Effects of SCH 58261, an adenosine A(2A) receptor antagonist, on quinpirole-induced turning in 6-hydroxydopamine-lesioned rats. Lack of tolerance after chronic caffeine intake.

In unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats, a rodent model of Parkinson's disease (PD), the adenosine A(2A) receptor antagonist SCH 58261 significantly increased (+180%, p <.01) the number of rotations induced by a low dose of quinpirole (a dopamine D(2) receptor agonist), while it did not significantly modify the effects of a comparably low dose of SKF 38393 (a dopamine D(1) receptor agonist). The dose-dependent potentiating effects of SCH 58261 on quinpirole-induced turning were similar in caffeine-treated rats (1 g/l in drinking water over 14 days) and control animals (tap water). The selective potentiating effects of SCH 58261 on D(2)-dependent turning confirm the existence of a potent and specific A(2A)/D(2) receptor-receptor interaction. The persistence of the potentiating effects of SCH 58261 after chronic caffeine intake suggests that no tolerance should develop towards the antiparkinsonian effects of adenosine A(2A) receptor antagonists with chronic treatment.