应激时活化cGMP通路对大鼠噪声所致耳鸣的保护作用及机制研究

Tinnitus is one of the most common clinical symptoms, varying considerably in characteristics, severity and vulnerability among patients. The underlying mechanism remains elusive. It has been a frequent observation that stress closely correlates with tinnitus. However, no evidence exists for a causal link between stress and tinnitus vulnerability. Previous study in our group revealed that stress increases noise vulnerability. Furthermore, activation of cGMP signaling via PDE5 inhibitor partially prevents noise induced auditory dysfunction and counteracts tinnitus behavior in stressed rats instead of non-stressed animals. The current study, therefore, aims to investigate whether stress increases the vulnerability of noise induced tinnitus and whether glucocorticoid receptors(GR) or mineralocorticoid receptors(MR) mainly involves in the modulation of noise-induced tinnitus behavior in stressed animals after the activation of cGMP signaling. In addition, the downstream cascades of PKG are also analyzed. We utilize tools of animal models associated with tinnitus behavior and social stress, auditory metrics, morphology and molecular biology, and pharmacological tools like GR/MR antagonist, PKG inhibitor. As a result, our study provides a new pharmacological target for intervention of noise induced tinnitus.

耳鸣是临床最常见主诉之一，其性质、严重程度、易感性有极大个体差异，机制至今不明。大量临床观察显示应激与耳鸣密切相关，但目前没有研究直接证实应激与耳鸣易感性之间存在因果联系并探索可能机制。我们前期研究显示应激可增加噪声所致听觉损害的易感性；应用PDE5抑制剂活化cGMP信号通路可显著改善噪声所致听觉损害，并能在应激大鼠干预噪声所致耳鸣行为学表现，而对非应激大鼠则无耳鸣改善作用。本项目拟采用社会应激及噪声致耳鸣大鼠行为学模型联合听觉电生理、组织与形态学、分子生物学等多种手段，阐明应激是否改变噪声所致耳鸣的易感性；同时运用GR或MR拮抗剂、PKG抑制剂等观察能否阻断PDE5抑制剂对应激时噪声所致耳鸣的干预作用，以期验证我们的科学假想：应激时活化的cGMP在上游通过GR抑或MR介导、下游通过PKG相关通路完成对噪声所致耳鸣的调控，为噪声性耳鸣的有效治疗提供新的分子靶点和理论依据。

临床上发现突发性耳聋、耳鸣常常发生于熬夜或睡眠不足之后。既往研究显示睡眠剥夺（sleep deprivation, SD）可影响动物的行为和生理功能，如学习记忆、认知能力和重要脏器功能等。结合临床观察实践，本研究假设睡眠剥夺可增加BALB/C小鼠听觉系统的噪声易感性，探寻其可能机制，为临床解释突发性耳聋的病因提供理论基础。我们的研究发现，单纯使用105dB宽频噪声暴露两小时后，小鼠出现永久性阈移和ABR波Ⅰ幅值不可逆性下降；如果其前进行短时（1天）睡眠剥夺(sleep deprivation, SD)，则ABR波Ⅰ幅值下降的程度减轻，而若是其前进行长时（5天）SD,则会导致ABR波Ⅰ幅值进一步下降，与各组带状突触计数水平相对应。无论有无叠加噪声暴露，经过5天SD的BALB/C小鼠耳蜗和海马GCR水平以及自噬蛋白LC3b水平显著低于对照组和经过1天SD的两个实验组（p﹤0.01）。综上，长时间睡眠剥夺能增加BALB/C小鼠听觉系统的噪声易感性,这可能是由于长时间睡眠剥夺作为一种慢性应激导致GCR减少，诱导自噬水平下调，从而削弱自噬对噪声损伤的保护作用。这一结果可能对解释临床上睡眠障碍后突聋和耳鸣提供理论依据。