Emotional but not physical stress enhances intravenous cocaine self-administration in drug-naive rats

Involvement of stress in the etiology of drug dependence has received little attention. In the present study a number of behavioural manipulations were applied and examined for an effect on intravenous cocaine self-administration in drug-naive rats with no prior training in leverpress responding. Self-administration rate was measured during five consecutive daily sessions. Stress reduction by handling rats daily for two weeks prior to testing for self-administration did not affect cocaine self-administration. Acute physical stress was induced either by a hot plate or by repeated footshocks, and emotional stress was induced by forcing rats to witness another rat being subjected to repeated footshocks. These stressors were applied immediately prior to each cocaine self-administration session. Emotional but not physical stress enhanced the rate of cocaine self-administration. It is concluded that emotional distress may increase the rewarding effects of cocaine and may render an individual more susceptible to development of drug dependence.