Primary afferent neurons containing calcitonin gene-related peptide but not substance P in forepaw skin, dorsal root ganglia, and spinal cord of mice

J Comp Neurol. 2015 Dec 1;523(17):2555-69. doi: 10.1002/cne.23804. Epub 2015 Jun 11.


In mice dorsal root ganglia (DRG), some neurons express calcitonin gene-related peptide (CGRP) without substance P (SP; CGRP(+) SP(-) ). The projections and functions of these neurons are unknown. Therefore, we combined in vitro axonal tracing with multiple-labeling immunohistochemistry to neurochemically define these neurons and characterize their peripheral and central projections. Cervical spinal cord, DRG, and forepaw skin were removed from C57Bl/6 mice and multiple-labeled for CGRP, SP, and either marker for the sensory neuron subpopulations transient receptor potential vanilloid type 1 (TRPV1), neurofilament 200 (NF200), or vesicular glutamate transporter 2 (VGluT1). To determine central projections of CGRP(+) SP(-) neurons, Neurobiotin (NB) was applied to the C7 ventral ramus and visualized in DRG and spinal cord sections colabeled for CGRP and SP. Half (50%) of the CGRP-immunoreactive DRG neurons lacked detectable SP and had a mean soma size of 473 ± 14 μm(2) (n = 5); 89% of the CGRP(+) SP(-) neurons expressed NF200 (n = 5), but only 32% expressed TRPV1 (n = 5). Cutaneous CGRP(+) SP(-) fibers were numerous within dermal papillae and around hair shafts (n = 4). CGRP(+) SP(-) boutons were prevalent in lateral lamina I and in lamina IV/V of the dorsal horn (n = 5). NB predominantly labeled fibers penetrating lamina IV/V, 6 ± 3% contained CGRP (n = 5), and 21 ± 2% contained VGluT1 (n = 3). CGRP(+) SP(-) afferent neurons are likely to be non-nociceptive. Their soma size, neurochemical profile, and peripheral and central targets suggest that CGRP(+) SP(-) neurons are polymodal mechanoceptors.

Keywords: AB_2313819; AB_2314983; AB_2315370; AB_2315546; AB_477257; CGRP; DRG; NF200; RRIDs: AB_572266; TRPV1; axonal tracing; nociception.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Afferent Pathways / physiology
  • Analysis of Variance
  • Animals
  • Biotin / analogs & derivatives
  • Biotin / metabolism
  • Calcitonin Gene-Related Peptide / metabolism*
  • Cell Count
  • Female
  • Ganglia, Spinal / cytology*
  • Mice
  • Mice, Inbred C57BL
  • Neurofilament Proteins / metabolism
  • Phosphopyruvate Hydratase / metabolism
  • Sensory Receptor Cells / metabolism*
  • Skin / cytology*
  • Skin / innervation
  • Spinal Cord / cytology*
  • Substance P / metabolism
  • TRPV Cation Channels / metabolism
  • Vesicular Glutamate Transport Protein 1 / metabolism


  • Neurofilament Proteins
  • TRPV Cation Channels
  • TRPV1 protein, mouse
  • Vesicular Glutamate Transport Protein 1
  • neurobiotin
  • neurofilament protein H
  • Substance P
  • Biotin
  • Phosphopyruvate Hydratase
  • Calcitonin Gene-Related Peptide