The striatum as a target for anti-rigor effects of an antagonist of mGluR1, but not an agonist of group II metabotropic glutamate receptors.

The aim of the present study was to find out whether the metabotropic receptor 1 (mGluR1) and group II mGluRs, localized in the striatum, are involved in antiparkinsonian-like effects in rats. Haloperidol (1 mg/kg ip) induced parkinsonian-like muscle rigidity, measured as an increased resistance of a rat's hind foot to passive flexion and extension at the ankle joint. (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA; 0.5-15 microg/0.5 microl), a potent and selective mGluR1 antagonist, or (2R,4R)-4-aminopyrrolidine-2,4-dicarboxylate (2R,4R-APDC; 7.5-15 microg/0.5 microl), a selective group II agonist, was injected bilaterally into the striatum of haloperidol-treated animals. AIDA in doses of 7.5-15 microg/0.5 microl diminished the haloperidol-induced muscle rigidity. In contrast, 2R,4R-APDC injections were ineffective. The present results may suggest that the blockade of striatal mGluR1, but not the stimulation of group II mGluRs, may ameliorate parkinsonian muscle rigidity.