Extended Data Fig. 2: Specificity of ChR2-tdTomato expression in the OT neurons of OT::Cre;Ai27(LSL-ChR2-tdTomato) mice.

a, The selective expression in OT neurons of the blue light gated cation channel ChR2 fused to the fluorescent protein tdTomato is induced by crossing OT::Cre mice with Ai27(LSL-ChR2-tdTomato) mice (n = 1 mouse). White arrows in insets indicate neurons counted as OT⁺ and ChR2-tdTomato⁺. A magenta arrow indicates a neuron counted as OT⁻ and ChR2-tdTomato⁺, therefore representing one of the rare neurons counted as non-specific expression (3% of OT⁻ ChR2⁺ neurons, Fig. 1c). This very low non-specific expression is likely overestimated by our count, because of the limited sensitivity of OT immunohistochemical labeling leading to an underestimation of the number of OT neurons⁷⁵, and because we counted neurons showing faint OT labeling as OT⁻ neurons (such as the one indicated by the magenta arrow). Scale bar, 200 µm. b, Littermates that did not express the Cre recombinase (Cre⁻), but were genotyped positive for the LSL-ChR2-tdTomato transgene, obtained from crossings between OT::Cre mice with Ai27(LSL-ChR2-tdTomato) mice, were used as control mice. No ChR2-tdTomato expression was found in these mice (n = 1 mouse). Scale bar, 200 µm.