The Electrophysiological Characteristics Of The Two Type Principal Neuron With Different Action Potential Waveform In Medial Nucleus Of Trapezoid Body

The timing of neural discharges, especially the first spike latency (FSL), which is of higher precision and efficiency than neural firing rate has been considered as an important parameter to encode sensory information. FSLs of most auditory neuronal response are determined by the primary stimulus parameters, which dertermine the envelope onset status, such as the steady-state sound pressure (SP), rise time (RT) and rise function (RF).Previous studies of our laboratory on the temporal response properties of auditory neurons were performed by using extracellular recording technique. However, when studing the principal neuron in medial nucleus of trapezoid body (MNTB) with whole-cell recording recently, we found two kinds of different action potential waveforms with respect to the same current stimulus. So what is the disparity of the electrophysiological characteristics of the two type principal neuron with different action potential waveforms in medial nucleus of trapezoid body?We investigated the differences of the principal neurons in MNTB by injecting currents using whole-cell patch-clamp recording technique and comparing action potential waveform and its duration of repolarization (DR, DR40%, DR60%, DR80%), the first spike latency (FSL) and the threshold potential (TH) using software of Clamfit.A total of 18 principal neurons were recorded. We divided them into two groups based on their different action potential waveforms. Nine neurons were in each group. The durations of repolarization (DR) of the two groups' action potential are significantly different (We process the data with Independent-Sample T Test, the respective DR40% of two groups is 2.309ms±0.204ms,3.221ms±0.529ms, t=-1.610, P=0.138; the respective DR60% of two groups is 3.696ms±0.326ms, 31.701ms±9.853ms, t=-2.841,P=0.022; the respective DR80% of two groups is 7.135ms±0.799ms,60.236ms±9.359ms, t=-5.653,P=0.000) and not related to amplitude of injected current; but there are no manifest differences on the two group's resting potential (RP), threshold potential (TH) and first spike latency (FSL) (We process the data with Independent-Sample T Test, the respective RP of two groups is-51.269mV±1.580mV,-51.917mV±1.630mV, t=0.285, P=0.779; the respective TH of two groups is-39.146mV±1.273mV,-42.077mV±1.142mV, t=1.714, P=0.106; the respective MFSL of two groups is 11.560ms±2.032ms,11.168ms±1.128ms, t=0.169, P=0.868; the respective LFSL of two groups is 72.108ms±14.582ms, 75.410ms±15.410ms, t=-0.156, P=0.878).Conclusion:①There are two type principal neurons with different action potential waveforms in medial nucleus of trapezoid body (MNTB), but their resting potential, threshold potential and first spike latency are not obvious different.②The significant difference of the two rows'duration of repolarization of action potential indicate that their refractory periods are various and it is possibly related to the principal neurons' coding frequency information of sounds.