视觉信息在视网膜中传递和调控

TRANSMISSION AND MODULATION OF VISUAL SIGNAL IN THE RETINA

视觉信息在视网膜中传递和调控杨雄里（中国科学院，上海生理研究所，上海生命科学联合开放实验室，上海２００３１）光感受器（视杆和视锥）信号在视网膜中是通过各种信息通道（ｃｈａｎｎｅｌ）进行传递的。这些通道包括：视杆一视锥通道，颜色信号通道，给光一撤光（Ｏ...

Abstract We have studied how photoreceptor signals are modulated by darkness, illumination and chemicals while being transmitted through a variety of channels-channels for rod and cone signals, ON-OFF channels and channels for chromatic signals inthe carp retina, using electrophysiological and pharmacological techniques.After prolonged darkness, cone-driven horizontal cells are strongly suppressed (dark suppression effect), while roddriven horizontal cells maintain high light responsiveness. This result suggests that the cone pathway is suppressed by prolonged darkness and it requires background illumination to maintain high light responsiveness of the cone pathway. Moreover, input from red-sensitive cones converging onto the cone horizontal cells is more significantly suppressed after prolonged dark adaptation than input from green-sensitive cones. We have demonstrated that dopamine released by the interplexiform cells may be involved in the dark suppression of the cone pathway.It is further found that cobalt ions of low concentrations (10-30 μmol/L) selectively suppress the rod horizontal cells,but without affecting the cone horizontal cells. The cobalt effect is unlikely due to the blockade of calcium channels at therod terminals. Since β-hydroxyaspartate, a blocker of glutamate transporters, mimics the low cobalt effect on horizontalcells, inactivation of glutamate transporters at the rod terminals by cobalt ions might be involved in the above-suppression.Furthermore, GABA is found to completely suppress the off-responses of ON-OFF transient amacrine cells, but unaffect the ON responses. GABA application also suppresses the initial transients of the OFF bipolar cell responses, which isthought to be responsible for the generation of the amacrine cell OFF responses. Using the whole cell clamp technique, wehave shown that GABA induced an inward current from bipolar cell terminals. The GABA response is completely blocked bypicrotoxin, but not by bicuculline, an indication of the presence of the novel GABAc receptor at the bipolar cell terminals. Inconsequence, GABA released by amacrine cells may be involved in the selective suppression of the OFF pathway through reciprocal synapses between bipolar and amacrine cells.