Adolescent morphine exposure induces immediate and long-term increases in impulsive behavior

Rationale Adolescence in humans represents a unique and critical developmental time point associated with increased risk-taking behavior. Converging clinical and epidemiological studies report a peak of drug use during adolescence, leading to the hypothesis that the developing adolescents brain is at risk to lose control over drug intake. Both adolescence and drug abuse are associated with significant cognitive and psychological changes such as lack of impulse control. A simple definition for impulsive behavior is the tendency to act prematurely without foresight. Increase in impulsivity is evident in acute morphine consumption, but to date, little is known with respect to subchronic morphine administration in impulsive behavior, particularly comparing time-dependent effects in adults, young adults, and adolescents. Methods To evaluate this, adult, young adult, and adolescent rats were treated with a subchronic regimen of morphine or saline during 5 days (s.c.). Thereafter, we examined impulsive behavioral effects of morphine administration, 24 h and 25 days after administration in rats, while responding under a five-choice serial reaction time task (5-CSRTT). Results Subchronic morphine administration increased premature responding 24 h after the last injection of morphine in adult, young adult, and adolescent rats without increasing motor activity but a significant change in motivation in adult and young adult rats only. After 25 days of abstinence, premature responses were significantly increased in comparison with baseline in adolescent rats but not in adults and young adults. Conclusion The main conclusion of this study is that morphine exposure in adolescents has a long-term profound effect on motor impulsive behavior later in adulthood. An implication of our findings might be that we should be especially careful about consuming and prescribing opioid drugs in adolescents.