EFFECTS OF HOUSING ON MALE AND FEMALE RATS - CROWDING STRESSES MALES BUT CALMS FEMALES

Housing conditions affect behavioral and biological responses of anima ls. Effects of same-sex grouped, crowded, or individually housed condi tions on plasma corticosterone levels of male and female Wistar rats w ere examined in two experiments. Experiment 1 examined the effects of individual vs. crowded housing conditions on corticosterone, a biochem ical index of stress, in seven male and seven female rats. Experiment 2 extended the findings of Experiment 1 by separately manipulating spa tial and population aspects of housing with 50 male and 50 female rats . Male rats had higher corticosterone levels under crowded conditions. In contrast, female rats had higher levels when individually housed. Spatial crowding was the key variable for males, whereas the number of other animals was more important for females. These results indicate that investigators must consider housing conditions as an intervening variable that is likely to differentially affect behaviors of male and female rats.