Psychology, Department of


Date of this Version

January 1995


Published in Experimental and Clinical Psychopharmacology, 3:1 (1995), pp. 9–14. Copyright © 1995 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.”


In previous work showing a taste-elicited decrease in pain sensitivity (J. S. Miller, K. S. Kelly, J. L. Neisewander, D. F. Mc- Coy, & M. T. Bardo, 1990), the rats (Rattus norvegicus) were always habituated to an inactive hot plate after each drug injection. The present report examined whether the analgesic response was a conditioned response to the taste or a response to the novelty of the hot plate resulting from morphine disrupting the habituation process. In 3 experiments, it was found that hot plate novelty was mainly responsible for the analgesic response. For example, increasing the number of conditioning trials did not enhance analgesia in morphine-treated rats. Rather, it attenuated analgesia in saline-treated controls (habituation). Also, rats given habituation in a drug-free state failed to show an analgesic response compared with controls.