INDIVIDUAL-DIFFERENCES IN VULNERABILITY TO INESCAPABLE SHOCK IN RATS

The present study determined whether individual differences in neophob ia during an open-field pretest predict vulnerability to inescapable e lectric shock, as measured by 2 tests of learned helplessness in rats. Shuttle-escape latencies and saccharin finickiness increased across g roups that had received increasing numbers of inescapable shocks 24 hr earlier. Dispersion in the test measure as well as the percentage of variance explained by pretest neophobia were greater when no or few sh ocks were delivered in the interpolated stress phase. Pretest neophobi a was positively related to stress vulnerability in both tests under t hese conditions. Further increments in stressor severity overwhelmed e ven the most stress-resistant rats, thereby decreasing dispersion in t he test measure and eliminating the predictive value of pretest neopho bia. This pattern of outcomes was more robust for the shuttle-escape m easure of helplessness.