compounds with opioid mu antagonist effects under other conditions ( e.g. , nalorphine ) substituted for naltrexone whereas a wide variety of opioid agonists ( e.g. , morphine , u-50,488 and butorphanol ) as well as nonopioids ( e.g. , pentobarbital and ketamine ) produced responding predominantly on the saline lever .
C1373059
opioid agonists
C0006491
butorphanol