Steele Christopher T, Tosini Gianluca, Siopes Thomas, Underwood Herbert
Department of Zoology, North Carolina State University, Raleigh, NC 27695, USA.
Gen Comp Endocrinol. 2006 Feb;145(3):232-6. doi: 10.1016/j.ygcen.2005.09.004. Epub 2005 Nov 8.
Previous studies have shown that eye removal disrupts the circadian body temperature and activity rhythms of Japanese quail supporting the hypothesis that the eyes act as pacemakers within the quail circadian system. Furthermore, the putative ocular pacemakers are coupled to the rest of the circadian system via neural and hormonal outputs. Although the neural pathway has yet to be identified, experiments suggest that the daily rhythm of ocular melatonin synthesis and release is the hormonal output. We sought to strengthen the hypothesis that the eyes are the loci of circadian pacemakers, and that melatonin output is involved, by examining melatonin secretion in cultured quail retinas. Using an in vitro flow-through system we demonstrated that (1) isolated retinal tissue could exhibit a rhythm of melatonin release, (2) the rhythm of melatonin synthesis is directly entrainable by 24-h light-dark cycles, and (3) supplementation of the culture medium with serotonin is necessary for robust, rhythmic production of melatonin in constant darkness. These results show definitively that the eyes are the loci of a biological clock and, in light of previous studies showing the disruptive effects of blinding on the circadian system, strengthen the hypothesis that the ocular clock is a circadian pacemaker that can affect the rest of the circadian system via the cyclic synthesis and release of melatonin. The quail retina is proving to be a valuable in vitro model for investigating properties of circadian pacemakers.
先前的研究表明，摘除眼球会扰乱日本鹌鹑的昼夜体温和活动节律，这支持了眼球在鹌鹑昼夜节律系统中充当起搏器的假说。此外，假定的眼部起搏器通过神经和激素输出与昼夜节律系统的其他部分相连。尽管神经通路尚未确定，但实验表明，眼部褪黑素合成和释放的每日节律是激素输出。我们试图通过检测培养的鹌鹑视网膜中的褪黑素分泌，来强化眼球是昼夜起搏器的位点且褪黑素输出参与其中的假说。使用体外流通系统，我们证明了：（1）分离的视网膜组织能够呈现褪黑素释放节律；（2）褪黑素合成节律可被24小时明暗周期直接调节；（3）在持续黑暗条件下，向培养基中添加血清素对于褪黑素的稳定节律性产生是必要的。这些结果明确表明，眼球是生物钟的位点，并且鉴于先前的研究表明致盲对昼夜节律系统有破坏作用，强化了眼部生物钟是一个昼夜起搏器的假说，它可通过褪黑素的周期性合成和释放来影响昼夜节律系统的其他部分。鹌鹑视网膜正被证明是研究昼夜起搏器特性的一种有价值的体外模型。
