Pharmacological Modulation of Glutamate Transmission in a Rat Model of L-DOPA-Induced Dyskinesia: Effects on Motor Behavior and Striatal Nuclear Signaling

L-DOPA-induced dyskinesia (LID) in Parkinson's disease has been linked to altered dopamine and glutamate transmission within the basal ganglia. In the present study, we compared compounds targeting specific subtypes of glutamate receptors or calcium channels for their ability to attenuate LID and the associated activation of striatal nuclear signaling and gene expression in the rat. Rats with 6-hydroxydopamine lesions were treated acutely or chronically with L-DOPA in combination with the following selective compounds: antagonists of group I metabotropic glutamate receptors (mGluR), (2-methyl-1,3-thiazol4-yl) ethynylpyridine (MTEP) for mGluR5 and (3-ethyl-2methyl-quinolin-6-yl)-(4-methoxy-cyclohexyl)-methanone methane sulfonate (EMQMCM) for mGluR1; an agonist of group II mGluR, 1R, 4R, 5S, 6R-2-oxa-4-aminobicyclo[3.1.0] hexane4,6-dicarboxylate (LY379268); N-methyl-D-aspartate (NMDA)R2B subunit (NR2B)-selective NMDA receptor antagonists 1-[2-(4-hydroxyphenoxy)ethyl]-4-[(4-methylphenyl)methyl]-4-piperidinol hydrochloride (Ro631908) and (+/-)-(R*, S*)-alpha-(4-hydroxyphenyl)-beta-methyl-4-(phenylmethyl) 1-piperidine propanol (Ro256981); and an L-type calcium channel antagonist, 4-(4-benzofurazanyl)-1,-4-dihydro- 2,6-dimethyl-3,5-pyridinedicarboxylic acid methyl 1- methylethyl ester (isradipine). Dyskinesia and rotarod performance were monitored during chronic drug treatment. The striatal expression of phospho-extracellular signal-regulated kinase (ERK) 1/2 and mitogen- and stress-activated kinase (MSK)-1, or prodynorphin mRNA was examined after acute or chronic treatment, respectively. In the acute treatment studies, only MTEP and EMQMCM significantly attenuated L-DOPA-induced phospho-ERK1/2 and/or phospho-MSK-1 expression, with MTEP being the most effective (70-80% reduction). In the chronic experiment, only MTEP significantly attenuated dyskinesia without adverse motor effects, whereas EMQMCM and LY379268 inhibited the L-DOPA-induced improvement in rotarod performance. The NR2B antagonist had positive antiakinetic effects but did not reduce dyskinesia. Only MTEP blocked the up-regulation of prodynorphin mRNA induced by L-DOPA. Among the pharmacological treatments examined, MTEP was most effective in inhibiting LID and the associated molecular alterations. Antagonism of mGluR5 seems to be a promising strategy to reduce dyskinesia in Parkinson's disease.