Effects of naltrexone and CCK on estrous behavior and food intake in Syrian hamsters

Food deprivation inhibits estrous behavior in several species of rodents, b ut little is known about the neurotransmitter systems mediating this phenom enon. We determined whether partial blockade of opioid receptors by continu ous infusion of naltrexone and/or acute peripheral injection of cholecystok inin (CCK) administration would overcome the suppressive effects of food de privation on estrous behavior in Syrian hamsters. Contrary to expectation, naltrexone produced a slight suppression of estrous behavior. and systemic CCK administration had no effect. This dose of naltrexone was sufficient to reduce in,vivo binding of [H]naloxone in the brain, and both compounds aff ected other parameters such as food intake and body weight gain. Thus, the doses of CCK and naltrexone that were used were physiologically effective. These findings suggest that neither peripheral CCK nor opioid systems are l ikely to play a major role in the suppression of hamster estrous behavior b y food deprivation. (C) 2001 Elsevier Science Inc. All rights reserved.