Department of Physiology, College of Medicine, King Saud University, P.O. Box 7805, Riyadh 11472, Saudi Arabia.
Neurosci Biobehav Rev. 2016 Feb;61:225-38. doi: 10.1016/j.neubiorev.2015.12.009. Epub 2015 Dec 30.
The sensation of gentle touch of the mammalian hairy skin is mediated by morphologically and physiologically distinct classes of low-threshold mechanoreceptors (LTMs) which are classified, according to their axonal conduction velocities, into Aβ-, Aδ- and C-LTMs. Although Aδ-LTMs (D-hair cells) were first described about five decades ago, and have been found in hairy skin of every species examined including humans, it is commonly assumed that all Aδ-fiber neurons are nociceptors. This view is endorsed by many textbooks. This article reviews the evidence that Aδ-LTMs exist in substantial proportions in different species, and that their peripheral and central axonal endings, molecular markers, receptive, electrophysiological and cytochemical properties are distinct from those of Aδ-high-threshold mechanoreceptors (Aδ-HTMs). A brief overview of some of the ion channels and markers that are expressed by the two populations of primary afferent neurons is also provided. Failure to recognize the existence and properties of Aδ-LTMs might lead/have led to misinterpretations of data. Aβ-LTMs and C-LTMs have been reviewed elsewhere and are not subject of this review.
哺乳动物有毛皮肤的轻柔触摸感觉是由形态和生理上不同类别的低阈值机械感受器（LTM）介导的，根据其轴突传导速度，可将这些感受器分为 Aβ、Aδ 和 C-LTM。虽然 Aδ-LTM（D-毛细胞）大约五十年前就被首次描述，并在包括人类在内的所有检查过的物种的有毛皮肤中都有发现，但人们普遍认为所有 Aδ 纤维神经元都是伤害感受器。许多教科书都支持这种观点。本文综述了证据表明，Aδ-LTM 在不同物种中以相当大的比例存在，其外周和中枢轴突末梢、分子标记物、感受野、电生理和细胞化学特性与 Aδ-高阈值机械感受器（Aδ-HTM）不同。本文还简要概述了这两种初级传入神经元群体表达的一些离子通道和标记物。未能认识到 Aδ-LTM 的存在及其特性可能导致/已经导致了对数据的误解。Aβ-LTM 和 C-LTM 已在其他地方进行了综述，不在本次综述范围内。
