Chronic ethanol vapor exposure suppresses ethanol self-administration and behavioral allocation in a concurrent operant choice paradigm in male and female Long Evans rats

Abstract

RATIONALE: Access to alternative non-drug rewards is known to influence alcohol use, yet how chronic exposure affects behavioral allocation under concurrent choice conditions remains poorly understood. OBJECTIVES: This study examined the effects of chronic, binge-like ethanol vapor on ethanol self-administration and behavioral allocation in a concurrent operant choice paradigm offering sweetened ethanol and sucrose. METHODS: Male and female Long Evans rats completed daily concurrent choice sessions in which completion of a fixed-ratio 5 produced 15 s access to either sweetened ethanol or sucrose alone. Following baseline assessment, rats were exposed to seven weeks of ethanol vapor (4 h/day, 4 days/week) or air control conditions while operant testing continued. Ethanol no-choice sessions were conducted to assess behavior in the absence of sucrose. Choice behavior and intake were also evaluated following cessation of vapor exposure. Data were analyzed using mixed-effects models. RESULTS: Replicating our previous findings, concurrent sucrose access reduced ethanol self-administration relative to ethanol no-choice sessions. During vapor exposure, vapor-exposed rats demonstrated progressive reductions in ethanol-directed choice and ethanol intake alongside concurrent increases in sucrose intake, while controls maintained stable behavior. Reverting to ethanol-only no-choice sessions increased ethanol intake across groups; however, vapor-exposed rats continued to consume less ethanol than controls. Following vapor cessation, lower ethanol-directed choice persisted in vapor-exposed rats. CONCLUSIONS: These results suggest that exposure to ethanol vapor alone may not be sufficient to increase ethanol-directed behavioral allocation when assessed in a concurrent choice operant paradigm. As such, conclusions drawn from vapor-based models may depend critically on the environmental context, such as availability of alternative reinforcers.