Abstract
The pituitary-hypothalamo-pineal complex involving MSH, MIF-I and melatonin has been strongly emphasized in the adaptive mechanism of the animal. A series of experiments was conducted to investigate the effects of α-MSH, MIF-I and melatonin on novelty-induced defecation, step-down activity, plasma 11-OHCS levels and whole brain DA and NE concentrations over days of novelty×drug treatment. α-MSH consistently enhanced and sustained novelty-induced defecation, increased plasma 11-OHCS levels in the resting intact rats and in the novelty exposed hypophysectomized (hypox) rats, and decreased brain DA and NE levels in intact, hypox and sham-hypox rats. MSH did not increase plasma 11-OHCS in intact and sham-hypox rats during exposure to novelty. MIF-I significantly habituated novelty-induced defecation and increased brain DA and NE levels over 5 days of drug×novelty treatment. Melatonin, on the other hand, inhibited novelty-induced defecation, decreased plasma 11-OHCS and increased brain DA level over 5 days of melatonin×novelty treatment. MSH, MIF-I or melatonin did not show any significant effect on the step-down activity of the rats. The results suggest the possibility that central CAs may be implicated in the behavioral changes observed after α-MSH, MIF-I and melatonin administration and in the interaction of the pituitary-hypothalamo-pineal complex involving MSH, MIF-I and melatonin.
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