We present a protocol using the tuina manipulation simulator to perform the “Three-Manipulation and Three-Acupoint” tuina therapy for minor chronic constriction injury rats and evaluate the effective analgesic time points of tuina within 24 h by testing pain changes through behavioral analysis and changes in inflammatory factor expression using enzyme-linked immunosorbent assay.
Tuina, as an external treatment method of traditional Chinese medicine, has been proven to have an analgesic effect on peripheral neuropathic pain (pNP) in clinical and basic research. However, the optimal time point for the analgesic effect of tuina may vary according to different injury sensations, affecting the exploration of the initiation mechanism of tuina analgesia.
The research used minor chronic constriction injury (minor CCI) model rats to simulate pNP and used the intelligent tuina manipulation simulator to simulate the three methods (point-pressing, plucking, and kneading) and three acupoints (Yinmen BL37, Chengshan BL57, and Yanglingquan GB34) for performing tuina therapy. The study evaluated the changes in pain within 24 h and the optimal time point for the efficacy of tuina analgesia in rats with minor CCI models by testing cold sensitivity threshold (CST), mechanical withdrawal threshold (MWT), and thermal withdrawal latency (TWL). Furthermore, the study evaluated IL-10 and TNF-α expression changes through Elisa detection. The results show that tuina has both immediate and sustained analgesic effects. For the three different injury sensitivity thresholds of CST, MWT, TWL, and two cytokines of IL-10 and TNF-α, the analgesic efficacy of tuina within 24 h after intervention is significantly different at different time points.
Peripheral neuropathic pain (pNP) refers to pain caused by a lesion or disease of the peripheral somatosensory nervous system, manifested as a series of symptoms and signs, with hyperalgesia as one of the main symptoms1,2. Hyperalgesia is a heightened experience of pain caused by a noxious stimulus, including pinprick, cold, and heat3. Large epidemiological studies have been conducted, which show pNP is the most common, with a prevalence rate of 6.9%-10% in neuropathic pain4. pNP can be caused by multiple diseases, including injury of the nerve, postherpetic neuralgia, painful diabetic polyneuropathy, multiple sclerosis, stroke, cancer, etc.5. Nowadays, the main method for treating pNP is medication, but the effect is not ideal; and the side effects are significant, which is the main reason for the high economic burden on individuals and society6.
Tuina is a green, economical, safe, and effective external treatment method of traditional Chinese medicine7. Many clinical studies have proven the analgesic effect of tuina on pNP, and basic studies have verified the immediate and cumulative analgesic effects of tuina8,9. The main cumulative analgesic mechanism of tuina is to reduce the levels of inflammatory factors and inhibit the activation of glial cells10,11. The previous research confirmed the cumulative analgesic effect of tuina and found differentially expressed genes (DEGs) in the dorsal root ganglia (DRG) and spinal dorsal horn (SDH) of rats with sciatic nerve injury after 20 times of tuina treatment, mainly related to protein binding, pressure response, and neuronal projection12. In recent studies, it has been confirmed that tuina has an immediate analgesic effect and that 1-time tuina intervention could alleviate the hyperalgesia of minor CCI rats and especially ease thermal hyperalgesia more effectively13. However, the optimal time point for the analgesic effect of tuina may vary depending on the injury sensation (cold, heat, mechanical), affecting the exploration of the initiation mechanism of tuina analgesia.
Inflammatory mediators can sensitize and activate pain receptors, leading to decreased discharge thresholds and ectopic discharges, thereby contributing to peripheral sensitization14,15. After peripheral nerve injury, TNF-α is an initiator of the inflammatory response, which can promote the synthesis of inflammatory factors such as IL-10 and IL-1β, causing direct tissue inflammatory injury, stimulating local nerve endings, and causing pain16,17,18. Tuina can achieve analgesic effects by reducing the expression of inflammatory factors such as TNF-α, IL-10, IL-6, and IL-1β19,20,21. The study selected minor CCI model rats to simulate clinical pNP and selected different time points for behavioral testing of cold, thermal, and mechanical stimulation pain after a 1-time tuina intervention by cold sensitivity threshold (CST), mechanical withdrawal threshold (MWT), thermal withdrawal latency (TWL), and choose IL-10 and TNF-α in the serum by enzyme-linked immunosorbent assay (ELISA), in order to select the time point at which the analgesic effect of tuina is significant, providing a basis for the study of the initiation mechanism of tuina analgesia in the later stage.
The Committee on Animal Protection and Use of Beijing University of Chinese Medicine (BUCM-4-2022082605-3043) approved all procedures used in this study.
