Recent optogenetic studies demonstrated that phasic dopamine release in the nucleus accumbens may play a causal role in multiple aspects of natural and drug reward-related behaviors. The role of tonic dopamine release in reward consummatory behavior remains unclear. The current study used a combinatorial viral-mediated gene delivery approach to express ChR2 on mesolimbic dopamine neurons in rats. We used optical activation of this dopamine circuit to mimic tonic dopamine release in the nucleus accumbens and to explore the causal relationship between this form of dopamine signaling within the ventral tegmental area (VTA)-nucleus accumbens projection and consumption of a natural reward. Using a two bottle choice paradigm (sucrose vs. water), the experiments revealed that tonic optogenetic stimulation of mesolimbic dopamine transmission significantly decreased reward consummatory behaviors. Specifically, there was a significant decrease in the number of bouts, licks and amount of sucrose obtained during the drin