Proliferation and migration of undifferentiated precursor cells in the rat during postnatal gliogenesis

It is concluded that the cells formed around the lateral ventricle, which are destined to reach the cortex, utilize the white matter and corpus callosum as a migratory pathway.

Abstract

Rats aged 13 days were injected with thymidine-H3 and were killed 6 hours, 1, 3, 6, 12, 20 and 60 days afterwards. Incorporation of this labeled precursor of chromosomal DNA was studied autoradiographically with reference to the origin of neuroglia cells in the neocortex. A large proportion of the subependymal cells of the lateral ventricle were labeled after brief survival, indicating rapid regional proliferation. In animals with longer survival there was considerable increase in the proportion of labeled cells, combined with label dilution. In spite of this evidence of rapid and continuous cell multiplication, the concentration of subependymal cells declined considerably with age, indicating that the bulk of new cells do not stay here. The rate of regional proliferation was lower in the white matter and corpus callosum, though there was a considerable increase in the proportion of labeled cells with prolonged survival. Significantly, the addition of this large number of new cells did not lead to a net increase in the total cell population. These facts imply that many of the cells found in these fibrous regions are migratory ones, and as new cells arrive here older ones depart. Finally, in the gray matter of the cortex regional cell proliferation was low at this age, but there was a steady gain in the proportion of labeled cells with increased survival time. On the basis of these findings it is concluded that the cells formed around the lateral ventricle, which are destined to reach the cortex, utilize the white matter and corpus callosum as a migratory pathway.