Bloomfield S A, Xin D, Persky S E
Department of Ophthalmology, New York University Medical Center, New York 10016, USA.
Vis Neurosci. 1995 Sep-Oct;12(5):985-99. doi: 10.1017/s0952523800009524.
The large receptive fields of retinal horizontal cells are thought to reflect extensive electrical coupling via gap junctions. It was shown recently that the biotinylated tracers, biocytin and Neurobiotin, provide remarkable images of coupling between many types of retinal neuron, including horizontal cells. Further, these demonstrations of tracer coupling between horizontal cells rivaled the size of their receptive fields, suggesting that the pattern of tracer coupling may provide some index of the extent of electrical coupling. We studied this question by comparing the receptive field and tracer coupling size of dark-adapted horizontal cells recorded in the superfused, isolated retina-eyecup of the rabbit. Both the edge-to-edge receptive field and space constants (lambda) were computed for each cell using a long, narrow slit of light displaced across the retinal surface. Cells were subsequently labeled by iontophoretic injection of Neurobiotin. The axonless A-type horizontal cells showed extensive, homologous tracer coupling in groups greater than 1000 covering distances averaging about 2 mm. The axon-bearing B-type horizontal cells were less extensively tracer coupled, showing homologous coupling of the somatic endings in groups of about 100 cells spanning approximately 400 microns and a separate homologous coupling of the axon terminal endings covering only about 275 microns. Moreover, we observed a remarkable, linear relationship between the size of the receptive fields of each of the three horizontal cell endings and the magnitude of their tracer coupling. Our findings suggest that the extent of tracer coupling provides a strong, linear index of the magnitude of electrical current flow, as derived from receptive-field measures, across groups of coupled horizontal cells. These data thus provide the first direct evidence that the receptive-field size of horizontal cells is related to the extent of their coupling via gap junctions.
视网膜水平细胞的大感受野被认为反映了通过缝隙连接的广泛电耦合。最近有研究表明，生物素化示踪剂生物胞素和神经生物素能提供多种视网膜神经元（包括水平细胞）之间耦合的显著图像。此外，这些水平细胞之间示踪剂耦合的展示与它们感受野的大小相当，这表明示踪剂耦合模式可能提供了电耦合程度的某种指标。我们通过比较在兔的灌注分离视网膜 - 眼杯中记录的暗适应水平细胞的感受野和示踪剂耦合大小来研究这个问题。使用在视网膜表面移动的长而窄的光缝为每个细胞计算从边缘到边缘的感受野和空间常数（λ）。随后通过离子电渗法注射神经生物素对细胞进行标记。无轴突的 A 型水平细胞在超过 1000 个细胞的群体中显示出广泛的同源示踪剂耦合，覆盖距离平均约为 2 毫米。有轴突的 B 型水平细胞的示踪剂耦合范围较小，在约 100 个细胞的群体中显示出体细胞末端的同源耦合，跨度约为 400 微米，轴突末端的单独同源耦合仅覆盖约 275 微米。此外，我们观察到三种水平细胞末端各自的感受野大小与其示踪剂耦合程度之间存在显著的线性关系。我们的研究结果表明，示踪剂耦合程度提供了一个强大的线性指标，用于衡量从感受野测量得出的跨耦合水平细胞群体的电流大小。因此，这些数据首次直接证明了水平细胞的感受野大小与其通过缝隙连接的耦合程度有关。
