Biting reduces acute stress-induced oxidative stress in the rat hypothalamus

Analgesic effect of gum chewing in patients with burning mouth syndrome

The cause of burning mouth syndrome (BMS) is unknown. Although no effective treatment has been established, BMS patients frequently chew gum to alleviate pain. To identify the cause and new treatments for BMS, this study investigated the psychophysical and pharmacological properties of gum chewing to better understand its pain-relieving effects. In this prospective, blinded study, plasma catecholamine and serotonin levels and Profile of Mood States (POMS) scores were assessed after gum chewing or simulated chewing in 40 women (20 BMS patients and 20 age-matched controls). Visual analogue scale (VAS) scores for pain decreased significantly in BMS patients after gum chewing and simulated chewing. Moreover, resting VAS scores of BMS patients were significantly positively correlated with plasma adrenaline level. Furthermore, gum chewing was significantly correlated with lower plasma adrenaline level, VAS score, and tension-anxiety score. These results suggest that adrenaline is important in the pathogenesis of BMS pain and that the analgesic effect of gum chewing is induced through the potential effects of anxiety reduction, although this effect might not be specific to BMS. In addition, the analgesic effect of gum chewing was not induced solely by chewing motion.

Uncovering the neural circuitry involved in the stress-attenuation effects of chewing

Previous animal studies have indicated that coupling restraint stress load with activation of the masticatory organs (chewing) causes a reduction in the systemic and central nervous system stress response. However, the brain mechanism underlying this effect is unknown. Therefore, in this review, we summarize the literature regarding brain regions involved in the attenuating effects of chewing and the systemic stress response attenuation effects induced by those brain regions. In addition, we also focusing on the amygdala, as the emotional control center, and the hypothalamic-pituitary-adrenal axis, as one of the outputs of the systemic response. In particular, we will report on one of the chewing-related stress attenuation mechanisms within the brain brought about by the activation of the inhibition pathway accompanying the activation of the amygdala's GABAergic function.

Autonomic nervous activities associated with bruxism events during sleep

OBJECTIVES

To confirm the relationship between sleep bruxism (SB) and autonomic nervous (AN) activities to elucidate SB physiology.

METHODS

Subjects included 11 healthy males (mean age, 24.7 ± 2.3 years). These data were recorded in the sleep laboratory using a system composed of a two-axis accelerometer, an infrared camera, electroencephalography, electromyography, and electrocardiography. Time lapse analysis confirmed correlations between AN activity and SB events during sleep in subjects. Relationships between SB strength and length and AN activity were evaluated.

RESULTS

Sympathetic nerve (SN) and parasympathetic nerve (PSN) activities occurred significantly in 93.3% of cases (p < 0.01), with similar predictable patterns during SB. Furthermore, SB length and SN activity in seven of the subjects (four subjects, p < 0.05; three subjects p < 0.01), and PSN and SB muscle activities (% maximum voluntary contraction) in five subjects (four subjects, p < 0.05; one subject, p < 0.01) were significantly correlated.

DISCUSSION

The authors believe that SB is closely related to SN as well as PSN activities and may control the AN system.

Mastication as a Stress-Coping Behavior

Exposure to chronic stress induces various physical and mental effects that may ultimately lead to disease. Stress-related disease has become a global health problem. Mastication (chewing) is an effective behavior for coping with stress, likely due to the alterations chewing causes in the activity of the hypothalamic-pituitary-adrenal axis and autonomic nervous system. Mastication under stressful conditions attenuates stress-induced increases in plasma corticosterone and catecholamines, as well as the expression of stress-related substances, such as neurotrophic factors and nitric oxide. Further, chewing reduces stress-induced changes in central nervous system morphology, especially in the hippocampus and hypothalamus. In rodents, chewing or biting on wooden sticks during exposure to various stressors reduces stress-induced gastric ulcer formation and attenuates spatial cognitive dysfunction, anxiety-like behavior, and bone loss. In humans, some studies demonstrate that chewing gum during exposure to stress decreases plasma and salivary cortisol levels and reduces mental stress, although other studies report no such effect. Here, we discuss the neuronal mechanisms that underline the interactions between masticatory function and stress-coping behaviors in animals and humans.

