Hypothalamic and Cerebral Cortical Inhibition of Melanocyte-Stimulating Hormone Secretion in the Frog,Rana pipiens

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Abstract
-Aqueous extracts of hypothalamic and cerebral cortical tissues of light and dark adapted frogs were assayed in vitro for their ability to inhibit the secretion of melanocyte-stimulating hormone (MSH) from the pars intermedia of the dark adapted frog. The extracts also were assayed for melanocyte-stimulating activity. The pars intermedia secreted large quantities of MSH in vitro. The extracts of the hypothalamus and of cerebral cortex of both light and dark adapted frogs contained a factor(s) that inhibited the secretion of MSH from the pars intermedia. Extracts of the hypothalamus, but not extracts of the cerebral cortex, also contained a melanocyte-stimulating substance. There was no significant difference between extracts of the hypothalamus and cerebral cortex of light and dark adapted frogs in their ability to inhibit MSH secretion. The possible chemical nature of the factor(s) was discussed. The ability of the cerebral cortex extracts to inhibit MSH secretion was attributed to the catecholamine content of the brain. The presence of a melanocyte-stimulating substance in the hypothalamus, but not the cortex, suggests that accumulated MSH may be involved in a feedback control loop which regulates the release of the hypothalamic factor that inhibits the secretion of MSH.

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