Effects of meperidine on operant behavioral thermoregulation in mice under conditions of symmetrical thermal drive.

The effects of meperidine on operant behavioral thermoregulation were investigated using a convective thermal controller and mice trained to alternate at will the thermal-drive condition, changing it from an air flow of 15 degrees C to one of 45 degrees C, and vice versa. Administration of 15 mg/kg meperidine resulted in significantly lower response rates, a significantly larger fraction of time spent in one (mostly cold) drive condition, and significantly lower body temperatures than administration of saline. In a second experiment the animal was automatically returned to the hot-drive condition every 3 min unless it had been exposed to this condition in the previous 0.4 min although otherwise it remained free to alternative drive conditions at will. Under these conditions, meperidine-treated animals also spent significantly more time in cold drive and had significantly lower body temperatures than control animals, in spite of lower response rates. Pretreatment with 4.5 mg/kg tranylcypromine (4 h prior) did not significantly alter the effects of meperidine administration in either experiment.