Time course of apomorphine-induced circling behaviour after striatal dopamine receptor denervation

The curve describing the time course of apomophine-induced circling behaviour in rats with a 6-hydroxydopamine-induced lesion of the nigrostriatal dopamine (DA) pathway was studied with a microcomputerized rotometer. Up to a 2-week interval after lesioning, the contralateral circling response was a single bell-shaped curve but this gradually became a double-peaked curve after 4-5 months. At this time the bell-shaped curve was, however, restored by haloperidol pretreatment. It is concluded that the response of striatal DA receptors was modified either by the lesion of another neuronal system and/or that the absence of DA nerve endings induced changes in the striatal DA receptor itself.