Subcellular localization of immunoreactive α-melanocyte stimulating hormone in human brain

The regional and subcellular distribution of immunoreactive α-melanocyte stimulating hormone (α-MSH₁) in the post mortem adult human brain was investigated. α-MSH_i was highly concentrated in medial basal hypothalamic tissue (1.02 ng/mg protein). Lower levels of α-MSH_i were present in the optic chiasm and mammillary bodies, 0.08 and 0.11 ng/mg protein, respectively. The concentrations of α-MSH_i in cerebellum and frontal cerebral cortex were 1/1,000th that of the medial basal hypothalamus. When medial basal hypothalamic homogenates were subjected to discontinuous or continuous sucrose density gradients, α-MSH_i was found to be associated primarily with subcellular particles which resembled isolated nerve terminals, i.e., synaptosomes. Low to undetectable amounts of α-MSH_i were found in the cytosol or the myelin/microsome fraction of the gradients. The results of these studies are consistent with the view that α-MSH is a neuronal peptide in the human brain.