Uebner Michael, Carr Richard W, Messlinger Karl, De Col Roberto
Institute of Physiology and Pathophysiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany; and.
Department of Anaesthesia and Intensive Care Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.
J Neurophysiol. 2014 Dec 15;112(12):3077-85. doi: 10.1152/jn.00243.2014. Epub 2014 Sep 24.
Activity-dependent processes in slowly conducting afferents have been shown to modulate conduction and receptive properties, but it is not known how the frequency of action potential firing determines the responses of such fibers to mechanical stimulation. We examined the responses of slowly conducting meningeal afferents to mechanical stimuli and the influence of preceding action potential activity. In hemisected rat heads with adhering cranial dura mater, recordings were made from meningeal nerves. Dural receptive fields of mechanically sensitive afferent fibers were stimulated with a custom-made electromechanostimulator. Sinusoidal mechanical stimuli of different stimulus durations and amplitudes were applied to produce either high-frequency (phasic) or low-frequency (tonic) discharges. Most fibers showed slowing of their axonal conduction velocity on electrically evoked activity at ≥2 Hz. In this state, the peak firing frequency of phasic responses to a 250-ms mechanical stimulus was significantly reduced compared with control. In contrast, the frequency of tonic responses induced by mechanical stimuli of >500 ms did not change. In a rare subtype of afferents, which showed conduction velocity speeding during activity, an increase in the phasic responses to mechanical stimuli was observed. Depending on the axonal properties of the afferent fibers, encoding of phasic components of mechanical stimuli is altered according to the immediate firing history. Preceding activity in mechanoreceptors slowing their conduction velocity seems to provide a form of low-pass filtering of action potential discharges predominantly reducing the phasic component. This may improve discrimination between harmless and potentially harmful mechanical stimuli in normal tissue.
研究表明，传导速度缓慢的传入神经纤维中与活动相关的过程可调节传导和感受特性，但尚不清楚动作电位发放频率如何决定此类纤维对机械刺激的反应。我们研究了传导速度缓慢的脑膜传入神经纤维对机械刺激的反应以及先前动作电位活动的影响。在硬脑膜粘连的半切大鼠头部，从脑膜神经进行记录。使用定制的机电刺激器刺激机械敏感传入纤维的硬脑膜感受野。施加不同刺激持续时间和幅度的正弦机械刺激，以产生高频（相位性）或低频（紧张性）放电。大多数纤维在≥2Hz的电诱发活动时，其轴突传导速度减慢。在这种状态下，与对照相比，对250ms机械刺激的相位性反应的峰值发放频率显著降低。相反，由>500ms机械刺激诱发的紧张性反应频率没有变化。在一种罕见的传入神经纤维亚型中，其在活动期间传导速度加快，观察到对机械刺激的相位性反应增加。根据传入纤维的轴突特性，机械刺激相位成分的编码会根据即时发放历史而改变。机械感受器中先前的活动使其传导速度减慢，这似乎提供了一种动作电位发放的低通滤波形式，主要减少了相位成分。这可能会改善正常组织中无害和潜在有害机械刺激之间的辨别。
