Effect of Limb Ablation on Neurones in Xenopus Larvæ

Abstract

IN the spinal cord of larval Anura, the motor cells which innervate the muscles of the hind limbs form ventral horns distinct both in position and time of appearance from the series of primary motor cells whose axons run to the trunk muscles. In the tadpole of Xenopus laevis, there are about 4,000 ventral horn cells at the time of their differentiation from the mantle layer of the cord, a number which has fallen to 1,200 by metamorphosis some eight weeks later¹. ‘Histogenic cell degeneration’² accompanies the differentiation of these neurones, but on a scale much beyond that required merely to reduce their number to the adult-level. It seems that, for every ventral horn cell that persists, some eight or nine undergo cell death during development. Differentiation of the ventral horn is thus accompanied by a continuous turnover of the constituent neuroblasts.