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Gauvin DV, Zimmermann ZJ, Dalton JA. De-risking in Tier I CNS safety assessments is the primary function of study design and technical training of laboratory staff observers. Regul Toxicol Pharmacol 2022; 129:105116. [PMID: 35017023 DOI: 10.1016/j.yrtph.2022.105116] [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: 11/01/2021] [Revised: 12/28/2021] [Accepted: 01/05/2022] [Indexed: 10/19/2022]
Abstract
Derisking is not a pharmaceutical industry strategy to reduce time, effort, or costs in drug development. Derisking strategies originated within the National Institutes of Health as a predicate to good science. There is a growing sentiment within drug development programs to diminish the importance of behavioral measures in toxicological studies and in the Tiered Safety assessment plans of the U.S. Regulatory Agencies and the International Commission on Harmonization. The validity and reliability of the Functional Observational Batter (FOB) is critically dependent on consistency and technical quality in each risk assessment plan. US Federal and International drug approval organizations have universally adopted the concept of principles of test construction rather than delineating specific behavioral assay endpoints for inclusion of the FOB in nonclinical safety protocols. The validity and reliability of behavioral observations in standardized neurotoxicity screening is critically dependent on the FOB developed by the Study Director with the Sponsor throughout all stages of testing.. The individual risk factors selected for observation to be included in the early Tier 1 safety program should be determined by the mechanism and mode of action of the test article. The results of Tier I testing are the basis for Tier II testing designs. Critical to the compliance with Good Laboratory Practices is the documentation of training of the operational staff scheduled to conduct all aspects of the established protocol.
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Affiliation(s)
- David V Gauvin
- Neurobehavioral Sciences, Charles River Laboratories, Mattawan, 49071, MI, USA.
| | | | - Jill A Dalton
- Neurobehavioral Sciences, Charles River Laboratories, Mattawan, 49071, MI, USA
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Łukawski K, Raszewski G, Czuczwar SJ. Interactions of aliskiren, a direct renin inhibitor, with antiepileptic drugs in the test of maximal electroshock in mice. Eur J Pharmacol 2018; 819:108-113. [PMID: 29191768 DOI: 10.1016/j.ejphar.2017.11.037] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2017] [Revised: 11/13/2017] [Accepted: 11/23/2017] [Indexed: 02/06/2023]
Abstract
Experimental studies showed that certain angiotensin-converting enzyme inhibitors and angiotensin AT1 receptor antagonists can decrease seizure severity in rodents. Additionally, some of these blockers of the renin-angiotensin system have been documented to enhance the anticonvulsant activity of antiepileptic drugs against maximal electroshock-induced seizures. The aim of the current study was to investigate the effect of aliskiren, a direct renin inhibitor and a novel antihypertensive drug, on the protective action of numerous antiepileptic drugs (carbamazepine, valproate, clonazepam, phenobarbital, oxcarbazepine, lamotrigine, topiramate and pregabalin) in the test of maximal electroshock in mice. The examined drugs were administered intraperitoneally. Aliskiren up to a dose of 75mg/kg did not affect the threshold for electroconvulsions, however, aliskiren (75mg/kg) enhanced the anticonvulsant action of clonazepam and valproate. Following aliskiren treatment, a higher brain concentration of valproate was noted, suggesting a pharmacokinetic interaction. In the rota-rod test, the concomitant treatment with aliskiren (50 or 75mg/kg) and clonazepam (22.6mg/kg) impaired motor coordination while clonazepam (22.6mg/kg) alone showed strong tendency towards this impairment. The combination of aliskiren (75mg/kg) with phenobarbital (25.5mg/kg) caused long-term memory deficits in the passive avoidance task. This study shows that there are no negative interactions between aliskiren and the examined antiepileptic drugs as concerns their anticonvulsant activity. Aliskiren even potentiated the anticonvulsant action of clonazepam and valproate against maximal electroshock. The impact of aliskiren alone on seizure activity or on the anticonvulsant and adverse activity of antiepileptic drugs needs further evaluation in other animal models of seizures.
