Priming of rotational behavior by a dopamine receptor agonist in hemiparkinsonian rats: movement-dependent induction

Repetitive stimulation of basal ganglia dopamine receptors leads to abnormal motor responses in dopamine-denervated rats. To study whether such responses were infl uenced by the previous execution of movement, we evaluated how “priming”, a phenomenon mimicking an abnormal motor response, depends on movement performance. To this end, unilaterally 6-hydroxydopamine-lesioned rats received apomorphine (0.2 mg/kg s.c.), being either allowed to move or immobilized (1 h) before, concomitantly to, or after its administration. Three days later, the dopamine D1 receptor agonist SKF 38393 (3 mg/kg s.c.) was administered. Rats that had rotated following apomorphine showed contraversive rotational behavior following SKF 38393, whilst rats that had been immobilized concomitantly to apomorphine, but neither before nor after, did not. To clarify whether immobiliztion-related stress infl uenced the results, additional rats received apomorphine plus immobilization and the corticosterone-synthesis inhibitor metyrapone (100 mg/ kg i.p.), or apomorphine plus a tail stressor, being not immobilized. Metyrapone did not affect the prevention of priming by immobilization, and tail stressor did not affect priming magnitude, suggesting that stress has minimal effect on the results observed. This study demonstrates how movement performance following initial dopaminergic stimulation governs the occurrence of an abnormal motor response to a subsequent dopaminergic challenge in dopamine-denervated rats.