Induction and Evaluation of Depression in Mice Through Chronic Stress Exposure

All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.  

1. Preparing Mice for the Experimental Procedure

NOTE: For the experimental procedure, healthy male C57BL/6J mice aged 12 weeks were selected, with each mouse weighing between 18 and 22 g.

1. Keep mice individually in cages in a typical Specific Pathogen Free (SPF) laboratory animal room (22 ± 1 °C, 12 h/12 h dark/light cycle, relative humidity: 30–40%) for one week before the CUMS procedure.
2. Randomly divide all mice into a control group and a model group according to their body weight. Each group has 15 mice.
3. Before the initiation of the experiment, number the mice in each group on their tail using a marking pen.

2. Induction of Depression in Mice

NOTE: To induce depression, the mice in the model group and two treatment groups underwent chronic unpredictable mild stress (CUMS) for 21 days. The plan can be changed according to the practical situation, but the principle that the same stressor cannot be used continuously should be followed.

1. Expose mice daily to any two of the following seven stressors for 21 consecutive days. Our modeling plan is designed as follows:
   1. On Monday, expose mice to food deprivation (empty the feed of each cage for 24 h, 8:00 a.m. to 8:00 a.m.) and water deprivation (remove the drinking bottle of each cage for 24 h, 8:00 a.m. to 8:00 a.m.).
   2. On Tuesday, expose mice to restraint stress (restrain mice in a small plastic tub for 3 h, 8:00 a.m. to 11:00 a.m.) and empty cages (remove the padding in each cage for 11 h, 8:00 a.m. to 19:00 p.m.).
   3. On Wednesday, expose mice to wet and soiled cages (pour water into each cage and keep wet for 24 h, 8:00 a.m. to 8:00 a.m.) and crowded cages (put five mice in one cage for 24 h, 8:00 a.m. to 8:00 a.m.).
   4. On Thursday, expose mice to restraint stress and ice-cold swimming (force each mouse to swim in a clear glass aquarium with ice water for 5 min).
   5. On Friday, expose mice to wet and soiled cages and food deprivation.
   6. On Saturday, expose mice to restraint stress and crowded cages.
   7. On Sunday, expose mice to empty cages and ice-cold swimming.
2. Record the coat state and body weight weekly until the end of modeling (day 21). Calculate the total score of the coat state as the sum of scores from seven different body parts: head, neck, dorsal coat, ventral coat, forepaws, tail, and hind paws. A score of one indicates a well-groomed coat, and a score of zero indicates an unkempt coat.