FORCED SWIMMING BEHAVIOR IS NOT RELATED TO THE CORTICOSTERONE LEVELS ACHIEVED IN THE TEST - A STUDY WITH 4 INBRED RAT STRAINS

The behavior of four inbred strains of rats in the holeboard and the f orced swimming tests, and its relationship with a physiological index of stress (serum corticosterone) were studied in adult male rats. The strains were: Fisher 344 (FIS), Lewis (LEW), Spontaneously hypertensiv e (SHR), and Wistar-Kyoto (WKY). in the holeboard, SHR rats were the m ost active and WKY the less active, the other strains showing intermed iate levels of activity. During the first exposure to forced swimming WKY were far more passive than the other three strains and the same wa s observed during the second exposure. When corticosterone levels afte r this second exposure to water was determined, LEW rats showed lower values than the other three strains. Therefore, no apparent relationsh ip between behavior and stress-induced corticosterone secretion exists . Although a single point measurement of only on physiological index o f stress has important limitations, the present data do not give suppo rt to a strong relationship between the behavior of the animals in the forced swimming test and emotional reactivity to stress. It is theref ore possible that forced swimming behavior might not be mainly a panic -like reaction, but the result of the tendency of the animals to adopt passive strategies in inescapable situations. Although more studies a re needed to firmly establish this assumption, WKY rats might be, at l east potentially, a useful model of depressive-like behavior.