Assessing pharmacologically induced dopamine receptor sensitivity changes with the Ungerstedt turning model

Rats were lesioned unilaterally in the substantia nigra with 6-hydroxydopamine. Turning in response to apomorphine and amphetamine was assessed before and 5 days after 3-week treatment with haloperidol. After haloperidol withdrawal, contralateral turning, measured at 5 min following IP injection of 1 mg/kg apomorphine, was significantly less than before haloperidol treatment and ipsilateral turning, measured at 30 min following IP injection of 2 mg/kg amphetamine, was significantly greater than before the haloperidol treatment. These results suggest that dopamine receptor sensitivity increased on the unlesioned side compared to the lesioned side.