Scott Luisa L, Mathews Paul J, Golding Nace L
Institute for Neuroscience, University of Texas, Austin, Texas 78712-0248, USA.
J Neurosci. 2005 Aug 31;25(35):7887-95. doi: 10.1523/JNEUROSCI.1016-05.2005.
In mammals, principal neurons of the medial superior olive (MSO) exhibit biophysical specializations that enable them to detect sound localization cues with microsecond precision. In the present study, we used whole-cell patch recordings to examine the development of the intrinsic electrical properties of these neurons in brainstem slices from postnatal day 14 (P14) to P38 gerbils. In the week after hearing onset (P14-P21), we observed dramatic reductions in somatic EPSP duration, input resistance, and membrane time constant. Surprisingly, somatically recorded action potentials also dramatically declined in amplitude over a similar period (38 +/- 3 to 17 +/- 2 mV; tau = 5.2 d). Simultaneous somatic and dendritic patch recordings revealed that these action potentials were initiated in the axon, which primarily emerged from the soma. In older gerbils, the rapid speed of membrane voltage changes and the attenuation of action potential amplitudes were mediated extensively by low voltage-activated potassium channels containing the Kv1.1 subunit. In addition, whole-cell voltage-clamp recordings revealed that these potassium channels increase nearly fourfold from P14 to P23 and are thus a major component of developmental changes in excitability. Finally, the electrophysiological features of principal neurons of the medial nucleus of the trapezoid body did not change after P14, indicating that posthearing regulation of intrinsic membrane properties is not a general feature of all time-coding auditory neurons. We suggest that the striking electrical segregation of the axon from the soma and dendrites of MSO principal neurons minimizes spike-induced distortion of synaptic potentials and thus preserves the accuracy of binaural comparisons.
在哺乳动物中，内侧上橄榄核（MSO）的主要神经元表现出生物物理特性，使它们能够以微秒级精度检测声音定位线索。在本研究中，我们使用全细胞膜片钳记录技术，研究了出生后第14天（P14）至P38沙鼠脑干切片中这些神经元内在电特性的发育情况。在听力开始后的一周内（P14 - P21），我们观察到体细胞兴奋性突触后电位（EPSP）持续时间、输入电阻和膜时间常数显著降低。令人惊讶的是，在同一时期，体细胞记录的动作电位幅度也显著下降（从38±3 mV降至17±2 mV；τ = 5.2天）。体细胞和树突同时进行的膜片钳记录显示，这些动作电位在轴突中起始，轴突主要从体细胞发出。在年龄较大的沙鼠中，膜电压变化的快速速度和动作电位幅度的衰减主要由含有Kv1.1亚基的低电压激活钾通道介导。此外，全细胞膜电压钳记录显示，这些钾通道从P14到P23增加了近四倍，因此是兴奋性发育变化的主要组成部分。最后，梯形体内侧核主要神经元的电生理特征在P14后没有变化，表明听力后内在膜特性的调节并非所有时间编码听觉神经元的普遍特征。我们认为，MSO主要神经元的轴突与体细胞和树突之间显著的电隔离可将突触电位的尖峰诱导失真降至最低，从而保持双耳比较的准确性。
