Immunocytochemical study of the hypothalamo-neurohypophysial system. I. Localization of neurosecretory neurons containing neurophysin-I and neurophysin-II in the domestic pig.

Antibodies raised against porcine neurophysin-I and porcine neurophysin-II using an injection regime in rabbits over a short time period, were used to localize neurophysin-I and neurophysin-II in hypothalamic neurosecretory elements of the domestic pig. In transverse section, neurophysin-II containing cells were more abundant in the dorsal medial region of the rostral supraoptic nucleus (SON) as compared with the distribution of neurophysin-I neurons. The main bulk of the cells of the SON were heavily stained for neurophysin-I with neurophysin-II containing cells positioned dorsal from the edge of the optic chiasma. Neurosecretory cells of the SON as seen in sagittal section also showed a differential staining for neurophysins-I and -II. Rostral regions of the pig paraventricular nucleus (PVN) contained magnocellular elements near the third ventricle which were stained predominantly for neurophysin-II. In regions corresponding to the caudal PVN there appeared two populations of neurosecretory neurons: (a) an area of cells adjacent to the third ventricle which contained neurophysin-II antigen and (b) a group of densely populated cells in the dorsal-lateral region which was stained for neurophysin-I. The results support the existence in the pig of at least two distinct populations of neurosecretory neurons corresponding to the neurophysin-I and neurophysin-II neurosecretory system.