Barlow R B, Kaplan E, Renninger G H, Saito T
J Gen Physiol. 1987 Mar;89(3):353-78. doi: 10.1085/jgp.89.3.353.
The sensitivity of the lateral eye of the horseshoe crab, Limulus polyphemus, is modulated by efferent optic nerve impulses transmitted from a circadian clock located in the brain (Barlow, R. B., Jr., S. J. Bolanowski, and M. L. Brachman. 1977. Science. 197:86-89). At night, the efferent impulses invade the retinular, eccentric, and pigment cells of every ommatidium, inducing multiple anatomical and physiological changes that combine to increase retinal sensitivity as much as 100,000 times. We developed techniques for recording transmembrane potentials from a single cell in situ for several days to determine what circadian changes in retinal sensitivity originate in the primary phototransducing cell, the retinular cell. We found that the direct efferent input to the photoreceptor cell decreases its noise and increases its response. Noise is decreased by reducing the rate of spontaneous bumps by up to 100%. The response is increased by elevating photon catch (photons absorbed per flash) as much as 30 times, and increasing gain (response per absorbed photon) as much as 40%. The cellular mechanism for reducing the rate of spontaneous quantum bumps is not known. The mechanism for increasing gain appears to be the modulation of ionic conductances in the photoreceptor cell membrane. The mechanism for increasing photon catch is multiple changes in the anatomy of retinal cells. We combine these cellular events in a proposed scheme for the circadian rhythm in the intensity coding of single photoreceptors.
鲎（美洲鲎）侧眼的敏感度受从位于大脑中的昼夜节律时钟传出的视神经冲动调节（Barlow, R. B., Jr., S. J. Bolanowski, and M. L. Brachman. 1977. 《科学》. 197:86 - 89）。在夜间，传出冲动侵入每个小眼的视杆细胞、偏心细胞和色素细胞，引发多种解剖学和生理学变化，这些变化共同作用可使视网膜敏感度提高多达100000倍。我们开发了在原位记录单个细胞跨膜电位数天的技术，以确定视网膜敏感度的昼夜变化起源于初级光转导细胞，即视杆细胞。我们发现，光感受器细胞的直接传出输入降低了其噪声并增强了其反应。通过将自发脉冲的速率降低多达100%来降低噪声。通过将光子捕获量（每次闪光吸收的光子数）提高多达30倍以及将增益（每个吸收光子的反应）提高多达40%来增强反应。降低自发量子脉冲速率的细胞机制尚不清楚。增加增益的机制似乎是对光感受器细胞膜中离子电导的调节。增加光子捕获量的机制是视网膜细胞解剖结构的多种变化。我们在一个关于单个光感受器强度编码的昼夜节律的提议方案中整合了这些细胞事件。
