L-Arginine potentiates excitatory amino acid-induced seizures elicited in the deep prepiriform cortex

Microinjection of N-methyl-D-aspartate (NMDA; 1 and 2.5 nmol) or kainate (KA; 50 pmol) into the deep prepiriform cortex elicited behavioral signs of seizure activity. No epileptiform activity was observed after deep prepiriform cortex microinjection of either L-arginine (L-Arg, 5 and 10 nmol) or its D-enantiomer, D-arginine (D-Arg, 2.5–10 nmol). However, both the seizure score and the incidence of electroencephalographic (EEG) epileptic discharges elicited NMDA (1 and 2.5 nmol) and KA (50 pmol) were significantly increased by L- but not D-Arg. The facilitatory effects of L-Arg on seizure activity elicited by both NMDA and KA were dose-dependent and could be prevented by co-administration of L-Arg (10 nmol) and the nitric oxide (NO) synthase inhibitor, N ω-nitro-L-arginine methyl ester (L-NAME, 20 nmol). Motor and electrocortical seizures were observed after microinjection of the NO donor sodium nitroprusside (SNP; 5 to 20 nmol) into the deep prepiriform cortex. Infusion of methylene blue (20 nmol), a soluble guanylate cyclase inhibitor, protected against SNP-induced seizures. Furthermore, prior infusion of a subconvulsant dose of SNP into the deep prepiriform cortex significantly potentiated the seizure activity elicited by either NMDA (1 and 2.5 nmol) or KA (50 pmol). These results support the proposal that NO is formed from L-Arg upon excitatory amino acid receptor activation within the deep prepiriform cortex, thereby contributing to the genesis of seizure activity.