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Lai S, Keeley J, Nolan D, Kring E, Rickard N, Froling AS, Obeid R. Electroencephalographic Patterns on Follow-Up Visits in Extremely Premature Infants With Periventricular Leukomalacia: An Observational Study. Pediatr Neurol 2024; 157:127-133. [PMID: 38917516 DOI: 10.1016/j.pediatrneurol.2024.05.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Revised: 04/24/2024] [Accepted: 05/22/2024] [Indexed: 06/27/2024]
Abstract
BACKGROUND Periventricular leukomalacia (PVL) is a common brain injury in premature infants, and epilepsy remains a significant complication. One concerning electroencephalographic (EEG) pattern found is developmental and/or epileptic encephalopathy with spike-and-wave activation in sleep (DEE-SWAS). This pattern is associated with persistent neuropsychological and motor deficits, even without a diagnosis of epilepsy. The purpose of this study is to identify the relationships between various PVL grades and EEG patterns in this population on follow-up visits, especially the occurrence of DEE-SWAS pattern on EEG. METHODS This is a retrospective study of <36 weeks gestational age newborns who were followed in the neurodevelopmental clinic at Corewell Health East/Corewell Health Children's Hospital in Royal Oak, Michigan, between 2020 and 2022. Patients' demographics along with prematurity complications, diagnostic head ultrasound (HUS), and EEG studies were reviewed and graded. EEG studies are usually ordered when seizures were suspected. RESULTS A total of 155 newborns met the inclusion criteria. Twenty-six patients had PVL. Nine patients had grade 2 to 3 PVL based on HUS review. EEG was performed on 15 patients with PVL at a mean age of 22 months. More severe PVL grades were significantly associated with worse EEG patterns (P = 0.005). Five patients had DEE-SWAS pattern on EEG, all of whom had grade 2 or 3 PVL. Epilepsy was eventually diagnosed in three infants with PVL. CONCLUSIONS EEG can help identify important abnormal electrographic patterns in premature infants with PVL early in life; this might give a window of opportunity to intervene early and improve long-term developmental outcomes in this population.
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Affiliation(s)
- Sammie Lai
- Division of Child and Adolescent Neurology, Mayo Clinic College of Medicine and Science, Jacksonville, Florida; Department of Pediatrics, University of Florida College of Medicine, Jacksonville, Florida.
| | - Jacob Keeley
- Oakland University William Beaumont School of Medicine, Auburn Hills, Michigan
| | - Danielle Nolan
- Oakland University William Beaumont School of Medicine, Auburn Hills, Michigan; Division of Pediatric Neurology, Department of Pediatrics, Corewell Health East/Corewell Health Children's, Royal Oak, Michigan
| | - Elizabeth Kring
- Division of Pediatric Neurology, Department of Pediatrics, Corewell Health East/Corewell Health Children's, Royal Oak, Michigan
| | - Nicole Rickard
- Department of Pediatric Rehabilitation, Corewell Health East/Corewell Health Children's, Royal Oak, Michigan
| | - Amanda S Froling
- Department of Pediatric Rehabilitation, Corewell Health East/Corewell Health Children's, Royal Oak, Michigan
| | - Rawad Obeid
- Oakland University William Beaumont School of Medicine, Auburn Hills, Michigan; Division of Pediatric Neurology, Department of Pediatrics, Corewell Health East/Corewell Health Children's, Royal Oak, Michigan
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2
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Jannati A, Oberman LM, Rotenberg A, Pascual-Leone A. Assessing the mechanisms of brain plasticity by transcranial magnetic stimulation. Neuropsychopharmacology 2023; 48:191-208. [PMID: 36198876 PMCID: PMC9700722 DOI: 10.1038/s41386-022-01453-8] [Citation(s) in RCA: 30] [Impact Index Per Article: 30.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Revised: 09/01/2022] [Accepted: 09/02/2022] [Indexed: 11/10/2022]
Abstract
Transcranial magnetic stimulation (TMS) is a non-invasive technique for focal brain stimulation based on electromagnetic induction where a fluctuating magnetic field induces a small intracranial electric current in the brain. For more than 35 years, TMS has shown promise in the diagnosis and treatment of neurological and psychiatric disorders in adults. In this review, we provide a brief introduction to the TMS technique with a focus on repetitive TMS (rTMS) protocols, particularly theta-burst stimulation (TBS), and relevant rTMS-derived metrics of brain plasticity. We then discuss the TMS-EEG technique, the use of neuronavigation in TMS, the neural substrate of TBS measures of plasticity, the inter- and intraindividual variability of those measures, effects of age and genetic factors on TBS aftereffects, and then summarize alterations of TMS-TBS measures of plasticity in major neurological and psychiatric disorders including autism spectrum disorder, schizophrenia, depression, traumatic brain injury, Alzheimer's disease, and diabetes. Finally, we discuss the translational studies of TMS-TBS measures of plasticity and their therapeutic implications.
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Affiliation(s)
- Ali Jannati
- Neuromodulation Program, Division of Epilepsy and Clinical Neurophysiology, Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA.
- F. M. Kirby Neurobiology Center, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA.
- Berenson-Allen Center for Noninvasive Brain Stimulation, Division of Cognitive Neurology, Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA.
| | - Lindsay M Oberman
- Center for Neuroscience and Regenerative Medicine, Henry M. Jackson Foundation for the Advancement of Military Medicine, Bethesda, MD, USA
| | - Alexander Rotenberg
- Neuromodulation Program, Division of Epilepsy and Clinical Neurophysiology, Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
- F. M. Kirby Neurobiology Center, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
- Berenson-Allen Center for Noninvasive Brain Stimulation, Division of Cognitive Neurology, Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA
| | - Alvaro Pascual-Leone
- Department of Neurology, Harvard Medical School, Boston, MA, USA.
- Hinda and Arthur Marcus Institute for Aging Research and Deanna and Sidney Wolk Center for Memory Health, Hebrew SeniorLife, Boston, MA, USA.
- Guttmann Brain Health Institute, Institut Guttmann, Barcelona, Spain.
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3
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Reorganization of Parvalbumin Immunopositive Perisomatic Innervation of Principal Cells in Focal Cortical Dysplasia Type IIB in Human Epileptic Patients. Int J Mol Sci 2022; 23:ijms23094746. [PMID: 35563137 PMCID: PMC9100614 DOI: 10.3390/ijms23094746] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2022] [Revised: 04/21/2022] [Accepted: 04/22/2022] [Indexed: 02/04/2023] Open
Abstract
Focal cortical dysplasia (FCD) is one of the most common causes of drug-resistant epilepsy. As several studies have revealed, the abnormal functioning of the perisomatic inhibitory system may play a role in the onset of seizures. Therefore, we wanted to investigate whether changes of perisomatic inhibitory inputs are present in FCD. Thus, the input properties of abnormal giant- and control-like principal cells were examined in FCD type IIB patients. Surgical samples were compared to controls from the same cortical regions with short postmortem intervals. For the study, six subjects were selected/each group. The perisomatic inhibitory terminals were quantified in parvalbumin and neuronal nuclei double immunostained sections using a confocal fluorescent microscope. The perisomatic input of giant neurons was extremely abundant, whereas control-like cells of the same samples had sparse inputs. A comparison of pooled data shows that the number of parvalbumin-immunopositive perisomatic terminals contacting principal cells was significantly larger in epileptic cases. The analysis showed some heterogeneity among epileptic samples. However, five out of six cases had significantly increased perisomatic input. Parameters of the control cells were homogenous. The reorganization of the perisomatic inhibitory system may increase the probability of seizure activity and might be a general mechanism of abnormal network activity.
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Ragot A, Luhmann HJ, Dipper-Wawra M, Heinemann U, Holtkamp M, Fidzinski P. Pathology-selective antiepileptic effects in the focal freeze-lesion rat model of malformation of cortical development. Exp Neurol 2021; 343:113776. [PMID: 34058228 DOI: 10.1016/j.expneurol.2021.113776] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Revised: 05/13/2021] [Accepted: 05/27/2021] [Indexed: 01/29/2023]
Abstract
Malformations of cortical development (MCD) represent a group of rare diseases with severe clinical presentation as epileptic and pharmacoresistant encephalopathies. Morphological studies in tissue from MCD patients have revealed reduced GABAergic efficacy and increased intracellular chloride concentration in neuronal cells as important pathophysiological mechanisms in MCD. Also, in various animal models, alterations of GABAergic inhibition have been postulated as a predominant factor contributing to perilesional hyperexcitability. Along with this line, the NKCC1 inhibitor bumetanide has been postulated as a potential drug for treatment of epilepsy, mediating its antiepileptic effect by reduction of the intracellular chloride and increased inhibitory efficacy of GABAergic transmission. In the present study, we focused on the focal freeze-lesion model of MCD to compare antiepileptic drugs with distinct mechanisms of action, including NKCC1 inhibition by bumetanide. For this purpose, we combined electrophysiological and optical methods in slice preparations and assessed the properties of seizure like events (SLE) induced by 4-aminopyridine. In freeze-lesioned but not control slices, SLE onset was confined to the perilesional area, confirming that this region is hyperexcitable and likely triggers pathological activity. Bumetanide selectively reduced epileptic activity in lesion-containing slices but not in slices from sham-treated control rats. Moreover, bumetanide caused a shift in the SLE onset site away from the perilesional area. In contrast, effects of other antiepileptic drugs including carbamazepine, lacosamide, acezatolamide and zonisamide occurred mostly independently of the lesion and did not result in a shift of the onset region. Our work adds evidence for the functional relevance of chloride homeostasis in the pathophysiology of microgyrus formation as represented in the focal freeze-lesion model. Further studies in different MCD models and human tissue will be required to validate the effects across different MCD subtypes and species and to assess the translational value of our findings.
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Affiliation(s)
- Aliénor Ragot
- Charité - Universitätsmedizin Berlin, Clinical and Experimental Epileptology, Department of Neurology, Charitéplatz 1, 10117 Berlin, Germany
| | - Heiko J Luhmann
- Institute of Physiology, University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Matthias Dipper-Wawra
- Charité - Universitätsmedizin Berlin, Clinical and Experimental Epileptology, Department of Neurology, Charitéplatz 1, 10117 Berlin, Germany
| | - Uwe Heinemann
- Charité - Universitätsmedizin Berlin, Institute of Neurophysiology, Charitéplatz 1, 10117 Berlin, Germany
| | - Martin Holtkamp
- Charité - Universitätsmedizin Berlin, Clinical and Experimental Epileptology, Department of Neurology, Charitéplatz 1, 10117 Berlin, Germany; Epilepsy-Center Berlin-Brandenburg, Institute for Diagnostics of Epilepsy, Berlin, Germany
| | - Pawel Fidzinski
- Charité - Universitätsmedizin Berlin, Clinical and Experimental Epileptology, Department of Neurology, Charitéplatz 1, 10117 Berlin, Germany; Epilepsy-Center Berlin-Brandenburg, Institute for Diagnostics of Epilepsy, Berlin, Germany; Berlin Institute of Health at Charité -Universitätsmedizin Berlin, NeuroCure Clinical Research Center, Charitéplatz 1, 10117 Berlin, Germany.
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5
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Nakatani M, Matsumoto R, Kobayashi K, Hitomi T, Inouchi M, Matsuhashi M, Kinoshita M, Kikuchi T, Yoshida K, Kunieda T, Miyamoto S, Takahashi R, Hattori N, Ikeda A. Electrical cortical stimulations modulate spike and post-spike slow-related high-frequency activities in human epileptic foci. Clin Neurophysiol 2020; 131:1741-1754. [PMID: 32504935 DOI: 10.1016/j.clinph.2020.03.042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2019] [Revised: 03/16/2020] [Accepted: 03/30/2020] [Indexed: 10/24/2022]
Abstract
OBJECTIVE Using interictal epileptiform discharges (IEDs), consisting of spikes and post-spike slow waves (PSSs), and IED-related high-frequency activities (HFAs), we elucidated inhibitory effects of electrical cortical stimulation (ECS) on human epileptic foci. METHODS We recruited 8 patients with intractable focal epilepsy, and 50-Hz ECS was applied to the seizure-onset zone (SOZ) and non-SOZ. Before (5-min) and after (20-min) ECS, we evaluated the number of IED, the amplitudes of spikes and PSSs, spike-related HFA power, and PSS-related low gamma (30-50 Hz) activities. RESULTS SOZ stimulation significantly decreased the number of IEDs and amplitude of spikes. Spike-related HFA power values in fast ripple (200-300 Hz) and ripple (80-150 Hz) bands were significantly suppressed only by SOZ stimulation in 4 and 3 patients, respectively. Among 4 patients with discrete PSSs, the amplitude ratio of spike/PSS decreased and the PSS-related low gamma activity power increased significantly in 2 patients and marginally in 1 patient. CONCLUSIONS ECS potentially modulates cortical excitability by reducing excitation and increasing inhibition, and monitoring IED-related HFAs may help achieve the optimal effects of ECS. SIGNIFICANCE IED and IED-related HFAs are dynamic, potential surrogate markers for epileptic excitability during the interictal period.
