Djouhri Laiche, Lawson Sally N
Department of Physiology, School of Medical Sciences, University of Bristol, University walk, Bristol BS8 1TD, United Kingdom.
Brain Res Brain Res Rev. 2004 Oct;46(2):131-45. doi: 10.1016/j.brainresrev.2004.07.015.
The existence of nociceptors with Abeta-fibers has often been overlooked, and many textbooks endorse the view that all nociceptors have either C- or Adelta-fibers. Here we review evidence starting from the earliest descriptions of A-fiber nociceptors, which clearly indicates that a substantial proportion of cutaneous/somatic afferent A-fiber nociceptors conduct in the Abeta conduction velocity (CV) range in all species in which CV was carefully examined, including mouse, rat, guinea pig, cat and monkey. Reported proportions of A-fiber nociceptors with Abeta-fibers vary from 18% to 65% in different species, usually >50% in rodents. In rat, about 20% of all somatic afferent neurons with Aalpha/beta-fibers were nociceptive. Distributions of CVs of A-fiber nociceptors usually appear unimodal, with a median/peak in the upper Adelta or lower Abeta CV range. We find no evidence to suggest discontinuous differences in electrophysiological or cytochemical properties of Adelta and Abeta nociceptors, rather there are gradual changes in relation to CV. However, some functional differences have been reported. In cat, A-fiber nociceptors with lower mechanical thresholds (moderate pressure receptors) tend to have faster CVs [P.R. Burgess, D. Petit, R.M. Warren. Receptor types in cat hairy skin supplied by myelinated fibers. J. Neurophysiol. 31 (1968) 833-848]. In primate (monkey) A-fiber nociceptors that responded to heat were divided into type I A mechano-heat (AMH) units (Adelta and Abeta CVs) with lower mechanical and higher heat thresholds and may include moderate pressure receptors, and type II AMH units (Adelta CVs) with higher mechanical/lower heat thresholds. It is important that the existence of Abeta nociceptors is recognised, because assumptions that fast conducting, large diameter afferents are always low threshold mechanoreceptors might lead/have led to misinterpretations of data.
具有 Aβ 纤维的伤害感受器的存在常常被忽视，许多教科书都支持这样一种观点，即所有伤害感受器要么具有 C 纤维，要么具有 Aδ 纤维。在此，我们回顾从最早对 A 纤维伤害感受器的描述开始的证据，这些证据清楚地表明，在仔细检测传导速度（CV）的所有物种中，包括小鼠、大鼠、豚鼠、猫和猴子，相当一部分皮肤/躯体传入 A 纤维伤害感受器的传导速度处于 Aβ 传导速度范围内。在不同物种中，报道的具有 Aβ 纤维的 A 纤维伤害感受器的比例从 18%到 65%不等，在啮齿动物中通常>50%。在大鼠中，所有具有 Aα/β 纤维的躯体传入神经元中约 20%是伤害性的。A 纤维伤害感受器的传导速度分布通常呈单峰，中位数/峰值处于较高的 Aδ 或较低的 Aβ 传导速度范围内。我们没有发现证据表明 Aδ 和 Aβ 伤害感受器在电生理或细胞化学特性上存在不连续差异，相反，与传导速度相关存在逐渐变化。然而，已经报道了一些功能差异。在猫中，具有较低机械阈值（中等压力感受器）的 A 纤维伤害感受器往往具有更快的传导速度[P.R. 伯吉斯、D. 佩蒂、R.M. 沃伦。有髓纤维供应的猫有毛皮肤中的感受器类型。《神经生理学杂志》31（1968）833 - 848]。在灵长类动物（猴子）中，对热有反应的 A 纤维伤害感受器被分为 I 型 A 机械热（AMH）单位（Aδ 和 Aβ 传导速度），其机械阈值较低且热阈值较高，可能包括中等压力感受器，以及 II 型 AMH 单位（Aδ 传导速度），其机械阈值较高/热阈值较低。认识到 Aβ 伤害感受器的存在很重要，因为认为快速传导、大直径传入纤维总是低阈值机械感受器的假设可能已经导致对数据的误解。
