Harsum, Steven; (1999) Cutaneous innervation and wound healing studies in the developing chick wing. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Using a chick embryo model I have investigated three related problems in patterning of cutaneous nerves in the developing wing. First, I have investigated the influence of diffusible cues in guiding cutaneous axons towards dorsal wing skin using an in vitro three dimensional collagen gel system. At embryonic day (E) 4 and E5, the stages that guidance decisions are made in vivo, dorsal root ganglia (DRG) outgrowth is biased towards ectoderm, but not mesenchyme. Further, when DRGs are cultured equidistant between ectoderm and mesenchyme, such that they are presented with a choice, outgrowth is almost exclusively ectoderm directed. In contrast, motor axon outgrowth is inhibited by ectoderm and encouraged by mesenchyme. These data suggest that diffusible signals emanating from wing tissues might selectively guide cutaneous axons away from the main mixed nerve trunk towards the ectoderm in vivo. Second, I have investigated the influences of excisional cutaneous wounds, made to the dorsum of the chick wing, on the developing pattern of innervation. Wounds made at a stage prior to nerves invading the limb, at E4, occasionally result in the absence of whole nerve trunks, but do not otherwise affect the subsequent pattern of branching, or the eventual density of innervation, as assessed at E10. In contrast, wounds made soon after cutaneous innervation, at E7, disrupt the pattern of branching, but not the number of nerve trunks or the density of innervation. These results indicate that the adult and neonatal phenomenon of hyperinnervation, activated by the healing process, does not occur in the embryo. Third, I have tested the role of nerves in embryonic wound healing, since nerves have long been known to have trophic effects on their target in adults. These studies reveal that at E7, chick wings deprived of innervation by UV ablation of neural progenitors, heal excisional cutaneous wounds significantly slower than normally innervated controls.

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