Smith R G
Department of Neuroscience, University of Pennsylvania, Philadelphia 19104-6058, USA.
Vis Neurosci. 1995 May-Jun;12(3):545-61. doi: 10.1017/s0952523800008440.
The outer plexiform layer of the retina contains a neural circuit in which cone synaptic terminals are electrically coupled and release glutamate onto wide-field and narrow-field horizontal cells. These are also electrically coupled and feed back through a GABAergic synapse to cones. In cat this circuit's structure is known in some detail, and much of the chemical architecture and neural responses are also known, yet there has been no attempt to synthesize this knowledge. We constructed a large-scale compartmental model (up to 50,000 compartments) to incorporate the known anatomical and biophysical facts. The goal was to discover how the various circuit components interact to form the cone receptive field, and thereby what possible function is implied. The simulation reproduced many features known from intracellular recordings: (1) linear response of cone and horizontal cell to intensity, (2) some aspects of temporal responses of cone and horizontal cell, (3) broad receptive field of the wide-field horizontal cell, and (4) center-surround cone receptive field (derived from a "deconvolution model"). With the network calibrated in this manner, we determined which of its features are necessary to give the cone receptive field a Gaussian center-surround shape. A Gaussian-like center that matches the center derived from the ganglion cell requires both optical blur and cone coupling: blur alone is too narrow, coupling alone gives an exponential shape without a central dome-shaped peak. A Gaussian-like surround requires both types of horizontal cell: the narrow-field type for the deep, proximal region and the wide-field type for the shallow, distal region. These results suggest that the function of the cone-horizontal cell circuit is to reduce the influence of noise by spatio-temporally filtering the cone signal before it passes through the first chemical synapse on the pathway to the brain.
视网膜的外网状层包含一个神经回路，其中视锥细胞的突触终末通过电耦合，并将谷氨酸释放到广域和窄域水平细胞上。这些水平细胞也通过电耦合，并通过一个γ-氨基丁酸能突触反馈到视锥细胞。在猫中，这个回路的结构已为人所知，其许多化学结构和神经反应也已明确，但尚未有人尝试整合这些知识。我们构建了一个大规模的房室模型（多达50,000个房室），以纳入已知的解剖学和生物物理学事实。目的是发现各种回路组件如何相互作用以形成视锥细胞感受野，从而推断其可能具有的功能。该模拟重现了许多细胞内记录中已知的特征：（1）视锥细胞和水平细胞对强度的线性反应；（2）视锥细胞和水平细胞时间反应的某些方面；（3）广域水平细胞的广阔感受野；（4）中心-周边视锥细胞感受野（源自“反卷积模型”）。通过以这种方式校准网络，我们确定了其哪些特征对于使视锥细胞感受野具有高斯中心-周边形状是必要的。与从神经节细胞得出的中心相匹配的类似高斯的中心需要光学模糊和视锥细胞耦合：单独的模糊太窄，单独的耦合会产生指数形状，而没有中央圆顶形峰值。类似高斯的周边需要两种类型的水平细胞：深部近端区域的窄域类型和浅部远端区域的广域类型。这些结果表明，视锥细胞-水平细胞回路的功能是在视锥细胞信号传递到大脑的途径中通过时空滤波视锥细胞信号来减少噪声的影响。
