[Pathways of substance penetration into the neurosecretory axons in the posterior lobe of the rat hypophysis].

The penetration of horseradish peroxidase and ferritin into the neurosecretory axones in the rat's posterior pituitary has been studied with the electron microscope. Markers were revealed in neurosecretory granules, in empty vesicles of the same size, in neurotubules, in lamellar bodies and in the axoplasm. Markers were taken up from the extracellular space by micropinocytotic "synaptic" vesicles and probably by larger empty vesicles. It is supposed that the contents of these vesicles penetrate into the granules to take part in their maturation. Besides, the contents of synaptic vesicles probably penetrate into neurotubules and are retrogradally transported to perikaryons of neusecretory cells. Ferritin is taken up from axoplasm by lamellar bodies that possess lysosomal activity.