Vardi N, Smith R G
Department of Neuroscience, University of Pennsylvania, Philadelphia 19104, USA.
Vision Res. 1996 Dec;36(23):3743-57. doi: 10.1016/0042-6989(96)00098-3.
Retinal ganglion cells in the cat respond to single rhodopsin isomerizations with one to three spikes. This quantal signal is transmitted in the retina by the rod bipolar pathway: rod-->rod bipolar-->AII-->cone bipolar-->ganglion cell. The two-dimensional circuit underlying this pathway includes extensive convergence from rods to an AII amacrine cell, divergence from a rod to several AII and ganglion cells, and coupling between the AII amacrine cells. In this study we explored the function of coupling by reconstructing several AII amacrine cells and the gap junctions between them from electron micrographs; and simulating the AII network with and without coupling. The simulation showed that coupling in the AII network can: (1) improve the signal/noise ratio in the AII network; (2) improve the signal/noise ratio for a single rhodopsin isomerization striking in the periphery of the ganglion cell receptive field center, and therefore in most ganglion cells responding to a single isomerization; (3) expand the AII and ganglion cells' receptive field center; and (4) expand the "correlation field". All of these effects have one major outcome: an increase in correlation between ganglion cell activity. Well correlated activity between the ganglion cells could improve the brain's ability to discriminate few absorbed external photons from the high background of spontaneous thermal isomerizations. Based on the possible benefits of coupling in the AII network, we suggest that coupling occurs at low scotopic luminances.
猫的视网膜神经节细胞对单个视紫红质异构化反应会产生一到三个峰电位。这种量子信号在视网膜中通过视杆双极通路进行传递：视杆细胞→视杆双极细胞→AII无长突细胞→锥双极细胞→神经节细胞。该通路背后的二维回路包括从视杆细胞到AII无长突细胞的广泛汇聚、从一个视杆细胞到多个AII无长突细胞和神经节细胞的发散，以及AII无长突细胞之间的耦合。在本研究中，我们通过从电子显微镜照片重建几个AII无长突细胞及其之间的缝隙连接，并模拟有耦合和无耦合的AII网络，来探索耦合的功能。模拟结果表明，AII网络中的耦合可以：（1）提高AII网络中的信噪比；（2）提高单个视紫红质异构化击中神经节细胞感受野中心周边时的信噪比，因此在大多数对单个异构化做出反应的神经节细胞中也是如此；（3）扩大AII和神经节细胞的感受野中心；（4）扩大“相关场”。所有这些效应都有一个主要结果：神经节细胞活动之间的相关性增加。神经节细胞之间良好的相关活动可以提高大脑从自发热异构化的高背景中区分少量吸收的外部光子的能力。基于AII网络中耦合的可能益处，我们认为耦合发生在低暗视亮度下。
