Effects of Vibration Therapy on Immobilization-Induced Hypersensitivity in Rats

Static stretching of the ankle prevents cold hypersensitivity associated with limb immobilization in model mice

BACKGROUND

Limb immobilization is considered to contribute to limb pain including hyperalgesia. Approximately 50% of patients with such chronic limb pain complain that their abnormal pain worsens after exposure to cold. However, there have been few studies on the relationship between limb immobilization and cold hypersensitivity. The aim of this study was to examine whether limb immobilization induces cold hypersensitivity, and whether physical exercise such as ankle stretching prevents its induction in model mice.

METHOD

We used forty-four 8-week-old male C57Bl/6J mice, consisting of 32 immobilized mice and 12 control mice. The bilateral hind limbs of the mice were immobilized by a thermoplastic cast. After limb-immobilization for 1 week, changes in mechanical, thermal and cold hypersensitivity, and the expression levels of TRPV1, TRPA1, TRPM8, IL-1β, IL-6, and TNFα in the spinal cord, dorsal root ganglia and the affected hind paw were evaluated in comparison with those in the control mice. In addition, we examined the effect of ankle stretching on the hypersensitivity and expression levels in the limb-immobilized mice.

RESULTS

Mechanical, thermal and cold hypersensitivity were significantly increased in the limb-immobilized mice. In addition, ankle stretching during the immobilization period significantly prevented the increases in those hypersensitivities. There were no significant differences in the expression levels of TRPV1, TRPA1 and TRPM8 among the control, and limb-immobilized mice with and without ankle stretching. The expression levels of IL-1 and IL-6 were significantly increased in the immobilized hind limb paw. Furthermore, ankle stretching significantly prevented the increases in their expression levels.

CONCLUSION

Limb-immobilization induced cold hypersensitivity as well as mechanical and thermal hypersensitivity, and ankle stretching significantly prevented the hypersensitivity induction in the model mice. It would be of great interest to clarify whether a patient with limb-immobilization experiences cold hypersensitivity and whether ankle stretching might prevent hypersensitivity induction in the future.

Beneficial effects of whole-body vibration exercise for brain disorders in experimental studies with animal models: a systematic review

Brain disorders have been a health challenge and is increasing over the years. Early diagnosis and interventions are considered essential strategies to treat patients at risk of brain disease. Physical exercise has shown to be beneficial for patients with brain diseases. A type of exercise intervention known as whole-body vibration (WBV) exercise gained increasing interest. During WBV, mechanical vibrations, produced by a vibrating platform are transmitted, to the body. The purpose of the current review was to summarize the effects of WBV exercise on brain function and behavior in experimental studies with animal models. Searches were performed in EMBASE, PubMed, Scopus and Web of Science including publications from 1960 to July 2021, using the keywords "whole body vibration" AND (animal or mice or mouse or rat or rodent). From 1284 hits, 20 papers were selected. Rats were the main animal model used (75%) followed by mice (20%) and porcine model (5%), 16 studies used males species and 4 females. The risk of bias, accessed with the SYRCLE Risk of Bias tool, indicated that none of the studies fulfilled all methodological criteria, resulting in possible bias. Despite heterogeneity, the results suggest beneficial effects of WBV exercise on brain functioning, mainly related to motor performance, coordination, behavioral control, neuronal plasticity and synapse function. In conclusion, the findings observed in animal studies justifies continued clinical research regarding the effectiveness and potential of WBV for the treatment of various types of brain disorders such as trauma, developmental disorders, neurogenetic diseases and other neurological diseases.