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Affiliation(s)
- Krzysztof Łukawski
- Department of Physiopathology, Institute of Rural Health, Jaczewskiego 2, 20-090 Lublin, Poland; Department of Pathophysiology, Medical University of Lublin, Jaczewskiego 8, 20-090 Lublin, Poland.
| | - Grzegorz Raszewski
- Department of Physiopathology, Institute of Rural Health, Jaczewskiego 2, 20-090 Lublin, Poland
| | - Stanisław J Czuczwar
- Department of Physiopathology, Institute of Rural Health, Jaczewskiego 2, 20-090 Lublin, Poland; Department of Pathophysiology, Medical University of Lublin, Jaczewskiego 8, 20-090 Lublin, Poland
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Lin EC, Combe CL, Gasparini S. Differential Contribution of Ca 2+-Dependent Mechanisms to Hyperexcitability in Layer V Neurons of the Medial Entorhinal Cortex. Front Cell Neurosci 2017; 11:182. [PMID: 28713246 PMCID: PMC5491848 DOI: 10.3389/fncel.2017.00182] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Accepted: 06/13/2017] [Indexed: 11/13/2022] Open
Abstract
Temporal lobe epilepsy is characterized by recurrent seizures in one or both temporal lobes of the brain; some in vitro models show that epileptiform discharges initiate in entorhinal layer V neurons and then spread into other areas of the temporal lobe. We previously found that, in the presence of GABAA receptor antagonists, stimulation of afferent fibers, terminating both at proximal and distal dendritic locations, initiated hyperexcitable bursts in layer V medial entorhinal neurons. We investigated the differential contribution of Ca2+-dependent mechanisms to the plateaus underlying these bursts at proximal and distal synapses. We found that the NMDA glutamatergic antagonist D,L-2-amino-5-phosphonovaleric acid (APV; 50 μM) reduced both the area and duration of the bursts at both proximal and distal synapses by about half. The L-type Ca2+ channel blocker nimodipine (10 μM) and the R- and T-type Ca2+ channel blocker NiCl2 (200 μM) decreased the area of the bursts to a lesser extent; none of these effects appeared to be location-dependent. Remarkably, the perfusion of flufenamic acid (FFA; 100 μM), to block Ca2+-activated non-selective cation currents (ICAN) mediated by transient receptor potential (TRP) channels, had a location-dependent effect, by abolishing burst firing and switching the suprathreshold response to a single action potential (AP) for proximal stimulation, but only minimally affecting the bursts evoked by distal stimulation. A similar outcome was found when FFA was pressure-applied locally around the proximal dendrite of the recorded neurons and in the presence of a selective blocker of melastatin TRP (TRPM) channels, 9-phenanthrol (100 μM), whereas a selective blocker of canonical TRP (TRPC) channels, SKF 96365, did not affect the bursts. These results indicate that different mechanisms might contribute to the initiation of hyperexcitability in layer V neurons at proximal and distal synapses and could shed light on the initiation of epileptiform activity in the entorhinal cortex.
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Affiliation(s)
- Eric C Lin
- Neuroscience Center of Excellence, Louisiana State University Health Sciences CenterNew Orleans, LA, United States
| | - Crescent L Combe
- Neuroscience Center of Excellence, Louisiana State University Health Sciences CenterNew Orleans, LA, United States
| | - Sonia Gasparini
- Neuroscience Center of Excellence, Louisiana State University Health Sciences CenterNew Orleans, LA, United States.,Department of Cell Biology and Anatomy, Louisiana State University Health Sciences CenterNew Orleans, LA, United States
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Badawy RAB, Johnson KA, Cook MJ, Harvey AS. A mechanistic appraisal of cognitive dysfunction in epilepsy. Neurosci Biobehav Rev 2012; 36:1885-96. [PMID: 22617705 DOI: 10.1016/j.neubiorev.2012.05.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2012] [Revised: 03/24/2012] [Accepted: 05/13/2012] [Indexed: 12/14/2022]
Abstract
A strong relationship between the clinical characteristics of epilepsy and the nature of cognitive impairments associated with the condition has been found, but the nature of this relationship appears to be quite complex and not well understood. This review presents a summary of the research on the interaction between cognition and epilepsy, surveyed from a mechanistic perspective with the aim of clarifying factors that contribute to the co-existence of both disorders. The physiological basis underpinning cognitive processing is first reviewed. The physiology of epilepsy is reviewed, with emphasis placed on interictal discharges and seizures. The nature of the impact of epilepsy on cognition is described, with transient and prolonged effects distinguished. Finally, the complexity of the co-morbidity between cognitive dysfunction and epilepsy is discussed in relation to childhood and adult-onset epilepsy syndromes and severe epileptic encephalopathies. Structural and functional abnormalities exist in patients with epilepsy that may underpin both the cognitive dysfunction and epilepsy, highlighting the complexity of the association. Research, possibly of a longitudinal nature, is needed to elucidate this multifactorial relationship between cognitive dysfunction and epilepsy.
