] Open
Abstract
Epileptic seizures result from a variety of pathophysiological processes, evidenced by different electrographic ictal onset patterns, as seen on direct brain recordings. The two most common electrographic patterns of focal ictal onset in patients are hypersynchronous (HYP) and low-voltage fast (LVF). Whereas LVF ictal onsets were believed to result from disinhibition; based on similarities with absence seizures, focal HYP ictal onsets were believed to result from increased synchronizing inhibition. Recent findings, however, suggest the differences between these seizure onset types are more complicated and, in some cases, the opposite of these concepts are true. The following review presents evidence that a reduction of tonic inhibition on small pathologically interconnected neuron (PIN) clusters generating pathological high-frequency oscillations (pHFOs), which reflect abnormal synchronously bursting neurons may be the cause of HYP ictal onsets. Increased inhibition preceding LVF ictal onsets are discussed in other reviews in this issue. We postulate that neuronal cell loss following epileptogenic insults can result in structural reorganization, giving rise to small PIN clusters, which generate pHFOs. These clusters have a heterogeneous distribution and are spatially stable over time. Studies have demonstrated that a transient reduction in tonic inhibition causes these clusters to increase in size. This could result in consolidation and synchronization of pHFOs until a critical mass leads to propagation of HYP ictal discharges. Viewed within a network neuroscience framework, local disturbances such as PIN clusters are likely to contribute to large-scale brain network alterations: a better understanding of these epileptogenic networks promises to elucidate mechanisms of ictogenesis, epileptogenesis, and certain comorbidities of epilepsy.
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Affiliation(s)
- Lin Li
- Department of Neurology, University of California, Los Angeles, CA, USA
| | - Anatol Bragin
- Department of Neurology, University of California, Los Angeles, CA, USA; Brain Research Institute, University of California, Los Angeles, CA, USA
| | - Richard Staba
- Department of Neurology, University of California, Los Angeles, CA, USA
| | - Jerome Engel
- Department of Neurology, University of California, Los Angeles, CA, USA; Brain Research Institute, University of California, Los Angeles, CA, USA; Department of Neurobiology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA; Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
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Vnencak M, Schölvinck ML, Schwarzacher SW, Deller T, Willem M, Jedlicka P. Lack of β-amyloid cleaving enzyme-1 (BACE1) impairs long-term synaptic plasticity but enhances granule cell excitability and oscillatory activity in the dentate gyrus in vivo. Brain Struct Funct 2019; 224:1279-1290. [PMID: 30701309 DOI: 10.1007/s00429-019-01836-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2018] [Accepted: 01/16/2019] [Indexed: 12/11/2022]
Abstract
BACE1 is a β-secretase involved in the cleavage of amyloid precursor protein and the pathogenesis of Alzheimer's disease (AD). The entorhinal cortex and the dentate gyrus are important for learning and memory, which are affected in the early stages of AD. Since BACE1 is a potential target for AD therapy, it is crucial to understand its physiological role in these brain regions. Here, we examined the function of BACE1 in the dentate gyrus. We show that loss of BACE1 in the dentate gyrus leads to increased granule cell excitability, indicated by enhanced efficiency of synaptic potentials to generate granule cell spikes. The increase in granule cell excitability was accompanied by prolonged paired-pulse inhibition, altered network gamma oscillations, and impaired synaptic plasticity at entorhinal-dentate synapses of the perforant path. In summary, this is the first detailed electrophysiological study of BACE1 deletion at the network level in vivo. The results suggest that BACE1 is important for normal dentate gyrus network function. This has implications for the use of BACE1 inhibitors as therapeutics for AD therapy, since BACE1 inhibition could similarly disrupt synaptic plasticity and excitability in the entorhinal-dentate circuitry.
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Affiliation(s)
- Matej Vnencak
- Institute of Clinical Neuroanatomy, Neuroscience Center, Goethe University, Frankfurt am Main, Germany. .,Otorhinolaryngology, Head and Neck Surgery, Turku University Hospital, University of Turku, PL 52, 20521, Turku, Finland.
| | - Marieke L Schölvinck
- Ernst Strüngmann Institute (ESI) for Neuroscience in Cooperation with Max Planck Society, Frankfurt am Main, Germany
| | - Stephan W Schwarzacher
- Institute of Clinical Neuroanatomy, Neuroscience Center, Goethe University, Frankfurt am Main, Germany
| | - Thomas Deller
- Institute of Clinical Neuroanatomy, Neuroscience Center, Goethe University, Frankfurt am Main, Germany
| | - Michael Willem
- BioMedical Center, Biochemistry, Ludwig-Maximilians-University, Munich, Germany
| | - Peter Jedlicka
- Institute of Clinical Neuroanatomy, Neuroscience Center, Goethe University, Frankfurt am Main, Germany. .,ICAR3R-Interdisciplinary Centre for 3Rs in Animal Research, Faculty of Medicine, Justus-Liebig-University, Rudolf-Buchheim-Str. 6, 35392, Giessen, Germany.
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6
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Lin EC, Combe CL, Gasparini S. Differential Contribution of Ca 2+-Dependent Mechanisms to Hyperexcitability in Layer V Neurons of the Medial Entorhinal Cortex. Front Cell Neurosci 2017; 11:182. [PMID: 28713246 PMCID: PMC5491848 DOI: 10.3389/fncel.2017.00182] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Accepted: 06/13/2017] [Indexed: 11/13/2022] Open
Abstract
Temporal lobe epilepsy is characterized by recurrent seizures in one or both temporal lobes of the brain; some in vitro models show that epileptiform discharges initiate in entorhinal layer V neurons and then spread into other areas of the temporal lobe. We previously found that, in the presence of GABAA receptor antagonists, stimulation of afferent fibers, terminating both at proximal and distal dendritic locations, initiated hyperexcitable bursts in layer V medial entorhinal neurons. We investigated the differential contribution of Ca2+-dependent mechanisms to the plateaus underlying these bursts at proximal and distal synapses. We found that the NMDA glutamatergic antagonist D,L-2-amino-5-phosphonovaleric acid (APV; 50 μM) reduced both the area and duration of the bursts at both proximal and distal synapses by about half. The L-type Ca2+ channel blocker nimodipine (10 μM) and the R- and T-type Ca2+ channel blocker NiCl2 (200 μM) decreased the area of the bursts to a lesser extent; none of these effects appeared to be location-dependent. Remarkably, the perfusion of flufenamic acid (FFA; 100 μM), to block Ca2+-activated non-selective cation currents (ICAN) mediated by transient receptor potential (TRP) channels, had a location-dependent effect, by abolishing burst firing and switching the suprathreshold response to a single action potential (AP) for proximal stimulation, but only minimally affecting the bursts evoked by distal stimulation. A similar outcome was found when FFA was pressure-applied locally around the proximal dendrite of the recorded neurons and in the presence of a selective blocker of melastatin TRP (TRPM) channels, 9-phenanthrol (100 μM), whereas a selective blocker of canonical TRP (TRPC) channels, SKF 96365, did not affect the bursts. These results indicate that different mechanisms might contribute to the initiation of hyperexcitability in layer V neurons at proximal and distal synapses and could shed light on the initiation of epileptiform activity in the entorhinal cortex.
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Affiliation(s)
- Eric C Lin
- Neuroscience Center of Excellence, Louisiana State University Health Sciences CenterNew Orleans, LA, United States
| | - Crescent L Combe
- Neuroscience Center of Excellence, Louisiana State University Health Sciences CenterNew Orleans, LA, United States
| | - Sonia Gasparini
- Neuroscience Center of Excellence, Louisiana State University Health Sciences CenterNew Orleans, LA, United States.,Department of Cell Biology and Anatomy, Louisiana State University Health Sciences CenterNew Orleans, LA, United States
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Extent of mossy fiber sprouting in patients with mesiotemporal lobe epilepsy correlates with neuronal cell loss and granule cell dispersion. Epilepsy Res 2017; 129:51-58. [DOI: 10.1016/j.eplepsyres.2016.11.011] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Accepted: 11/20/2016] [Indexed: 11/21/2022]
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8
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Boulogne S, Andre-Obadia N, Kimiskidis VK, Ryvlin P, Rheims S. Cortico-cortical and motor evoked potentials to single and paired-pulse stimuli: An exploratory transcranial magnetic and intracranial electric brain stimulation study. Hum Brain Mapp 2016; 37:3767-3778. [PMID: 27312488 DOI: 10.1002/hbm.23274] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2015] [Revised: 05/16/2016] [Accepted: 05/17/2016] [Indexed: 11/06/2022] Open
Abstract
BACKGROUND Paired-pulse (PP) paradigms are commonly employed to assess in vivo cortical excitability using transcranial magnetic stimulation (TMS) to stimulate the primary motor cortex and modulate the induced motor evoked potential (MEP). Single-pulse cortical direct electrical stimulation (DES) during intracerebral EEG monitoring allows the investigation of brain connectivity by eliciting cortico-cortical evoked potentials (CCEPs). However, PP paradigm using intracerebral DES has rarely been reported and has never been previously compared with TMS. OBJECTIVE The work was intended (i) to verify that the well-established modulations of MEPs following PP TMS remain similar using DES in the motor cortex, and (ii) to evaluate if a similar pattern could be observed in distant cortico-cortical connections through modulations of CCEP. METHODS Three patients undergoing intracerebral EEG monitoring with electrodes implanted in the central region were studied. Single-pulse DES (1-3 mA, 1 ms, 0.2 Hz) and PP DES using six interstimulus intervals (5, 15, 30, 50, 100, and 200 ms) in the motor cortex with concomitant recording of CCEPs and MEPs in contralateral muscles were performed. Finally, a navigated PP TMS session targeted the intracranial stimulation site to record TMS-induced MEPs in two patients. RESULTS MEP modulations elicited by PP intracerebral DES proved similar among the three patients and to those obtained by PP TMS. CCEP modulations elicited by PP intracerebral DES usually showed a pattern comparable to that of MEP, although a different pattern could be observed occasionally. CONCLUSION PP intracerebral DES seems to involve excitatory and inhibitory mechanisms similar to PP TMS and allows the recording of intracortical inhibition and facilitation modulation on cortico-cortical connections. Hum Brain Mapp 37:3767-3778, 2016. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Sébastien Boulogne
- Department of Functional Neurology and Epileptology, Hospices Civils De Lyon, 59 Boulevard Pinel, Bron, 69675, France. .,Lyon's Research Neuroscience Center, Institut National De La Santé Et De La Recherche Médicale U1028, Centre National De La Recherche Scientifique 5292, Lyon, France, CH Le Vinatier, Bâtiment 452, 95 Boulevard Pinel, 69675 Bron, France. .,Lyon 1 University, 43 Boulevard Du 11 Novembre 1918, Villeurbanne, 69100, France.
