[Morphometric analysis of the formation of the external zone of the median eminence of the rat hypothalamus in the perinatal period].

Morphometric electron microscopy data were obtained using a semiautomatic image analysis which demonstrate that the main stages of formation of the external zone of median eminence in the rat hypothalamus take place during the perinatal period. From the 20th day of prenatal period to the 9th day of postnatal period, the length of contact between the neurosecretory axons and the primary portal plexus increases twice, whereas that between the basal processes of ependyma cells and the primary portal plexus by a factor of 1.5. At the same time, the number of secretory granules and microvesicles in axons and that of pinocytotic vesicles in the basal processes markedly increases. Regional differences in the distribution of vesicular structures were noted in neonatal animals: secretory granules were more numerous in the axon swellings remote from the external basal lamina; pinocytotic vesicles were more numerous in the basal processes which terminated in the medial median eminence.