Diazepam modulation of stress-induced analgesia depends on the type of analgesia.

Factors that determine the impact of diazepam on the hypoalgesia produced by electric shocks were investigated. Tailshocks (1, 5, & 20) were followed by an initial hypoalgesia, lasting 2-4 min, that was unaffected by prior administration of diazepam. This hypoalgesic reaction was followed by a second hypoalgesia if subjects were allowed to remain in the shock environment during testing, and this reaction was reduced or eliminated by prior diazepam. If subjects were removed from the shock situation, this second reaction did not occur. In contrast, 80 shocks were followed by a single hypoalgesia that was sensitive to blockade by diazepam throughout its entire course and was not affected by removing subjects from the shock environment. These results have implications for the perceptual-defensive-recuperative, working memory, and unconditioned response-learned helplessness interpretations of shock-produced analgesia.