Effects of unpredictable chronic mild stress on anxiety and depression-like behavior in mice.

The widely accepted stress-diathesis hypothesis of depression postulates that genetic factors contribute to biological vulnerability. Based on this concept, the unpredictable chronic mild stress (UCMS) animal model was developed. Most effects of UCMS can be reversed by antidepressant agents, illustrating a strong predictive validity. In rodents, UCMS also has good face validity as it can elicit depression-like symptoms. While abundant for rats, the UCMS literature on mice is relatively limited. Reports sometimes are contradictory, making it difficult to establish a clear profile of stress-induced depression-like behaviors in mice. As different groups often use different strains for their experiments, differential strain susceptibility to UCMS may provide at least a partial explanation of these discrepancies. Moreover, differences in testing methodology add another level of complexity. Very little is known about the role of genetic factors and their interactions with the environment in the development of stress-induced behavioral changes relevant to depression, though recent studies unequivocally demonstrated the effects of specific gene polymorphisms on stress-induced depressive symptoms, as well as the effects of stress on gene expression. In the present study, we investigated the effects of UCMS on a battery of different tests measuring anxiety and depression-like behaviors in three behaviorally and genetically distinct inbred strains. The goals of these experiments are to obtain a clearer behavioral profile of genetically/phenotypically distant mouse strains after UCMS treatment and to evaluate the limitations and strengths of the UCMS model in mice.