Ultra-Low Frequency Transcutaneous Electrical Nerve Stimulation on Pain Modulation in a Rat Model with Myogenous Temporomandibular Dysfunction.

Yueh-Ling Hsieh,Nian-Pu Yang,Chen-Chia Yang

doi:10.3390/ijms22189906

Abstract

Masticatory myofascial pain (MMP) is one of the most common causes of chronic orofacial pain in patients with temporomandibular disorders. To explore the antinociceptive effects of ultra-low frequency transcutaneous electrical nerve stimulation (ULF-TENS) on alterations of pain-related biochemicals, electrophysiology and jaw-opening movement in an animal model with MMP, a total of 40 rats were randomly and equally assigned to four groups; i.e., animals with MMP receiving either ULF-TENS or sham treatment, as well as those with sham-MMP receiving either ULF-TENS or sham treatment. MMP was induced by electrically stimulated repetitive tetanic contraction of masticatory muscle for 14 days. ULF-TENS was then performed at myofascial trigger points of masticatory muscles for seven days. Measurable outcomes included maximum jaw-opening distance, prevalence of endplate noise (EPN), and immunohistochemistry for substance P (SP) and μ-opiate receptors (MOR) in parabrachial nucleus and c-Fos in rostral ventromedial medulla. There were significant improvements in maximum jaw-opening distance and EPN prevalence after ULF-TENS in animals with MMP. ULF-TENS also significantly reduced SP overexpression, increased MOR expression in parabrachial nucleus, and increased c-Fos expression in rostral ventromedial medulla. ULF-TENS may represent a novel and applicable therapeutic approach for improvement of orofacial pain induced by MMP.

Highlights

Masticatory myofascial pain (MMP) is a regional muscle pain disorder characterized by myofascial trigger points localized in taut bands of masticatory muscles [1], and is one of the most common causes of chronic orofacial pain in patients with temporomandibular disorders (TMD) [2]
Before MMP induction, there was no significant difference in endplate noise (EPN) prevalence among the groups (χ2(3) = 7.32, p = 0.06, Table 1)
This research found increased MOR-LI and reduced substance P (SP)-LI in the parabrachial nucleus and increased c-Fos-LI in the rostral ventromedial medulla, as well as improvements of jaw-opening distance and EPN prevalence after ULF-TENS treatment in the MMP animal model, indicating that MMP can be modulated by ULF-TENS

Summary

Introduction

Masticatory myofascial pain (MMP) is a regional muscle pain disorder characterized by myofascial trigger points localized in taut bands of masticatory muscles [1], and is one of the most common causes of chronic orofacial pain in patients with temporomandibular disorders (TMD) [2]. The mechanisms responsible for the analgesia produced by ULF-TENS remain unclear, especially regarding the involvement of connections in central pain-modulating neurons. An alteration in the descending inhibitory or excitatory influences from some structures such as the rostral ventromedial medulla and central opioid pathway seems to be the most powerful in reducing pain behavior and nociceptive neuronal activity [15].

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