PROJECT SUMMARY While cocaine use disorder (CUD) is often studied in the context of dysregulated drug taking, less often studied is how chronic drug use alters the processing of non-drug stimuli within the brain. One prominent example is the fact that individuals suffering from CUD have deficits in responding to aversive stimuli. It is hypothesized that these deficits influence a range of behaviors and render these individuals insensitive to negative consequences associated with specific actions. Importantly, these deficits in stimulus processing are associated with worse treatment outcomes in individuals suffering from CUD. Thus, understanding how drug use alters the neural encoding of non-drug, aversive stimuli is critical to better treating individuals with CUD. At the center of drug-induced neural dysfunction is the mesolimbic dopamine system. Importantly, the ability of aversive stimuli to evoke dopamine release is the nucleus accumbens core (NAcc) is necessary for both conditioned and unconditioned aversive stimulus responses. Importantly, a hallmark of prolonged cocaine use in both human and animal models is deficits in both basal and aversive stimulus-evoked dopamine release. Thus, the goal of this proposal is to understand how dopamine release regulates the cellular responses of genetically-defined cell types in the NAc and define how this relationship is disrupted by cocaine use. The first aim seeks to define the temporal parameters under which dopamine release modulates the activity of D1 or D2-containing MSN populations in the NAc, at baseline and in response to an aversive stimulus. Dopamine is a modulatory neurotransmitter that does not induce action potential firing on its own, but rather acts to modulate the activity patterns of medium spiny neurons (MSNs) that are characterized by their expression of D1 and D2 type dopamine receptors. While nearly all of our understanding of this relationship has been defined in acute slice preparations, here we will employ single-cell calcium imaging with simultaneous optogenetic manipulation of dopamine terminals in behaving animals to establish the precise temporal conditions during which dopamine modulates MSN activity at baseline and in response to a range of aversive stimuli (aim 1). Next, I will establish how cocaine self-administration disrupts the capacity for dopamine to modulate MSN activity during aversive stimulus processing (aim 2). The present proposal will provide training in integrating traditional addiction models (self-administration) with cutting-edge microdendoscopic tools, which I intend to employ towards defining how drug-induced dysfunction in the brain gives rise to phenotypes associated with CUD.