α‐MELANOCYTE‐STIMULATING HORMONE: A POSSIBLE NEURONAL MARKER OF THE AGEING BRAIN

Abstract— The amount of α‐melanocyte‐stimulating hormone (α‐MSH) in the entire hypothalamus as well as the amount of α‐MSH in free granule and synaptosome fractions of hypothalamic homogenates was investigated throughout the lifespan of female rats (1‐24 months). A 900 g supernatant fluid was prepared from hypothalami following homogenization in an iso‐osmotic sucrose solution, and free granules and synaptosomes containing α‐MSH were fractionated by means of continuous sucrose density gradient centrifugation. α‐MSH was quantified by radioimmunoassay. The total amount of α‐MSH in the hypothalamus, as well as the amount in free granules and synaptosomes prepared from hypothalami increased progressively from the 1st to the 5th month of life, and this increase was more pronounced in the free granules than in the synaptosomes. On the other hand, the amount of α‐MSH in the hypothalamus and the amount present in free granules and synaptosomes prepared from 5‐24‐month‐old animals decreased with age, and this decrease appeared to proceed at similar rates in both subcellular compartments. Based on these results, it is suggested that ageing of α‐MSH neurons in the hypothalamus is accompanied by a degeneration of the axons and/or an alteration in the biosynthetic and degradative activities of the neuron.