The effect of β-(Tyr9)melanotropin-(9-18) and amphetamine on the open-field behavior and the striatal dopamine uptake and release were compared. β-(Tyr9)melanotropin-(9-18) at doses of 1 μg (icv) or 2 μg (icv) increased the ambulation of the rats, while in a dose of 5 μg (icv), it had no effect. Amphetamine had a similar dose-related effect on ambulation. This peptide also increased the rearing activity, in doses of 2 μg or 5 μg (icv), while amphetamine was effective only in a dose of 2 μg (icv). β-(Tyr9)melanotropin-(9-18) at doses of 1 μg, 2 μg or 5 μg (icv) increased the grooming, while amphetamine at the same doses decrease it. The peptide had no significant influence on the striatal dopamine uptake and release, whereas amphetamine markedly decreased the uptake and facilitated the release in a dose-related manner. These results suggest that although β-(Tyr9)melanotropin-(9-18) and amphetamine have similar effects on the open-field behavior, the mechanisms of action of the two substances are different.
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