Pain in masticatory muscles is among the most prominent symptoms of temperomandibular disorders (TMDs) that have diverse and complex etiology. A common complaint of TMD is that unilateral pain of craniofacial muscle can cause a widespread of bilateral pain sensation, although the underlying mechanism remains unknown. To investigate whether unilateral inflammation of masseter muscle can cause a bilateral allodynia, we generated masseter muscle inflammation induced by unilateral injection of complete Freund's adjuvant (CFA) in rats, and measured the bilateral head withdrawal threshold at different time points using a von Frey anesthesiometer. After behavioral assessment, both right and left trigeminal ganglia (TRG) were dissected and examined for histopathology and transient receptor potential vanilloid 1 (TRPV1) mRNA expression using quantitative real-time PCR analysis. A significant increase in TRPV1 mRNA expression occurred in TRG ipsilateral to CFA injected masseter muscle, whereas no significant alteration in TRPV1 occurred in the contralateral TRG. Interestingly, central injection of TRPV1 antagonist 5-iodoresiniferatoxin into the hippocampus significantly attenuated the head withdrawal response of both CFA injected and non-CFA injected contralateral masseter muscle. Our findings show that unilateral inflammation of masseter muscle is capable of inducing bilateral allodynia in rats. Upregulation of TRPV1 at the TRG level is due to nociception caused by inflammation, whereas contralateral nocifensive behavior in masticatory muscle nociception is likely mediated by central TRPV1, pointing to the involvement of altered information processing in higher centers.

Introduction: Sarcopenic obesity (SO) is a condition characterized by the coexistence of age-related obesity and sarcopenia. This systematic review and network meta-analysis (NMA) aimed to compare the effects of different training modalities, such as aerobic training (AT), resistance training (RT), combined resistance with AT (CT), and multicomponent training (MCT) on body composition, muscle strength, and physical performance in elderly patients with SO.Methods: We electronically searched randomized controlled trials, published from inception to March 2024 in PubMed, Embase, Cochrane Library, Web of Science and Scopus. Effect estimates were presented as mean differences (MD) or Standard Mean Difference (SMD) with 95% confidence interval (CI). The comprehensive effects of all treatments were ranked by the surface under the cumulative ranking (SUCRA) probabilities.Results: 14 trials enrolling 955 participants were included. The body fat percentage (BFP) in MCT (MD= −6.37, 95% CI: −8.67, −4.07), CT (MD = −2.08, 95% CI: −4.00, −0.16), and RT (MD = −1.85, 95% CI: −3.25, −0.44) was significantly lower than in the normal control group, with MCT showing superior effects compared to CT and RT. Furthermore, only MCT significantly improved fat-free mass (FFM; MD = 5.21, 95% CI:1.51, 8.91), as well as in body mass index (BMI; MD = 0.74, 95% CI:0.08, 1.40). In addition, handgrip strength (HGS) significantly improved under both MCT (SMD = 0.87, 95% CI: 0.19, 1.5) and RT(SMD = 0.84, 95% CI: 0.43, 1.25). The performance on the 30s chair stand test also yielded better outcomes for MCT (MD = 3.10, 95% CI: 1.33, 4 0.86), CT(MD = 2 0.50, 95% CI: 0.18, 5.18), and RT(MD = 3.91, 95% CI: 2.30, 5.52) when compared to the control group. Lastly, gait speed was enhanced by both MCT (MD = 0.35, 95% CI: 0.30, 0.41) and CT(MD = 0.14, 95% CI: 0.06, 0.21). The ranking results indicated that MCT was superior to other training modalities in enhancing body composition and gait speed. In contrast, RT appears to be more advantageous in the 30-second chair standing test and in improving HGS.Conclusion: MCT outperformed other training modalities in improving body composition and gait speed. RT was more beneficial for the 30-second chair standing test and enhancing HGS. These findings provide valuable insights for clinicians and researchers to customize exercise prescriptions for older patients with SO.Systematic review registration: http://www.crd.york.ac.uk/PROSPERO/display_record.asp?ID=CRD42024544962.