Day-night rhythms in opiate modulation of body temperature in male Japanese quail

Summary Male Japanese quail,Coturnix coturnix japonica, displayed day-night rhythms in their body temperature, with significantly higher temperatures during the day than at night. There were individual variations in both the temperatures attained and amplitude of the day-night rhythm of body temperature in the group-housed birds. Accompanying these diurnal patterns in body temperature there were day-night rhythms in the effects of intraperitoneal administrations of the opiate agonist, morphine (1.0 and 10 mg·kg^-1) and prototypic opiate antagonist, naloxone (10 mg·kg^-1) on colonic body temperature. In the daytime, the body temperature response profiles of quail treated with morphine were dependent on the initial body temperature of the bird. In those birds with the lower daytime body temperatures, morphine caused an initial hyperthermic response that was followed by a hypothermia and then a weak hyperthermia; whereas, in birds with the higher initial body temperatures there was a pronounced hypothermia followed by a marked hyperthermia. At night, morphine induced a hyperthermic response in all quail that was followed by a hypothermia. These effects of morphine were blocked by naloxone, with naloxone by itself significantly decreasing the daytime temperature of those quail with the higher initial body temperature. Naloxone had no significant effects on the nighttime body temperatures of any of the quail. These results show that there are day-night rhythms and individual differences in opiate sensitivity and modulation of body temperature in male quail. These findings also suggest that endogenous opioid systems are involved in either the generation and/or expression of the day-night rhythm of body temperature in quail.Abbreviations LD light-dark - T _L low initial body temperatures - T _H high initial body temperatures