GLYCINE SITE ANTAGONISTS ABOLISH DOPAMINE D2 BUT NOT D1 RECEPTOR-MEDIATED CATALEPSY IN RATS

Catalepsy-a state of postural immobility (akinesia) with muscular rigi dity (rigor)-and reduced locomotion in animals are behavioral deficits showing similarities with symptoms of Parkinson's disease (PD). The e ffects of the glycine site antagonists 7-chlorokynurenate and (R)-HA-9 66 on haloperidol- (D2 antagonist) and SCH 23390- (D1 antagonist) indu ced catalepsy and reduced locomotion are investigated in rats. Both an tagonists dose-dependently counteract dopamine D2 receptor mediated ca talepsy but they have no influence on locomotion. Neither 7-chlorokynu renate nor (R)-HA-966 has any effect on dopamine D1 receptor mediated catalepsy. This finding is surprising, since NMDA receptor antagonists counteract both, dopamine D1 and D2 receptor mediated catalepsy. D1 a nd D2 receptors are located on different populations of neurons. Thus, the present findings suggest that these different neuronal population s have different sensitivity for ligands binding at the glycine bindin g site of the NMDA receptor.