Influence of cimetidine, ranitidine and imidazole on the behavioral effects of (+/-) N-n-propylnorapomorphine in male rats.

Cimetidine injected IP 15 min before (+/-) N-n-propylnorapomorphine (NPA) antagonized in dose-dependent fashion the penile erections (PE) and stretching and yawning (SY) induced by this typical dopaminergic agonist in male rats. Ranitidine, which acts on H2 histamine receptors in much the same way as cimetidine despite its lack of an imidazole ring, failed to produce the same effect. On the other hand, imidazole itself was similar to cimetidine in antagonizing PE and SY induced by (+/-) NPA, whether injected IP or ICV. Neither imidazole nor cimetidine antagonized the stereotyped behaviour (SB) induced by (+/-) NPA. Indeed, imidazole reduced the latency of this response. A mechanism which may underly these effects is discussed, as well as the possible preclinical use of this test in animals.