The Roles of Different Types of Afferent Fibres in the Process of Acupuncture Analgesia

Abstract

In previous work, the reflex movement of the lower jaw was taken as an objective index of pain in awakening rabbits. It was found that analgesic action of various types of fibres were types I.II < types I.II.III < types I.II.III.IV, i.e. the effects were stronger with the involvement of those small-sized fibres. However, opinions differ as to whether small-sized fibres (includng Aδ wave and C wave) have analgesic effects. Therefore, the reaction of vascular movement which reflects the function of autonomic nerves was taken as an objective index of pain. 42 paralytic, awake rabbits with body weight of 2kg or so were used. In the peroneal nerve innervating "Zusanli'' point (from their distal to proximal ends) were placed the electrodes of electro-needling (limiting electro-needling) and Ag-AgCl, and those of recording and pain stimulation. The pain stimulations used were of single square-wave, of 2 times per second, of the pulse duration of 0.3 msec and of a continuance of 5 sec; their intensity being just enough to elicit the steady reaction of vascular movement. The electrodes of electric needling, electric pulses with a speed of 0.2 msec per second and the pulse duration of 0.2 msec were applied successively to stimulate those peroneal nerves. The roles played by various types of fibres in analgesic effects were further observed after different intensities, exciting the fibres of types I.II, tpes I.II.III and types I.II.III.IV respectively, and then through the Ag-AgCl electrode, D.C. anodal-blocking used to block the large-sized fibres and to excite type III or types III.IV of fibres respectively. Each experimental series was divided comparing, needling and after the withdrawal of the needle. Observations were made from three times in each step continually; the temperature was maintained at 16-28°C. The results have shown that the fibres of types I.II, types I.II.III and types I.II.III.IV were excited, respectively. It has turned out that their effective rates (including complete inhibition, apparent inhibition and slight inhibition) were 50% (types I.II), 78.6% (types I.II.III) and 92.8% (types I.II.III.IV); after the large-sized fibres had been blocked, the fibres of type IV and types III.IV were excited, with the effective rates of 90% (type IV) and 100% (types III.IV). Therefore, the analgesic effects of different types of fibres are I.II < III < IV, i.e. the smaller fibres the stronger the analgesic effects. The results are quite analogous to the previous work. This further proves the small-sized fibres have stronger analgesic effects upon pain response thatn large-sized fibres.