Redistribution of neuronal lysosomes induced by colchicine: an electron microscopic quantitative study

We have previously demonstrated that a single injection of the microtubule poison colchicine, into the lateral cerebral ventricle of the rat, induced a rapid redistribution of the lysosomal marker enzymes, dipeptidylaminopeptidase II (Dpp II) and acid phosphatase, from their normal location in neuronal cell bodies out into the dendrites. In the present study, we have quantitatively analyzed this phenomenon at the electron microscopic level by identifying and counting the number of lysosomes and mitochondria in neuronal cell bodies and dendrites of control and colchicine-treated rats. Areas examined included the anterior dorsal (AD) thalamus, pontine nucleus, and facial nucleus. The results show that the cytoplasm of these neurons contains significantly fewer large lysosomes after treatment with colchicine while the dendrites become abnormally enriched with large and small lysosomes after treatment. Lysosomes were rarely seen in the axons of either control or colchicine-treated animals. A significant increase in the density and the shape of mitochondria was also observed in the dendrites following colchicine treatment. The data presented support the hypothesis that neurons contain a transport system which selectively translocates lysosomes, and possibly other organelles, into dendrites. The size, shape, and number of these organelles may change as a result of this transport.