Dopamine agonists suppress cholinomimetic-induced tremulous jaw movements in an animal model of Parkinsonism: tremorolytic effects of pergolide, ropinirole and CY 208-243.

Considerable evidence indicates that cholinomimetic-induced tremulous jaw movements in rats share many characteristics with human Parkinsonian tremor, and several antiparkinsonian drugs suppress cholinomimetic-induced tremulous jaw movements. The present study investigated three different types of dopamine agonists, which have known antiparkinsonian characteristics, for their ability to suppress the tremulous jaw movements induced by tacrine (5.0 mg/kg). The non-selective dopamine agonist pergolide, a widely used antiparkinsonian drug, was highly potent at suppressing tacrine-induced jaw movements (e.g. 0.125-1.0 mg/kg). The selective D2 agonist ropinirole, which also is used clinically as an antiparkinsonian drug, suppressed jaw movements in the dose range of 2.5-20.0 mg/kg. The D1 agonist CY 208-243, which has been reported to suppress tremor, also reduced jaw movement activity (4.0 mg/kg). Across several studies, the rank order of potency for suppressing cholinomimetic-induced jaw movements in rats is related to the potency for producing antiparkinsonian effects in humans. Together with previous studies, the present results suggest that cholinomimetic-induced jaw movements in rats can be used to characterize dopaminergic antiparkinsonian agents and to investigate the basal ganglia circuits involved in the generation of tremulous movements.