| Electro-acupuncture (EA) is a therapy combining electro-stimulation and traditional acupuncture. In the late 1960s, EA was widely applied in veterinary surgeries. Characterized by convenient operation, low interference, rapid recovery after surgeries, and the capacity of overcoming heart and respiratory inhibition resulting from medical anesthesia and stomach content regurgitation and gastrointestinal bloat of ruminants, it has a great prospect for application.The studies on small animals (such as rat) revealed that endogenous opioid peptides are the essential material basis for analgesia by EA. The EA could induce nerve center to release internal opioids, mainly including enkephalin,β-endorphin and dynorphin, which were able to bind their receptors respectively and exert analgesia effect. The frequency is one of the important parameters for EA. It was shown that EA at low frequency (2 Hz-15 Hz) induced nerve center to release enkephalin andβ-endorphin, and when stimulated by 2 Hz and 15 Hz in rotation, nerve center released enkephalin, P-endorphin and dynorphin at the same time, and had the best effect of analgesia on small animals. The practice of acupuncture indicated that analgesia effect on ruminants (cattle and goats) was superior to animals of other species, with a proper analgesia frequency (30Hz-100Hz) higher than that of small animals (2Hz-15Hz). It can be inferred that there is some special central molecular regulation mechanism for acupuncture analgesia of ruminants.Analgesia by EA not only has an immediate analgesia effect (the analgesia effect appears immediately when acupuncture beginning), but also a late effect as pain threshold drops slowly after EA. By now, it is not well understood whether the late effect induced by acupuncture is due to the start of gene expression of opioid peptides. Among all of the internal opioid peptides,β-endorphin is most widely distributed in brain and has the strongest analgesia effect. Thus, observing the pain threshold and the expression level of pro-opiomelanocortin (POMC) mRNA witch is the precursor ofβ-endorphin of ruminants, represented by goats, will help to further demonstrate the mechanism of analgesia at high frequency by studying the changes of both.In this study,42 healthy male adult goats of crossing breed weighing between 23 and 27 kg were selected and divided into two groups at random. Control group contained 6 goats and EA group 36. The goats in acupuncture were given a electro-acupuncture for 30 min, at Baihui-Qijia and Ergen-Sanyangluo, with a fixed frequency at 60 Hz and a volt at 3 V-4 V. The pain threshold of goats were tested at before and 0 h,2 h,4 h,6 h,8 h,12 h, 24h after EA, and nuclei tissue associated with analgesia in brain (corpus striatum, amygdale, hypophysis, arcuate nucleus, paraventricular hypothalamic nucleus, ventromedial hypothalamic nucleus, periaqueductal gray, nucleus raphes magnus, gigantocellular reticular nucleus, nucleus tractus solitarius) were quickly collected at 2 h, 4 h,6 h,8 h,12 h,24 h after EA (6 goats for each time point), we take the nuclei tissue of control group directly without EA. Total RNA was extracted and reverse-transcription was performed, followed by a real-time relative quantitative PCR. The mRNA expression of POMC in the nuclei above was observed.The result showed the pain threshold of goats was significantly enhanced 30 min after EA and reached the highest point at 0 h after EA, which increased by 88% to that before acupuncture. Then the pain threshold began to decrease, re-rouse slightly at 8 h, and continued to drop until 24 h after acupuncture when it had the lowest value, but it was increased by 12% compared to that before EA.Real-time relative quantitative PCR was conducted to detect POMC mRNA expression in goat (corpus striatum, amygdale, hypophysis, arcuate nucleus, paraventricular hypothalamic nucleus, ventromedial hypothalamic nucleus, periaqueductal gray, nucleus raphes magnus, gigantocellular reticular nucleus and nucleus tractus solitarius at different time point after electro-acupuncture. It was found that the POMC mRNA expression in EA group was higher than that of control group, with a significant difference. The accelerated POMC mRNA expression after EA could last for at least 24 hours.
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