Endogenous nitric oxide modulates morphine-induced changes in locomotion and food intake in mice.

Opioids increase the dopaminergic turnover in nucleus striatum and nucleus accumbens of mice, causing behavioural changes such as increased locomotion and food intake. We have now shown that L-arginine administration increases morphine-induced locomotion and changes in food intake in mice. D-Arginine had no effect, suggesting a stereospecific mechanism. Furthermore NG-nitro-L-arginine methyl ester, a specific inhibitor of nitric oxide synthase, reduced the morphine-induced effects. These results suggest that endogenous nitric oxide could play a role in the modulation of dopaminergic effects elicited by morphine.