Drug versus sweet reward: greater attraction to and preference for sweet versus drug cues.
Addiction Biology. 2014-03-07; 20(3): 433-444
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1. Addict Biol. 2015 May;20(3):433-44. doi: 10.1111/adb.12134. Epub 2014 Mar 7.
Drug versus sweet reward: greater attraction to and preference for sweet versus
Madsen HB(1), Ahmed SH.
(1)Institut des Maladies Neurodégénératives, Université de Bordeaux, France;
Institut des Maladies Neurodégénératives, CNRS, France; Florey Institute of
Neuroscience and Mental Health, University of Melbourne, Australia.
Despite the unique ability of addictive drugs to directly activate brain reward
circuits, recent evidence suggests that drugs induce reinforcing and incentive
effects that are comparable to, or even lower than some nondrug rewards. In
particular, when rats have a choice between pressing a lever associated with
intravenous cocaine or heroin delivery and another lever associated with sweet
water delivery, most respond on the latter. This outcome suggests that sweet
water is more reinforcing and attractive than either drug. However, this outcome
may also be due to the differential ability of sweet versus drug levers to elicit
Pavlovian feeding-like conditioned responses that can cause involuntary lever
pressing, such as pawing and biting the lever. To test this hypothesis, rats
first underwent Pavlovian conditioning to associate one lever with sweet water
(0.2% saccharin) and a different lever with intravenous cocaine (0.25 mg) or
heroin (0.01 mg). Choice between these two levers was then assessed under two
operant choice procedures: one that permitted the expression of
Pavlovian-conditioned lever press responses during choice, the other not. During
conditioning, Pavlovian-conditioned lever press responses were considerably
higher on the sweet lever than on either drug lever, and slightly greater on the
heroin lever than on the cocaine lever. Importantly, though these differences in
Pavlovian-conditioned behavior predicted subsequent preference for sweet water
during choice, they were not required for its expression. Overall, this study
confirms that rats prefer the sweet lever because sweet water is more reinforcing
and attractive than cocaine or heroin.
© 2014 Society for the Study of Addiction.
PMID: 24602027 [Indexed for MEDLINE]