Effect of Earthing Mats on Sleep Quality in Rats.

Grounding, a therapeutic technique involving direct contact with the earth, has been proposed by various studies to potentially have beneficial effects on pressure, sleep quality, stress, inflammation, and mood. However, the scientific evidence supporting its sedative effects remains incomplete. This study examined the sedative effectiveness of an earthing mat on sleep quality and investigated the underlying neural mechanisms using electroencephalography (EEG) analysis in rodents, focusing on orexin and superoxide dismutase (SOD) levels in the brain. Rats were randomly assigned to four groups: the naïve normal group (Nor), the group exposed to an earthing mat for 7 days (A-7D), the group exposed to an earthing mat for 21 days (A-21D), and the group exposed to an electronic blanket for 21 days (EM). EEG results revealed that the A-21D group exhibited significantly reduced wake time and increased rapid eye movement (REM), non-rapid eye movement (NREM), and total sleep time compared to the Nor group (p < 0.05). Moreover, the A-21D group demonstrated a significant increase in NREM sleep (p < 0.001), REM sleep (p < 0.01), and total sleep time (p < 0.001), along with a decrease in wake time compared to the EM group (p < 0.001). The orexin level in the A-21D group was significantly lower compared to the Nor group (p < 0.01), while SOD1 expression was markedly elevated in the A-21D group compared to the Nor group (p < 0.001). These results suggest that the earthing mat may represent a promising new method for promoting sleep quality and could serve as an effective therapeutic technique.

Sedative-Hypnotic Effects of Glycine max Merr. Extract and Its Active Ingredient Genistein on Electric-Shock-Induced Sleep Disturbances in Rats.

Glycine max Merr. (GM) is a functional food that provides many beneficial phytochemicals. However, scientific evidence of its antidepressive and sedative activities is scarce. The present study was designed to investigate the antidepressive and calmative effects of GM and its biologically active compound, genistein (GE), using electroencephalography (EEG) analysis in an electric foot shock (EFS)-stressed rat. The underlying neural mechanisms of their beneficial effects were determined by assessing corticotropin-releasing factor (CRF), serotonin (5-HT), and c-Fos immunoreactivity in the brain using immunohistochemical methods. In addition, the 5-HT2C receptor binding assay was performed because it is considered a major target of antidepressants and sleep aids. In the binding assay, GM displayed binding affinity to the 5-HT2C receptor (IC50 value of 14.25 ± 11.02 µg/mL). GE exhibited concentration-dependent binding affinity, resulting in the binding of GE to the 5-HT2C receptor (IC50, 77.28 ± 26.57 mg/mL). Administration of GM (400 mg/kg) increased non-rapid eye movement (NREM) sleep time. Administration of GE (30 mg/kg) decreased wake time and increased rapid eye movement (REM) and NREM sleep in EPS-stressed rats. In addition, treatment with GM and GE significantly decreased c-Fos and CRF expression in the paraventricular nucleus (PVN) and increased 5-HT levels in the dorsal raphe in the brain. Overall, these results suggest that GM and GE have antidepressant-like effects and are effective in sleep maintenance. These results will benefit researchers in developing alternatives to decrease depression and prevent sleep disorders.

Tinnitus Generation and Behavioral Changes Caused by Chronic Stress: A Behavioral and Brain Study in a Rat Model.

OBJECTIVES: This study explores the connection between chronic stress and tinnitus, a phantom auditory perception, using an animal model. METHODS: Rats were subjected to 2 h of daily restraint stress for 10 days. Tinnitus was assessed on the last day of stress exposure using the gap response of pre-pulse inhibition acoustic reflex, measured at 60 dB background sound level at 8, 16, and 20 kHz. Chronic stress-exposed rats were categorized into two groups: tinnitus (RTG) and non-tinnitus (RNTG). Various tests, including hearing assessments (distortion product otoacoustic emissions and auditory brainstem response), behavioral evaluations (elevated plus maze test and forced swimming test), and immunohistochemical studies in the auditory and limbic brain regions, were conducted to understand the relationship between chronic stress, tinnitus, and behavioral changes. RESULTS: Following chronic restraint stress, 64.3% of the rats exhibited tinnitus with no audiometric changes. EPM and FST indicated an increase of anxiety- and depression-related behavior in RTG. Immunohistochemical analyses identified specific alterations in the expression of neurotransmitter receptors within brain regions implicated in tinnitus. Specifically, we observed a decrease in γ-aminobutyric acid A receptor α1 expression and an increase in glutamate receptor (N-methyl-D-aspartate receptor subunit 1 and receptor subunit 2B) expression in specific brain region. These changes suggest a reorganization of neural circuits associated with the tinnitus generation and behavioral changes of the rats after chronic stress exposure. CONCLUSION: Chronic stress alone can be a causal factor for the generation of tinnitus and behavioral changes through altered neural activities in tinnitus-related brain networks. LEVEL OF EVIDENCE: NA Laryngoscope, 2024.

The Effect of Earthing Mat on Stress-Induced Anxiety-like Behavior and Neuroendocrine Changes in the Rat.

