Effects of L-arginine and of its functional antagonist N-nitro-L-arginine on the behavior of rats, with special reference to motor activity

L-arginine and N-nitro-L-arginine were tested for their effects on the motor activity of white rats under conditions of free behavior. After oral administration of L-arginine in doses of 50 to 500 mg/kg, the horizontal and vertical components of motor activity were increased both at minute 10 and at 24 h postadministration. N-nitro-L-arginine, on the contrary, reduced the motor activity of rats (mainly its horizontal component). Oral administration of L-arginine 5 min after an intraperitoneal injection of N-nitro-L-arginine did not prevent the effects of the latter compound. The observed behavioral changes probably resulted from the combined action of two mechanisms, namely a direct influence of nitric oxide on brain cells and its action on peripheral systems of the body.