The postnatal developmental localization of pro-opiomelanocortin and alpha melanocyte stimulating hormone in the medio-basal hypothalamus of the rat.

This immunocytochemical study of the late postnatal development of the medio-basal hypothalamus revealed the presence of ACTH 1-39 like positivity in neurons of the arcuate nucleus form the begin of this study (day E 18-20) onwards. Alpha MSH positivity, on the contrary, is not present in cells of the same area before day P 16. No other areas in the developing medio-basal hypothalamus contain perikaryal positivity for alpha M-SH or ACTH 1-39. The pituitary contains ACTH 1-39 like positivity from the begin of this study (day E 18-20) onwards. Fibers are positive for alpha MSH during the fetal development of the medio-basal hypothalamus, demonstrating an overal reactivity without varicosities and restricted to bundles or neuropil areas. Towards P 16 the alpha MSH positivity diminishes in the whole medio-basal hypothalamus, remaining present only in large fibre systems like the fornix. ACTH 1-39 like fiber positivity is already distributed in arcuate and periventricular regions at days E 20-PO, reaching its mature extension at day P2. After P16 alpha MSH positive threads, possessing varicosities are restricted to the same areas as ACTH 1-39 like fiber positivity is.