Effect of inescapable tones on behavioral despair in Wistar rats

The present experiment investigated the potentially differential effects of presenting inescapable tones with progressively increasing or decreasing durations on performance in behavioral despair, an animal model of depression based on two forced swim tests. Groups of female Wistar rats (n=8 each) were exposed to 60 inescapable tones (2000 Hz, 120 dB) either in a series of increasing or decreasing durations. Duration of tone exposure was incrementally increased (from 1 to 10 s) or decreased (from 10 to 1 s) by 1 s every six trials. A third group (n=8) was kept in the experimental chamber for a similar period but not exposed to tones. Animals were exposed to a 15 min forced swim test a day after tone (or control) treatment, followed by a 5 min swim test 24 h later. Analyses were done on diving, jumping, head shakes, duration and time of onset of immobility for the two swim tests. Compared to controls, animals that received tone exposure displayed greater immobility in the second swim test, indicating aggravation of behavioral despair due to inescapable tones.