Experimental models of status epilepticus and neuronal injury for evaluation of therapeutic interventions.

This article describes current experimental models of status epilepticus (SE) and neuronal injury for use in the screening of new therapeutic agents. Epilepsy is a common neurological disorder characterized by recurrent unprovoked seizures. SE is an emergency condition associated with continuous seizures lasting more than 30 min. It causes significant mortality and morbidity. SE can cause devastating damage to the brain leading to cognitive impairment and increased risk of epilepsy. Benzodiazepines are the first-line drugs for the treatment of SE, however, many people exhibit partial or complete resistance due to a breakdown of GABA inhibition. Therefore, new drugs with neuroprotective effects against the SE-induced neuronal injury and degeneration are desirable. Animal models are used to study the pathophysiology of SE and for the discovery of newer anticonvulsants. In SE paradigms, seizures are induced in rodents by chemical agents or by electrical stimulation of brain structures. Electrical stimulation includes perforant path and self-sustaining stimulation models. Pharmacological models include kainic acid, pilocarpine, flurothyl, organophosphates and other convulsants that induce SE in rodents. Neuronal injury occurs within the initial SE episode, and animals exhibit cognitive dysfunction and spontaneous seizures several weeks after this precipitating event. Current SE models have potential applications but have some limitations. In general, the experimental SE model should be analogous to the human seizure state and it should share very similar neuropathological mechanisms. The pilocarpine and diisopropylfluorophosphate models are associated with prolonged, diazepam-insensitive seizures and neurodegeneration and therefore represent paradigms of refractory SE. Novel mechanism-based or clinically relevant models are essential to identify new therapies for SE and neuroprotective interventions.

[The anticonvulsive effect of 4,4-bis(hydroxymethyl)-2-phenyl-2-oxazoline]. / Efecto anticonvulsionante de la 2-fenil-4,4-bis (hidroximetil)-2-oxazolina.

INTRODUCTION: Certain compounds belonging to the family of the 2-aryl oxazolines have been reported to act on the central nervous system with a number of different effects and applications, which make them useful as depressants, anaesthetics, anticonvulsants, and so on. AIMS: Our aim was to study the possible effect of 4,4-bis(hydroxymethyl)-2-phenyl-2-oxazoline (OX), obtained by chemical synthesis using microwaves, in two experimental models of epilepsy. MATERIALS AND METHODS: Two models were used: one involving (repeated stimulation) electroconvulsive shock in mice and the other consisted in inducing audiogenic seizures in Mongolian gerbils. Recordings were performed of the potentials in the dentate gyrus (DG) generated in response to electrical stimulation of the entorhinal cortex in anaesthetised gerbils, using the stereotactic technique. RESULTS: A 150 mg/kg dose of OX lowered the number of electrical pulses required to induce the tonic seizures triggered by the electroshock, as well as their duration. This same dose blocked the seizures induced by audiogenic stimuli in the gerbils and significantly reduced their severity (degrees of seizures) and occurrence. OX diminished, in a dose-dependent manner, the amplitude of the excitatory post-synaptic potential and that of the population spike, triggered by stimulating the entorhinal cortex in the DG. CONCLUSIONS: OX acts as an antiepileptic agent and its mechanism of action could be related to the inhibiting effect it exerts on the entorhinal cortex-DG synapses in the hippocampus.

Increased afterdischarge threshold during kindling in epileptic rats.