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Affiliation(s)
- Radwa A B Badawy
- Department of Clinical Neurosciences, St. Vincent's Hospital, Melbourne, Victoria, Australia; Department of Medicine, Melbourne, Victoria, Australia; Electrical and Electronic Engineering, Melbourne, Victoria, Australia. ,
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Interactions between ACE inhibitors and classical antiepileptic drugs in the mouse maximal electroshock seizures. Pharmacol Biochem Behav 2011; 100:152-6. [DOI: 10.1016/j.pbb.2011.06.030] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/07/2011] [Revised: 06/17/2011] [Accepted: 06/26/2011] [Indexed: 12/15/2022]
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Parks GS, Okumura SM, Gohil K, Civelli O. Mice lacking Melanin Concentrating Hormone 1 receptor are resistant to seizures. Neurosci Lett 2010; 484:104-7. [PMID: 20709149 DOI: 10.1016/j.neulet.2010.08.018] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2010] [Revised: 08/02/2010] [Accepted: 08/06/2010] [Indexed: 11/16/2022]
Abstract
The Melanin Concentrating Hormone (MCH) system is widely expressed throughout the central nervous system and regulates a variety of physiological functions. It has been reported that acute central administration of MCH inhibits pentylenetetrazol (PTZ)-induced seizures in rats. In the present study MCH(1) receptor knockout mice (MCH(1)R-KO) were used to investigate the role of MCH signaling in modulating seizure susceptibility. Seizure behaviors were compared between MCH(1)R-KO and wild type (MCH(1)R-WT) mice following administration of the convulsant compounds PTZ or pilocarpine. PTZ injection induced clonic seizures in MCH(1)R-WT mice but failed to induce them in MCH(1)R-KO mice. More than twice as many injections of intermittently administered low dose PTZ were required to induce clonic seizures in MCH(1)R-KO mice than in MCH(1)R-WT mice. Following pilocarpine injection, MCH(1)R-WT mice experienced clonic seizures and most had tonic seizures and entered status epilepticus, while all MCH(1)R-KO mice were completely resistant to these effects. MCH(1)R-KO mice were also observed to be strongly protected from the development of PTZ kindling. Genetic deletion of MCH(1)R conferred resistance to all seizure models tested in this study. The data indicate that the MCH system is involved in the regulation of PTZ and pilocarpine seizure threshold.
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Affiliation(s)
- Gregory S Parks
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA 92697, USA
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Łukawski K, Janowska A, Jakubus T, Tochman-Gawda A, Czuczwar SJ. Angiotensin AT1 receptor antagonists enhance the anticonvulsant action of valproate in the mouse model of maximal electroshock. Eur J Pharmacol 2010; 640:172-7. [DOI: 10.1016/j.ejphar.2010.04.053] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2009] [Revised: 03/30/2010] [Accepted: 04/24/2010] [Indexed: 10/19/2022]
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Hellier JL, Grosshans DR, Coultrap SJ, Jones JP, Dobelis P, Browning MD, Staley KJ. NMDA receptor trafficking at recurrent synapses stabilizes the state of the CA3 network. J Neurophysiol 2007; 98:2818-26. [PMID: 17728388 DOI: 10.1152/jn.00346.2007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Metaplasticity describes the stabilization of synaptic strength such that strong synapses are likely to remain strong while weak synapses are likely to remain weak. A potential mechanism for metaplasticity is a correlated change in both N-methyl-D-aspartate (NMDA) receptor-mediated postsynaptic conductance and synaptic strength. Synchronous activation of CA3-CA3 synapses during spontaneous bursts of population activity caused long-term potentiation (LTP) of recurrent CA3-CA3 glutamatergic synapses under control conditions and depotentiation when NMDA receptors were partially blocked by competitive antagonists. LTP was associated with a significant increase in membrane-bound NMDA receptors, whereas depotentiation was associated with a significant decrease in membrane-bound NMDA receptors. During burst activity, further depotentiation could be induced by sequential reductions in antagonist concentration, consistent with a depotentiation-associated reduction in membrane-bound NMDA receptors. The decrease in number of membrane-bound NMDA receptors associated with depotentiation reduced the probability of subsequent potentiation of weakened synapses in the face of ongoing synchronous network activity. This molecular mechanism stabilizes synaptic strength, which in turn stabilizes the state of the CA3 neuronal network, reflected in the frequency of spontaneous population bursts.