1. Animals and study design
2. Establishment of a rat model of minor CCI (Figure 1)
NOTE: The method of modeling the minor CCI was as described in previous studies22,23,24.
3. Intelligent tuina manipulation simulator intervention (Figure 2)
NOTE: The treatment began on the 7th day after the model was established.
4. Behavioral measurement
NOTE: After the intervention, the threshold cold sensitivity threshold (CST), mechanical withdrawal threshold (MWT), and thermal withdrawal latency (TWL) were tested in the 5 tuina subgroups, model group, and sham operation group, respectively. The testing time for the model and sham groups is the same as that for the tuina group (i.e., 24 h).
5. ELISA
CST: Compared with the model group, the number of foot lifts in the group 6 h after tuina was significantly reduced, and the difference was statistically significant (P < 0.05). Compared with the sham group, the number of foot lifts in the model group was significantly increased, and the difference was statistically significant (P < 0.05) (Table 3, Figure 3).
MWT: Compared with the model group, the MWT of each sub-group of tuina was significantly higher than that of the model group except for 18 h after tuina, and the MWT of the 24 h after tuina was significantly higher than that of the model group, with a statistically significant difference (P < 0.05). Compared with the sham operation group, the MWT in the model group was significantly lower, with a statistically significant difference (P < 0.01) (Table 3, Figure 4).
TWL:
Compared with the model group, there was a significant increase immediately after tuina, 6 h after tuina, and 18 h after tuina, with a statistically significant difference. Compared with the sham operation group, the model group significantly decreased, with a statistically significant difference (P < 0.01) (Table 3, Figure 5)
ELISA
IL-10: Compared with the model group, there was a significant decrease 6 h and 24 h after tuina, with a statistically significant difference (P < 0.01) (Table 4, Figure 6).
TNF-α: Compared with the model group, there was a significant decrease immediately after tuina (**P < 0.01), 6 h after tuina (**P < 0.01), and 24 h after tuina(**P < 0.05), with a statistically significant difference (Table 4, Figure 6)
Figure 1: Establishment of a rat model of minor CCI. (A) A chromic intestinal suture (4-0).(B) Skin preparation. (C) Incision. (D) Exposing the sciatic nerve. (E) Absorbable chromic intestinal suture (4-0 type) around the nerve. (F) Suturing the muscle layer and the skin. Please click here to view a larger version of this figure.
Figure 2: Intelligent tuina manipulation simulator treatment. (A) The Intelligent Tuina Manipulation Simulator (patent No. ZL ZL 2023 20511277.5). (B) The positions of Yinmen (BL37), Chengshan (BL57) and Yanglingquan (GB34). (C) Stimulating Yinmen (BL37). Please click here to view a larger version of this figure.
Figure 3: Results of cold sensitivity threshold (CST) of rats in each group. *P < 0.05, compared with the model group, #P <0.05, compared with the sham group. Please click here to view a larger version of this figure.
Figure 4: Results of mechanical withdrawal threshold (MWT) of rats in each group. *P <0.05, compared with the model group, #P < 0.05, compared with the sham group. Please click here to view a larger version of this figure.
Figure 5: Results of thermal withdrawal latency (TWL) of rats in each group. *P < 0.05, **P < 0.01, compared with the model group; #P <0.05, ##P < 0.01, compared with the sham group. Please click here to view a larger version of this figure.
Figure 6: Changes in serum IL-10 and TNF-α levels of rats in each group (Mean ± SD, n = 7), “*P<0.05, **P<0.01, compared with the model group. Please click here to view a larger version of this figure.
Three-Method | Methods | Classifications | Functions |
Point-pressing | Warming and unblocking | Warming meridians and unblocking collaterals | |
Plucking | Relaxation | Acting on the nerve trunk and treating numbness or pain in the limbs | |
Kneading | Relaxation | Alleviating muscle spasms |
Table 1: Three methods of stimulation.
Three-Acupoint | Acupoints | Meridians | Nerves | Muscles |
Yinmen (BL37) | Bladder Meridian of Foot-Taiyang | Sciatic nerve trunk | Biceps femoris muscle | |
Chengshan(BL57) | Tibial nerve | Gastrocnemius muscle | ||
Yanglingquan(GB34) | Gallbladder Meridian of foot-Shaoyang | Common peroneal nerve | Anterior tibial muscles |
Table 2: Three acupoints used in this study.
