NITRIC-OXIDE SYNTHASE INHIBITOR FACILITATES FOCAL SEIZURES INDUCED BYAMINOPYRIDINE IN RAT

The effects of N-nitro-L-arginine (NA), a nitric oxide (NO) synthase i nhibitor, were investigated on the focal ictal-like seizure induced by 3-aminopyridine in rat neocortex in vivo. Intraperitoneal and intrace rebroventricular (i.c.v.) injections of NA markedly facilitated propag ation of epileptiform events. In addition, NA injected i.c.v. increase d the number/hour of individual ictal periods while decreasing their d uration. In the presence of NA and an N-methyl-D-aspartate (NMDA) rece ptor antagonist D(-)2-amino-5-phosphonovaleric acid (APV) the number o f ictal periods increased while their duration synergically decreased. APV by itself did not change the number of ictal episodes but decreas ed their duration. Our results suggest that NO inhibits the induction and propagation of seizure activity. We cannot distinguish the proport ion of neuronal and/or vascular MO involved in our experimental condit ions, but these effects seem to be independent of the NMDA receptors.