Synaptic Mechanisms in the Mammalian Retina

我们的工作集中在视网膜内层的特殊突触上。 最近对视网膜神经元的转录组学分析产生了许多有趣的假设，我们计划进行测试。例如，GluA 1是一种AMPA受体亚单位，在大脑的其余部分广泛表达，但在视网膜中的表达明显受限。在视网膜内层，GluA 1主要表达在一个单一的无长突细胞和一个单一的视网膜神经节细胞（RGC），我们计划电生理，成像和免疫组化实验，以确定特定的角色，该受体在这些神经元内的视觉处理。 目前实验室的工作已经确定了以前未报道的杆通路中的突触。具体而言，A2无长突细胞直接在OFF α神经节细胞的近端树突、胞体和轴突上形成突触。我们正在进行电生理学和Ca 2+成像实验，以检查这些突触的特性，我们假设这些突触对OFF α神经节细胞的尖峰活动产生非常强大的抑制控制。 我们对视网膜色素变性rd 10小鼠模型的病理活动的研究已经提出了几个关于在此过程中改变的突触特征和缓解突触和电路功能障碍的潜在疗法的假设。具体来说，我们正在测试红细胞的病理性去极化是否会减少视杆细胞通路中的信号传导。这个问题的答案将建议特定的药理学方法，以保持信号和减轻损害电路重塑在疾病发作期间。 许多神经科学实验室，包括我们的实验室（Poleg-Polsky和Diamond，2016，J. Neurosci），已经使用iGluSnFR，一种遗传编码的谷氨酸指示剂，来研究电路特征的各个方面。最近，我们使用计算、电生理和成像方法来检查iGluSnFR对谷氨酸扩散和摄取的影响（Armbruster等人，2020年，eLife）。我们发现iGluSnFR大大延迟谷氨酸摄取，如突触转运体电流减慢所示。这些结果强调了使用这一宝贵工具时的重要考虑因素和警告。

Our work focuses on specialized synapses in the inner retina. Recent transcriptomic analyses of retinal neurons have generated many interesting hypotheses that we plan to test. For example, GluA1, an AMPA receptor subunit that is expressed widely throughout the rest of the brain, exhibits markedly restricted expression in the retina. In the inner retina, GluA1 is expressed primarily in a single amacrine cell and a single retinal ganglion cell (RGC), and we have planned electrophysiological, imaging and immunohistochemical experiments to determine specific roles for that receptor in visual processing within these neurons. Current work in the lab has identified previously unreported synapses in the rod pathway. Specifically, A2 amacrine cells make synapses directly onto the proximal dendrites, somata and axons of OFF alpha ganglion cells. We are performing electrophysiological and Ca2+ imaging experiments to examine the properties of these synapses, which we hypothesize exert extremely powerful inhibitory control over the spiking activity of OFF alpha ganglion cells. Our studies of pathological activity in the rd10 mouse model of retinitis pigmentosa have given rise to several hypotheses regarding synaptic features that are altered during this process and potential therapies to alleviate synaptic and circuit dysfunction. Specifically, we are testing whether pathological depolarization of RBCs diminishes signaling in the rod pathway. Answers to this question would suggest specific pharmacological approaches to preserve signaling and alleviate damaging circuit remodeling during the onset of the disease. Many neuroscience laboratories, including ours (Poleg-Polsky and Diamond, 2016, J. Neurosci), have used iGluSnFR, a genetically encoded glutamate indicator, to study various aspects of circuit features. Recently, we used computational, electrophysiological and imaging methods to examine the effects that iGluSnFR has on glutamate diffusion and uptake (Armbruster, et al., 2020, eLife). We find that iGluSnFR substantially delays glutamate uptake, as indicated by a slowing of synaptic transporter currents. These results highlight important considerations and caveats when using this valuable tool.