Intrinsic light responses of retinal ganglion cells projecting to the circadian system
Intrinsic light responses of retinal ganglion cells projecting to the circadian system
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DOI：
10.1046/j.1460-9568.2003.02594.x
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发表时间：
2003-05-01
影响因子：
3.4
通讯作者：
Robinson, DW
中科院分区：
文献类型：
--
作者：
Warren, EJ;Allen, CN;Robinson, DW
在哺乳动物中，位于视交叉上核（SCN）的生物钟的光夹带需要视网膜输入。然而，不需要传统的杆状和锥状感光器。相反，SCN 投射的视网膜神经节细胞 (RGC) 充当自主光感受器，并表现出独立于视杆和视锥驱动输入的光响应。使用全细胞膜片钳记录技术，我们研究了这类独特的 RGC 的形态学和电生理学特性。尽管投射 SCN 的 RGC 在形式上类似于 III 型细胞，但它们表现出与这些神经元截然不同的生理特性。首先，为了响应持续去极化电流的注入，SCN 投射细胞会以短暂的方式放电，这与大多数 RGC 发出强烈的动作电位序列相反。其次，在没有视杆细胞和视锥细胞输入的情况下，SCN 投射的 RGC 响应光而表现出强度依赖性的瞬时去极化。这种去极化在 5 秒内达到峰值，并在衰减至稳定状态之前产生增加的尖峰活性。电压钳记录用于表征产生这种去极化的光激活电导。为了响应不同的光强度，SCN 投射的 RGC 表现出分级的瞬态内向电流，该电流在 5 秒内达到峰值并衰减至稳定水平。光激活电流的电压依赖性是通过减去照明之前和照明期间的电压斜坡引起的电流来获得的。光激活电流显示出向内和向外的整流，并且基本上不受用胆碱替代细胞外Na+的影响。在这两个方面，在 SCN 投射的 RGC 中观察到的固有光激活电流类似于瞬时受体电位 (trp) 家族的离子通道携带的电流，已知该电流可以介导无脊椎动物感光器的光响应。
In mammals, light entrainment of the circadian clock, located in the suprachiasmatic nuclei (SCN), requires retinal input. Traditional rod and cone photoreceptors, however, are not required. Instead, the SCN-projecting retinal ganglion cells (RGCs) function as autonomous photoreceptors and exhibit light responses independent of rod- and cone-driven input. Using whole-cell patch-clamp recording techniques, we have investigated the morphological and electrophysiological properties of this unique class of RGCs. Although SCN-projecting RGCs resemble Type III cells in form, they display strikingly different physiological properties from these neurons. First, in response to the injection of a sustained depolarizing current, SCN-projecting cells fired in a transient fashion, in contrast to most RGCs which fired robust trains of action potentials. Second, in response to light, SCN-projecting RGCs exhibited an intensity-dependent transient depolarization in the absence of rod and cone input. This depolarization reached a peak within 5 s and generated increased spiking activity before decaying to a plateau. Voltage-clamp recordings were used to characterize the light-activated conductance which generated this depolarization. In response to varying light intensities, SCN-projecting RGCs exhibited a graded transient inward current which peaked within 5 s and decayed to a plateau. The voltage dependence of the light-activated current was obtained by subtracting currents elicited by a voltage ramp before and during illumination. The light-activated current displayed both inward and outward rectification and was largely unaffected by substitution of extracellular Na+ with choline. In both respects, the intrinsic light-activated current observed in SCN-projecting RGCs resembles currents carried by ion channels of the transient receptor potential (trp ) family, which are known to mediate the light response of invertebrate photoreceptors.