The procedures of chronic unpredictable mild stress (CUMS)

C57BL/6J juvenile mice were used to analyze the molecular profiles associated with major depression. The male mice were used starting at postnatal days 21 for making depression model. In week one for their adaptation to the experiments, the body weight, locomotion, sucrose preference and Y-maze tests of these mice were measured to select the healthy ones for our study. The mice of showing consistent values in these measurements were separated into two groups, CUMS and control, in order to reduce the variations among these mice. The control mice lived without the following stresses.

Based on depression risk factors, such as weaknesses in cognitive function, emotional regulation, social interaction skill, circadian and stress responses [36], we used chronic stress to produce depression-like mice in the following principle. The mice lived in stressful environment, made efforts to challenge these conditions and experienced defeat outcomes, which drove them to feel cognitive and emotional inabilities and in turn to be anhedonia and low self-esteem. The procedures for the CUMS mice include their adaptation, the CUMS and the behavioral tests [34].

The stressful environments included social isolation, tilted cage, empty cage, damp sawdust cage, restraint space, white noise, strobe light and circadian disturbance [1, 5, 37–39]. Except for the social isolation, these conditions were randomly selected to treat the mice in the manners of their separations or combinations every day. These treatments were applied about 1~14 hours in durations and 1~12 hours in intervals [34]. The duration and interval were unpredictable to the mice. The CUMS was sustained for three weeks until some of these mice expressed anhedonia and low self-esteem.