Chen Chao-Yin, Bonham Ann C, Plopper Charles G, Joad Jesse P
Department of Internal Medicine, School of Medicine, University of California at Davis, 95616, USA.
J Appl Physiol (1985). 2003 Feb;94(2):819-27. doi: 10.1152/japplphysiol.00552.2002. Epub 2002 Oct 25.
Acute ozone exposure evokes adverse respiratory responses, particularly in children. With repeated ozone exposures, however, despite the persistent lung inflammation and increased sensory nerve excitability, the central nervous system reflex responses, i.e., rapid shallow breathing and decreased lung function, adapt, suggesting changes in central nervous system signaling. We determined whether repeated ozone exposures altered the behavior of nucleus tractus solitarius (NTS) neurons where reflex respiratory motor outputs are first coordinated. Whole cell recordings were performed on NTS neurons in brain stem slices from infant monkeys exposed to filtered air or ozone (0.5 ppm, 8 h/day for 5 days every 14 days for 11 episodes). Although episodic ozone exposure depolarized the membrane potential, increased the membrane resistance, and increased neuronal spiking responses to depolarizing current injections (P < 0.05), it decreased the excitability to vagal sensory fiber activation (P < 0.05), suggesting a diminished responsiveness to sensory transmission, despite overall increases in excitability. Substance P, implicated in lung and NTS signaling, contributed to the increased responsiveness to current injections but not to the diminished sensory transmission. The finding that NTS neurons undergo plasticity with repeated ozone exposures may help to explain the adaptation of the respiratory motor responses.
急性臭氧暴露会引发不良的呼吸道反应，尤其是在儿童中。然而，在反复接触臭氧后，尽管肺部炎症持续存在且感觉神经兴奋性增加，但中枢神经系统的反射反应，即快速浅呼吸和肺功能下降，会出现适应性变化，这表明中枢神经系统信号传导发生了改变。我们确定反复接触臭氧是否会改变孤束核（NTS）神经元的行为，在该部位反射性呼吸运动输出首先得到协调。对暴露于过滤空气或臭氧（0.5 ppm，每14天中每天8小时，共5天，共11次发作）的幼年猴子脑干切片中的NTS神经元进行全细胞记录。尽管间歇性臭氧暴露使膜电位去极化、增加了膜电阻，并增加了神经元对去极化电流注入的放电反应（P < 0.05），但它降低了对迷走神经感觉纤维激活的兴奋性（P < 0.05），这表明尽管总体兴奋性增加，但对感觉传导的反应性降低。与肺部和NTS信号传导有关的P物质，导致了对电流注入反应性的增加，但对感觉传导的减弱没有影响。NTS神经元在反复接触臭氧后发生可塑性变化这一发现，可能有助于解释呼吸运动反应的适应性。