| | - Nathalie Andre-Obadia
- Department of Functional Neurology and Epileptology, Hospices Civils De Lyon, 59 Boulevard Pinel, Bron, 69675, France
| | - Vasilios K Kimiskidis
- Laboratory of Clinical Neurophysiology, Medical School, Aristotle University of Thessaloniki, Thessaloniki, 54124, Greece
| | - Philippe Ryvlin
- Department of Functional Neurology and Epileptology, Hospices Civils De Lyon, 59 Boulevard Pinel, Bron, 69675, France.,Lyon's Research Neuroscience Center, Institut National De La Santé Et De La Recherche Médicale U1028, Centre National De La Recherche Scientifique 5292, Lyon, France, CH Le Vinatier, Bâtiment 452, 95 Boulevard Pinel, 69675 Bron, France.,Lyon 1 University, 43 Boulevard Du 11 Novembre 1918, Villeurbanne, 69100, France.,Department of Clinical neurosciences, CHU Vaudois, 46 Rue Du Bugnon, Lausanne, 1011, Switzerland
| | - Sylvain Rheims
- Department of Functional Neurology and Epileptology, Hospices Civils De Lyon, 59 Boulevard Pinel, Bron, 69675, France.,Lyon's Research Neuroscience Center, Institut National De La Santé Et De La Recherche Médicale U1028, Centre National De La Recherche Scientifique 5292, Lyon, France, CH Le Vinatier, Bâtiment 452, 95 Boulevard Pinel, 69675 Bron, France.,Lyon 1 University, 43 Boulevard Du 11 Novembre 1918, Villeurbanne, 69100, France
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9
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Boulogne S, Ryvlin P, Rheims S. Single and paired-pulse electrical stimulation during invasive EEG recordings. Rev Neurol (Paris) 2016; 172:174-81. [PMID: 26993563 DOI: 10.1016/j.neurol.2016.02.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2015] [Revised: 01/11/2016] [Accepted: 02/23/2016] [Indexed: 12/01/2022]
Abstract
Invasive EEG recordings are frequently required during the presurgical exploration of patients with drug-resistant focal epilepsy in order to clarify the epileptic zone location. Intracranial direct electrical stimulations (DES) induce EEG and/or clinical responses that participate in this evaluation. Clinical DES protocols (1Hz and/or 50Hz) trigger massive cortical activation that can elicit seizures, after-discharges or complex clinical signs. In contrast, low-energy (<1Hz) protocols activate more localized cortical regions using single-pulse electrical stimulations (SPES). SPES can elicit two main types of responses. Cortico-cortical evoked potentials (CCEPs) correspond to highly consistent early responses, appearing before 100ms after stimulation, with fixed latency; they are considered physiological and assess the effective connectivity between the recorded regions. Late responses appear after 100ms; they are rare, inconsistent with variable latency and are suggestive of an underlying epileptogenic cortex. Paired-pulse stimulation paradigm associates a conditioning and a test stimulation to induce intracortical inhibition or facilitation by modifying the response amplitude. Largely used in transcranial magnetic stimulation, it has rarely been applied to CCEP although the mechanisms put in place seem highly similar. Low frequency intracerebral stimulations allow analysing brain connectivity and cortical excitability with a high temporal and spatial resolution. The development of new stimulation protocols and the combination with imaging or statistical techniques recently offered promising results.
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Affiliation(s)
- S Boulogne
- Department of Functional Neurology and Epileptology, Hospices civils de Lyon, 59, boulevard Pinel, 69003 Lyon, France; Lyon's Research Neuroscience Center, Inserm U1028/CNRS UMPR 5292, CH Le Vinatier, Bâtiment 452, 95, boulevard Pinel, 69675 Bron, France
| | - P Ryvlin
- Department of clinical neurosciences, CHU Vaudois, 46, rue du Bugnon, 1011 Lausanne, Switzerland
| | - S Rheims
- Department of Functional Neurology and Epileptology, Hospices civils de Lyon, 59, boulevard Pinel, 69003 Lyon, France; Lyon's Research Neuroscience Center, Inserm U1028/CNRS UMPR 5292, CH Le Vinatier, Bâtiment 452, 95, boulevard Pinel, 69675 Bron, France.
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10
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O'Sullivan GA, Jedlicka P, Chen HX, Kalbouneh H, Ippolito A, Deller T, Nawrotzki RA, Kuhse J, Kalaidzidis YL, Kirsch J, Schwarzacher SW, Betz H. Forebrain-specific loss of synaptic GABAA receptors results in altered neuronal excitability and synaptic plasticity in mice. Mol Cell Neurosci 2016; 72:101-13. [PMID: 26829712 DOI: 10.1016/j.mcn.2016.01.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2015] [Revised: 11/16/2015] [Accepted: 01/25/2016] [Indexed: 10/22/2022] Open
Abstract
Mutations that result in the defective trafficking of γ2 subunit containing GABAA receptors (γ2-GABAARs) are known to reduce synaptic inhibition. Whether perturbed clustering of non-mutated GABAARs similarly reduces synaptic inhibition in vivo is less clear. In this study we provide evidence that the loss of postsynaptic γ2-GABAARs upon postnatal ablation of gephyrin, the major scaffolding protein of inhibitory postsynapses, from mature principal neurons within the forebrain results in reduced induction of long-term potentiation (LTP) and impaired network excitability within the hippocampal dentate gyrus. The preferential reduction in not only synaptic γ2-GABAAR cluster number at dendritic sites but also the decrease in γ2-GABAAR density within individual clusters at dendritic inhibitory synapses suggests that distal synapses are more sensitive to the loss of gephyrin expression than proximal synapses. The fact that these mice display behavioural features of anxiety and epilepsy emphasises the importance of postsynaptic γ2-GABAAR clustering for synaptic inhibition.
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Affiliation(s)
- Gregory A O'Sullivan
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Deutschordenstrasse 46, 60318 Frankfurt/Main, Germany; Max-Planck-Institute of Cell Biology & Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany.
| | - Peter Jedlicka
- Institute of Clinical Neuroanatomy, Neuroscience Center, Goethe-University, 60590 Frankfurt/Main, Germany
| | - Hong-Xing Chen
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Deutschordenstrasse 46, 60318 Frankfurt/Main, Germany
| | - Heba Kalbouneh
- Institute of Anatomy & Cell Biology, University of Heidelberg, Im Neuenheimer Feld 307, 69120 Heidelberg, Germany
| | - Angelo Ippolito
- Institute of Clinical Neuroanatomy, Neuroscience Center, Goethe-University, 60590 Frankfurt/Main, Germany
| | - Thomas Deller
- Institute of Clinical Neuroanatomy, Neuroscience Center, Goethe-University, 60590 Frankfurt/Main, Germany
| | - Ralph A Nawrotzki
- Institute of Anatomy & Cell Biology, University of Heidelberg, Im Neuenheimer Feld 307, 69120 Heidelberg, Germany
| | - Jochen Kuhse
- Institute of Anatomy & Cell Biology, University of Heidelberg, Im Neuenheimer Feld 307, 69120 Heidelberg, Germany
| | - Yannis L Kalaidzidis
- Max-Planck-Institute of Cell Biology & Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany
| | - Joachim Kirsch
- Institute of Anatomy & Cell Biology, University of Heidelberg, Im Neuenheimer Feld 307, 69120 Heidelberg, Germany
| | - Stephan W Schwarzacher
- Institute of Clinical Neuroanatomy, Neuroscience Center, Goethe-University, 60590 Frankfurt/Main, Germany
| | - Heinrich Betz
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Deutschordenstrasse 46, 60318 Frankfurt/Main, Germany
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11
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Enhanced expression of potassium-chloride cotransporter KCC2 in human temporal lobe epilepsy. Brain Struct Funct 2015; 221:3601-15. [PMID: 26427846 DOI: 10.1007/s00429-015-1122-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2015] [Accepted: 09/23/2015] [Indexed: 12/19/2022]
Abstract
Synaptic reorganization in the epileptic hippocampus involves altered excitatory and inhibitory transmission besides the rearrangement of dendritic spines, resulting in altered excitability, ion homeostasis, and cell swelling. The potassium-chloride cotransporter-2 (KCC2) is the main chloride extruder in neurons and hence will play a prominent role in determining the polarity of GABAA receptor-mediated chloride currents. In addition, KCC2 also interacts with the actin cytoskeleton which is critical for dendritic spine morphogenesis, and for the maintenance of glutamatergic synapses and cell volume. Using immunocytochemistry, we examined the cellular and subcellular levels of KCC2 in surgically removed hippocampi of temporal lobe epilepsy (TLE) patients and compared them to control human tissue. We also studied the distribution of KCC2 in a pilocarpine mouse model of epilepsy. An overall increase in KCC2-expression was found in epilepsy and confirmed by Western blots. The cellular and subcellular distributions in control mouse and human samples were largely similar; moreover, changes affecting KCC2-expression were also alike in chronic epileptic human and mouse hippocampi. At the subcellular level, we determined the neuronal elements exhibiting enhanced KCC2 expression. In epileptic tissue, staining became more intense in the immunopositive elements detected in control tissue, and profiles with subthreshold expression of KCC2 in control samples became labelled. Positive interneuron somata and dendrites were more numerous in epileptic hippocampi, despite severe interneuron loss. Whether the elevation of KCC2-expression is ultimately a pro- or anticonvulsive change, or both-behaving differently during ictal and interictal states in a context-dependent manner-remains to be established.
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Kunieda T, Yamao Y, Kikuchi T, Matsumoto R. New Approach for Exploring Cerebral Functional Connectivity: Review of Cortico-cortical Evoked Potential. Neurol Med Chir (Tokyo) 2015; 55:374-82. [PMID: 25925755 PMCID: PMC4628165 DOI: 10.2176/nmc.ra.2014-0388] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
There has been a paradigm shift in the understanding of brain function. The intrinsic architecture of neuronal connections forms a key component of the cortical organization in our brain. Many imaging studies, such as noninvasive magnetic resonance imaging (MRI) studies, have now enabled visualization of the white matter fiber tracts interconnecting the functional cortical areas in the living brain. Although such a structural connectome is essential for understanding of cortical function, the anatomical information alone is not sufficient. Practically, few techniques allow the investigation of the excitatory and inhibitory mechanisms of the cortex in vivo in humans. Several attempts have been made to track neuronal connectivity by applying direct electrical stimuli to the brain in order to stimulate subdural and/or depth electrodes and record responses from the functionally connected cortex. In vivo single-pulse electrical stimulation (SPES) and/or cortico-cortical evoked potential (CCEP) were recently introduced to track various brain networks. This article reviews the concepts, significance, methods, mechanisms, limitations, and clinical applications of CCEP in the analysis of these dynamic connections.
