ON ULTRASTRUCTURE OF NEUROSECRETORY ELEMENTARY GRANULES

The elementary granules of the neurohypophysial neurosecretory material are enveloped by a double-membrane. The envelope of the granules in the neural lobe of the hedgehog hypophysis is associated with parallelized filamentous structures of unknown significance. The core of the elementary granules is composed of small granular particles. These sub-units are often condensed into rod-shaped hexagonal crystals with a regular ultrastructure. The granular cores and the crystals are considered to be mainly the carrier substance of the hypothalamic octapeptide hormones (neurophysins). Since forms of transition between granular cores and rod-shaped crystals exist, two sharpely separated types of neurosecretory granules cannot be distinguished by means of electron microscopy. It seems to be unlikely that the complexes vasopressin-neurophysin and oxytocin-neurophysin have different electron microscopical equivalents. The release of hormones is accompanied by changes of the carrier-proteins entering into the cytoplasm that surrounds the elementary granules or vesicles. © 1969 Springer-Verlag.