Heat and other physiological stress-induced analgesia: Catecholamine mediated and naloxone reversible response

Acute environmental heat (40±2°C) and other physiological stressful situations increased the pain threshold to radiant heat in rats and mice. Naloxone pretreatment or chronic exposure to stress antagonised this response. After pretreatment with catecholamine depleters, α-methyl-p-tyrosine, reserpine or with adrenoceptor blockers, haloperidol and chlorpromazine, the stress-induced analgesic effect was abolished. Cyproheptadine, a serotonin antagonist, also blocked this response. The results suggest the role of brain monoamines in stress-mediated analgesia.