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Affiliation(s)
- Takeharu Kunieda
- Department of Neurosurgery, Kyoto University Graduate School of Medicine
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Winden KD, Bragin A, Engel J, Geschwind DH. Molecular alterations in areas generating fast ripples in an animal model of temporal lobe epilepsy. Neurobiol Dis 2015; 78:35-44. [PMID: 25818007 DOI: 10.1016/j.nbd.2015.02.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2014] [Revised: 01/26/2015] [Accepted: 02/13/2015] [Indexed: 01/05/2023] Open
Abstract
The molecular basis of epileptogenesis is poorly characterized. Studies in humans and animal models have identified an electrophysiological signature that precedes the onset of epilepsy, which has been termed fast ripples (FRs) based on its frequency. Multiple lines of evidence implicate regions generating FRs in epileptogenesis, and FRs appear to demarcate the seizure onset zone, suggesting a role in ictogenesis as well. We performed gene expression analysis comparing areas of the dentate gyrus that generate FRs to those that do not generate FRs in a well-characterized rat model of epilepsy. We identified a small cohort of genes that are differentially expressed in FR versus non-FR brain tissue and used quantitative PCR to validate some of those that modulate neuronal excitability. Gene expression network analysis demonstrated conservation of gene co-expression between non-FR and FR samples, but examination of gene connectivity revealed changes that were most pronounced in the cm-40 module, which contains several genes associated with synaptic function and the differentially expressed genes Kcna4, Kcnv1, and Npy1r that are down-regulated in FRs. We then demonstrate that the genes within the cm-40 module are regulated by seizure activity and enriched for the targets of the RNA binding protein Elavl4. Our data suggest that seizure activity induces co-expression of genes associated with synaptic transmission and that this pattern is attenuated in areas displaying FRs, implicating the failure of this mechanism in the generation of FRs.
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Affiliation(s)
- Kellen D Winden
- Interdepartmental Program for Neuroscience, University of California, Los Angeles, Los Angeles, CA, USA; Program in Neurogenetics, University of California, Los Angeles, Los Angeles, CA, USA; Department of Neurology, University of California, Los Angeles, Los Angeles, CA, USA
| | - Anatol Bragin
- Department of Neurology, University of California, Los Angeles, Los Angeles, CA, USA; The Brain Research Institute, University of California, Los Angeles, Los Angeles, CA, USA
| | - Jerome Engel
- Department of Neurology, University of California, Los Angeles, Los Angeles, CA, USA; Department of Neurobiology, University of California, Los Angeles, Los Angeles, CA, USA; The Brain Research Institute, University of California, Los Angeles, Los Angeles, CA, USA; Semel Institute for Neuroscience and Human Behavior, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
| | - Dan H Geschwind
- Interdepartmental Program for Neuroscience, University of California, Los Angeles, Los Angeles, CA, USA; Program in Neurogenetics, University of California, Los Angeles, Los Angeles, CA, USA; Department of Neurology, University of California, Los Angeles, Los Angeles, CA, USA; Semel Institute for Neuroscience and Human Behavior, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA; Department of Human Genetics, University of California, Los Angeles, Los Angeles, CA, USA.
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Jacobs J, Golla T, Mader M, Schelter B, Dümpelmann M, Korinthenberg R, Schulze-Bonhage A. Electrical stimulation for cortical mapping reduces the density of high frequency oscillations. Epilepsy Res 2014; 108:1758-69. [PMID: 25301524 DOI: 10.1016/j.eplepsyres.2014.09.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2013] [Revised: 09/10/2014] [Accepted: 09/20/2014] [Indexed: 10/24/2022]
Abstract
BACKGROUND High frequency oscillations (HFOs, 80-500 Hz) are EEG biomarkers for epileptogenic areas. HFOs are also indicators of disease activity as HFO rates increase after reduction of antiepileptic medication. Electrical stimulation (ES) can be used for diagnostic purposes as well as therapy in patients with refractory epilepsy. This study investigates the occurrence and changes of HFOs during ES in patients with refractory epilepsy. OBJECTIVE Analysis of the effects of ES using intracranial ES on the occurrence of epileptic HFOs. METHODS Patients underwent ES for diagnostic purposes. Ripples (80-200 Hz) and fast ripples (200-500 Hz) were visually marked in a baseline EEG segment prior to ES, after each period of ES as well as after the end of ES. In patients in whom ES triggered a seizure a pre- and postictal segment was marked. Rates of HFOs were compared for the different time periods using a Spearman's correlation and Wilcoxon rank sum test (p<0.05). RESULTS 12 patients with 911 EEG channels were analyzed. Ripple (r=-0.42, p<0.001) as well as fast ripple (r=-0.21, p<0.001) rates decreased significantly over the course of stimulation. This phenomenon was not focal over the seizure onset or neighboring contacts but even observed over distant contacts. CONCLUSIONS ES resulted in a gradual decrease of HFO-Rates over time. The decrease of HFOs was not limited to SOZ areas. If HFOs are considered as markers of disease activity the reduction in HFO-rates as a result of intracranial ES has to be interpreted as a reduction of disease activity.
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Affiliation(s)
- Julia Jacobs
- Department of Neuropediatrics and Muscular Disease, University Medical Center Freiburg, Germany.
| | - Tilin Golla
- Department of Neuropediatrics and Muscular Disease, University Medical Center Freiburg, Germany; Epilepsy Center, University Medical Center Freiburg, Germany
| | - Malenka Mader
- Department of Neuropediatrics and Muscular Disease, University Medical Center Freiburg, Germany
| | - Björn Schelter
- Institute for Complex Systems and Mathematical Biology, University of Aberdeen, Meston Building, AB24 3UE Aberdeen, UK
| | | | - Rudolf Korinthenberg
- Department of Neuropediatrics and Muscular Disease, University Medical Center Freiburg, Germany
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Boido D, Kapetis D, Gnatkovsky V, Pastori C, Galbardi B, Sartori I, Tassi L, Cardinale F, Francione S, de Curtis M. Stimulus-evoked potentials contribute to map the epileptogenic zone during stereo-EEG presurgical monitoring. Hum Brain Mapp 2014; 35:4267-81. [PMID: 24706574 PMCID: PMC6869715 DOI: 10.1002/hbm.22516] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Revised: 02/03/2014] [Accepted: 03/18/2014] [Indexed: 11/07/2022] Open
Abstract
Presurgical monitoring with intracerebral electrodes in patients with drug-resistant focal epilepsy represents a standard invasive procedure to localize the sites of seizures origin, defined as the epileptogenic zone (EZ). During presurgical evaluation, intracerebral single-pulse electrical stimulation (SPES) is performed to define the boundaries of eloquent areas and to evoke seizure-associated symptoms. Extensive intracranial exploration and stimulation generate a large dataset on brain connectivity that can be used to improve EZ detection and to understand the organization of the human epileptic brain. We developed a protocol to analyse field responses evoked by intracranial stimulation. Intracerebral recordings were performed with 105-162 recording sites positioned in fronto-temporal regions in 12 patients with pharmacoresistant focal epilepsy. Recording sites were used for bipolar SPES at 1 Hz. Reproducible early and late phases (<60 ms and 60-500 ms from stimulus artefact, respectively) were identified on averaged evoked responses. Phase 1 and 2 responses recorded at all and each recording sites were plotted on a 3D brain reconstructions. Based on connectivity properties, electrode contacts were primarily identified as receivers, mainly activators or bidirectional. We used connectivity patterns to construct networks and applied cluster partitioning to study the proprieties between potentials evoked/stimulated in different regions. We demonstrate that bidirectional connectivity during phase 1 is a prevalent feature that characterize contacts included in the EZ. This study shows that the application of an analytical protocol on intracerebral stimulus-evoked recordings provides useful information that may contribute to EZ detection and to the management of surgical-remediable epilepsies.
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Affiliation(s)
- Davide Boido
- Experimental Neurophysiology and Epileptology UnitFondazione Istituto Neurologico Carlo BestaMilanoItaly
| | - Dimos Kapetis
- Bioinformatics Unit of Scientific DirectionFondazione Istituto Neurologico Carlo BestaMilanoItaly
| | - Vadym Gnatkovsky
- Experimental Neurophysiology and Epileptology UnitFondazione Istituto Neurologico Carlo BestaMilanoItaly
| | - Chiara Pastori
- Experimental Neurophysiology and Epileptology UnitFondazione Istituto Neurologico Carlo BestaMilanoItaly
| | - Barbara Galbardi
- Bioinformatics Unit of Scientific DirectionFondazione Istituto Neurologico Carlo BestaMilanoItaly
| | - Ivana Sartori
- Claudio Munari Epilepsy Surgery CenterOspedale Niguarda Cà GrandaMilanoItaly
| | - Laura Tassi
- Claudio Munari Epilepsy Surgery CenterOspedale Niguarda Cà GrandaMilanoItaly
| | - Francesco Cardinale
- Claudio Munari Epilepsy Surgery CenterOspedale Niguarda Cà GrandaMilanoItaly
| | - Stefano Francione
- Claudio Munari Epilepsy Surgery CenterOspedale Niguarda Cà GrandaMilanoItaly
| | - Marco de Curtis
- Experimental Neurophysiology and Epileptology UnitFondazione Istituto Neurologico Carlo BestaMilanoItaly
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Grasse DW, Karunakaran S, Moxon KA. Neuronal synchrony and the transition to spontaneous seizures. Exp Neurol 2013; 248:72-84. [DOI: 10.1016/j.expneurol.2013.05.004] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2013] [Revised: 04/30/2013] [Accepted: 05/07/2013] [Indexed: 11/28/2022]
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Kokkinos V, Alarcón G, Selway RP, Valentín A. Role of single pulse electrical stimulation (SPES) to guide electrode implantation under general anaesthesia in presurgical assessment of epilepsy. Seizure 2013; 22:198-204. [DOI: 10.1016/j.seizure.2012.12.012] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2012] [Revised: 12/04/2012] [Accepted: 12/07/2012] [Indexed: 10/27/2022] Open
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Abnormal neuronal patterning occurs during early postnatal brain development of Scn1b-null mice and precedes hyperexcitability. Proc Natl Acad Sci U S A 2012; 110:1089-94. [PMID: 23277545 DOI: 10.1073/pnas.1208767110] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Voltage-gated Na(+) channel (VGSC) β1 subunits, encoded by SCN1B, are multifunctional channel modulators and cell adhesion molecules (CAMs). Mutations in SCN1B are associated with the genetic epilepsy with febrile seizures plus (GEFS+) spectrum disorders in humans, and Scn1b-null mice display severe spontaneous seizures and ataxia from postnatal day (P)10. The goal of this study was to determine changes in neuronal pathfinding during early postnatal brain development of Scn1b-null mice to test the hypothesis that these CAM-mediated roles of Scn1b may contribute to the development of hyperexcitability. c-Fos, a protein induced in response to seizure activity, was up-regulated in the Scn1b-null brain at P16 but not at P5. Consistent with this, epileptiform activity was observed in hippocampal and cortical slices prepared from the P16 but not from the P5-P7 Scn1b-null brain. On the basis of these results, we investigated neuronal pathfinding at P5. We observed disrupted fasciculation of parallel fibers in the P5 null cerebellum. Further, P5 null mice showed reduced neuron density in the dentate gyrus granule cell layer, increased proliferation of granule cell precursors in the hilus, and defective axonal extension and misorientation of somata and processes of inhibitory neurons in the dentate gyrus and CA1. Thus, Scn1b is critical for neuronal proliferation, migration, and pathfinding during the critical postnatal period of brain development. We propose that defective neuronal proliferation, migration, and pathfinding in response to Scn1b deletion may contribute to the development of hyperexcitability.
