Fig. 1: Phasic excitation of SuM GLU neurons is reinforcing.

a Schematic of hSyn-ChR2 viral injection targeting SuM neuron cell bodies and optic fiber implantation targeting the SuM, MB, or VTA placements. The group nomenclature box describes how injection site and stimulation site are abbreviated (e.g., SuM:SuM). b Examples of histology showing ChR2-eYFP expression in SuM and surrounding tissues with optic fiber placements (yellow dotted) in SuM (top), MB (middle), and VTA (bottom). Scale bar = 200 µm. See Supplementary Fig. 1 for histological results of all mice (n = 22). c Schematic of mouse operant-conditioning chamber equipped with two levers. d Active (closed circles) and inactive (open circles) lever presses per session (mean − SEM). SuM-stimulation group has significantly higher ICSS rates than the other two groups during acquisition sessions 3–7 and reacquisition sessions 11–12. ^***p < 0.001 and ^**p < 0.01, with Tukey post hoc HSD test, SuM:SuM^WT (n = 10), SuM:MB^WT (n = 6), and SuM:VTA^WT (n = 6). All animals pressed very little on inactive lever, so their data are shown but not further analyzed. e Lever reversal experiment. The data are mean lever presses − SEMs. SuM-stimulation group responded on lever 1 significantly more than on lever 2 when lever 1 was active, ^#p < 0.012; and they reversed responding and responded on lever 2 significantly more than on lever 1 when lever 2 became active, ^*p < 0.001 (Tukey HSD post hoc test). See (d) for the n of each group. f Schematic showing Cre-specific ChR2 viral injection targeting SuM neurons and optic fiber implantation targeting SuM performed in vGlut2-Cre, TH-Cre, and vGat-Cre mice. g Examples of histology showing ChR2-eYFP expression in SuM in vGlut2-Cre (top), TH-Cre (middle), and vGat-Cre mice with optic fiber tracts (yellow) in SuM. Scale bar = 200 µm. See Supplementary Fig. 2 for histological results of all mice (n = 46). h Active lever-presses per session (mean − SEM). vGlut2-Cre group (n = 18) responded greater than TH- or vGat-Cre group (n = 7 and 11, respectively), p_{vGlut2 vs TH} = 0.037, p_{vGlut2 vs vGat} = 0.016, p_{vGat vs TH} = 0.99 (Tukey HSD post hoc test). vGlut2-Cre groups consisted of the mice (n = 6) that received a 50 nL volume of the AAV to minimize the diffusion of the vector and the mice (n = 12) that received 200 nL. Source data are provided as a Source Data file.