Interictal discharges in the hippocampus of rats with long-term pilocarpine seizures.

Systemic administration of pilocarpine to adult rats induces an acute status epilepticus followed by spontaneous recurrent seizures after a 1-2-week silent period. We recorded field potentials in hippocampal slices obtained from rats with spontaneous recurrent seizures after pilocarpine-induced status. The frequency of the interictal discharges induced in these slices by 4-aminopyridine (4AP) was reduced and their duration was increased. Cutting the Schaffer collaterals caused interictal discharges in CA1 to disappear in normal rats and in rats 3 weeks after pilocarpine-induced status. However, 12 weeks after pilocarpine, these discharges remained in CA1 after such a cut but occurred at a lower frequency. These findings show that in rat hippocampi with a lesion similar to that of human Ammon's horn sclerosis some electrophysiological features of 4AP-induced interictal discharges are altered in comparison to those induced in normal hippocampi.