Comparison Of Action Potential Recorded From Medial Nucleus Of Trapezoid Body And Dorsal Cochlear Nucleus Neurons

One of the main functions of the auditory system is to detect the spatial location of sound sources, which is of ultimate important to animal survival. Historically, the research of sound localization has been focused on the nature of the physical acoustical parameters of sound arriving at the ears that relate to localization. Nowadays, it is known that there are three primary cues of sound location, each of them is created by sound waves that interfere with the head and outer ears, or pinnae: interaural time difference (ITD) which is encoded by medial superior olive and lateral superior olive; interaural intensity difference (â…¡D) which is encoded by LSO; monaural spectral cues which is encoded by dorsal cochlear nucleus (DCN)Previous studies of the auditory neurons encoding the spatial signal of the sound source were performed with extracellular recording in vivo, but how is the temporal response properties of single neuron to spatial cues? We recorded the resposes of principal neurons in medial nucleus of trapezoid body which process commonly ITD and IID cues in the horizontal plane and fusiform cells in the dorsal cochlear nucleus which process monaural spectral cues in the vertical plane. We used whole-cell patch recording to inverstigate the membrane response properties of single neuron, and compared the different response properties of different nuclei. We investigated the differences of the principal neuron in principal neuron in medial nucleus of trapezoid body (MNTB) and DCN fusiform cell, in whole-cell patch-clamp recording model by comparing action potential waveform, peak value, the dur duration of depolarization, duration of repolarization, interspike interval at threshold value, interspike interval at peak value, actional potential count, the first spike latency, by using software of clamfit, we revealed the electrophysiology properties of two type neurons that process different auditory spatial cues.A Total of36neurons were recorded,including25of MNTB principal cells and11of DCN fusiform cells. Experimental results showed that MNTB principal cells discharged two types of action potential waveforms, which nominated as API (Action potential wareforml, n=6) and AP2(Action potential wareform2, n=19). The duration of repolarization, interspike interval at threshold value, interspike interval at peak value of API and AP2in MNTB principal cells were significantly different (p<0.01). But there were no significant difference on the action potential amplitude and first spike latency between API and AP2(p>0.05). Action potentials could be elicited in MNTB cells by a small stimulus current (30pA), and the discharge pattern did not change with amplitude of injected current. But DCN fusiform cells would not response until stimulus current at200pA, and their discharge pattern of changed with increasing injected current, frombuildup, pauser to chopper. The Action potential amplitude, duration of depolarization, duration of repolarization, interspike interval at threshold value, the interspike interval at peak value, the first spike latency of DCN fudiform cells and MNTB principal cells were significantly different (p<0.05).Conclusions:1. MNTB cells showed two types of action potential waveforms, and these two action potential waveform were mutual exclusive. Comparing their morphology and electrical physiology characteristics, these two types of MNTB neurons were basically the same but different in the duration of repolarization and interspike interval. This result suggeated that this is the same type of neuron. DCN fusiform cells only showed a classic action potential waveform.2. The discharge pattern of DCN fusiform cells three discharge patterns:buildup, pauser, chopper. The discharge pattern of MNTB principal cells did not change with the stimulus intensity.3. Action potential amplitude of DCN fusiform cells was significantly higher than that of the MNTB principal cells. Other properties, like duration of depolarization, duration of repolarization, interspike interval at threshold value and the interspike interval at peak value, the first spike latency of DCN fudiform cell were significantly lower than that of the MNTB principal cells. Different electrophysiological properties reflected different characteristics of these neurons, suggesting they encoded the spectral cues in the vertical plane and the â…¡D cues in horizontal plane respectively.