FM 1-43FX

C57BL/6J, HoxB8^Cre+;Piezo2^f/f, Phox2b^Cre+;Piezo2^f/f (mixed sexes; 10-24 weeks)^[3]

1.12 mg/kg

i.p.; single injection

At 24 h after i.p. administration, bright cell-body labeling was seen in DRGs; widespread DRG labeling was nearly absent from caudal DRGs in HoxB8^Cre+;Piezo2^f/f mice.
Quantification revealed a gradient of decreasing fluorescence in HoxB8^Cre+;Piezo2^f/f KO ganglia corresponding to the rostral-to-caudal gradient of HoxB8^Cre expression.
In Phox2b^Cre+;Piezo2^f/f mice, nodose neuronal cell-body labeling was virtually absent, whereas labeling in the adjacent jugular ganglion remained.
Aortic arch baroreceptor endings showed a subset of labeled neurons in WT mice; these endings were not labeled in Phox2b^Cre+;Piezo2^f/f animals.
Cutaneous end-organ structures, including lanceolate, circumferential, and Merkel-cell neurite complexes, frequently labeled 24 h post i.p. injection in WT mice; labeling of terminal endings on hind-leg skin was absent in HoxB8^Cre+;Piezo2^f/f mice, though NFH-immunostained innervation remained.
At 48 h post-injection, 50.6% of NFH-positive DRGs showed uptake, 68.3% of calbindin-expressing neurons accumulated label, and 95% of TH-positive neurons were co-labeled; among labeled neurons, overlap was low with TRKA (0.6%), CGRP (3.3%), and IB4 (2.2%).
In hairy skin, 45% of signal overlapped with NFH, 51% of total NFH signal overlapped, 25% of total calbindin signal overlapped, and about 2.5% of labeling colocalized with CGRP; less than 1% of CGRP signal was positive for myelin-like labeling of Merkel-cell neurite afferents.
Terminal Schwann cell marker S100b showed minimal overlap, and no clearly labeled Schwann cell bodies were detected.
Time-course analysis showed baroreceptor ending labeling at the periphery before nodose cell bodies (1.5 vs 6 h), robust DRG cell-body labeling at 12 h, and bright labeling after 7 weeks.
Mice housed with touch stimuli accumulated more labeling in back and caudal regions than mice housed with no touch stimuli.
In the male pelvic urethra, WT mice showed 24 h neuronal labeling, while HoxB8^Cre+;Piezo2^f/f KO mice showed no neuronal labeling; urethral mean pixel intensity was lower in KO animals.
Tree-like urethral neurons were nearly all NFH positive, were not CGRP positive, and were still present in HoxB8^Cre+;Piezo2^f/f KO animals by immunostaining.

C57BL/6J (adult animals)^[3]

10 µL/g at 200 µM

i.p.; single injection

Labeling of lanceolate endings was reduced in shaved and depilated hind-leg skin, whereas the hairy regions in the contralateral control leg displayed bright labeling.
At the border between hairy and depilated skin, lanceolate labeling was present in hairy skin immediately adjacent to unlabeled depilated skin.