Summary
We have tested the hypothesis that the avian pineal hormone, melatonin, which is produced in and secreted from the pineal body in a circadian temporal pattern is a chemical mediator which drives overt circadian functions. Pinealectomized European starlings (Sturnus vulgaris) kept in continuous dim light, received intramuscular injections of melatonin at the same time each day for several weeks. Control birds received only sesame oil injections. In 21 out of 22 birds, melatonin treatment resulted in the synchronization of locomotor activity with the 24 h injection rhythm. In contrast, activity of only one out of 10 control birds became synchronized with the daily control injections. These results are consistent with the hypothesis that the endogenous circadian rhythm of melatonin concentration provides an internal synchronizing agent, acting directly on other circadian oscillators. Alternatively, it seems possible that the exogenous rhythm exerts its effect indirectly by modifying the sleep-wake cycle.
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Dedicated to Professor Colin S. Pittendrigh on the occasion of his 60th birthday
This work was supported by the Deutsche Forschungsgemeinshaft. (SPP Biologie der Zeitmessung). We are grateful to Prof. A. Oksche for his help in evaluating the histological slides of brains from pinealectomized starlings. Prof. J. Aschoff, John Dittami, Prof. D.S. Farner and Dr. K. Hoffmann gave valuable comments on the manuscript.
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Gwinner, E., Benzinger, I. Synchronization of a circadian rhythm in pinealectomized European starlings by daily injections of melatonin. J. Comp. Physiol. 127, 209–213 (1978). https://doi.org/10.1007/BF01350111
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DOI: https://doi.org/10.1007/BF01350111