Ventral Tegmental Area Dopamine Neurons Flexibly Code Taste Valence in Conditioned Taste Aversion

Our behaviors are constantly shaped by both internal and external environments to optimize favorable outcomes and protect ourselves from potential harm. Our experiences heavily influence these adaptations, which serve as driving forces, allowing us to integrate information and form associations between stimuli and their consequences. Associative learning, therefore, plays a crucial role in driving goal-directed behavior. The mesolimbic-dopamine pathway is well-established as critical in motivating behaviors, such as approach and avoidance. Rewards and their predictors have been shown to reliably evoke increases in dopamine signaling. However, the extent to which mesolimbic dopamine codes a stimulus's valence or salience to further promote goal-directed behaviors remains a subject of debate. To address this debate, I examined whether ventral tegmental area (VTA) dopamine neurons code the change in the valence of the same taste before and after a conditioned taste aversion (CTA) paradigm. Here, in all experiments, naïve rats received brief intra-oral infusions of sucrose and, immediately after, were randomly assigned to injection conditions: 20ml/kg 0.15M NaCl (Unpaired) or equal volume 0.15M LiCl (Paired) to induce malaise and form a CTA. CTA expression was measured in later sessions of brief intra-oral infusions of sucrose, where VTA dopamine responses were measured using in vivo fiber photometry. Concurrently, the rats' behavioral reactions during intra-oral infusions and avoidance of the conditioned taste were measured in separate experiments. I found dopamine initially responds with increases to sucrose but is suppressed after a single sucrose-LiCl pairing. Behavioral reactivity data supported more movement in response to sucrose after CTA – suggesting that a decrease in dopamine to sucrose in Paired rats was not due to a loss of stimulus salience. My overall findings support 1) that VTA dopamine neurons code changes in taste valence, as opposed to salience, based on post-ingestion experiences, 2) that VTA dopamine neurons track changes in taste valence in CTA extinction, 3) that changes in VTA dopamine responses are experience-dependents and correlate with avoidance behavior, 4) that changes in VTA dopamine responses are unaffected by a minimal dose of LiCl, and 5) that VTA dopamine responses scale with multiple conditioning and extinction trials.