Factors influencing behavior of group-housed male rats in the social interaction test Focus on cohort removal

The rat social interaction (SI) test is used widely to measure anxiety-like behavior, yet the influence of various factors such as testing time, pre-e xperimental manipulations (transport stress), and testing of animals from t he same cage (cohort removal, CR) on SI has not been systematically studied . We measured SI behavior of male triad-housed Wistar rats in a novel dimly lit arena (low light unfamiliar, LU) and found that Sl time is higher in t he beginning of the activity (dark) phase when compared with SI time in fir st half of the light phase. Furthermore, SI time is significantly increased by habituation of animals to the testing room during light phase, but this intervention has no effect in early dark phase when SI behavior is already maximal. Sequential removal of rats from the home cage led to the stress-l ike behavioral and physiological consequences. Rats removed in the last pos ition had shorter SI time and higher body temperature. These data demonstra te that SI is higher during early dark vs. early light phase and confirm th at CR has anxiogenic-like effects in rats. We conclude that the usage of se quentially removed group-housed rats in behavioral tests can be a source fo r considerable variation due to anxiety that develops in animals remaining in the cage. On the other hand, CR may be a useful method to study behavior al/neurochemical mechanisms of psychogenic stress in rats. (C) 2001 Elsevie r Science Inc. All rights reserved.