早期耳鸣和持续耳鸣对大鼠听觉中枢GAP43和egr-1基因表达的影响及变化

The effect of the early and persistent tinnitus on the expressions of GAP43 and egr-1 in auditory pathway of rats with tinnitus induced by sodium salicylate

目的通过检测早期耳鸣与持续耳鸣大鼠听觉通路中GAP43和egr-1基因的表达情况来探讨耳鸣发生的中枢源性机制。方法将48只大鼠随机分为6组,每组均8只:水杨酸钠组分为早期组与持续组,每次训练前2小时腹腔注射10%水杨酸钠溶液(400mg/kg),其中持续组在耳鸣模型建立成功后,继续每天同一时间腹腔注射相同剂量水杨酸钠溶液10天;盐水1组与盐水2组,每次训练前2小时腹腔注射与水杨酸钠组相同体积生理盐水,其中盐水2组在造模成功后,继续每天同一时间腹腔注射同体积生理盐水10天;空白对照组也分为空白1组与空白2组。早期组、盐水1组、空白1组同时断头取标本,而盐水2组、空白2组与持续组一同断头取标本。再利用实时荧光(sybgreena染料法)相对定量PCR检测GAP43和egr-1的mRNA在听觉通路四个核团中的表达情况。结果空白组与生理盐水组相比较,听皮层GAP43与egr-1的mRNA表达水平明显提高(P<0.01)。耳蜗核中GAP43的mRNA随着水杨酸钠注射次数的增加先下降(P<0.01),后又逐渐回升(P<0.01);egr-1mRNA明显下降(P<0.01)。下丘GAP43、egr-1的mRNA表达水平均有明显提高。上橄榄核中,仅持续组GAP43的mRNA有明显降低(P<0.01);两组水杨酸钠组的egr-1的mRNA随着水杨酸钠注射次数的增多而逐渐降低(P<0.05)。结论 GAP43和egr-1基因表达水平的改变不但证实了由水杨酸钠诱导的耳鸣大鼠的听觉通路中听觉神经元发生了可塑性改变,并且能够维持这种可塑性改变,从而使大鼠耳鸣症状得以长期持续。

Objective To investigate the expression of GAP43 and egr-1 in auditory system of the rats with early and persistent tinnitus, analyzing the central nerve mechanism of tinnitus. Methods 48 Wistar rats were grouped into 6 teams randomly （n=8）. Two groups of sodium salicylate included the early tinnitus and the persistent tinnitus group, which received intraperitoneally injected （i.p.） dose of 400 mg sodium salicylate per kg bodyweight dissolved in physiological saline 2 hours before training everyday. Persistent tinnitus group was continued receiving the same dose sodium salicylate injection for ten days. Saline group 1 and saline group 2 were injected the same dose physiological saline as the sodium salicylate groups did, and salicylate group 2 was received a 10-day injection of the same dose physiological saline until model was built. There were the blank control 1 and 2 groups. Samples fromthe early tinnitus, the salinel and control 1 were harvested at same time points, meanwhile samples from the saline 2, the control2 and the persistent tinnitus group were collected at the time point. Real time quantitative RT-PCR was used to detect the expression of GAP43 and egr-1 gene in these four auditory nucleis. Results Compared with the saline 1, 2 and control 1, 2, the expressions of GAP43 and egr-1 mRNA in auditory cortex were significantly increased （P〈0.01）. Expression of GAP43 mRNA in the cochlear nucleus was down-regulated at first（P〈0.01）, and then up-regulated in the end（P〈0.01）. Expression of egr-1 mRNA was declined dramatically （P〈0.01）. An up-regulation of GAP43 and egr-1 mRNA was observed in the colliculus inferior （P〈0.01）. Expression of GAP43 mRNA decreased in persistent tinnitus group in nuclei olivaris superior（P〈0.01）. Expression of egr-1 mRNA reduced according to injection of sodium salicylate in two sodium salicylate groups（P〈0.05）. Conclusions The variation of GAP43 and egr-1 expression not only supports that a shaped changes of the auditory pathway in the rats with tinnitus were induced by sodium salicylate, but also showed that these changes can maintain the long-term tinnitus.