Primary afferent neurons containing calcitonin gene‐related peptide but not substance P in forepaw skin, dorsal root ganglia, and spinal cord of mice. Issue 17 (11th June 2015)

• Record Type: Journal Article
• Authors: Kestell, Garreth R.; Anderson, Rebecca L.; Clarke, Jennifer N.; Haberberger, Rainer V.; Gibbins, Ian L.
• Is Part Of: Journal of comparative neurology. Volume 523:Issue 17(2015:Nov. 01)
• Page Start: 2555
• Page End: 2569
• Publication Date: 2015-06-11
• Subjects: Comparative neurobiology -- Periodicals; Neurology -- Periodicals; 616
• DOI: 10.1002/cne.23804
• Languages: English
• ISSNs: 0021-9967

Abstract

<abstract abstract-type="main"> <title>ABSTRACT</title> <p>In mice dorsal root ganglia (DRG), some neurons express calcitonin gene–related peptide (CGRP) without substance P (SP; CGRP<sup>+</sup>SP<sup>‐</sup>). 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<sup>+</sup>SP<sup>‐</sup> 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<sup>2</sup> (<italic>n</italic> = 5); 89% of the CGRP<sup>+</sup>SP<sup>‐</sup> neurons expressed NF200 (<italic>n</italic> = 5), but only 32% expressed TRPV1 (<italic>n</italic> = 5). Cutaneous CGRP<sup>+</sup>SP<sup>‐</sup> fibers were numerous within dermal papillae and around hair shafts (<italic>n</italic> = 4). CGRP<sup>+</sup>SP<sup>‐</sup> boutons were prevalent in lateral lamina I and in lamina IV/V of the dorsal horn (<italic>n</italic> = 5). NB predominantly labeled fibers penetrating lamina IV/V, 6 ± 3% contained CGRP (<italic>n</italic> = 5), and 21 ± 2% contained VGluT1 (<italic>n</italic> = 3). CGRP<sup>+</sup>SP<sup>‐</sup> afferent neurons are likely to be non‐nociceptive. Their soma size, neurochemical profile, and peripheral and central targets suggest that CGRP<sup>+</sup>SP<sup>‐</sup> neurons are polymodal mechanoceptors. J. Comp. Neurol. 523:2555–2569, 2015. © 2015 Wiley Periodicals, Inc.</p> </abstract>