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Affiliation(s)
- Mitsuyoshi Nakatani
- Department of Neurology, Kyoto University Graduate School of Medicine, Kyoto, Japan; Department of Neurology, Juntendo University Graduate School of Medicine, Tokyo, Japan
| | - Riki Matsumoto
- Department of Neurology, Kyoto University Graduate School of Medicine, Kyoto, Japan; Division of Neurology, Kobe University Graduate School of Medicine, Kobe, Japan.
| | - Katsuya Kobayashi
- Department of Neurology, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Takefumi Hitomi
- Department of Laboratory Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Morito Inouchi
- Department of Epilepsy, Movement Disorders and Physiology, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Masao Matsuhashi
- Department of Epilepsy, Movement Disorders and Physiology, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Masako Kinoshita
- Department of Neurology, National Hospital Organization Utano National Hospital, Kyoto, Japan
| | - Takayuki Kikuchi
- Department of Neurosurgery, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Kazumichi Yoshida
- Department of Neurosurgery, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Takeharu Kunieda
- Department of Neurosurgery, Kyoto University Graduate School of Medicine, Kyoto, Japan; Department of Neurosurgery, Ehime University Graduate School of Medicine, Ehime, Japan
| | - Susumu Miyamoto
- Department of Neurosurgery, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Ryosuke Takahashi
- Department of Neurology, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Nobutaka Hattori
- Department of Neurology, Juntendo University Graduate School of Medicine, Tokyo, Japan
| | - Akio Ikeda
- Department of Epilepsy, Movement Disorders and Physiology, Kyoto University Graduate School of Medicine, Kyoto, Japan.
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Alhourani A, Fish KN, Wozny TA, Sudhakar V, Hamilton RL, Richardson RM. GABA bouton subpopulations in the human dentate gyrus are differentially altered in mesial temporal lobe epilepsy. J Neurophysiol 2019; 123:392-406. [PMID: 31800363 DOI: 10.1152/jn.00523.2018] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Medically intractable temporal lobe epilepsy is a devastating disease, for which surgical removal of the seizure onset zone is the only known cure. Multiple studies have found evidence of abnormal dentate gyrus network circuitry in human mesial temporal lobe epilepsy (MTLE). Principal neurons within the dentate gyrus gate entorhinal input into the hippocampus, providing a critical step in information processing. Crucial to that role are GABA-expressing neurons, particularly parvalbumin (PV)-expressing basket cells (PVBCs) and chandelier cells (PVChCs), which provide strong, temporally coordinated inhibitory signals. Alterations in PVBC and PVChC boutons have been described in epilepsy, but the value of these studies has been limited due to methodological hurdles associated with studying human tissue. We developed a multilabel immunofluorescence confocal microscopy and a custom segmentation algorithm to quantitatively assess PVBC and PVChC bouton densities and to infer relative synaptic protein content in the human dentate gyrus. Using en bloc specimens from MTLE subjects with and without hippocampal sclerosis, paired with nonepileptic controls, we demonstrate the utility of this approach for detecting cell-type specific synaptic alterations. Specifically, we found increased density of PVBC boutons, while PVChC boutons decreased significantly in the dentate granule cell layer of subjects with hippocampal sclerosis compared with matched controls. In contrast, bouton densities for either PV-positive cell type did not differ between epileptic subjects without sclerosis and matched controls. These results may explain conflicting findings from previous studies that have reported both preserved and decreased PV bouton densities and establish a new standard for quantitative assessment of interneuron boutons in epilepsy.NEW & NOTEWORTHY A state-of-the-art, multilabel immunofluorescence confocal microscopy and custom segmentation algorithm technique, developed previously for studying synapses in the human prefrontal cortex, was modified to study the hippocampal dentate gyrus in specimens surgically removed from patients with temporal lobe epilepsy. The authors discovered that chandelier and basket cell boutons in the human dentate gyrus are differentially altered in mesial temporal lobe epilepsy.
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Affiliation(s)
- Ahmad Alhourani
- Department of Neurological Surgery, University of Louisville School of Medicine, Louisville, Kentucky
| | - Kenneth N Fish
- Department of Psychiatry, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Thomas A Wozny
- Department of Neurological Surgery, University of California, San Francisco, California
| | - Vivek Sudhakar
- Department of Neurological Surgery, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Ronald L Hamilton
- Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - R Mark Richardson
- Department of Neurological Surgery, Massachusetts General Hospital, Boston, Massachusetts.,Harvard Medical School, Boston, Massachusetts
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7
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Kassiri H, Chen FD, Salam MT, Chang M, Vatankhahghadim B, Carlen P, Valiante TA, Genov R. Arbitrary-Waveform Electro-Optical Intracranial Neurostimulator With Load-Adaptive High-Voltage Compliance. IEEE Trans Neural Syst Rehabil Eng 2019; 27:582-593. [PMID: 30802868 DOI: 10.1109/tnsre.2019.2900455] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
A hybrid 16-channel current-mode and the 8-channel optical implantable neurostimulating system is presented. The system generates arbitrary-waveform charge-balanced current-mode electrical pulses with an amplitude ranging from 50 [Formula: see text] to 10 mA. An impedance monitoring feedback loop is employed to automatically adjust the supply voltage, yielding a load-optimized power dissipation. The 8-channel optical stimulator drives an array of LEDs, each with a maximum of 25 mA current amplitude, and reuses the arbitrary-waveform generation function of the electrical stimulator. The LEDs are assembled within a custom-made 4×4 ECoG grid electrode array, enabling precise optical stimulation of neurons with a 300 [Formula: see text] pitch between the LEDs and simultaneous monitoring of the neural response by the ECoG electrode, at different distances of the stimulation site. The hybrid stimulation system is implemented on a mini-PCB, and receives power and stimulation commands inductively through a second board and a coil stacked on top of it. The entire system is sized at 3×2 . 5×1 cm3 and weighs 7 grams. The system efficacy for electrical and optical stimulation is validated in-vivo using separate chronic and acute experiments.
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8
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Hsieh TH, Lee HHC, Hameed MQ, Pascual-Leone A, Hensch TK, Rotenberg A. Trajectory of Parvalbumin Cell Impairment and Loss of Cortical Inhibition in Traumatic Brain Injury. Cereb Cortex 2018; 27:5509-5524. [PMID: 27909008 DOI: 10.1093/cercor/bhw318] [Citation(s) in RCA: 58] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Accepted: 09/21/2016] [Indexed: 11/13/2022] Open
Abstract
Many neuropsychiatric symptoms that follow traumatic brain injury (TBI), including mood disorders, sleep disturbance, chronic pain, and posttraumatic epilepsy (PTE) are attributable to compromised cortical inhibition. However, the temporal trajectory of cortical inhibition loss and its underlying mechanisms are not known. Using paired-pulse transcranial magnetic stimulation (ppTMS) and immunohistochemistry, we tracked functional and cellular changes of cortical inhibitory network elements after fluid-percussion injury (FPI) in rats. ppTMS revealed a progressive loss of cortical inhibition as early as 2 weeks after FPI. This profile paralleled the increasing levels of cortical oxidative stress, which was accompanied by a gradual loss of parvalbumin (PV) immunoreactivity in perilesional cortex. Preceding the PV loss, we identified a degradation of the perineuronal net (PNN)-a specialized extracellular structure enwrapping cortical PV-positive (PV+) inhibitory interneurons which binds the PV+ cell maintenance factor, Otx2. The trajectory of these impairments underlies the reduced inhibitory tone, which can contribute to posttraumatic neurological conditions, such as PTE. Taken together, our results highlight the use of ppTMS as a biomarker to track the course of cortical inhibitory dysfunction post-TBI. Moreover, the neuroprotective role of PNNs on PV+ cell function suggests antioxidant treatment or Otx2 enhancement as a promising prophylaxis for post-TBI symptoms.
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Affiliation(s)
- Tsung-Hsun Hsieh
- Neuromodulation Program, Division of Epilepsy and Clinical Neurophysiology, Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA.,Department of Physical Therapy and Graduate Institute of Rehabilitation Science, College of Medicine, Chang Gung University, Taoyuan 33302, Taiwan.,Neuroscience Research Center, Chang Gung Memorial Hospital, Linkou Medical Center, Taoyuan 33305, Taiwan
| | - Henry Hing Cheong Lee
- Department of Neurology, F.M. Kirby Neurobiology Center, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA
| | - Mustafa Qadir Hameed
- Neuromodulation Program, Division of Epilepsy and Clinical Neurophysiology, Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA.,Department of Neurology, F.M. Kirby Neurobiology Center, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA.,Department of Neurosurgery, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA
| | - Alvaro Pascual-Leone
- Berenson-Allen Center for Noninvasive Brain Stimulation, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02115, USA
| | - Takao K Hensch
- Department of Neurology, F.M. Kirby Neurobiology Center, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA.,Department of Molecular and Cellular Biology, Center for Brain Science, Harvard University, MA 02138, USA
| | - Alexander Rotenberg
- Neuromodulation Program, Division of Epilepsy and Clinical Neurophysiology, Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA.,Department of Neurology, F.M. Kirby Neurobiology Center, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA.,Berenson-Allen Center for Noninvasive Brain Stimulation, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02115, USA
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9
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Michelson NJ, Vazquez AL, Eles JR, Salatino JW, Purcell EK, Williams JJ, Cui XT, Kozai TDY. Multi-scale, multi-modal analysis uncovers complex relationship at the brain tissue-implant neural interface: new emphasis on the biological interface. J Neural Eng 2018; 15:033001. [PMID: 29182149 PMCID: PMC5967409 DOI: 10.1088/1741-2552/aa9dae] [Citation(s) in RCA: 89] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
OBJECTIVE Implantable neural electrode devices are important tools for neuroscience research and have an increasing range of clinical applications. However, the intricacies of the biological response after implantation, and their ultimate impact on recording performance, remain challenging to elucidate. Establishing a relationship between the neurobiology and chronic recording performance is confounded by technical challenges related to traditional electrophysiological, material, and histological limitations. This can greatly impact the interpretations of results pertaining to device performance and tissue health surrounding the implant. APPROACH In this work, electrophysiological activity and immunohistological analysis are compared after controlling for motion artifacts, quiescent neuronal activity, and material failure of devices in order to better understand the relationship between histology and electrophysiological outcomes. MAIN RESULTS Even after carefully accounting for these factors, the presence of viable neurons and lack of glial scarring does not convey single unit recording performance. SIGNIFICANCE To better understand the biological factors influencing neural activity, detailed cellular and molecular tissue responses were examined. Decreases in neural activity and blood oxygenation in the tissue surrounding the implant, shift in expression levels of vesicular transporter proteins and ion channels, axon and myelin injury, and interrupted blood flow in nearby capillaries can impact neural activity around implanted neural interfaces. Combined, these tissue changes highlight the need for more comprehensive, basic science research to elucidate the relationship between biology and chronic electrophysiology performance in order to advance neural technologies.
