Sekaran S, Lupi D, Jones S L, Sheely C J, Hattar S, Yau K-W, Lucas R J, Foster R G, Hankins M W
Department of Visual Neuroscience, Division of Neuroscience and Mental Health, Imperial College London, Charing Cross Hospital Campus, London, W6 8RF, United Kingdom.
Curr Biol. 2005 Jun 21;15(12):1099-107. doi: 10.1016/j.cub.2005.05.053.
The visual system is now known to be composed of image-forming and non-image-forming pathways. Photoreception for the image-forming pathway begins at the rods and cones, whereas that for the non-image-forming pathway also involves intrinsically photosensitive retinal ganglion cells (ipRGCs), which express the photopigment melanopsin. In the mouse retina, the rod and cone photoreceptors become light responsive from postnatal day 10 (P10); however, the development of photosensitivity of the ipRGCs remains largely unexplored.
Here, we provide direct physiological evidence that the ipRGCs are light responsive from birth (P0) and that this photosensitivity requires melanopsin expression. Interestingly, the number of ipRGCs at P0 is over five times that in the adult retina, reflecting an initial overproduction of melanopsin-expressing cells during development. Even at P0, the ipRGCs form functional connections with the suprachiasmatic nucleus, as assessed by light-induced Fos expression.
The findings suggest that the non-image-forming pathway is functional long before the mainstream image-forming pathway during development.
现在已知视觉系统由成像和非成像通路组成。成像通路的光感受始于视杆细胞和视锥细胞，而非成像通路的光感受还涉及表达光色素黑视蛋白的内在光敏视网膜神经节细胞（ipRGCs）。在小鼠视网膜中，视杆和视锥光感受器从出生后第10天（P10）开始对光产生反应；然而，ipRGCs光敏感性的发育在很大程度上仍未得到探索。
在这里，我们提供了直接的生理学证据，表明ipRGCs从出生时（P0）就对光有反应，并且这种光敏感性需要黑视蛋白的表达。有趣的是，P0时ipRGCs的数量是成年视网膜中的五倍多，这反映出发育过程中表达黑视蛋白的细胞最初过度产生。即使在P0时，通过光诱导的Fos表达评估，ipRGCs也与视交叉上核形成功能性连接。
这些发现表明，在发育过程中，非成像通路在主流成像通路之前很久就开始发挥作用。
