Oral tremor induced by the muscarinic agonist pilocarpine is suppressed by the adenosine A2A antagonists MSX-3 and SCH58261, but not the adenosine A1 antagonist DPCPX

Tremulous jaw movements in rats, which can be induced by dopamine (DA) antagonists, DA depletion, and cholinomimetics, have served as a useful model for studies of tremor. Although adenosine A2A antagonists can reduce the tremulous jaw movements induced by DA antagonists and DA depletion, there are conflicting reports about the interaction between adenosine antagonists and cholinomimetic drugs. The present studies investigated the ability of adenosine antagonists to reverse the tremorogenic effect of the muscarinic agonist pilocarpine. While the adenosine A2A antagonist MSX-3 was incapable of reversing the tremulous jaw movements induced by the 4.0 mg/kg dose of pilocarpine, both MSX-3 and the adenosine A2A antagonist SCH58261 reversed the tremulous jaw movements elicited by 0.5 mg/kg pilocarpine. Systemic administration of the adenosine A1 antagonist DPCPX failed to reverse the tremulous jaw movements induced by either an acute 0.5 mg/kg dose of the cholinomimetic pilocarpine or the DA D2 antagonist pimozide, indicating that the tremorolytic effects of adenosine antagonists may be receptor subtype specific. Behaviorally active doses of MSX-3 and SCH 58261 showed substantial in vivo occupancy of A2A receptors, but DPCPX did not. The results of these studies support the use of adenosine A2A antagonists for the treatment of tremor.