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Affiliation(s)
| | - Alberto L Vazquez
- Department of Bioengineering, University of Pittsburgh
- Department of Radiology, University of Pittsburgh
- Center for the Neural Basis of Cognition, University of Pittsburgh
- Center for Neuroscience, University of Pittsburgh
| | - James R Eles
- Department of Bioengineering, University of Pittsburgh
- Center for the Neural Basis of Cognition, University of Pittsburgh
| | | | - Erin K Purcell
- Department of Biomedical Engineering, Michigan State University
| | | | - X. Tracy Cui
- Department of Bioengineering, University of Pittsburgh
- Center for the Neural Basis of Cognition, University of Pittsburgh
- McGowan Institute of Regenerative Medicine, University of Pittsburgh
| | - Takashi DY Kozai
- Department of Bioengineering, University of Pittsburgh
- Center for the Neural Basis of Cognition, University of Pittsburgh
- Center for Neuroscience, University of Pittsburgh
- McGowan Institute of Regenerative Medicine, University of Pittsburgh
- NeuroTech Center, University of Pittsburgh Brain Institute
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10
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Chang M, Dian JA, Dufour S, Wang L, Moradi Chameh H, Ramani M, Zhang L, Carlen PL, Womelsdorf T, Valiante TA. Brief activation of GABAergic interneurons initiates the transition to ictal events through post-inhibitory rebound excitation. Neurobiol Dis 2017; 109:102-116. [PMID: 29024712 DOI: 10.1016/j.nbd.2017.10.007] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2016] [Revised: 09/12/2017] [Accepted: 10/08/2017] [Indexed: 12/14/2022] Open
Abstract
Activation of γ-aminobutyric acid (GABAA) receptors have been associated with the onset of epileptiform events. To investigate if a causal relationship exists between GABAA receptor activation and ictal event onset, we activated inhibitory GABAergic networks in the superficial layer (2/3) of the somatosensory cortex during hyperexcitable conditions using optogenetic techniques in mice expressing channelrhodopsin-2 in all GABAergic interneurons. We found that a brief 30ms light pulse reliably triggered either an interictal-like event (IIE) or ictal-like ("ictal") event in the in vitro cortical 4-Aminopyridine (4-AP) slice model. The link between light pulse and epileptiform event onset was lost following blockade of GABAA receptors with bicuculline methiodide. Additionally, recording the chronological sequence of events following a light pulse in a variety of configurations (whole-cell, gramicidin-perforated patch, and multi-electrode array) demonstrated an initial hyperpolarization followed by post-inhibitory rebound spiking and a subsequent slow depolarization at the transition to epileptiform activity. Furthermore, the light-triggered ictal events were independent of the duration or intensity of the initiating light pulse, suggesting an underlying regenerative mechanism. Moreover, we demonstrated that brief GABAA receptor activation can initiate ictal events in the in vivo 4-AP mouse model, in another common in vitro model of epileptiform activity, and in neocortical tissue resected from epilepsy patients. Our findings reveal that the synchronous activation of GABAergic interneurons is a robust trigger for ictal event onset in hyperexcitable cortical networks.
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Affiliation(s)
- Michael Chang
- Division of Fundamental Neurobiology, Krembil Research Institute, Toronto, ON, Canada; Institute of Medical Science, Faculty of Medicine, University of Toronto, Toronto, ON, Canada
| | - Joshua A Dian
- Division of Fundamental Neurobiology, Krembil Research Institute, Toronto, ON, Canada; Department of Electrical and Computer Engineering, University of Toronto, Toronto, ON, Canada
| | - Suzie Dufour
- Division of Fundamental Neurobiology, Krembil Research Institute, Toronto, ON, Canada; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, Canada
| | - Lihua Wang
- Division of Fundamental Neurobiology, Krembil Research Institute, Toronto, ON, Canada
| | - Homeira Moradi Chameh
- Division of Fundamental Neurobiology, Krembil Research Institute, Toronto, ON, Canada
| | - Meera Ramani
- Division of Fundamental Neurobiology, Krembil Research Institute, Toronto, ON, Canada
| | - Liang Zhang
- Division of Fundamental Neurobiology, Krembil Research Institute, Toronto, ON, Canada; Division of Neurology, Department of Medicine, University of Toronto, Toronto, ON, Canada
| | - Peter L Carlen
- Division of Fundamental Neurobiology, Krembil Research Institute, Toronto, ON, Canada; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, Canada; Division of Neurology, Department of Medicine, University of Toronto, Toronto, ON, Canada; Department of Physiology, University of Toronto, Toronto, ON, Canada; Institute of Medical Science, Faculty of Medicine, University of Toronto, Toronto, ON, Canada
| | - Thilo Womelsdorf
- Department of Psychology, Vanderbilt University, Nashville, TN, USA
| | - Taufik A Valiante
- Division of Fundamental Neurobiology, Krembil Research Institute, Toronto, ON, Canada; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, Canada; Division of Neurosurgery, Department of Surgery, University of Toronto, Toronto, ON, Canada; Institute of Medical Science, Faculty of Medicine, University of Toronto, Toronto, ON, Canada.
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11
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Takahashi DK, Gu F, Parada I, Vyas S, Prince DA. Aberrant excitatory rewiring of layer V pyramidal neurons early after neocortical trauma. Neurobiol Dis 2016; 91:166-81. [PMID: 26956396 DOI: 10.1016/j.nbd.2016.03.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2016] [Revised: 02/24/2016] [Accepted: 03/02/2016] [Indexed: 12/27/2022] Open
Abstract
Lesioned neuronal circuits form new functional connections after a traumatic brain injury (TBI). In humans and animal models, aberrant excitatory connections that form after TBI may contribute to the pathogenesis of post-traumatic epilepsy. Partial neocortical isolation ("undercut" or "UC") leads to altered neuronal circuitry and network hyperexcitability recorded in vivo and in brain slices from chronically lesioned neocortex. Recent data suggest a critical period for maladaptive excitatory circuit formation within the first 3days post UC injury (Graber and Prince 1999, 2004; Li et al. 2011, 2012b). The present study focuses on alterations in excitatory connectivity within this critical period. Immunoreactivity (IR) for growth-associated protein (GAP)-43 was increased in the UC cortex 3days after injury. Some GAP-43-expressing excitatory terminals targeted the somata of layer V pyramidal (Pyr) neurons, a domain usually innervated predominantly by inhibitory terminals. Immunocytochemical analysis of pre- and postsynaptic markers showed that putative excitatory synapses were present on somata of these neurons in UC neocortex. Excitatory postsynaptic currents from UC layer V Pyr cells displayed properties consistent with perisomatic inputs and also reflected an increase in the number of synaptic contacts. Laser scanning photostimulation (LSPS) experiments demonstrated reorganized excitatory connectivity after injury within the UC. Concurrent with these changes, spontaneous epileptiform bursts developed in UC slices. Results suggest that aberrant reorganization of excitatory connectivity contributes to early neocortical hyperexcitability in this model. The findings are relevant for understanding the pathophysiology of neocortical post-traumatic epileptogenesis and are important in terms of the timing of potential prophylactic treatments.
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Affiliation(s)
- D Koji Takahashi
- Epilepsy Research Laboratories, Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA 94305, United States
| | - Feng Gu
- Epilepsy Research Laboratories, Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA 94305, United States
| | - Isabel Parada
- Epilepsy Research Laboratories, Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA 94305, United States
| | - Shri Vyas
- Epilepsy Research Laboratories, Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA 94305, United States
| | - David A Prince
- Epilepsy Research Laboratories, Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA 94305, United States.
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12
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Abstract
All brain normal or pathological activities occur in one of the states of vigilance: wake, slow-wave sleep, or REM sleep. Neocortical seizures preferentially occur during slow-wave sleep. We provide a description of neuronal behavior and mechanisms mediating such a behavior within neocortex taking place in natural states of vigilance as well as during seizures pointing to similarities and differences exhibited during sleep and seizures. A concept of epileptic focus is described using a model of cortical undercut, because in that model, the borders of the focus are well defined. In this model, as in other models of acquired epilepsy, the main factor altering excitability is deafferentation, which upregulates neuronal excitability that promotes generation of seizures. Periods of disfacilitation recorded during slow-wave sleep further upregulate neuronal excitability. It appears that the state of neurons and neuronal network in the epileptic focus produced by deafferentation are such that seizures cannot be generated there. Instead, seizures always start around the perimeter of the undercut cortex. Therefore, we define these areas as the seizure focus. In this zone, neuronal connectivity and excitability are moderately enhanced, lowering the threshold for seizure generation.
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13
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De Grandis E, Mancardi MM, Carelli V, Carpaneto M, Morana G, Prato G, Mirabelli-Badenier M, Pinto F, Veneselli E, Baglietto MG. Epileptic encephalopathy with continuous spike and wave during sleep associated to periventricular leukomalacia. J Child Neurol 2014; 29:1479-85. [PMID: 24293309 DOI: 10.1177/0883073813508223] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Periventricular leukomalacia is the most common type of brain injury in premature infants. Our aim is to describe the frequency and the features of epilepsy in a single-center population of 137 children with periventricular leukomalacia. Forty-two of the 137 (31%) patients presented epilepsy. Twelve percent of these patients presented West syndrome, whereas 19% showed a pattern of continuous spike-waves during slow sleep syndrome. In the latter group, outcome was frequently unfavorable, with a greater number of seizures and more drug resistance. A significant association was found between epilepsy and neonatal seizures, spastic tetraplegia, and mental retardation. Although less common than in other forms of brain injury, epilepsy is nevertheless a significant complication in children with periventricular leukomalacia. The fairly frequent association with continuous spike-waves during slow sleep syndrome deserves particular attention: electroencephalographic sleep monitoring is important in order to provide early treatment and prevent further neurologic deterioration.
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Affiliation(s)
- Elisa De Grandis
- Child Neuropsychiatry Unit, Istituto Giannina Gaslini, Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal and Children's Sciences, University of Genoa, Genoa, Italy
| | - Maria Margherita Mancardi
- Epilepsy Center, Child Neuropsychiatry Unit, Istituto Giannina Gaslini, Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal and Child Health, University of Genoa, Genoa, Italy
| | - Valentina Carelli
- Child Neuropsychiatry Unit, Istituto Giannina Gaslini, Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal and Children's Sciences, University of Genoa, Genoa, Italy
| | - Manuela Carpaneto
- Child Neuropsychiatry Unit, Istituto Giannina Gaslini, Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal and Children's Sciences, University of Genoa, Genoa, Italy
| | - Giovanni Morana
- Neuroradiology Service, Istituto Giannina Gaslini, Genoa, Italy
| | - Giulia Prato
- Epilepsy Center, Child Neuropsychiatry Unit, Istituto Giannina Gaslini, Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal and Child Health, University of Genoa, Genoa, Italy
| | - Marisol Mirabelli-Badenier
- Child Neuropsychiatry Unit, Istituto Giannina Gaslini, Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal and Children's Sciences, University of Genoa, Genoa, Italy
| | - Francesca Pinto
- Child Neuropsychiatry Unit, Istituto Giannina Gaslini, Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal and Children's Sciences, University of Genoa, Genoa, Italy
| | - Edvige Veneselli
- Child Neuropsychiatry Unit, Istituto Giannina Gaslini, Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal and Children's Sciences, University of Genoa, Genoa, Italy
| | - Maria Giuseppina Baglietto
- Epilepsy Center, Child Neuropsychiatry Unit, Istituto Giannina Gaslini, Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal and Child Health, University of Genoa, Genoa, Italy
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14
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Boido D, Gnatkovsky V, Uva L, Francione S, de Curtis M. Simultaneous enhancement of excitation and postburst inhibition at the end of focal seizures. Ann Neurol 2014; 76:826-36. [PMID: 24916758 DOI: 10.1002/ana.24193] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2014] [Revised: 06/04/2014] [Accepted: 06/04/2014] [Indexed: 11/10/2022]
Abstract
OBJECTIVE Comprehension of the events that lead to seizure termination contributes to the development of strategies to confine propagation of ictal discharges. It is commonly assumed that the inhibitory control fails during seizures and recovers after the end of the ictal event. We examine the possibility that a progressive increase of inhibition that counters an increase in the strength of excitation contributes to terminating a focal seizure. METHODS We analyzed seizures acutely induced by pharmacological manipulations (bicuculline and 4-aminopyridine) in the entorhinal cortex and in the hippocampus of the in vitro isolated guinea pig brain. RESULTS As seizures ended, extracellular and intracellular recordings showed periodic bursting that progressively decreased in frequency. During the late bursting phase, the duration, number, and rate of occurrence of spikes within single bursts remained constant, whereas cumulative spike amplitude (index of excitation during a burst) and interburst interval (index of inhibition between bursts) progressively increased. The increment of average/cumulative burst excitation and interburst interval toward seizure end was confirmed in human focal seizures recorded with intracerebral electrodes in patients with drug-resistant partial epilepsies. A postburst refractory period of circa 2 seconds that increases with time toward the end of the seizure was confirmed in the experimental model by probing interburst epochs in the CA1 region with local dentate gyrus stimulation just suprathreshold for burst generation. INTERPRETATION Our findings support the concept that focal seizures are terminated by the simultaneous and opposing enhancement of excitation (burst activity) in addition to postburst inhibition. We hypothesize that a seizure stops when postburst inhibition becomes large enough to prevent reactivation of excitation.
