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Perinatal development of circadian melatonin production in domestic chicks
M Zeman1, E Gwinner, I Herichová
1Institute of Animal Biochemistry and Genetics, Slovak Academy of Sciences, Ivanka pri Dunaji. mzeman@ubgz.savba.sk
Insights
Avian embryos develop circadian melatonin production before hatching, unlike mammals. This embryonic system is crucial for precocial birds due to their external development.
Area of Science:
- Chronobiology
- Developmental Biology
- Avian Physiology
Background:
- Mammalian circadian melatonin production begins postnatally.
- Precocial avian development necessitates distinct embryonic adaptations.
Purpose of the Study:
- To investigate the onset and control of circadian melatonin production in avian embryos.
- To determine if melatonin rhythmicity is an embryonic event in domestic fowl.
Main Methods:
- Measuring melatonin levels in chick embryos (19-day-old) under different light:dark cycles (LD 16:8, LD 8:16).
- Assessing melatonin rhythm persistence in constant darkness (DD) after embryonic light exposure.
- Evaluating the entrainment of the melatonin rhythm after postembryonic light exposure.
Main Results:
- A distinct melatonin rhythm was observed in 19-day-old chick embryos under LD 16:8.
- No significant melatonin variation occurred under LD 8:16.
- Melatonin rhythmicity persisted for 2 days in DD in 18-day-old embryos, indicating embryonic circadian control.
- One day of light:dark exposure post-hatching rapidly entrained the melatonin rhythm.
Conclusions:
- Circadian melatonin production is an embryonic event in domestic fowl, unlike in mammals.
- The avian embryo possesses an intrinsic circadian melatonin system, essential for extrauterine development.
- This system is established early in embryonic life and is responsive to light cues.
Abstract:
In contrast to the situation in mammals, in which circadian melatonin production by the pineal gland does not begin until some time after birth, the development of pineal gland rhythmicity is an embryonic event in the precocial domestic fowl. A distinct melatonin rhythm was found in 19-d-old chick embryos maintained under light:dark (LD) 16:8. No significant variation in melatonin levels was detected in embryos exposed to LD 8:16. The melatonin rhythm in the pineal gland and plasma of chick embryos incubated for 18 d in LD 12:12 persisted for 2 d in constant darkness indicating that melatonin production is under circadian control at least from the end of embryonic life. A 1-d exposure to a LD cycle during the first postembryonic day was sufficient to entrain the melatonin rhythm, and previous embryonic exposure to either LD or constant darkness (DD) neither modified this rapid synchronization nor did it affect the melatonin pattern during the two subsequent days in DD. It is suggested that, in contrast to the situation in mammals, the avian embryo has evolved its own early circadian melatonin-producing system because, as a consequence of its extrauterine development, it cannot use the system of its mother.