Long-term colony housing in Long Evans rats: immunological, hormonal, and behavioral consequences

The distribution pattern and the function of blood immune cells were invest igated for 10 weeks in three mixed-sex colonies of Long Evans rats. After c olony formation, a despotic dominance system was established between the ma les. This paper focuses on differences between subdominant colony and pair- housed control males. A reduced body mass development and hormonal status i n subdominant males indicate stressful colony conditions. Subdominant males had lower numbers of CD4 and CD8 T cells, pronounced granulocytosis and re duced lymphocyte proliferation rates as compared with controls. The persist ency of changes in subdominant males offers the opportunity to investigate the effects of long-term immune-modulation on health. (C) 2001 Elsevier Sci ence B.V. All rights reserved.