Circadian Rhythms and Sleep Disorders Program, Neuroscience Institute, Morehouse School of Medicine; Atlanta, GA, USA.
J Glaucoma. 2013 Jun-Jul;22 Suppl 5(0 5):S49-50. doi: 10.1097/IJG.0b013e3182934bb4.
Melatonin in the mammalian eye is synthesized by the photoreceptors and its levels show a clear daily pattern with high levels at night and lower levels during the day. It is synthesized in the ciliary body and secreted into the aqueous humor with a pattern similar to what has been reported for the retina. It acts by interacting with a family of G-protein coupled receptors that are negatively coupled with adenylate cyclase. Melatonin receptor subtypes MT1 and MT2 have been identified in the retina. Both are found in the inner nuclear layer (horizontal and amacrine cells), in the inner plexiform layer, ganglion cells (RGC) and retinal pigmented epithelium. They are also present in the ciliary body. Several studies implicate melatonin in the rhythmic regulation of intraocular pressure. MT1 and MT2 melatonin receptors are expressed in many parts of the eye. Melatonin receptors are expressed in the iris and ciliary body. Recent studies showed that mice lacking MT1 receptors have elevated intraocular pressure during the night and show a significantly reduced number of RGCs. These new studies suggest that dysfunctional melatonin signaling may be considered a possible risk factor in the pathogenesis of glaucoma and that mice deficient in MT1 receptors may be an animal model of glaucoma.
哺乳动物眼中的褪黑素由光感受器合成，其水平呈现出明显的日周期模式，夜间水平较高，白天水平较低。褪黑素在睫状体合成，并以与视网膜报道相似的方式分泌到房水中。它通过与一组与腺苷酸环化酶负耦联的 G 蛋白偶联受体相互作用而发挥作用。在视网膜中已经鉴定出褪黑素受体亚型 MT1 和 MT2。两者都存在于内核层（水平和无长突细胞）、内丛状层、节细胞（RGC）和视网膜色素上皮中。它们也存在于睫状体中。多项研究表明褪黑素参与了眼内压的节律调节。MT1 和 MT2 褪黑素受体在眼睛的许多部位表达。褪黑素受体在虹膜和睫状体中表达。最近的研究表明，缺乏 MT1 受体的小鼠在夜间眼内压升高，并显示出明显减少的 RGC 数量。这些新的研究表明，褪黑素信号功能障碍可能被认为是青光眼发病机制中的一个潜在危险因素，并且缺乏 MT1 受体的小鼠可能是青光眼的动物模型。
