The hypothalamic magnocellular neurosecretory system of the guinea pig. II. Immunohistochemical localization of neurophysin and vasopressin in the fetus

The development of the hypothalamic magnocellular neurosecretory system of the fetal guinea pig was examined by immunohistochemistry. Neurophysin was first observed in the supraoptic nucleus (SON), median eminence (ME) and posterior pituitary (PP) on day 40 of gestation. It was not regularly present in the paraventricular nucleus (PVN) until day 47. Vasopressin was first observed in the SON, ME and PP on day 45. In the median eminence immunoreactive deposits indicative of both peptides were observed in both the fibers of the hypothalamo-hypophysial tract (H-HT) in the presumptive zona interna as well as in axons projecting to the developing primary portal plexus.