我们以前的工作曾发现电针大鼠的“足三里”或刺激坐骨神经可通过交感神经抑制直流电——钾离子刺激皮肽诱发的背根和尾神经的传入冲动。由于当时记录的背根和尾神经传入冲动含有不同类型的纤维活动

因而难以确定哪种感受器的活动受到了抑制。为了分析针刺激活的中枢传出抑制作用

是否抑制Aδ纤维机械痛感受器(简称The experiments were performed on 59 rats anesthetized with Chloralose-Urethane. The tail nerve was dissected into small bundles of fibers for recordingafferent discharges evoked by mechanical pressure stimulation and so on. Theeffect of stimulation of the central end of the sciatic nerve or peripheral endof the lumbosacral sympathetic trunk on the Aδ-mechanical nociceptors (meanconduction velocity=11.4m/sec) were studied respectively. The results obtained are as follows: (1) Of the 29 units of Aδ-mechanical nociceptor recorded

24 appearedobviously inhibitory effect after stimulation of the central end of the sciaticnerve for 5 min. The number of discharges evoked by machanical pressuredecreased to 70% of control value and its after-effect lasted for about 8 min. (2) After cutting the lumbosacral sympathetic trunk

the inhibitory effectof stimulation of the sciatic nerve was almost completely abolished in the unitsrecorded. (3) Stimulation of the peripheral end of the lumbosacral sympathetic trunkcould inhibit the unit discharges of the Aδ-mechanical nociceptors cvoked bymachnical pressure. The number of discharges decreased to 49.4% of controlvalue and its after effect lasted for about 10 min in 20 units. (4) The partial touch (13/23) and stretch (11/29) receptors appeared lightlyinhibitory effect after stimulation of central end of the sciatic nerve. These results show that stimulation of the sciatic nrve might inhibit dischargesof the Aδ-mechanical nociceptor evoked by mechanical pressure and the efferentpathway was the sympathetic nerve. The conclusion therefore support thehypothesis that the acupuncture might activate centrifugal inhibitory effect onthe nociceptors.