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Affiliation(s)
- Jennifer L Hellier
- Department of Pediatrics, University of Colorado Health Sciences Center, Denver, USA
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Swiercz W, Cios K, Hellier J, Yee A, Staley K. Effects of synaptic depression and recovery on synchronous network activity. J Clin Neurophysiol 2007; 24:165-74. [PMID: 17414972 DOI: 10.1097/wnp.0b013e318033756f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
SUMMARY The output of an artificial neural network of spiking neurons linked by glutamatergic synapses subject to use-dependent depression was compared with physiologic data obtained from rat hippocampal area CA3 in vitro. The authors evaluated how network burst initiation and termination was affected by activity-dependent depression and recovery under a variety of experimental conditions including neuronal membrane depolarization, altered glutamate release probability, the strength of synaptic inhibition, and long-term potentiation and long-term depression of recurrent glutamatergic synapses. The results of computational experiments agreed with the in vitro data and support the idea that synaptic properties, including activity-dependent depression and recovery, play important roles in the timing and duration of spontaneous bursts of network activity. This validated network model is useful for experiments that are not feasible in vitro, and makes possible the investigation of two-dimensional aspects of burst propagation and termination.
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Affiliation(s)
- Waldemar Swiercz
- From the Neurology Department, Massachusetts General Hospital, Boston, MA 02114, USA
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Abstract
A critical goal of neuroscience is to fully understand neural processes and their relations to mental processes, and cognitive, affective, and behavioral disorders. Computational modeling, although still in its infancy, continues to play a central role in this endeavor. Presented here is a review of different aspects of computational modeling that help to explain many features of neuropsychological syndromes and psychiatric disease. Recent advances in computational modeling of epilepsy, cortical reorganization after lesions, Parkinson's and Alzheimer diseases are also reviewed. Additionally, this chapter will also identify some trends in the computational modeling of brain functions.
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Affiliation(s)
- Włodzisław Duch
- Department of Informatics, Nicolaus Copernicus University, Torun, Poland
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Solger J, Heinemann U, Behr J. Electrical and Chemical Long-term Depression Do Not Attenuate Low-Mg2+-induced Epileptiform Activity in the Entorhinal Cortex. Epilepsia 2005; 46:509-16. [PMID: 15816944 DOI: 10.1111/j.0013-9580.2005.41204.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
PURPOSE Low-frequency electrical and magnetic stimulation of cortical brain regions has been shown to reduce cortical excitability and to decrease the susceptibility to seizures in humans and in vivo models of epilepsy. The induction of long-term depression (LTD) or depotentiation of a seizure-related long-term potentiation has been proposed to be part of the underlying mechanism. With the low-Mg(2+)-model of epilepsy, this study investigated the effect of electrical LTD, chemical LTD, and depotentiation on the susceptibility of the entorhinal cortex to epileptiform activity. METHODS The experiments were performed on isolated entorhinal cortex slices obtained from adult Wistar rats and mice. With extracellular recording techniques, we studied whether LTD induced by (a) three episodes of low-frequency paired-pulse stimulation (3 x 900 paired pulses at 1 Hz), and by (b) bath-applied N-methyl-D-aspartate (NMDA, 20 microM) changes time-to-onset, duration, and frequency of seizure-like events (SLEs) induced by omitting MgSO(4) from the artificial cerebrospinal fluid. Next we investigated the consequences of depotentiation on SLEs themselves by applying low-frequency stimulation after onset of low-Mg(2+)-induced epileptiform activity. RESULTS LTD, induced either by low-frequency stimulation or by bath-applied NMDA, had no effect on time-to-onset, duration, and frequency of SLEs compared with unconditioned slices. Low-frequency stimulation after onset of SLEs did not suppress but induced SLEs that lasted for the time of stimulation and were associated with a simultaneous increase of the extracellular K(+) concentration. CONCLUSIONS Our study demonstrates that neither conditioning LTD nor brief low-frequency stimulation decreases the susceptibility of the entorhinal cortex to low-Mg(2+)-induced epileptiform activity. The present study does not support the hypothesis that low-frequency brain stimulation exerts its anticonvulsant effect via the induction of LTD or depotentiation.