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Staba RJ, Bragin A. High-frequency oscillations and other electrophysiological biomarkers of epilepsy: underlying mechanisms. Biomark Med 2012; 5:545-56. [PMID: 22003903 DOI: 10.2217/bmm.11.72] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
In the normal mammalian brain, neuronal synchrony occurs on a spatial scale of submillimeters to centimeters and temporal scale of submilliseconds to seconds that is reflected in the occurrence of high-frequency oscillations, physiological sharp waves and slow wave sleep oscillations referred to as Up-Down states. In the epileptic brain, the well-studied pathologic counterparts to these physiological events are pathological high-frequency oscillations and interictal spikes that could be electrophysiological biomarkers of epilepsy. Establishing these abnormal events as biomarkers of epilepsy will largely depend on a better understanding of the mechanisms underlying their generation, which will not only help distinguish pathological from physiological events, but will also determine what roles these pathological events play in epileptogenesis and epileptogenicity. This article focuses on the properties and neuronal mechanisms supporting the generation of high-frequency oscillations and interictal spikes, and introduces a new phenomenon called Up-spikes.
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Affiliation(s)
- Richard J Staba
- Department of Neurology, 710 Westwood Plaza, Reed Neurological Research Center, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA.
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20
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Tamura R, Nishida H, Eifuku S, Nagao K, Fushiki H, Watanabe Y, Ono T. Short-term synaptic plasticity in the dentate gyrus of monkeys. PLoS One 2011; 6:e20006. [PMID: 21625444 PMCID: PMC3098860 DOI: 10.1371/journal.pone.0020006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2011] [Accepted: 04/07/2011] [Indexed: 11/18/2022] Open
Abstract
The hippocampus plays an important role in learning and memory. Synaptic plasticity in the hippocampus, short-term and long-term, is postulated to be a neural substrate of memory trace. Paired-pulse stimulation is a standard technique for evaluating a form of short-term synaptic plasticity in rodents. However, evidence is lacking for paired-pulse responses in the primate hippocampus. In the present study, we recorded paired-pulse responses in the dentate gyrus of monkeys while stimulating to the medial part of the perforant path at several inter-pulse intervals (IPIs) using low and high stimulus intensities. When the stimulus intensity was low, the first pulse produced early strong depression (at IPIs of 10–30 ms) and late slight depression (at IPIs of 100–1000 ms) of field excitatory postsynaptic potentials (fEPSPs) generated by the second pulse, interposing no depression IPIs (50–70 ms). When the stimulus intensity was high, fEPSPs generated by the second pulse were depressed by the first pulse at all IPIs except for the longest one (2000 ms). Population spikes (PSs) generated by the second pulse were completely blocked or strongly depressed at shorter IPIs (10–100 or 200 ms, respectively), while no depression or slight facilitation occurred at longer IPIs (500–2000 ms). Administration of diazepam slightly increased fEPSPs, while it decreased PSs produced by the first pulse. It also enhanced the facilitation of PSs produced by the second stimulation at longer IPIs. The present results, in comparison with previous studies using rodents, indicate that paired-pulse responses of fEPSPs in the monkey are basically similar to those of rodents, although paired-pulse responses of PSs in the monkey are more delayed than those in rodents and have a different sensitivity to diazepam.
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Affiliation(s)
- Ryoi Tamura
- Department of Integrative Neuroscience, Graduate School of Medicine and Pharmaceutical Sciences for Research, University of Toyama, Toyama, Japan.
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21
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David O, Bastin J, Chabardès S, Minotti L, Kahane P. Studying network mechanisms using intracranial stimulation in epileptic patients. Front Syst Neurosci 2010; 4:148. [PMID: 21060722 PMCID: PMC2972750 DOI: 10.3389/fnsys.2010.00148] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2010] [Accepted: 09/20/2010] [Indexed: 11/13/2022] Open
Abstract
Patients suffering from focal drug-resistant epilepsy who are explored using intracranial electrodes allow to obtain data of exceptional value for studying brain dynamics in correlation with pathophysiological and cognitive processes. Direct electrical stimulation (DES) of cortical regions and axonal tracts in those patients elicits a number of very specific perceptual or behavioral responses, but also abnormal responses due to specific configurations of epileptic networks. Here, we review how anatomo-functional brain connectivity and epilepsy network mechanisms can be assessed from DES responses measured in patients. After a brief summary of mechanisms of action of brain electrical stimulation, we recall the conceptual framework for interpreting DES results in the context of brain connectivity and review how DES can be used for the characterization of functional networks, the identification of the seizure onset zone, the study of brain plasticity mechanisms, and the anticipation of epileptic seizures. This pool of exceptional data may be underexploited by fundamental research on brain connectivity and leaves much to be learned.
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Affiliation(s)
- Olivier David
- INSERM U836, Grenoble Institut des Neurosciences Grenoble, France
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22
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Zhan RZ, Timofeeva O, Nadler JV. High ratio of synaptic excitation to synaptic inhibition in hilar ectopic granule cells of pilocarpine-treated rats. J Neurophysiol 2010; 104:3293-304. [PMID: 20881195 DOI: 10.1152/jn.00663.2010] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
After experimental status epilepticus, many dentate granule cells born into the postseizure environment migrate aberrantly into the dentate hilus. Hilar ectopic granule cells (HEGCs) have also been found in persons with epilepsy. These cells exhibit a high rate of spontaneous activity, which may enhance seizure propagation. Electron microscopic studies indicated that HEGCs receive more recurrent mossy fiber innervation than normotopic granule cells in the same animals but receive much less inhibitory innervation. This study used hippocampal slices prepared from rats that had experienced pilocarpine-induced status epilepticus to test the hypothesis that an imbalance of synaptic excitation and inhibition contributes to the hyperexcitability of HEGCs. Mossy fiber stimulation evoked a much smaller GABA(A) receptor-mediated inhibitory postsynaptic currents (IPSC) in HEGCs than in normotopic granule cells from either control rats or rats that had experienced status epilepticus. However, recurrent mossy fiber-evoked excitatory postsynaptic currents (EPSCs) of similar size were recorded from HEGCs and normotopic granule cells in status epilepticus-experienced rats. HEGCs exhibited the highest frequency of miniature excitatory postsynaptic currents (mEPSCs) and the lowest frequency of miniature inhibitory postsynaptic currents (mIPSCs) of any granule cell group. On average, both mEPSCs and mIPSCs were of higher amplitude, transferred more charge per event, and exhibited slower kinetics in HEGCs than in granule cells from control rats. Charge transfer per unit time in HEGCs was greater for mEPSCs and much less for mIPSCs than in the normotopic granule cell groups. A high ratio of excitatory to inhibitory synaptic function probably accounts, in part, for the hyperexcitability of HEGCs.
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Affiliation(s)
- Ren-Zhi Zhan
- Dept. of Pharmacology and Cancer Biology, Box 3813, Duke Univ. Medical Center, Durham, NC 27710, USA
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23
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Terney D, Alving J, Skaarup CN, Wolf P, Beniczky S. The slow-wave component of the interictal epileptiform EEG discharges. Epilepsy Res 2010; 90:228-33. [PMID: 20554157 DOI: 10.1016/j.eplepsyres.2010.05.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2010] [Revised: 04/27/2010] [Accepted: 05/03/2010] [Indexed: 11/27/2022]
Abstract
The interictal epileptiform discharges (IEDs) consist of a fast component (FC; spike or sharp-wave) followed by a slow-wave component (SC). Our purpose was to assess the intra-individual variance, the diagnostic significance and the effect of sleep on the SC. Ninety-nine EEG recordings from 50 consecutive patients with IEDs were analysed. We measured the duration (ms) of the SC (SC-duration), while the amplitude of the SC was divided by the amplitude of the FC yielding a normalized value (SC/FC amplitude-ratio). Intra-individual, intra- and inter-recording coefficients of variation (CV) were calculated for the SC-duration and SC/FC amplitude-ratio. The correlation with the diagnosis, and the effect of sleep was analysed. The SC-duration and the SC/FC amplitude-ratio had low CV (<27%). The SC-duration was not correlated with the diagnosis. The SC/FC amplitude-ratio was significantly higher in the patients with generalized epilepsies as compared with the localization-related ones, and it was higher in the patients with idiopathic epilepsies as compared with the symptomatic ones. These predictors were independent. The SC/FC amplitude-ratio of the patients with idiopathic epilepsy increased significantly during sleep. We conclude that the SC-duration and SC/FC amplitude-ratio are stable parameters. The amplitude of the SC in relation to the fast component is larger in patients with generalized and idiopathic epilepsies, suggesting higher degree of cortical inhibition in these patients, possibly corresponding to specific protective mechanisms.
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Zhan RZ, Nadler JV. Enhanced tonic GABA current in normotopic and hilar ectopic dentate granule cells after pilocarpine-induced status epilepticus. J Neurophysiol 2009; 102:670-81. [PMID: 19474175 DOI: 10.1152/jn.00147.2009] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In temporal lobe epilepsy, loss of inhibitory neurons and circuit changes in the dentate gyrus promote hyperexcitability. This hyperexcitability is compensated to the point that dentate granule cells exhibit normal or even subnormal excitability under some conditions. This study explored the possibility that compensation involves enhanced tonic GABA inhibition. Whole cell patch-clamp recordings were made from normotopic granule cells in hippocampal slices from control rats and from both normotopic and hilar ectopic granule cells in slices from rats subjected to pilocarpine-induced status epilepticus. After status epilepticus, tonic GABA current was an order of magnitude greater than control in normotopic granule cells and was significantly greater in hilar ectopic than in normotopic granule cells. These differences could be observed whether or not the extracellular GABA concentration was increased by adding GABA to the superfusion medium or blocking plasma membrane transport. The enhanced tonic GABA current had both action potential-dependent and action potential-independent components. Pharmacological studies suggested that the small tonic GABA current of granule cells in control rats was mediated largely by high-affinity alpha(4)beta(x)delta GABA(A) receptors but that the much larger current recorded after status epilepticus was mediated largely by the lower-affinity alpha(5)beta(x)gamma(2) GABA(A) receptors. A large alpha(5)beta(x)gamma(2)-mediated tonic current could be recorded from controls only when the extracellular GABA concentration was increased. Status epilepticus seemed not to impair the control of extracellular GABA concentration by plasma membrane transport substantially. Upregulated tonic GABA inhibition may account for the unexpectedly modest excitability of the dentate gyrus in epileptic brain.
