Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, Michigan.
Department of Molecular, Cellular & Developmental Biology, University of Michigan, Ann Arbor, Michigan.
J Comp Neurol. 2019 Jan 1;527(1):117-132. doi: 10.1002/cne.24313. Epub 2017 Sep 15.
The mammalian retina encodes visual information in dim light using rod photoreceptors and a specialized circuit: rods→rod bipolar cells→AII amacrine cell. The AII amacrine cell uses sign-conserving electrical synapses to modulate ON cone bipolar cell terminals and sign-inverting chemical (glycinergic) synapses to modulate OFF cone cell bipolar terminals; these ON and OFF cone bipolar terminals then drive the output neurons, retinal ganglion cells (RGCs), following light increments and decrements, respectively. The AII amacrine cell also makes direct glycinergic synapses with certain RGCs, but it is not well established how many types receive this direct AII input. Here, we investigated functional AII amacrine→RGC synaptic connections in the retina of the guinea pig (Cavia porcellus) by recording inhibitory currents from RGCs in the presence of ionotropic glutamate receptor (iGluR) antagonists. This condition isolates a specific pathway through the AII amacrine cell that does not require iGluRs: cone→ON cone bipolar cell→AII amacrine cell→RGC. These recordings show that AII amacrine cells make direct synapses with OFF Alpha, OFF Delta and a smaller OFF transient RGC type that co-stratifies with OFF Alpha cells. However, AII amacrine cells avoid making synapses with numerous RGC types that co-stratify with the connected RGCs. Selective AII connections ensure that a privileged minority of RGC types receives direct input from the night-vision pathway, independent from OFF bipolar cell activity. Furthermore, these results illustrate the specificity of retinal connections, which cannot be predicted solely by co-stratification of dendrites and axons within the inner plexiform layer.
视杆→视杆双极细胞→AII 无长突细胞。AII 无长突细胞使用信号守恒的电突触来调制 ON 锥体双极细胞末梢,使用信号反转的化学(甘氨酸能)突触来调制 OFF 锥体双极细胞末梢;这些 ON 和 OFF 锥体双极细胞末梢随后分别驱动光增加和减少时的输出神经元,即视网膜神经节细胞(RGC)。AII 无长突细胞还与某些 RGC 形成直接的甘氨酸能突触,但尚未确定有多少种 RGC 接受这种直接的 AII 输入。在这里,我们通过在离子型谷氨酸受体(iGluR)拮抗剂存在的情况下从 RGC 记录抑制电流,研究了豚鼠(Cavia porcellus)视网膜中功能性 AII 无长突→RGC 突触连接。这种条件分离了通过 AII 无长突细胞的特定通路,该通路不依赖于 iGluRs:视锥细胞→ON 锥体双极细胞→AII 无长突细胞→RGC。这些记录显示,AII 无长突细胞与 OFF Alpha、OFF Delta 和较小的 OFF 瞬时 RGC 类型形成直接突触,这些细胞与 OFF Alpha 细胞共层。然而,AII 无长突细胞避免与许多与连接的 RGC 类型形成突触,这些 RGC 类型与连接的 RGC 共层。选择性的 AII 连接确保少数特权 RGC 类型接收来自夜间视觉通路的直接输入,而与 OFF 双极细胞活动无关。此外,这些结果说明了视网膜连接的特异性,这些特异性不能仅通过内丛状层内树突和轴突的共层来预测。