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

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.