Nitric oxide (NO) mediates the glutamate-induced increase in cyclic guanosine monophosphate (cGMP) levels in the cerebellum. The study shows that glutamate and related amino acids, such as N-methyl-D-aspartate (NMDA), stimulate the conversion of arginine to NO and citrulline. This process is blocked by Nω-monomethyl-L-arginine (MeArg), a potent inhibitor of arginine to NO conversion. Arginine can reverse this effect, indicating competitive inhibition. Hemoglobin, which binds NO, prevents glutamate-induced cGMP stimulation, while superoxide dismutase, which increases NO levels, enhances cGMP formation. These findings confirm that NO is a messenger molecule mediating glutamate's effects on cGMP. The study used cerebellar slices from 10-day-old rats, and measured NO and cGMP levels using radioactive assays. NO was detected as its breakdown product, nitrite (NO₂⁻). The conversion of arginine to citrulline was found to be stoichiometric with NO production. Glutamate and NMDA significantly enhanced this conversion, with NMDA being the most potent. MeArg inhibited both citrulline and cGMP formation, and this inhibition was reversed by arginine. The concentration-response curves for NMDA on cGMP and citrulline formation were superimposable, indicating a direct link between NO production and cGMP formation. Hemoglobin inhibited NMDA-induced cGMP levels, consistent with its ability to bind NO. Superoxide dismutase enhanced cGMP formation, suggesting that NO levels are influenced by superoxide. The study also showed that the effects of MeArg on cGMP formation were specifically reversed by arginine, indicating competitive inhibition of arginine conversion to NO. The findings suggest that NO is a key mediator in the glutamate-induced increase in cGMP levels in the cerebellum. The study provides evidence that NO is involved in the signaling pathways of excitatory amino acid receptors, particularly those associated with climbing fibers. The results support the idea that NO is a crucial messenger in the regulation of cGMP levels in the cerebellum, with implications for understanding the role of NO in brain function and disease.Nitric oxide (NO) mediates the glutamate-induced increase in cyclic guanosine monophosphate (cGMP) levels in the cerebellum. The study shows that glutamate and related amino acids, such as N-methyl-D-aspartate (NMDA), stimulate the conversion of arginine to NO and citrulline. This process is blocked by Nω-monomethyl-L-arginine (MeArg), a potent inhibitor of arginine to NO conversion. Arginine can reverse this effect, indicating competitive inhibition. Hemoglobin, which binds NO, prevents glutamate-induced cGMP stimulation, while superoxide dismutase, which increases NO levels, enhances cGMP formation. These findings confirm that NO is a messenger molecule mediating glutamate's effects on cGMP. The study used cerebellar slices from 10-day-old rats, and measured NO and cGMP levels using radioactive assays. NO was detected as its breakdown product, nitrite (NO₂⁻). The conversion of arginine to citrulline was found to be stoichiometric with NO production. Glutamate and NMDA significantly enhanced this conversion, with NMDA being the most potent. MeArg inhibited both citrulline and cGMP formation, and this inhibition was reversed by arginine. The concentration-response curves for NMDA on cGMP and citrulline formation were superimposable, indicating a direct link between NO production and cGMP formation. Hemoglobin inhibited NMDA-induced cGMP levels, consistent with its ability to bind NO. Superoxide dismutase enhanced cGMP formation, suggesting that NO levels are influenced by superoxide. The study also showed that the effects of MeArg on cGMP formation were specifically reversed by arginine, indicating competitive inhibition of arginine conversion to NO. The findings suggest that NO is a key mediator in the glutamate-induced increase in cGMP levels in the cerebellum. The study provides evidence that NO is involved in the signaling pathways of excitatory amino acid receptors, particularly those associated with climbing fibers. The results support the idea that NO is a crucial messenger in the regulation of cGMP levels in the cerebellum, with implications for understanding the role of NO in brain function and disease.