[A study on the cumulative effect of repeated electroacupuncture on chronic pain]

Clinical and animal studies were performed to evaluate the effect of repeated transcutaneous electric nerve stimulation (TENS) applied on acupoints of pain patients and the effect of repeated electroacupuncture (EA) at acupoints of the rat on experimental arthritic pain models. Attempts were also made to evaluate whether substance P (SP), cholecystokinin octopeptide (CCK-8), and met5-enkephalin (MEK) are involved in the mechanism of the cumulative effect of repeated EA on experimental arthritis using neuropharmacological (receptor antagonists) and neurochemical (radioimmunoassay, RIA) approach. The main results show that repeated TENS of 100 Hz relieves spinal spasticity in a cumulative manner, while TENS of 2/15 Hz is effective in relieving chronic pain. In animal chronic pain models, repeated EA suppressed the hyperalgesia in arthritic rats in a cumulative manner. Further studies revealed that in pain patients there was a plastic change in the release and metabolic rate of spinal opioid peptides. In arthritic rats there was also a change in the releasing rate of spinal SP, CCK-8, and MEK as compared to control rats, an effect modulated by repeated EA. These plastic changes occured under chronic pain condition and their modulation by repeated acupoint stimulation may explain the mechanisms of the cumulative effect of acupuncture on chronic pain.