[Electroacupuncture enhances enkephalin mRNA expression in the spinal cord and medulla, an in situ hybridization...

Previous studies in this laboratory have shown that electroacupuncture (EA) accelerated the release of enkephalin in the spinal cord. The present study was undertaken to investigate the effect of EA stimulation on the expression of preproenkephalin (PPE) mRNA in the rat spinal cord and medulla by in situ hybridization histochemical technique. Animals were administrated with 2 Hz EA stimulation (1-2-3 mA, 30 min) applied at acupoints sanyingjiao and zusanli of one hind leg. The rats were perfused 24 h after EA, and quantitative changes of PPE-mRNA expression were determined by emulsion autoradiography. EA stimulation was found to increase the number of neurons expressing PPE-mRNA in spinal cord and medulla. Increased expression of PPE-mRNA was more marked in ipsilateral dorsal horn of spinal cord (especially in laminae III-IV and contralateral ventromedial medulla (especially in the lateral paragigantocellular reticular nucleus). The results provide evidence in support of the enkephalinergic hypothesis of acupuncture analgesia. It is suggested that increased biosynthesis of enkephalin precursor would help to compensate for the loss of tissue storage of enkephalin during the period of EA stimulation.