Examination of the transient distribution of lysosomes in neurons of developing rat brains.

We have previously observed that lysosomes redistribute from their normal location in neuronal cell bodies to the dendrites following an intracerebroventricular injection of an antimitotic such as colchicine, vinblastine or vincristine. In the present study, we have followed the developmental distribution of lysosomes in the brains of untreated rats, using a lysosomal marker enzyme, dipeptidylaminopeptidase II. A relatively high concentration of neuronal lysosomes was found in the dendrites of olfactory bulb mitral cell neurons and in hippocampal granule and pyramidal cell neurons from postnatal day 1 (P1) to P8. As the animals matured, the pattern of lysosomal enzyme distribution was reversed. Lysosomes became progressively less concentrated in the dendrites and more concentrated in neuronal cell bodies. In cerebellar Purkinje cells, lysosomes were only found in the cell bodies during the first week after birth. Between P9 and P19, lysosomes appeared in the dendrites of these neurons and, with maturity, progressively disappeared from the dendrites and were concentrated mainly in cell bodies. The presence of lysosomes in the dendrites of developing animals suggests that the transport of lysosomes to the dendrites, induced by microtubule poisons, mimics a physiological process which is normally present during development.