van Wyk Michiel, Taylor W Rowland, Vaney David I
Vision, Touch and Hearing Research Centre, School of Biomedical Sciences, University of Queensland, Brisbane, Queensland 4072, Australia.
J Neurosci. 2006 Dec 20;26(51):13250-63. doi: 10.1523/JNEUROSCI.1991-06.2006.
Visual acuity is limited by the size and density of the smallest retinal ganglion cells, which correspond to the midget ganglion cells in primate retina and the beta-ganglion cells in cat retina, both of which have concentric receptive fields that respond at either light-On or light-Off. In contrast, the smallest ganglion cells in the rabbit retina are the local edge detectors (LEDs), which respond to spot illumination at both light-On and light-Off. However, the LEDs do not predominate in the rabbit retina and the question arises, what role do they play in fine spatial vision? We studied the morphology and physiology of LEDs in the isolated rabbit retina and examined how their response properties are shaped by the excitatory and inhibitory inputs. Although the LEDs comprise only approximately 15% of the ganglion cells, neighboring LEDs are separated by 30-40 microm on the visual streak, which is sufficient to account for the grating acuity of the rabbit. The spatial and temporal receptive-field properties of LEDs are generated by distinct inhibitory mechanisms. The strong inhibitory surround acts presynaptically to suppress both the excitation and the inhibition elicited by center stimulation. The temporal properties, characterized by sluggish onset, sustained firing, and low bandwidth, are mediated by the temporal properties of the bipolar cells and by postsynaptic interactions between the excitatory and inhibitory inputs. We propose that the LEDs signal fine spatial detail during visual fixation, when high temporal frequencies are minimal.
视力受最小视网膜神经节细胞的大小和密度限制，这些细胞对应于灵长类动物视网膜中的侏儒神经节细胞和猫视网膜中的β神经节细胞，二者都具有在光开或光关时做出反应的同心感受野。相比之下，兔视网膜中最小的神经节细胞是局部边缘探测器（LED），它们在光开和光关时都对点状照明做出反应。然而，LED在兔视网膜中并不占主导地位，于是问题出现了，它们在精细空间视觉中起什么作用？我们研究了离体兔视网膜中LED的形态和生理学，并研究了它们的反应特性是如何由兴奋性和抑制性输入塑造的。尽管LED仅占神经节细胞的约15%，但在视觉条纹上相邻的LED之间相距30 - 40微米，这足以解释兔子的光栅视力。LED的空间和时间感受野特性是由不同的抑制机制产生的。强烈的抑制性周边在突触前起作用，以抑制中心刺激引发的兴奋和抑制。其时间特性表现为起始缓慢、持续放电和低带宽，这是由双极细胞的时间特性以及兴奋性和抑制性输入之间的突触后相互作用介导的。我们提出，在视觉注视期间，当高频时间频率最小时，LED对精细空间细节进行信号传递。
