Department of Animal Physiology and Ethology, Faculty of Natural Sciences, Comenius University, Bratislava, Slovak Republic.
Gen Comp Endocrinol. 2011 May 15;172(1):23-30. doi: 10.1016/j.ygcen.2010.12.022. Epub 2011 Jan 1.
The development of circadian rhythmicity of melatonin biosynthesis in the pineal gland starts during embryonic period in birds while it is delayed to the postnatal life in mammals. Daily rhythms of melatonin in isolated pinealocytes and in intact pineal glands under in vivo conditions were demonstrated during the last third of embryonic development in chick embryos, with higher levels during the dark (D) than during the light (L) phase. In addition to the LD cycle, rhythmic temperature changes with the amplitude of 4.5°C can entrain rhythmic melatonin biosynthesis in chick embryos, with higher concentrations found during the low-temperature phase (33.0 vs 37.5°C). Molecular clockwork starts to operate during the embryonic life in birds in line with the early development of melatonin rhythmicity. Expression of per2 and cry genes is rhythmic at least at day 16 and 18, respectively, and the circadian system operates in a mature-like manner soon after hatching. Rhythmic oscillations are detected earlier in the central oscillator (the pineal gland) than in the peripheral structures, reflecting the synchronization of individual cells which is necessary for detection of the rhythm. The early development of the circadian system in birds reflects an absence of rhythmic maternal melatonin which in mammals synchronizes physiological processes of offspring. Developmental consequences of modified development of circadian system for its stability later in development are not known and should be studied.
松果腺中褪黑素生物合成的昼夜节律的发展在鸟类胚胎期开始，而在哺乳动物中则延迟到产后生活。在鸡胚胚胎发育的最后三分之一期间，在分离的松果体细胞和在体内条件下的完整的松果腺中证明了褪黑素的日周期，其在黑暗（D）期比在光（L）期更高。除了 LD 周期外，具有 4.5°C 幅度的节律性温度变化可以使鸡胚中的褪黑素生物合成产生节律性，在低温阶段（33.0 与 37.5°C）发现更高的浓度。在鸟类的胚胎生命中，分子时钟开始与褪黑素节律性的早期发育一起运行。per2 和 cry 基因的表达至少在第 16 天和第 18 天具有节律性，并且昼夜节律系统在孵化后不久以成熟的方式运行。在中央振荡器（松果腺）中比在周围结构中更早地检测到节律性摆动，反映了单个细胞的同步性，这对于检测节律性是必要的。鸟类昼夜节律系统的早期发育反映了没有节律性的母体褪黑素，而在哺乳动物中，母体褪黑素使后代的生理过程同步。后来在发育过程中，对昼夜节律系统发育的改变对其稳定性的发展后果尚不清楚，应该进行研究。
