DeBerry Jennifer J, Samineni Vijay K, Copits Bryan A, Sullivan Christopher J, Vogt Sherri K, Albers Kathryn M, Davis Brian M, Gereau Robert W
Department of Anesthesiology and Perioperative Medicine, University of Alabama at Birmingham, Birmingham, AL, United States.
Department of Anesthesiology, Washington University Pain Center, St. Louis, MO, United States.
Front Integr Neurosci. 2018 Feb 12;12:5. doi: 10.3389/fnint.2018.00005. eCollection 2018.
Bladder-innervating primary sensory neurons mediate reflex-driven bladder function under normal conditions, and contribute to debilitating bladder pain and/or overactivity in pathological states. The goal of this study was to examine the respective roles of defined subtypes of afferent neurons in bladder sensation and function via direct optogenetic activation. To accomplish this goal, we generated transgenic lines that express a Channelrhodopsin-2-eYFP fusion protein (ChR2-eYFP) in two distinct populations of sensory neurons: TRPV1-lineage neurons (;Ai32, the majority of nociceptors) and Na1.8 neurons (;Ai32, nociceptors and some mechanosensitive fibers). In spinal cord, eYFP+ fibers in ;Ai32 mice were observed predominantly in dorsal horn (DH) laminae I-II, while in ;Ai32 mice they extended throughout the DH, including a dense projection to lamina X. Fiber density correlated with number of retrogradely-labeled eYFP+ dorsal root ganglion neurons (82.2% ;Ai32 vs. 62% ;Ai32) and degree of DH excitatory synaptic transmission. Photostimulation of peripheral afferent terminals significantly increased visceromotor responses to noxious bladder distension (30-50 mmHg) in both transgenic lines, and to non-noxious distension (20 mmHg) in ;Ai32 mice. Depolarization of ChR2+ afferents in ;Ai32 mice produced low- and high-amplitude bladder contractions respectively in 53% and 27% of stimulation trials, and frequency of high-amplitude contractions increased to 60% after engagement of low threshold (LT) mechanoreceptors by bladder filling. In ;Ai32 mice, low-amplitude contractions occurred in 27% of trials before bladder filling, which was pre-requisite for light-evoked high-amplitude contractions (observed in 53.3% of trials). Potential explanations for these observations include physiological differences in the thresholds of stimulated fibers and their connectivity to spinal circuits.
支配膀胱的初级感觉神经元在正常情况下介导反射驱动的膀胱功能，并在病理状态下导致使人衰弱的膀胱疼痛和/或膀胱过度活动。本研究的目的是通过直接光遗传学激活来研究传入神经元的特定亚型在膀胱感觉和功能中的各自作用。为实现这一目标，我们构建了转基因品系，其在两种不同的感觉神经元群体中表达通道视紫红质-2-eYFP融合蛋白（ChR2-eYFP）：TRPV1谱系神经元（；Ai32，大多数伤害感受器）和Na1.8神经元（；Ai32，伤害感受器和一些机械敏感纤维）。在脊髓中，；Ai32小鼠中的eYFP+纤维主要在背角（DH）I-II层中观察到，而在；Ai32小鼠中，它们延伸至整个DH，包括向X层的密集投射。纤维密度与逆行标记的eYFP+背根神经节神经元数量相关（；Ai32为82.2%，；Ai32为62%）以及DH兴奋性突触传递程度。对两种转基因品系的外周传入终末进行光刺激均显著增加了对有害膀胱扩张（30 - 50 mmHg）的内脏运动反应，在；Ai32小鼠中还增加了对无害扩张（20 mmHg）的反应。；Ai32小鼠中ChR2+传入纤维的去极化分别在53%和27%的刺激试验中产生了低幅度和高幅度膀胱收缩，在膀胱充盈使低阈值（LT）机械感受器激活后，高幅度收缩的频率增加到60%。在；Ai32小鼠中，27%的试验在膀胱充盈前出现低幅度收缩，这是光诱发高幅度收缩（在53.3%的试验中观察到）的先决条件。对这些观察结果的潜在解释包括受刺激纤维阈值的生理差异及其与脊髓回路的连接情况。
