"Swimming-induced head twitching" in rats in the forced swimming test induced by overcrowding stress: a new marker in the animal model of depression?

We have used overcrowding stress to study the pathogenesis of depression and the action of antidepressant drugs. In the present study, the influence of overcrowding on behavior was assessed by the forced swimming test. All the stressed rats revealed highly characteristic head twitching movement, which was not inhibited by repeated administration of diazepam and haloperidol, but was markedly suppressed by repeated administration of desipramine and mianserine. A significant positive correlation in the number of twitching episodes in each stressed rat between the first and second forced swimming test was seen. These findings support the use of overcrowding of rats as a stressor in the animal depression model because it fulfills the criteria of the model; face validity, construct validity and predictive validity. We propose the adoption of "swimming head twitching" as a new marker in the animal model of depression.