Sham | Model | Tuina | |||||
0 h | 6 h | 12 h | 18 h | 24 h | |||
CST | 12.8 ± 2.38 | 25 ± 5.15# | 19.6 ± 10.99 | 13.2 ± 2.49* | 16.4 ± 8.41 | 17 ± 5.57 | 19 ± 8.34 |
MWT | 69.47 ± 10.35 | 40.63 ± 9.65## | 44.19 ± 10.72 | 46.58 ± 9.47 | 42.83 ± 11.41 | 40.1 ± 5.59 | 48.33 ± 8.7* |
TWL | 12.06 ± 3.45 | 8.16 ± 2.09## | 12.09 ± 3.86** | 10.07 ± 2.7* | 9.44 ± 2.52 | 10.42 ± 2.49** | 9.72 ± 2.29 |
Table 3: CST, MWT, and TWL results of rats in each group (Mean ± SD, n = 7). *P<0.05, **P<0.01, compared with the model group; #P<0.05, ##P<0.01, compared with the sham group.
Sham | Model | Tuina | |||||
0 h | 6 h | 12 h | 18 h | 24 h | |||
IL-10 | 55.10 ± 1.37** | 70.27 ± 6.22 | 67.28 ± 1.28 | 61.41 ± 3.36** | 67.98 ± 1.85 | 69.03 ± 6.29 | 57.16 ± 1.30** |
TNF-α | 311.52 ± 13.45** | 339.33 ± 24.50 | 309.47 ± 8.37** | 309.99 ± 14.95** | 334.62 ± 21.85 | 319.22 ± 10.38 | 316.24 ± 8.72* |
Table 4: Changes in serum IL-10 and TNF-α levels of rats in each group(Mean ± SD, n = 7, pg/mL). *P < 0.05, **P < 0.01, compared with group model (*P < 0.05, **P < 0.01.)
The study used the minor CCI model to simulate pNP caused by clinical sciatic nerve injury. The minor CCI model involves the continuous, chronic compression and restraint of the nerve trunk through ligation, accompanied by the gradual swelling of the ligature, resulting in edema within the sciatic nerve and forming stable chronic pain in 3-5 days27,28. In the preliminary study, the research group found that the minor CCI model group was more stable than the classical model group on the 7th day after modeling, making it more suitable for short-term experimental design. Therefore, we chose this time point for the tuina intervention.
The previous research has verified that the intelligent tuina manipulation simulator (animal) can effectively alleviate pain in rats with sciatic nerve injury after 20 sessions of tuina treatment using the "Three-Method and Three-Acupoint"29,30,31. Moreover, the research group found that tuina once can effectively alleviate the pain hypersensitivity symptoms of minor CCI rats, especially the thermal hyperalgesia13. The study adopts the point-pressing, plucking, and kneading methods as the three methods for treatment. The point-pressing method is a warming and unblocking technique that has the function of warming meridians and unblocking collaterals. The plucking method is a relaxation technique that acts on the nerve trunk and can treat numbness or pain in the limbs. The kneading method is a relaxation technique that can alleviate muscle spasms, eliminate fatigue, and relieve pain in the injured area (Table 1). The study selects Yinmen (BL37), Chengshan(BL57), and Yanglingquan(GB34) as the three acupoints for treatment (Table 2). According to the principle of acupoint selection along meridians and locally in acupuncture and moxibustion, three acupoints belong to the Bladder Meridian of Foot-Taiyang and the Gallbladder Meridian of foot-Shaoyang. According to anatomical nerve localization, Yinmen(BL37) is located on the sciatic nerve and its branches, Chengshan (BL57) is located on the tibial nerve, and Yanglingquan (GB34) is located on the common peroneal nerve. According to the anatomical muscle location, the three acupoints are located around the biceps femoris muscle, gastrocnemius muscle, and anterior tibial muscles (Table 2). Therefore, through the intervention of the three methods and three acupoints, the relevant areas of acupoint-nerve-muscle can be stimulated. In this study, after forming stable chronic pain and one intervention with tuina, behavioral changes in pain were detected, further verifying that tuina has an immediate analgesic effect and has different therapeutic significance time points for different injury receptors, providing therapeutic support for the next step in the study of tuina analgesia initiation mechanism.
