The role of endogenous opioids in footshock-induced hyperthermia

Either opioid or nonopioid forms of stress-induced analgesia can be elicited depending on the intensity or duration of the stressor. Several forms of stress have also been shown to cause hyperthermia in the rat. The present study investigated whether opioid and nonopioid forms of such stress-induced hyperthermia can be elicited in the rat as a function of footshock current intensity. Rats were given footshock after pretreatment with saline or naltrexone, or chronic morphinization. Footshock produced hyperthermia, the degree of which was found to be a function of current intensity. While the peak rise in temperature was not affected by naltrexone or chronic morphine administration, the rate of return to baseline temperature was slowed by these treatments. Thus, the endogenous opioid system appears to be involved in the return to normal body temperature following footshock, but not in the footshock-induced rise in temperature.