Changes in apomorphine pharmacodynamics following repeated treatment in 6-hydroxydopamine-lesioned rats.

Rats with 6-OHDA lesions were repeatedly treated with apomorphine and dose-response relationships compared before and after treatment to better understand the pharmacological mechanisms which result in sensitization. A progressive increase in the magnitude and duration of rotational behavior was observed following repeated treatment and was associated with a nonparallel (upward) shift in apomorphine dose-response curves. These changes are inconsistent with simple shifts in drug potency, and instead are more consistent with changes in the ability of apomorphine to stimulate postsynaptic, striatal efferent pathways which result from repeated drug administration.