"a , Experimental setup for perinatal mechanoreceptor optical activation assay. P0 or E18.5 mice are placed on a clear acrylic stage, and LED illumination is directed to the paw or back hairy skin. Parts created with BioRender.com . b , Average displacement responses to 5 optical stimuli (20-30 second ISIs) delivered to mechanoreceptor subtypes in forepaw, back hairy skin, and hindpaw compared to control littermates that lack opsin expression (controls include opsin-positive, Cre-negative and opsin-negative, Cre-positive animals). c , Average displacement responses to 5 optical stimuli activating Ret + Aβ LTMRs to the forepaws of P0 Ret CreER ; Advillin FlpO ; <t>Rosa26</t> LSL-FSF-ReaChR-mCitrine ; Gabrb3 +/+ and Gabrb3 +/- animals. P =0.0169, unpaired one-tailed Welch’s t test. d , Example displacement traces from a E18.5 Gabrb3 +/+ mouse and Gabrb3 +/- mouse to optical activation of Ret + Aβ LTMRs in the forepaw. e , Average displacement responses to 5 optical stimuli activating Ret + Aβ LTMRs in the forepaws of E18.5 control and mutant animals. P =0.0029, unpaired one-tailed Welch’s t test. For b , c and e , data represent means±s.e.m. "