Effects of a novel fentanyl derivative on drug discrimination and learningin rhesus monkeys

Three monkeys discriminated 1.78 mg/kg of mirfentanil while responding unde r a fixed-ratio 5 schedule of stimulus-shock termination. Two mirfentanil d erivatives, OHM3295 and OHM10579, substituted for mirfentanil in all subjec ts. However, other drugs produced variable effects among monkeys; for examp le, mu and kappa opioid agonists and clonidine substituted for mirfentanil on some occasions in two monkeys. Cocaine, amphetamine, and ketamine did no t substitute in any subject. Opioid antagonists did not attenuate the effec ts of mirfentanil. In monkeys responding under a repeated acquisition and p erformance procedure: errors increased only during the acquisition phase at doses of mirfentanil that decreased response rates. Thus, unlike fentanyl, the discriminative stimulus effects of mirfentanil do not appear to be med iated exclusively through opioid receptors. Finally, mirfentanil does not a ppear to disrupt complex behavioral processes. (C) 1999 Elsevier Science In c.