Basal ganglia group II metabotropic glutamate receptors specific binding in non-human primate model of L-Dopa-induced dyskinesias

L-Dopa-induced dyskinesias (LIDs), the disabling abnormal involuntary movements induced by chronic use of L-Dopa, limit the quality of life in Parkinson's disease (PD) patients. Modulation of group II metabotropic glutamate receptors (mGluR2/3) in the basal ganglia, a brain region critically involved in motor control, is considered as an alternative approach in therapy of PD. In this study, receptor binding autoradiography of [3H]LY341495, a mGluR2/3 selective radioligand, was used to investigate possible changes in mGluR2/3 in the basal ganglia of L-Dopa-treated 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkeys having developed LIDs compared to animals in which LIDs were prevented by adjunct treatments with CI-1041, a selective antagonist of the NR1A/2B subtype of NMDA receptor, or low doses of the dopamine D2 receptor agonist, cabergoline. Our study is the first to provide evidence of: (1) the similar localization of [3H]LY341495 specific binding to mGluR2/3 in the primate basal ganglia as compared to receptor distribution measured by immunohistochemistry in human and rat as well as this ligand binding in intact rat brain; (2) no change of [3H]LY341495 specific binding in basal ganglia after nigrostriatal denervation by MPTP; and (3) a widespread reduction of [3H]LY341495 specific binding to mGluR2/3 in the caudate nucleus (−17% to −31%), putamen (−12% to −45%) and globus pallidus (−56 to −59%) of non-dyskinetic animals treated with L-Dopa + cabergoline as compared to controls, MPTP monkeys treated with saline, L-Dopa alone (dyskinetic) or L-Dopa + CI-1041 (non-dyskinetic). This study is the first to propose a close interaction between mGluR2/3 and dopamine D2 receptors activation in the basal ganglia.