Open AccessOpioid mediation of odor preferences induced by sugar and fat in 6-day-old rats
Author(s) -
David J. Shide,
Elliott M. Blass
Publication year - 1991
Publication title -
physiology and behavior
Language(s) - English
Resource type - Journals
eISSN - 1873-507X
pISSN - 0031-9384
DOI - 10.1016/0031-9384(91)90422-k
Subject(s) - odor , naltrexone , endogenous opioid , opioid , chemistry , sucrose , endocrinology , psychology , food science , medicine , biochemistry , receptor , organic chemistry
Intraoral infusions of sucrose, fat or polycose reduce ultrasonic vocalizations during isolation, and increase pain threshold in infant rats. These effects are naltrexone reversible. The present study determined whether these substances, when paired with an odor, caused a change in preference for that odor. In 6-day-old rats, pairing orange odor with intraoral infusions of sucrose or corn oil, but not polycose, water, mineral oil or 0.01% quinine hydrochloride, caused a substantial increase in preference for orange. Preference formation was blocked by systemic injection of naltrexone (0.25 mg/kg) prior to pairing orange with either sucrose or corn oil. Moreover, preference expression was prevented by naltrexone injection prior to testing. Thus certain substances thought to reduce stress in infant rats via endogenous opioid release can also cause preference for substances that predict their occurrence. Preference formation depends upon the availability of endogenous opioids. Preference expression reflects the conditioned stimulus causing opioid release.