Lynch, C. A., Porter, B., Butler, T. R. 2019. Access to voluntary running wheel exercise: Prevention of anxiety-like behavior in chronically stressed rats, but potentiation of ethanol intake/preference. Physiology & Behavior 206, 118-124.

The current study tested the effect of voluntary running on future anxiety-like behavior, physiological response to stress, and ethanol intake/preference, while including a chronically stressed group and healthy group housed conspecifics. When given concurrently, voluntary running reduces ethanol intake, though it is unknown what effect voluntary running will have on anxiety-like behavior, corticosterone response to stress, and ethanol intake/preference when exercise is allowed only prior to ethanol access. Adolescent male Long Evans rats arrived in the lab at postnatal day (PND) 21. At PND 27, rats were either socially isolated (SI; n = 1/cage) or group housed (GH; n = 4/cage). Half of each group was allowed access to a running wheel for 30 min for 24 days from PND 35–66, and half of each group was not allowed access to a running wheel. After the housing/running procedure, we tested anxiety-like behavior using the elevated plus maze and stress responsivity by measuring corticosterone (CORT) levels before and after a swim stressor; then, rats were allowed intermittent access to ethanol in two-bottle choice design for four weeks. In accord with our hypothesis, running reduced anxiety-like behavior in SI runners compared to non-runners. Swim stress increased CORT levels but there was no difference in the response among groups. In regard to ethanol intake and preference, running (irrespective of housing group) increased intake at the 30 min time point and preference at the 24 h time point. Altogether, these data show that access to voluntary exercise was successful in reducing anxiety-like behavior, but withdrawal of exercise access appeared to enhance ethanol intake/preference. We suggest that these data reflect hedonic substitution.