Inhibition in the eye of Limulus.
Inhibition in the eye of Limulus.
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DOI：
10.1085/jgp.39.5.651
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发表时间：
1956-05-20
期刊：
影响因子：
--
通讯作者：
RATLIFF F
中科院分区：
文献类型：
--
作者：
HARTLINE HK;WAGNER HG;RATLIFF F
在鲎的复合侧眼中，每个小眼在视神经的脉冲放电中作为单个受体单位发挥作用。冲动起源于每个小眼的偏心细胞，并在其轴突中传导，轴突不间断地穿过广泛的神经纤维丛，成为视神经的纤维。神经丛使小眼之间相互连接，但其确切的组织尚不清楚。一个小眼在其偏心细胞轴突中释放脉冲的能力会因邻近其他小眼的照明而降低：光的阈值升高，响应阈上闪光而释放的脉冲数量减少，在稳定照明期间释放脉冲的频率降低。此外，在某些条件下，当小眼处于黑暗中时，可以引起的活动也可以类似地被抑制。没有证据表明兴奋性影响在鲎的眼睛中传播。对以稳定速率释放脉冲的小眼施加的抑制影响开始于邻近小眼的照明开始后不久，放电频率突然达到最低。在部分恢复之后，频率保持在降低的水平，直到关闭对相邻受体的照射，之后迅速恢复到原始频率，尽管不是瞬时恢复到原始频率。这种抑制作用直接作用于小眼内的敏感结构：当脉冲被插入小眼的微电极记录时，以及当它们被记录在从视神经解剖出的更近端的单纤维中时，都可以观察到。眼睛的感受器单位经常相互抑制。这是通过同时记录两个视神经纤维的活动而观察到的。抑制作用的调节似乎取决于神经丛中神经相互连接的完整性：切断小眼的侧向连接会消除施加在小眼上的抑制作用，由神经丛介导的抑制作用的性质及其对受体单位施加抑制作用的机制尚不清楚。从小眼神经冲动的放电频率的抑郁症的增加近似线性与其附近的受体上的照明强度的对数。小眼附近被照亮的眼睛面积越大，对小眼放电的抑制作用就越大。然而，随着总面积的增加，面积的相等增量变得不那么有效。小眼的反应最有效地抑制小眼的照明是接近它;有效性随着距离的增加而减少，但可能会延长几毫米。以恒定强度照明眼睛的固定区域产生来自附近小眼的脉冲放电频率的降低，该频率近似恒定，而与小眼的激发水平无关。鲎眼中的抑制性相互作用是一个整合过程，在决定视觉系统的神经活动模式方面非常重要。它类似于发生在脊椎动物视网膜中的相互作用的抑制成分。抑制性相互作用导致来自以不同强度照明的眼睛的不同区域的感觉活动的差异被放大，从而增强视觉对比度。
In the compound lateral eye of Limulus each ommatidium functions as a single receptor unit in the discharge of impulses in the optic nerve. Impulses originate in the eccentric cell of each ommatidium and are conducted in its axon, which runs without interruption through an extensive plexus of nerve fibers to become a fiber of the optic nerve. The plexus makes interconnections among the ommatidia, but its exact organization is not understood. The ability of an ommatidium to discharge impulses in the axon of its eccentric cell is reduced by illumination of other ommatidia in its neighborhood: the threshold to light is raised, the number of impulses discharged in response to a suprathreshold flash of light is diminished, and the frequency with which impulses are discharged during steady illumination is decreased. Also, the activity that can be elicited under certain conditions when an ommatidium is in darkness can be inhibited similarly. There is no evidence for the spread of excitatory influences in the eye of Limulus. The inhibitory influence exerted upon an ommatidium that is discharging impulses at a steady rate begins, shortly after the onset of the illumination on neighboring ommatidia, with a sudden deep minimum in the frequency of discharge. After partial recovery, the frequency is maintained at a depressed level until the illumination on the neighboring receptors is turned off, following which there is prompt, though not instantaneous recovery to the original frequency. The inhibition is exerted directly upon the sensitive structure within the ommatidium: it has been observed when the impulses were recorded by a microelectrode thrust into an ommatidium, as well as when they were recorded more proximally in single fibers dissected from the optic nerve. Receptor units of the eye often inhibit one another mutually. This has been observed by recording the activity of two optic nerve fibers simultaneously. The mediation of the inhibitory influence appears to depend upon the integrity of nervous interconnections in the plexus: cutting the lateral connections to an ommatidium abolishes the inhibition exerted upon it. The nature of the influence that is mediated by the plexus and the mechanism whereby it exerts its inhibitory action on the receptor units are not known. The depression of the frequency of the discharge of nerve impulses from an ommatidium increases approximately linearly with the logarithm of the intensity of illumination on receptors in its vicinity. Inhibition of the discharge from an ommatidium is greater the larger the area of the eye illuminated in its vicinity. However, equal increments of area become less effective as the total area is increased. The response of an ommatidium is most effectively inhibited by the illumination of ommatidia that are close to it; the effectiveness diminishes with increasing distance, but may extend for several millimeters. Illumination of a fixed region of the eye at constant intensity produces a depression of the frequency of discharge of impulses from a nearby ommatidium that is approximately constant, irrespective of the level of excitation of the ommatidium. The inhibitory interaction in the eye of Limulus is an integrative process that is important in determining the patterns of nervous activity in the visual system. It is analogous to the inhibitory component of the interaction that takes place in the vertebrate retina. Inhibitory interaction results in the exaggeration of differences in sensory activity from different regions of the eye illuminated at different intensities, thus enhancing visual contrast.