Biological and immunological characterization of α-melanocyte-stimulating hormone (α-MSH) in two neuronal systems of the rat brain

Abstract

Recent immunocytochemical studies have demonstrated the existence of two different neuronal systems containing α-MSH-like material in the brain: one originating from the arcuate nucleus and the other one from the dorsolateral hypothalamus. The aim of the present study was to further characterize α-MSH in these two discrete regions of the rat diencephalon. Intracerebroventricular administration of colchicine resulted in a marked decrease in the number of ACTH and β-endorphin nerve fibers and a significant reduction in ACTH and β-endorphin content in the dorsolateral hypothalamus. Conversely, colchicine treatment did not alter α-MSH, ACTH or β-endorphin content in the arcuate nucleus and did not significantly affect α-MSH concentration in the dorsal region. Reverse-phase high-performance liquid chromatography showed that the major α-MSH-like compound localized in the dorsal hypothalamus co-migrated exactly with synthetic α-MSH, whereas the arcuate nucleus contained 5 peptides cross-reacting with α-MSH antibodies, 4 of them being different from standard α-MSH. Significant amounts of biologically active melanotropin, which migrated on Sephadex G-25 columns like synthetic α-MSH, were also detected in both the arcuate nucleus and dorsolateral hypothalamus. Taken together, these data demonstrate that the α-MSH cell bodies located in the dorsolateral hypothalamus specifically produce authentic α-MSH, whereas the α-MSH cell bodies in the arcuate nucleus also contain ACTH, β-endorphin and several peptides immunologically related but not identical to α-MSH.