Chick wing innervation. III. Formation of axon collaterals in developing peripheral nerves

Michael J Ferns, M. Hollyday

Research output: Contribution to journalArticle

7 Scopus citations

Abstract

Axon navigation during vertebrate limb innervation has been shown to be associated with position-dependent changes in size and complexity of the axon growth cones, and sometimes with bifurcation of terminal growth cones and axon branching (Hollyday and Morgan-Carr, companion paper). We have further examined axon branching and asked whether it extends to the projection of collaterals to different nerves. Injections of horseradish peroxidase or Dil were made into individual peripheral nerves in the wings of chick embryos at stages 28-35, and the trajectories of solidly labeled axons were traced proximally from the injection site in tissue sections. During stages when the peripheral nerves were first forming in the shoulder region, collaterals of retrogradely labeled axons were frequently observed to project into uninjected nerves proximal to the injection site. These two-nerve collaterals were formed by a small percentage of axons in a high percentage of the embryos studied and could occur in both motor and sensory axons. Two-nerve collateral projections were observed between nerves separated along both the proximodistal and anteroposterior axes of the limb, but they were limited in spatial extent to nerves supplying adjacent limb regions and were never seen between nerves projecting to widely disparate regions of the limb. Collaterals were not seen at the plexus projecting to both dorsal and ventral pathways. The apparent frequency of two-nerve collaterals was found to decline progressively from stage 28-29 to stage 32; no two-nerve collaterals were seen in the proximal wing at stage 33 and older. The mechanism of their elimination is presently unknown. These observations suggest that some axon branching seen during outgrowth is sufficiently divergent to result in axon collaterals which project to two different peripheral nerves. Presumably, two-nerve collaterals reflect both the neuron's ability to branch and some imprecision in the axonal guidance mechanisms. Together these give rise to minor errors in projection which are subsequently removed.

Original languageEnglish (US)
Pages (from-to)272-280
Number of pages9
JournalJournal of Comparative Neurology
Volume357
Issue number2
DOIs
StatePublished - 1995

Keywords

  • axonal guidance
  • motoneurons
  • sensory neurons

ASJC Scopus subject areas

  • Neuroscience(all)

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