The effect of irradiation on cell degeneration among developing neurones in Xenopus laevis.

Abstract

In the development of the vertebrate nervous system not all the neuroblasts complete their development into neurones. In the lumbar ventral horns of the larvae of Xenopus laevis, the number of viable and degenerating cells has been counted throughout development. Given an estimate of the duration of cell death, the total number of cells which degenerate can be calculated; for every cell which finally differentiates, eight or nine die during development. The death rate of cells in the ventral horns can be reduced or abolished by X rays at a dosage of 80–160 r. This arrest may persist for nearly three weeks with relatively young tadpoles, but for only a few days with older animals. When larvae are irradiated near the maximal period of normal degeneration, the arrest of degeneration is evident within a few hours after treatment. The effect is thus shown to be more than a secondary consequence of a general halt in development.