ASIC3 is not expressed by muscle spindle afferents. A, Section of DRG labeled for ASIC3 (red) and for the calcium-binding protein parvalbumin (green), which labels muscle spindle afferents. Only 2 of 1400 parvalbumin-positive cells had detectable ASIC3 staining. B, Section of brainstem containing a string of sensory neurons in the mesencephalic nucleus of the 5th nerve (MesV) stained with either an antibody to a neurofilament protein (N52) to reveal all the sensory neurons (left, string of large cells arranged vertically; top punctuate labeling are MesV axons in cross section) or with the ASIC3 antibody (right). No MesV cells expressed ASIC3 (n = 3 rats). "IV" marks the fourth ventricle. Scale bars, 40 μm.