Modulation of the behavioral effects of amphetamine in rats by clonidine.

Clonidine (0.01, 0.05, 0.5 mg/kg) dramatically reduced the locomotor response to amphetamine (2 mg/kg) in a dose related fashion. In contrast, the same doses of clonidine had no effect on locomotions produced by a higher dose of amphetamine (6 mg/kg). Clonidine also had no effect on stereotyped head movements or the duration of the behavioral response to amphetamine. The lower dose of clonidine reduced amphetamine induced licking/biting while the two higher doses potentiated amphetamine induced licking/biting. Thus the behavioral effects of clonidine vary depending upon the dose of amphetamine and the particular behavior selected for study. The known neurochemical effects of clonidine do not account for this phenomenon.