Nelson R, Kolb H
J Neurophysiol. 1985 Sep;54(3):592-614. doi: 10.1152/jn.1985.54.3.592.
A17 amacrine cells of the cat retina have been penetrated with horseradish peroxidase (HRP)-filled microelectrodes and their light responses recorded. These cells depolarize in sustained fashion to steps of light. Viewed in retinal wholemounts, HRP-injected cells have a spokelike radiating splay of very fine dendrites (0.1 micron diam) passing diffusely through all strata of the inner plexiform layer (IPL) to run primarily in strata 4 and 5. There are as many as 1,000 large, regularly spaced beads borne on the 500- to 1,200-micron diameter dendritic field. Cell body sizes range from 9 to 13 micron. In the electron microscope, the dendritic beads in sublamina b of the IPL are seen to synapse reciprocally with rod bipolar axon terminals. Dendritic beads in sublamina a rarely make synapses, but between the beads in this layer, input from at least three distinctive amacrine profiles occurs. Though diffuse at the light microscopic level, A17 thus appears to be structurally bistratified, with amacrine input in sublamina a and bipolar input in sublamina b. It is likely that A17 can be identified with AI. A17 signals are driven almost exclusively by rods. The spectral sensitivity peaks at 507 nm, identical with that of pigment epithelial cells. Light adaptation abolishes all but a small hyperpolarizing component of the signal. The overall intensity-response range is similar to that of AII amacrine cells. When receptive fields of A17 cells are mapped with slit stimuli, a broad, single-component curve is measured approximately covering the dendritic field. The receptive field is well described by a linear electrical model with a mean space constant of 259 +/- 97 micron (SD). On the other hand, responses to centered slit stimuli of varying width yielded space constants of only 38 +/- 29 micron. A17 amacrines are thus broad-field components of the cat's rod system but with very little capacity for spatial integration. Receptive-field measurements are not supportive of the notion of isolated dendritic regions.
用充满辣根过氧化物酶（HRP）的微电极刺入猫视网膜的A17无长突细胞，并记录其光反应。这些细胞对光阶跃以持续的方式去极化。在视网膜整装标本中观察，注入HRP的细胞有非常细的树突（直径0.1微米）呈轮辐状放射状散开，弥漫地穿过内网状层（IPL）的所有层，主要在第4和第5层中延伸。在直径500至1200微米的树突野上有多达1000个大的、规则间隔的颗粒。细胞体大小在9至13微米之间。在电子显微镜下，可见IPL b亚层中的树突颗粒与视杆双极轴突终末相互形成突触。a亚层中的树突颗粒很少形成突触，但在该层的颗粒之间，至少有三种不同的无长突细胞形态的输入。因此，尽管在光学显微镜水平上是弥散的，但A17在结构上似乎是双分层的，a亚层有无长突细胞输入，b亚层有双极细胞输入。A17可能与AI是同一细胞。A17的信号几乎完全由视杆驱动。光谱敏感性在507纳米处达到峰值，与色素上皮细胞的相同。光适应消除了信号中除一小部分超极化成分外的所有成分。总的强度-反应范围与AII无长突细胞相似。当用狭缝刺激测绘A17细胞的感受野时，测得一条宽的单成分曲线，大致覆盖树突野。用平均空间常数为259±97微米（标准差）的线性电模型可以很好地描述感受野。另一方面，对不同宽度的中心狭缝刺激的反应产生的空间常数仅为38±29微米。因此，A17无长突细胞是猫视杆系统的宽视野成分，但空间整合能力非常小。感受野测量不支持孤立树突区域的概念。
