Pineal Influences on Circannual Cycles in European Starlings: Effects Through the Circadian System?

Abstract

The pineal organ plays a significant role in the control of circadian rhythms among passerine birds. In house sparrows (Passer domesticus), white-throated sparrows (Zono-trichia albicollisj and Java sparrows (Padda oryzivora) maintained in continuous dark-nness, pinealectomy has been shown to abolish the circadian rhythm of locomotor activity (Gaston and Menaker 1968, McMillan 1972, Ebihara and Kawamura 1980). In addition, the rhythm of body temperature disappeared in house sparrows following the same procedure (Binkley et al. 1971). In European starlings (Sturnus vulgaris), free-running locomotor activity rhythms became heavily disrupted after pineal removal (Gwinner 1978). Pinealectomy has affected circadian activity rhythms in the house sparrow even when entrained to a 24-h light-dark cycle (Gaston 1971, Laitman and Turek 1979). The results obtained from these and several other experiments are consistent with the hypothesis that the pineal organ contains a circadian pacemaker which drives overt circadian functions (Menaker and Zimmerman 1976, Takahashi and Menaker 1979).