Cycle times of the neural epithelial cells of various types of neuron in the rat. An autoradiographic study

Abstract

Abstract Cell kinetic studies of the proliferation of the neural epithelium during the embryonic development of the rat brain are described. Pregnant rats received a single injection of 3 H‐thymidine ( 3 H‐TdR) between the tenth and twenty‐first day of pregnancy. Autoradiographs of the brains of the 25‐day‐old offspring were prepared. For a number of different cell types (table 1, II) the percentage of labeled neurons as a function of time of prenatal 3 H‐TdR injection was determined. The end of the proliferating period of the neural epithelial cells of certain cell types can be derived from these percentages of labeled cells (table 1, V). Further‐more, it can be demonstrated that the percentage of labeled neurons is equal to the labeling index of the neural epithelial cells of these cell types at the time of prenatal 3 H‐TdR injection. Based on the labeling index of the neural epithelial cells and their S phase, cycle times can be calculated. This way it is possible for the first time to determine the cycle times of those neural epithelial cells that later on differentiate into a certain type of neuron (table 1, IV). The calculated cycle times show that up to the sixteenth prenatal day the neural epithelial cells behave like a homogeneous cell population which proliferates with an approximately constant cycle time of about half a day. The cycle time seems to increase with increasing fetal age. From the total number of a certain type of neuron the number of mitotic divisions or cycle times respectively can be derived which is necessary to produce the number of neural epithelial cells providing these neurons. With regard to the mean cycle time of the neural epithelial cells it can be concluded that the beginning of proliferation of the neural epithelial cells coincides with the formation of the neural plate on the ninth day of embryonic development or starts even shortly before this time.