Pro-opiomelanocortin-containing neurons in rat median eminence

A significant number of pro-opiomelanocortin (POMC)-containing cells were detected in the rat median eminence (ME) by immunocytochemistry using an antibody raised against a synthetic peptide corresponding to the cleavage site between adrenocorticotropin and beta-lipotropin moieties. Distribution of POMC-positive cells was restricted to the internal zone of the anterior parts of the ME. Such cells were observed as early as the 14th day of gestation in the area of the primitive ME, long before glial fibrillary acidic protein-positive cells appeared postnatally in this structure. Dissociated cell cultures obtained from the ME of 1-day-old rats produced cells immunoreactive for neurofilaments and the POMC moiety. Such cells displayed a neuronal morphology: the cell body was oval (13-18 microns) with long and fine beaded fibers. These findings clearly demonstrate the early appearance of POMC neurons in the developmental ME, a target organ of the hypothalamic infundibular neurons.