Signal processing at olivocochlear neuron

位于上橄榄复合体的耳蜗神经元(OC)接受耳蜗神经的传出神经支配。OC神经元在解剖学上按来源和靶点分为外侧和内侧OC(分别为LOC和MOC)神经元。组织化学研究表明，大多数OC神经元是胆碱能神经元。两组OC神经元均接受来自传入听道的兴奋性抽动。因此，由于OC神经元在切片制作过程中难以辨认，因此OC神经元形成反射弓以恢复周围听觉信号的处理，尽管OC神经元具有生理意义，但对OC神经元的直接电生理研究很少。我们成功地用逆行标记方法对活的OC神经元进行了染色。在荧光显微镜下鉴定染色的OC神经元，并进行全细胞记录。LoC和MOC神经元具有不同的电生理特性。当膜轻微超极化(-72~-76 mV)时，LOC神经元表现为沿第一棘波间期的棘波串，而MOC神经元表现为长潜伏期的棘波串。电压钳下，LOC神经元呈现两种不同失活动力学的瞬时外向电流。在MOC神经元中，只有一种瞬时外向电流。这些瞬时外向电流在LOC和MOC神经元之间的不同表达似乎是导致这两组神经元放电特性不同的原因。

The cochlea recieves an efferent innervation from olovocochlear neurons(OC)located in the superior olivary complex OC neurons have been anatomically classified into two groups by their origins and targets ; the lateral and medial OC (LOC and MOC,respectively) neurons. The majority of OC neurons is known to be cholinergic from histochemical investigations. Both groups of OC neurons recieves excitatory voley from afferent auditory tract. Thus, OC neurons form reflex arch to regurate peripheral auditory signal processing Because of the difficulty of their identfication in slice preparation, there were few direct electrophysiological study of OC neurons in spite of their physiological significance. We succeeded to stain living OC neurons by retrograde labeling. Stained OC neurons were identified under a fluorescence microscope and they were sujected to whole-cell recording. LOC and MOC neurons had different electrophysiological properties. When the membrane was slightly hyperpolarized (-72 to -76 mV), LOC neurons showed spike trains with along first interspike interval, whereas MOC neurons showed spike trains with a long latency to the first spike. Under voltage clamp, LOC neurons revealed two transient outward current with different inactivation kinetics. In MOC neurons, there was only one transient outward current. The different expression of these transient outward current between LOC and MOC neurons seems to be responsible for the difference in firing properties of these two groups of neurons.