EFFECTS OF MIDAZOLAM AND NALOXONE IN RATS TESTED FOR SENSITIVITY REACTIVITY TO FORMALIN PAIN IN A FAMILIAR, NOVEL OR AVERSIVELY CONDITIONEDENVIRONMENT/

Rats tested for sensitivity/reactivity to formalin-induced pain in eit her an aversively conditioned or a novel environment displayed immedia te but transient hypoalgesic responses that were insensitive to either a benzodiazepine (midazolam) or an opioid antagonist (naloxone). Expo sure to the aversively conditioned, but not to the novel environment a lso provoked a more enduring hypoalgesic response that was abolished b y either midazolam or naloxone. The results were taken to mean that fe ar is sufficient but not necessary for the production of hypoalgesic r esponses to environmental stimuli.