H3-THYMIDINE AUTORADIOGRAPHIC STUDIES ON CYTOKINETIC RESPONSES TO X-RAY IRRADIATION AND TO THIO-TEPA IN THE NEURAL TUBE OF MOUSE EMBRYOS.

Abstract

AbstractFirst, using the methods of H3‐thymidine autoradiography and counting mitotic index, cytokinetics of the matrix cells were studied in the telencephalon of normal mouse embryos at ten‐days‐postconcetpion, and various kinetic constants of the matrix cells were determined: Generation time, five hours 20 minutes; mitotic duration, 24 minutes; presynthetic resting time, two hours 36 minutes–one hour 36 minutes; DNA synthetic time, one hour 20 minutes; and post synthetic resting time, one‐two hours. Based on this information, effects of two teratogenetic agents, x‐rays and thio‐TEPA, on the cellular proliferation were analyzed. By x‐ray irradiation (200 r) only proliferating matrix cells are damaged in the neural tube, but not neuroblasts. The radiation induces a temporary block of the flow of the matrix cells through the cell cycle at the late t2 period so that the mitotic and DNA synthetic cells subsequently decrease in number. Some of the matrix cells that are captured at t2 period fail to tolerate the block, degenerate and are eliminated from the matrix layer. On the other hand, thio‐TEPA, which was proved non teratogenetic to the C. N. S. in this experimental condition, causes a slight prologation of t2 duration, but does not significantly influence the proliferative process in the neural tube.