REPEATED EXPOSURE OF RAT PUPS TO ISOLATION ATTENUATES ISOLATION-INDUCED ULTRASONIC VOCALIZATION RATES - REVERSAL WITH NALTREXONE

Young rat pups are dependent on the dam for their survival, thus isola tion of the neonatal rat pup from the dam presents the young organism with a variety of stressors. The question examined in this study conce rns the ability of the young rat pup to modify its response to isolati on following repeated exposure to that isolation as well as the role p layed by endogenous opiates in this process. Following repeated isolat ions, pups were seen to decrease vocalization rates. Altering the cont ext in an attempt to dishabituate animals failed to reverse the decrea sed vocalization rate. However, opiate receptor blockade attenuated th is decrease when administered subsequent to the first isolation period but not prior to the last isolation period. These results suggest tha t the development of this attenuated response to isolation stress is o piate-mediated but that once established, its expression is not depend ent on endogenous opiate release. (C) 1994 John Wiley and Sons, Inc.