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Affiliation(s)
- Ren-Zhi Zhan
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA
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25
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King-Stephens D. Epilepsy. Neuromodulation 2009. [DOI: 10.1016/b978-0-12-374248-3.00050-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Nishida M, Asano E, Juhász C, Muzik O, Sood S, Chugani HT. Cortical glucose metabolism correlates negatively with delta-slowing and spike-frequency in epilepsy associated with tuberous sclerosis. Hum Brain Mapp 2008; 29:1255-64. [PMID: 17948886 DOI: 10.1002/hbm.20461] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mechanism of altered glucose metabolism seen on positron emission tomography (PET) in focal epilepsy is not fully understood. We determined the association between interictal glucose metabolism and interictal neuronal activity, using PET and electrocorticography (ECoG) measures derived from 865 intracranial electrode sites in 11 children with focal epilepsy associated with tuberous sclerosis complex (TSC) (age: 0.5-16 years) undergoing epilepsy surgery. A multiple linear regression analysis was applied to each patient, to determine whether the glucose uptake at each electrode site on interictal PET was predicted by ECoG amplitude powers and interictal spike-frequency measured in the given electrode site. The regression slopes as well as R-square values (an indicator of fitness of the regression models) were finally averaged across the 11 patients. The mean regression slope for delta amplitude power was -0.0025 (95% CI: -0.0045 to -0.0004; P = 0.02 based on one-sample t-test) and that for spike frequency was -0.023 (95% CI: -0.042 to -0.0038; P = 0.02). On the other hand, the mean regression slopes for the remaining ECoG amplitude powers (theta, alpha, sigma, beta, and gamma activities) were not significantly different from zero. The mean R-square value was 0.39. These results suggest that increased delta-slowing and frequent spike activity were independently and additively associated with glucose hypometabolism in children with focal epilepsy associated with TSC. Association between frequent interictal spike activity and low glucose metabolism may be attributed to slow-wave components following spike discharges on ECoG recording, and a substantial proportion of the variance in regional glucose metabolism on PET could be explained by electrophysiological traits derived from conventional subdural ECoG recording.
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Affiliation(s)
- Masaaki Nishida
- Department of Pediatrics, Children's Hospital of Michigan, Wayne State University, Detroit, Michigan 48201, USA
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Waldbaum S, Dudek FE. Single and repetitive paired-pulse suppression: a parametric analysis and assessment of usefulness in epilepsy research. Epilepsia 2008; 50:904-16. [PMID: 19170733 DOI: 10.1111/j.1528-1167.2008.01939.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
PURPOSE The paired-pulse technique has been widely used as a convenient but indirect measure of "inhibition" in hippocampal circuits of normal and epileptic animals. Most investigators have used a single paired-pulse protocol, whereas others have utilized repetitive paired pulses. This study investigated which parameters influence results from paired-pulse tests, focusing on the repetitive paired-pulse technique; it aims to assess how this technique may be used in an unbiased and quantitative manner across animal preparations for comparisons of control and experimental epileptic animals. METHODS The perforant path was stimulated while field potentials were recorded from the granule cell layer under isoflurane anesthesia. Paired-pulse suppression was analyzed as a function of stimulation intensity and interpulse interval and frequency. RESULTS Paired-pulse suppression was greater with increased stimulus intensity and decreased interpulse interval (20-100 ms). During repetitive protocols, stimulation frequencies <or=1.0 Hz produced paired-pulse suppression similar to single paired-pulse responses, but caused more paired-pulse suppression between 1.0 and 4.0 Hz at all but the lowest intensities. The amplitude of the population spike produced by the conditioning pulse increased progressively during stimulation at higher frequencies (1.0-4.0 Hz). DISCUSSION The single paired-pulse technique is highly dependent on stimulation parameters, as is the repetitive paired-pulse protocol, which is more variable. To generate reliable, consistent, and unbiased data in comparisons of control and experimental epileptic groups, all parameters should be specified and controlled across experiments. Paired-pulse suppression is susceptible to alterations in many mechanisms, and, therefore, represents a circuit response rather than an assay of gamma-aminobutyric acid (GABA)ergic inhibition in epilepsy research.
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Affiliation(s)
- Simon Waldbaum
- Department of Biomedical Sciences, Anatomy and Neurobiology Section, Colorado State University, Fort Collins, Colorado, USA
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Le Van Quyen M, Bragin A, Staba R, Crépon B, Wilson CL, Engel J. Cell type-specific firing during ripple oscillations in the hippocampal formation of humans. J Neurosci 2008; 28:6104-10. [PMID: 18550752 PMCID: PMC2693199 DOI: 10.1523/jneurosci.0437-08.2008] [Citation(s) in RCA: 113] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2008] [Revised: 03/26/2008] [Accepted: 04/06/2008] [Indexed: 11/21/2022] Open
Abstract
High-frequency field ripples occur in the rodent hippocampal formation and are assumed to depend on interneuron type-specific firing patterns, structuring the activity of pyramidal cells. Ripples with similar characteristics are also present in humans, yet their underlying cellular correlates are still unknown. By in vivo recording interneurons and pyramidal cells in the human hippocampal formation, we find that cell type-specific firing patterns and phase-locking on a millisecond timescale can be distinguished during ripples. In particular, pyramidal cells fired preferentially at the highest amplitude of the ripple, but interneurons began to discharge earlier than pyramidal cells. Furthermore, a large fraction of cells were phase-locked to the ripple cycle, but the preferred phase of discharge of interneurons followed the maximum discharge probability of pyramidal neurons. These relationships between human ripples and unit activity are qualitatively similar to that observed in vivo in the rodents, suggesting that their underlying mechanisms are similar.
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Affiliation(s)
- Michel Le Van Quyen
- Centre National de la Recherche Scientifique, Cognitive Neuroscience and Brain Imaging Laboratory, Unité Propre de Recherche 640, Hôpital de la Pitié-Salpêtrière, 75651 Paris, France
- Université Pierre et Marie Curie-Paris 6, 75005 Paris, France, and
| | - Anatol Bragin
- Neurology Department, David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, California 90095
| | - Richard Staba
- Neurology Department, David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, California 90095
| | - Benoit Crépon
- Centre National de la Recherche Scientifique, Cognitive Neuroscience and Brain Imaging Laboratory, Unité Propre de Recherche 640, Hôpital de la Pitié-Salpêtrière, 75651 Paris, France
- Université Pierre et Marie Curie-Paris 6, 75005 Paris, France, and
| | - Charles L. Wilson
- Neurology Department, David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, California 90095
| | - Jerome Engel
- Neurology Department, David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, California 90095
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Tallent MK, Qiu C. Somatostatin: an endogenous antiepileptic. Mol Cell Endocrinol 2008; 286:96-103. [PMID: 18221832 PMCID: PMC2843391 DOI: 10.1016/j.mce.2007.12.004] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/09/2007] [Revised: 08/02/2007] [Accepted: 12/01/2007] [Indexed: 02/07/2023]
Abstract
The neuropeptide somatostatin (SST) is highly expressed in brain regions associated with seizures. In hippocampus, SST expression and release is regulated by seizures, and SST-containing neurons within the hilus of the dentate gyrus are sensitive to seizure-induced death. In vivo and in vitro studies suggest that the loss of SST function in the dentate could contribute to epileptogenesis and seizure susceptibility. SST also has inhibitory actions in the CA1 and CA3 hippocampus indicating this peptide is an important homeostatic regulator throughout the hippocampus. In vivo studies show SST has robust antiepileptic properties with the major site of action being hippocampus. In rodents, somatostatin receptor subtype 2 (SST(2)) and SST(4) appear to mediate the majority of the antiepileptic actions of SST, with SST(2) predominate in rat and SST(4) in mouse. Thus SST receptors may be appropriate targets for new antiepileptic drugs (AEDs), although validation in human tissue is lacking.
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Affiliation(s)
- Melanie K Tallent
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102, USA.
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David O, Woźniak A, Minotti L, Kahane P. Preictal short-term plasticity induced by intracerebral 1 Hz stimulation. Neuroimage 2008; 39:1633-46. [PMID: 18155929 DOI: 10.1016/j.neuroimage.2007.11.005] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2007] [Revised: 10/02/2007] [Accepted: 11/02/2007] [Indexed: 11/17/2022] Open
Affiliation(s)
- Olivier David
- Inserm, U836, Grenoble Institut des Neurosciences, CHU Grenoble-Bât E Safra-BP 217, Grenoble, France.
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31
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Ma DL, Tang YC, Tang FR. Cytoarchitectonics and afferent/efferent reorganization of neurons in layers II and III of the lateral entorhinal cortex in the mouse pilocarpine model of temporal lobe epilepsy. J Neurosci Res 2008; 86:1324-42. [DOI: 10.1002/jnr.21583] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Lacruz ME, García Seoane JJ, Valentin A, Selway R, Alarcón G. Frontal and temporal functional connections of the living human brain. Eur J Neurosci 2007; 26:1357-70. [PMID: 17767512 DOI: 10.1111/j.1460-9568.2007.05730.x] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Connections between human temporal and frontal cortices were investigated by intracranial electroencephalographic responses to electrical stimulation with 1-ms single pulses in 51 patients assessed for surgery for treatment of epilepsy. The areas studied were medial temporal, entorhinal, lateral temporal, medial frontal, lateral frontal and orbital frontal cortices. Findings were assumed to be representative of human brain as no differences were found between epileptogenic and non-epileptogenic hemispheres. Connections between intralobar temporal and frontal regions were common (43-95%). Connections from temporal to ipsilateral frontal regions were relatively uncommon (seen in 0-25% of hemispheres). Connections from frontal to ipsilateral temporal cortices were more common, particularly from orbital to ipsilateral medial temporal regions (40%). Contralateral temporal connections were rare (< 9%) whereas contralateral frontal connections were frequent and faster, particularly from medial frontal to contralateral medial frontal (61%) and orbital frontal cortices (57%), and between both orbital cortices (67%). Orbital cortex receives profuse connections from the ipsilateral medial (78%) and lateral (88%) frontal cortices, and from the contralateral medial (57%) and orbital (67%) frontal cortices. The high incidence of intralobar temporal connections supports the presence of temporal reverberating circuits. Frontal cortex projects within the lobe and beyond, to ipsilateral and contralateral structures.
