Pramipexole reduces parkinsonian tremor induced by pilocarpine infusion in the rat striatum.

Objective: Pramipexole is widely prescribed for the treatment of Parkinson's disease. This dopamine (DA) receptor agonist has a higher affinity for D3 over D2 receptors. We compared the effect of pramipexole to apomorphine, a non-specific DA receptor agonist, on the suppression of tremulous jaw movements (TJMs) in a rat model, to elucidate the possible ameliorating effect of D3 receptor activation on parkinsonian tremor.

Results: In experiment 1, pilocarpine (4.0mg/kg) was injected into rats intraperitoneally, and the number of rapid vertical deflections of the lower jaw was counted for 20min immediately after the injection, to evaluate TJMs. TJMs were reduced by intraperitoneal administration of pramipexole (1.0mg/kg). In experiment 2, the number of TJMs was counted after the rats received intraperitoneal administration of either apomorphine (0.25, 1.0, 4.0mg/kg) or vehicle, followed by the micro-infusion of pilocarpine (50μg/1μL/side) or vehicle into the ventrolateral striatum (VLS) via implanted guide cannulae. In experiment 3, either pramipexole (0.25, 1.0, 4.0mg/kg) or vehicle was intraperitoneally administered, followed by the micro-infusion of pilocarpine or vehicle into the VLS 30min later. Pramipexole (1.0 and 4.0mg/kg) and apomorphine (1.0 and 4.0mg/kg) significantly reduced the number of TJMs induced by micro-infusion of pilocarpine into the VLS.

Conclusions: These findings suggest that activation of D3, as well as D2 receptors could play important roles in the suppression of parkinsonian tremor.