Effects of nortriptyline treatment on learned helplessness in the rat.

Using an escape delay procedure previously shown to elicit behavioral deficits in mice exposed to uncontrollable shock, rats treated with inescapable but not escapable shock or no shock displayed comparable interference effects when tested in a two-way shuttle box 24 hr later. Treatment with 12.5 mg/kg nortriptyline for 4 or 6 days counteracted the escape deficits produced by inescapable shock while the 0 or 2 day administration regimens were without any appreciable effect. The finding that interference effects produced by inescapable shock were sensitive to sub-acute but not acute drug administration supports the utility of the learned helplessness model in evaluating potential antidepressant agents in experimental animals.