Optogenetic activation of dopamine neurons in the ventral tegmental area induces reanimation from general anesthesia

Significance Although dopamine is known to promote wakefulness, the specific dopamine circuits in the brain that regulate arousal are not clear. Here we report that selective optogenetic stimulation of ventral tegmental area (VTA) dopamine neurons in mice produces a powerful arousal response sufficient to restore conscious behaviors, including the righting reflex, during continuous, steady-state general anesthesia. Although previous studies found that VTA dopamine neurons do not appear to play a central role in regulating sleep–wake transitions, our findings demonstrate that selective stimulation of these neurons is sufficient to induce the transition from an unconscious, anesthetized state to an awake state. These results suggest that VTA DA neurons play a critical role in promoting wakefulness. Dopamine (DA) promotes wakefulness, and DA transporter inhibitors such as dextroamphetamine and methylphenidate are effective for increasing arousal and inducing reanimation, or active emergence from general anesthesia. DA neurons in the ventral tegmental area (VTA) are involved in reward processing, motivation, emotion, reinforcement, and cognition, but their role in regulating wakefulness is less clear. The current study was performed to test the hypothesis that selective optogenetic activation of VTA DA neurons is sufficient to induce arousal from an unconscious, anesthetized state. Floxed-inverse (FLEX)-Channelrhodopsin2 (ChR2) expression was targeted to VTA DA neurons in DA transporter (DAT)-cre mice (ChR2+ group; n = 6). Optical VTA stimulation in ChR2+ mice during continuous, steady-state general anesthesia (CSSGA) with isoflurane produced behavioral and EEG evidence of arousal and restored the righting reflex in 6/6 mice. Pretreatment with the D1 receptor antagonist SCH-23390 before optical VTA stimulation inhibited the arousal responses and restoration of righting in 6/6 ChR2+ mice. In control DAT-cre mice, the VTA was targeted with a viral vector lacking the ChR2 gene (ChR2− group; n = 5). VTA optical stimulation in ChR2− mice did not restore righting or produce EEG changes during isoflurane CSSGA in 5/5 mice. These results provide compelling evidence that selective stimulation of VTA DA neurons is sufficient to induce the transition from an anesthetized, unconscious state to an awake state, suggesting critical involvement in behavioral arousal.