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Affiliation(s)
- M E Lacruz
- Department of Clinical Neuroscience, Institute of Psychiatry, 16 De Crespigny Park, London SES 8AF, UK
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Fenoglio KA, Wu J, Kim DY, Simeone TA, Coons SW, Rekate H, Rho JM, Kerrigan JF. Hypothalamic hamartoma: basic mechanisms of intrinsic epileptogenesis. Semin Pediatr Neurol 2007; 14:51-9. [PMID: 17544947 DOI: 10.1016/j.spen.2007.03.002] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The hypothalamic hamartoma (HH) is a rare developmental malformation commonly associated with gelastic seizures that are notoriously refractory to medical therapy. Recent evidence supports the intrinsic seizure propensity of HH. Despite increasing clinical recognition of this condition, the mechanisms of seizure genesis in HH tissue remain unclear. This review summarizes the histochemical and electrophysiological properties of HH neurons, and relates these findings to those characteristics identified in other types of epileptic tissue. Initial studies have revealed two distinct populations of neurons in surgically resected HH tissue. One group consisted of small gamma-aminobutyric acid (GABA)-expressing neurons that occurred principally in clusters and displayed spontaneous rhythmic firing. The second group was composed of large, quiescent, pyramidal-like neurons with more extensive dendritic and axonal arborization. We propose that the small, spontaneously firing GABAergic neurons send inhibitory projections to and drive the synchrony of large output neurons. These observations constitute the basis for future investigations aimed at elucidating the mechanisms of subcortical epileptogenesis.
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Affiliation(s)
- Kristina A Fenoglio
- Division of Neurology and Pediatric Neurology, Barrow Neurological Institute and Children's Health Center, St. Joseph's Hospital and Medical Center, Phoenix, AZ 85013, USA.
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Jiang FL, Tang YC, Chia SC, Jay TM, Tang FR. Anticonvulsive Effect of a Selective mGluR8 Agonist (S)-3,4-Dicarboxyphenylglycine (S-3,4-DCPG) in the Mouse Pilocarpine Model of Status Epilepticus. Epilepsia 2007; 48:783-92. [PMID: 17430409 DOI: 10.1111/j.1528-1167.2007.01000.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
PURPOSE We sought to investigate the anticonvulsive and neuroprotective effect of a selective metabotropic glutamate receptor 8 (mGluR8) agonist (S)-3,4-dicarboxyphenylglycines (S-3,4-DCPG) on pilocarpine-induced status epilepticus (PISE) and subsequent loss of hilar neurons in the dentate gyrus after systemic (intravenous) or local (intracerebroventricular) administration. We compared the difference in granular cell responses after paired-pulse stimulation of the perforant pathway and the sensitivity to local injection of S-3,4-DCPG into the stratum granulosum in the control and mice at 2 months after PISE. METHODS We used intravenous, intracerebroventricular, or intrahippocampal administration of S-3,4-DCPG to mice with status epilepticus or temporal lobe epilepsy and neurophysiologic recording of somatic field excitatory postsynaptic potential (sfEPSP) and population spike (PS) of granular cells in response to perforant-pathway stimulation or S-3,4-DCPG treatment. RESULTS Intracerebroventricular (1.91 micromol) but not systemic administration of S-3,4-DCPG (at doses of 12.5, 50, 100, 200, 400, 800, and 1,200 mg/kg) could control PISE with no neuroprotective effect. In epileptic mice, mGluR8-mediated inhibition of fEPSPs was reduced significantly in granular cell bodies. CONCLUSIONS At doses ranging from 12.5 to 1,200 mg/kg, intravenous administration of S-3,4-DCPG may not be effective in controlling status epilepticus. Down-regulation of mGluR8 may be related to reduced S-3,4-DCPG-mediated inhibition and the subsequent occurrence of spontaneously recurrent seizures.
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Affiliation(s)
- Feng Li Jiang
- Epilepsy Research Lab, National Neuroscience Institute, Singapore
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Dudek FE, Sutula TP. Epileptogenesis in the dentate gyrus: a critical perspective. PROGRESS IN BRAIN RESEARCH 2007; 163:755-73. [PMID: 17765749 DOI: 10.1016/s0079-6123(07)63041-6] [Citation(s) in RCA: 185] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The dentate gyrus has long been a focal point for studies on the molecular, cellular, and network mechanisms responsible for epileptogenesis in temporal lobe epilepsy (TLE). Although several hypothetical mechanisms are considered in this chapter, two that have garnered particular interest and experimental support are: (1) the selective loss of vulnerable interneurons in the region of the hilus and (2) the formation of new recurrent excitatory circuits after mossy fiber sprouting. Histopathological data show that specific GABAergic interneurons in the hilus are lost in animal models of TLE, and several lines of electrophysiological evidence, including intracellular analyses of postsynaptic currents, support this hypothesis. In particular, whole-cell recordings have demonstrated a reduction in the frequency of miniature inhibitory postsynaptic currents in the dentate gyrus and other areas (e.g., CA1 pyramidal cells), which provides relatively specific evidence for a reduction in GABAergic input to granule cells. These studies support the viewpoint that modest alterations in GABAergic inhibition can have significant functional impact in the dentate gyrus, and suggest that dynamic activity-dependent mechanisms of GABAergic regulation add complexity to this local synaptic circuitry and to analyses of epileptogenesis. In regard to mossy fiber sprouting, a wide variety of experiments involving intracellular or whole-cell recordings during electrical stimulation of the hilus, glutamate microstimulation, and dual recordings from granule cells support the hypothesis that mossy fiber sprouting forms new recurrent excitatory circuits in the dentate gyrus in animal models of TLE. Similar to previous studies on recurrent excitation in the CA3 area, GABA-mediated inhibition and the intrinsic high threshold of granule cells in the dentate gyrus tends to mask the presence of the new recurrent excitatory circuits and reduce the likelihood that reorganized circuits will generate seizure-like activity. How cellular alterations such as neuron loss in the hilus and mossy fiber sprouting influence functional properties is potentially important for understanding fundamental aspects of epileptogenesis, such as the consequences of primary initial injuries, mechanisms underlying network synchronization, and progression of intractability. The continuous nature of the axonal sprouting and formation of recurrent excitation could account for aspects of the latent period and the progressive nature of the epileptogenesis. Future studies will need to identify precisely how these hypothetical mechanisms and others contribute to the process whereby epileptic seizures are initiated or propagated through an area such as the dentate gyrus. Finally, in addition to its unique features and potential importance in epileptogenesis, the dentate gyrus may also serve as a model for other cortical structures in acquired epilepsy.
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Affiliation(s)
- F Edward Dudek
- Department of Physiology, University of Utah School of Medicine, Salt Lake City, UT 84108, USA.
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Ang CW, Carlson GC, Coulter DA. Massive and specific dysregulation of direct cortical input to the hippocampus in temporal lobe epilepsy. J Neurosci 2006; 26:11850-6. [PMID: 17108158 PMCID: PMC2175390 DOI: 10.1523/jneurosci.2354-06.2006] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Epilepsy affects 1-2% of the population, with temporal lobe epilepsy (TLE) the most common variant in adults. Clinical and experimental studies have demonstrated hippocampal involvement in the seizures underlying TLE. However, identification of specific functional deficits in hippocampal circuits associated with possible roles in seizure generation remains controversial. Significant attention has focused on anatomic and cellular alterations in the dentate gyrus. The dentate gyrus is a primary gateway regulating cortical input to the hippocampus and, thus, a possible contributor to the aberrant cortical-hippocampal interactions underlying the seizures of TLE. Alternate cortical pathways innervating the hippocampus might also contribute to seizure initiation. Despite this potential importance in TLE, these pathways have received little study. Using simultaneous voltage-sensitive dye imaging and patch-clamp recordings in slices from animals with epilepsy, we assessed the relative degree of synaptic excitation activated by multiple cortical inputs to the hippocampus. Surprisingly, dentate gyrus-mediated regulation of the relay of cortical input to the hippocampus is unchanged in epileptic animals, and input via the Schaffer collaterals is actually decreased despite reduction in Schaffer-evoked inhibition. In contrast, a normally weak direct cortical input to area CA1 of hippocampus, the temporoammonic pathway, exhibits a TLE-associated transformation from a spatially restricted, highly regulated pathway to an excitatory projection with >10-fold increased effectiveness. This dysregulated temporoammonic pathway is critically positioned to mediate generation and/or propagation of seizure activity in the hippocampus.
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Affiliation(s)
- Chyze W. Ang
- Department of Bioengineering, University of Pennsylvania
- Division of Neurology, Children's Hospital of Philadelphia, and
| | | | - Douglas A. Coulter
- Department of Bioengineering, University of Pennsylvania
- Division of Neurology, Children's Hospital of Philadelphia, and
- Departments of Pediatrics, Neurology and Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104
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Urrestarazu E, Jirsch JD, LeVan P, Hall J, Avoli M, Dubeau F, Gotman J. High-frequency intracerebral EEG activity (100-500 Hz) following interictal spikes. Epilepsia 2006; 47:1465-76. [PMID: 16981862 DOI: 10.1111/j.1528-1167.2006.00618.x] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
PURPOSE High-frequency activity has been recorded with intracerebral microelectrodes in epileptic patients and related to seizure genesis. Our goal was to analyze high-frequency activity recorded with electroencephalograph (EEG) macroelectrodes during the slow wave immediately following interictal spikes, given the potential importance of this presumed hyperpolarization in transforming spikes into seizures. METHODS Depth electrode EEG recordings from 10 patients with intractable focal epilepsy were low-pass filtered at 500 Hz and sampled at 2,000 Hz. Spikes were categorized according to localization and morphology. Segments of 256 ms were selected immediately following (postspike), and 2 s before each spike (baseline). Power was estimated in subgamma (0-40 Hz), gamma (40-100 Hz), high frequency (100-200 Hz), and very high frequency (250-500 Hz) bands. RESULTS Changes in power above 100 Hz were seen in 22 of 29 spike categories, consisting primarily of a widespread decrease in frequencies above 100 Hz. This decrease became spatially more restricted as frequencies increased, and coincided with the localization of largest spikes for the highest frequencies. High-frequency power decreases were prominent in the hippocampus but less common in amygdala and neocortex. High-frequency power increases were observed in the amygdala. CONCLUSIONS Thus high-frequency EEG activity can be recorded with macroelectrodes in humans and may provide insights on neuronal mechanisms related to human epilepsy. This activity undergoes consistent modifications after EEG spikes. We propose that the reduction in high frequencies reflects a postspike depression in neuronal activity that is more pronounced in the region of spike generation. This depression is almost always seen in hippocampus but less in amygdala.
