(S)-4C3HPG, a mixed group I mGlu receptor antagonist and a group II agonist, administered intrastriatally, counteracts parkinsonian-like muscle rigidity in rats

The aim of the present study was to determine whether S-4-carboxy-3-hydroxy phenylglycine (S)-4C3HPG, a mixed group I glutamate metabotropic receptor a ntagonist and a group II agonist, attenuated parkinsonian-like muscle rigid ity in rats. Muscle tone was examined using a combined mechano and electrom yographic method, which measured simultaneously the muscle resistance (MMG) of the rat's hind foot to passive extension and flexion in the ankle joint and the electromyographic activity (EMG) of the antagonistic muscles of th at joint: gastrocnemius and tibialis anterior. Muscle rigidity was induced by pretreatment with haloperidol (1 mg/k_p i.p.). (S)-4C3HPG injected in do ses of 5 and 15 mug/0.5 mul bilaterally, into the rostral region of the str iatum, decreased both the haloperidol-induced muscle rigidity (MMG) and the enhanced electromyographic activity (EMG). The present results suggest tha t blockade of mGluR1 receptors and/or activation of mGluR2 ones, localized in the rostral part of the striatum, may be responsible for the anti-parkin sonian effect of (S)-4C3HPG. (C) 2001 Elsevier Science B.V. All rights rese rved.