Generation times of the matrix cells during embryonic brain development: An autoradiographic study in rats

Abstract

In the first part of this work matrix cells were examined by [ 3H]TdR autoradiography in rat embryos from the twelfth to the eighteenth day of gestation. A time-table of the cell cycle during embryonic development was calculated from the generation time (T c) and the duration of the DNA-synthetic phase (T S), which were determined by the labeling index and by a modified double-labeling technique. The results show that the generation time (T c) lenghtens from the twelfth to the eighteenth day of gestation (11 h and 19 h respectively). There is a significant increase in T C between days 14 and 15. The mean DNA-synthetic phase (T S) remains fairly constant within the time studied, ranging from 6 to 8 h. The lengthening of T C results mainly from an increase of the pre-synaptic phase (G1). Calculations were made both for steady-state and exponential cell proliferations. These results are mean values based on the presumption that all cells are equally distributed throughout the cell cycle and that the entire cell population participates in the proliferating activity. In order to obtain more detailed information concerning the growth characteristics of the matrix cell population the second part of this work was performed, using continuous [ 3H]TdR infusions for 4, 6, 8, 10 and 14 h. It was shown that the matrix cell layer comprises at least two different cell populations with different generation times. Details of the calculations are discussed in the Appendix.