Dorsal root ganglia development in chicks following partial ablation of the neural crest

To assess the effects of reduced competition for peripheral targets on developing brachial dorsal root ganglia (DRG), chick embryos were subjected to partial ablations of the brachial neural crest at stages 13 or 14 (Hamburger, V., and H.L. Hamilton (1951) J. Morphol. 88: 49-92), using an ophthalmological cauterization unit. In the initial studies reported here, ganglia developing from the remaining crest material were examined for ganglionic volume and neuronal size, neuronal number, and degenerative activity at stage 35. Results showed that the lesion procedure resulted in the reduction or absence of one or two ganglia on each side at the level of DRG 15 to DRG 17. Hypertrophies occurred in other ganglia remaining at these and at more rostral levels and ranged up to 220%. These hypertrophies were most pronounced, however, not in the ganglia adjacent to those lesioned but rather in more remote ganglia, including those at cervical levels. Accompanying these ganglionic changes were significant alterations in all three neuronal parameters examined. The findings clearly demonstrate a responsiveness of chick brachial DRG to reduced competition resulting from neural crest ablations and that such responsiveness occurs along several axial segments.