Recruitment and disruption of value encoding during alcohol seeking

A critical area of inquiry in the neurobiology of alcohol abuse is the neural mechanisms by which cues gain the ability to elicit alcohol use. We previously showed that cue-evoked activity in rat ventral pallidum (VP) robustly encodes the value of cues trained under both Pavlovian and instrumental contingencies, despite a stronger relationship between cue-evoked responses and behavioral latency after instrumental training. Here, we assessed VP neural representations of cue value in rats trained with a Pavlovian conditioned stimulus (CS+) that predicted alcohol delivery, and in rats trained with an instrumental discriminative stimulus (DS) that predicted alcohol availability if the rat entered the reward port during the cue. We also examined the impact of alcohol exposure itself on the integrity of this type of signaling in rats trained with sucrose. Decoding of cue value based on VP firing was blunted for an alcohol CS+ versus an alcohol DS, as well as in comparison to a sucrose DS or CS+. Further, homecage alcohol exposure had opposing effects on VP encoding of cue value for a sucrose DS versus a sucrose CS+, enhancing decoding accuracy for the DS and reducing decoding accuracy for the CS+. These findings suggest that problem alcohol seeking may result from biased engagement of specific reward-related processes via changes in VP signaling.