Project Summary / Abstract Ventral tegmental area (VTA) dopamine neurons are essential for associative learning of reward and aversion- related cues, updating learned associations by prediction errors, as well as supporting a value of rewarding and aversive outcomes. While it is well established that VTA dopamine neurons show heterogenous signaling patterns related to these motivationally-relevant events, as well as express diverse molecular characteristics, our understanding of how dopaminergic molecular heterogeneity contributes to VTA dopamine neuron functions are unclear. A primary distinction between subtypes of VTA dopamine neurons is whether they release dopamine alone or co-release dopamine with glutamate. We propose to test the hypothesis that VTA dopamine neuron signaling patterns and roles in motivated behavior are genetically-determined by whether they co-release dopamine with glutamate or they release dopamine without glutamate. In AIM 1, we will determine the neuronal activity signaling patterns of VTA glutamate-dopamine co-releasing neurons, nonglutamate-dopamine neurons, or glutamate-only neurons that do not co-release GABA or dopamine, in a variety of reward and aversion-based motivated behavior tasks involving associative learning, outcome prediction and errors, and outcome values. In AIM 2, we will causally determine the roles of these same neurons in reward and aversion-based motivated behavior tasks involving associative learning, outcome prediction, reward, and aversion. Finally in AIM 3, we will causally determine the roles of dopamine and/or glutamate release from these distinct VTA neuronal phenotypes in reward and aversion-based tasks involving associative and nonassociative learning as well as other motivationally-relevant behaviors. Together these studies will comprehensively identify how the molecular heterogeneity of the midbrain dopamine system contributes to associative learning and motivated behaviors.