Pharmacology of the acquisition and expression of flavor preference conditioning to fructose: Roles of dopamine and opioid receptors in rats.
Item
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Title
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Pharmacology of the acquisition and expression of flavor preference conditioning to fructose: Roles of dopamine and opioid receptors in rats.
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Identifier
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AAI3127847
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identifier
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3127847
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Creator
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Baker, Robert W.
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Contributor
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Adviser: Richard J. Bodnar
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Date
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2004
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Language
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English
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Publisher
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City University of New York.
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Subject
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Psychology, Physiological | Health Sciences, Pharmacology
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Abstract
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For omnivores, such as humans and rats, learning to associate flavor with postingestive consequences of palatable food is essential for survival. Research into the neurochemical substrate(s) mediating this adaptive behavior consistently demonstrates the involvement of dopamine, whereas the role of opioids is equivocal. The effects of dopamine and opioid receptor antagonists on the acquisition and expression of flavor preferences conditioned (CFP) by the sweet taste of fructose were examined in real-feeding rats. Rats were trained to drink fructose paired with one novel flavor and less-preferred saccharin paired with another flavor. Groups of rats received either vehicle, D1 (SCH23390, 200 nmol/kg, sc) or D2 (raclopride, 200 nmol/kg, sc) antagonists, or vehicle with intakes matched to the dopamine groups (D1-yoked, D2-yoked). Preferences were assessed in two-bottle tests with both flavors presented in saccharin following vehicle or antagonist doses (50--800 nmol/kg).;Acquisition of a significant conditioned flavor preference (CFP: ∼75%) to fructose observed in the control and yoked groups was eliminated in D1-trained and D2-trained rats. SCH23390, and to a lesser degree raclopride, also blocked the expression of an existing conditioned flavor preference. Raclopride also attenuated fructose preferences in rats exposed to two-bottle training with fructose and saccharin solutions. Thus, both D1 and D2 antagonists block the acquisition of fructose CFP, whereas D1, and to a lesser extent D2, antagonists attenuate fructose CFP expression. The ability of the general opioid antagonist, naltrexone to alter the acquisition and expression of fructose CFP was also examined. Although naltrexone (0.1--5.0 mg/kg) reduced fructose and saccharin intakes during training, it failed to interfere with the acquisition of a fructose CFP. Further, although naltrexone (0.1--5 mg/kg) reduced saccharin intake in two-bottle tests, it again failed to alter the expression of an established fructose flavor preference. Thus, dopamine D1 and D2 receptor antagonism, but not general opioid receptor antagonism, reduces flavor-flavor conditioning by fructose in free-feeding rats. These results strongly suggest that dopamine mediates the association of flavor cues with ingestive consequences, whereas opioids appear to mediate the hedonics of consummatory behavior, playing a very minor role in CFP learning for simple carbohydrates.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
