Autoradiographic and histological studies of postnatal neurogenesis. II. A longitudinal investigation of the kinetics, migration and transformation of cells incorporating tritiated thymidine in infant rats, with special reference to postnatal neurogenesis in some brain regions

Abstract

Thymidine-H³ was injected intraperitoneally into 6- and 13-day old rats and they lived afterwards for periods ranging from one hour to 60 days. Autoradiographic data obtained from animals surviving for short periods were used to estimate rates of regional cell proliferation. Animals with longer survival were used to deduce the movements of new cells from germinal sites, through migratory channels, to target areas, and to determine their mode of differentiation. The formation and differentiation of microneurons goes on during infancy, though in most structures at a declining rate. In the wall of the olfactory ventricle cell multiplication continued at a high rate at six days, with a decline at 13 days, and the new cells migrated to the layers of the olfactory bulb. The migration of labeled cells from the lateral ventricle was traced, by way of the fimbria, to the polymorph cell layer of the dentate gyrus, and from there to the granular layer. The “older” granule cells were located in the upper part of the granular layer, the “younger” cells at its base. Cell multiplication continued at a very high rate in the external granular layer of the cerebellar cortex, whence cells migrated to the molecular layer and internal granular layer. Speed of migration was approximately 50 μU/day in the olfactory bulb, and 60–70 μ/day in the cerebellum. The possible significance of these findings was discussed.