| Since the beginning of acupuncture theory researching, a great number of studies have been done on animals including rats, mice, rabbits and cats, and rich accomplishments have been made, which provide theoretical supports for the therapeutic application of acupuncture in human diseases. Analgesia is the most significant effect in the application of acupuncture. Currently, it was identified by study that the suitable analgesia frequency for rats, mice and human are 2 hertz,15 hertz, or a rotation of 2/15 hertz and 2/100 hertz, at which the endogenous opioid peptides (mainly includingβ-endorphin, dynorphin and enkephalin) can be mobilized and released to a large extent, and the endurance to pain is enhanced. The effect of low frequency (<30 hertz) is better than that of high frequency. However, it differs in ruminants. The clinical practice for many years revealed that the proper frequency for ruminant is high (≥30 hertz), but which particular frequency is still uncertain.In this study, we observed the effect of different electro-acupuncture(EA) frequency on goat pain threshold, and determined the analgesia frequency of EA for goats. The expression level of goat nerve center P-endorphin (P-EP) and dynorphinA(1-17) (DynA(1-17)) was investigated by immunohistochemical methods, to offer some theoretical basis for the analgesia frequency suitable to goats.35 healthy male cross-breeding goats weighing from 23 to 27 kg were randomly divided into 5 groups,2 hertz,40 hertz,60 hertz,100 hertz group of EA and control group. Each group contained 7 goats. The pain threshold value was tested by potassium ion penetration method at the beginning of EA and after treatment of EA for 30 min (EA group). The test was conducted at the same time point in the control group which was without the treatment of EA. The change rate of goat pain threshold before and after E A treatment was investigated, and the expression ofβ-EP and DynA(1-17) in analgesia-related nuclei was compared.The result showed that in the group of 60 hertz, goat pain threshold was increased by 91% after EA, and the increase rate was 69%,42%,35% in 40 hertz,2 hertz, and 100 hertz respectively. The increase rate of 60 hertz group was highly significantly different from those in other groups (P<0.01). The pain threshold increase rate in 40 hertz group was highly significantly different from 2 hertz and 100 hertz group. But the difference was not significant for the pain threshold increase rate between 2 hertz and 100 hertz group (P>0.05).The immunohistochemistry result exhibited that after EA stimulation for 30 min, the P-EP-like immune-positive cells have an expression level in some nuclei significantly higher than other EA groups and control groups (P<0.05), including nucleus accumbens, septal area, paraventricular hypothalamic nucleus, periaqueductal gray (PAG), nucleus raphes dorsalis, locus ceruleus, nucleus raphes magnus, nucleus tractus solitaries and spinal dorsal horn. The expression level had no significant difference with 40 hertz group in caudate nucleus, parabrachial nuclei, and amygdale, but was significantly different from other groups (P<0.05). In supraoptic nucleus, no significant difference was found with 40 hertz or 100 hertz group, but the difference was significant with 2 hertz and control group (P<0.05). In arcuate nucleus,β-EP-like immune-positive cells had the lowest expression level in 60 hertz group, which was not significantly different from 40hertz group (P>0.05). The expression level ofβ-EP-like immune-positive cells in habenular nucleus was not significantly different from that in 100 hertz (P>0.05), but it was significantly higher than 40 hertz group,2hertz group and control group (P<0.05). In 100 hertz group, DynA(1-17)-like immune-positive cells has a higher expression level in caudate nucleus, septal area, supraoptic nucleus, ventromedial hypothalamic nucleus, PAG, parabrachial nuclei, spinal dorsal horn and amygdale than in 60 hertz,40 hertz,2 hertz and control group, with a significant difference (P<0.05). The DynA positive cell expression level in paraventricular hypothalamic nucleus and gigantocellular reticular nucleus was slightly increased compared with that in 60 hertz group, but the difference was not significant (P>0.05). However, the difference with 40 hertz,2 hertz and control group was significant (P＜0.05). In 60 hertz group, DynA(1-17) has a significantly higher expression level of positive cells in nuclei like caudate nucleus, septal area, paraventricular hypothalamic nucleus, ventromedial hypothalamic nucleus, PAG, parabrachial nuclei, gigantocellular reticular nucleus and amygdale than in 40 hertz, 2hertz and control group (P<0.05). The expression in supraoptic nucleus and spinal dorsal horn was not significantly changed in 40 hertz,2 hertz and control group (P>0.05).The result of this study indicated that among the selected frequency, the increase rate of goat pain threshold was highest when stimulated by EA at 60 hertz. Thus 60 hertz is a proper analgesia frequency for goats; in an assay that stimulated goats by EA for 30 min, we found that 60 hertz was the most efficient frequency to promote the expression of P-EP in analgesia-related nuclei in central nervous system of goats; 100 hertz had a best effect to induce the release of DynA(1-17) and the effect of 60 hertz was also nice. |
