title: Neurochemical Characterization of the TRPV1-Positive Nociceptive Primary Afferents Innervating Skeletal Muscles in the Rats.
abstract: OBJECTIVE
  Transient receptor potential vanilloid subfamily type 1 (TRPV1), a most specific marker of the nociceptive primary afferent, is expressed in peptidergic and non-pepetidergic primary afferents innervating skin and viscera. However, its expression in sensory fibers to skeletal muscle is not well known. In this study, we studied the neurochemical characteristics of TRPV1-positive primary afferents to skeletal muscles.
  
  
  METHODS
  Sprague-Dawley rats were injected with total 20 microl of 1% fast blue (FB) into the gastrocnemius and erector spinae muscle and animals were perfused 4 days after injection. FB-positive cells were traced in the L4-L5 (for gastrocnemius muscle) and L2-L4 (for erector spinae muscle) dorsal root ganglia. The neurochemical characteristics of the muscle afferents were studied with multiple immunofluorescence with TRPV1, calcitonin gene-related peptide (CGRP) and P2X(3). To identify spinal neurons responding to noxious stimulus to the skeletal muscle, 10% acetic acids were injected into the gastrocnemius and erector spinae muscles and expression of phospho extracellular signal-regulated kinase (pERK) in spinal cords were identified with immunohistochemical method.
  
  
  RESULTS
  TRPV1 was expressed in about 49% of muscle afferents traced from gastrocnemius and 40% of erector spinae. Sixty-five to 60% of TRPV1-positive muscles afferents also expressed CGRP. In contrast, expression of P2X(3) immnoreaction in TRPV1-positive muscle afferents were about 20%. TRPV1-positive primary afferents were contacted with spinal neurons expressing pERK after injection of acetic acid into the muscles.
  
  
  CONCLUSIONS
  It is consequently suggested that nociception from skeletal muscles are mediated by TRPV1-positive primary afferents and majority of them are also peptidergic.
authors.affiliation: Department of Neurosurgery , Seoul Medical Center, Seoul, Korea.
authors.forename: Dong Su
authors.initials: DS
authors.lastname: Shin
authors.forename: Eun Hyun
authors.initials: EH
authors.lastname: Kim
authors.forename: Kwan Young
authors.initials: KY
authors.lastname: Song
authors.forename: Hyun Jong
authors.initials: HJ
authors.lastname: Hong
authors.forename: Min Ho
authors.initials: MH
authors.lastname: Kong
authors.forename: Se Jin
authors.initials: SJ
authors.lastname: Hwang