The interaction between beta-[Tyr9]melanotropin-(9-18), haloperidol and amphetamine in different behavior tests of rats.

The effects of beta-[Tyr9]melanotropin-(9-18) on the extinction of the active avoidance reflex in (dopamine receptor blocker) haloperidol-treated animals, and on the open-field activity in haloperidol and amphetamine-treated rats were studied. It was shown that a systemically given 100 microgram dose of the peptide, which had no action on the ambulation and rearing activity in the open-field test, could still delay the extinction of the active avoidance reflex. Haloperidol treatment was able to partially block the effects of the ICV administered beta-[Tyr9]melanotropin-(9-18) on both the extinction and open-field activity. After intracerebroventricular administration, the effect of the peptide on the open-field test was partially similar to that of amphetamine: it facilitated the ambulation and rearing activity, and (in contrast with amphetamine) was able to facilitate the grooming activity, even in the presence of amphetamine. The results suggest that dopaminergic innervation might play a mediating role in the effect of beta-[Tyr9]melanotropin-(9-18) on the extinction of the active avoidance reflex and open-field activity. The effect on the open-field activity differens in part from that of amphetamine.