Effect of melatonin on circadian rhythm, locomotor activity and body temperature in the intact house sparrow, Japanese quail and owl

We compared the effect of melatonin on circadian rhythm, body temperature, and locomotion in the intact house sparrow, Japanese quail and owl. Daily t reatment with melatonin at a fixed time did not entrain the free-running rh ythm of locomotor activity in the house sparrow and the disrupted rhythm in Japanese quail under constant dim light. However, melatonin clearly inhibi ted movement for several hours after treatment. The duration of resting aft er injection of melatonin was dose-dependent. Body temperature was signific antly decreased after melatonin treatment, the effect being more potent dur ing the active phase than in the resting phase. Although this effect of mel atonin on body temperature was also dose-dependent, the magnitude of the de crease in body temperature after injection of melatonin was greater in the house sparrow than in the Japanese quail. On the other hand, melatonin indu ced a further large decrease of body temperature in a nocturnal bird, the o wl, whose pineal gland is degenerate. The decrease of body temperature was larger in the active phase than in the resting phase, and melatonin did not prevent movement in spite of the decrease in body temperature. These resul ts suggest that the effects of melatonin on circadian rhythm, locomotor act ivity and body temperature differ among avian species, and that these mecha nisms may not be linked to each other. (C) 2001 Elsevier Science B.V. All r ights reserved.