Status epilepticus induced by pilocarpine and picrotoxin

Since its original description over 10 years ago, the pilocarpine model of status epilepticus (SE) has gained considerable attention. Much work has been done with the model in order to characterize the involvement of different brain structures in seizure genesis and spread. Electrophysiological studies of temporal lobe epileptic slices of both human and animal models, have failed to reveal hyperexcitability, unless blockade of GABAergic inhibition is performed. Thus, we have decided to evaluate potential contributions of picrotoxin, a GABA, channel blocker, on pilocarpine-induced SE. Animals injected with three specific dose combinations (pilocarpine dose/picrotoxin dose), 150/0.5, 75/1.5 and 50/2.0 mg/kg, evoked status epilepticus (SE) within 23, 31 and 27 min, respectively. Ictal events and EEG spikes were initially observed either in the amygdala or in the hippocampus, with a later spread to cerebral cortex. Neuropathological analysis, performed 5-7 days after SE, has shown a high degree of cell loss predominantly in the piriform cortex, amygdala, hippocampus, thalamus and substantia nigra. Mortality rates for 150/0.5, 75/1.5 and 50/2.0 mg/kg (pilocarpine dose/picrotoxin dose) were 53, 42 and 51%, respectively. Single injections of 150 mg/kg of pilocarpine or 3 mg/kg of picrotoxin did not evoke any form of sustained epileptic activity. Previous studies in which simultaneous injections of other GABA(A) antagonists (i.e. bicuculline) and pirocarpine were performed, did not show clear evidences of a synergistic action between these two systems. the present study reveals a proconvulsant role for picrotoxin when co-administered with subconvulsant doses of pilocarpine. Possible mechanisms that might account for the interactions between the cholinergic and GABAergic systems in regard to epileptogenesis are discussed. (C) 1997 Elsevier Science B.V.UNIFESP,EPM,DEPT PHYSIOL,R BOTUCATU 862,BR-04023900 São Paulo,BRAZILUNIFESP,EPM,DEPT PHYSIOL,R BOTUCATU 862,BR-04023900 São Paulo,BRAZILWeb of Scienc

Spontaneous recurrent seizures and neuropathology in the chronic phase of the pilocarpine and picrotoxin model epilepsy

In a recent publication, we have shown a potent interaction between the cholinergic and GABAergic systems in regard to seizure generation and developed the pilocarpine(pilo)/picrotoxin(PTX) model, in which combined injections of these agents have induced status epilepticus (SE) in rats. Here we report on the chronic features of this new animal model of epilepsy. Adult male Wistar rats were systemically injected with solutions containing 750/0.5 mg kg(-1), 75/1.5 mg kg(-1) and 50/2.0 mg kg(-1) (pilo dose/PTX dose). Six epileptic and six control animals were observed for 120-131 days for the occurrence of spontaneous recurrent seizures (SRS). Electroencephalographic, neuropathologic and behavioral analyses were subsequently performed. Following SE, the animals went through a latent period and, subsequently, towards a state of 'chronic' epilepsy, characterized by the emergence of SRS. Animals that received 150/0.5 mg kg(-1) presented a relatively short latent period, partial events as their most common initial seizure manifestations and a considerable subsequent progression towards generalization. the group injected with 75/7.5 mg kg(-1) presented an extensive period during which the majority of the animals exclusively developed partial seizures (50 days). Animals injected with 50/2.0 mg kg(-1) presented an average latent period of over 100 days. Only few animals within this group developed SRS. Our EEG, neuropathological and ictal behavioral findings, in conjunction with the fact that SE was required for the posterior development of SRS, suggest that our model parallels a human TLE condition. Even though diverse TLE models have been described, the pilo/PTX model has as a major feature the intriguing occurrence of disparities among these three groups in the chronic period, although no differences could be observed during SE induction. Future experiments conducted in this sense, might lead to important results in regard to the elucidation of mechanisms of epileptogenesis.UNIFESP, EPM, Dept Physiol, BR-04023062 São Paulo, SP, BrazilUNIFESP, EPM, Dept Physiol, BR-04023062 São Paulo, SP, BrazilWeb of Scienc

