RO 15-1788 produces naloxone-reversible analgesia in the rat

Intraperitoneal and intracerebroventricular administration of the benzodiazepine antagonist RO 15-1788 produced analgesia to both thermal and mechanical pain. This effect was reversed by pretreatment with the opioid antagonist naloxone but was unaffected by pretreatment with the benzodiazepine agonist midazolam. Furthermore, administration of the benzodiazepine antagonist RO 15-3505 was without analgesic effect. It is, therefore, proposed that the intrinsic action induced by RO 15-1788 is exerted via the indirect activation of endogenous opioid systems and that the observed effect is not due to the action of the antagonist on the benzodiazepine receptor.