Newlands S D, Perachio A A
Department of Otolaryngology, University of Texas Medical Branch, Galveston 77550.
Exp Brain Res. 1990;82(2):359-72. doi: 10.1007/BF00231255.
The spontaneous activity and dynamic responses to two frequencies (1.3 and 0.13 Hz) of sinusoidal angular horizontal head acceleration of type I neurons in the medial vestibular nucleus were recorded bilaterally in decerebrate Mongolian gerbils (Meriones unguiculatus) under three experimental conditions; normal labyrinth intact, acutely following unilateral labyrinthine lesion, and four to seven weeks following labyrinthine lesion. The mean spontaneous activity and number of detected type I neurons decreased immediately ipsilateral to the lesion but recovered significantly with time. In contrast, spontaneous activity on the contralateral side increased during compensation following hemilabyrinthectomy. The mean response gains at both frequencies of head oscillation were depressed bilaterally and asymmetrically acutely following the lesion such that the response gain of cells on the intact side exceeded that of the neurons recorded on the injured side. After compensation the number of detected type I neurons on the side ipsilateral to the injury increased but remained below normal levels. The mean gains remained depressed but became symmetric with compensation as a result of improvement in the response of ipsilateral neurons. The phase of responses were significantly advanced in the compensated animals. Although response gain is not fully restored, the linearity of the dynamic modulation in compensated animals is improved as evidenced by a continuous modulation of the increased spontaneous activity of neurons contralateral to the hemilabyrinthectomy. It is proposed that this effect is related to the concurrent improvement in the linearity of the horizontal vestibulo-ocular response. Electrical cathodal polarization of the vestibular nerve ipsilateral to the ablated labyrinth was utilized to investigate the relationship between recovery of spontaneous activity and dynamic function. Acutely following hemilabyrinthectomy, cathodal polarization restored activity in second-order type I neurons to near normal levels but their response gain to head rotation remained depressed. Similar galvanic stimulation in compensated animals also elevated ipsilateral spontaneous activity. As in the acute preparation, such stimulation did not modify the response gain or phase. Thus, the improvement in response of type I neurons in the compensated gerbil was not a direct consequence of restoration of spontaneous activity on the side of the injury.
在内耳迷路完整正常、单侧迷路急性损伤后以及迷路损伤四至七周这三种实验条件下，对去大脑蒙古沙鼠（长爪沙鼠）双侧内侧前庭核中I型神经元对两种频率（1.3和0.13赫兹）正弦角水平头部加速度的自发活动和动态反应进行了记录。损伤同侧的I型神经元平均自发活动和检测到的神经元数量立即减少，但随时间显著恢复。相反，在半规管切除术后的代偿过程中，对侧的自发活动增加。损伤后，头部摆动的两个频率下的平均反应增益在双侧均急性降低且不对称，使得完整侧细胞的反应增益超过损伤侧记录的神经元的反应增益。代偿后，损伤同侧检测到的I型神经元数量增加，但仍低于正常水平。平均增益仍然降低，但由于同侧神经元反应的改善而在代偿后变得对称。代偿动物的反应相位明显提前。尽管反应增益未完全恢复，但代偿动物中动态调制的线性得到改善，半规管切除对侧神经元自发活动增加的持续调制证明了这一点。有人提出，这种效应与水平前庭眼反射的线性同时改善有关。利用对切除迷路同侧的前庭神经进行阴极极化来研究自发活动恢复与动态功能之间的关系。半规管切除术后急性阶段，阴极极化将二级I型神经元的活动恢复到接近正常水平，但其对头部旋转的反应增益仍然降低。在代偿动物中进行类似的电刺激也提高了同侧的自发活动。与急性实验一样，这种刺激并未改变反应增益或相位。因此，代偿沙鼠中I型神经元反应的改善不是损伤侧自发活动恢复的直接结果。
