Nguyen Quoc-Thang, Wessel Ralf, Kleinfeld David
Department of Physics and Graduate Program in Neurosciences, University of California at San Diego, La Jolla, CA 92093, USA.
J Physiol. 2004 Apr 1;556(Pt 1):203-19. doi: 10.1113/jphysiol.2003.060087. Epub 2004 Feb 6.
We characterized the electrophysiological properties of vibrissa motoneurones (vMNs) in rat. Intracellular recordings of vMNs in brainstem slices from animals aged P4 to P5 and P9 to P11, i.e. newborn animals, showed that the subthreshold membrane impedance has the form of passive decay. In particular, the impedance follows the 1/ radical f signature for long dendrites beyond a cut-off frequency of f(c)= 8 Hz. In contrast, the impedance has the form of a resonant filter in vMNs from slices prepared from animals aged P17 to P23, i.e. young animals. The resonance has a peak near 4 Hz and an amplitude of 1.2 times that at low frequencies (f approximately 0.1Hz). The low frequency onset of the resonance is shown to depend on a hyperpolarization-activated depolarizing current, I(h). This current functions as a high-pass filter. The high frequency cut-off of the resonance results from passive decay in long dendrites, similar to the case with newborn animals but with f(c)= 20Hz. In addition to a resonance in subthreshold properties, an enhanced resonance in spiking is observed in young as opposed to newborn animals. The transition from solely passive decay in vMNs from newborn animals to resonance in young animals coincides with the onset of whisking. Further, the width of the resonance encompasses the 4-15Hz range of exploratory whisking. Nonetheless, it remains to be shown if there is a causal relation between the regulation of currents in vMNs and the onset of whisking. In particular, we further observed that the membrane impedance of hypoglossal motoneurones from both newborn and young animals exhibits a subthreshold resonance that also peaks near 4Hz. The amplitude of this resonance increases from 1.1 to 1.4 times that at low frequencies in newborn versus young animals. We conjecture that resonance properties in vibrissa, hypoglossal, and potentially other motoneurones, may serve to transiently and purposely synchronize different orofacial behaviours.
我们对大鼠触须运动神经元（vMNs）的电生理特性进行了表征。对出生后第4至5天以及第9至11天（即新生动物）的动物脑干切片中的vMNs进行细胞内记录，结果显示阈下膜阻抗呈被动衰减形式。具体而言，在截止频率f(c)=8Hz以上，阻抗遵循长树突的1/√f特征。相比之下，从出生后第17至23天（即幼龄动物）制备的切片中的vMNs，其阻抗呈共振滤波器形式。该共振在4Hz附近有一个峰值，幅度是低频（f约为0.1Hz）时的1.2倍。共振的低频起始取决于超极化激活的去极化电流I(h)。该电流起到高通滤波器的作用。共振的高频截止是由长树突中的被动衰减导致的，这与新生动物的情况类似，但截止频率f(c)=20Hz。除了阈下特性中的共振外，与新生动物相比，幼龄动物的动作电位发放中观察到了增强的共振。新生动物vMNs中仅被动衰减到幼龄动物中共振的转变与拂动的开始相吻合。此外，共振的宽度涵盖了探索性拂动的4 - 15Hz范围。然而，vMNs中电流调节与拂动开始之间是否存在因果关系仍有待证明。特别是，我们进一步观察到，新生和幼龄动物舌下运动神经元的膜阻抗在阈下也表现出共振，且共振峰值也在4Hz附近。与幼龄动物相比，新生动物中该共振的幅度从低频时的1.1倍增加到1.4倍。我们推测，触须、舌下以及可能其他运动神经元中的共振特性可能有助于暂时且有目的地同步不同的口面部行为。
