[Effect of Transection or Pretreatment of the Infraorbital Nerve with Snake Venom on the Analgesia Induced by Electroacupuncture of "sibai" (ST 2) Acupoint in Visceral Pain Rats].

OBJECTIVE:To observe the role of large-diameter fibers of infraorbital nerve (ION) in "Sibai" (ST 2)-electroacupuncture (EA) induced analgesia in visceral pain (VP) rats. METHODS:A total of 36 SD rats were randomized into control, VP, EA, ION transaction, snake venom (SV) and saline groups, with 6 rats in each group. EA(2 Hz/20 Hz) was applied to bilateral "Sibai" (ST 2) for 20 min. VP model was established by intraperitoneal injection of 0.6% acetic acid (10 mL/kg). Bilateral ION were transacted or pretreated by regional application of snake venom to selectively destroy A fibers,respectively. Behavior reactions were assessed by counting abdominal muscular contractions. Meanwhile, c-fos expression in the nucleus of the solitary tract (NTS) and paratrigeminal nucleus (PTN) was displayed by immunohistochemistry. RESULTS:In comparison with control group, the numbers of abdominal muscular contraction,and c-fos immuno-reaction (IR) positive neurons in both NTS and PTN increased significantly in VP group (P < 0.001); while in comparison with VP group, the numbers of the abdominal contraction, and c-fos IR-positive neurons of both NTS and PTN in EA and SV and saline groups decreased considerably (P < 0.05, P < 0.01). No significant differences were found between ION transaction and VP groups in the abdominal contraction number, and c-fos IR-positive neurons in both NTS and PTN areas,and among EA and SV and saline groups in the numbers of abdominal contraction and c-fos IR-positive neurons of both NTS and PTN (P > 0.05). CONCLUSION:The large-diameter (A) fibers of ION are not the major afferent fibers affecting EA-ST 2 induced analgesia in visceral pain rats; and somatic sensory afferents from orofacial areas and visceral pain input converge in the NTS and PTN, which may be the basis of the EA analgesia in the present study.