The circadian rhythm of thermoregulation in Japanese quail

Japanese quail exhibit a robust circadian rhythm in body temperature. This rhythm is readily entrainable by 24 h light-dark (LD) cycles and persists under constant conditions. Because both the pineal organ and the eyes have been implicated as major components of the circadian system of birds, the role of these organs in generating the rhythm of body temperature was investigated. Pinealectomy, when performed alone, had little effect on the body temperature rhythm of quail either under LD or under constant darkness (DD). Most birds subjected to optic nerve section alone remained rhythmic in DD although the robustness of the rhythm was decreased, and 25% became arrhythmic. Birds subjected to both pinealectomy and optic nerve section behaved similarly to birds subjected to optic nerve section alone. However, complete eye removal, when performed alone or in combination with pinealectomy, caused all birds to become arrhythmic in DD. The data support the hypothesis that the eyes are the loci of circadian pacemakers in quail that act, via both neural and hormonal outputs, to preserve the integrity of (self-sustaining or damped) circadian oscillators located elsewhere.