Discrete trial choice procedure: effects of naloxone and methadone on choice between food and heroin

The results of the current study indicate that naxolone produces dose related increases in selection of heroin over food while methadone produces decreases in this same measure. Since the response requirements are virtually identical for completing a heroin or food trial, these results are not readily explained by a number of behavioral mechanisms. The results do not represent disruption or external stimulus control or disruption of the ability of the subjects to make a response. Such nonspecific drug effects would not have resulted in the systematic shift in choice performance observed in the present study.