Casey Eye Institute, Department of Ophthalmology, Oregon Health & Science University, Portland, Oregon 97239, USA.
J Neurosci. 2010 Nov 17;30(46):15664-76. doi: 10.1523/JNEUROSCI.2081-10.2010.
Cells sensitive to the orientation of edges are ubiquitous in visual systems, and have been described in the vertebrate retina, yet the synaptic mechanisms that generate orientation selectivity in the retina are largely unknown. Here, we analyze the synaptic mechanisms that generate selective responses to vertically and horizontally oriented stimuli in rabbit retinal ganglion cells. The data indicate that the excitatory and inhibitory inputs to orientation-selective ganglion cells are rendered orientation selective within the presynaptic circuitry. In accordance with previous extracellular recordings, presynaptic GABAergic inhibition is critical to generate orientation selectivity, and we show that it includes lateral inhibition of glutamatergic bipolar cells and serial inhibitory connections between GABAergic and glycinergic amacrine cells. Despite very similar spiking properties, vertically and horizontally selective ganglion cells (VS-GCs and HS-GCs, respectively) show marked differences in their underlying synaptic mechanisms. Both cell types receive glutamatergic inputs via non-NMDA (AMPA/kainate) and NMDA receptors, while VS-GCs receive additional excitation mediated by glycinergic disinhibition. A striking difference between these cells is that during nonpreferred simulation, excitation is suppressed and direct glycinergic inhibition is increased in HS-GCs, whereas for VS-GCs, both excitatory and inhibitory inputs are suppressed. Thus, orientation selectivity is generated presynaptically both by modulation of bipolar cell output and by serial inhibitory connections between amacrine cells. Minimal circuit models are proposed that account for these observations.
在视觉系统中，对边缘方向敏感的细胞无处不在，在脊椎动物视网膜中已有描述，但产生视网膜方向选择性的突触机制在很大程度上尚不清楚。在这里，我们分析了在兔视网膜神经节细胞中产生对垂直和水平方向刺激选择性反应的突触机制。数据表明，对方向选择性神经节细胞的兴奋性和抑制性输入在突触前电路中具有方向选择性。与先前的细胞外记录一致，突触前 GABA 能抑制对于产生方向选择性至关重要，我们表明它包括谷氨酸能双极细胞的侧向抑制和 GABA 能和甘氨酸能无长突细胞之间的串联抑制连接。尽管具有非常相似的放电特性，但垂直和水平选择性神经节细胞（分别为 VS-GCs 和 HS-GCs）在其潜在的突触机制中显示出明显的差异。这两种细胞类型都通过非 NMDA（AMPA/海人藻酸）和 NMDA 受体接收谷氨酸能输入，而 VS-GCs 还通过甘氨酸能去抑制介导额外的兴奋。这些细胞之间的一个显著差异是，在非优势模拟期间，HS-GCs 中的兴奋被抑制，直接的甘氨酸能抑制增加，而对于 VS-GCs，兴奋性和抑制性输入都被抑制。因此，方向选择性是通过双极细胞输出的调制和无长突细胞之间的串联抑制连接在突触前产生的。提出了最小的电路模型来解释这些观察结果。