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Affiliation(s)
- Jörg Solger
- Neuroscience Research Center of the Charité, Humboldt University Berlin, Berlin, Germany
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Rivera C, Li H, Thomas-Crusells J, Lahtinen H, Viitanen T, Nanobashvili A, Kokaia Z, Airaksinen MS, Voipio J, Kaila K, Saarma M. BDNF-induced TrkB activation down-regulates the K+-Cl- cotransporter KCC2 and impairs neuronal Cl- extrusion. J Cell Biol 2002; 159:747-52. [PMID: 12473684 PMCID: PMC2173387 DOI: 10.1083/jcb.200209011] [Citation(s) in RCA: 384] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2002] [Revised: 10/31/2002] [Accepted: 11/01/2002] [Indexed: 01/19/2023] Open
Abstract
Pathophysiological activity and various kinds of traumatic insults are known to have deleterious long-term effects on neuronal Cl- regulation, which can lead to a suppression of fast postsynaptic GABAergic responses. Brain-derived neurotrophic factor (BDNF) increases neuronal excitability through a conjunction of mechanisms that include regulation of the efficacy of GABAergic transmission. Here, we show that exposure of rat hippocampal slice cultures and acute slices to exogenous BDNF or neurotrophin-4 produces a TrkB-mediated fall in the neuron-specific K+-Cl- cotransporter KCC2 mRNA and protein, as well as a consequent impairment in neuronal Cl- extrusion capacity. After kindling-induced seizures in vivo, the expression of KCC2 is down-regulated in the mouse hippocampus with a spatiotemporal profile complementary to the up-regulation of TrkB and BDNF. The present data demonstrate a novel mechanism whereby BDNF/TrkB signaling suppresses chloride-dependent fast GABAergic inhibition, which most likely contributes to the well-known role of TrkB-activated signaling cascades in the induction and establishment of epileptic activity.
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Affiliation(s)
- Claudio Rivera
- Department of Biosciences, Division of Animal Physiology, Institute of Biotechnology, University of Helsinki, Finland.
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Finnerty GT, Jefferys JGR. Investigation of the neuronal aggregate generating seizures in the rat tetanus toxin model of epilepsy. J Neurophysiol 2002; 88:2919-27. [PMID: 12466418 DOI: 10.1152/jn.00211.2002] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A key question in epilepsy is the organization and size of the neuronal networks necessary for generating seizures. Hypotheses include: a single focal neuronal network drives seizure discharges across the brain, which may or may not be identical with the circuits that generate interictal spikes; or multiple neuronal networks link together in re-entrant loops or other long-range networks. It remains unclear whether any of these hypotheses apply to spontaneous seizures in freely moving animals. We used the tetanus toxin chronic model of epilepsy to test the different predictions made by each hypothesis about the propagation and interaction of epileptic discharges during seizures. Seizures could start in either the injected or noninjected dorsal hippocampus, suggesting that seizures have multifocal onsets in the tetanus toxin model. During seizures, individual bursts propagated in either direction, both between the right and left dorsal hippocampi, and between CA3 and the dentate gyrus in the same hippocampus. These findings argue against one site "driving" seizures or seizures propagating around a limbic loop. Specifically, the side leading each burst switched a median of three times during the first 20 s of a seizure. Analysis of bursts during seizures suggested that the network at each recording site acted like a neuronal oscillator. Coupling of population spikes in right and left CA3 increased during the early part of seizures, but the cross-correlation of their whole-discharge waveforms changed little over the same period. Furthermore, the polarity of the phase difference between population spikes did not follow the phase difference for complete discharges. We concluded that the neuronal aggregate necessary for seizures in our animals comprises multiple spatially distributed neuronal networks and that the increased synchrony of the output (population spike firing) of these networks during the early part of seizures may contribute to seizure generation.
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Affiliation(s)
- G T Finnerty
- Neuronal Networks Group, Department of Physiology and Biophysics, St. Mary's Hospital Medical School, Imperial College of Science, Technology and Medicine, London W2 1PG, United Kingdom
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Barbarosie M, Louvel J, D'Antuono M, Kurcewicz I, Avoli M. Masking synchronous GABA-mediated potentials controls limbic seizures. Epilepsia 2002; 43:1469-79. [PMID: 12460247 DOI: 10.1046/j.1528-1157.2002.17402.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE We determined how CA3-driven interictal discharges block ictal activity generated in the entorhinal cortex during bath application of 4-aminopyridine (4AP, 50 microM). METHODS Field potential and [K+]o recordings were obtained from mouse combined hippocampus-entorhinal cortex slices maintained in vitro. RESULTS 4AP induced N-methyl-d-aspartate (NMDA) receptor-dependent ictal discharges that originated in the entorhinal cortex, disappeared over time, but were reestablished by cutting the Schaffer collateral (n = 20) or by depressing CA3 network excitability with local application of glutamatergic receptor antagonists (n = 5). In addition, two types of interictal activity occurred throughout the experiment. The first type was CA3 driven and was abolished by a non-NMDA glutamatergic receptor antagonist. The second type was largely contributed by gamma-aminobutyric acid type A (GABAA) receptor-mediated conductances and persisted during blockade of glutamatergic transmission. The absence of CA3-driven interictal discharges in the entorhinal cortex after Schaffer collateral cut facilitated the GABA-mediated interictal potentials that corresponded to large [K+]o elevations and played a role in ictal discharge initiation. Accordingly, ictal discharges along with GABA-mediated interictal potentials disappeared during GABAA-receptor blockade (n = 7) or activation of mu-opioid receptors that inhibit GABA release (n = 4). CONCLUSIONS Our findings suggest that CA3-driven interictal events restrain ictal discharge generation in the entorhinal cortex by modulating the size of interictal GABA-mediated potentials that lead to large [K+]o elevations capable of initiating ictal discharges in this structure.
