Dkhissi-Benyahya Ouria, Rieux Camille, Hut Roelof A, Cooper Howard M
Institut National de la Santé et de la Recherche Médicale (INSERM) U371, Cerveau et Vision, Department of Chronobiology, Bron, France.
Invest Ophthalmol Vis Sci. 2006 Apr;47(4):1636-41. doi: 10.1167/iovs.05-1459.
Melanopsin, expressed in a subset of intrinsically photosensitive ganglion cells that project to the suprachiasmatic nucleus (SCN), is involved in the photic entrainment of circadian rhythms and other non-image-forming functions (pupil light reflex, masking, acute heart rate response, and alertness). Melanopsin has recently been shown to be a "bireactive" photopigment that functions as a photosensory opsin using 11-cis retinaldehyde as a chromophore and has intrinsic photoisomerase activity. Melanopsin is widely distributed in the retina of vertebrates and, depending on the species, is expressed in ganglion, amacrine, horizontal, and photoreceptor cells. The present study was conducted to determine the distribution of this opsin in the human retina.
Human donor eyes were obtained from donors and fixed shortly after death. Immunohistochemistry was used to determine melanopsin expression in the retinas of three donors. The possible coexpression of this photopigment with other opsins was studied by double-labeling immunocytochemistry and confocal analysis.
In addition to the expected labeling in ganglion cells of the inner retinal layers, an unexpected finding showed melanopsin-immunopositive label in the outer segments of cones that did not coexpress other known opsins. These melanopsin-expressing cones are extremely sparse (5-25 cones/mm2; 0.1%-0.5% of the entire cone population) and are located in the peripheral retina.
The presence of melanopsin in human cones suggests image and non-image-forming roles in visual responses at both the cone input and ganglion cell output stages and their involvement in a broad spectrum of irradiance detection functions in the visual system.
黑视蛋白表达于一小部分向视交叉上核（SCN）投射的内在光敏神经节细胞中，参与昼夜节律的光调节及其他非成像功能（瞳孔对光反射、掩盖效应、急性心率反应和警觉性）。最近研究表明，黑视蛋白是一种“双反应性”光色素，作为一种光感觉视蛋白发挥作用，以11-顺式视黄醛作为发色团，并且具有内在的光异构酶活性。黑视蛋白广泛分布于脊椎动物的视网膜中，根据物种不同，在神经节细胞、无长突细胞、水平细胞和光感受器细胞中表达。本研究旨在确定这种视蛋白在人视网膜中的分布。
从供体获取人供体眼，并在死后不久进行固定。采用免疫组织化学方法确定三名供体视网膜中黑视蛋白的表达。通过双重标记免疫细胞化学和共聚焦分析研究这种光色素与其他视蛋白的可能共表达情况。
除了在内侧视网膜层的神经节细胞中出现预期的标记外，一个意外发现是在不共表达其他已知视蛋白的视锥细胞外段中发现了黑视蛋白免疫阳性标记。这些表达黑视蛋白的视锥细胞极其稀少（5 - 25个视锥细胞/平方毫米；占整个视锥细胞群体的0.1% - 0.5%），且位于周边视网膜。
人视锥细胞中存在黑视蛋白表明其在视锥细胞输入和神经节细胞输出阶段的视觉反应中兼具成像和非成像功能，并参与视觉系统广泛的辐照度检测功能。
