Antagonistic effects of psycholeptic drugs on stress-induced analgesia.

Stress-induced analgesia was significantly antagonized by naloxone and was dose-dependently reduced by diazepam, chlordiazepoxide, flurazepam, medazepam, nitrazepam, estazolam, phenobarbital, chlorpromazine, levomepromazine, haloperidol and propranolol. In contrast to psycholeptics, morphine substantially increased in threshold of nociceptive response in the post-stress session. Centrally acting muscle relaxants, tolperisone and carosiprodol had no substantial anti-stress effects. These results suggest that the stress-induced analgesia is probably mediated through endogenous opioids in the central nervous system. The approach used in our study provides a simple method for assessing the anti-stress action of psycholeptics.