Ontogeny of neurophysin in the rat pituitary gland. An electron microscope immunohistochemical study.

The ontogenic development of neurophysin has not been investigated so far. To study this problem, electron microscopic immunohistochemistry was performed on ultrathin sections of the posterior pituitary of foetal and newborn rats. A concomitant appearance of secretory granules and neurophysin was first noted in the posterior pituitary of 18-day foetus. Neurophysin was detected only in the secretory granules, all of which were labelled. The number of granules (75-110 nm in diameter) as well as the intensity of the reaction for neurophysin increased as the foetus became older. In the newborn rat, the secretory granules were more numerous and showed a strong neurophysin positive reaction. The results support the hypothesis that neurophysin is an essential component for the formation of the secretory granules in the hypothalamo-neurophypophysial system.