Development and Trial of a Prototype Device for Sensorimotor Therapy in Patients with Distal Radius Fractures

This study examined the clinical feasibility of a prototype device (development name: Ghost) for facilitating range of motion (RoM) recovery in the acute phase in patients with distal radius fractures (DRF). The Ghost device involves the administration of a combination of vibratory and visual stimuli. We divided the patients into the Ghost (n = 10) and control group (n = 4; tendon vibration only) groups. The experimental interventions were administered between the day after surgery and day 7 postoperatively. Traditional hand therapy was provided to both groups once daily from day 7 until day 84 postoperatively and once a week from day 84 until the end of the intervention period. Because vibratory stimulation makes the patient focus on wrist flexion, the primary outcome was the arc of wrist flexion-extension on the injured side, which was measured on days 7, 14, 28, 42, 56, 70, and 84. Analysis of covariance was applied using a bootstrap method to evaluate changes over time and compare them between the groups. Analyses was performed after stratification by age and body mass index. Both interventions improved RoM over time in patients with DRF. Results showed that Ghost has greater efficacy for improving wrist RoM in DRF patients than vibration alone. Treatment with Ghost can result in good RoM improvement during the acute phase of DRF in young patients and those with and normal or low body mass index. Further study is needed to verify our findings and assess the extent of RoM recovery.

Voluntary Forelimbs Exercise Reduces Immobilization-Induced Mechanical Hyperalgesia in the Rat Hind Paw

Voluntary exercise is sufficient to protect against neuropathic pain. However, it is unclear whether voluntary exercise reduces immobilization-induced hyperalgesia. We examined the effect of voluntary forelimb exercise on immobilized-induced hyperalgesia in hind paws of rats. Wistar rats were randomly divided into the (1) both hind limbs immobilized group (IM group), (2) immobilization and exercise with nonimmobilized fore limbs group (EX group), and (3) control group. In the IM and EX groups, the bilateral ankle joints of each rat were immobilized in full plantar flexion with a plaster cast for eight weeks. In the EX group, voluntary exercise using nonimmobilized forelimbs in the running wheel was administered during the immobilization period, while hind limbs were kept immobilized (60 min/day, 5 days/week). Mechanical hyperalgesia in the hind paw was measured using a digital von Frey device every week. To investigate the abnormality of primary sensory neurons and central sensitization, the number of calcitonin gene-related peptide-positive cells in the dorsal root ganglion and the expression level of calcitonin gene-related peptide in the spinal dorsal horn were analyzed by immunohistochemical staining. Immobilization-induced mechanical hyperalgesia was inhibited in the EX group compared to the IM group at three weeks after immobilization. In the EX group, the number of calcitonin gene-related peptide-positive cells in the dorsal root ganglion and the expression level of calcitonin gene-related peptide were significantly decreased compared to those in the IM group. Our results therefore suggest that voluntary forelimb exercise during hind limb immobilization partially reduces immobilization-induced hyperalgesia by suppressing that the plastic changes of the primary sensory nerves that excessively transmit pain and increased responsiveness of nociceptive neurons in the spinal dorsal horn.

Effects of Cryotherapy Applied at Different Temperatures on Inflammatory Pain During the Acute Phase of Arthritis in Rats

OBJECTIVE

The biological mechanisms of cryotherapy for managing acute pain remain unclear. Additionally, it is unknown whether the effectiveness of cryotherapy depends on the applied temperature. This study aimed to clarify the biological effects of cryotherapy and to examine the therapeutic effects of cryotherapy applied at different temperatures in rats.

METHODS

This was an experimental study using a rat knee joint arthritis model. Thirty-five Wistar rats were randomly divided into arthritis (AR), arthritis with 5°C cryotherapy (CR-5), arthritis with 10°C cryotherapy (CR-10), and sham-arthritis control (CON) groups. Arthritis was induced by injecting a mixture of kaolin/carrageenan into the right knee joint. Cryotherapy was applied for 7 days starting the day after injection by immersing the right knee joint in 5°C or 10°C water. Joint transverse diameter, pressure pain threshold, and pain-related behaviors were assessed for 7 days. The number of CD68-positive cells in the knee joint and the expression of calcitonin gene-related peptide in the spinal dorsal horn 8 days after injection were analyzed by immunohistochemical staining.

RESULTS

Improvements in transverse diameter, pressure pain threshold, and pain-related behaviors were observed in the CR-5 and CR-10 groups on the 3rd day compared with the AR group. The number of CD68-positive cells and the expression of calcitonin gene-related peptide in the CR-5 and CR-10 groups were significantly decreased compared with the AR group. There were no significant differences in all results between the CR-5 and CR-10 groups.

