NITRO-L-ARGININE ATTENUATES SKF 38393-INDUCED ORAL ACTIVITY IN NEONATAL 6-HYDROXYDOPAMINE-LESIONED RATS

Nitric oxide (NO) in brain has been implicated in neuronal regulatory processes and in neuropathologies. Previously we showed that NO modifi ed quinpirole-induced yawning, a behavioral measure of dopamine (DA) D -3 receptor activation in rats. The aim of this study was to character ize the effect of nitro-L-arginine methyl ester HCl (NAME) and L-argin ine HCl on reactivity of rats to the DA D-1 receptor agonist SKF 38393 and DA D-1 antagonist SCH 23390 in intact and neonatal 6-hydroxydopam ine (6-OHDA)-lesioned rats (134 mu g of base ICV at 3rd day after birt h). L-arginine HCl (300 mg/kg IP) increased the oral activity response in 6-OHDA-lesioned rats, like SKF 38393, and induced catalepsy in int act control rats, like SCH 23390. In contrast, NAME had no effect on o ral activity or catalepsy, but fully attenuated SKF 38393-induced oral activity. These findings indicate that L-arginine HCl has no apparent effect at the DA D-1 receptor, but that NAME is effective in attenuat ing a DA D-1 agonist-induced effect. Consequently NO may be an intrace llular second messenger for supersensitized receptors associated with DA D-1 agonist-induced oral activity.