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Abstract
Systemic administration of pilocarpine in rats can result in a chronic behavioral
state that is similar to human temporal lobe epilepsy. The pilocarpine model of epilepsy
is widely used for studying the factors that contribute to the development of epilepsy
as a consequence of status epilepticus (SE). For this purpose, pilocarpine is either
administered alone at a high systemic dose or in combination with lithium, which markedly
potentiates the convulsant effect of pilocarpine. Both experimental protocols, however,
are associated with high mortality rates. In the present study, we evaluated whether
mortality rate in rats can be decreased by repeated administration of low doses of
pilocarpine. The time the rats spent in SE was limited by diazepam. Preliminary experiments
in lithium-free rats indicated that repeated low-dose administration of pilocarpine
is too time-consuming to produce SE compared to single high-dose administration. All
subsequent experiments were performed in lithium-pretreated rats. Single-dose injection
of 30 mg/kg pilocarpine produced SE in approximately 70% of the animals, but 45% of
the rats died although SE was interrupted by diazepam after 90 min. Repeated i.p.
administration of 10 mg/kg pilocarpine at 30-min intervals resulted in SE after 2-4
injections; the mean dose of pilocarpine needed to induce SE was 26 mg/kg. When SE
was interrupted after 90 min, mortality rate was below 10%, which was significantly
lower compared to the protocol with one single administration of 30 mg/kg pilocarpine.
In contrast to mortality rate, the development of spontaneous recurrent seizures did
not differ between experimental protocols. Almost all rats which had experienced a
SE of at least 60 min developed chronic epilepsy. Average latency to the first spontaneous
seizure was approximately 40 days. The frequency and severity of spontaneous seizures
was not significantly different between protocols, although animal groups with repeated
low-dose treatment tended to have higher frequencies of spontaneous seizures compared
to single-dose administration. The present study demonstrates that systemic treatment
of lithium-pretreated rats with several low doses of pilocarpine efficiently produces
SE and chronic epilepsy with much lower mortality rates than single-dose pilocarpine.