Objective To explore the afferent pathway of signals from electroacupuncture(EA)at "Sibai"(ST 2)acupoint.Methods A total of 36 SD rats were randomly divided into control

sham operation(sham)

capsaicin

vehicle

capsaicin+EA

and vehicle+EA groups

with 6 cases in each.EA(1/20 Hz

1-3 mA)was applied to "Sibai"(ST 2).After anesthesia(10% urethane)

unilateral infraorbital nerve was separated to be immersed in a 1.5% capsaicin-fluid-soaked cotton ball for lesion of C fibers.Vehicle(20% tween)was used to immerse infraorbital nerve for vehicle and vechile+EA groups.The expression of c-fos in the caudal spinal trigeminal nucleus(cSTN)was detected by immunohistochemistry.Results In control group

c-fos immune-reaction(IR)positive neurons were observed to scatter in every layer of cSTN.No significant differences were found among vehicle

capsaicin

sham and control groups in the number of c-fos IR positive neurons in cSTN.The number of c-fos positive neurons in theⅠ-Ⅱ layers of cSTN was obviously increased following EA at ST2

being significant more than that in control

vehicle

capsaicin and sham groups(P<0.01 respectively).However

the number of c-fos IR-positive neurons in Ⅲ-Ⅳ layers of cSTN had no marked change.In capsaicin+EA group

the number of c-fos-IR positive neurons in theⅠ-Ⅱ layers of cSTN was obviously less than that in vehicle and vehicle+EA groups(P<0.01)

but no significant changes were found in Ⅲ-Ⅳ layers of cSTN.Conclusion C afferent fibers of the infraorbital nerve are the primary afferent pathway of EA signals from Sibai(ST 2)stimulation in the rat.