Adaptation to changes in ambient light intensity, in retinal cells and circuits, optimizes visual functions. In the retina, light-adaptation results in changes in light-sensitivity and spatiotemporal tuning of ganglion cells. Under light-adapted conditions, contrast sensitivity (CS) of ganglion cells is a bandpass function of spatial frequency; in contrast, dark-adaptation reduces CS, especially at higher spatial frequencies. In this work, we aimed to understand intrinsic neuromodulatory mechanisms that underlie retinal adaptation to changes in ambient light level. Specifically, we investigated how CS is affected by dopamine (DA), nitric oxide (NO), and modifiers of electrical coupling through gap junctions, under different conditions of adapting illumination.

Using the optokinetic response as a behavioral readout of direction-selective ganglion cell activity, we characterized the spatial CS of chicks under high- and low-photopic conditions and how it was regulated by DA, NO, and gap-junction uncouplers. We observed that: (1) DA D2R-family agonists and a donor of NO increased CS tested in low-photopic illumination, as if observed in the high-photopic light; whereas (2) removing their effects using either DA antagonists or NO- synthase inhibitors mimicked low-photopic CS; (3) simulation of high-photopic CS by DA agonists was abolished by NO-synthase inhibitors; and (4) selectively blocking coupling via connexin 35/36-containing gap junctions, using a “designer” mimetic peptide, increased CS, as does strong illumination.

We conclude that, in the chicken retina: (1) DA and NO induce changes in spatiotemporal processing, similar to those driven by increasing illumination, (2) DA possibly acts through stimulating NO synthesis, and (3) blockade of coupling via gap junctions containing connexin 35/36 also drives a change in retinal CS functions. As a noninvasive method, the optokinetic response can provide rapid, conditional, and reversible assessment of retinal functions when pharmacological reagents are injected into the vitreous humor. Finally, the chick's large eyes, and the many similarities between their adaptational circuit functions and those in mammals such as the mouse, make them a promising model for future retinal research.

适应视网膜细胞和电路中环境光强度的变化，可以优化视觉功能。在视网膜中，光适应导致神经节细胞的光敏感性和时空调谐变化。在光适应的条件下，神经节细胞的对比敏感度（CS）是空间频率的带通函数；相反，暗适应会降低CS，尤其是在较高的空间频率下。在这项工作中，我们旨在了解内在的神经调节机制，这些机制是视网膜适应环境光水平变化的基础。具体来说，我们研究了在不同的照明条件下，多巴胺（DA），一氧化氮（NO）和通过缝隙连接的电耦合改性剂如何影响CS。

使用视动反应作为方向选择性神经节细胞活性的行为读数，我们表征了高和低照度条件下雏鸡的空间CS以及如何通过DA，NO和间隙连接解偶联剂对其进行调节。我们观察到：（1）DA D2R家族激动剂和NO的供体在低光照明下测试的CS增加，就像在高光照明下观察到的一样；（2）通过使用DA拮抗剂或NO合酶抑制剂来模拟低光CS，从而消除其影响；（3）NO合酶抑制剂取消了DA激动剂对高光CS的模拟。（4）使用“ designer”模拟肽，选择性地阻止含有连接蛋白35/36的间隙连接的偶联，增加CS，强光照也是如此。

我们得出的结论是，在鸡视网膜中：（1）DA和NO诱导时空过程的变化，与光照增加所驱动的变化类似；（2）DA可能通过刺激NO的合成起作用；（3）通过间隙连接的耦合阻断含有连接蛋白35/36的药物还可以改变视网膜CS功能。作为一种非侵入性方法，当将药理学试剂注入玻璃体液中时，视动反应可以提供视网膜功能的快速，有条件和可逆的评估。最后，小鸡的大眼睛，以及它们的适应性电路功能与哺乳动物（如小鼠）之间的许多相似之处，使它们成为未来视网膜研究的有希望的模型。