Mesoaccumbal glutamate neurons drive reward via glutamate release but aversion via dopamine co-release

Ventral tegmental area (VTA) projections to the nucleus accumbens (NAc) drive reward -related motivation. Although dopamine neurons are predominant, a substantial glutamatergic projection is also present, and a subset of these co -release both dopamine and glutamate. Optogenetic stimulation of VTA glutamate neurons not only supports self -stimulation but can also induce avoidance behavior, even in the same assay. Here, we parsed the selective contribution of glutamate or dopamine co -release from VTA glutamate neurons to reinforcement and avoidance. We expressed channelrhodopsin-2 (ChR2) in mouse VTA glutamate neurons in combination with CRISPR-Cas9 to disrupt either the gene encoding vesicular glutamate transporter 2 (VGLUT2) or tyrosine hydroxylase (Th). Selective disruption of VGLUT2 abolished optogenetic self -stimulation but left real-time place avoidance intact, whereas CRISPR-Cas9 deletion of Th preserved self -stimulation but abolished place avoidance. Our results demonstrate that glutamate release from VTA glutamate neurons is positively reinforcing but that dopamine release from VTA glutamate neurons can induce avoidance behavior.