Exercise or saccharin during abstinence block estrus-induced increases in nicotine-seeking

Recent evidence suggests that adolescent and young adult females may be particularly responsive to nicotine use interventions that include exercise or environmental enrichment This possibility was addressed in the current study by comparing the efficacy of exercise versus non-exercise environmental enrichment (saccharin) during abstinence at reducing subsequent nicotine-seeking/relapse vulnerability in an adolescent-onset rat model. The efficacy of each intervention was examined as a function of estrous cycle phase given findings indicating that hormonal status influences relapse vulnerability and treatment outcome in females. Once adolescent female rats acquired nicotine self-administration, they were given 23-h/day access to nicotine (0.01 mg/kg/infusion) for 10 days. Following the last self-administration session, rats began a 10-day forced abstinence period with 2-h/day access to an unlocked wheel (exercise, n = 15), a bottle containing a saccharin-sweetened solution (0.25%; saccharin, n = 19), or without access to a wheel or saccharin (control, n = 20). Nicotine-seeking, as assessed under an extinction/cued-induced reinstatement procedure, was examined on day 11 of abstinence. Levels of nicotine-seeking were highest in females tested during estrus as compared to females tested during non-estrus phases. Exercise or saccharin during abstinence reduced nicotine-seeking in females tested during estrus, but neither affected the low levels of nicotine-seeking observed in females tested during non-estrus phases, presumably due to a floor effect. These results demonstrate that exercise or saccharin during abstinence decrease nicotine-seeking, and suggest that either would be effective as an early intervention for nicotine use and addiction in females.