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Affiliation(s)
- Davide Boido
- Unit of Epileptology and Experimental Neurophysiology, Carlo Besta Neurological Institute Foundation, Milan, Italy
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15
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Kobow K, Auvin S, Jensen F, Löscher W, Mody I, Potschka H, Prince D, Sierra A, Simonato M, Pitkänen A, Nehlig A, Rho JM. Finding a better drug for epilepsy: antiepileptogenesis targets. Epilepsia 2012; 53:1868-76. [PMID: 23061663 DOI: 10.1111/j.1528-1167.2012.03716.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
For several decades, both in vitro and in vivo models of seizures and epilepsy have been employed to unravel the molecular and cellular mechanisms underlying the occurrence of spontaneous recurrent seizures (SRS)-the defining hallmark of the epileptic brain. However, despite great advances in our understanding of seizure genesis, investigators have yet to develop reliable biomarkers and surrogate markers of the epileptogenic process. Sadly, the pathogenic mechanisms that produce the epileptic condition, especially after precipitating events such as head trauma, inflammation, or prolonged febrile convulsions, are poorly understood. A major challenge has been the inherent complexity and heterogeneity of known epileptic syndromes and the differential genetic susceptibilities exhibited by patients at risk. Therefore, it is unlikely that there is only one fundamental pathophysiologic mechanism shared by all the epilepsies. Identification of antiepileptogenesis targets has been an overarching goal over the last decade, as current anticonvulsant medications appear to influence only the acute process of ictogenesis. Clearly, there is an urgent need to develop novel therapeutic interventions that are disease modifying-therapies that either completely or partially prevent the emergence of SRS. An important secondary goal is to develop new treatments that can also lessen the burden of epilepsy comorbidities (e.g., cognitive impairment, mood disorders) by preventing or reducing the deleterious changes during the epileptogenic process. This review summarizes novel antiepileptogenesis targets that were critically discussed at the XIth Workshop on the Neurobiology of Epilepsy (WONOEP XI) meeting in Grottaferrata, Italy. Further, emerging neurometabolic links among several target mechanisms and highlights of the panel discussion are presented.
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Affiliation(s)
- Katja Kobow
- Department of Neuropathology, University Hospital Erlangen, Erlangen, Germany
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16
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Chang WP, Wu JS, Lee CM, Vogt BA, Shyu BC. Spatiotemporal organization and thalamic modulation of seizures in the mouse medial thalamic-anterior cingulate slice. Epilepsia 2011; 52:2344-55. [DOI: 10.1111/j.1528-1167.2011.03312.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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17
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Avoli M, de Curtis M. GABAergic synchronization in the limbic system and its role in the generation of epileptiform activity. Prog Neurobiol 2011; 95:104-32. [PMID: 21802488 PMCID: PMC4878907 DOI: 10.1016/j.pneurobio.2011.07.003] [Citation(s) in RCA: 193] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2011] [Revised: 07/14/2011] [Accepted: 07/15/2011] [Indexed: 11/30/2022]
Abstract
GABA is the main inhibitory neurotransmitter in the adult forebrain, where it activates ionotropic type A and metabotropic type B receptors. Early studies have shown that GABA(A) receptor-mediated inhibition controls neuronal excitability and thus the occurrence of seizures. However, more complex, and at times unexpected, mechanisms of GABAergic signaling have been identified during epileptiform discharges over the last few years. Here, we will review experimental data that point at the paradoxical role played by GABA(A) receptor-mediated mechanisms in synchronizing neuronal networks, and in particular those of limbic structures such as the hippocampus, the entorhinal and perirhinal cortices, or the amygdala. After having summarized the fundamental characteristics of GABA(A) receptor-mediated mechanisms, we will analyze their role in the generation of network oscillations and their contribution to epileptiform synchronization. Whether and how GABA(A) receptors influence the interaction between limbic networks leading to ictogenesis will be also reviewed. Finally, we will consider the role of altered inhibition in the human epileptic brain along with the ability of GABA(A) receptor-mediated conductances to generate synchronous depolarizing events that may lead to ictogenesis in human epileptic disorders as well.
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Affiliation(s)
- Massimo Avoli
- Montreal Neurological Institute and Departments of Neurology & Neurosurgery, and of Physiology, McGill University, Montreal H3A 2B4 Quebec, Canada.
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18
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de Curtis M, Gnatkovsky V. Reevaluating the mechanisms of focal ictogenesis: The role of low-voltage fast activity. Epilepsia 2009; 50:2514-25. [PMID: 19674056 DOI: 10.1111/j.1528-1167.2009.02249.x] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The mechanisms that control the transition into a focal seizure are still uncertain. The introduction of presurgical intracranial recordings to localize the epileptogenic zone in patients with drug-resistant focal epilepsies opened a new window to the interpretation of seizure generation (ictogenesis). One of the most frequent focal patterns observed with intracranial electrodes at seizure onset is characterized by low-voltage fast activity in the beta-gamma range that may or may not be preceded by changes of ongoing interictal activities. In the present commentary, the mechanisms of generation of focal seizures are reconsidered, focusing on low-voltage fast activity patterns. Experimental findings on models of temporal lobe seizures support the view that the low-voltage fast activity observed at seizure onset is associated with reinforcement and synchronization of inhibitory networks. A minor role for the initiation of the ictal pattern is played by principal neurons that are progressively recruited with a delay, when inhibition declines and synchronous high-voltage discharges ensue. The transition from inhibition into excitatory recruitment is probably mediated by local increase in potassium concentration associated with synchronized interneuronal firing. These findings challenge the classical theory that proposes an increment of excitation and/or a reduction of inhibition as a cause for the transition to seizure in focal epilepsies. A new definition of ictogenesis mechanisms, as herewith hypothesized, might possibly help to develop new therapeutic strategies for focal epilepsies.
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Affiliation(s)
- Marco de Curtis
- Unit of Experimental Neurophysiology and Epileptology, Fondazione Istituto Neurologico Carlo Besta, Milano, Italy.
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19
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Chu Y, Parada I, Prince DA. Temporal and topographic alterations in expression of the alpha3 isoform of Na+, K(+)-ATPase in the rat freeze lesion model of microgyria and epileptogenesis. Neuroscience 2009; 162:339-48. [PMID: 19362129 DOI: 10.1016/j.neuroscience.2009.04.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2008] [Revised: 03/31/2009] [Accepted: 04/02/2009] [Indexed: 12/20/2022]
Abstract
Na(+),K(+)-ATPase contributes to the asymmetrical distribution of sodium and potassium ions across the plasma membrane and to maintenance of the membrane potential in many types of cells. Alterations in this protein may play a significant role in many human neurological disorders, including epilepsy. We studied expression of the alpha3 isoform of Na(+),K(+)-ATPase in the freeze lesion (FL) microgyrus model of developmental epileptogenesis to test the hypothesis that it is downregulated following neonatal cortical injury. FL and sham-operated rat brains were examined at postnatal day (P)7, P10, P14, P21-28 and P50-60 after placement of a transcranial freeze lesion at P0 or P1. Immunohistochemistry and in situ hybridization were used to assess the expression of the alpha3 isoform of Na(+),K(+)-ATPase (termed alpha3, or alpha3 subunit below) in neuropil and the perisomatic areas of pyramidal cells and parvalbumin-containing interneurons. There was a significant decrease (P<0.05) in alpha3 subunit immunoreactivity (IR) in the neuropil of FL cortical layer V of the P14 and P21-28 groups that extended up to 360 mum from the border of the microgyrus, an area that typically exhibits evoked epileptiform activity. Alpha-3 was decreased in the perisomatic area of pyramidal but not parvalbumin-containing cells in P21-28 FL animals. A reduction in alpha3 mRNA was observed in the neuropil of FL cortical layer V up to 1610 mum from the microgyral edge. The developmental time course for expression of the alpha3 subunit between P7 and P60 was examined in naive rat cortices and results showed that there was a significant increase in alpha3 IR between P7 and P10. The significant decreases in Na(+),K(+)-ATPase in the paramicrogyral cortex may contribute to epileptogenesis.
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Affiliation(s)
- Y Chu
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, 300 Pasteur Drive, M016, Stanford University, Stanford, CA 94305, USA
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Prince DA, Parada I, Scalise K, Graber K, Jin X, Shen F. Epilepsy following cortical injury: cellular and molecular mechanisms as targets for potential prophylaxis. Epilepsia 2009; 50 Suppl 2:30-40. [PMID: 19187292 DOI: 10.1111/j.1528-1167.2008.02008.x] [Citation(s) in RCA: 107] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The sequelae of traumatic brain injury, including posttraumatic epilepsy, represent a major societal problem. Significant resources are required to develop a better understanding of the underlying pathophysiologic mechanisms as targets for potential prophylactic therapies. Posttraumatic epilepsy undoubtedly involves numerous pathogenic factors that develop more or less in parallel. We have highlighted two potential "prime movers": disinhibition and development of new functional excitatory connectivity, which occur in a number of animal models and some forms of epilepsy in humans. Previous experiments have shown that tetrodotoxin (TTX) applied to injured cortex during a critical period early after lesion placement can prevent epileptogenesis in the partial cortical ("undercut") model of posttraumatic epilepsy. Here we show that such treatment markedly attenuates histologic indices of axonal and terminal sprouting and presumably associated aberrant excitatory connectivity. A second finding in the undercut model is a decrease in spontaneous inhibitory events. Current experiments show that this is accompanied by regressive alterations in fast-spiking gamma-aminobutyric acid (GABA)ergic interneurons, including shrinkage of dendrites, marked decreases in axonal length, structural changes in inhibitory boutons, and loss of inhibitory synapses on pyramidal cells. Other data support the hypothesis that these anatomic abnormalities may result from loss of trophic support normally provided to interneurons by brain-derived neurotrophic factor (BDNF). Approaches that prevent these two pathophysiologic mechanisms may offer avenues for prophylaxis for posttraumatic epilepsy. However, major issues such as the role of these processes in functional recovery from injury and the timing of the critical period(s) for application of potential therapies in humans need to be resolved.
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Affiliation(s)
- David A Prince
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, California 94305, USA.
