Figure 1.

TrkC expression in peripheral ganglia

(A–F) Immunofluorescent staining of DRG sections from TrkC^CreERT2::Rosa26^ChR2-YFP (yellow) showed that 9.6% of DRG neurons co-express markers of proprioceptors (Pvalb, red; NF200, magenta) (A and F) and 11.6% of slowly adapting (SA) field mechanoreceptors (Ret, green; NF200, red) (B and F). Very few TrkC⁺ neurons overlap with markers of non-peptidergic nociceptors (IB4, red) (C and F) or peptidergic nociceptors (CGRP, blue) (D and F); 7% of all DRG neurons are also positive for Th (red), a marker of C-fiber low-threshold mechanoreceptors (C-LTMRs) (E and F). (F) Quantification of TrkC co-expression with the other markers in DRGs showing the percentage of total neurons.

(G) TrkC⁺/Th⁺ DRG neurons are significantly larger than TrkC⁻/Th⁺ neurons and smaller than TrkC⁺/Th⁻ neurons (298 neurons from three mice). ^∗p < 0.001.

(H) Quantification of the number of DRG neurons co-expressing TrkC and Th at different spinal segmental levels, expressed as the percentage of the total number of DRG neurons (n = 3).

(I and J) TrkC is not expressed in the nodose-petrosal-jugular ganglion complex (I) and is not expressed in the superior cervical ganglion (J).

(K) Left, sketch depicting the mechanical-stimulation protocol and an example trace of a mechanically activated current (MA current) in a small TrkC⁺ neuron. Right, distribution of the different types of MA currents in the small TrkC⁺ neurons (24 neurons from three mice): rapidly adapting (RA), intermediate adapting (IA), and non-responding (NR).

(L) Left, example responses to capsaicin and pH 5.4 in a small TrkC⁺ neuron. Right, number of neurons responding (R) and non-responding (NR) to capsaicin or pH in small TrkC⁺ neurons. Arrows indicate co-expression of TrkC⁺ neurons with the other markers. Scale bars, 50 μm.