Behavioral Effects of Chronic WIN 55,212-2 Administration During Adolescence and Adulthood in Mice

Marijuana, a psychoactive drug that activates cannabinoid-1 (CB1) receptors in the brain, is the most prevalently abused illicit drug among American adolescents and young adults. However, the long-term consequences of adolescent exposure to cannabinoids on the brain and behavior remain poorly understood. In both humans and nonhumans, adolescence is characterized by the maturation of the endocannabinoid neurotransmitter system in the prefrontal cortex and striatum-brain regions that underlie choice and decision making and are densely packed with CB1 receptors. In the current study, the effects of chronic WIN 55,212-2 (a CB1 agonist) exposure during adolescence on reversal learning and delay discounting were compared with those of adult-onset exposure using mice. Mice were administered 3.0 mg/kg/day WIN 55,212-2 or vehicle for 21 days beginning in adolescence (postnatal days 28-49) or adulthood (postnatal days 90-111). For the reversal-learning task, there was no difference in errors or omissions to criterion following a reversal in adolescent-exposed mice but adult-exposed mice showed a delay in beginning the reversal, suggesting that adolescents, but not adults, are resilient to this drug. Adult mice given WIN 55,212-2 in adolescence displayed greater impulsivity in the form of preference for smaller-sooner reinforcers over larger-delayed ones in the delay-discounting procedure, but this was seen to a lesser extent with adult-onset exposure. These data underscore the importance of variables related to the timing and duration of exposure as well as the specific and persistent behavioral endpoints affected by chronic cannabinoid administration. Public Health Significance With the growing legalization of marijuana, understanding how repeated cannabinoid use impacts the brain and behavior later in life is important. We demonstrate that cannabinoid administration during development can impair choice and increase impulsivity later in life, long after drug administration has ceased. Adolescent and adult mice were differentially susceptible to cannabinoids, indicating these age groups may display differing vulnerabilities to the long-term psychological effects of repeated cannabinoid exposure.