Kenyon G T, Marshak D W
Department of Neurobiology and Anatomy, University of Texas Medical School, Houston 77225, USA.
Proc Biol Sci. 1998 May 22;265(1399):919-25. doi: 10.1098/rspb.1998.0379.
In primates, one type of retinal ganglion cell, the parasol cell, makes gap junctions with amacrine cells, the inhibitory, local circuit neurons. To study the effects of these gap junctions, we developed a linear, mathematical model of the retinal circuitry providing input to parasol cells. Electrophysiological studies have indicated that gap junctions do not enlarge the receptive field centres of parasol cells, but our results suggest that they make other contributions to their light responses. According to our model, the coupled amacrine cells enhance the responses of parasol cells to luminance contrast by disinhibition. We also show how a mixed chemical and electrical synapse between two sets of amacrine cells presynaptic to the parasol cells might make the responses of parasol cells more transient and, therefore, more sensitive to motion. Finally, we show how coupling via amacrine cells can synchronize the firing of parasol cells. An action potential in a model parasol cell can excite neighbouring parasol cells, but only when the coupled amacrine cells also fire action potentials. Passive conduction was ineffective due to low-pass temporal filtering. Inhibition from the axons of the coupled amacrine cells also produced oscillations that might synchronize the firing of more distant ganglion cells.
在灵长类动物中，一种视网膜神经节细胞，即伞状细胞，与无长突细胞（抑制性局部回路神经元）形成缝隙连接。为了研究这些缝隙连接的作用，我们构建了一个为伞状细胞提供输入的视网膜神经回路的线性数学模型。电生理研究表明，缝隙连接不会扩大伞状细胞的感受野中心，但我们的结果表明，它们对伞状细胞的光反应有其他贡献。根据我们的模型，耦合的无长突细胞通过去抑制增强了伞状细胞对亮度对比度的反应。我们还展示了两组位于伞状细胞突触前的无长突细胞之间的化学和电混合突触如何使伞状细胞的反应更短暂，从而对运动更敏感。最后，我们展示了通过无长突细胞的耦合如何使伞状细胞的放电同步。模型中伞状细胞的一个动作电位可以激发相邻的伞状细胞，但只有当耦合的无长突细胞也产生动作电位时才行。由于低通时间滤波，被动传导无效。耦合的无长突细胞轴突的抑制也产生了振荡，这可能使更远距离的神经节细胞放电同步。
