Immunocytochemical demonstration of dynorphin(PH-8P)-like immunoreactive elements in the human hypothalamus

PH-8P (dynorphin[1-8])-like immunoreactive neuronal perikarya, processes, and terminals located within the human hypothalamus were investigated by the avidin-biotin peroxidase complex (ABC) immunocytochemical procedure. Immunopositive neurons were distributed throughout the hypothalamus. The distributional pattern was found to be similar to that in other mammalian species by the use of antisera against dynorphin. A large number of immunoreactive neuronal perikarya were detected in the supraoptic nucleus (SON) and the magnocellular portion of the paraventricular nucleus (PVN). Their processes appeared to project to the posterior pituitary via the internal layer of the median eminence and their distribution seemed to be less dense than in other mammalian species. PH-8P and vasopressin were colocalized in the neuronal perikarya in the human SON unlike the colocalization of these peptides in the rat SON and PVN. There were a few immunoreactive terminals in the external layer of the median eminence; their immunoreactive substances may be released into the portal veins to act on anterior pituitary cells. In addition, PH-8P-like immunoreactive neurons in the human hypothalamus may project to the extrahypothalamic area.