Two dopamine receptors: Supportive evidence with the rat rotational model

Di-isobutyryl apomorphine (5 mg/kg i.p.) and lergotrile (5 mg/kg i.p.) produce long lasting turning behaviour in rats with 6-hydroxydopamine lesions at the level of the substantia nigra. Haloperidol (1.5 and 3.0 mg/kg p.o.) blocks the rotational behaviour due to the apomorphine ester but has no effect on lergotrile turning. Clozapine (10 and 20 mg/kg p.o.) blocks the lergotrile turning but stimulates the rotational behaviour produced by the apomorphine ester. The results support the concept of two anatomically separate dopamine receptors and their relevance to the study of antipsychotic activity is discussed.