De Koninck Y, Henry J L
Department of Physiology, McGill University, Montréal, Québec, Canada.
J Physiol. 1994 Apr 1;476(1):89-100.
To study the central processing mechanisms of sensory input from low threshold afferents to the spinal cord, we examined the excitatory response of single lumbar dorsal horn neurones to stimulation of hairs in the receptive field using a mechanically driven probe, and to activation of single hair follicle afferents using an intracellular current pulse to the cell bodies in the dorsal root ganglion. Experiments were done on anaesthetized, paralysed cats, spinalized at the L1 lumbar level. Responses of spinal neurones to two types of hair afferent input were characteristically different. The excitatory response to input from a single group II hair afferent (A beta; innervating guard hair follicle receptors) was multimodal, characterized by a small early depolarization followed by a sharp, large component with a slow, prolonged decay phase, whereas the response to input from a single group III hair afferent (A delta; innervating down hair follicle receptors) was unimodal. The unitary EPSPs in response to activation of group III hair afferents had a slower rise time and longer decay time constant than those in response to activation of group II hair afferents. When the receptive field of the afferent was located in the centre of the receptive field of the dorsal horn neurone, the gain of the central response was greater for the input from a single group II afferent (> 1) than that for the input from a single group III afferent (< 1). In the case of single group II hair afferents, when pairs of single action potentials or pairs of trains of action potentials were generated at intervals of 20 ms to 3 s, the response in the dorsal horn neurone to the second volley was markedly depressed at intervals of less than 2 s, without any apparent inhibition of the on-going rate of firing. The response to the second volley in single group III afferents was less depressed. This inhibition of the response to the second of a paired volley in single group II hair afferents was attenuated by administration of bicuculline, but not strychnine or naloxone. This indicates that the inhibition involves a GABAA-receptor-mediated mechanism. Bicuculline did not affect the late component of the response to single group II hair afferent input, but unmasked a late component of the response to mechanical stimulation of hairs.(ABSTRACT TRUNCATED AT 400 WORDS)
为研究低阈值传入纤维至脊髓的感觉输入的中枢处理机制，我们使用机械驱动探针检测了单个腰段背角神经元对感受野内毛发刺激的兴奋性反应，以及使用细胞内电流脉冲刺激背根神经节内的细胞体来激活单个毛囊传入纤维时的兴奋性反应。实验在L1腰段水平脊髓横断的麻醉、麻痹猫上进行。脊髓神经元对两种类型毛发传入输入的反应具有特征性差异。对单个II类毛发传入纤维（Aβ；支配保护毛囊感受器）输入的兴奋性反应是多峰的，其特征为早期小的去极化，随后是一个尖锐、大的成分，伴有缓慢、延长的衰减期，而对单个III类毛发传入纤维（Aδ；支配绒毛毛囊感受器）输入的反应是单峰的。对III类毛发传入纤维激活的单位EPSP的上升时间比II类毛发传入纤维激活时的上升时间慢，衰减时间常数更长。当传入纤维的感受野位于背角神经元感受野的中心时，单个II类传入纤维输入的中枢反应增益（>1）大于单个III类传入纤维输入的中枢反应增益（<1）。对于单个II类毛发传入纤维，当以20毫秒至3秒的间隔产生成对的单个动作电位或成对的动作电位串时，背角神经元对第二个波群的反应在间隔小于2秒时明显受到抑制，而对持续放电率没有明显抑制。单个III类传入纤维对第二个波群的反应受抑制程度较小。单个II类毛发传入纤维对成对波群中第二个波群反应的这种抑制作用可被荷包牡丹碱减弱，但不能被士的宁或纳洛酮减弱。这表明该抑制涉及GABAA受体介导的机制。荷包牡丹碱不影响对单个II类毛发传入纤维输入反应的晚期成分，但揭示了对毛发机械刺激反应的晚期成分。（摘要截短于400字）
