Psychology, Department of


Date of this Version

December 1998


Published in Experimental and Clinical Psychopharmacology, 6:2 (1998), pp. 131-138. Copyright © 1998 American Psychological Association. Used by permission. “This article may not exactly replicate the final version published in the APA journal. It is not the copy of record.”


When a multisensory environment was reliably paired with morphine (2 mg/kg) in rats, that environment, in a drug-free test, evoked a hyperactive conditioned response (CR). When an olfactory cue (banana odor) was the only stimulus element reliably paired with morphine, it also elicited a hyperactive CR. However, a gustatory cue (saccharin solution) evoked a hypoactive CR. This taste-elicited decrease in activity was dose dependent; morphine at 2 and 4 mg/kg conditioned hypoactivity, whereas a higher dose (8 mg/kg) did not. A robust conditioned saccharin aversion occurred only at the highest dose of morphine, suggesting disassociation between the hypoactive CR and taste aversion. A taste cue present during context conditioning also prevented either acquisition or expression of the hyperactive CR to the context. The modality of the conditioned stimulus is a critical determinant of the form of the CR in a morphine locomotor conditioning paradigm.