The effects of dl- p-chlorophenylalanine on learned helplessness in the rat

Abstract

Experiment I investigated the replicability of the learned helplessness effect. For 1 hr, one group of Long—Evans hooded rats was exposed to a series of inescapable 4.0-mA electric shocks in a restraining tube. Control subjects were simply restrained in the tube. Twenty-four hours later, all animals received 20 trials of shock—escape in a two-way shuttle-box. Animals which received prior inescapable shock were significantly slower in escaping from shock than were controls, replicating the learned helplessness effect. Experiment II examined the effect of p -chlorophenylalanine-induced depletion of brain serotonin (5-HT) levels on the learned helplessness effect. Thirty-two rats were randomly assigned to treatment conditions in a 2 × 2 factorial design: inescapable shock versus no-shock pretreatment and drug plus vehicle versus vehicle. Forty-eight hours after pretreatment with drug plus vehicle or vehicle, animals received inescapable shock or no-shock pretreatment and were tested 24 hr later for shock—escape in a two-way shuttle-box. PCPA pretreatment increased the subject's reactivity to shock but had no effect upon the learned helplessness phenomenon.