单侧迷路破坏后大鼠前庭神经内侧核区氨基酸含量的变化

本实验用脑部微量透析法和高效液相色谱法观察单侧迷路破坏(unilateral labyrinthectomy,经利多卡因或对氨基苯胂酸盐预处理以阻断单侧外周前庭器官)后大鼠同侧及对侧前庭神经内侧核(medial vestibular nucleus,MVN)区部分氨基酸(天冬氨酸、谷氨酸、谷氨酰胺、甘氨酸、牛磺酸和丙氨酸)含量的变化,以了解前庭代偿的部分神经化学机制.实验观察到,对照组大鼠MVN区天冬氨酸、谷氨酸、谷氨酰胺、甘氨酸、牛磺酸和丙氨酸浓度分别为(6.15±0.59),(18.13±1.21),(33.73±1.67),(9.26±0.65),(9.56±0.77)和(10.07±0.83)pmol/8 μL透析样本.左侧中耳内灌注2%利多卡因后10 min,同侧MVN区天冬氨酸、谷氨酸含量立即减少(P＜0.05),牛磺酸含量增加(P＜0.05);对侧MVN区谷氨酸含量立即增加(P＜0.05),甘氨酸和丙氨酸含量减少;双侧核团间谷氨酸、甘氨酸和丙氨酸含量失衡.而用对氨基苯胂酸盐永久阻断单侧前庭器官2周后,同侧MVN区谷氨酸和丙氨酸含量减少,谷氨酰胺含量增高;对侧MVN区谷氨酸含量也减少;同侧MVN区谷氨酰胺含量明显高于对侧MVN区.结果提示,单侧迷路破坏后双侧MVN区氨基酸含量立即失去平衡,随着前庭代偿的进展,此差异减少,但是在前庭代偿后却出现双侧前庭核区谷氨酰氨的含量失衡,说明在前庭代偿过程中氨基酸含量变化起着重要作用.

Changes of amino acid concentrations in the rat medial vestibular nucleus following unilateral labyrinthectomy

To understand the neurochemical mechanisms underlying the vestibular compensation, we determined the levels of amino acids such as aspartate, glutamate, glutamine, glycine, taurine, alanine in the medial vestibular nucleus (MVN) following unilateral labyrinthectomy (UL), by using in vivo brain microdialysis and high-performance liquid chromatography technique. Rats were pretreated by infusing 2% lidocaine 1.2 mL or 10 mg arsanilic acid into the tympanic cavity to obstruct uni-periphery vestibular organ, and then the levels of amino acids were determined in MVN of normal control and ipsilateral or contralateral lesional (ipsi-/contra-lesional) rats. In the control experiment, the levels of aspartate, glutamate, glutamine, glycine, taurine, and alanine were (6.15 +/- 0.59), (18.13 +/- 1.21), (33.73 +/- 1.67), (9.26 +/- 0.65), (9.56 +/- 0.77) and (10.07 +/- 0.83) pmol/8 muL sample, respectively. The concentrations of aspartate and glutamate decreased, while the concentration of taurine increased in the ipsi-lesional MVN of rats 10 min after infusing 2% lidocaine into middle ear to obstruct uni-periphery vestibular organ. Whereas the concentration of glutamate increased, the concentrations of glycine and alanine decreased in the contra-lesional MVN, accompanied by imbalances of glutamate, glycine and alanine in the bilateral nuclei. In contrast, the levels of glutamate and alanine decreased, the level of glutamine increased in the ipsi-lesional MVN, and the level of glutamate decreased in the contra-lesional MVN of rats 2 weeks after infusing 10 mg arsanilic acid into the tympanic cavity to obstruct uni-periphery vestibular organ. Furthermore, the level of glutamine in the ipsi-lesional MVN was obviously higher than that in the contra-lesional MVN. These results demonstrate that an imbalance of different amino acids appeared in bilateral MVN after UL, and this imbalance decreased after the development of vestibular compensation. Whereas the imbalance of glutamine release in bilateral nuclei appeared after vestibular compensation.