Immunocytochemical demonstration of GAP-like immunoreactive neuronal elements in the human hypothalamus and pituitary.

GnRH-associated peptide (GAP)-like immunonreactive elements located in the human hypothalamus were investigated by PAP immunocytochemistry using specific antiserum against [pro-GnRH (14-69) OH]. Immunoreactive neuronal perikarya were distributed in the MPOA, PVN and infundibular nucleus, with the largest numbers of GAP-like immunoreactive perikarya found in the infundibular nucleus. We also detected the coexistence of GAP-like and GnRH-like immunoreactivities in the same neuronal perikarya in the MPOA by using a double immunolabelling procedure. In addition to the above regions immunoreactive neuronal perikarya were present in the region dorsal to the medial mammillary nucleus. GAP-like immunoreactive fibers were distributed in same areas that immunoreactive perikarya were observed. Many immunoreactive terminals were found adjacent to capillaries in the infundibulum. Immunoreactive dots, presumably terminals, were observed in the posterior pituitary and these were particularly evident along the margin adjacent to the anterior pituitary. The distribution pattern and density of GAP-like immunoreactive neuronal elements are compared with those of other mammalian species. We also compared GAP-like immunoreactive elements with that of GnRH as has been previously observed in the human hypothalamus.