Soucy E, Wang Y, Nirenberg S, Nathans J, Meister M
Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Neuron. 1998 Sep;21(3):481-93. doi: 10.1016/s0896-6273(00)80560-7.
Current understanding suggests that mammalian rod photoreceptors connect only to an ON-type bipolar cell. This rod-specific bipolar cell excites the All amacrine cell, which makes connections to cone-specific bipolar cells of both ON and OFF type; these, in turn, synapse with ganglion cells. Recent work on rabbit retina has shown that rod signals can also reach ganglion cells without passing through the rod bipolar cell. This route was thought to be provided by electrical gap junctions, through which rods signal directly to cones and thence to cone bipolar cells. Here, we show that the mouse retina also provides a rod pathway bypassing the rod bipolar cell, suggesting that this is a common feature in mammals. However, this alternative pathway does not require cone photoreceptors; it is perfectly intact in a transgenic mouse whose retina lacks cones. Instead, the results can be explained if rods connect directly to OFF bipolar cells.
目前的认识表明，哺乳动物的视杆光感受器仅与ON型双极细胞相连。这种视杆细胞特异性双极细胞会兴奋所有无长突细胞，而所有无长突细胞会与ON型和OFF型的视锥细胞特异性双极细胞建立联系；反过来，这些视锥细胞特异性双极细胞会与神经节细胞形成突触。最近对兔视网膜的研究表明，视杆信号也可以不通过视杆双极细胞而直接到达神经节细胞。人们认为这条途径是由电突触提供的，视杆细胞通过电突触直接向视锥细胞发出信号，进而传递给视锥双极细胞。在此，我们表明小鼠视网膜也存在一条绕过视杆双极细胞的视杆细胞通路，这表明这是哺乳动物的一个共同特征。然而，这条替代通路并不需要视锥光感受器；在一种视网膜缺乏视锥细胞的转基因小鼠中，该通路完全完好无损。相反，如果视杆细胞直接与OFF双极细胞相连，那么这些结果就能得到解释。
