Effects of raclopride and haloperidol on spontaneous motor activity and on conditioned avoidance behavior in rats. A comparison of potency, efficacy and time-course of action.

The spontaneous locomotor activity of rats was used as an index of centrally mediated effects of raclopride (CAS 84225-95-6). The results indicate a duration of less than 2 h after s.c. administration of 2 mumol kg-1. In support of a rapid first-pass metabolism in the rat, the effect was considerably weaker after i.p. administration. This difference was further supported by comparing the dose-effect curves after s.c. and i.p. raclopride administration. Haloperidol (CAS 52-86-8) appears to be slightly more potent than raclopride, the estimated ED50 values being 0.15 and 0.24 mumol kg-1 s.c., respectively. Both compounds (s.c. administration) produced a complete suppression of the conditioned avoidance behavior with approximately the same potency. As assessed in the latter situation, the duration of the effects of raclopride is considerably shorter than that of haloperidol.