Immunohistochemical and immunocytochemical localization of gamma-melanocyte stimulating hormone (gamma-MSH)-like immunoreactivity in human and rat hypothalamus.

Immunohistochemical localization of gamma-MSH was studied in human and rat hypothalamus by peroxidase-labeled antibody method both at light and electron microscopic levels. Human and rat hypothalamus contained immunoreactive gamma-MSH neurons and varicose nerve fibers. The distribution of gamma-MSH-positive nerve fibers was similar to that of beta-endorphin previously reported. By our "re-staining method," gamma-MSH and ACTH were localized in the same neurons and nerve fibers. In the rat, the immunologic staining of gamma-MSH in hypothalamic neurons and nerve fibers was not diminished after hypophysectomy. These findings strongly suggest the possibility of actual precursor production in the hypothalamus which is similar to that in the anterior pituitary. The presence of gamma-MSH at the synapse-like structure of the nerve terminal may indicate that gamma-MSH could function as a neurotransmitter or a neuromodulator.