Transcutaneous auricular vagus nerve stimulation modulates masseter muscle activity, pain perception, and anxiety levels in university students: a double-blind, randomized, controlled clinical trial.

Introduction: Chronic anxiety is a statemarked by sustained activation of the masseter muscle, manifesting in both mental and physical strain. This prolonged tension can significantly impact mental wellbeing and cognitive abilities, posing a risk for a range of health complications. This double-blind, randomized, controlled clinical trial investigated the impact of transcutaneous auricular vagus nerve stimulation (TAVNS) on masseter muscle activity, pressure pain threshold (PPT), and anxiety levels in university students with elevated anxiety. Methods: Forty-two participants meeting inclusion criteria were randomly assigned to either active TAVNS or sham TAVNS groups. Various parameters, including masseter muscle electromyographic (EMG) signals, PPT, and Beck Anxiety Inventory (BAI) scores, were assessed before pretreatment, immediately after the intervention week, and 2 weeks follow-up. Results: Active TAVNS significantly reduced both left and right masseter activation during resting mandibular position, persisting for 2 weeks post-intervention. Additionally, TAVNS induced a lasting decrease in both left and right masseter PPT, indicative of altered pain perception. Notably, BAI scores showed a substantial reduction, emphasizing TAVNS as a potential intervention for anxiety, with effects maintained at the 2-week follow-up. Discussion: This study provides comprehensive insights into the multifaceted effects of TAVNS on physiological and psychological aspects associated with anxiety in university students. The promising results underscore TAVNS as a potential neuromodulatory intervention for anxiety-related conditions, warranting further research and clinical exploration. Clinical Trial Registration: https://ensaiosclinicos.gov.br/rg/RBR-4s4kt2r.

Infralimbic medial prefrontal cortex alters electroacupuncture effect in animals with neuropathic chronic pain.

INTRODUCTION: Morphological reorganization in the neural networks of the medial prefrontal cortex (mPFC) may be involved in the development of chronic neuropathic pain (NP). OBJECTIVES: We investigated whether inactivation and neurostimulation of the infralimbic division (IFL) of the mPFC alter electroacupuncture-induced analgesia (EIA) at 2 Hz and 2/100 Hz in animals with chronic NP. METHODS: Wistar rats were submitted to chronic constrictor injury of the ischiadicus nerve (CCI). Von Frey and acetone tests were performed to evaluate mechanical or cold allodynia. Animals were submitted to electroacupuncture (EA) at 2 Hz and 2/100 Hz for 20 min. After EA, the IFL cortex synaptic contacts were inactivated by cobalt chloride (200 nL of 1.0 mM CoCl2). Neurostimulation of the IFL cortex was also performed at 20 µA for 15 s, after EA, using a deep brain stimulation device. RESULTS: EA at 2 Hz and 2/100 Hz attenuated mechanical or cold allodynia in CCI rats. Microinjection of CoCl2 into the IFL division of the mPFC blocked the EA effect. EA at 2 Hz and 2/100 Hz, in association with neurostimulation of the IFL cortex, attenuated mechanical and thermal allodynia. CONCLUSION: EA induces antinociception in CCI rats. The analgesia was potentiated in association with neurostimulation in the IFL division of the mPFC.