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

Michael J. Glass, Eugene O'Hare, James P. Cleary, Charles J. Billington, Allen S. Levine

Research output: Contribution to journalArticlepeer-review

38 Scopus citations

Abstract

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.

Original languageEnglish (US)
Pages (from-to)378-384
Number of pages7
JournalPsychopharmacology
Volume141
Issue number4
DOIs
StatePublished - May 3 1999

Keywords

  • Obesity
  • Operant behavior
  • Zucker rat

Fingerprint Dive into the research topics of 'The effect of naloxone on food-motivated behavior in the obese Zucker rat'. Together they form a unique fingerprint.

Cite this