Comparative effects of repeated administration of dopamine agonists on circling behavior in rats.

A paucity of studies are available concerning the comparative therapeutic effectiveness of presently available dopamine agonist agents in the control of Parkinson symptoms. To provide a basis for resolving this issue, we measured the circling response in unilaterally nigrotomized (6-OHDA) rats following the administration of ropinirole, pramipexole, pergolide, bromocriptine, and cabergoline. Cabergoline, and to a lesser extent pergolide, produced the most vigorous and longest lasting circling response. This response was sustained with administration of these agents over a nine day period. Bromocriptine, pramipexole and ropinirole were all less effective. These results suggest that dopamine agonists whose effect is primarily on D1 and D2 receptors are more effective than those whose actions do not include D1 activation.