Matsuo R, Inoue T, Masuda Y, Nakamura O, Yamauchi Y, Morimoto T
Department of Oral Physiology, Faculty of Dentistry, Osaka University, Japan.
Brain Res. 1995 Aug 21;689(2):289-98. doi: 10.1016/0006-8993(95)00582-b.
The chorda tympani nerve, supplying the anterior two-thirds of the tongue, contains gustatory and mechanosensitive afferent fibers. We have analyzed discharge patterns in rats of various fibers recorded from dissected nerve filaments during licking behavior of which 4 were taste-sensitive and 12 mechanosensitive. The incidence of these two types were estimated electrophysiologically under anesthesia and their conduction velocity measured. Recordings in freely moving animals showed that the mechanosensitive fibers innervating the dorsal part of the tongue gave two burst discharges per lick, suggesting that contact of the tongue with the upper incisors and/or lip occurred during tongue protrusion and retraction. The fibers from the tip of the tongue showed one burst discharge per lick, which was the response to contact with a drinking spout. No rhythmical discharges synchronized with lick signals were observed in the fibers from the lateral part of the tongue or the taste-sensitive fibers. Such mechanoreceptor discharges were difficult to detect in recordings from the whole chorda tympani nerve. This masking of responses was due mainly to activation of a small number of mechanosensitive fibers by licking-induced mechanical stimulation. The lubricating action of saliva also decreased mechanoreceptor sensitivity. Despite their small number, the mechanosensitive fibers had axons with faster conduction velocities (larger diameter) than the taste-sensitive fibers. This was probably the reason why dissected nerve bundles more frequently showed mechanical than taste responses in conscious rats.
鼓索神经支配舌前三分之二部分，包含味觉和机械感觉传入纤维。我们分析了在大鼠舔舐行为期间从解剖的神经细丝记录的各种纤维的放电模式，其中4条为味觉敏感纤维，12条为机械敏感纤维。在麻醉状态下通过电生理学方法估计这两种纤维的发生率，并测量其传导速度。在自由活动动物中的记录显示，支配舌背侧部分的机械敏感纤维每舔舐一次会产生两次爆发性放电，这表明在舌伸出和缩回过程中，舌与上门齿和/或嘴唇发生了接触。来自舌尖的纤维每舔舐一次显示一次爆发性放电，这是对与饮水口接触的反应。在来自舌外侧部分的纤维或味觉敏感纤维中未观察到与舔舐信号同步的节律性放电。在整个鼓索神经的记录中很难检测到这种机械感受器放电。这种反应的掩盖主要是由于舔舐引起的机械刺激激活了少数机械敏感纤维。唾液的润滑作用也降低了机械感受器的敏感性。尽管数量很少，但机械敏感纤维的轴突传导速度比味觉敏感纤维更快（直径更大）。这可能就是为什么在清醒大鼠中，解剖的神经束更频繁地显示出机械反应而非味觉反应的原因。
