Synaptic reoponses in Olivocochlear neurons of the rat.

耳蜗神经元是一种投射到耳蜗并调节外周信号处理的输出听觉神经元。我们之前报道过使用全细胞贴片记录配置的大鼠切片制备中它们的内在膜特性（J.神经生理学77,2788,1997）。在这项研究中，我们进一步研究了这些神经元的突触输入。我们记录了两组OC（LOC和MOC）神经元和外侧上橄榄（LSO）主要神经元（传入听觉神经元）的EPSCs作为参考。三组神经元均存在非NMDA和NMDA受体介导的突触后电流。三组单个神经元均表现出甘氨酸能和gaba能突触反应。除了这些氨基酸反应外，乙酰胆碱对LOC神经元也表现出对烟氨酸敏感的尼古丁受体介导的反应。先前的解剖学研究已经报道了LOC神经元中周期性侧支轴突的存在，包括LOC神经元本身。由于已知LOC神经元具有胆碱能，这些观察结果表明邻近LOC神经元之间存在同步兴奋机制。LOC神经元被认为是在LSO中局部排列，并投射到耳蜗相应的特征频率区域。因此，对一组LOC神经元进行同步激励可以有效地增强特定频率区域的听觉信号。

Olivocochlear (OC) neurons are efferent auditory neurons that project to the cochlea, and regulate the peripheral signal processing. We have previously reported on their intrinsic membrane properties in slice preparation of the rat using the whole-cell patch recording configuration (J. Neurophysiology 77,2788,1997). In this study, we further investigated the synaptic inputs to these neurons. We recorded EPSCs from two groups of OC(LOC and MOC)neurons and the principal neurons of the lateral superior olive(LSO neurons)which is the afferent auditory neurons, as a reference. Both non-NMDA and NMDA receptor mediated postsynaptic currents were present in the three groups of neurons. Individual neurons of these three groups showed glycinergic and GABAergic synaptic responses. Besides these amino acid responses, LOC neurons also showed dtubocularine-sensitive nicotinic receptor mediated responses when acetylcholine was puff applied. Previous anatomical studies have reported the presence of recurrent collateral axons in LOC neurons that innervate LSO including LOC neurons themselves. Since LOC neurons are known to be cholinergic, these observations suggest a synchronous excitation mechanism among neighbored LOC neurons. LOC neurons are supposed to be arranged tonotopically in LSO, and to project to the corresponding characteristic frequency region of the cochlea. Therefore, the synchronous excitation of a group of LOC neurons might effectively enhance the auditory signals in a particular frequency region.