On the various other hand, dynorphin has been revealed to be the endogenous ligand of the n-opioid receptor. Undoubtedly, the withdrawal disorder observed in rats dependent on morphine can be subdued by high-frequency electroacupuncture, which increases the launch of dynorphin in the spinal cord as well as brain. Morphine-induced conditioned-place choice, an experimental design simulating the food craving of heroin addicts, can be properly reduced by low-frequency electroacupuncture. This effect can be obstructed by a little dosage of naloxone, showing the involvement of endogenous opioid peptides. At the same time, the medical research by V. Clement-Jones et al. also revealed that EA was associated with an increase in cerebrospinal liquid met-enkephalin degrees in all addicts studied.