Anticipatory contrast effect in rats: a new view with lick response analysis and the effect of dopamine blocking.
A negative anticipatory contrast effect (NACE) is manifested as a suppression of the effect of a reward stimulus to elicit consummatory or instrumental responses when a second more potent reward is presented right afterward. No well-supported theory explains the effect. We analyzed NACE with rats' licking responses to 3 solutions with varying reward value: 8% sucrose mixed with 0.008% quinine (A), 8% sucrose with 0.002% quinine (B), and 32% sucrose with 0.008% quinine (C). 3 groups (n = 4) of rats were given 2 solutions in succession, each 5 min with 15 s in between, for a total of 11 days: Group AA (control), A then A; Group AB, A then B; Group AC, A then C. On days 13 to 16, and 12 and 17, pimozide (0.4 mg/kg, i.p.), and the vehicle solution were injected, respectively. Results show that the licking of A was a function of what solution to follow: In AC, the total number of licks, the short interlick interval (SILI), and the number of licks per s during the initial contact were less than AA. In AB, only SILI was less. Licking of A was initially low but increased over days, except for AC. The failure of AC to increase the licking was attributed to a "retroactive overshadowing" effect of a more potent stimulus C blocking stimulus A to form a reward learning, thus preventing its rewarding property to be fully manifested. It may also be due to stimulus A becoming a "signal" for incoming reward, thus degrading its own rewarding function. The shorter SILI in AB and AC suggested a reward devaluation; however, devaluation alone did not predict the consummatory response. Pimozide reduced licking number overall without altering the relative reward property or SILI suggesting that NACE was not a dopamine-mediated motivated choosing behavior.
Chen
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BH
Department of Psychology, National Chung Cheng University, Chia-Yi, Taiwan, ROC.
Hsiao
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D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects* / Q000502:physiology*; D018492:Dopamine Antagonists / Q000494:pharmacology*; D004327:Drinking Behavior / Q000187:drug effects* / Q000502:physiology*; D008297:Male; D010868:Pimozide / Q000494:pharmacology; D011803:Quinine; D051381:Rats; D017207:Rats, Sprague-Dawley; D012201:Reward; D012996:Solutions; D013395:Sucrose
D018492:Dopamine Antagonists; D012996:Solutions; D010868:Pimozide; D013395:Sucrose; D011803:Quinine