LESIONS OF THE ENTOPEDUNCULAR NUCLEUS AND THE SUBTHALAMIC NUCLEUS REDUCE DOPAMINE-RECEPTOR ANTAGONIST-INDUCED CATALEPSY IN THE RAT

The role of the entopeduncular nucleus (EP) and the subthalamic nucleu s (STN) in mediating dopamine receptor antagonist-induced catalepsy in the rat was investigated. Five days after bilateral lesions of EP and STN respectively with the excitotoxin quinolinic acid (15, 30 nmol/0. 5 mu l/side and 24 nmol/0.5 mu l/side, respectively) rats were injecte d intraperitoneally with the dopamine D1 receptor antagonist SCH 23390 (0.5 mg/kg) or the dopamine D2 receptor antagonist haloperidol(0.5 mg /kg). Complete EP lesions prevented both SCH 23390- and haloperidol-in duced catalepsy. STN lesions exerted pronounced anticataleptic effects in case of haloperidol-induced catalepsy, but less pronounced in case of SCH 233390-induced catalepsy. Further characterization of these an ticataleptic effects in an open field demonstrated, that neither EP- n or STN lesions reversed bradykinesia, which occurred after selective d opamine receptor blockade. In conclusion, both EP and STN participate in the mediation of catalepsy induced by dopamine D1- and dopamine D2 receptor antagonists. Thereby these nuclei preferentially mediate rigi dity and akinesia, but to a lesser extent bradykinesia.