Levels of three opioid peptides in goats’ CNS induced by different electroacupuncture frequencies

Acupuncture is a traditional therapeutic technique in Oriental medicine,which has a long history of 4000 years. As a modern version of hand acupuncture,electroacupuncture (EA) can provide a valid analgesic effect and has little physiological interference. It was successfully used to ameliorate pain not only in varieties of painful diseases,but in various operations,such as cesarean section,gastrectomy,enterectomy and castration,in animals during the 1970s. Since then,analgesia-regulating mechanism of EA has been extensively investigated. Previous studies found that electroacupuncture analgesia (EAA) was involved in modulations of neurotransmitters or neuromodulators in the central nerve system (CNS),and most early studies focused on the role of neurotransmitters such as serotonin,noradrenaline, dopamine and acetylcholine. Later,it was certified that some endogenous opioid peptides (EOPs),mainly including enkephalin,β-endorphin and dynorphin,played a more important role in EAA. EA of different frequencies can promote the release of different EOPs in the CNS. Studies showed that EAA induced by 2 Hz (low frequency) was mediated by the release of met-enkephalin (M-ENK) and β-endorphin (β-EP),while EAA by 100 Hz (high frequency) was mediated by the release of dynorphin-A (DYN-A) in the CNS in rats. Although these results in rats above are extrapolated to give reasonable explanations for acupuncture analgesia phenomenon and its treatment of related diseases in human,there are still some unknown mechanisms to be investigated. It has been proved that analgesia induced by EA varies in animal species. In order to quantitatively estimate the degree of acupuncture-induced analgesia,some researchers used an anesthetic to ensure a complete analgesia and to assess the reduction of the amount of the anesthetics consumed in the EA plus anesthetic group as compared to the anesthetic group without acupuncture. Studies showed EA in combination with anesthetics resulted in the reduction of the dosage of the anesthetics in human,ra