[Induction of Fos-like protein in the rat spinal cord following electroacupuncture stimulation].

The expression of the c-fos proto-oncogene has been regarded as a marker for noxious stimulation. We now report that electroacupuncture (EA) stimulation (100 Hz, 0.3 ms, 1-2-3 mA, 30 min) delivered into the acupoint Sanyinjiao (SP6) could also induce the c-fos expression in the rat spinal cord as demonstrated by immunohistochemical technique using antibody against the c-fos protein product Fos. In rats receiving EA stimulation, numerous cells with Fos-like immunoreactivity (FLI) were observed in both dorsal and ventral horn of the spinal cord with dense labelling in laminae III and IV of the ipsilateral side. Only scattered FLI cells were found in laminae I and II. In contrast, FLI evoked by noxious stimulation (5% formalin injected at the hindfoot subcutaneously) was shown mainly in laminae I and II, rather than in III and IV. The c-fos expression was very low in control animals receiving neither formalin nor EA administration. The present study indicates that the site specificity of the c-fos expression induced by EA is different from that evoked by noxious stimulation. The possibility that EA-induced Fos protein might participate in acupuncture analgesia is currently under investigation.