Blockade of the development of analgesic tolerance to morphine by psychological stress through benzodiazepine receptor mediated mechanism.

beta-Carboline-3-carboxylic acid ethyl ester (beta-CCE) dose-dependently potentiated psychological-stress induced analgesia (PSY-SIA), and the effect was reversed by diazepam. Concurrent exposure to PSY stress or concomitant treatment with beta-CCE blocked the development of analgesic tolerance to morphine; the effect of PSY stress was antagonized by diazepam, and that of beta-CCE was reversed by Ro 15-1788. These results suggest that psychological factors which are mediated through benzodiazepine receptors are involved in the mechanism for blocking the development of analgesic tolerance to morphine by PSY stress.