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Affiliation(s)
- Michaela Barbarosie
- Montreal Neurological Institute and Department of Neurology, McGill University, Montreal, Quebec, Canada
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Quilichini PP, Diabira D, Chiron C, Ben-Ari Y, Gozlan H. Persistent epileptiform activity induced by low Mg2+ in intact immature brain structures. Eur J Neurosci 2002; 16:850-60. [PMID: 12372021 DOI: 10.1046/j.1460-9568.2002.02143.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We have determined the properties of seizures induced in vitro during the first postnatal days using intact rat cortico-hippocampal formations (CHFs) and extracellular recordings. Two main patterns of activity were generated by nominally Mg2+-free ACSF in hippocampal and cortical regions: ictal-like events (ILEs) and late recurrent interictal discharges (LRDs). They were elicited at distinct developmental periods and displayed different pharmacological properties. ILEs were first observed in P1 CHFs 52 +/- 7 min after application of low-Mg2+ ACSF (frequency 1.5 +/- 0.3 h-1, duration 86 +/- 3 s). There is a progressive age-dependent maturation of ILEs characterized by a decrease in their onset and an increase in their frequency and duration. ILEs were abolished by d-APV and Mg2+ ions. From P7, ILEs were followed by LRDs that appeared 89 +/- 8 min after application of low-Mg2+ ACSF (frequency approximately 1 Hz, duration 0.66 s, amplitude 0.31 +/- 0.03 mV). LRDs were no longer sensitive to d-APV or Mg2+ ions and persisted for at least 24 h in low-Mg2+ or in normal ACSF. ILEs and LRDs were synchronized in limbic and cortical regions with 10-40 ms latency between the onsets of seizures. Using a double chamber that enables independent superfusion of two interconnected CHFs, we report that ILEs and LRDs generated in one CHF propagated readily to the other one that was being kept in ACSF. Therefore, at a critical period of brain development, recurrent seizures induce a permanent form of hyperactivity in intact brain structures and this preparation provides a unique opportunity to study the consequences of seizures at early developmental stages.
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Affiliation(s)
- P P Quilichini
- INMED-INSERM Unité 29, 163, route de Luminy, BP 13, 13273 Marseille cedex 9, France
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Cyclic nucleotide-gated channels contribute to the cholinergic plateau potential in hippocampal CA1 pyramidal neurons. J Neurosci 2001. [PMID: 11698582 DOI: 10.1523/jneurosci.21-22-08707.2001] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Plateau potentials are prolonged membrane depolarizations that are observed in hippocampal pyramidal neurons when spiking and Ca(2+) entry occur in combination with muscarinic receptor activation. In this study, we used whole-cell voltage clamping to study the current underlying the plateau potential and to determine the cellular signaling pathways contributing to this current. When combined with muscarinic stimulation, depolarizing command potentials that evoked Ca(2+) influx elicited a prolonged tail current (I(tail)) that had an extrapolated reversal potential of -20 mV. I(tail) was not observed when intracellular Ca(2+) levels were chelated with 10 mm intracellular BAPTA, and I(tail) was reversibly depressed in low external sodium. When I(tail) was evoked at intervals >3 min, current amplitudes were stable for up to 1 hr. However, at shorter intervals, I(tail) was refractory, with a time constant of recovery of 43.5 sec. The inhibitors of soluble guanylate cyclase 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one and 6-anilino-5,8-quinolinequinone depressed I(tail) and zaprinast, which blocks cGMP-specific phosphodiesterase, enhanced I(tail), suggesting that a component of I(tail) was activated by cGMP. The inhibitors of cyclic nucleotide-gated (CNG) channels l-cis-diltiazem and 2',4'-dichlorobenzamil reversibly depressed I(tail). However, protein kinase G inhibition had no effect. Therefore, these results indicate that a component of I(tail) is attributable to activation of CNG channels. We conclude that Ca(2+) influx when combined with muscarinic receptor activation activates soluble guanylate cyclase and increases cGMP levels. The increased cGMP activates CNG channels and leads to prolonged depolarization. The cation conductance of the CNG channel contributes to the prolonged depolarization of the plateau potential.
