Circadian organization in the pigeon,Columba livia: the role of the pineal organ and the eye

The pineal organ of the house sparrow, Passer domesticus, is essential for persistence of the circadian locomotor rhythm in constant conditions. Upon removal of the pineal body, activity becomes arrhythmic. However, pinealectomy does not abolish the rhythm of locomotor activity in birds exposed to light-dark cycles. Pinealectomized birds are entrained by light cycles in much the same manner as are normal birds. Our data demonstrate that the pineal organ is a crucial component of the endogenous time-measuring system of the sparrow.

Transplantation of pineal tissue into the anterior chamber of the eye rapidly reestablishes rhythmicity in arhythmic pinealectomized sparrows and also transfers the phase of the donor bird's rhythm to the host. Thus, the transplanted pineal does not merely permit rhythmicity to be expressed but rather transfers an oscillation that controls the remainder of the circadian system and restores the capacity for self-sustained rhythmicity. Long-term recordings, during which sparrosw were exposed to various lighting conditions, demonstrate a remarkable similarity between the circadian system in normal birds and that in birds bearing pineal transplants.