ALPHA-MELANOCYTE-STIMULATING HORMONE - A POSSIBLE NEURONAL MARKER OF THE AGING BRAIN

The amount of .alpha.-melanocyte-stimulating hormone [melanotropin] (.alpha.-MSH) in the entire hypothalamus and the amount of .alpha.-MSH in free granule and synaptosome fractions of hypothalamic homogenates was investigated throughout the lifespan of female rats (1-24 mo.). A 900 g supernatant fluid was prepared from hypothalami following homogenization in an iso-osmotic sucrose solution. Free granules and synaptosomes containing .alpha.-MSH were fractionated by continuous sucrose density gradient centrifugation. .alpha.-MSH was quantified by radioimmunoassay. The total amount of .alpha.-MSH in the hypothalamus and in free granules and synaptosomes prepared from hypothalami increased progressively from the 1st-5th mo. of life. This increase was more pronounced in the free granules than in the synaptosomes. The amount of .alpha.-MSH in the hypothalamus and the amount present in free granules and synaptosomes prepared from 5-24 mo. old animals decreased with age. This decrease appeared to proceed at similar rates in both subcellular compartments. Aging of .alpha.-MSH neurons in the hypothalamus apparently is accompanied by axon degeneration and/or an alteration in the biosynthetic and degradative activities of the neuron.