Grounding is a therapeutic technique that involves doing activities that "ground" or electrically reconnect us to the earth. The physiological effects of grounding have been reported from a variety of perspectives such as sleep or pain. However, its anti-stress efficacy is relatively unknown. The present study investigated the stress-related behavioral effects of earthing mat and its neurohormonal mechanisms in the Sprague−Dawley male rat. Rats were randomly divided into four groups: the naïve normal (Normal), the 21 days immobilization stressed (Control), the 21 days stressed + earthing mat for 7 days (A7) or 21 days (A21) group. The depressive-and anxiety like behaviors were measured by forced swimming test (FST), tail suspension test (TST) and elevated plus maze (EPM). Using immunohistochemistry, the expression of corticotrophin-releasing factor (CRF) and c-Fos immunoreactivity were analyzed in the brain. In the EPM, time spent in the open arm of the earthing mat groups was significantly increased compared to the Control group (p < 0.001), even though there were without effects among groups in the FST and TST. The expression of CRF immunoreactive neurons in the earthing mat group was markedly decreased compared to the Control group. Overall, the earthing mat reduced stress-induced behavioral changes and expression of c-Fos and CRF immunoreactivity in the brain. These results suggest that the earthing mat may have the potential to improve stress-related responses via the regulation of the corticotrophinergic system.

Safety and Efficacy of Intratympanic Alpha-Lipoic Acid Injection in a Mouse Model of Noise-Induced Hearing Loss.

Alpha-lipoic acid (ALA) is an antioxidant with oto-protective effects. In the present study, the safety and effectiveness of ALA therapy after noise-induced hearing loss was confirmed based on the administration method. The safety of intratympanic ALA (IT-ALA) was evaluated with oto-endoscopy and middle ear mucosa morphologic study. Perilymph ALA concentrations according to the administration routes were compared, and the efficacy of ALA was investigated through hearing tests and cochlear histological studies. The middle ear mucosa was swollen 1 week after IT-ALA but completely recovered within 3 weeks. ALA concentration in the perilymph was significantly higher in the IT-ALA group. Recovery of organ of Corti morphology and hearing levels were predominant in the IT-ALA group compared with the intraperitoneal injection group (IP-ALA) and showed similar rescue effects in the IT-dexamethasone group (IT-DEX). Interleukin-1 beta and nuclear factor-kappa B expression was significantly downregulated in the IT-ALA group. IT-ALA showed better cochlear recovery from acoustic trauma with higher inner ear penetration rate than IP-ALA. The rescue effect of IT-ALA after noise-induced hearing loss was similar to IT-DEX; however, the ALA and DEX mechanisms are different. IT-ALA appears to be another safe and effective treatment modality after acoustic trauma and comparable to IT-DEX.

Safety and efficacy of intratympanic histamine injection as an adjuvant to dexamethasone in a noise-induced murine model.

The safety and efficacy of intratympanic (IT) histamine (HIS) injection as an adjuvant to increase the inner ear penetration of dexamethasone (DEX) was investigated in this study. IT injections of DEX-only, 1% HIS+DEX and 4% HIS+DEX were performed in mice with noise-induced hearing loss. An inflammatory reaction in the middle ear was observed only in the 4% HIS+DEX group although no serious cytotoxic effects on the organ of Corti (OC) were observed at that concentration. Compared with the DEX-only group, the perilymphatic concentration of DEX was approximately two times higher in the 1% HIS+DEX group and approximately five times higher in the 4% HIS+DEX group. The expression of the DEX receptor in the cochlea was significantly increased in the 4%-HIS+DEX group. HIS appeared to induce transient damage the microstructure of the RWM with recovery observed within 3 weeks. The 1 and 4% HIS + DEX groups showed a significant recovery of the OC compared with the control group and they also achieved significantly better hearing restoration at 8 kHz in the DPOAE hearing test (P < .05) when compared to the DEX-only group. IT HIS temporarily disrupts the structure of the RWM and middle ear mucosa and significantly enhances the inner ear penetration of DEX. Therefore, IT HIS injection could be a simple and effective adjuvant therapy to increase perilymph concentration of DEX and achieve OC recovery after cochlear damage.

Evidence of Tinnitus Development Due to Stress: An Experimental Study in Rats.

OBJECTIVES/HYPOTHESIS: Tinnitus can develop due to, or be aggravated by, stress in a rat model. To investigate stress as a possible causal factor in the development of tinnitus, we designed an animal study that included tinnitus behavior and excitatory/inhibitory neurotransmitter expression after noise exposure as well as restraint stress. STUDY DESIGN: An experimental animal study. METHODS: Wistar rats were grouped according to single or double exposure to noise and restraint stress. The noise exposure (NE) group was subjected to 110 dB sound pressure level (SPL) of 16 kHz narrow-band noise (NBN) for 1 hour, and the restraint stress (RS) group was restrained for 1 hour with or without noise exposure. Gap prepulse inhibition of the acoustic startle (GPIAS) reflex was measured at an NBN of 16 kHz to investigate tinnitus development. Various immunohistopathologic and molecular biologic studies were undertaken to evaluate possible mechanisms of tinnitus development after noise and/or restraint stress. RESULTS: The RS-only group showed a reduced GPIAS response, which is a reliable sign of tinnitus development. In the double-stimulus groups, more tinnitus-development signs of reduced GPIAS responses were observed. The expression of γ-aminobutyric acid A receptor α1 (GABAAR α1) in the hippocampus decreased in the NE│RS group. Increased N-methyl-d-aspartate receptor1 intensities in the NE│RS group and decreased GABAAR α1 intensities in the RS and NE│RS groups were observed in the CA3 region of the hippocampus. CONCLUSIONS: Tinnitus appeared to develop after stress alone in this animal study. An imbalance in excitatory and inhibitory neurotransmitters in the hippocampus may be related to the development of tinnitus after acute NE and/or stress. LEVEL OF EVIDENCE: NA Laryngoscope, 131:2332-2340, 2021.