CHRONIC ADMINISTRATION OF A NITRIC-OXIDE SYNTHASE INHIBITOR, N-OMEGA-NITRO-L-ARGININE, AND DRUG-INDUCED INCREASE IN CEREBELLAR CYCLIC-GMP IN-VIVO

N(omega)-nitro-L-arginine (N(G)-nitro-L-arginine) is a potent nitric oxide synthase inhibitor which crosses the blood brain barrier and does not undergo extensive metabolism in vivo. In this study, effect of chronic pretreatment of N(omega)-nitro-L-arginine (75 mg/kg, i.p., twice daily for 7 days) on the harmaline- (100 mg/kg, s.c.), picrotoxin- (4 mg/kg, s.c.), pentylenetetrazole- (50 mg/kg, i.p.), and L-glutamic acid- (400 mug/10 mul/mouse, i.c.v.) induced increase in cerebellar cGMP was assessed. All the four drugs produced significant increase in cerebellar cGMP in vehicle pretreated control animals. Cerebellar cGMP increase induced by harmaline, picrotoxin, and L-glutamic acid was attentuated in N(omega)-nitro-L-arginine pretreated animals. These results indicate that in vivo cerebellar cGMP levels are increased by the prototype excitatory amino acid receptor agonist, L-glutamic acid and also by the drugs which augment the excitatory amino acid transmission. Furthermore, parenteral chronic administration of N(omega)-nitro-L-arginine blocks NO synthase in the brain and hence cerebellar cGMP response in chronic N(omega)-nitro-L-arginine treated animals could be used as a tool to assess the physiological functions of nitric oxide in vivo.