[The role of peripheral C afferent fiber in electroacupuncture analgesia]

Experiments were carried out in rats anaesthetized with urethane (1 g/kg). Late discharges of spinal dorsal horn neurons were recorded as noxious responses to strong stimulation of right tibial nerve (a train of 3 pulses, 25V, 1ms). Left St.36 and Sp.6 were stimulated electrically (100Hz, 3V or 6V, 1ms). Left sciatic nerve was exposed and soaked for 15 min in 1.5% capsaicin or vehicle 24 hours before experiment. Left femoral nerve was sectioned. Spinal cord was transected at T4 level in spinal rat. Intact rats: 1) EA group (N = 12). Sciatic nerve was not treated. Late discharges of neuron were reduced to 44.6 +/- 18.3% of control (P less than 0.02) by EA(3v). 2) Capsaicin group (N = 15). Late discharges were reduced to 89.8 +/- 6.0% of control (P greater than 0.05) by EA(3V). 3) Vehicle group (N = 10). Late discharges were reduced to 51.2 +/- 15.6% of control (P less than 0.05) by EA(3V). 4) There was a statistical difference (P less than 0.05) between capsaicin and vehicle group. Spinal rats: 1) EA group. Late discharges of neuron were reduced to 67.6 +/- 10.3% of control (P less than 0.02) in 11 neurons by EA(3V), 72.7 +/- 8.8% (P less than 0.01) in 9 neurons by EA(6V). 2) Capsaicin group. Late discharges were 110 +/- 21.0% of control (P greater than 0.05) in 13 neurons after termination of EA (3V), 90.7 +/- 12.9% (P greater than 0.05) in 10 neurons after EA (6V). 3) Vehicle group. Late discharges were reduced to 67.7 +/- 8.1% of control (P less than 0.02) in 12 neurons by EA (3V), 68.1 +/- 5.0% (P less than 0.01) in 10 neurons by EA (6V). 4) There was a statistical difference (P less than 0.05) between capsaicin and vehicle group for 3V, no statistical difference (P greater than 0.05) for 6V. C fiber of peripheral nerve is main component involved in effect of EA analgesia in intact rats. Both A and C fiber of peripheral nerve involved in effect of EA analgesia in spinal rats.