Supragranular mossy fiber sprouting is not necessary for spontaneous seizures in the intrahippocampal kainate model of epilepsy in the rat

In a previous study, we suggested a dissociation between spontaneous recurrent epileptic seizures (SRS) and hippocampal supragranular mossy fiber sprouting (MFS) in the pilocarpine model of epilepsy (PILO). One possible explanation, would be that SRS in the PILO model do not originate in the hippocampus and thus would not depend on MFS. Tn the present study, we investigated whether MFS is necessary for the SRS that develop after a small intrahippocampal dose of kainic acid (KA), a model where seizures are more likely to start in the hippocampus. Intrahippocampal injections of ECA were performed in rats, with and without the concomitant administration of cycloheximide (CHX) (0.5 mu g of KA and 6 mu g of CHX). After injection, recording electrodes were positioned in the same stereotaxic location. Hen again, CHX was able to completely block (5/8 animals) MFS, visualized by neo-Timm staining, without altering the frequency and intensity of spontaneous ictal and interictal EEG events. From these data, we can conclude that, in the intra-hippocampal KA model, MFS is not necessary for the occurrence of ictal events. We suggest that CHX can be used together with classic epileptogenic agents, as a means to study temporal lobe epilepsy (TLE) without the contributing effect of MFS-as seen in TLE patients with mass lesions in the lateral temporal lobe. (C) 1999 Elsevier Science B.V. All rights reserved.Universidade Federal de São Paulo, Dept Physiol, EPM, BR-04023900 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Physiol, EPM, BR-04023900 São Paulo, BrazilWeb of Scienc

BEHAVIORAL, ELECTROENCEPHALOGRAPHIC and NEUROPATHOLOGICAL EFFECTS of the INTRAHIPPOCAMPAL INJECTION of the VENOM of the SOUTH-AMERICAN RATTLESNAKE (CROTALUS-DURISSUS-TERRIFICUS)

ESCOLA PAULISTA MED,NEUROL EXPTL LAB,BR-04023 São Paulo,SP,BRAZILESCOLA PAULISTA MED,NEUROL EXPTL LAB,BR-04023 São Paulo,SP,BRAZILWeb of Scienc

Ultrastructural identification of dentate granule cell death from pilocarpine-induced seizures

Cell loss in the hippocampal formation is a common event in patients with temporal lobe epilepsy. the belief that dentate granule neurons are relatively resistant to excitotoxic injury has recently been challenged both, in epileptic patients and in animal models of temporal lobe epilepsy. the nature of dentate granule cell damage in epilepsy has been reported as either apoptotic, necrotic or both. the lack of a consensus on this topic stems from use of different animal models and different experimental techniques for characterizing the apoptotic/necrotic process. Using electron microscopy for defining the, nature of cell loss and one of the main animal models of status epilepticus (SE) we have focussed on the nature of the degenerative process in dentate granule cells. Ultrastructural morphological changes of these cells were evaluated 2.5-48 h after pilocarpine-induced status epilepticus. A variety of morphologies ranging from apoptosis to necrosis, could be seen at 2.5 h after SE onset and continued at least over the following 48 h. Some cells displayed coalescence of chromatin against nuclear membranes. in such cases however, chromatin did not have well-defined edges las it should, if it were apoptosis). Condensation of cytoplasm. present in both processes was also frequently found. Neither obvious apoptotic budding-off of cytoplasm nor typical membrane-bound apoptotic bodies were found. Our results indicate that in the dentate granule cell layer pilocarpine-induced SE promotes a degenerative process in which apoptotic and necrotic features overlap. (C) 2000 Elsevier Science B.V. All rights reserved.UNIFESP, Dept Physiol, BR-04023900 São Paulo, BrazilUNIFESP, Dept Morphol, BR-04023900 São Paulo, BrazilUNIFESP, Dept Physiol, BR-04023900 São Paulo, BrazilUNIFESP, Dept Morphol, BR-04023900 São Paulo, BrazilWeb of Scienc