The fate of the neurosecretory granulated vesicles that accumulate in the empty Herring bodies of the neurohypophysial stalk of the rat following intracisternal injection of 7.0 micron colchicine will be investigated electronmicroscopically and autoradiographically. Similar studies will be carried out on Herring bodies induced through iontophoretic injection of vinblastine into the preopticohypophsial tract of the frog. The participation of pituicytes in the regeneration of neurosecretory axons in the frog will be investigated by transplanting pituicytes obtained from disconnected neural lobes into the neurosecretory pathway, at various levels of transection. Biochemical characterization of the dilated endoplasmic reticulum which is present in pituicytes of transected neural lobes in the frog will be attempted. Immunocytochemical and cytochemical studies will be carried out to determine the participation of the smooth axonal endoplasmic reticulum in the transport of hormones and other substances. The regeneration of neurosecretory axons in the frog will be investigated in a correlative transmission and scanning electronmicroscopic study.