Department of Ophthalmology and Visual Science, Yale School of Medicine, New Haven, CT 06510.
Department of Ophthalmology and Visual Science, Yale School of Medicine, New Haven, CT 06510;
Proc Natl Acad Sci U S A. 2017 Oct 24;114(43):11518-11523. doi: 10.1073/pnas.1711622114. Epub 2017 Sep 27.
A basic scheme of neuronal organization in the mammalian retina is the segregation of ON and OFF pathways in the inner plexiform layer (IPL), where glutamate is released from ON and OFF bipolar cell terminals in separate inner (ON) and outer (OFF) sublayers in response to light intensity increments and decrements, respectively. However, recent studies have found that vGluT3-expressing glutamatergic amacrine cells (GACs) generate ON-OFF somatic responses and release glutamate onto both ON and OFF ganglion cell types, raising the possibility of crossover excitation in violation of the canonical ON-OFF segregation scheme. To test this possibility, we recorded light-evoked Ca responses from dendrites of individual GACs infected with GCaMP6s in mouse. Under two-photon imaging, a single GAC generated rectified local dendritic responses, showing ON-dominant responses in ON sublayers and OFF-dominant responses in OFF sublayers. This unexpected ON-OFF segregation within a small-field amacrine cell arose from local synaptic processing, mediated predominantly by synaptic inhibition. Multiple forms of synaptic inhibition compartmentalized the GAC dendritic tree and endowed all dendritic varicosities with a small-center, strong-surround receptive field, which varied in receptive field size and degree of ON-OFF asymmetry with IPL depth. The results reveal a form of short-range dendritic autonomy that enables a small-field, dual-transmitter amacrine cell to process diverse dendritic functions in a stratification level- and postsynaptic target-specific manner, while preserving the fundamental ON-OFF segregation scheme for parallel visual processing and high spatial resolution for small object motion and uniformity detection.
哺乳动物视网膜神经元组织的一个基本方案是在神经内丛状层 (IPL) 中分离 ON 和 OFF 通路,谷氨酸在 IPL 中从 ON 和 OFF 双极细胞末端释放,分别响应光强的增加和减少。然而,最近的研究发现,vGluT3 表达的谷氨酸能无长突细胞 (GAC) 产生 ON-OFF 体反应,并将谷氨酸释放到 ON 和 OFF 两类神经节细胞上,这增加了违反经典 ON-OFF 分离方案的交叉兴奋的可能性。为了验证这种可能性,我们在感染了 GCaMP6 的小鼠单个 GAC 上记录了光诱发的 Ca 反应。在双光子成像下,单个 GAC 产生了整流的局部树突反应,在 ON 亚层中表现出 ON 优势反应,在 OFF 亚层中表现出 OFF 优势反应。这种小场无长突细胞内出乎意料的 ON-OFF 分离来自局部突触处理,主要由突触抑制介导。多种形式的突触抑制使 GAC 树突分支发生分区,并赋予所有树突膨体一个小中心、强环绕的感受野,其感受野大小和 ON-OFF 不对称性随 IPL 深度而变化。结果揭示了一种短程树突自主性形式,使小场、双递质无长突细胞能够以分层水平和突触后靶标特异性的方式处理不同的树突功能,同时保持平行视觉处理的基本 ON-OFF 分离方案和对小物体运动和均匀性检测的高空间分辨率。