Figure 7: Disproportionate glabrous skin representation in the brainstem is maintained in mice that do not sense gentle touch.

A. (left) MEA recordings from L4 DRGs in wild-type mice expressing ReaChR in all sensory neurons. (center) Representative units responded to optical stimulation of the skin with short-latency spikes. (right) Mechanical stimulation with stroke, indentation, air puff to the thigh, glabrous skin pull, and strong pinch to the hindpaw. Stroke and indentation were delivered at multiple points on the paw and thigh, and the maximal responses are displayed and quantified.

B. MEA recordings from L4 DRG in Piezo2 conditional knockout animals that express ReaChR in all sensory neurons (Cdx2-Cre; Piezo2^flox/flox; Avil^FlpO; R26^FsF-ReaChR). Optical stimulation of the skin produces short-latency spikes (center), as seen in control mice (A), while responses to innocuous mechanical stimuli are largely absent (right). Responses to strong pinch to the hindpaw were preserved.

C. The number of DRG units responsive to mechanical and optical stimulation in wildtype and conditional Piezo2 knockout mice (n=6 wt, n=5/7 Piezo2 cKO with mechanical/optical stimulation). Equivalent numbers of Piezo2 cKO and wildtype mouse DRG respond to noxious pinch and optical stimulation, but responses to one or more innocuous mechanical stimuli are reduced in the Piezo2 ckO mutant (one-way ANOVA p < .005, p = 0.33, p=0.46, p < .005, respectively, Mann-Whitney U test).

D. Optical stimulation of the receptive fields of neurons innervating glabrous or hairy skin evoked equivalent numbers of spikes in Piezo2 cKO DRG neurons (p=0.49, Mann-Whitney U test).

E. (left) Optogenetic receptive fields were computed for neurons in the GN of Piezo2 cKO mice. (right) Representative receptive field spots of GN neurons computed after hairy skin stimulation (top) or glabrous skin stimulation (bottom).

F. The number spikes evoked in units recorded from the GN following optical stimulation of receptive field spots in hindpaw glabrous skin, hindpaw hairy skin, and thigh skin (after hair removal). Glabrous skin optical stimulation evoked more spikes in GN units than hairy skin stimulation (p < .001, Mann-Whitney U-test).

G. Disproportionate expansion of glabrous skin representation in the brain reflects the skin region innervated by sensory neurons independent of touch-evoked activity.