The effect of naloxone on food-motivated behavior in the obese Zucker rat

We assessed differences in food reinforced behavior between obese and lean Zucker rats with a progressive ratio schedule 3 (PR3) in which a subject emitted three additional lever-presses each time a reinforcer was delivered. The number of responses required for a reinforcer eventually exceeded its v...

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Bibliographic Details
Published in:Psychopharmacologia 1999-02, Vol.141 (4), p.378-384
Main Authors: GLASS, M. J, O'HARE, E, CLEARY, J. P, BILLINGTON, C. J, LEVINE, A. S
Format: Article
Language:English
Subjects:
Animals
Biological and medical sciences
Eating - drug effects
Feeding behavior
Feeding Behavior - drug effects
Food
Food consumption
Food intake
Genotypes
Male
Medical sciences
Metabolic diseases
Motivation
Naloxone
Naloxone - pharmacology
Narcotic Antagonists - pharmacology
Obesity
Obesity - physiopathology
Rats
Rats, Zucker
Reinforcement
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Summary:We assessed differences in food reinforced behavior between obese and lean Zucker rats with a progressive ratio schedule 3 (PR3) in which a subject emitted three additional lever-presses each time a reinforcer was delivered. The number of responses required for a reinforcer eventually exceeded its value, termed the "break point", a sensitive measure of food motivated behavior. Break points were higher in obese rats than lean controls for grain pellets (27.5 versus 9.5, P = 0.01) but not for sweet pellets (51.6 versus 38.5, P = 0.31). We determined if naloxone (0.01-3.0 mg/kg, SC), which reduces free food intake in obese Zucker rats, affects food motivated behavior in obese Zuckers and lean controls. Naloxone reduced break points in both obese and lean rats to a similar extent when working for either grain pellets or sweet pellets. Under free-access feeding conditions, naloxone again decreased pellet intake similarly in the obese and lean Zucker rats. Naloxone appeared to decrease free-access pellet consumption to a greater extent than break point in both groups. These results show that (1) obese rats exhibit higher levels of performance for food than lean rats only when working for the less valued grain pellet, (2) naloxone reduces both break points and free-access pellet consumption independent of genotype, and (3) naloxone appears to decrease food more effectively in rats given free access to food than in rats working for food.
ISSN:0033-3158
1432-2072
DOI:10.1007/s002130050847