[Chronic psychogenic stress as a factor of formation depressive behavior in rats]

The problem of adequate animal model of depression still remains. In our experiments depression-like condition on white rats were reached by the chronic stressors of psychogenic nature. Stress was carried out in a modified shuttle chamber of active avoidance. At the very beginning of the study (the first stage of stress) an animal was forced to develop a reaction of active avoidance on metronome beats (2 Hz), later, after its fixation, the same reaction was developed on tone (500 Hz). Then simultaneous testing of two developed reactions of active avoidance was performed (the second stage of stress). The simultaneous testing of active avoidance in rats is a difficult task and on the first day of the experiment the number of the right answers doesn't exceed 5-30 % that is stable and does not reach the criteria (80-100%) on the antidepressant fluoxetine. At the second stage of stress, increased motor activity, duration and number of vertical supports, inter-signal transitions in rats, which is even more increased on the background of antidepressant flueksetine. At this stage, in the "open field - OF" test statistically significantly reduced motor and research activity (number of crossed squares) and latency of motor activity. Reduced mobility of the animals in tests of "forced swim - FST" and "tail suspension test - TST" was not statistically significant. After the long-term application of stressors (35-48 days, III stage of stress) animals showed decreased motor activity in the "OF" test, decreased mobility in "FST" and "TST", changes being statistically valid. All behavioral changes indicating depression-like condition in animals were normalized after per os administration of antidepressant Fluoxetine at doses of 40 mg/kg. For those that were in a two-week "rest" (eliminating stressors within 14 days) and did not receive pharmacological preparations, improvements were not observed.