Effects of transcutaneous electrical nerve stimulation based on wrist-ankle acupuncture theory on the skeletal muscle repair and gut microbiota modulation in rats with gastrocnemius muscle injury.

Abstract

Background: In recent years, the gut microbiota has attracted considerable attention as a critical regulator of inflammation and metabolism, particularly due to its involvement in muscle repair via the "gut-muscle axis." This study aims to evaluate the therapeutic efficacy of transcutaneous electrical nerve stimulation based on wrist-ankle acupuncture theory (WAA-TENS) in a rat model of gastrocnemius muscle injury, and subsequently to explore whether its effects are associated with alterations in the gut microbiota.

Methods: Twenty-four 8-week-old rats were randomly allocated to three groups (n = 8 per group): a control group (CON), a model group (MOD), and a WAA-TENS group. The CON group received intramuscular saline, whereas gastrocnemius injury induced by complete Freund's adjuvant (CFA) was established in the MOD and WAA-TENS groups; the latter received WAA-TENS. Mechanical pain threshold, local cytokines, and histological outcomes were assessed, and fecal samples were analyzed by 16S rRNA gene sequencing.

Results: Behavioral studies indicated that WAA-TENS significantly increased the pain threshold of model rats (p < 0.001). Histological analysis revealed that the degree of inflammatory cell infiltration in the WAA-TENS group was less than that in the MOD group, and the degree of fibrosis was significantly lower than that in the MOD group. Bacterial diversity analysis indicated that the microbiota structure in the MOD group did not differ significantly from that in the CON group, suggesting that CFA-induced local muscle injury alone may be insufficient to induce systemic gut dysbiosis under the present experimental conditions. Notably, WAA-TENS significantly altered the microbiota structure (characterized by a significant decrease in evenness and an increase in the abundance of Lactobacillus), suggesting that WAA-TENS may exert distinct modulatory effects on the intestinal microenvironment independent of the injury-induced response.

Conclusion: WAA-TENS effectively alleviated mechanical allodynia, attenuated local inflammation, and promoted muscle repair in a rat model of CFA-induced gastrocnemius injury. Concurrently, WAA-TENS was associated with significant alterations in gut microbiota composition, including the enrichment of Lactobacillus reuteri. These parallel findings suggest a potential association between WAA-TENS-induced microbiota modulation and its therapeutic effects on skeletal muscle, providing a hypothesis-generating foundation for future mechanistic investigations into the gut-muscle axis. The causal contribution of specific microbial taxa to muscle repair, however, remains to be established.