PHARMACOLOGICAL CLASSICAL-CONDITIONING IN HUMANS

Two groups, each with five healthy male volunteers, received pairings of a distinct environment, the laboratory, with administrations of the muscle relaxant carisoprodol (CSP group), or pairings of the same env ironment with administrations of an inactive agent (control group). Th e control group received carisoprodol at home. This procedure was in e ffect in three sessions, each spaced 1 week apart. The CSP group recei ved an inactive agent in the fourth session, and the control group rec eived carisoprodol. The administration procedure was hypothesized to c onstitute a conditioned stimulus (CS) in the CSP group. The results sh owed that carisoprodol decreased blink reflex amplitude and duration. However, increased blink reflex amplitude was seen in the CSP group wh en the inactive agent was administered, which is opposite to the effec t of carisoprodol. This indicates that a drug-antagonistic conditioned response was elicited by the CS in the CSP group. Moreover, blink ref lex amplitude was increased in the CSP group compared to the control g roup when carisoprodol was administered, indicating that the antagonis tic conditioned response decreased the effect of carisoprodol. The res ults suggest a role for antagonistic conditioned responses in human dr ug tolerance. (C) 1997 John Wiley & Sons, Ltd.