Brew Helen M, Forsythe Ian D
Department of Cell Physiology and Pharmacology, University of Leicester, P.O. Box 138, Leicester LE1 9HN, UK.
Hear Res. 2005 Aug;206(1-2):116-32. doi: 10.1016/j.heares.2004.12.012.
Many central auditory nuclei preserve the tonotopic organization of their afferent inputs, generating a frequency "map" across the nucleus. In the medial nucleus of the trapezoid body (MNTB) the most medial neurons receive inputs corresponding to the highest frequency sounds and the most lateral neurons have the lowest characteristic frequencies. Whole-cell patch recording from MNTB principal neurons in rat brainstem slices demonstrates a corresponding tonotopic organization of voltage-gated outward potassium currents. Medial MNTB neurons had larger total outward K+ current amplitudes than lateral neurons and similar medial to-lateral gradients were observed for two K+ current subtypes distinguished by their low and high voltage activation thresholds. In contrast, a third K+ conductance with an intermediate voltage threshold and slower kinetics showed an inverse gradient (being smallest in medial MNTB). The orthogonal axes of MNTB did not exhibit potassium current gradients (dorsal-to-ventral, or rostral-to-caudal). The input resistance was unchanged across the MNTB, but a slow capacitative component was enhanced in lateral neurons. These data demonstrate that the intrinsic properties of rat MNTB neurons are tuned across the tonotopic axis so as to promote shorter action potentials, faster firing and therefore greater accuracy in transmission of auditory information in the high characteristic frequency regions.
许多中枢听觉核团保留了其传入输入的音频拓扑组织，在整个核团中生成一个频率“图谱”。在梯形体内侧核（MNTB）中，最内侧的神经元接收对应最高频率声音的输入，而最外侧的神经元具有最低的特征频率。对大鼠脑干切片中MNTB主神经元进行全细胞膜片钳记录，结果显示电压门控外向钾电流也存在相应的音频拓扑组织。MNTB内侧神经元的总外向K⁺电流幅度大于外侧神经元，并且在通过低电压和高电压激活阈值区分的两种K⁺电流亚型中，也观察到了类似的从内侧到外侧的梯度变化。相比之下，第三种具有中间电压阈值和较慢动力学的K⁺电导则呈现相反的梯度（在MNTB内侧最小）。MNTB的正交轴（背腹向或头尾向）未表现出钾电流梯度。整个MNTB的输入电阻没有变化，但外侧神经元中一个缓慢的电容性成分增强。这些数据表明，大鼠MNTB神经元的内在特性在音频拓扑轴上进行了调整，从而在高特征频率区域促进更短的动作电位、更快的放电，进而提高听觉信息传递的准确性。
