Detection of serotonergic and noradrenergic antidepressants in the rat forced swimming test: the effects of water depth.

A new scoring technique is described that measures active behaviors of rats in the forced swimming test, a test that predicts antidepressant drug effects. The technique distinguishes the effects of selective serotonin reuptake inhibitors, which reduce immobility and increase swimming behavior, from selective norepinephrine reuptake inhibitors, which reduce immobility and increase climbing behavior. The magnitude of behavioral effects described for each drug (i.e., reduced immobility for both drugs, increased swimming for fluoxetine, increased climbing for desipramine) was greater when testing was conducted at the deeper 30-cm rather than the shallow 15-cm water depth. Results obtained with the technique demonstrate that selective serotonin reuptake inhibitors are not false negatives in the rat forced swimming test, as previously thought.