Investigations on the hypothalamo-neurohypophysial neurosecretory system of the grass frog (Rana pipiens) after transection of the proximal neurohypophysis. II. Light- and electron microscopic findings in the disconnected distal neurohypophysis with special emphasis on the pituicytes.

Abstract

With the onset of degeneration of the neurosecretory nerve fibers following transection of the proximal neurohypophysis, the pituicytes phagocytize these nerve fibers. Concomitant with a considerable increase in the size of the pituicytes, which reaches a peak between 8 and 10 days after the transection, the following sequence of events can be observed: reduction of the amount of intergranular axoplasm, increase in the size of some granules, partial or total loss of the electron density of the neurosecretory granules, loss of granule membranes, fusion of some granules, polymorphous axonal content in digestion vacuoles, formation of multilamellate bodies, digestion vacuoles with moderately electron dense peripheral material, empty digestion vacuoles. At about 12 days after the transection many vacuoles appear which subsequently disappear as the pituicytes shrink. Free neurosecretory granules resulting from the disappearance of the axolemma remain intact in the intercellular and perivascular connective tissue spaces and are eventually phagocytized by pituicytes and pericytes. Phagocytosis is considered to be a basic function of pituicytes. The problems related to this function as well as the possible implications for the interpretation of Herring bodies are discussed.