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Affiliation(s)
- Elena Urrestarazu
- Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada
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Frotscher M, Jonas P, Sloviter RS. Synapses formed by normal and abnormal hippocampal mossy fibers. Cell Tissue Res 2006; 326:361-7. [PMID: 16819624 DOI: 10.1007/s00441-006-0269-2] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2006] [Accepted: 05/31/2006] [Indexed: 11/29/2022]
Abstract
The axon terminals (mossy fibers) of hippocampal dentate granule cells form characteristic synaptic connections with large spines or excrescences of both hilar mossy cells and CA3 pyramidal neurons. Interneurons of the hilar region and area CA3 are also prominent targets of mossy fibers. The tracing of biocytin-filled mossy fibers and immunolabeling of target cells with interneuron markers has revealed that the majority of mossy fiber synapses project to gamma aminobutyric acid (GABA)-ergic inhibitory interneurons rather than to excitatory principal cells, although the functional implications of these quantitative differences are unclear. Following a brief description of the "classical" mossy fiber synapse on excrescences of CA3 pyramidal cells, the present review focuses on the contacts formed between granule cells and GABAergic interneurons, both normally and after synaptic reorganization. In response to deafferentation of mossy cell target cells, which include both granule cells and interneurons, mossy fibers "sprout" new axon collaterals that form a band of supragranular mossy fibers in the inner molecular layer of the dentate gyrus. Although most newly formed recurrent mossy fibers establish synapses with granule cells, there is an apparently convergent input of new mossy fibers onto GABA-immunoreactive interneuron dendrites that traverse the inner molecular layer. These mossy fiber-interneuron synapses in the dentate gyrus are observed in chronically epileptic rats and may be the structural correlate of the granule cell hyperinhibition observed in these animals in vivo. Together, the findings reviewed here establish mossy fiber synapses as an important component of inhibitory circuits in the hippocampus.
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Affiliation(s)
- Michael Frotscher
- Institut für Anatomie und Zellbiologie und Zentrum für Neurowissenschaften, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany.
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Avoli M, Louvel J, Pumain R, Köhling R. Cellular and molecular mechanisms of epilepsy in the human brain. Prog Neurobiol 2006; 77:166-200. [PMID: 16307840 DOI: 10.1016/j.pneurobio.2005.09.006] [Citation(s) in RCA: 118] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2005] [Revised: 07/27/2005] [Accepted: 09/20/2005] [Indexed: 12/20/2022]
Abstract
Animal models have provided invaluable data for identifying the pathogenesis of epileptic disorders. Clearly, the relevance of these experimental findings would be strengthened by the demonstration that similar fundamental mechanisms are at work in the human epileptic brain. Epilepsy surgery has indeed opened the possibility to directly study the functional properties of human brain tissue in vitro, and to analyze the mechanisms underlying seizures and epileptogenesis. Here, we summarize the findings obtained over the last 40 years from electrophysiological, histochemical and molecular experiments made with the human brain tissue. In particular, this review will focus on (i) the synaptic and non-synaptic properties of neocortical neurons along with their ability to produce synchronous activity; (ii) the anatomical and functional alterations that characterize limbic structures in patients presenting with mesial temporal lobe epilepsy; (iii) the issue of antiepileptic drug action and resistance; and (iv) the pathophysiology of seizure genesis in Taylor's type focal cortical dysplasia. Finally, we will address some of the problems that are inherent to this type of experimental approach, in particular the lack of proper controls and possible strategies to obviate this limitation.
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Affiliation(s)
- Massimo Avoli
- Montreal Neurological Institute and Departments of Neurology and Neurosurgery, and of Physiology, McGill University, Montreal, Canada.
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Sloviter RS, Zappone CA, Harvey BD, Frotscher M. Kainic acid-induced recurrent mossy fiber innervation of dentate gyrus inhibitory interneurons: possible anatomical substrate of granule cell hyper-inhibition in chronically epileptic rats. J Comp Neurol 2006; 494:944-60. [PMID: 16385488 PMCID: PMC2597112 DOI: 10.1002/cne.20850] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Kainic acid-induced neuron loss in the hippocampal dentate gyrus may cause epileptogenic hyperexcitability by triggering the formation of recurrent excitatory connections among normally unconnected granule cells. We tested this hypothesis by assessing granule cell excitability repeatedly within the same awake rats at different stages of the synaptic reorganization process initiated by kainate-induced status epilepticus (SE). Granule cells were maximally hyperexcitable to afferent stimulation immediately after SE and became gradually less excitable during the first month post-SE. The chronic epileptic state was characterized by granule cell hyper-inhibition, i.e., abnormally increased paired-pulse suppression and an abnormally high resistance to generating epileptiform discharges in response to afferent stimulation. Focal application of the gamma-aminobutyric acid type A (GABA(A)) receptor antagonist bicuculline methiodide within the dentate gyrus abolished the abnormally increased paired-pulse suppression recorded in chronically hyper-inhibited rats. Combined Timm staining and parvalbumin immunocytochemistry revealed dense innervation of dentate inhibitory interneurons by newly formed, Timm-positive, mossy fiber terminals. Ultrastructural analysis by conventional and postembedding GABA immunocytochemical electron microscopy confirmed that abnormal mossy fiber terminals of the dentate inner molecular layer formed frequent asymmetrical synapses with inhibitory interneurons and with GABA-immunopositive dendrites as well as with GABA-immunonegative dendrites of presumed granule cells. These results in chronically epileptic rats demonstrate that dentate granule cells are maximally hyperexcitable immediately after SE, prior to mossy fiber sprouting, and that synaptic reorganization following kainate-induced injury is temporally associated with GABA(A) receptor-dependent granule cell hyper-inhibition rather than a hypothesized progressive hyperexcitability. The anatomical data provide evidence of a possible anatomical substrate for the chronically hyper-inhibited state.
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Affiliation(s)
- Robert S Sloviter
- Department of Pharmacology and the Graduate Program in Neuroscience, University of Arizona College of Medicine, Tucson, Arizona 85724, USA.
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Gorji A, Straub H, Speckmann EJ. Epilepsy surgery: perioperative investigations of intractable epilepsy. ACTA ACUST UNITED AC 2006; 210:525-37. [PMID: 16180018 DOI: 10.1007/s00429-005-0043-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Recent advances in our understanding of the basic mechanisms of epilepsy have derived, to a large extent, from increasing ability to carry out detailed studies on patients surgically treated for intractable epilepsy. Clinical and experimental perioperative studies divide into three different phases: before the surgical intervention (preoperative studies), on the intervention itself (intraoperative studies), and on the period when the part of the brain that has to be removed is available for further investigations (postoperative studies). Before surgery, both structural and functional neuroimaging techniques, in addition to their diagnostic roles, could be used to investigate the pathophysiological mechanisms of seizure attacks in epileptic patients. During epilepsy surgery, it is possible to insert microdialysis catheters and electroencephalogram electrodes into the brain tissues in order to measure constituents of extracellular fluid and record the bioelectrical activity. Subsequent surgical resection provides tissue that can be used for electrophysiological, morphological, and molecular biological investigations. To take full advantage of these opportunities, carefully designed experimental protocols are necessary to compare the data from different phases and characterize abnormalities in the human epileptic brain.
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Affiliation(s)
- A Gorji
- Institut für Physiologie I, Universität Münster, Robert-Koch-Strasse 27a, 48149 Münster, Germany.
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Matsumoto R, Kinoshita M, Taki J, Hitomi T, Mikuni N, Shibasaki H, Fukuyama H, Hashimoto N, Ikeda A. In Vivo Epileptogenicity of Focal Cortical Dysplasia: A Direct Cortical Paired Stimulation Study. Epilepsia 2005; 46:1744-9. [PMID: 16302853 DOI: 10.1111/j.1528-1167.2005.00284.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
PURPOSE Alternation of the intracortical inhibitory and excitatory mechanisms in focal cortical dysplasia (FCD) has not been well elucidated in vivo in humans. We investigated in vivo alternation of these mechanisms in epileptogenesis of FCD by means of paired-pulse direct cortical electrical stimulation. METHODS A 31-year-old man with FCD at the left foot primary somatosensory (SI) and motor areas who underwent invasive monitoring with subdural electrodes was studied. By means of subdural electrodes, paired-pulse electrical stimulation was performed at the epileptic focus (foot SI) and control cortex (hand SI) with interstimulus interval (ISI) of 1-100 ms. Instead of using motor evoked potentials to investigate the degree of cortical excitability in response to motor cortex stimulation, we evaluated the size change of corticocortical evoked potentials (CCEPs), which are elicited at the adjacent cortex by direct cortical stimulation via fiber projection and thus reflect direct and indirect excitation of corticocortical projection neurons at the site of stimulation. RESULTS During the interictal state, paired-pulse stimulation of the focus revealed abnormally enhanced intracortical inhibition at ISI of 1-10 ms (maximum, 22%) compared with control stimulation of the hand SI (ISI of 1-2 ms; maximum, 18%) (p < 0.01). While the patient was having the somatosensory aura that later evolved into the left-leg clonic seizure, single and paired stimulation at the focus showed increased cortical excitability (enlarged CCEP) and decreased intracortical inhibition, respectively. CONCLUSIONS During the aura, interictally enhanced intracortical inhibition at the focus was replaced by increased cortical excitability and decreased intracortical inhibition, suggesting increased net intrinsic epileptogenicity during seizure generation in this patient with FCD.
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Affiliation(s)
- Riki Matsumoto
- Department of Neurology, Kyoto Univeristy Graduate School of Medicine, Kyoto, Japan
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Bausch SB. Axonal sprouting of GABAergic interneurons in temporal lobe epilepsy. Epilepsy Behav 2005; 7:390-400. [PMID: 16198153 DOI: 10.1016/j.yebeh.2005.07.019] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2005] [Accepted: 07/23/2005] [Indexed: 11/23/2022]
Abstract
Temporal lobe epilepsy is one of the most common forms of epilepsy. Numerous contributing factors and compensatory mechanisms have been associated with temporal lobe epilepsy. One feature found in both humans and animal models is sprouting of hippocampal principal cell axons, which suggests that axonal sprouting may be a general phenomenon associated with temporal lobe epilepsy. This article highlights the evidence showing that hippocampal GABAergic interneurons also undergo axonal sprouting in temporal lobe epilepsy. The caveats and unanswered questions associated with the current data and the potential physiological consequences of reorganizations in GABAergic circuits are discussed.
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Affiliation(s)
- Suzanne B Bausch
- Department of Pharmacology, Program in Neuroscience, Uniformed Services University, Room C2007, 4301 Jones Bridge Road, Bethesda, MD 20814, USA.
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44
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Valentín A, Alarcón G, Honavar M, García Seoane JJ, Selway RP, Polkey CE, Binnie CD. Single pulse electrical stimulation for identification of structural abnormalities and prediction of seizure outcome after epilepsy surgery: a prospective study. Lancet Neurol 2005; 4:718-26. [PMID: 16239178 DOI: 10.1016/s1474-4422(05)70200-3] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
BACKGROUND Abnormal late responses to single pulse electrical stimulation (SPES) in patients with intracranial recordings can identify epileptogenic cortex. We aimed to investigate the presence of neuropathological abnormalities in abnormal SPES areas and to establish if removal of these areas improved postsurgical seizure control. METHODS We studied abnormal responses to SPES during chronic intracranial recordings in 40 consecutive patients who were thereafter operated on because of refractory epilepsy and had a follow-up period of at least 12 months. FINDINGS 22 patients had abnormal responses to SPES exclusively located in resected regions (96% with favourable outcome), seven had abnormal responses to SPES located in resected and non-resected regions (71% with favourable outcome), three had abnormal responses to SPES exclusively outside the resected region (none with favourable outcome), and eight did not have abnormal responses to SPES (62.5% with favourable outcome). Surgical outcome was significantly better when areas with abnormal responses to SPES were completely resected compared with partial or no removal of abnormal SPES areas (p=0.006). Neuropathological examination showed structural abnormalities in the abnormal SPES areas in 26 of the 29 patients in whom these regions were resected, despite the absence of clear MRI abnormalities in nine patients. INTERPRETATION Abnormal responses to SPES are functional markers of epileptogenic structural abnormalities, and can identify epileptogenic cortex and predict surgical outcome, especially when a frontal or temporal focus is suspected.