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21
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Sabesan S, Chakravarthy N, Tsakalis K, Pardalos P, Iasemidis L. Measuring resetting of brain dynamics at epileptic seizures: application of global optimization and spatial synchronization techniques. JOURNAL OF COMBINATORIAL OPTIMIZATION 2009; 17:74-97. [PMID: 21709753 PMCID: PMC3120844 DOI: 10.1007/s10878-008-9181-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Epileptic seizures are manifestations of intermittent spatiotemporal transitions of the human brain from chaos to order. Measures of chaos, namely maximum Lyapunov exponents (STL(max)), from dynamical analysis of the electroencephalograms (EEGs) at critical sites of the epileptic brain, progressively converge (diverge) before (after) epileptic seizures, a phenomenon that has been called dynamical synchronization (desynchronization). This dynamical synchronization/desynchronization has already constituted the basis for the design and development of systems for long-term (tens of minutes), on-line, prospective prediction of epileptic seizures. Also, the criterion for the changes in the time constants of the observed synchronization/desynchronization at seizure points has been used to show resetting of the epileptic brain in patients with temporal lobe epilepsy (TLE), a phenomenon that implicates a possible homeostatic role for the seizures themselves to restore normal brain activity. In this paper, we introduce a new criterion to measure this resetting that utilizes changes in the level of observed synchronization/desynchronization. We compare this criterion's sensitivity of resetting with the old one based on the time constants of the observed synchronization/desynchronization. Next, we test the robustness of the resetting phenomena in terms of the utilized measures of EEG dynamics by a comparative study involving STL(max), a measure of phase (ϕ(max)) and a measure of energy (E) using both criteria (i.e. the level and time constants of the observed synchronization/desynchronization). The measures are estimated from intracranial electroencephalographic (iEEG) recordings with subdural and depth electrodes from two patients with focal temporal lobe epilepsy and a total of 43 seizures. Techniques from optimization theory, in particular quadratic bivalent programming, are applied to optimize the performance of the three measures in detecting preictal entrainment. It is shown that using either of the two resetting criteria, and for all three dynamical measures, dynamical resetting at seizures occurs with a significantly higher probability (α = 0.05) than resetting at randomly selected non-seizure points in days of EEG recordings per patient. It is also shown that dynamical resetting at seizures using time constants of STL(max) synchronization/desynchronization occurs with a higher probability than using the other synchronization measures, whereas dynamical resetting at seizures using the level of synchronization/desynchronization criterion is detected with similar probability using any of the three measures of synchronization. These findings show the robustness of seizure resetting with respect to measures of EEG dynamics and criteria of resetting utilized, and the critical role it might play in further elucidation of ictogenesis, as well as in the development of novel treatments for epilepsy.
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Affiliation(s)
- Shivkumar Sabesan
- Department of Electrical Engineering, Arizona State University, Tempe, AZ 85287, USA
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22
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Abstract
Epilepsy affects 1-2 % of the population. For 30 % of these patients, their syndrome will be refractory to medical treatment. To improve our understanding and treatment of the epilepsies, we need to develop clinically relevant animal models. As temporal lobe epilepsy is often preceded by prolonged febrile seizures and in our population associated with a focal cortical dysplasia, we hypothesised that an underlying predisposing anatomical lesion would predispose individuals to develop prolonged febrile seizures and that temporal lobe epilepsy would later develop. As predicted, all the lesioned animals developed prolonged febrile seizures, while all other control groups only showed simple febrile seizures. After a latent period, 86 % of the animals who had experienced a prolonged seizure developed spontaneously recurrent limbic seizures. We now need to understand the anatomical and electrophysiological changes underlying this new epilepsy model to try and develop more effective treatments for the condition.
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Affiliation(s)
- Lionel Carmant
- D.Clinique d'Epilepsie et Centre de Recherche sur lEpilepsie, Service de Neurologie, CHU Sainte-Justine, Université de Montréal, 3175, Côte Sainte-Catherine, Bureau A-714, Montréal, Québec, H3T 1C5 Canada.
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Bazhenov M, Timofeev I, Fröhlich F, Sejnowski TJ. Cellular and network mechanisms of electrographic seizures. DRUG DISCOVERY TODAY. DISEASE MODELS 2008; 5:45-57. [PMID: 19190736 PMCID: PMC2633479 DOI: 10.1016/j.ddmod.2008.07.005] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Epileptic seizures constitute a complex multiscale phenomenon that is characterized by synchronized hyperexcitation of neurons in neuronal networks. Recent progress in understanding pathological seizure dynamics provides crucial insights into underlying mechanisms and possible new avenues for the development of novel treatment modalities. Here we review some recent work that combines in vivo experiments and computational modeling to unravel the pathophysiology of seizures of cortical origin. We particularly focus on how activity-dependent changes in extracellular potassium concentration affects the intrinsic dynamics of neurons involved in cortical seizures characterized by spike/wave complexes and fast runs.
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Affiliation(s)
- Maxim Bazhenov
- The Salk Institute for Biological Studies, La Jolla, CA 92037
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24
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Rajasekaran K, Kapur J, Bertram EH. Alterations in GABAA Receptor Mediated Inhibition in Adjacent Dorsal Midline Thalamic Nuclei in a Rat Model of Chronic Limbic Epilepsy. J Neurophysiol 2007; 98:2501-8. [PMID: 17855591 DOI: 10.1152/jn.00139.2007] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
There is evidence that the dorsal midline thalamus is involved in the seizures of limbic epilepsy. However, little is known about the inhibitory synaptic function in this region. In the present study, inhibitory postsynaptic currents (IPSCs) mediated by GABAA receptors were recorded from the mediodorsal (MD) and paraventricular (PV) nuclei from control and epileptic animals. In the MD, the spontaneous (s)IPSCs for epileptic animals had a lower frequency, prolonged rise time, prolonged decay, but unaltered net charge transfer compared with controls. The miniature (m)IPSC parameters were unaltered in the epileptic animals. In contrast, in the PV, both sIPSCs and mIPSCs in the epileptic animals were more frequent with larger amplitudes and there was an increase in the net charge transfer compared with controls. The rise times of the sIPSCs of the PV neurons were significantly prolonged, whereas the weighted decay time of the mIPSC was significantly shortened in epileptic animals. These findings suggest that the changes associated with inhibitory synaptic transmission in limbic epilepsy are not uniform across regions in the thalamus that are part of the seizure circuit.
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Affiliation(s)
- Karthik Rajasekaran
- Department of Neurology, University of Virginia, Health Sciences Center, Charlottesville, VA 22908, USA
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Andrioli A, Alonso-Nanclares L, Arellano JI, DeFelipe J. Quantitative analysis of parvalbumin-immunoreactive cells in the human epileptic hippocampus. Neuroscience 2007; 149:131-43. [PMID: 17850980 DOI: 10.1016/j.neuroscience.2007.07.029] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2007] [Revised: 07/16/2007] [Accepted: 07/16/2007] [Indexed: 10/23/2022]
Abstract
Hippocampal sclerosis is the most frequent pathology encountered in mesial temporal structures resected from patients with intractable temporal lobe epilepsy and it mainly involves hippocampal neuronal loss and gliosis. These alterations are accompanied by changes in the expression of a variety of molecules in the surviving neurons, as well as axonal reorganization in both excitatory and inhibitory circuits. The alteration of a subpopulation of GABAergic interneurons that expresses the calcium binding protein parvalbumin (PV) is thought to be a key factor in the epileptogenic process. We investigated the distribution and density of parvalbumin-immunoreactive (PV-ir) neurons in surgically resected hippocampal tissue from epileptic patients with and without sclerosis. Using quantitative stereological methods, we show for the first time that there is no correlation between total neuronal loss and PV-ir neuronal loss in any of the hippocampal fields. We also observed higher values of the total neuronal density in the sclerotic subiculum, which is accompanied by a lower density of PV-ir when compared with non-sclerotic epileptic and autopsy hippocampi. These findings suggest that, the apparently normal subiculum from sclerotic patients also shows unexpected changes in the density and proportion of PV-ir neurons.
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Affiliation(s)
- A Andrioli
- Instituto Cajal (CSIC), Avda Dr Arce 37, 28002 Madrid, Spain
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REORGANIZATION OF BARREL CIRCUITS LEADS TO THALAMICALLY-EVOKED CORTICAL EPILEPTIFORM ACTIVITY. ACTA ACUST UNITED AC 2007; 3:261-273. [PMID: 18185849 DOI: 10.1017/s1472928807000283] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
We studied circuit activities in layer IV of rat somatosensory barrel cortex containing microgyri induced by neonatal freeze lesions. Structural abnormalities in GABAergic interneurons are present in the epileptogenic paramicrogyral area (PMG) and we therefore tested the hypothesis that decreased postsynaptic inhibition within barrel microcircuits occurs in the PMG and contributes to epileptogenesis when thalamocortical afferents are activated. In thalamocortical (TC) slices from naïve animals, single electrical stimuli within the thalamic ventrobasal (VB) nucleus evoked transient cortical multi-unit activity lasting 65±42 ms. Similar stimuli in TC slices from lesioned barrel cortex elicited prolonged 850 ±100 ms paroxysmal discharges that originated in the PMG and propagated laterally over several mm. Paroxysmal discharges were shortened in duration by ~70 % when APV was applied, and were totally abolished by CNQX. The cortical paroxysmal discharges did not evoke thalamic oscillations. Whole cell patch clamp recordings showed that there was a shift in the balance of TC evoked responses in the PMG that favored excitation over inhibition. Dual whole-cell recordings in layer IV of the PMG indicated that there was selective loss of inhibition from fast-spiking interneurons to spiny neurons in the barrel circuits that likely contributed to unconstrained cortical recurrent excitation with generation and spread of paroxysmal discharges.
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Kim JE, Kim DS, Kwak SE, Choi HC, Song HK, Choi SY, Kwon OS, Kim YI, Kang TC. Anti-glutamatergic effect of riluzole: comparison with valproic acid. Neuroscience 2007; 147:136-45. [PMID: 17507170 DOI: 10.1016/j.neuroscience.2007.04.018] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2006] [Revised: 04/04/2007] [Accepted: 04/06/2007] [Indexed: 11/28/2022]
Abstract
Riluzole, an anti-amyotrophic lateral sclerosis drug, known to decrease presynaptic glutamate release, is viewed as a candidate supplementary medication for epilepsy. In the present study, we compared the effects of riluzole and valproate (VPA) in the pilocarpine-induced limbic seizure model and in the gamma-hydroxybutyrate lactone (GBL)-induced absence seizure model. We applied immunohistochemical study for vesicular transporter 1 (VGLUT1) and extracellular recording in the rat dentate gyrus of both pilocarpine- and GBL-induced seizure models to measure effects of riluzole and VPA. Both VPA and riluzole treatments reduced VGLUT1 immunoreactivity. Riluzole treatment completely inhibited pre-ictal spikes and spike-wave discharges in the pilocarpine- and GBL-induced epilepsy models, whereas VPA partially inhibited these phenomena. In both seizure models, the anti-epileptic effects of VPA and riluzole are basically related to anti-glutamatergic (reducing field excitatory postsynaptic potential slope and excitability ratio), not GABAergic (paired-pulse inhibition) effect. Riluzole was more effective at reducing seizure activity in both epilepsy models than VPA. These results suggest that riluzole is a potential antiepileptic drug with activity against limbic seizure and absence seizure.
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Affiliation(s)
- J-E Kim
- Department of Anatomy, College of Medicine, Hallym University, Chunchon 200-702, South Korea
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Humphreys P, Deonandan R, Whiting S, Barrowman N, Matzinger MA, Briggs V, Hurteau J, Wallace E. Factors associated with epilepsy in children with periventricular leukomalacia. J Child Neurol 2007; 22:598-605. [PMID: 17690068 DOI: 10.1177/0883073807302599] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Children with cerebral palsy associated with periventricular leukomalacia frequently develop unprovoked epileptic seizures. This article reports an analysis of risk factors for epilepsy in children with radiologically confirmed periventricular leukomalacia. This cohort was screened for epilepsy and for an array of clinical and demographic factors. Of 154 subjects with radiologically confirmed periventricular leukomalacia, 40 (26.0%) had epilepsy. In the epileptic group, radiologic pathology other than periventricular leukomalacia was uncommon. Significant associations were found between epilepsy and cerebral palsy patterns other than spastic diparesis, mental handicap, cortical visual impairment, neonatal seizures, and severe periventricular leukomalacia. Only the presence of neonatal seizures was significantly associated with epilepsy once other risk factors were controlled in the regression model. Some previous studies have shown an association between neonatal seizures and later epilepsy for cerebral palsy in general. This is the first report of such an association for a single predominant type of cerebral pathology.
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Affiliation(s)
- Peter Humphreys
- Division of Neurology, Department of Pediatrics, Children's Hospital of Eastern Ontario, Ottawa Children's Treatment Centre Ottawa, Ontario, Canada.
