Some Observations of Anxiety-related Behavior in Young Adult Rats Following Late Adolescent Exposure to Methamphetamine with and without Environmental Enrichment

Background: Methamphetamine (MA) is an anxiogenic drug that is abused by adolescents for whom there is a risk of later developing high anxiety. This risk may be reduced by concomitant environmental enrichment which can reduce anxiety in laboratory rodents. Objective: As enrichment can attenuate anxiogenic effects of other drugs such as amphetamine sulfate and scopolamine, the present study aimed to determine if MA treatment of adolescent rats would affect their later level of anxiety, and if the outcome could be modified by exposure to enrichment. Methods: Male and female PVG/c hooded rats received 2 mg/kg/day of MA for 10 consecutive days during late adolescence (41-50 days after birth) while housed in standard or enriched cages (containing objects) before and during drug treatment and before and during testing in young adulthood, when anxiety-related behavior was recorded in a light-dark box and an elevated plus maze, as well as the rats' responsiveness to a novel Y-maze arm. Results: MA-treated rats from standard cages showed increased anxiety suggested by their longer emergence latencies into the light side of the light-dark box and no significant preference for entering a novel Y-maze arm. The lack of a similar drug effect for males from enriched cages suggested that enrichment attenuated their subsequent MA-related anxiety. Conclusion: Late adolescent treatment with MA increased later anxiety which, for males only, can be attenuated by exposure to enrichment during and following late adolescence. Consequently, deleterious effects of MA abuse on adolescent emotional development might be reduced by appropriate enrichment.