title: CGRP peptide and regenerating sensory axons.
abstract: CGRP peptide, a widely expressed constituent of sensory neurons, plays important roles in nerve function and repair when axons are severed. CGRP synthesis declines, yet peptide nonetheless accumulates in severed axon endbulbs. In this work we explore an apparent selective and ongoing expression of CGRP peptide in regenerative sensory axon sprouts. Following sural nerve crush in rats out to 14 days, regenerating and branching sensory axons had intense and selective expression of CGRP, not associated with endbulbs. Parent L4 and L5 perikarya and axons in the sural nerve proximal to crush, however, did not exhibit such heightened CGRP presence. Instead, back labeling of regenerating axons with fluorogold or diamidino yellow labeled perikarya with reduced CGRP expression. Similarly, ATF-3, a robust marker of axotomized neurons, was associated with reduced, rather than elevated expression of alphaCGRP mRNA. Unexpectedly, however, we identified an enlarged secondary population of intact uninjured neurons, frequently smaller and projecting to the dorsal horn with new and heightened intense CGRP expression but not ATF-3- or tracer-labeled. Distal regenerating sensory axons selectively express CGRP peptide despite reduced perikaryal content, a phenomenon not explained by simple accumulation. Having an injured neighbor neuron, however, may also paradoxically alter how CGRP is expressed in intact neurons.
authors.affiliation: Department of Clinical Neurosciences, Neuroscience Research Group, University of Calgary, Alberta, Canada.
authors.forename: Xia-Qing
authors.initials: XQ
authors.lastname: Li
authors.forename: Valerie M K
authors.initials: VM
authors.lastname: Verge
authors.forename: Jayne M
authors.initials: JM
authors.lastname: Johnston
authors.forename: Douglas W
authors.initials: DW
authors.lastname: Zochodne
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology; D015740:Calcitonin Gene-Related Peptide / Q000235:genetics / Q000378:metabolism*; D017950:Ganglia, Sensory / Q000378:metabolism; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008297:Male; D008856:Microscopy, Fluorescence; D009416:Nerve Regeneration / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology*; D020671:Posterior Horn Cells / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000378:metabolism; D013497:Sural Nerve / Q000378:metabolism / Q000502:physiology
chemical_list: D020033:Protein Isoforms; D012333:RNA, Messenger; D015740:Calcitonin Gene-Related Peptide