DEVELOPMENT OF THE NEUROGLIOHEMAL COMPLEX IN THE MOUSE NEUROHYPOPHYSIS

The mouse neurohypophysis was studied at different ages of development in order to analyse the ultrastructural changes that lead to the matu ration of the neurogliohemal complex and to determine the existence of permeability between the blood capillaries and the neurohypophysial c hannels. In all the studied ages, two groups of 5 animals each were in travenously injected with different tracer solutions: to one group, 10 mu l of cationized ferritin were used and to the other, 10 mu l of fe rrous fumarate were applied. For the ultrastructural studies the tissu e samples were processed using the conventional techniques for electro n microscopy. At day 17 of prenatal age, some hypothalamic axons (10 a xenic profiles/20 mu m(2)) were already seen within the neurohypophysi s, increasing threefold (26 to 30 axenic profiles/20 mu m(2)) at prena tal day 19. In these axons terminals, the first neurosecretory vesicle s began to appear. At this early age, the glial cells formed few prolo ngations. Between postnatal days 1 and 9, numerous axon terminals cont aining dense neurosecretory vesicles composed the neuropile areas. Aft er day 9, there was a broadening of the intercellular space, which we have termed as neurohypophysial channels; these were actually expansio ns of the existing extracellular space in the neurohypophysis. Between days 9 and 21, the population of axon terminals showing a higher dens ity of neurosecretory vesicles continued to increase in number. Some o f these axon terminals were separated by irregular neurohypophysial ch annels. The glial cells showed scarce cytoplasm and formed numerous la mellar prolongations, which became increasingly finer surrounding bund les of individual axons. The experiments with the electron-dense trace rs permitted us to determine the permeability of the neurohypophysial channels and their continuity with the extracellular space. We conclud e that these channels facilitate the migration and transport of the ne urosecretory materials to the hypophysial capillaries.