The selective D3 receptor antagonist, S33084, improves parkinsonian-like motor dysfunction but does not affect l-DOPA-induced dyskinesia in 6-hydroxydopamine hemi-lesioned rats

Despite evidence linking dopamine D3 receptors to the etiology of Parkinson's disease and l-DOPA-induced dyskinesia, the potential therapeutic utility of D3 receptor ligands remains unclear. In the present study, we investigated whether the selective D3 receptor antagonist, S33084, affects development and expression of abnormal involuntary movements (AIMs), a behavioural correlate of dyskinesia, in rats hemi-lesioned with 6-hydroxydopamine and chronically treated with l-DOPA. The ability of S33084, alone or in combination with l-DOPA, to attenuate 6-hydroxydopamine induced motor deficits was also investigated employing a battery of behavioural tests. Acute administration of S33084 (0.64 mg/kg, s.c.) did not attenuate the induction of AIMs in dyskinetic rats upon challenge with l-DOPA (6 mg/kg, s.c.). Moreover, S33084 (0.64 mg/kg) did not prevent the development of AIMs affecting axial, limb and orolingual muscles when chronically administered together with l-DOPA (6 mg/kg for 21 days). However, both acute and chronic administration of S33084 enhanced l-DOPA-induced contralateral turning, suggesting potential antiparkinsonian properties. Furthermore, S33084 (0.01–0.64 mg/kg) dose-dependently attenuated parkinsonian disabilities, including bradykinesia, in drag and rotarod tests, although, in these procedures, the combination of S33084 with l-DOPA did not produce synergistic effect. It is concluded that sustained D3 receptor blockade does not blunt l-DOPA-induced dyskinesia in hemiparkinsonian rats. However, D3 receptor antagonism may be associated with antiparkinsonian properties. The clinical relevance of these observations will be of interest to explore further.