Rats will decrease intake of a saccharin conditioned stimulus (CS) following pairing with an illness-inducing agent such as LiCI, a preferred high concentration of sucrose, or a drug of abuse such as morphine or cocaine. The suppressive effects of the illness inducing agent are clear evidence for aversive conditioning and are referred to as conditioned taste aversions. The suppressive effects of the rewarding sucrose solution reflect appetitive conditioning and are referred to as anticipatory contrast effects because the saccharin CS is thought to be devalued as it comes to predict the future availability of the preferred sucrose reward. Finally, despite the well-known rewarding properties of drugs of abuse, the suppressive effects of these drugs have been viewed as conditioned taste aversions for over 25 years. We have, however, recently posed an alternative interpretation that eliminates this apparent paradox. Specifically, we have suggested that rats suppress intake of a saccharin CS following saccharin-morphine pairings, for example, because the saccharin CS is devalued as it comes to predict the future availability of the highly rewarding drug of abuse. Thus, we postulate that the same rewarding properties that increase self-administration of the drug also serve to devalue the gustatory cue that predicts its availability. The results from the Progress Report support this new hypothesis by showing that the suppressive effects of drugs of abuse and sucrose, but not LiCI, are influenced by the deprivation state of the animal, the nature of the gustatory CS, the caloric value of the CS, lesions of the gustatory thalamus, and the strain of the rat. The goals of this project are to (I) further identify the relevant parameters of the phenomenon, (II) establish the merits of the reward comparison hypothesis and (III), introduce self-administration to this paradigm. The addition of the self- administration procedure will not only more closely approximate the contrast protocol, but also will allow us to begin to study how reward comparison ma affect drug-seeking and drug-taking behavior.
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