The genetic liability to stress and postweaning isolation have a competitive influence on behavioral organization in rats

Rats housed in social isolation postweaning (isolates) show profound behavi oral and neurobiological differences when compared to socially housed rats (socials). Fischer rats (F344) relative to Lewis rats are hyperresponsive a nd significantly more susceptible to stressful stimuli. This investigation tested the hypothesis that the behavioral effects of postweaning isolation are more pronounced in a strain of rats with high susceptibility to stress compared to a strain with low susceptibility to stress. Seventy male Spragu e-Dawley, Lewis, and F344 rats were housed individually or in groups at wea ning on Day 21 and tested on Day 85 in the Behavioral Pattern Monitor. Ther e was no interaction between strain and postweaning isolation for measures of locomotor activity and exploratory behavior (holepoking). However, the p ostweaning isolation-induced increase in the frequency of repetitive straig ht movements, a measure of behavioral organization, was more pronounced in Lewis isolates compared to Sprague-Dawley and F344 isolates. These results do not support the hypothesis that rats with a higher susceptibility to str ess show more pronounced changes in behavior following postweaning isolatio n; instead. increased susceptibility to stress may counteract the repetitiv e movement patterns induced by social isolation. (C) 2000 Elsevier Science Inc. All rights reserved.