The effects of a customized over-the-counter mouth guard on neuromuscular force and power production in trained men and women

Although mouth guards were originally designed for injury prevention, even elite athletes are now using performance mouth guards to improve athletic success. Both expensive custom models and over-the-counter models are available, but the efficacy is not well known. Some athletes remain wary of the perceived potential for detriments using a mouth guard to their performance. Thus, the purpose of this study was to examine various physical performance tests when using a mouth guard including a customized over-the-counter mouth guard. Twenty-six trained men (25 ± 4 years; 1.78 ± 0.07 m; 83.3 ± 11.4 kg) and 24 trained women (23 ± 3 years; 1.65 ± 0.08 m; 62.6 ± 7.8 kg) volunteered for the investigation. The subjects completed a familiarization period and then balanced and randomized treatment conditions that included: (a) a customized Power Balance performance mouth guard (PB MG); (b) a regular over the counter boil-and-bite mouth guard (Reg MG); and (c) a no mouth guard (No MG) treatment condition. At each visit, the subjects completed a testing protocol that was sequenced in the following order: sit-and-reach flexibility, medial-lateral balance, visual reaction time, vertical jump, 10-m sprint, bench throw, and plyo press power quotient (3PQ). Heart rate and rating of perceived exertion (RPE) were recorded around the 3PQ. Significance was set at p ≤ 0.05. Expected significant sex differences existed for all power, strength, and speed variables. Bench throw power (watts) and force (newtons) were significantly higher under PB MG than either Reg MG or No MG or in both men and women. The 3PQ power and force production were higher than that for the other 2 treatments for the PB MG for men only. There were no significant differences for treatment conditions in the heart rate or RPE after the 3PQ test. Men were better able to maintain significantly higher 3PQ power production under PB MG treatment condition compared with the other 2 treatment conditions. Rate of power development was significantly higher in men for the vertical jump when using the PB MG compared with that for other treatment conditions in men only. No differences were observed in flexibility, balance, visual reaction time, or sprint time. The PB MG performance mouth guard improves performance of upper-body loaded power exercises in both men and women and lower body power exercise in men without compromising performance on any other performance parameters.

Masticatory function and cognitive function

Recent studies have suggest that masticatory (chewing) function is useful for maintaining neurocognitive function in the elderly. For example, a reduced ability to masticate, such as that resulting from toothlessness or soft-diet feeding, causes learning and memory deficits in aged animals and pathologic changes in the hippocampus. In addition, occlusal disharmony impairs hippocampal memory processes via chronic stress, and induces similar hippocampal pathology. Chewing, however, rescues stress-induced suppression of long-term potentiation in the hippocampus and the stress-induced impairment of hippocampal-dependent learning. These findings strongly suggest a link between mastication and neurocognitive function.

A method for measuring brain partial pressure of oxygen in unanesthetized unrestrained subjects: the effect of acute and chronic hypoxia on brain tissue PO(2)

