Abstract
Rationale
Cannabinoid antagonists purportedly have greater effects in reducing the intake of highly palatable food compared to less palatable food. However, this assertion is based on free-feeding studies in which the amount of palatable food eaten under baseline conditions is often confounded with other variables, such as unequal access to both food options and differences in qualitative features of the foods.
Objective
We attempted to reduce these confounds by using a model of choice that programmed the delivery rates of sucrose and carrot-flavored pellets.
Methods
Lever pressing of ten lean (Fa/Fa or Fa/fa) and ten obese (fa/fa) Zucker rats was placed under three conditions in which programmed ratios for food pellets on two levers were 5:1, 1:1, and 1:5. In phase 1, responses on the two levers produced one type of pellet (sucrose or carrot); in phase 2, responses on one lever produced sucrose pellets and on the other lever produced carrot pellets. After responses stabilized under each food ratio, acute doses of rimonabant (0, 3, and 10 mg/kg) were administered before experimental sessions. The number of reinforcers and responses earned per session under each ratio and from each lever was compared.
Results and conclusions
Rimonabant reduced reinforcers in 1:5 and 5:1 food ratios in phase 1, and across all ratios in phase 2. Rimonabant reduced sucrose and carrot-flavored pellet consumption similarly; rimonabant did not affect bias toward sucrose, but increased sensitivity to amount differences in lean rats. This suggests that relative amount of food, not palatability, may be an important behavioral mechanism in the effects of rimonabant.
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Acknowledgments
We thank Steven Boomhower, Megan Brinton, Brent Call, Tiffany Doherty, Kory Farley, Vanessa Hanson, Conrad Hillman, Casey Johnson, Mathew Luras, Zachary Schumacher, Sasha Scott, Jennifer Stoll, and Jennifer White for assistance with data collection.
This manuscript is part of the first author’s Master’s thesis at Idaho State University and was supported by funding from the WeLEAD project (National Science Foundation SBE-0620073), the Idaho INBRE Program, NIH grant nos. P20 RR016454 (National Center for Research Resources) and P20 GM103408 (National Institute of General Medical Sciences), and grants from the Humanities and Social Sciences Research and Graduate Research Committees at Idaho State University.
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Buckley, J.L., Rasmussen, E.B. Rimonabant’s reductive effects on high densities of food reinforcement, but not palatability, in lean and obese Zucker rats. Psychopharmacology 231, 2159–2170 (2014). https://doi.org/10.1007/s00213-013-3366-4
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DOI: https://doi.org/10.1007/s00213-013-3366-4