Operant effort-based decision-making task reveals sex differences in motivational behavior but no long-term effects of adolescent intermittent ethanol in Sprague Dawley rats

Abstract

Loss of motivated behavior, or apathy, is a key feature across multiple affective disorders, and is assessed via operant effort-based decision-making (EBDM). The mechanisms of amotivation have been connected to pro-inflammatory signaling which can directly impact dopamine signaling. Chronic alcohol exposure is associated with altered immune signaling and impaired goal-directed behavior, so the present studies assessed the impact of adolescent intermittent ethanol (AIE) on EBDM in adulthood across sex. Adolescent male and female (N = 32/n = 8 per group) Sprague-Dawley rats were exposed to ethanol (4 g/kg) intragastrically on a 3 days on/2 days off schedule during postnatal days ~30–50 or given vehicle, and allowed to age into adulthood (P80+). All rats were then trained on the operant EBDM concurrent FR5/chow task, after which we tested the impact of sex and AIE history on responding 1) during breakpoint challenge raising the FR requirement in a log₂ pattern, 2) 90 min after immune challenge (2 μg/kg IL-1β), 3) 18 h after 3.5 g/kg intraperitoneal ethanol challenge (hangover), and 4) immediately after a 30-min restraint stress challenge. Immune challenge disrupted motivated behavior without affecting appetite. No effects of AIE emerged and sex differences were evident throughout all challenges. Females responded less for pellets yet persisted responding until a higher breakpoint. This work indicates that AIE does not alter baseline or evoked EBDM as can be measured with this approach. Testing across aging and using other modalities should be performed to continue examining the effects of chronic alcohol on apathy.