The study used CST, MWT, and TWL as indicators to explore the efficacy of tuina for different injury sensations. The clinical manifestations of induced pain in pNP mainly include hyperalgesia and allodynia, namely, cold and hot stimulation-induced pain and mechanical tactile-induced pain4. Currently, the classic quantitative behavioral research indicators for these two pain sensations are CST, MWT, and TWL. In CST testing, the cold plate test, the ZH-6C intelligent cold and hot plate pain tester used in this experiment, is relatively objective, less affected by surrounding environmental factors, has constant temperature, and has high precision32,33. In basic research, Von Frey filaments are commonly used to estimate MWT, which is one of the classic indicators for evaluating neuropathic pain. It is mainly aimed at acupuncture pain induced by mechanical stimulation to evaluate mechanical tactile-induced pain in rodents34,35. The Hargreaves test uses a thermal pain stimulator to detect and evaluate the response of rodents to thermal pain sensitivity and is used to evaluate the recovery of pain sensitivity or thermal pain response after nerve injury to observe whether the animal's hind paws have a constriction reaction due to heat. The instrument detects the movement of the animal's hind paws36, and the controller will automatically turn off the infrared stop timer34, which is known as TWL. Experiments show that the sensitivity of minor CCI model rats to TWL is optimal38. Therefore, the quantitative research method for the behavior of minor CCI model rats this time is to use a cold plate experiment, electronic mechanical pricking apparatus, and thermal pricking apparatus to detect.
The significant time points of curative effects on different nociceptive sensations after early tuina intervention are different. Currently, preliminary exploration has been conducted on the clinical efficacy and mechanism of tuina analgesia. Our previous research mainly focused on the analgesic mechanism after a certain number of tuina. In the past 2 years, research has been conducted on the analgesic mechanism at the initial stage of tuina to explore how tuina analgesia is initiated. In this study, "three methods and three acupoints" were used to intervene in minor CCI model rats once. Then 5 time points were selected for CST, MWT, and TWL detection to observe the changes in temperature and mechanical tactile sensation of minor CCI model rats. This study used ELISA to detect changes in serum IL-10 and TNF-α levels of rats after behavioral testing. The results showed that after one intervention with tuina, compared with the model group, both improved immediately. This again confirmed the previous research results that tuina had an immediate analgesic effect. However, for different types of pain sensations, the time points at which the analgesic effect is significant are not the same. In terms of CST, there was statistical significance 6 h after tuina; In terms of MWT, there was statistical significance 24 h after tuina; In terms of TWL, there was significant statistical significance 6 h after tuina, and significant statistical significance immediately and 18 h after tuina; In terms of serum IL-10 level, there was a significant decrease 6 h after tuina, and 24 h after tuina, with a statistically significant difference. In terms of serum TNF-α level, there was a significant decrease immediately after tuina, 6 h after tuina, and 24 h after tuina, with a statistically significant difference. It indicates that while the analgesic effect of tuina can be sustained, there is a significant delay in the time point of efficacy for cold stimulation-induced pain and mechanical tactile-induced pain, and it is immediately effective and has a more significant and lasting efficacy for thermal stimulation-induced pain. Our lab is further exploring the changes in proteins and genes related to the transient receptor potential (TRP) proteins and genes related to cold, hot, and mechanical sensitivity, as well as other inflammatory factors such as TGF-β and IL-6, to explore the analgesic initiation mechanism of tuina further.
In summary, based on the results of this study, it can be inferred that the time points at which the proteins or pathways affected by tuina may function may be different, resulting in different time points for significant analgesic effects. Further in-depth research is needed to explore the initiation mechanism of tuina analgesia and provide a basis for clinical efficacy research of tuina.
The authors have nothing to disclose.
The authors have received funding for research, writing, and publication of this paper from the National Natural Science Foundation of China (Nos. 82074573 and 82274675) and the Beijing Natural Science Foundation (No. 7232278).
Anesthesia machine | Ruiwode Life Technology Co., Ltd., Shenzhen, China | R500 | Animal respiratory anesthesia related equipment |
Chromic intestinal suture | Shandong Boda Medical Products Co., Ltd., China | BD210903 | An absorbable surgical suture mainly made from collagen protein processed from the intestines of healthy young goats |
Electronic Von Frey instrument | Bioseb, USA | BIO-EVF5 | An instrument for detecting mechanical withdrawal threshold |
Intelligent cold and hot plate pain detector | Anhui Zhenghua Biological Instrument Equipment Co., Ltd,China. | ZH-6C | An instrument for detecting cold sensitivity threshold |
Isoflurane | Ruiwode Life Technology Co., Ltd., Shenzhen, China | R510-22-10 | An anesthetic |
Multi-function full-wavelength microplate reader | Molecular Devices (Shanghai) Co., Ltd. | SpectraMax M2 | An instrument for detecting optical density (OD) |
Thermal analgesia device | Chengdu Techman Software Co., Ltd., China | PL-200 | An instrument for detecting thermal withdrawal latency |