FIGURE 2. In vivo stimulation of RMTg_GABA→VTA synapses is aversive.

A. Real-time place preference (RTPP) experimental timeline. Days 1 and 3 have no light stimulation on either chamber side. On Day 2, entry into the light-paired side triggers 60 Hz blue light stimulation (light test). On day 3, mice are returned to the testing chamber without any light delivery (posttest). B. Left, Diagram: LED stimulation of RMTg terminals in the VTA. Right, ChR2 mice spend less time in the light-paired chamber vs. pre-test values compared to mice expressing the reporter only (light; n = 6 mice per group). 24 hours later, without any optical stimulation, mice still avoid the previously light-paired chamber (posttest). C. Velocity (compared to pre-test values) in the light-paired chamber, and D. total distance traveled in the apparatus (compared to pre-test values) are not different between experimental and reporter-only groups (2-way ANOVAs). E. Representative location plot of a control mCherry- expressing mouse (left) and ChR2-expressing mouse (right) during a 10 minute RTPP test session.<p/>LED light was delivered whenever the mouse entered the light-paired chamber. Data are represented as mean ± SEM. See related Supplemental Figure 2. *p < .05, 2-way ANOVA, post hoc Sidak’s multiple comparisons of reporter-only vs. ChR2 mice.