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Trevelyan AJ, Sussillo D, Watson BO, Yuste R. Modular propagation of epileptiform activity: evidence for an inhibitory veto in neocortex. J Neurosci 2006; 26:12447-55. [PMID: 17135406 PMCID: PMC6674895 DOI: 10.1523/jneurosci.2787-06.2006] [Citation(s) in RCA: 240] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
What regulates the spread of activity through cortical circuits? We present here data indicating a pivotal role for a vetoing inhibition restraining modules of pyramidal neurons. We combined fast calcium imaging of network activity with whole-cell recordings to examine epileptiform propagation in mouse neocortical slices. Epileptiform activity was induced by washing Mg2+ ions out of the slice. Pyramidal cells receive barrages of inhibitory inputs in advance of the epileptiform wave. The inhibitory barrages are effectively nullified at low doses of picrotoxin (2.5-5 microM). When present, however, these inhibitory barrages occlude an intense excitatory synaptic drive that would normally exceed action potential threshold by approximately a factor of 10. Despite this level of excitation, the inhibitory barrages suppress firing, thereby limiting further neuronal recruitment to the ictal event. Pyramidal neurons are recruited to the epileptiform event once the inhibitory restraint fails and are recruited in spatially clustered populations (150-250 microm diameter). The recruitment of the cells within a given module is virtually simultaneous, and thus epileptiform events progress in intermittent (0.5-1 Hz) steps across the cortical network. We propose that the interneurons that supply the vetoing inhibition define these modular circuit territories.
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Affiliation(s)
- Andrew J Trevelyan
- Howard Hughes Medical Institute, Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
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Kang TC, Kim DS, Kwak SE, Kim JE, Won MH, Kim DW, Choi SY, Kwon OS. Epileptogenic roles of astroglial death and regeneration in the dentate gyrus of experimental temporal lobe epilepsy. Glia 2006; 54:258-71. [PMID: 16845674 DOI: 10.1002/glia.20380] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Recent studies have demonstrated that blockade of neuronal death in the hippocampus cannot prevent epileptogenesis in various epileptic models. These reports indicate that neurodegeneration alone is insufficient to cause epilepsy, and that the role of astrocytes in epileptogenesis should be reconsidered. Therefore, the present study was designed to elucidate whether altered morphological organization or the functionalities of astrocytes induced by status epilepticus (SE) is responsible for epileptogenesis. Glial responses (reactive microgliosis followed by astroglial death) in the dentate gyrus induced by pilocarpine-induced SE were found to precede neuronal damage and these alterations were closely related to abnormal neurotransmission related to altered vesicular glutamate and GABA transporter expressions, and mossy fiber sprouting in the dentate gyrus. In addition, newly generated astrocytes showed down-regulated expressions of glutamine synthase, glutamate dehydrogenase, and glial GABA transporter. Taken together, our findings suggest that glial responses after SE may contribute to epileptogenesis and the acquisition of the properties of the epileptic hippocampus. Thus, we believe that it is worth considering new therapeutic approaches to epileptogenesis involving targeting the inactivation of microglia and protecting against astroglial loss.
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Affiliation(s)
- Tae-Cheon Kang
- Department of Anatomy, College of Medicine, Hallym University, Chunchon, Kangwon-Do, South Korea.
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Abstract
Epilepsy is a major unfavorable long-term consequence of traumatic brain injury (TBI). Moreover, TBI is one of the most important predisposing factors for the development of epilepsy, particularly in young adults. Understanding the molecular and cellular cascades that lead to the development of post-traumatic epilepsy (PTE) is key for preventing its development or modifying the disease process in such a way that epilepsy, if it develops, is milder and easier-to-treat. Tissue from TBI patients undergoing epileptogenesis is not available for such studies, which underscores the importance of developing clinically relevant animal models of PTE. The goal of this review is to (1) provide a description of PTE in humans, which is critical for the development of clinically relevant models of PTE, (2) review the characteristics of currently available PTE models, and (3) provide suggestions for the development of future models of PTE based on our current understanding of the mechanisms of TBI and epilepsy. The development of clinically relevant models of PTE is critical to advance our understanding of the mechanisms of post-traumatic epileptogenesis and epilepsy, as well as for producing breakthroughs in the development and testing of novel antiepileptogenic treatments.
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Affiliation(s)
- Asla Pitkänen
- Epilepsy Research Laboratory, AI Virtanen Institute for Molecular Sciences, University of Kuopio, Kuopio, Finland.
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Patrick SL, Connors BW, Landisman CE. Developmental changes in somatostatin-positive interneurons in a freeze-lesion model of epilepsy. Epilepsy Res 2006; 70:161-71. [PMID: 16737797 DOI: 10.1016/j.eplepsyres.2006.04.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2005] [Revised: 03/03/2006] [Accepted: 04/12/2006] [Indexed: 10/24/2022]
Abstract
Somatostatin-expressing (SS) cells are inhibitory interneurons critical to the regulation of excitability in the cerebral cortex. It has been suggested in several animal models of epilepsy that the activity of these neurons reduces the occurrence and strength of epileptiform activity. The physiological properties of SS cells further support these hypotheses. Freeze lesions of neonatal rats serve as a model of human polymicrogyria, which is often characterized by severe seizures. Here we investigate the effects of neonatal freeze lesions on SS-expressing neurons by measuring their densities in control and lesioned hemispheres at two ages. We found that in late juveniles (P30-P32), SS-expressing neurons were depleted by 20% in areas adjacent to the freeze lesion, but at an earlier developmental age (P14-15), there was no significant loss. Since the deficit in SS-expressing neurons occurs well after the onset of epileptiform activity (P12-P18), we conclude that the death of these interneurons does not initiate hyperexcitability in this model.
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Affiliation(s)
- Saundra L Patrick
- Department of Neuroscience Division of Biology and Medicine, Brown University Providence, RI 02912, USA
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Abstract
Pediatric epilepsy models are needed to help with development of drugs for specific childhood and infantile epilepsy syndromes. The major forms of pediatric epilepsy can be divided into those that occur in the neonatal period, infancy, early childhood and late childhood. Seizures in the immature brain are different from those in adult brain, often resulting in neuronal death. Rodent models are useful in mimicking seizures in the immature brain (neonatal seizures, infantile spasms, and febrile seizures). No specific models exist for syndromes (e.g., Lennox-Gastaut, Landau-Kleffner). The interaction between brain development and epilepsy in humans can be assisted by use of high resolution MRI, diffusion tensor imaging, and functional MRI.
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Schwindt W, Burke M, Pillekamp F, Luhmann HJ, Hoehn M. Functional magnetic resonance imaging and somatosensory evoked potentials in rats with a neonatally induced freeze lesion of the somatosensory cortex. J Cereb Blood Flow Metab 2004; 24:1409-18. [PMID: 15625415 DOI: 10.1097/01.wcb.0000143535.84012.ca] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Brain plasticity is an important mechanism for functional recovery from a cerebral lesion. The authors aimed to visualize plasticity in adult rats with a neonatal freeze lesion in the somatosensory cortex using functional magnetic resonance imaging (fMRI), and hypothesized activation outside the primary projection area. A freeze lesion was induced in the right somatosensory cortex of newborn Wistar rats (n = 12). Sham-operated animals (n = 7) served as controls. After 6 or 7 months, a neurologic examination was followed by recording of somatosensory evoked potentials (SSEPs) and magnetic resonance experiments (anatomical images, fMRI with blood oxygen level-dependent contrast and perfusion-weighted imaging) with electrical forepaw stimulation under alpha-chloralose anesthesia. Lesioned animals had no obvious neurologic deficits. Anatomical magnetic resonance images showed a malformed cortex or hyperintense areas (cysts) in the lesioned hemisphere. SSEPs were distorted and smaller in amplitude, and fMRI activation was significantly weaker in the lesioned hemisphere. Only in a few animals were cortical areas outside the primary sensory cortex activated. The results are discussed in respect to an apparent absence of plasticity, loss of excitable tissue, the excitability of the lesioned hemisphere, altered connectivity, and a disturbed coupling of increased neuronal activity to the hemodynamic response.
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Affiliation(s)
- Wolfram Schwindt
- Max-Planck-Institute for Neurological Research, Cologne, Germany.
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35
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Santhakumar V, Soltesz I. Plasticity of interneuronal species diversity and parameter variance in neurological diseases. Trends Neurosci 2004; 27:504-10. [PMID: 15271499 DOI: 10.1016/j.tins.2004.06.002] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Interneuronal diversity reflects the division of labor between numerous highly specialized interneuronal species, each performing a set of specific functions in neuronal networks. The rich diversity of interneurons found in the normal healthy brain is often significantly altered in neurological and psychiatric diseases. In genetic and developmental disorders, the diversity of interneuronal networks is compromised because of disturbances in the generation, specification or migration of specific interneuronal subtypes. Following insults related to trauma and seizures, the relative abundance of interneuronal subtypes might change, and entire interneuronal species can be lost from the network. In addition to the complete or partial loss of interneuronal subgroups, heterogeneity can also be altered in more subtle ways, as a result of changes in cell-to-cell variance of a particular parameter within specific interneuronal populations. Computational and experimental studies show that alterations in cellular and synaptic GABAergic heterogeneity can significantly modulate both firing rates and network coherence, indicating that plasticity of interneuronal diversity is likely to be an important mechanistic component of malfunctioning cortical networks in many pathological states.
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Affiliation(s)
- Vijayalakshmi Santhakumar
- Department of Anatomy and Neurobiology, and Center for the Neurobiology of Learning and Memory, University of California, Irvine, CA 92697-1280, USA
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Timofeev I, Grenier F, Steriade M. Contribution of Intrinsic Neuronal Factors in the Generation of Cortically Driven Electrographic Seizures. J Neurophysiol 2004; 92:1133-43. [PMID: 14749320 DOI: 10.1152/jn.00523.2003] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Some electrographic seizures are generated intracortically. The cellular and ionic bases of cortically generated spontaneous seizures are not fully understood. Here we investigated spontaneously occurring seizures consisting of spike-wave complexes intermingled with fast runs in ketamine-xylazine anesthetized cats, using dual intracellular recordings in which one pipette contained a control solution and another pipette contained blockers of K+, Na+, or Ca2+ currents. We show that closely located neocortical neurons display virtually identical fluctuations of the membrane potential during electrographic seizures, thus directly demonstrating a high degree of focal synchrony during paroxysmal activity. In addition to synaptic drives, the persistent Na+ current [ INa(p)] and probably the high-threshold Ca2+ current contributed to the generation of paroxysmal depolarizing shifts (PDSs) during cortically driven seizures. Ca2+-activated K+ current [ IK(Ca)] took also part in the control of the amplitude and duration of PDSs. The hyperpolarizing components of seizures largely depended on Cs+-sensitive K+ currents. IK(Ca) played a significant, while not exclusive, role in the mediation of hyperpolarizing potentials related to EEG “waves” during spike-wave seizures. We conclude that intrinsic cellular factors have significant role in the generation of depolarizing and hyperpolarizing components of seizures.
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Affiliation(s)
- Igor Timofeev
- Laboratory of Neurophysiology, Faculty of Medicine, Laval University, Quebec G1K 7P4, Canada.
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Schwaller B, Tetko IV, Tandon P, Silveira DC, Vreugdenhil M, Henzi T, Potier MC, Celio MR, Villa AEP. Parvalbumin deficiency affects network properties resulting in increased susceptibility to epileptic seizures. Mol Cell Neurosci 2004; 25:650-63. [PMID: 15080894 DOI: 10.1016/j.mcn.2003.12.006] [Citation(s) in RCA: 131] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2003] [Revised: 12/01/2003] [Accepted: 12/09/2003] [Indexed: 10/26/2022] Open
Abstract
Networks of GABAergic interneurons are of utmost importance in generating and promoting synchronous activity and are involved in producing coherent oscillations. These neurons are characterized by their fast-spiking rate and by the expression of the Ca(2+)-binding protein parvalbumin (PV). Alteration of their inhibitory activity has been proposed as a major mechanism leading to epileptic seizures and thus the role of PV in maintaining the stability of neuronal networks was assessed in knockout (PV-/-) mice. Pentylenetetrazole induced generalized tonic-clonic seizures in all genotypes, but the severity of seizures was significantly greater in PV-/- than in PV+/+ animals. Extracellular single-unit activity recorded from over 1000 neurons in vivo in the temporal cortex revealed an increase of units firing regularly and a decrease of cells firing in bursts. In the hippocampus, PV deficiency facilitated the GABA(A)ergic current reversal induced by high-frequency stimulation, a mechanism implied in the generation of epileptic activity. We postulate that PV plays a key role in the regulation of local inhibitory effects exerted by GABAergic interneurons on pyramidal neurons. Through an increase in inhibition, the absence of PV facilitates synchronous activity in the cortex and facilitates hypersynchrony through the depolarizing action of GABA in the hippocampus.
