Naloxone prevents hyperthermia induced convulsions in the immature rat

There is increasing evidence suggesting that endogenous opioid peptides play a role both in temperature regulation and in the etiopathology of seizures. We have studied the effects of the opioid antagonist naloxone on hyperthermia-induced seizures in unrestrained 15 day old rat pups. Saline injected control animals exposed to an ambient temperature of 40 degrees C for one hr showed a gradual increase in body temperature reaching a maximum of 42 degrees C at 50 min of exposure; at this time, all animals had convulsions and 86% died. Animals pre-treated with 10 mg/kg naloxone reached a maximum core temperature of 41 degrees C after 60 min at 40 degrees C and no convulsions or deaths were observed. When animals were exposed for 60 min to a 27 degrees C environment, saline controls maintained their normal body temperature throughout the experiment, while 5 mg/kg naloxone produced a marked hyperthermic effect. These experiments suggest that endogenous opioids may play a role in both temperature adaptation and hyperthermia-induced seizures in the rat pup.