Abnormal pattern of amphetamine locomotion after 6-OHDA lesion of anteromedial caudate.

6-Hydroxydopamine (6-OHDA) injections into the anteromedial caudate nucleus (AMCN) produced severe loss of dopamine (DA) fibers in this region of the caudate. After a low dose of d'amphetamine (1.5 mg/kg), AMCN 6-OHDA rats made fewer traverses of the length of the activity cage than control rats. In contrast, AMCN 6-OHDA rats interrupted a photocell bema that passed across the middle of the long axis of the activity cage as often as control rats. 6-OHDA injections into the nucleus accumbens (NAc) produced severe loss of DA fibers in NAc without significantly damaging the adjacent anteromedial caudate or olfactory tubercle. After d-amphetamine (1.5 mg/kg), NAc 6-OHDA rats interrupted the photocell beam and traversed the length of the activity cage as frequently as control rats. We conclude that the DA innervation to the anteromedial caudate, but not to the nucleus accumbens, is necessary for that part of the normal locomotor response to a low dose of d'amphetamine that is required for the performance of long traverses of an activity cage.