Zeman M, Gwinner E, Herichová I, Lamosová D, Kost'ál L
Institute of Animal Biochemistry and Genetics, Slovak Academy of Sciences, Ivanka pri Dunaji.
J Pineal Res. 1999 Jan;26(1):28-34. doi: 10.1111/j.1600-079x.1999.tb00563.x.
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.
与哺乳动物的情况不同，哺乳动物松果体的昼夜节律性褪黑素分泌直到出生后的一段时间才开始，而在早成雏家禽中，松果体节律性的发育是一个胚胎期事件。在16:8光照:黑暗（LD）条件下饲养的19日龄鸡胚中发现了明显的褪黑素节律。在暴露于8:16 LD条件下的胚胎中未检测到褪黑素水平的显著变化。在12:12 LD条件下孵化18天的鸡胚的松果体和血浆中的褪黑素节律在持续黑暗中持续了2天，这表明褪黑素的分泌至少从胚胎末期开始就受到昼夜节律的控制。在胚胎后第一天暴露于LD周期1天就足以使褪黑素节律同步，并且先前胚胎期暴露于LD或持续黑暗（DD）既不会改变这种快速同步，也不会影响随后两天在DD中的褪黑素模式。有人提出，与哺乳动物的情况不同，鸟类胚胎已经进化出了自己早期的昼夜节律性褪黑素产生系统，因为由于其宫外发育，它无法利用其母体的系统。
