Abstract
Background Manual acupuncture (MA) with different stimulus frequencies may give rise to varying acupuncture effects. However, the intensity-effect relationship and the underlying mechanisms of MA remain unclear. Objective To compare the analgesic effects of different frequencies of twirling-rotating MA on rats with complete Freund's adjuvant- (CFA-) induced pain and explore the underlying mechanism via peripheral sensory nerves. Methods First, 36 healthy male Wistar rats were randomly divided into 6 groups: control group, 2 r/s MA group (twirling-rotating MA with the frequency of 2 revolutions per second), 4 r/s MA group (twirling-rotating MA with the frequency of 4 revolutions per second), CFA group, CFA + 2 r/s MA group, and CFA + 4 r/s MA group. Rats in three CFA groups received an intraplantar injection of CFA to establish a pain model, while the rats in other three groups received an intraplantar injection of saline. Rats in the 2 r/s MA group and 4 r/s MA group were treated with the corresponding frequencies of twirling-rotating MA on bilateral Zusanli (ST36) and Kunlun (BL60) for 7 days. The ipsilateral nociceptive thresholds (paw withdrawal latency; PWL) were tested to evaluate the analgesic effects. Second, 9 healthy male Wistar rats were randomly divided into 3 groups: control group, 2 r/s MA group, and 4 r/s MA group. The proportion of C-fiber neurons (calcitonin gene-related peptide- (CGRP-) positive neurons) and A-fiber neurons (neurofilament 200- (NF200-) positive neurons) in the dorsal root ganglia (DRG) activated by MA were quantitatively analyzed with the morphological immunofluorescence staining method. Third, 30 healthy male Wistar rats were randomly divided into 6 groups: control group, CFA group, CFA + 2 r/s MA group, CFA + 2 r/s MA + RTX group, CFA + 4 r/s MA group, and CFA + 4 r/s MA + RTX group. Resiniferatoxin (RTX) was injected into the acupoints before acupuncture. PWL was evaluated to investigate the analgesic effect. Results Both types of MA treatment increased the PWL of saline-injecting rats and pain model rats. Moreover, 4 r/s MA was superior to 2 r/s MA in increasing PWL. A higher quantity of excited C-fiber neurons was observed following 4 r/s MA than 2 r/s MA, while the reverse was observed in the activation of A-fiber neurons. Following the injection of RTX to inhibit the activation of C-fibers, the analgesic effect of 4 r/s MA reduced significantly but not of 2 r/s MA. Conclusion Strong MA (4 r/s MA) has superior analgesic effects to gentle MA (2 r/s MA) on CFA model rats, which is associated with C-fiber activation.
Highlights
Acupuncture is an invaluable heritage of Chinese medicine that is being practiced in 183 countries for treating diseases [1]
A total of 9 healthy male Wistar rats were randomly assigned into 3 groups: control, 2 r/s Manual acupuncture (MA), and 4 r/s MA groups. e proportion of C-fiber neurons (CGRP-positive neurons) and A-fiber neurons (NF200-positive neurons) in the dorsal root ganglia (DRG) activated by MA were quantitatively analyzed with the morphological immunofluorescence staining method to ascertain the activated DRG neurons influenced by different frequencies of MA. e rats in the two MA groups received acupuncture once and sacrificed for the collection of tissue samples
Compared with the control group, the PWL in the complete Freund’s adjuvant (CFA) + 2 r/s MA group was increased significantly on day 5 (6.57 ± 0.20 s vs. 8.90 ± 0.34 s, P < 0.05) and day 6 (7.20 ± 0.19 s vs. 9.32 ± 0.64 s, P < 0.05). ere was no significant difference between the CFA + 2 r/s MA group and the CFA + 2 r/s MA + RTX group (Figure 4(e)). ese results indicated that C-fiber participated in the analgesic effect of 4 r/s MA but not of 2 r/s MA
Summary
Manual acupuncture (MA) with different stimulus frequencies may give rise to varying acupuncture effects. To compare the analgesic effects of different frequencies of twirling-rotating MA on rats with complete Freund’s adjuvant- (CFA-) induced pain and explore the underlying mechanism via peripheral sensory nerves. Ird, 30 healthy male Wistar rats were randomly divided into 6 groups: control group, CFA group, CFA + 2 r/s MA group, CFA + 2 r/s MA + RTX group, CFA + 4 r/s MA group, and CFA + 4 r/s MA + RTX group. Both types of MA treatment increased the PWL of saline-injecting rats and pain model rats. Following the injection of RTX to inhibit the activation of C-fibers, the analgesic effect of 4 r/s MA reduced significantly but not of 2 r/s MA. Strong MA (4 r/s MA) has superior analgesic effects to gentle MA (2 r/s MA) on CFA model rats, which is associated with C-fiber activation
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