Tracheal Occlusion Modulates the Gene Expression Profile of the Medial Thalamus in Anesthetized Rats

Conscious awareness of breathing requires the activation of higher brain centers. The sensation of breathing is believed to be a neural gating process. The thalamus provides the brain structure that could be responsible for the gating of respiratory sensory information to the cortex. It was reasoned that if the thalamus is the neural gate, then tracheal obstructions will modulate the gene expression profile of the thalamus. Anesthetized rats were instrumented with an inflatable cuff sutured around the trachea. The cuff was inflated to obstruct 2-4 breaths, then deflated for a minimum of 15 breaths. The obstructions were repeated for 10 min followed by immediate brain removal, and the medial thalamus was dissected and prepared for microarray analysis. Gene expression profiles were measured using Agilent Technology Oligo Microarrays. Following the occlusion protocol, 588 genes were found to be altered (p < 0.05, log2 fold change = 0.4), with 327 down-regulated and 261 genes up-regulated. A significant up-regulation of the serotonin HTR2A receptor and significant down-regulation of the dopamine DRD1 receptor genes were found. A pathway analysis was performed targeting serotonin and dopamine receptor pathways. The mitogen activated protein kinase 1 (MAPK1) gene was significantly down-regulated. MAPK1 is an inhibitory regulator of the serotonin HTR2A receptor and facilitatory regulator for the dopamine DRD1 receptor. Down-regulation of MAPK1 may be related to the 2-fold up-regulation of HTR2A and 2-fold down-regulation of DRD1 suggesting an interaction in the medial thalamus serotonin-dopamine pathway elicited by airway obstruction. These results demonstrate an immediate change in gene expression in thalamic arousal-fear-anxiety-motivation related serotonin and dopamine receptors in response to airway obstruction. The results support the hypothesis that the thalamus is a component in the respiratory mechanosensory neural pathway.对呼吸的有意识觉知需要高级脑中枢的激活。呼吸感知被认为是一种神经门控过程。丘脑（thalamus）作为脑内核心结构，可能负责将呼吸感觉信息门控传递至大脑皮层。据此推论，若丘脑为该神经门控位点，则气管阻塞会调控丘脑的基因表达谱。本研究对麻醉大鼠实施手术，于其气管处缝合可充气袖带：将袖带充气以阻断2~4次呼吸，随后放气并维持至少15次呼吸周期。上述阻塞操作重复10分钟后，立即取出大鼠脑组织，分离内侧丘脑并制备样本用于微阵列分析。采用安捷伦科技（Agilent Technology）的寡核苷酸微阵列（Oligo Microarrays）检测基因表达谱。按照阻塞方案处理后，共检测到588个基因表达发生显著改变（p<0.05，log2折叠变化=0.4），其中327个基因表达下调，261个基因表达上调。研究发现血清素（serotonin）HTR2A受体基因表达显著上调，多巴胺（dopamine）DRD1受体基因表达显著下调。针对血清素与多巴胺受体通路开展了通路富集分析，结果显示丝裂原活化蛋白激酶1（mitogen activated protein kinase 1, MAPK1）基因表达显著下调。MAPK1对血清素HTR2A受体具有抑制性调控作用，而对多巴胺DRD1受体则发挥促进性调控功能。MAPK1的下调可能与HTR2A受体的2倍上调以及DRD1受体的2倍下调存在关联，这提示气道阻塞可引发内侧丘脑内血清素-多巴胺通路的相互作用。上述结果表明，气道阻塞可引发丘脑内与觉醒、恐惧、焦虑及动机调控相关的血清素与多巴胺受体基因表达的快速改变。本研究结果支持“丘脑是呼吸机械感受神经通路的组成部分”这一假说。