Abstract

We have previously reported that stress early in life resulted in long-term behavioral and neurochemical alter-ations in later life. In this study, we aimed to examine the effect of stress early in life on drug abuse at adolescent period using experimental animals, Sprague-Dawley rats. We used a 60 times exposure to an inescapable and unpredictable footshock as a stressor, and rats were exposed to the stressor twice on postnatal days (PNDs) 14 and 21. Two different classes of drugs of abuse, methamphetamine and dextromethorphan, were tested in this study. Rats were treated with methamphetamine4 mg/kg/day or dextromeethorphan 40 mg/kg/day intraperitoneally during PND 28-37, and methamphetamine 0.8 mg/kg or dextromethorphan 40 mg/kg was challenged on PND 45 after 7 days of drug free period. Locomotor activity of a rat was measured just after injection of drugs. Two drugs elicited behavioral sensitization which implied abuse liability of drugs. Interestingly, rats with experience of footshock stress early in life showed more increased locomotor activity on the challenging day, reflecting enhanced behavioral sensitization. These data suggest that experience of severe stress early in life can make the organism more susceptible to the drugs of abuse at adolescent period when the habit of abusing drug usually starts.

• Keywords: Stress, Early life, Drug abuse, Methamphetamine, Dextromethorphan, Adolescent;