Antidepressants reduce inactivity during both inescapable shock administration and shuttle-box testing.

The occurrence of inactivity during inescapable shock is a good predictor of escape deficit because a positive correlation was obtained between the two factors. Chronic desipramine (DMI) administration prior to inescapable shock clearly reduced the inactivity during this aversive experience. Moreover, repeated DMI administration either before or after inescapable shock reversed the increase, in escape failures and in inactivity during shuttle-box testing produced by this inescapable shock. A single injection with DMI before either inescapable shock or shuttle-box test altered neither inactivity nor escape deficit. Clomipramine and phenelzine were also effective to reduce inactivity and escape failures. However, other drugs without antidepressant properties, such as haloperidol, amphetamine, and diazepam reduced neither inactivity nor escape deficit. These data suggest that an anti-inactivity effect is critically involved in the reversal of inescapable shock-induced escape deficit following chronic antidepressants. The involvement of antidepressant-induced changes in beta-adrenoceptors with this behavioral reversal is discussed.