An Experimental Study on the Relationships between Limb and Spinal Cord in the Embryo of Eleutherodactylus martinicensis

Open Access
Publisher Website
Google Scholar
Abstract
A technique for grafting limb-buds in Eleutherodactylus is outlined, and the early development of the limb-nerves and of the ventral horns of the cord is described. Limb ablation of 6-day embryos results in marked reduction after 24 hours of the number of cells in the related ventral horn. Axon severance by amputation after 8 days first leads to chromatolysis of ventral horn cells followed by a period of degeneration some 10 days after the operation. If another limb-bud is grafted in place of a forelimb and becomes in-nervated, the loss in number of neurones in the related ventral horn is checked, mainly through the differentiation of fresh cells. When grafted at 5 days, a transplanted limb can maintain the number of ventral horn cells at 80 per cent, of the normal level. This effect declines with increasing age of operation, especially with hind limbs transplanted in the place of forelimbs. The proportion of innervations in batches of embryos bearing grafted limbs decreases with advancing age of the embryo at the time of operation. The host neurones lose their ability to innervate fresh territory as their axons become capable of regeneration along a previous path. When a hind limb bud is grafted above an undisturbed forelimb, it may be innervated from collaterals of the brachial nerve, fibres of which have already made contact with the ipsilateral limb. With such transplants, the frequency of innervation for operations at six days is much higher for autografts than for homografts when the animals are kept at 30° C. At a lower temperature, both types of graft are innervated equally readily. At the higher temperature, some degree of hypertrophy of the sympathetic system of the host is occasionally seen with transplanted hind limbs, or with homografts of front limbs.