CONCLUSIONS

Cryotherapy can ameliorate inflammatory pain through reduction of synovium and central sensitization. Additionally, the effects of cryotherapy lower than 10°C are observed independent of applied temperature.

IMPACT

Cryotherapy may be beneficial as a physical therapy modality for pain and swelling management in the acute phase of inflammation. Translational human study is needed to determine the effective cryotherapy temperature for the inflammatory pain.

Effects of cyclic stretching exercise on long-lasting hyperalgesia, joint contracture, and muscle injury following cast immobilization in rats

The effects of exercise on mechanical hyperalgesia, joint contracture, and muscle injury resulting from immobilization are not completely understood. This study aimed to investigate the effects of cyclic stretching on these parameters in a rat model of chronic post-cast pain (CPCP). Seventeen 8-week-old Wistar rats were randomly assigned to (1) control group, (2) immobilization (CPCP) group, or (3) immobilization and stretching exercise (CPCP+STR) group. In the CPCP and CPCP+STR groups, both hindlimbs of each rat were immobilized in full plantar flexion with a plaster cast for a 4-week period. In the CPCP+STR group, cyclic stretching exercise was performed 6 days/week for 2 weeks, beginning immediately after cast removal prior to reloading. Although mechanical hyperalgesia in the plantar skin and calf muscle, ankle joint contracture, and gastrocnemius muscle injury were observed in both immobilized groups, these changes were significantly less severe in the CPCP+STR group than in the CPCP group. These results clearly demonstrate the beneficial effect of cyclic stretching exercises on widespread mechanical hyperalgesia, joint contracture, and muscle injury in a rat model of CPCP.

Local Vibration Stimuli Induce Mechanical Stress-Induced Factors and Facilitate Recovery From Immobilization-Induced Oxidative Myofiber Atrophy in Rats

Muscle atrophy can be caused by unloading stress such as microgravity environments or cast immobilization. Therapies for such disuse muscle atrophy and their underlying mechanisms are incompletely understood. Here, we investigated the therapeutic effects of local vibration stimulation on immobilization-induced skeletal muscle atrophy. A rat model was made by placing the left hindlimb in a cast for 1 week, leading to oxidative myofiber atrophy without myopathic changes in soleus skeletal muscle. Vibration stimulus (90 Hz, 15 min) to the plantar fascia of the atrophic hindlimb was performed once a day using a hand-held vibration massager after removal of a cast at the end of the immobilization period. After 2 weeks, rats were dissected, and quantitative analysis of the cross-sectional areas of soleus myofibers was performed. The results revealed that vibration induced significant recovery from disuse muscle atrophy, compared with untreated immobilized samples. Furthermore, vibration treatment suppressed the fiber transition from slow to fast fiber types compared with vibration-untreated immobilized samples. Western blotting analyses of mechanical stress-induced factors revealed that the expression of mechano-growth factor (MGF), systemic insulin-like growth factor I, and the mechanotransduction protein, Yes-associated protein 1 (YAP1), was decreased in untreated immobilized soleus muscle, whereas vibration stimulation restored their expression. No change in the level of phosphorylation of YAP1^Ser127 was observed, leading to no change in p-YAP1/YAP1 ratio in vibration-treated immobilized soleus muscle. The results indicate that vibration stimulus is effective to restore immobilization-induced inactivation of YAP1 pathway. Phosphorylation of ERK 1/2, but not AKT, was enhanced in vibration-treated immobilized soleus muscle. Furthermore, vibration stimuli restored immobilization-induced downregulation of the paired box transcription factor, PAX7, a critical factor for regenerative myogenesis in muscle satellite cells. Our results indicate that cyclic vibration stimuli are effective in activating satellite cells and facilitate recovery from immobilization-induced oxidative myofiber atrophy through upregulation of MGF and YAP1.

