Projection Neuron Axon Collaterals in the Dorsal Horn: Placing a New Player in Spinal Cord Pain Processing.
Projection Neuron Axon Collaterals in the Dorsal Horn: Placing a New Player in Spinal Cord Pain Processing.
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DOI：
10.3389/fphys.2020.560802
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发表时间：
2020
影响因子：
4
通讯作者：
Graham BA
中科院分区：
文献类型：
--
作者：
Browne TJ;Hughes DI;Dayas CV;Callister RJ;Graham BA
疼痛体验依赖于从脊髓背角到高级脑中心的伤害性信号的中继。这个功能最终是由一小群高度特化的神经元（称为投射神经元（PN））的输出来实现的。与其他中枢神经系统（CNS）区域的输出神经元一样，PN具有大量轴突侧支系统，该系统在局部回路中广泛分支。这些轴突侧支广泛分布在脊髓节段内和节段之间。自Cajal时代以来，PN轴突侧支的解剖学数据已经存在，然而，它们在脊髓疼痛信号传导中的功能仍然不清楚，并且在当前的脊髓疼痛处理模型中缺失。尽管存在这些遗漏，但可以从其他CNS区域（如海马、杏仁核、嗅皮质和脊髓腹角）的主要或输出神经元的轴突侧支系统中了解PN轴突侧支的潜在作用。轴突侧支在这些系统中的连接和作用已经得到了很好的定义，并分别用于确认记忆、恐惧、嗅觉和运动控制中的关键作用。我们在这里回顾这些信息，并提出了一个框架，在背角的PN轴突侧支功能的特点。我们强调，传统上用于描绘在其他中枢神经系统区域的轴突侧支功能的实验方法不容易应用到PN，因为它们相对于脊髓中间神经元（IN）的稀缺性，以及缺乏背角的细胞组织。最后，我们强调如何快速发展的技术，如病毒表达的光遗传学或化学遗传学探针可以克服这些挑战，并允许PN轴突侧支功能的表征。获得这种类型的详细信息是将PN侧支系统功能纳入脊髓感觉处理模型的必要的第一步。
The pain experience depends on the relay of nociceptive signals from the spinal cord dorsal horn to higher brain centers. This function is ultimately achieved by the output of a small population of highly specialized neurons called projection neurons (PNs). Like output neurons in other central nervous system (CNS) regions, PNs are invested with a substantial axon collateral system that ramifies extensively within local circuits. These axon collaterals are widely distributed within and between spinal cord segments. Anatomical data on PN axon collaterals have existed since the time of Cajal, however, their function in spinal pain signaling remains unclear and is absent from current models of spinal pain processing. Despite these omissions, some insight on the potential role of PN axon collaterals can be drawn from axon collateral systems of principal or output neurons in other CNS regions, such as the hippocampus, amygdala, olfactory cortex, and ventral horn of the spinal cord. The connectivity and actions of axon collaterals in these systems have been well-defined and used to confirm crucial roles in memory, fear, olfaction, and movement control, respectively. We review this information here and propose a framework for characterizing PN axon collateral function in the dorsal horn. We highlight that experimental approaches traditionally used to delineate axon collateral function in other CNS regions are not easily applied to PNs because of their scarcity relative to spinal interneurons (INs), and the lack of cellular organization in the dorsal horn. Finally, we emphasize how the rapid development of techniques such as viral expression of optogenetic or chemogenetic probes can overcome these challenges and allow characterization of PN axon collateral function. Obtaining detailed information of this type is a necessary first step for incorporation of PN collateral system function into models of spinal sensory processing.
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