Dendritic transport. II. Somatofugal movement of neuronal lysosomes induced by colchicine: evidence for a novel transport system in dendrites.

The effect of colchicine injections on the ultrastructural localization of dipeptidyl peptidase II (Dpp II) was studied in the mitral cells of the rat olfactory bulb. In control animals, electron-dense reaction product representing Dpp II activity was observed in lysosomes, lipofuscin granules, short cisternae located close to the granular endoplasmic reticulum, and dense granules. Lysosomes and lipofuscin granules were the most intensely stained organelles. Dpp II-containing organelles were localized mainly to the cell body and were randomly distributed in the perikaryal cytoplasm. Twenty-four hours after a 100-micrograms intracerebroventricular colchicine injection, the distribution of Dpp II-containing organelles was drastically altered. Short cisternae and dense granules containing Dpp II reaction product were noticeably absent in these preparations. Lysosomes and lipofuscin granules were depleted from the perikaryal cytoplasm and were concentrated in dendrites. Lysosomes were observed to extend for considerable distances in dendrites where they acquired elongated and dumbbell shapes. The shapes of some of these labeled lysosomes gave the impression that they were actively being "pulled" into the dendrites. These results indicate that microtubules sequester lysosomes to the perikaryal cytoplasm and suggest the presence of a novel transport system responsible for the movement of lysosomes from the cell body to the dendrites.