Experimental febrile convulsions in the developing rat: effects on the cholinergic system

Hyperthermia-induced seizures with a servo system: neurophysiological roles of age, temperature elevation rate and regional GABA content in the rat

A servo system including a microwave generator was applied to raise a rat's body temperature at a pre-set rate. Using this system the effects of age and the temperature elevation rate upon febrile seizures in rats were studied. The relationship between the brain GABA content and hyperthermia was also studied. From the results of the present study, the seizure occurrence rate was found to be highest at the age of 20 days, brain damage was speculated to be severe after hyperthermia-induced seizures with a slow temperature rise, and the regional GABA concentration in subcortical structures was found to increase during hyperthermia. These data indicate that a servo system with a microwave generator is useful for experimental febrile convulsions, and that GABA neurotransmission in subcortical structures might contribute to feed-back regulation against seizures during hyperthermia.

Brain neurotransmitters in glycine encephalopathy

We measured neurotransmitter markers in autopsied brain of infants with glycine encephalopathy (GE). Because patients with GE develop intractable seizures, special attention was devoted to those neurotransmitter systems implicated in human epilepsy. Mean levels of glycine in the frontal cortex of GE patients were three times higher than control values. No abnormalities were observed for concentrations of gamma-aminobutyric acid (and related receptors), other major neurotransmitter amino compounds, or activities of cholineacetyltransferase and aspartate aminotransferase. Mean acetylcholinesterase activity was significantly elevated by 46%. As experimental data suggest, glycine markedly potentiates the action of the excitatory neurotransmitter glutamic acid. To the extent that the brain seizures in patients with GE can be explained by this mechanism, pharmacotherapy with excitatory amino acid antagonists may represent a new approach to the treatment of GE.

Increased activity of choline acetyltransferase and acetylcholinesterase in actively epileptic human cerebral cortex

We measured the activities of the cholinergic marker synthetic and catabolic enzymes choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) in surgical specimens obtained from 38 patients immediately following anterior temporal lobectomy for intractable epilepsy. Samples from patients with actively spiking lateral temporal cortex were compared to non-spiking lateral temporal cortex obtained from patients in whom the epileptic discharges were confined to the hippocampus. Mean activities of ChAT and AChE were increased by 25% (P less than 0.01) and 30% (P less than 0.025) respectively in the spiking vs. non-spiking cortex. We suggest that the above-normal activity of these cholinergic marker enzymes may reflect sprouting of cholinergic nerve terminals in spontaneously spiking cortex of some patients and/or increased acetylcholine metabolism secondary to the stimulatory effect of the ongoing epileptic discharge.

Kindling phenomenon of hyperthermic seizures in the epilepsy-prone versus the epilepsy-resistant rat

A kindling-like effect was produced by exposing 30-day-old rats to repeated hyperthermia-induced seizures. Naive audiogenic seizure (AGS)-susceptible rats (P77PMC) were easier to be kindled than AGS-resistant rats (Wistar). This hyperthermic kindling model may be used to study the outcome and mechanisms of human febrile seizures. The mechanisms underlying hyperthermic kindling remain to be investigated.

Long-term effects of febrile convulsion on seizure susceptibility in P77PMC rat--resistant to acoustic stimuli but susceptible to kainate-induced seizures

A new audiogenic seizure (AGS)-susceptible strain of rats (P77PMC) was evaluated as a possible model of human febrile seizures. The long-term effects of experimental febrile seizures were observed. All 30-day-old rat pups exhibited clonic seizures during exposure to an ambient temperature of 45 +/- 0.5 degree C. The mean latency from the beginning of the hyperthermic stimulus to the onset of convulsion was 16.9 +/- 2.2 min. The rats survived this hyperthermic seizure, developed a resistance to acoustic stimulations, but were more susceptible at the age of 50 to 60 days to kainate-induced limbic seizures than controls. The results of this study imply that febrile seizures of developing P77PMC rats can change later seizure susceptibility, and there may be some correlation between febrile convulsion and temporal lobe epilepsy.