逆向电刺激大鼠背侧皮神经对相邻脊髓节段Aδ类传入纤维机械感受特性的影响

Changes of Mechano-receptive Properties of Aδ-fibers of the Adjacent Spinal Segments after Antidromical Electrical Stimulation of the Dorsal Cutaneous Nerve

目的 :分析循经分布的Aδ类初级传入纤维在跨脊髓节段信息传递中机械感受特性的改变和意义 ,从而探讨外周神经参与经络活动的机制。方法 :自近中端断离循足太阳膀胱经分布的胸 9至胸 1 2脊神经背侧皮支 ,在其中一支上施加逆向电刺激 ,以相邻脊髓节段的一支上Aδ类单位放电为指征 ,测定单位的适应特性、机械感受阈值、感受野形状和面积、感受野的敏感点数及其位置、传导速度等机械感受特性。在相邻脊髓节段皮神经上施加逆向电刺激后 ,观察上述各种机械感受特性的改变。结果 :在 6 7只大鼠上观察了 90个Aδ类初级传入纤维的机械感受特性和跨节段刺激对这些特性的影响。快适应和慢适应单位分别占 3 1 1 %和 6 8 9% ,适应时程为 2 0 82±2 51sec (n =90 )。机械感受阈值 0 2 1± 0 0 3mN。平均感受野面积 1 7 76± 3 40mm2 ,感受野内敏感点数为 1 79± 0 1 1个 ,77 3 % (n =88)的敏感点循足太阳膀胱经背部二直行脉之间分布。逆向电刺激相邻脊髓节段皮神经背侧皮支后 ( 0 45mA ,0 1ms,2 0Hz,持续 1 0sec) ,71 9% (n =6 4)的单位感受野增大 ,全部单位感受野均值增大为 71 98± 1 3 0 7mm2 ,显著大于对照 ,P <0 0 0 1。每个感受野内平均敏感点数显著增至 3 0 8± 0 2 5个 ,P <0 0 1。 71 7%

Objective:To observe whether the primary afferent Aδ-fiber is involved in the signal transmission of the peripheral terminals distributing in the adjacent dermatomes and to investigate the mechanism of sensory transmission along meridian.Methods:SD rats anesthetized with 20% urethane (1 g/kg) were used in this study. The dorsal cutaneous nerve branches of spinal nerves from T 9 to T 12 segments innervating the Bladder Meridian of Foot-Taiyang (BL) area were cut proximally.One peripheral stump end of the cut nerves was dissected into a few filaments for the examination of mechanoceptive properties of single Aδ-fibers and their changes of electrical activity, while another one for antidromically electrical stimulation.Results:Ninety Aδ-units were recorded on 67 intact rats. There were 31.1% rapid adaptation (RA) units and 65.9% slow adaptation (SA) units, with the mean adaptation duration being 20.82±2.51 sec (n=90), the receptive field 17.76±3.40 mm 2 and the mechanoreceptive threshold 0.21±0.03 mN.There were 1 to 3 sensitive points (1.79±0.11) in each receptive field and 77.3% (n=88) of them distributed along BL. After an electrical stimulation(0.45 mA,0.1 ms, 20 Hz, for 10 sec) was delivered to the stimulated nerve, the size of the receptive field of 71.9% (n=64) of Aδ-fibers extended. The mean area of receptive fields of all the examined units enlarged from 17.76±3.40 mm 2 to 71.98±13.07 mm 2 (P<0.001) and the receptive field of 74.6% (n=60) units changed from a dot, round or ellipse shape, with its long axis being in parallel with the longitudinal axis of the body. The number of sensitive point in each receptive field increased to 3.08±0.25 from 1.79±0.11, (P<0.01). The mechanoceptive threshold of 71.7% (n=60) units decreased to 0.12±0.04 mN (P<0.001). The changes of mechanoceptive properties appeared simultaneously with discharge changes but lasted longer than that of discharge change (P<0.01).Conclusion:These results suggest that low-threshold mechanoreceptive Aδ-fibers can be activated by antidromically electrical stimulation of cutaneous nerve of the adjacent spinal segment, indicating that the signal transmission occurs between two endings of peripheral afferent nerves from the adjacent spinal segments without any involvement of central nervous system, and Aδ-fibers are involved in the process of signal transmission. This may be an important mechanism of sensory transmission along meridian in traditional Chinese medicine.