Egger Veronica, Diamond Jeffrey S
Department of Neurophysiology, Institute of Zoology, Universität Regensburg, Regensburg, Germany.
Synaptic Physiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States.
Front Cell Neurosci. 2020 Nov 5;14:600537. doi: 10.3389/fncel.2020.600537. eCollection 2020.
Neurons typically receive synaptic input in their dendritic arbor, integrate inputs in their soma, and send output action potentials through their axon, following Cajal's law of dynamic polarization. Two notable exceptions are retinal amacrine cells and olfactory granule cells (GCs), which flout Cajal's edict by providing synaptic output from the same dendrites that collect synaptic input. Amacrine cells, a diverse cell class comprising >60 subtypes, employ various dendritic input/output strategies, but A17 amacrine cells (A17s) in particular share further interesting functional characteristics with GCs: both receive excitatory synaptic input from neurons in the primary glutamatergic pathway and return immediate, reciprocal feedback GABAergic inhibitory synapses to the same synaptic terminals that provided input. Both neurons thereby process signals locally within their dendrites, shaping many parallels, signaling pathways independently. The similarities between A17s and GCs cast into relief striking differences that may indicate distinct processing roles within their respective circuits: First, they employ partially dissimilar molecular mechanisms to transform excitatory input into inhibitory output; second, GCs fire action potentials, whereas A17s do not. Third, GC signals may be influenced by cortical feedback, whereas the mammalian retina receives no such retrograde input. Finally, A17s constitute just one subtype within a diverse class that is specialized in a particular task, whereas the more homogeneous GCs may play more diverse signaling roles multiple processing modes. Here, we review these analogies and distinctions between A17 amacrine cells and granule cells, hoping to gain further insight into the operating principles of these two sensory circuits.
根据卡哈尔的动态极化定律，神经元通常在其树突分支中接收突触输入，在其胞体中整合输入，并通过其轴突发送输出动作电位。两个显著的例外是视网膜无长突细胞和嗅觉颗粒细胞，它们违反了卡哈尔的法则，从收集突触输入的同一树突提供突触输出。无长突细胞是一类多样的细胞，包含60多种亚型，采用各种树突输入/输出策略，但A17无长突细胞（A17s）尤其与颗粒细胞具有进一步有趣的功能特征：两者都从初级谷氨酸能通路中的神经元接收兴奋性突触输入，并向提供输入的相同突触终末返回即时的、相互的反馈性GABA能抑制性突触。因此，这两种神经元都在其树突内局部处理信号，独立塑造许多平行的信号通路。A17s和颗粒细胞之间的相似性凸显了显著的差异，这可能表明它们在各自回路中具有不同的处理作用：首先，它们采用部分不同的分子机制将兴奋性输入转化为抑制性输出；其次，颗粒细胞能产生动作电位，而A17s不能。第三，颗粒细胞的信号可能受皮质反馈的影响，而哺乳动物视网膜不接受这种逆行输入。最后，A17s只是专门执行特定任务的多样细胞类中的一个亚型，而更为同质的颗粒细胞可能在多种处理模式中发挥更多样化的信号作用。在这里，我们综述了A17无长突细胞和颗粒细胞之间的这些相似性和差异，希望能进一步深入了解这两种感觉回路的运作原理。
