Activation of striatal group II metabotropic glutamate receptors has a differential effect on dopamine-D1 and -D2 receptor antagonist-induced hypokinesia in the rat

Motor function of group II metabotropic glutamate receptors was investigated by quantifying motor effects of bilateral infusions of the preferential group II metabotropic glutamate receptor agonist (2S,3S,4S)-alpha-carboxycyclopropyl-glycine (15, 30, 60 nmol/0.5 µl) into the striatum of conscious rats. (2S,3S,4S)-alpha-carboxycyclopropyl-glycine reduced spontaneous sniffing activity in an experimental chamber, but did not affect spontaneous locomotor (line crossings) or exploratory behaviour (rearings, hole visits) in an open field equipped with a hole-board. Intrastriatal infusion of the selective group III metabotropic glutamate receptor agonist l-2-amino-4-phosphobutyric acid (15, 30, 60, 120 nmol/0.5 µl) did not influence spontaneous motor behaviour. Intrastriatal infusion of (2S,3S,4S)-alpha-carboxycyclopropyl-glycine (15 nmol/0.5 µl and 30 nmol/0.5 µl) further depressed spontaneous motor behaviour in rats pretreated with the dopamine-D1 receptor antagonist (-)-trans-6,7,7a,8,9,13b-hexahydro-3-chloro-2-hydroxy-N-methyl-5H-benzo[d]naphtho-(2,1-b)azepine, but not if rats were pretreated with the preferential dopamine-D2 receptor antagonist haloperidol.