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Tomkins O, Kaufer D, Korn A, Shelef I, Golan H, Reichenthal E, Soreq H, Friedman A. Frequent blood-brain barrier disruption in the human cerebral cortex. Cell Mol Neurobiol 2001; 21:675-91. [PMID: 12043841 DOI: 10.1023/a:1015147920283] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
1. The blood-brain barrier (BBB) protects the brain from circulating xenobiotic agents. The pathophysiology, time span, spatial pattern, and pathophysiological consequences of BBB disruptions are not known. 2. Here, we report the quantification of BBB disruption by measuring enhancement levels in computerized tomography brain images. 3. Pathological diffuse enhancement associated with elevated albumin levels in the cerebrospinal fluid (CSF) was observed in the cerebral cortex of 28 out of 43 patients, but not in controls. Four patients displayed weeks-long focal BBB impairment. In 19 other patients, BBB disruption was significantly associated with elevated blood pressure, body temperature, serum cortisol, and stress-associated CSF 'readthrough" acetylcholinesterase. Multielectrode electroencephalography revealed enhanced slow-wave activities in areas of focal BBB disruption. Thus, quantification of BBB disruption using minimally invasive procedures, demonstrated correlations with molecular, clinical, and physiological stress-associated indices. 4. These sequelae accompany a wide range of neurological disorders, suggesting that persistent, detrimental BBB disruption is considerably more frequent than previously assumed.
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Affiliation(s)
- O Tomkins
- Department of Physiology and Neurosurgery, Soroka University Hospital, Zlotowski Center of Neuroscience, Ben-Gurion University, Beersheva, Israel
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Mehta A, Eberle-Wang K, Chesselet MF. Increased m-CPP-induced oral dyskinesia after lesion of serotonergic neurons. Pharmacol Biochem Behav 2001; 68:347-53. [PMID: 11267640 DOI: 10.1016/s0091-3057(00)00476-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Peripheral administration of the 5-hydroxytryptamine (5-HT)(2C/1B) agonist 1-(m-chlorophenyl)piperazine (m-CPP) produces abnormal orofacial movements in rats. We have previously shown that this behavior is mediated by 5-HT(2C) receptors in the subthalamic nucleus [Neuroscience 72 (1996) 117]. The present studies examined this effect after serotonin depletion to determine whether removal of endogenous serotonin affected this behavioral response and/or subthalamic 5-HT(2C) receptors. Rats received an intraventricular infusion of the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT, 100 mg/10 ml) or vehicle after desipramine pretreatment (25 mg/kg ip). The efficacy of serotonin depletion was confirmed by a decrease in serotonin uptake sites measured by autoradiography. Oral dyskinesia induced by peripheral administration of m-CPP (1.0 mg/kg ip) was markedly increased in lesioned rats compared to sham-operated controls 4 and 8 but not 12 days after the lesion. A subset of lesioned rats that displayed transient seizures after m-CPP injection did not prevent the measurement of oral dyskinesia during the observation period. No differences in 5-HT(2C) receptor levels were found with ligand-binding autoradiography in the subthalamic nucleus, or in other brain regions that express this receptor, in rats sacrificed 5 days following 5,7-DHT lesions. The data indicate that lesion of serotonergic neurons in adult rats induces a transient increase in motor responses mediated by subthalamic 5-HT(2C) receptors. These data suggest that functional alterations in serotonergic transmission in the subthalamic nucleus may be involved in the pathophysiology of hyperkinetic movement disorders.
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Affiliation(s)
- A Mehta
- Department of Neurology, UCLA School of Medicine, Los Angeles, CA 90095, USA
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Sargsyan AR, Papatheodoropoulos C, Kostopoulos GK. Modeling of evoked field potentials in hippocampal CA1 area describes their dependence on NMDA and GABA receptors. J Neurosci Methods 2001; 104:143-53. [PMID: 11164240 DOI: 10.1016/s0165-0270(00)00334-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
A computer model of the hippocampal CA1 area, which receives synaptic inputs from CA3 neurons via the Schaffer collaterals, was constructed. Pyramidal cells (PC) and two types of interneurons were represented by compartmental models, and mechanisms of feed-forward inhibition (FFI) and recurrent inhibition were incorporated. Four types of receptor mediated synaptic conductances were used in the model: those of AMPA, GABA(A), GABA(B) and N-methyl-D-aspartate (NMDA). The output of the model, i.e. the field potential calculated at various points in space, was able to qualitatively reproduce the main features of field potentials, which were recorded in hippocampal slices maintained in vitro for both subthreshold and suprathreshold stimulation. In both the experiments and the model, the influence of NMDA and GABA synaptic currents affected mostly the late, decaying phase of evoked field potentials. The modeled interaction of NMDA and GABA components could explain the enhancement of the field potential late phase, which was observed experimentally during paired-pulse stimulation.
