Articles
Pimozide Does Not Shift Palatability: Separation of Anhedonia from Sensorimotor Suppression by Taste Reactivity

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Abstract

PECIÑA, S., K. C. BERRIDGE AND L. A. PARKER. Pimozide does not shift palatability: separation of anhedonia from sensorimotor suppression by taste reactivity. PHARMACOL BIOCHEM BEHAV 58(3) 801–811, 1997.—Several “taste reactivity” studies of dopamine and reward have concluded that pimozide suppresses the hedonic reaction patterns normally elicited by sucrose but enhances aversive reaction patterns elicited by quinine. However, other taste reactivity studies have failed to find hedonic/aversive shifts in reaction patterns after dopamine antagonists or dopamine lesions. The divergent conclusions have come from two different laboratories. To resolve the controversy regarding dopamine blockade and palatability, the present study joined the two laboratories to investigate the effect of pimozide on taste reactivity patterns elicited by sucrose and quinine. The results replicated many (but not all) of the earlier findings and identified procedural factors responsible for different outcomes. Overall, the results provide evidence for sensorimotor effects of pimozide on taste reactivity but not for a hedonic shift in palatability. Pimozide suppressed both hedonic and aversive reaction patterns in a gradual sensorimotor fashion when the eliciting taste stimulus was repeated or continued for several minutes. The general suppression typically did not alter the initial reaction to a taste but emerged only after an oral infusion of sucrose or quinine continued for several minutes or trials. Aversive reactions were never enhanced. The balance between hedonic and aversive reaction patterns was not shifted by pimozide. We conclude that pimozide produces a sensorimotor impairment of taste reactivity patterns but does not shift taste palatability toward anhedonia or aversion.

Section snippets

Experiment 1: does pimozide modify the palatability of a sucrose solution?

In experiment 1, the ability of pimozide to modify sucrose palatability in a 10-min test across 3 trials was assessed in both laboratories, once in a between-subjects design [a replication of a design by Leeb et al. [37]] and once in a within-subjects design (in which each rat serves as its own control, being tested both in drug and vehicle conditions). The tapes from the four experiments were shared and scored by both laboratories. Because the analyses performed by both laboratories were

Experiment 2: does pimozide modify the emission of aversive reactions to quinine?

At first sight, this question would seem to have been answered by the finding of Parker and Lopez [43]that pimozide administration increases aversive gapes to oral infusions of highly concentrated quinine. However, Parker and Lopez reported the absolute number of gapes observable, which is complicated by the suppression of locomotion by pimozide demonstrated in experiment 1 (and found by Parker and Lopez). The complication is that suppression of locomotion could conceivably bias the

General discussion

These results directly contradict the hypothesis that dopamine blockade makes tastes seem more unpalatable. Rather, reactions from all categories (aversive, hedonic, and general activity) appear to be reduced similarly by pimozide administration. The most parsimonious interpretation of these results (and those of previous taste reactivity studies) is that pimozide produces a general sensorimotor impairment of the ability to sustain high rates of effortful taste reactivity components (active

Acknowledgements

We thank Suzanne Erb, Hardy Rideout and Sharon Clarke for their assistance in data collection and scoring of the videotapes. We thank Prof. Brenda Wilson Gillespie and Kathy Welch of the University of Michigan Center for Statistical Consultation and Research for running the statistical analysis for experiment 1B. We also thank Prof. Ray Heller, Wilfrid Laurier University, and Prof. Marc Berridge, Case Western Reserve University, for their assessments of the chemical potency of pimozide

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