Influence of catecholamines on dexamphetamine-induced changes in locomotor activity.

In the mouse, central noradrenaline receptor stimulation by clonidine, or intracerebroventricular injection of noradrenaline or alpha-methylnoradrenaline, caused marked enhancement of the locomotor stimulant effects of dexamphetamine in doses that were without effect when given alone. A minimally locomotor-stimulant dose of apomorphine reduced the effect of dexamphetamine. Pimozide and phenoxybenzamine each virtually abolished locomotor stimulation after dexamphetamine, while FLA63 caused significant reduction. Phenoxybenzamine also abolished the enhancement by clonidine. The intensity of the dexamphetamine effect was dose-related, while in the case of apomorphine the duration rather than the intensity was related to the dose administered. Clonidine potentiated apomorphine locomotor stimulation; following this drug combination, the nature of the movements more closely resembled those seen after dexamphetamine. The results suggest the involvement of both noradrenaline and dopamine in the dexamphetamine response.