Drug discrimination learning using a taste aversion paradigm: An assessment of the role of safety cues

Abstract

In drug discriminations using conditioned taste aversions one drug signals a taste—toxin pairing while a second drug, or vehicle, signals the same taste in the absence of the toxin. Here we examine the role of safety signals, the cues that predict the absence of the toxin and further characterize the properties of drug states as danger cues, the cues that predict the toxin. Drugs, as safety cues, result in slightly faster acquisition and better discriminative performance than does conditioning using a saline vehicle or no explicit stimulus as the safety signal. Saline injections, as safety cues, provided no additional cueing information when a drug state serves as a danger cue. Drug states, as safety cues, were treated like conditioned inhibitors when saline served as the danger cue. Interposing a naloxone-induced trace between the morphine-induced state and the presentation of the flavor revealed that overlap of the drug and the flavor was necessary when morphine was a safe cue but not when morphine was a danger cue. These data suggest that morphine as a danger cue acts as an occasion setter but that morphine as a safety cue acts as a conditioned inhibitor.