Aversive stimulus properties of morphine: evaluation using the drug preexposure conditioned taste aversion paradigm.
Interpretation of the finding that positive-reinforcing drugs such as morphine also possess possible aversive properties, as revealed by their ability to induce a conditioned taste aversion (CTA), remains problematic. This issue was addressed in the present study using the drug preexposure CTA paradigm. Water-deprived rats were given noncontingent preexposure to one of three doses of morphine (2.5, 5.0, or 15.0 mg/kg) or drug vehicle. Subsequently, animals in each of these preexposure groups were presented with a novel 0.1% saccharin-flavored solution followed immediately by injection with one of the same three morphine doses or drug vehicle. This procedure was repeated at 5-day intervals until six saccharin presentations had been performed. Results indicated that while the three morphine doses were differentially potent as taste aversion-conditioning agents, they were equipotent as preexposure agents serving to disrupt CTA. These data suggest that preexposure to morphine's predominantly positive-reinforcing (and non-CTA-inducing) properties is sufficient for preexposure disruption of subsequent morphine CTA. A second experiment indicated that the minimal effective preexposure dose is between 0.3 and 1.25 mg/kg of morphine. It is suggested that an important commonality may exist between the discriminative stimulus properties of morphine as a CTA-inducing agent and as a positive reinforcer.
D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D003214:Conditioning, Classical / Q000187:drug effects*; D004193:Discrimination Learning / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004327:Drinking Behavior / Q000187:drug effects; D005795:Generalization, Stimulus / Q000187:drug effects; D008297:Male; D009020:Morphine / Q000008:administration & dosage* / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012439:Saccharin / Q000008:administration & dosage; D013649:Taste / Q000187:drug effects*; D013997:Time Factors
D009020:Morphine; D012439:Saccharin