Sex Differences in Low-dose Ethanol Effects on Motivated Behavior and Limbic Corticostriatal Activity

In 2023, the World Health Organization declared that there is no safe amount of alcohol consumption. It is becoming increasingly clear that even at lower doses, ethanol exposure impacts both the brain and behavior. Emerging work has shown that chronic exposure to lower doses of ethanol may lead to inflexible behaviors and promote aberrant reward seeking. This study aimed to determine the impact of chronic, low-dose ethanol exposure on neural substrates of reward and associated alterations in behavioral strategy in response to change in reward value.

Female and male C57BL/6J mice underwent operant training to self-administer 10% sucrose under a fixed ratio schedule. After acquisition, response criteria were graduated to a random interval schedule to promote automated behaviors. Throughout training, mice were given an i.p. injection of low-dose ethanol (0.5g/kg) or saline, 1 hour after each training session. Mice did not receive low-dose ethanol or saline i.p. injections after completion of training. Mice were then tested in a PR task in which the reward magnitude of reinforcer was reduced (small or large) or increased (small or large). A subset of mice expressed a retrograde tracer in the nucleus accumbens (NAc), and cFos expression within NAc circuits was analyzed following a sucrose self-administration session.

Chronic low-dose ethanol exposure altered behavioral responding in female mice following small changes in reward magnitude. Female mice showed divergent response patterns when there was a small reduction in reward magnitude, with greater proportions of ethanol-exposed female mice either increasing or decreasing responding versus controls. Following a small increase, low-dose ethanol female mice significantly increased responding versus controls. Female mice exposed to chronic low-dose ethanol shifted behavioral strategy with a reduction in 'checking' behavior (magazine entry after a lever press) in response to changes in reward magnitude. This effect was not observed in male mice. Low-dose ethanol exposure altered cFos expression within the prelimbic cortex and its projections to the NAc during reward seeking.

Chronic, low-dose ethanol altered behavioral responding and strategy in female mice in response to changes in reward value. During reward seeking, low-dose ethanol exposure impacted prelimbic cortex and its projections to the nucleus accumbens activity in both female and male mice. Future studies should investigate the consequences of chronic low-dose ethanol on both the brain and behavior to further understand what underlying processes drive aberrant reward-seeking behaviors.