(a) Overview showing viral injection of CAV2-Cre into the VTA or SNR and ChR2 (green) into the dorsal horn (lower image) of the spinal cord (L4-L5) of Ai14 mice (DAPI: blue; scale bar 100 μm). (b) ChR2-expressing terminals from the dorsal horn (green) are more frequently detected in the LPBd adjacent to retrogradely labeled (tdTomato-positive, red) cells projecting to SNR (right image) than in the LPBc, which contains mainly retrogradely labeled (tdTomato-positive, red) cells projecting to VTA (left image; DAPI: blue; scp: superior cerebellar peduncle; scale bar 50 μm). Insets show higher magnification images of LPB→VTA and LPB→SNR neurons in the LPBc and LPBd, respectively. (c) Schematic showing dorsal horn spinal cord projections to different LPB subregions, which are highlighted in different colors to demonstrate the locations of LPB subpopulations projecting to SNR (violet) or VTA (magenta). Note that CeA-projecting LPB neurons are predominantly located in the lateral parabrachial nucleus - external part (LPBe) (MPB: medial parabrachial nucleus). (d) EPSC generated at −70 mV by light stimulation of dorsal horn inputs to a retrogradely-labeled LPB neuron projecting to SNR (red trace: sample response after bath application of 20 μM CNQX; n = 10 cells; left) and mean EPSC amplitudes generated by light stimulation of dorsal horn inputs to LPB→SNR (n = 33 cells) and LPB→VTA neurons (n = 32 cells; right). Significance was calculated by means of unpaired t-test (q). Comparisons with no asterisk had p > 0.05 and were not considered significant. Data represent mean ± SEM.