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Affiliation(s)
- B Schwaller
- Department of Medicine, University of Fribourg, CH-1700 Fribourg, Switzerland.
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38
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Abstract
Different forms of electrical paroxysms in experimental animals mimic the patterns of absence seizures associated with spike-wave complexes at approximately 3 Hz and of Lennox-Gastaut seizures with spike-wave or polyspike-wave complexes at approximately 1.5-2.5 Hz, intermingled with fast runs at 10-20 Hz. Both these types of electrical seizures are preferentially generated during slow-wave sleep. Here, we challenge the hypothesis of a subcortical pacemaker that would account for suddenly generalized spike-wave seizures as well as the idea of an exclusive role of synaptic excitation in the generation of paroxysmal depolarizing components, and we focus on three points, based on multiple intracellular and field potential recordings in vivo that are corroborated by some clinical studies: (a) the role of neocortical bursting neurons, especially fast-rhythmic-bursting neurons, and of very fast oscillations (ripples, 80-200 Hz) in seizure initiation; (b) the cortical origin of both these types of electrical paroxysms, the synaptic propagation of seizures from one to other, local and distant, cortical sites, finally reaching the thalamus, where the synchronous cortical firing excites thalamic reticular inhibitory neurons and thus leads to steady hyperpolarization and phasic inhibitory postsynaptic potentials in a majority of thalamocortical neurons, which might explain the obliteration of signals from the external world and the unconsciousness during absence seizures; and (c) the cessation of seizures, whose cellular mechanisms have only begun to be investigated and remain an open avenue for research.
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Affiliation(s)
- I Timofeev
- Laboratoire de Neurophysiologie, Faculté de Médecine, Université Laval, Québec, Canada G1K 7P4.
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Bailey SJ, Dhillon A, Woodhall GL, Jones RSG. Lamina-specific differences in GABA(B) autoreceptor-mediated regulation of spontaneous GABA release in rat entorhinal cortex. Neuropharmacology 2004; 46:31-42. [PMID: 14654095 DOI: 10.1016/j.neuropharm.2003.07.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Spontaneous synaptic inhibition plays an important role in regulating the excitability of cortical networks. Here we have investigated the role of GABA(B) autoreceptors in regulating spontaneous GABA release in the entorhinal cortex (EC), a region associated with temporal lobe epilepsies. We have previously shown that the level of spontaneous inhibition in superficial layers of the EC is much greater than that seen in deeper layers. In the present study, using intracellular and whole cell patch clamp recordings in rat EC slices, we have demonstrated that evoked GABA responses are controlled by feedback inhibition via GABA(B) autoreceptors. Furthermore, recordings of spontaneous, activity-independent inhibitory postsynaptic currents in layer II and layer V neurones showed that the GABA(B) receptor agonist, baclofen, reduced the frequency of GABA-mediated currents indicating the presence of presynaptic GABA(B) receptors in both layers. Application of the antagonist, CGP55845, blocked the effects of baclofen and also increased the frequency of GABA-mediated events above baseline, but the latter effect was restricted to layer V. This demonstrates that GABA(B) autoreceptors are tonically activated by synaptically released GABA in layer V, and this may partly explain the lower level of spontaneous GABA release in the deep layer.
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Affiliation(s)
- Sarah J Bailey
- Department of Physiology and MRC Synaptic Plasticity Centre, School of Medical Sciences, University of Bristol, University Walk, BS8 1TD, Bristol, UK.
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Abstract
Since 1993, nine new antiepileptic drugs (AEDs) have been introduced into the U.S. market for the symptomatic treatment of partial epilepsy. Their antiepileptic activity was, for the most part, defined by acute seizure models such as the maximal electroshock (MES) and subcutaneous pentylenetetrazol (scPTZ) seizure tests and the kindled rat. Unfortunately, the clinical evidence to date would suggest that none of these models, albeit useful, are likely to identify those therapeutics that will effectively manage the patient with refractory seizures. In recent years, a number of in vivo and in vitro models have been developed that display varying degrees of pharmacoresistance. As such, they may provide a unique opportunity for identifying the truly novel AED. Through a greater understanding of the pathophysiology of acquired epilepsy at the molecular and genetic level, it may be possible to identify a new therapeutic approach that reaches beyond the symptomatic treatment of epilepsy to modify the progression, or, dare we suggest, prevent the development of epilepsy in the susceptible patient. The realization of such a possibility will necessitate a change in our current AED discovery approach. The present review describes the current approach used in the search for new AEDs and offers some insight into future directions incorporating new and emerging models of therapy resistance and epileptogenesis.
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Affiliation(s)
- H Steve White
- Anticonvulsant Drug Development Program, Department of Pharmacology and Toxicology, University of Utah, Salt Lake City, Utah 84112, USA.
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Genetic disruption of cortical interneuron development causes region- and GABA cell type-specific deficits, epilepsy, and behavioral dysfunction. J Neurosci 2003. [PMID: 12533622 DOI: 10.1523/jneurosci.23-02-00622.2003] [Citation(s) in RCA: 221] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The generation of properly functioning circuits during brain development requires precise timing of cell migration and differentiation. Disruptions in the developmental plan may lead to neurological and psychiatric disorders. Neocortical circuits rely on inhibitory GABAergic interneurons, the majority of which migrate from subcortical sources. We have shown that the pleiotropic molecule hepatocyte growth factor/scatter factor (HGF/SF) mediates interneuron migration. Mice with a targeted mutation of the gene encoding urokinase plasminogen activator receptor (uPAR), a key component in HGF/SF activation and function, have decreased levels of HGF/SF and a 50% reduction in neocortical GABAergic interneurons at embryonic and perinatal ages. Disruption of interneuron development leads to early lethality in most models. Thus, the long-term consequences of such perturbations are unknown. Mice of the uPAR-/- strain survive until adulthood, and behavior testing demonstrates that they have an increased anxiety state. The uPAR-/- strain also exhibits spontaneous seizure activity and higher susceptibility to pharmacologically induced convulsions. The neocortex of the adult uPAR-/- mouse exhibits a dramatic region- and subtype-specific decrease in GABA-immunoreactive interneurons. Anterior cingulate and parietal cortical areas contain 50% fewer GABAergic interneurons compared with wild-type littermates. However, interneuron numbers in piriform and visual cortical areas do not differ from those of normal mice. Characterization of interneuron subpopulations reveals a near complete loss of the parvalbumin subtype, with other subclasses remaining intact. These data demonstrate that a single gene mutation can selectively alter the development of cortical interneurons in a region- and cell subtype-specific manner, with deficits leading to long-lasting changes in circuit organization and behavior.
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Timofeev I, Grenier F, Steriade M. The role of chloride-dependent inhibition and the activity of fast-spiking neurons during cortical spike-wave electrographic seizures. Neuroscience 2003; 114:1115-32. [PMID: 12379264 DOI: 10.1016/s0306-4522(02)00300-7] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The conventional view is that the cortical paroxysmal depolarizing shift is a giant excitatory postsynaptic potential enhanced by various intrinsic neuronal currents. Other results point out, however, that synaptic inhibition remains functional in many forms of paroxysmal activities and that intense activation of GABAergic interneurons may accentuate the excitation of target pyramidal cells. To determine the role played by cortical inhibitory neurons in paroxysmal discharges, we used single and dual intracellular recordings from electrophysiologically identified neocortical neurons during spontaneously occurring and electrically induced spike-wave electrographic seizures in vivo. Conventional fast-spiking neurons (presumably local inhibitory interneurons) fired at a very high frequency during paroxysmal depolarizing shifts, which corresponded to the electroencephalogram 'spike' components of spike-wave complexes. The firing of fast-spiking neurons preceded the discharges of neighboring regular-spiking neurons. During electrographic seizures, the reversal potential of the GABA (type A)-mediated potentials in regular-spiking neurons was shifted to positive values by 20-30 mV. Data also show that the prolonged hyperpolarizations during the electroencephalogram 'wave' components of spike-wave electrographic seizures do not contain Cl(-)-dependent inhibitory potentials. Moreover, Cl(-)-dependent mechanisms were reduced or absent during the fast runs that are associated with spike-wave complexes in some paroxysms. We conclude that the strong activity of cortical inhibitory neurons during paroxysmal depolarizing shifts induces Cl(-)-dependent depolarizing postsynaptic potentials in target pyramidal neurons, which facilitate the development of electrographic seizures.
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Affiliation(s)
- I Timofeev
- Laboratoire de Neurophysiologie, Faculté de Médecine, Université Laval, Québec, QC, Canada G1K 7P4.
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Hains BC, Black JA, Waxman SG. Primary motor neurons fail to up-regulate voltage-gated sodium channel Na(v)1.3/brain type III following axotomy resulting from spinal cord injury. J Neurosci Res 2002; 70:546-52. [PMID: 12404508 DOI: 10.1002/jnr.10402] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Epilepsy occurs in a small proportion of patients with spinal cord injury (SCI), but whether it is due to concomitant traumatic head injury or to changes in cortical motor neurons secondary to axotomy within the spinal cord is not known. Na(v)1.3/brain type III sodium channel expression is up-regulated following peripheral axotomy of dorsal root ganglion (DRG) and facial motor neurons, but, to date, Na(v)1.3 expression has not been examined in upper (cortical) motor neurons following axotomy associated with SCI. In the present study, we examine Na(v)1.3 expression in upper motor neurons within rat primary motor cortex following midthoracic (T9) dorsal column transection, which severs the axons of those cells. Axotomized pyramidal cells were identified by retrograde transport of fluorogold. Immunolabeled cells were confined to layer V of the primary motor cortex and exhibited low levels of Na(v)1.3 staining. After axotomy, no significant changes were detected in Na(v)1.3 density or distribution in injured or uninjured cells, compared with control brains, in contrast to up-regulation of Na(v)1.3 in ipsilateral DRG neurons after sciatic nerve transection. These results do not preclude a role for voltage-gated sodium channels in post-SCI epilepsy but suggest that up-regulated expression of Na(v)1.3 channel is not involved.
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Affiliation(s)
- Bryan C Hains
- Department of Neurology and Paralyzed Veterans of America/Eastern Paralyzed Veterans Association Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut 06510, USA
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Staba RJ, Wilson CL, Bragin A, Fried I, Engel J. Quantitative analysis of high-frequency oscillations (80-500 Hz) recorded in human epileptic hippocampus and entorhinal cortex. J Neurophysiol 2002; 88:1743-52. [PMID: 12364503 DOI: 10.1152/jn.2002.88.4.1743] [Citation(s) in RCA: 435] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
High-frequency oscillations (100-200 Hz), termed ripples, have been identified in hippocampal (Hip) and entorhinal cortical (EC) areas of rodents and humans. In contrast, higher-frequency oscillations (250-500 Hz), termed fast ripples (FR), have been described in seizure-generating limbic areas of rodents made epileptic by intrahippocampal injection of kainic acid and observed in humans ipsilateral to areas of seizure initiation. However, quantitative studies supporting the existence of two spectrally distinct oscillatory events have not been carried out in humans nor has the preferential appearance of FR within seizure generating areas received statistical evaluation based on analysis of a large sample of oscillatory events. Interictal oscillations within the bandwidth of 80-500 Hz were detected in Hip and EC areas of patients with mesial temporal lobe epilepsy using wideband EEG recorded during non-rapid eye-movement sleep from chronically implanted depth electrodes. Power spectral analysis showed that oscillations detected from Hip and EC areas were composed of two spectrally distinct groups. The lower-frequency ripple group was defined by a frequency of 96 +/- 14 Hz (median +/- width), while the higher-frequency FR group had a frequency of 262 +/- 59 Hz. FR oscillations were significantly shorter in duration compared with ripple oscillations (P < 0.0001). In regard to the occurrence of FR and ripples in epileptic Hip and EC, the mean ratio of the number of FR to ripples generated in areas ipsilateral to seizure onset was significantly higher compared with the mean ratio of FR to ripple generation from contralateral areas (P = 0.008). Furthermore, sites ipsilateral to seizure onset with hippocampal atrophy had significantly higher ratios compared with sites contralateral to both seizure onset and hippocampal atrophy (P = 0.001). These data provide compelling quantitative and statistical evidence for the existence of two spectrally distinct groups of limbic oscillations that have frequency and duration characteristics similar to those previously described in epileptic rat and human Hip and EC. The strong association between FR and regions of seizure initiation supports the view that FR reflects pathological hypersynchronous events crucially associated with seizure genesis.
