Identification, characterization and stereotaxic mapping of intraneuronal α-melanocyte stimulating hormone-like immunoreactive peptides in discrete regions of the rat brain

Abstract

A highly specific antibody to α-melanocyte stimulating hormone (α-MSH) was used to histochemically localize and biochemically identify and quantitate α-MSH immunoreactivity in nerve fibers and cell bodies of the rat brain. α-MSH-like immunoreactivity was contained in fibers throughout the brain. The distribution of α-MSH was determined by immunocytochemistry as well as by radioimmunoassay combined with microdissection techniques. High concentrations of α-MSH were contained in the nucleus interstitialis stria terminalis, the median eminence and the medial preoptic, anterior hypothalamic, periventricular, paraventricular, arcuate, dorsomedial, and posterior hypothalamic nuclei. Moderate α-MSH concentrations were noted in the amygdala, septum, central gray, dorsal raphe, and the nucleus tractus solitarius. Cell bodies containing α-MSH were observed only in the arcuate nucleus. The α-MSH-like compound in brain had similar immunochemical and electrophoretic properties of standard α-MSH but high pressure liquid chromatographic analysis demonstrated that the α-MSH-like immunoreactivity was comprised of one major and two minor components. The major immunoreactive peak had an identical retention time as α-MSH and therefore may be chemically identical to α-MSH. The similar retention times and immunoreactivity of the other two compounds suggest a similarity in size and structure to α-MSH. These observations demonstrate that fibers containing α-MSH emanate from the arcuate nucleus to innervate many other regions of the rat brain.