Maturation of the hypothalamo-neurohypophysial system. II. Neurophysin, vasopressin and oxytocin in the median eminence of the developing rat brain.

Transverse sections of the median eminence from fetal and neonatal rats were examined by the immunoperoxidase technique to detect the presence of oxytocin, vasopressin and neurophysin. Neurophysin was observed in the 18-day fetus. Vasopressin and oxytocin were not detected until after birth, on the 4th and 8th days respectively. There was an accumulation of material crossreactive with neurophysin and vasopressin antibodies in the palisade layer of the median eminence between the 4th and 9th days after birth. This distribution of immunoreactive material in the palisade layer was suggestive of neurosecretory substances localized in two fibre tracts on either side of the median eminence. The data are consistent with the accumulation of corticotropin releasing factor and an associated neurophysin in this area. It is suggested that the accumulation of material occurs because of the relative immaturity of the capillary loops that constitute the primary plexus of the hypophysial portal system.