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Affiliation(s)
- Richard J Staba
- Department of Neurobiology, David Geffen School of Medicine at UCLA, Los Angeles, California 90095, USA
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Heterotopic neurons with altered inhibitory synaptic function in an animal model of malformation-associated epilepsy. J Neurosci 2002. [PMID: 12196583 DOI: 10.1523/jneurosci.22-17-07596.2002] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Children with brain malformations often exhibit an intractable form of epilepsy. Although alterations in cellular physiology and abnormal histology associated with brain malformations has been studied extensively, synaptic function in malformed brain regions remains poorly understood. We used an animal model, rats exposed to methylazoxymethanol (MAM) in utero, featuring loss of lamination and distinct nodular heterotopia to examine inhibitory synaptic function in the malformed brain. Previous in vitro and in vivo studies demonstrated an enhanced susceptibility to seizure activity and neuronal hyperexcitability in these animals. Here we demonstrate that inhibitory synaptic function is enhanced in rats exposed to MAM in utero. Using in vitro hippocampal slices and whole-cell voltage-clamp recordings from visualized neurons, we observed a dramatic prolongation of GABAergic IPSCs onto heterotopic neurons. Spontaneous IPSC decay time constants were increased by 195% and evoked IPSC decay time constants by 220% compared with age-matched control CA1 pyramidal cells; no change in IPSC amplitude or rise time was observed. GABA transport inhibitors (tiagabine and NO-711) prolonged evoked IPSC decay kinetics of control CA1 pyramidal cells (or normotopic cells) but had no effect on heterotopic neurons. Immunohistochemical staining for GABA transporters (GAT-1 and GAT-3) revealed a low level of expression in heterotopic cell regions, suggesting a reduced ability for GABA reuptake at these synapses. Together, our data demonstrate that GABA-mediated synaptic function at heterotopic synapses is altered and suggests that inhibitory systems are enhanced in the malformed brain.
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Klitgaard H, Matagne A, Vanneste-Goemaere J, Margineanu DG. Pilocarpine-induced epileptogenesis in the rat: impact of initial duration of status epilepticus on electrophysiological and neuropathological alterations. Epilepsy Res 2002; 51:93-107. [PMID: 12350385 DOI: 10.1016/s0920-1211(02)00099-2] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
This study characterized the electrophysiological and neuropathological changes in rat brains caused by pilocarpine (PILO)-induced status epilepticus (SE) of different duration. SE induced by PILO (375 mg/kg, i.p. adm.) were terminated with a bolus dose of diazepam (10 mg/kg, i.v. adm.) injected 7.5, 15, 30, 60 or 120 min after initiation of the secondary generalization of the SE. Three weeks later, the gain in body weight was significantly reduced in the rats exposed to PILO-induced SE lasting 30 min or more, when compared to controls. Spontaneous seizures were not detected in rats with PILO-induced SE of 7.5 min duration whereas 50 and 25% of the rats exposed to seizure durations of 30 and 120 min expressed motor seizures. Significant alterations reflecting hyperexcitability (increased number of population spikes (PSs)) and reduced paired-pulse inhibition were observed in recordings of hippocampal field potentials from rats with PILO-induced SE of at least 30 min duration. This was substantiated by brain lesions (necrosis in olfactory cortex, hippocampus, amygdala and thalamus) in all rats manifesting a SE of at least 30 min duration. Thus, the results of the present study demonstrate that rats exposed to PILO-induced SE of at least 30 min duration manifest an epileptogenic process, revealed 3 weeks later by several parameters. Among these, hippocampal field potentials appear to represent the most sensitive marker, potentially useful for pharmacological evaluation of drugs with putative antiepileptogenic properties.
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Affiliation(s)
- Henrik Klitgaard
- Preclinical CNS Research, UCB SA Pharma Sector, Chemin du Foriest, B-1420 Braine-l'Alleud, Belgium.
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Benardete EA, Kriegstein AR. Increased excitability and decreased sensitivity to GABA in an animal model of dysplastic cortex. Epilepsia 2002; 43:970-82. [PMID: 12199722 DOI: 10.1046/j.1528-1157.2002.40901.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE Cortical dysplasia (CD) is associated with epilepsy in both the pediatric and adult populations. The mechanism underlying seizures with cortical malformations is still poorly understood. To study the physiology of dysplastic cortex, we developed an experimental model of CD. METHODS Pregnant rats were given intraperitoneal injections of carmustine (1-3-bis-chloroethyl-nitrosourea; BCNU) on embryonic day 15 (E15). Cortical histology was examined in the resulting pups at P0, P28, and P60. In addition, evoked and spontaneous field potential recordings were obtained in cortical slices from adult control and BCNU-exposed rats. Finally, we used whole-cell recordings to compare physiologic properties of pyramidal neurons and gamma-aminobutyric acid (GABA) responses in control and BCNU-treated animals. RESULTS Features characteristic of CD were found in the offspring, including laminar disorganization, cytomegalic neurons, and neuronal heterotopias. Dysplastic cortex also contained abnormal clusters of Cajal-Retzius (CR) cells and disruption of radial glial fibers, as demonstrated with immunohistochemistry. Under conditions of partial GABAA-receptor blockade with 10 microM bicuculline methiodide (BMI), slices of dysplastic cortex demonstrated a significant increase in the number of spontaneous and evoked epileptiform discharges. Individual pyramidal neurons in dysplastic cortex were less sensitive to application of GABA compared with controls. CONCLUSIONS BCNU exposure in utero produces histologic alterations suggestive of CD in rat offspring. Dysplastic cortex from this model demonstrates features of hyperexcitability and decreased neuronal sensitivity to GABA. Such physiologic alterations may underlie the increased epileptogenicity of dysplastic cortex.
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Affiliation(s)
- Ethan A Benardete
- Department of Neurology and Center for Neurobiology and Behavior, Columbia University College of Physicians and Surgeons; and Department of Neurosurgery, NYU Medical Center, New York, New York 10032, USA
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Medvedev AV. Epileptiform spikes desynchronize and diminish fast (gamma) activity of the brain. An "anti-binding" mechanism? Brain Res Bull 2002; 58:115-28. [PMID: 12121821 DOI: 10.1016/s0361-9230(02)00768-2] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Fast (20-100 Hz) rhythms of electrical activity of the brain have been suggested to be important for perception and cognition providing a mechanism for temporal binding of neural activities underlying mental representations. Also, fast rhythms often precede epileptiform discharges in patients and some experimental models. Generalized slow (2-3 Hz) spike activity after systemic kainic acid (KA) in the rat has been shown to be preceded by intense gamma activity. A relationship between the intensified gamma rhythms and the subsequent spike activity was studied during kainate-induced acute epileptogenesis. Power, multiple coherence and phase were analyzed at frequencies 1-100 Hz in the EEG recorded from the hippocampal-neocortical structures of the rat. Gamma rhythms, extremely intense and highly coherent at the onset of discharges, were followed by a slow rhythm of epileptiform spikes/sharp waves. During this spike activity and immediately afterwards, the gamma power and coherence were significantly decreased. These data show an antagonism between gamma rhythms and spike activity and ability of the latter to desynchronize and suppress the former. They are supportive to the hypothesis that epileptiform spike activity may result from the extreme activation of the "anti-binding" mechanism controlling temporal binding at high frequencies. It is suggested that when fast activity is abnormally intensified, "over-binding" with global synchrony of gamma rhythms can occur in the neural networks. It may lead to inadequate synaptic modifications. To prevent this process, epileptiform discharge develops as a protective mechanism suppressing fast activity. This proposal has implications for our understanding of temporal binding in the brain and how its excessive activation may precipitate the development of pathological states.
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Affiliation(s)
- Andrei V Medvedev
- Department of Medicine and Centre for Neuroscience, Flinders University of South Australia, Bedford Park, SA, Australia.
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Abstract
Cortical dysplasias are associated with both epilepsy and cognitive impairments in humans. Similarly, several animal models of cortical dysplasia show that dysplasia causes increased seizure susceptibility and behavioral deficits in vivo and increased levels of excitability in vitro. As most current animal models involve either global disruptions in cortical architecture or the induction of lesions, it is not yet clear whether small spontaneous neocortical malformations are also associated with increased excitability or seizure susceptibility. Small groups of displaced neurons in layer I of the neocortex, ectopias, have been identified in patients with cognitive impairments, and similar malformations occur sporadically in some inbred lines of mice where they are associated with behavioral and sensory-processing deficits. In a previous study, we characterized the physiology of cells within neocortical ectopias, in one of the inbred lines (NXSM-D/Ei) and showed that the presence of multiple ectopias is associated with the generation of spontaneous epileptiform activity in slices. In this study, we use extracellular recordings from brain slices to show that even single-layer I ectopias are associated with higher excitability. Specifically, slices that contain single ectopias display epileptiform activity at significantly lower concentrations of the GABA(A) receptor antagonist bicuculline than do slices without ectopias (either from opposite hemispheres or animals without ectopias). Moreover, because removal of ectopias from slices does not restore normal excitability, enhanced excitability is not generated within the ectopia. Finally, we show that in vivo, mice with ectopias are more sensitive to the convulsant pentylenetetrazole than are mice without ectopias. Together these results suggest that alterations in cortical hemispheres containing focal layer I malformations increase cortical excitability and that even moderately small spontaneous cortical dysplasias are associated with increased excitability in vitro and in vivo.
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Affiliation(s)
- Lisa A Gabel
- Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut 06269, USA
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Wittner L, Maglóczky Z, Borhegyi Z, Halász P, Tóth S, Eross L, Szabó Z, Freund TF. Preservation of perisomatic inhibitory input of granule cells in the epileptic human dentate gyrus. Neuroscience 2002; 108:587-600. [PMID: 11738496 DOI: 10.1016/s0306-4522(01)00446-8] [Citation(s) in RCA: 138] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Temporal lobe epilepsy is known to be associated with hyperactivity that is likely to be generated or amplified in the hippocampal formation. The majority of granule cells, the principal cells of the dentate gyrus, are found to be resistant to damage in epilepsy, and may serve as generators of seizures if their inhibition is impaired. Therefore, the parvalbumin-containing subset of interneurons, known to provide the most powerful inhibitory input to granule cell somata and axon initial segments, were examined in human control and epileptic dentate gyrus. A strong reduction in the number of parvalbumin-containing cells was found in the epileptic samples especially in the hilar region, although in some patches of the granule cell layer parvalbumin-positive terminals that form vertical clusters characteristic of axo-axonic cells were more numerous than in controls. Analysis of the postsynaptic target elements of parvalbumin-positive axon terminals showed that they form symmetric synapses with somata, dendrites, axon initial segments and spines as in the control, but the ratio of axon initial segment synapses was increased in the epileptic tissue (control: 15.9%, epileptic: 31.3%). Furthermore, the synaptic coverage of granule cell axon initial segments increased more than three times (control: 0.52, epileptic: 2.10 microm synaptic length/100 microm axon initial segment membrane) in the epileptic samples, whereas the amount of somatic symmetric synapses did not change significantly. Although the number of parvalbumin-positive interneurons is decreased, the perisomatic inhibitory input of dentate granule cells is preserved in temporal lobe epilepsy. Basket and axo-axonic cell terminals - whether positive or negative for parvalbumin - are present, moreover, the axon collaterals targeting axon initial segments sprout in the epileptic dentate gyrus. We suggest that perisomatic inhibitory interneurons survive in epilepsy, but their somadendritic compartment and partly the axon loses parvalbumin or immunoreactivity for parvalbumin. The hyperinnervation of axon initial segments might be a compensatory change in the inhibitory network, but at the same time may lead to a more effective synchronization of granule cell firing that could contribute to the generation or amplification of epileptic seizures.
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Affiliation(s)
- L Wittner
- Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary
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