Effects of narcotic abstinence on schedule-controlled behavior in dependent rats

Female Sprague-Dawley rats were trained to lever press for food on a variable interval one minute schedule of reinforcement. Four of these rats were then made tolerant to and physically dependent on morphine by a series of automatic IV injections. Four other rats were made tolerant to and physically dependent on LAAM. During the dependence state behavioral tolerance was exhibited to the suppressant effect of morphine on lever pressing, but not to the suppressant effect of LAAM. Abstinence was induced by discontinuation of injections. During both the morphine and LAAM abstinence states from the fourth through twelfth days mean lever presses per session were significantly higher than pre-drug control values. However, there were quantitative differences. Mean lever presses per session were significantly higher during morphine abstinence than during LAAM abstinence. This difference in degree of increased lever pressing observed during morphine and LAAM abstinence in this study extends our previous reports which demonstrated that in the rat morphine abstinence was associated with more severe behavioral disruptions than LAAM abstinence.