Inhibition of d-amphetamine-induced locomotor activity by injection of haloperidol into the nucleus accumbens of the rat.

The effect of intracerebral administraton of antagonists of dopamine and noradrenaline upon the locomotor stimulation induced by intraperitoneal injection of d-amphetamine sulfate in rats was investigated. Inj ection of low doses of the dopamine antagonist haloperidol (2.5 mug and 5 mug) bilaterally into the nucleus accumbens antagonized the locomotor stimulation following d-amphetamine. No significant inhibition was observed following administration of the alpha-adrenergic antagonist phentolamine or thhe beta-adrenergic antagonist propranolol into the nucleus accumbens. Injection of the dame doses of haloperidol into the caudate nucleus did not inhibit the d-amphetamine induced locomotor activity in contrast to the effects seen following injection into the nucleus accumbens. The results confirm the significance of dopaminergic mechanisms for the locomotor stimulant effect of d-amphetamine and indicate that the mesolimbic dopamine system plays an important role in this respect.