A peptidase-resistant cyclic octapeptide analogue of somatostatin (SMS 201-995) modulates seizures induced by quinolinic and kainic acids differently in the rat hippocampus.

Electroencephalographic (EEG) seizures were measured in rats after intrahippocampal injection of 120 nmol quinolinic acid into the stratum radiatum CA1 or 0.19 nmol kainic acid in the dentate gyrus or in the stratum radiatum. Injection of 5 micrograms SMS 201-995, a peptidase-resistant cyclic octapeptide analogue of somatostatin, into the stratum radiatum, 15 min before quinolinic acid, did not significantly modify the number of seizures and the total time in seizures. Five micrograms SMS 201-995 injected into the stratum radiatum reduced the number of seizures induced by kainic acid in the same area and the total time spent in seizures by 58% and 75%, respectively (Student's t-test; P less than 0.01). In both instances the latency to the first ictal episode was not significantly modified. Lesions of the medial septum, which reduced the activity of choline-o-acetyl-transferase (CAT) in the dorsal hippocampus by greater than 90% after one week did not significantly affect seizures induced by quinolinic acid. In rats lesioned in the medial septum, 5 micrograms SMS 201-995 reduced the total time spent in seizures by 43%, without changing the number of ictal episodes and raised the latency to the first quinolinic acid-induced seizure by 53% (ANOVA 2 x 2, P less than 0.05) but had no effect on these measures in the corresponding sham-operated group.(ABSTRACT TRUNCATED AT 250 WORDS)