Weiss, Stanley J.; Reilly, Mark P.; Kearns, David N.
This special issue of the International Journal of Comparative Psychology is based on presentations delivered at the Focus Session of the 2004 Winter Conference on Animal Learning and Behavior (WCALB) held in Winter Park, Colorado. The Associative Mechanisms and Drug-Related Behavior Focus Session began with an invited address by Shepard Siegel titled The Ghost in the Addict: Drug Anticipation and Drug Addiction. He described an impressive body of research showing that conditioning mechanisms underlie drug tolerance and withdrawal. Siegel's address underscored the important contribution of associative mechanisms to drug-related behavior and set the stage for the six papers presented in this issue. Siegel began by describing his landmark study that first demonstrated the ''situational specificity of tolerance'' (Siegel, 1975). In that study, tolerance to morphine was only observed when rats were injected with morphine in an environment where they had previously experienced morphine. In contrast, no tolerance to morphine was observed when rats were injected in a novel environment. This result demonstrated that environmental factors might be as important, or even more important, than pharmacological factors in the expression of tolerance to drugs. Siegel pointed out that these results were anticipated by Subkov and Zilov (1937) who demonstrated conditioned tolerance of epinephrine-induced tachycardia. Siegel hypothesized that this situational specificity of tolerance was mediated by conditioned compensatory responses (CCRs) that counteracted the analgesic effects of morphine. According to this conditioning account of tolerance, the environmental stimuli present before and during morphine (the unconditioned stimulus or US) administration should act as Pavlovian conditioned stimuli (CSs). Through these pairings, the CSs come to elicit a conditioned response (CR) that opposes the direct effects of morphine. Therefore, since morphine itself produces analgesia, the environmental CSs that are paired with morphine come to elicit hyperalgesia. These oppositional processes then summate to produce a zero net effect, which manifests itself as tolerance, when morphine is administered in the presence of cues previously paired with morphine.
2005
International Journal of Comparative Psychology
18/2
Weiss, Stanley J.; Reilly, Mark P.; Kearns, David N.