Behavioral effects of amphetamine and apomorphine after striatal lesions in the rat

It is well established that denervation of the dorsal striatum by its dopaminergic afferents attenuates the stereotyped response to d-amphetamine, which can be considered as an extreme form of motor activation. However, it is difficult to sustain the view that this structure serves primary motor control function because the role of dopamine in the striatum remains difficult to understand. In this study, we compared the effects of two dopaminergic agonists, d-amphetamine and apomorphine, after dorsal striatal lesions with ibotenic acid using a computerized scoring of the behavior. Although d-amphetamine- and apomorphine-induced locomotor activity was no different between lesioned and nonlesioned rats in photobeam activity cages, the structure of their behavioral pattern was quite different. Freezing, a usual response after d-amphetamine, was blocked by the lesion. Lesioned rats exhibited less standing than nonlesioned after d-amphetamine, apomorphine, or saline treatment. Moving was increased in lesioned rats after a low dose of d-amphetamine (0.5 mg/kg) or apomorphine (0.5 mg/kg), while d-amphetamine induced in the same rats an increase of rearing. Stereotyped behavior after both drugs at high doses was not affected by striatal lesion. These results indicate that the dorsal striatum is not involved only in the control of stereotypy, as has been suggested using 6-hydroxydopamine lesions, but also plays a major role in the mediation of behavioral activation in response to stimulant drugs.