Cook P B, McReynolds J S
Department of Physiology, The University of Michigan, Ann Arbor, Michigan 48109-0622, USA.
J Neurophysiol. 1998 Jan;79(1):197-204. doi: 10.1152/jn.1998.79.1.197.
Two functionally and anatomically distinct types of lateral inhibition contribute to the receptive field organization of ganglion cells in the vertebrate retina: sustained lateral inhibition (SLI), which is present during steady illumination and transient lateral inhibition (TLI), evoked by changes in illumination. We studied adaptive changes in these two lateral inhibitory mechanisms in the mudpuppy retina by measuring the responses of ON-OFF ganglion cells to spots of light in the receptive field center, in the absence and presence of a concentric broken annulus (windmill) pattern, which was either stationary or rotating. SLI was measured as the percent suppression of the centered spot response by the stationary windmill and TLI was measured as the additional suppression produced when the windmill was rotating. In dark-adapted retinas SLI was elicited by windmills of 600 or 1,200 micron ID, but TLI could not be elicited by windmills of any size, over a wide range of windmill intensities and rotation rates. Exposure of dark-adapted retinas to diffuse adapting light caused an immediate decrease in the response to the spot alone, followed by slowly developing changes in both SLI and TLI: SLI produced by 1,200 micron ID windmills became weaker, whereas SLI produced by 600 micron ID windmills became stronger. After several minutes strong TLI could be elicited by both 600 and 1,200 micron ID windmills. The changes in SLI and TLI were usually complete within 5 and 15 min, respectively, and recovered to dark-adapted levels slightly more slowly after the adapting light was turned off. However the changes in sensitivity of the spot response were complete within one minute after onset and termination of the adapting light. The adaptive changes in SLI and TLI did not depend on the presence of the adapting light; after a brief (1 min) exposure to the adapting light, the changes in SLI and TLI slowly developed and then decayed back to the dark-adapted level. The effects of the adapting light on SLI were mimicked by dopamine and blocked by D1 dopamine receptor antagonists. However dopamine did not enable TLI in dark-adapted retinas and dopamine antagonists did not prevent enablement of TLI when dark-adapted retinas were exposed to light or disable TLI when applied to light-adapted retinas. The results suggest that light-adaptive changes in SLI are mediated by dopamine and are consistent with a reduction in electrical coupling between neurons that conduct the SLI signal laterally in the retina. In contrast, TLI appears to be switched off or suppressed in the dark-adapted retina and enabled in light-adapted retinas, by a relatively slow modulatory mechanism that does not involve dopamine.
在脊椎动物视网膜中，两种在功能和解剖学上截然不同的侧向抑制类型有助于神经节细胞的感受野组织形成：持续性侧向抑制（SLI），在稳定光照期间存在；以及瞬态侧向抑制（TLI），由光照变化诱发。我们通过测量开-关神经节细胞对感受野中心光点的反应，研究了泥螈视网膜中这两种侧向抑制机制的适应性变化，反应是在不存在和存在同心断裂环（风车）图案的情况下测量的，该图案可以是静止的或旋转的。SLI通过静止风车对中心光点反应的抑制百分比来测量，TLI通过风车旋转时产生的额外抑制来测量。在暗适应视网膜中，600或1200微米内径的风车可引发SLI，但在广泛的风车强度和旋转速率范围内，任何尺寸的风车都无法引发TLI。将暗适应视网膜暴露于漫射适应光下，会导致对单独光点的反应立即下降，随后SLI和TLI都缓慢发生变化：1200微米内径风车产生的SLI变弱而600微米内径风车产生的SLI变强。几分钟后，600和1200微米内径的风车都能引发强烈的TLI。SLI和TLI的变化通常分别在5分钟和15分钟内完成，在适应光关闭后恢复到暗适应水平的速度稍慢。然而，光点反应敏感性的变化在适应光开始和终止后一分钟内完成。SLI和TLI的适应性变化不依赖于适应光的存在；在短暂（1分钟）暴露于适应光后，SLI和TLI的变化缓慢发展，然后衰减回暗适应水平。多巴胺模拟了适应光对SLI的影响，而D1多巴胺受体拮抗剂则阻断了这种影响。然而，多巴胺并不能在暗适应视网膜中引发TLI，当暗适应视网膜暴露于光下时，多巴胺拮抗剂也不能阻止TLI的引发，而当应用于光适应视网膜时也不能使其失效。结果表明，SLI的光适应性变化由多巴胺介导，并且与在视网膜中横向传导SLI信号的神经元之间电耦合的减少一致。相比之下，TLI在暗适应视网膜中似乎被关闭或抑制，而在光适应视网膜中通过一种不涉及多巴胺的相对缓慢的调节机制被启用。