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Affiliation(s)
- A R Sargsyan
- Department of Physiology, Medical School, University of Patras, 26500 Patras, Greece
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20
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Borck C, Jefferys JG. Seizure-like events in disinhibited ventral slices of adult rat hippocampus. J Neurophysiol 1999; 82:2130-42. [PMID: 10561393 DOI: 10.1152/jn.1999.82.5.2130] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Epileptic discharges lasting 2-90 s, were studied in vitro in slices from the ventral hippocampus of adult rats, in which inhibition was blocked acutely with bicuculline methiodide (BMI, 5-30 microM) and potassium ([K(+)](o)) raised to 5 mM. These seizure-like events (SLEs) comprised three distinct phases, called here primary, secondary, and tertiary bursts. Primary bursts lasted 90-150 ms. Secondary bursts lasted a further 70-250 ms, comprising a short series of afterdischarges riding on the same depolarization as the primary burst. Finally a train of tertiary bursts started with a peak frequency of 5-10 Hz and could last >1 min. Slices from the ventral hippocampus showed significantly higher susceptibility to SLEs than did dorsal slices. SLEs proved sensitive to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonists. They were insensitive to N-methyl-D-aspartate (NMDA) receptor antagonists; 50 microl D-2-amino-5-phosphonopentanoic acid (D-AP5) did block the transient secondary bursts selectively. SLEs were restricted to the hippocampus proper even if the entorhinal cortex was present. Entorhinal bursts could last <2 s and were only coupled with hippocampal bursts in a minority of slices. Reentry of epileptic bursts occasionally occurred during interictal discharges, but not during the later stages of SLEs. Full-length SLEs always started in CA3 region and could be recorded in minislices containing CA3 plus dentate hilus. Ion-sensitive microelectrodes revealed that interictal discharges were followed by short (2-3 s) [K(+)](o) waves, peaking at approximately 7.5 mM. SLEs were always accompanied by increases in [K(+)](o) reaching approximately 8.5 mM at the start of tertiary bursts; [K(+)](o) then increased more slowly to a ceiling of 11-12 mM. After the end of each SLE, [K(+)](o) fell back to baseline within 10-15 s. SLEs were accompanied by significant increase in synaptic activity, compared with baseline and/or interictal activity, estimated by the variance of the intracellular signal in the absence of epileptic bursts and action potentials (0. 38 mV(2), compared with 0.13 mV(2), and 0.1 mV(2), respectively). No significant increases were observed in the interval preceding spontaneous interictal activity. These studies show that focal assemblies of hippocampal neurons, without long reentrant loops, are sufficient for the generation of SLEs. We propose that a key factor in the transition from interictal activity to SLEs is an increase in axonal and terminal excitability, resulting, at least in part, from elevations in [K(+)](o).
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Affiliation(s)
- C Borck
- Department of Physiology and Biophysics, St. Mary's Hospital Medical School, Imperial College, London W2 1PG
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Bains JS, Longacher JM, Staley KJ. Reciprocal interactions between CA3 network activity and strength of recurrent collateral synapses. Nat Neurosci 1999; 2:720-6. [PMID: 10412061 DOI: 10.1038/11184] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In hippocampal slices, synchronous CA3 network activity induced persistent strengthening of active positive-feedback synapses. This altered network operation by increasing probability of future synchronous network activation. Long-term depression of synaptic strength induced by partial blockade of NMDA receptors during synchronous network activity reversed changes in probability of spontaneous network activation. These results suggest that specific network activity patterns selectively alter strength of active synapses. Stable, reversible alterations in network activity can also be effected by corresponding alterations in synaptic strength. These findings confirm the Hebb memory model at the neural-network level and suggest new therapies for pathological patterns of network activity in epilepsy.
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Affiliation(s)
- J S Bains
- Departments of Neurology and Pediatrics, B182, University of Colorado Health Sciences Center, 4200 East Ninth Avenue, Denver, Colorado 80262, USA
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