FUNCTIONAL ACTIVATION OF SOMATOSTATIN-CONTAINING AND NEUROPEPTIDE-Y-CONTAINING NEURONS IN THE ENTORHINAL CORTEX OF CHRONICALLY EPILEPTIC RATS

The in vitro release of somatostatin and neuropeptide Y, their tissue concentration and immunocytochemical pattern were examined in the ento rhinal cortex of chronically epileptic rats. A systemic administration of 12 mg/kg kainic acid causing generalized tonic-clonic seizures for at least 3 h after injection was used to induce, 60 days later, a chr onically enhanced susceptibility to seizures in the rats. The release of both peptides under depolarizing conditions was significantly reduc ed by 15% on average from slices of the entorhinal cortex two days aft er kainic acid-induced status epilepticus. At 60 days, the spontaneous and 30 mM KCl-induced release of somatostatin was significantly enhan ced by 30% on average. The release induced by 100 mM KCI was raised by 70%. The spontaneous, 30 mM and 100 mM KCl-induced release of neurope ptide Y from the same slices was increased, respectively, by 120%, 76% and 36%. The late changes were associated with an increased tissue co ncentration of neuropeptide Y but not of somatostatin. This was confir med by immunocytochemical evidence showing that neuropeptide Y-, but n ot somatostatin-immunoreactive neurons were increased in the entorhina l cortex of kainic acid-treated rats. These results indicate that neur otransmission mediated by somatostatin and neuropeptide Y, two peptide s previously shown to play a role in limbic epileptogenesis, is enhanc ed in the entorhinal cortex of chronically epileptic rats. Copyright ( C) 1996 IBRO.