A, DRN dopamine neurons were targeted by injecting cre-induced (“cre-ON”) vectors expressing ChR2-eYFP (n=10) or eYFP (n=14) into the DRN of THiCre mice. Inset shows eYFP (green) double-labeled with tyrosine hydroxylase (TH, red). B, Nose pokes in the first day of testing. C, Active nose pokes on three consecutive days of testing. D, Percent of time spent on laser side in real-time place preference task. E, DRN GABA neurons were targeted by injecting cre-ON ChR2-eYFP (n=8) or eYFP (n=4) into the DRN of VgatiCre mice. Inset shows eYFP (green) cell bodies in the lateral DRN, which do not co-label for serotonin (5-HT, red) or tyrosine hydroxylase (TH, blue). Laser stimulation did not reinforce nose poke self-stimulation (F,G) but did induce a real-time place preference (H), p<0.05. Scale bars = 200 μm.