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Affiliation(s)
- Antonio Valentín
- Department of Clinical Neurophysiology, Guy's, King's and St Thomas' School of Medicine, London, UK
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Maglóczky Z, Freund TF. Impaired and repaired inhibitory circuits in the epileptic human hippocampus. Trends Neurosci 2005; 28:334-40. [PMID: 15927690 DOI: 10.1016/j.tins.2005.04.002] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2005] [Revised: 03/14/2005] [Accepted: 04/08/2005] [Indexed: 10/25/2022]
Abstract
This review focuses on the epileptic human temporal lobe, primarily on recent findings related to changes in hippocampal GABAergic interneuron circuits that have a central role in epileptogenesis. Relying on correlations to animal studies, we provide a functional interpretation of the different changes in perisomatic inhibition (controlling output synchrony) and dendritic inhibition (controlling input plasticity), and the potential consequences of the loss of interneuron-selective interneurons. The highly heterogeneous, but specific, alterations of GABAergic interneuron circuits have important implications for the pharmacotherapy of epilepsy.
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Affiliation(s)
- Zsófia Maglóczky
- Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, POB 67, H-1450, Hungary
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Holtkamp M, Matzen J, van Landeghem F, Buchheim K, Meierkord H. Transient loss of inhibition precedes spontaneous seizures after experimental status epilepticus. Neurobiol Dis 2005; 19:162-70. [PMID: 15837571 DOI: 10.1016/j.nbd.2004.12.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2004] [Revised: 11/30/2004] [Accepted: 12/02/2004] [Indexed: 10/25/2022] Open
Abstract
The pathophysiological mechanisms that cause spontaneous seizures following status epilepticus are largely unknown. Erosion of inhibition is regarded as an important pathophysiological hallmark of ongoing status epilepticus. Therefore, we investigated if loss of inhibitory functions also plays an important role in the development of spontaneous seizures after status epilepticus. Furthermore, we analyzed possible changes in excitation that might contribute to epileptogenesis. Finally, neuronal cell loss in the dentate gyrus granule cell layer was analyzed. In rats, inhibition and excitation in the dentate gyrus were monitored 1, 4, and 8 weeks after electrically induced self-sustaining status epilepticus (SSSE). Control animals had electrodes implanted either without subsequent stimulation or with stimulation but under barbiturate anesthesia, neither of which resulted in subsequent spontaneous seizures or impairment of inhibition. Following SSSE 80% of animals developed seizures after 8 weeks. A pronounced impairment of inhibition 1 week after SSSE was followed by gradual recovery over 8 weeks. In the dentate gyrus, cell damage was highly variable most likely explaining the heterogeneity of changes in excitatory parameters. Loss of GABAergic inhibition in the dentate gyrus may facilitate initiation of epileptogenesis but impaired inhibition is not required for the process of epileptogenesis to be maintained.
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Affiliation(s)
- M Holtkamp
- Department of Neurology, Charité-Universitätsmedizin Berlin (Campus Mitte), Schumannstr. 20/21, 10117 Berlin, Germany.
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Koch UR, Musshoff U, Pannek HW, Ebner A, Wolf P, Speckmann EJ, Köhling R. Intrinsic excitability, synaptic potentials, and short-term plasticity in human epileptic neocortex. J Neurosci Res 2005; 80:715-26. [PMID: 15880382 DOI: 10.1002/jnr.20498] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Although studies of epileptic human hippocampus suggest changes of synaptic and intrinsic excitability, few changes, save the appearance of spontaneous field/synaptic potentials, are known in epileptic neocortical tissue. However, invasive EEG and histological studies suggest that neocortical tissue, even in mesial temporal lobe epilepsy, can play an important role as an irritative zone or extrahippocampal focus. We hypothesized that intrinsic neuronal and synaptic excitability, as well as short-term plasticity, are altered in neocortical areas, particularly with elevated K+ levels as occur during seizures. We analyzed neuronal firing properties, synaptic responses, and paired-pulse plasticity in human neocortical slices from tissue resected during epilepsy surgery, both under normal and under pathological conditions, i.e., after elevating K+ (4/8 mM), with rat neocortical slices as controls. Neuronal firing properties were not different. We did find, however, alterations of synaptic responsiveness in epileptic tissue, i.e., an elevated network excitability with K+ elevations, and reduction of paired-pulse depression.
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Affiliation(s)
- Uwe-Robert Koch
- Institute of Physiology, University of Münster, Münster, Germany
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Shao LR, Dudek FE. Changes in mIPSCs and sIPSCs after kainate treatment: evidence for loss of inhibitory input to dentate granule cells and possible compensatory responses. J Neurophysiol 2005; 94:952-60. [PMID: 15772233 DOI: 10.1152/jn.01342.2004] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
How inhibition is altered after status epilepticus and the role of inhibition during epileptogenesis remain unsettled issues. The present study examined acute (4-7 days) and chronic (>3 mo) changes of GABA(A) receptor-mediated inhibitory synaptic input to dentate granule cells after kainate-induced status epilepticus. Whole cell patch-clamp techniques were used to record spontaneous and miniature inhibitory postsynaptic currents (sIPSCs and mIPSCs) in the presence of 6,7-dinitroquinoxaline-2,3-dione and dl-2-amino-5-phosphonopentanoic acid to block glutamatergic excitatory synaptic transmission. In both groups, mean sIPSC frequency of dentate granule cells from the saline- and kainate-treated rats was not significantly different. However, mIPSC frequency from the kainate-treated rats of both groups was approximately 30% lower than that of the respective saline controls. The mean amplitude of sIPSCs and mIPSCs from kainate-treated rats was not reduced in either the acute or chronic groups. The mean 10-90% rise time of IPSCs was not altered in kainate-treated rats, but the decay time constant was slightly longer than in controls, and the charge transfer 4-7 days after kainate treatment was significantly larger. The similar reduction of mIPSC frequency (i.e., approximately 30%) in the two groups of kainate-treated rats suggests a decreased inhibitory input to dentate granule cells (presumably due to a partial loss of inhibitory interneurons that innervate them) without recovery during epileptogenesis. The lack of effect on sIPSC frequency and the decreased mIPSC frequency in both groups suggests a possible compensatory increase in firing rate of interneurons, which may involve a hypothetical reduction of inhibitory input to the remaining interneurons.
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Affiliation(s)
- Li-Rong Shao
- Department of Biomedical Sciences, Anatomy and Neurobiology Section, Colorado State University, Fort Collins, CO 80523, USA
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Kalitzin S, Velis D, Suffczynski P, Parra J, da Silva FL. Electrical brain-stimulation paradigm for estimating the seizure onset site and the time to ictal transition in temporal lobe epilepsy. Clin Neurophysiol 2005; 116:718-28. [PMID: 15721087 DOI: 10.1016/j.clinph.2004.08.021] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2004] [Revised: 08/04/2004] [Accepted: 08/19/2004] [Indexed: 11/19/2022]
Abstract
OBJECTIVE To explore and validate a novel stimulation and analysis paradigm proposed to monitor spatial distribution and temporal changes of the excitability state in patients with temporal lobe epilepsy (TLE). METHODS We use intermittent pulse stimulation in the frequency range 10-20Hz. A quantitative measure of spectral phase de-modulation, the relative phase clustering index (rPCI) was applied to the evoked EEG signals, measured from electrodes implanted in the hippocampal formation. RESULTS We found that in the interictal periods, high values of rPCI recorded from specific sites were correlated with the most probable seizure onset sites (SOS). Furthermore we found that high values of rPCI from certain locations correlated with shorter time intervals to the next seizure. CONCLUSIONS Our clinical findings indicate that although the precise moment of ictal transitions is in general unpredictable, it may be possible to estimate the probability of occurrence of some epileptic seizures. SIGNIFICANCE The use of the rPCI for probabilistic forecasting of upcoming epileptic seizures is warranted. rPCI measurements may be used to guide interventions with the aim of modifying local tissue excitability that ultimately might prevent ictal transitions.
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Affiliation(s)
- S Kalitzin
- Medical Physics Department, Dutch Epilepsy Clinics Foundation, Achterweg 5, 2103 SW Heemstede, The Netherlands.
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Harvey BD, Sloviter RS. Hippocampal granule cell activity and c-Fos expression during spontaneous seizures in awake, chronically epileptic, pilocarpine-treated rats: Implications for hippocampal epileptogenesis. J Comp Neurol 2005; 488:442-63. [PMID: 15973680 DOI: 10.1002/cne.20594] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The process of postinjury hippocampal epileptogenesis may involve gradually developing dentate granule cell hyperexcitability caused by neuron loss and synaptic reorganization. We tested this hypothesis by repeatedly assessing granule cell excitability after pilocarpine-induced status epilepticus (SE) and monitoring granule cell behavior during 235 spontaneous seizures in awake, chronically implanted rats. During the first week post-SE, granule cells exhibited diminished paired-pulse suppression and decreased seizure discharge thresholds in response to afferent stimulation. Spontaneous seizures often began during the first week after SE, recruited granule cell discharges that followed behavioral seizure onsets, and evoked c-Fos expression in all hippocampal neurons. Paired-pulse suppression and epileptiform discharge thresholds increased gradually after SE, eventually becoming abnormally elevated. In the chronic epileptic state, interictal granule cell hyperinhibition extended to the ictal state; granule cells did not discharge synchronously before any of 191 chronic seizures. Instead, granule cells generated only low-frequency voltage fluctuations (presumed "field excitatory postsynaptic potentials") during 89% of chronic seizures. Granule cell epileptiform discharges were recruited during 11% of spontaneous seizures, but these occurred only at the end of each behavioral seizure. Hippocampal c-Fos after chronic seizures was expressed primarily by inhibitory interneurons. Thus, granule cells became progressively less excitable, rather than hyperexcitable, as mossy fiber sprouting progressed and did not initiate the spontaneous behavioral seizures. These findings raise doubts about dentate granule cells as a source of spontaneous seizures in rats subjected to prolonged SE and suggest that dentate gyrus neuron loss and mossy fiber sprouting are not primary epileptogenic mechanisms in this animal model.
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Affiliation(s)
- Brian D Harvey
- Department of Pharmacology, University of Arizona College of Medicine, Tucson, Arizona 85724, USA
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