Muscle nociceptors more likely express ASIC3 than do skin nociceptors. A, Photomicrographs on the left and right are the same DRG section photographed for ASIC3 immunoreactivity (right) and fluorogold (left) that was retrogradely transported from injections into muscle (top) or skin (bottom). Arrows indicate cells that are 25 μm or smaller and contain both fluorogold and ASIC3 immunoreactivity. Scale bar, 40 μm. B, The percent of small (<25 μm) muscle or skin afferents that stain for ASIC3 (Immuno) or exhibit more than 0.3 nA of current evoked by a step to pH 6.8 from pH 7.4 (Ephys). 37 and 32 small neurons were recorded for skin and muscle, respectively. 117 and 113 small neurons were counted for skin and muscle immunocytochemistry.