EVALUATION OF DEPRESSION IN RATS EXPOSED TO CHRONIC (UNPREDICTABLE) ELECTRIC-SHOCK

The present study was undertaken to evaluate the applicability of a pr oposed behavioral stress paradigm as an animal model for depression. R ats were trained to press a lever under a fixed ratio (FR) 5 schedule in a Skinner box for 10 days and were subsequently exposed to a daily regimen of 20 cycles of FR 5 and 10 cycles of variable ratio (VR) 10 f or about a week. This exposure resulted in a reduction of the number o f lever presses and successful escapes compared to the level achieved after training. In addition, weight gain was significantly suppressed compared with other treatments. Acute and chronic administration of ps ychotropic drugs (imipramine and chlordiazepoxide) showed that treatme nt with imipramine increased both the number of lever presses and succ essful escapes while chlordiazepoxide increased only the number of lev er presses. The results suggest that this simplified animal model util izing chronic unpredictable electric shock may be useful in the study of human depression.