by a population of small-diameter, putative cold-sensitive
neurons ( Fig. 4B), accounting for 8.3 6 0.27% of FB-labelled
neurons in contralateral DRG. This decreased to 4.2 6 0.96%
ipsilateral to SNI trans injury ( Fig. 4E), indicating a partial loss of
Trpm81 afferents. When examining peptidergic afferents, we
found that 48.1 6 2.42% of FB-labelled neurons in contralateral
DRG were Calca-YFP 1,c o m p a r e dw i t h3 4 . 36 2.54% 4 weeks
after SNItrans injury (Figs. 4C and F), consistent with a partial loss
of CGRP 1 afferents. We used a Thy1-CFP line that demon-
strates consistent expression postinjury 61 and labels a sample of
medium/large diameter myelinated afferents. CFP was largely
restricted to NF200 1 neurons, labelling 56% of this population.
Expression was present in a heterogenous population of
nociceptive (TrkA 1) and nonnociceptive (TrkA-) myelinated
neurons (Fig. S5, http://links.lww.com/PAIN/C84). Contralateral
to injury, 15.66 1.8% of FB-labelled neurons expressed Thy1-
CFP ( Figs. 4D and G). In contrast to unmyelinated subpopula-
tions, this proportion was higher in ipsilateral DRG following
SNItrans (23.3 6 3.2%), consistent with no (or minimal) loss of
Thy1-CFP-expressing afferents, accompanied by a loss of Thy1-
CFP-negative neurons. We did not observe significant alter-
ations in the population distributions of the cross-sectional area
of surviving, damaged Trpm8-tdTom1,C a l c a - Y F P1,o rT h y 1 -
CFP1 DRG neurons when compared with DRG contralateral to
Figure 4.Spared nerve injury induces a loss of Trpm8 1 and CGRP1 but not myelinated DRG neurons. (A) Schematic of experimental approach. (B–D) FastBlue
labelling and Trpm8-tdTom (B), Calca-YFP (C), or Thy1-CFP expression (D) 28 days after SNI trans in the L4 DRG, contralateral (top) or ipsilateral (bottom) to injury.
Images are projections of optical sections at 3- mm intervals through the entirety of 30- mm-thick tissue sections. Scale bars 5 100 mm. (E–G) Quantification of the
proportion of FB-labelled neurons also expressing Trpm8-tdTom (E), Calca-YFP (F), or Thy1-CFP (G) in L4 DRG contralateral or ipsilateral to SNI trans. Paired t tests;
Trpm8-tdTom: t2 55.31, P 50.034, n 53 mice; Calca-YFP: t 3 54.12, P 50.026, n 54 mice; Thy1-CFP: t 3 54.42, P 50.022, n 54 mice. *P ,0.05. CFP, cyan
fluorescent protein; CGRP, calcitonin gene-related peptide; DRG, dorsal root ganglion; FB, FastBlue.
December 2024 ·Volume 165 ·Number 12 www.painjournalonline.com 2871