The effects of daily electrical kindling stimulation of the perforant pathway were investigated in an excitotoxic rat model of epilepsy with chronic seizures in order to learn whether the preexisting epileptic condition would facilitate or retard kindling. Sprague-Dawley rats with recurrent spontaneous seizures 4-8 months after unilateral intrahippocampal kainic acid (KA) injection were implanted with recording electrodes in the hippocampus and stimulating electrodes in the perforant path. Daily stimulation for 10 s at 5 Hz was given for 15 days. The afterdischarge (AD) threshold and the AD duration of kindled KA rats were compared before and during kindling with those of a kindled control group. In the control group, as expected, mean AD thresholds decreased ( P<0.01), while AD duration progressively increased. Although AD threshold was the same in KA and control groups at the start of kindling, in the KA group a significant increase in threshold occurred from the beginning to the end of kindling ( P<0.01). Behaviorally, KA rats showed stage 4 or 5 seizures on the first stimulation, and stage 3-5 seizures during the remainder of kindling. Paired pulse testing showed facilitation of late components of the dentate gyrus field potential at the beginning of kindling, and suppression of late components at the end, in the KA rats. A significant decrease in the rate of spontaneous seizures in KA rats was noted during the period of kindling ( P=0.04). These results suggest that electrical stimulation of the perforant path may strengthen homeostatic seizure suppressing mechanisms, and may provide insights into novel approaches to the treatment of clinical seizures in temporal lobe epilepsy.

Felbamate in experimental model of status epilepticus.

PURPOSE: To examine the putative seizure-protective properties of felbamate in an animal model of self-sustaining status epilepticus (SSSE). METHODS: SSSE was induced by 30-min stimulation of the perforant path (PPS) through permanently implanted electrodes in free-running male adult Wistar rats. Felbamate (FBM; 50, 100, and 200 mg/kg), dizepam (DZP; 10 mg/kg), or phenytoin (PHT; 50 mg/kg) were injected i.v. 10 min after SSSE induction. Electrographic manifestations of SSSE and the severity of SSSE-induced neuronal injury were analyzed. RESULTS: Felbamate injected during the early stages of SSSE (10 min after the end of PPS), shortened the duration of seizures in a dose-dependent manner. Total time spent in seizures after FBM and 290 +/- 251 min (50 mg/kg), 15.3 +/- 9 min (100 mg/kg), and 7 +/- 1 min (200 mg/kg), whereas control animals spent 410 +/- 133 min seizing. This effect of FBM was stronger than that of DZP (10 mg/kg, 95 +/- 22 min) and comparable to that of PHT (50 mg/kg, 6.3 +/- 2.5 min). In the applied doses, FBM (200 mg/kg) was more effective than PHT (50 mg/kg) or DZP (10 mg/kg) in shortening seizure duration and decreasing spike frequency, when administered on the pleateau of SSSE (injection 40 min after the end of PPS). Anticonvulsant action of FBM was confirmed by milder neuronal injury compared with control animals. CONCLUSIONS: Felbamate, a clinically available AED with a moderate affinity for the glycine site of the NMDA receptor, displayed a potent seizure-protective effect in an animal model of SSSE. These results suggest that FBM might be useful when standard AEDs fail in the treatment of refractory cases of SE.

Age-related changes in synaptic function: analysis of the effect of dietary supplementation with omega-3 fatty acids.

Depolarization-induced transmitter release in synaptosomes prepared from the hippocampus of aged rats is decreased compared with release from young animals. Although the underlying cause of this deficit is not known, some evidence suggests that increased membrane rigidity may contribute to these age-related synaptic changes. One possible consequence of the decreased transmitter release in the hippocampus of aged rats is a reduced ability to sustain long-term potentiation in perforant path-granule cell synapses, a pathway in which maintenance of long-term potentiation and increased glutamate release have been coupled. The observation that there is an age-dependent impairment in long-term potentiation is consistent with this view. If the age-related deficits in release and long-term potentiation are a consequence of increased membrane rigidity, it must be predicted that any manoeuvre which reverses membrane rigidity should reverse these functional deficits. In the present study, we investigated the effect of dietary manipulation of aged rats with omega-3 fatty acids on synaptic function. The data obtained indicate that an eight-week modified feeding schedule reversed the age-related impairments in long-term potentiation and depolarization-induced glutamate transmitter release. We also report that the concentrations of both docosahexanoic acid and arachidonic acid, two main polyunsaturated fatty acids in neuronal membranes, were decreased in the hippocampus of aged rats, and were restored by dietary manipulation. The data are consistent with the hypothesis that these deficits results from a change in membrane composition.