Intraarticularly-Injected Mesenchymal Stem Cells Stimulate Anti-Inflammatory Molecules and Inhibit Pain Related Protein and Chondrolytic Enzymes in a Monoiodoacetate-Induced Rat Arthritis Model

Persistent inflammation is well known to promote the progression of arthropathy. mesenchymal stem cells (MSCs) have been shown to possess anti-inflammatory properties and tissue differentiation potency. Although the experience so far with the intraarticular administration of mesenchymal stem cell (MSC) to induce cartilage regeneration has been disappointing, MSC implantation is now being attempted using various surgical techniques. Meanwhile, prevention of osteoarthritis (OA) progression and pain control remain important components of the treatment of early-stage OA. We prepared a shoulder arthritis model by injecting monoiodoacetate (MIA) into a rat shoulder, and then investigated the intraarticular administration of MSC from the aspects of the cartilage protective effect associated with their anti-inflammatory property and inhibitory effect on central sensitization of pain. When MIA was administered in this rat shoulder arthritis model, anti-Calcitonin Gene Related Peptide (CGRP) was expressed in the joint and C5 spinal dorsal horn. Moreover, expression of A disintegrin and metalloproteinase with thrombospondin motifs 5 (ADAMTS5), a marker of joint cartilage injury, was similarly elevated following MIA administration. When MSC were injected intraarticularly after MIA, the expression of CGRP in the spinal dorsal horn was significantly deceased, indicating suppression of the central sensitization of pain. The expression of ADAMTS 5 in joint cartilage was also significantly inhibited by MSC administration. In contrast, a significant increase in the expression of TNF-α stimulated gene/protein 6 (TSG-6), an anti-inflammatory and cartilage protective factor shown to be produced and secreted by MSC intraarticularly, was found to extend to the cartilage tissue following MSC administration. In this way, the intraarticular injection of MSC inhibited the central sensitization of pain and increased the expression of the anti-inflammatory and cartilage protective factor TSG-6. As the least invasive conservative strategies possible are desirable in the actual clinical setting, the intraarticular administration of MSC, which appears to be effective for the treatment of pain and cartilage protection in early-stage arthritis, may achieve these aims.

Sole vibration improves locomotion through the recovery of joint movements in a mouse cast model

We investigated the effects of a vibratory stimulus on the plantar surface of the hind limb for motor, sensory, and locomotive function using a mouse cast model. The right knee joint of C57BL/6 male mice (7 weeks, 20 g, n = 31) was flexed with aluminum splint and tape for 6 weeks. These mice were randomly divided into 2 groups (control group, n = 11 and vibration group, n = 12). The mice in the vibration group received vibration on the sole of the ankle for 15 minutes per day, 5 days per week. After the knee joint cast was removed, we measured the range of motion (ROM) of both knee and ankle joints and the sensory threshold of the sole. Further, both walking and swimming movements were analyzed with a digital video. The sole vibration did not affect the passive ROM of the knee joint and sensory threshold after cast removal. However, it increased the ankle dorsiflexion range and improved free walking, swimming, and active movement of the knee joint. In conclusion, we show that the vibration recovered both walking and swimming movements, which resulted from improvements in both the passive ankle dorsiflexion and active knee movement.

Effect of Continuous Passive Motion Initiated After the Onset of Arthritis on Inflammation and Secondary Hyperalgesia in Rats

This study investigated the effect of continuous passive motion (CPM) initiated after the onset of arthritis in rats. Rats were injected with 3 % kaolin/carrageenan in the knee joint and randomized to the control, immobilization (IM), or CPM group. The knee joints of the IM and CPM groups were immobilized with a cast for 56 days. In the CPM group, CPM exercise was administered for 60 min/day (6 times/week). Joint transverse diameter and pressure pain threshold (PPT) were assessed as indicators of inflammation, and paw withdrawal response (PWR) was assessed as indicator of secondary hyperalgesia. Central sensitization was analyzed by measuring calcitonin gene-related peptide (CGRP) expression levels in the spinal dorsal horn. In the CPM group, the PPT was significantly increased compared with the IM group from 14 to 35 days, and PWR was significantly decreased from 14 to 56 days. Additionally, CGRP expression in the super facial layer (I-II) of the spinal dorsal horn (L4-5) in the CPM group was significantly decreased compared with the IM group. Our study found the CPM initiated after the onset of arthritis promoted the recovery of inflammation and mitigated secondary hyperalgesia