McGuire B A, Stevens J K, Sterling P
J Neurosci. 1986 Apr;6(4):907-18. doi: 10.1523/JNEUROSCI.06-04-00907.1986.
We reconstructed from electron micrographs of 189 serial ultrathin sections a major portion of the dendritic tree of an on-beta ganglion cell through its sixth order of branching. One hundred three contacts from three cone bipolar cells were identified. Forty-seven contacts were from a single CBb1 cone bipolar. These were distributed widely over the dendritic tree but were frequently found on the slender "basal tuft" dendrites. Twenty-two additional contacts from a second CBb1 cell were found but not studied in detail. Thirty-four contacts were from a single CBb2 cone bipolar; these also were distributed widely but were primarily on the branches of the main dendritic arborization. A major portion of the dendritic tree of an off-beta cell was also reconstructed through its seventh order of branching. Thirty-five contacts from two cone bipolar cells were identified. Twenty-three contacts were from a single CBa1 cone bipolar and 12 widely distributed over the off-beta cell dendritic tree. We propose that the photopic receptive field center of a beta cell corresponds to the envelope of the receptive fields of the bipolar cells that connect it to the cones. The center response of a beta cell may be generated by a "push-pull" mechanism. For the on-beta cell there would be excitation at light on from CBb1 and disinhibition from CBb2 and the reverse at light off. For the off-beta cell there would be inhibition at light on from CBa2 and withdrawal of excitation from CBa1. Should the bipolars have antagonistic surrounds (so far reported only for CBb1), the beta cell surrounds as well as their centers might be generated by this push-pull mechanism.
我们从189个连续超薄切片的电子显微照片中重建了一个on-β神经节细胞树突树的主要部分，直至其第六级分支。识别出了来自三个视锥双极细胞的103个接触点。47个接触点来自单个CBb1视锥双极细胞。这些接触点广泛分布于树突树上，但经常出现在细长的“基部簇”树突上。还发现了来自第二个CBb1细胞的另外22个接触点，但未进行详细研究。34个接触点来自单个CBb2视锥双极细胞；这些接触点也广泛分布，但主要位于主要树突分支上。还通过其第七级分支重建了一个off-β细胞树突树的主要部分。识别出了来自两个视锥双极细胞的35个接触点。23个接触点来自单个CBa1视锥双极细胞，另外12个广泛分布于off-β细胞树突树上。我们提出，β细胞的明视觉感受野中心对应于将其与视锥细胞相连的双极细胞感受野的包络。β细胞的中心反应可能由“推挽”机制产生。对于on-β细胞，在光照时会受到CBb1的兴奋作用和CBb2的去抑制作用，在光照熄灭时则相反。对于off-β细胞，在光照时会受到CBa2的抑制作用和CBa1的兴奋作用的撤回。如果双极细胞具有拮抗的外周（迄今为止仅报道了CBb1），那么β细胞的外周以及它们的中心可能由这种推挽机制产生。