The level of tissue oxygenation provides information related to the balance between oxygen delivery, oxygen utilization, tissue reactivity and morphology during physiological conditions. Tissue partial pressure of oxygen (PtO(2)) is influenced by the use of anesthesia or restraint. These factors may impact the absolute level of PtO(2). In this study we present a novel fiber optic method to measure brain PtO(2). This method can be used in unanesthetized, unrestrained animals, provides absolute values for PO(2), has a stable calibration, does not consume oxygen and is MRI compatible. Brain PtO(2) was studied during acute hypoxia, as well as before and after 28 days of high altitude acclimatization. A sensor was chronically implanted in the frontal cortex of eight Wistar rats. It is comprised of a fiber optic probe with a tip containing material that fluoresces with an oxygen dependent lifetime. Brain PtO(2) declines by 80% and 76% pre- and post-acclimatization, respectively, when the fraction of inspired oxygen declines from 0.21 to 0.08. In addition, a linear relationship between brain PtO(2) and inspired O(2) levels was demonstrated r(2)=0.98 and r(2)=0.99 (pre- and post-acclimatization). Hypoxia acclimatization resulted in an increase in the overall brain PtO(2) by approximately 35%. This paper demonstrates the use of a novel chronically implanted fiber optic based sensor for measuring absolute PtO(2). It shows a very strong linear relationship in awake animals between inspired O(2) and tissue O(2), and shows that there is a proportional increase in PtO(2) over a range of inspired values after exposure to chronic hypoxia.

Occlusion and brain function: mastication as a prevention of cognitive dysfunction

Research in animals and humans has shown that mastication maintains cognitive function in the hippocampus, a brain area important for learning and memory. Reduced mastication, an epidemiological risk factor for the development of dementia in humans, attenuates spatial memory and causes hippocampal neurons to deteriorate morphologically and functionally, especially in aged animals. Active mastication rescues the stress-attenuated hippocampal memory process in animals and attenuates the perception of stress in humans by suppressing endocrinological and autonomic stress responses. Active mastication further improves the performance of sustained cognitive tasks by increasing the activation of the hippocampus and the prefrontal cortex, the brain regions that are essential for cognitive processing. Abnormal mastication caused by experimental occlusal disharmony in animals produces chronic stress, which in turn suppresses spatial learning ability. The negative correlation between mastication and corticosteroids has raised the hypothesis that the suppression of the hypothalamic-pituitary-adrenal (HPA) axis by masticatory stimulation contributes, in part, to preserving cognitive functions associated with mastication. In the present review, we examine research pertaining to the mastication-induced amelioration of deficits in cognitive function, its possible relationship with the HPA axis, and the neuronal mechanisms that may be involved in this process in the hippocampus.

Sleep deprivation-induced gnawing—relationship to changes in feeding behavior in rats

We have recently reported that food spillage increases during sleep deprivation in rats, which may lead to an overestimation of food intake in this condition. The objective of this study was to verify whether sleep deprivation induces an increase in gnawing behavior that could account for increased food spillage and apparent increase in food intake. We introduced wood blocks as objects for gnawing and determined the effects of their availability on food consumption and food spillage during sleep deprivation. Wood block availability reduced the amount of food removed from hoppers and decreased the amount of food spilled. However, weight loss still occurred during the sleep deprivation period, especially in the first 24 h, and it was related to a reduction in food intake. Sleep deprivation causes an increase in stereotyped gnawing behavior which largely accounts for increased food spillage observed during deprivation. Specifically, the observed increase in food removed from feeders seems to be due to an increase in gnawing and not to increased hunger. However, even when appropriately corrected for spillage, food intake decreased in the first 24 h of sleep deprivation, which accounted for most of the body weight loss seen during the 96 h of sleep deprivation.

The effect of stress on the antioxidative potential of serum: implications for Alzheimer's disease

There is growing consensus in the literature that oxidation status is increased in Alzheimer's disease (AD), and that antioxidant supplementation as prevention or treatment strategy should be investigated further. In the present study the total antioxidant status (TAS) was found to be highly significantly lower in 22 AD patients (p < 0.0001) than in 22 age- and gender matched non-demented controls. The TAS was also lower than controls in 22 patients with vascular dementia, but not significantly. The increased oxidation status in AD was verified using the benzoate hydroxylation method. The origin of the enhanced oxidation status in AD has not been elucidated. To determine whether a causal effect between stress and oxidative status of serum can be demonstrated, a rat model was used with two different kinds of stressors, swim stress (exercise) and restraint stress (non-exercise stress). Following swim stress the maximum oxidative effect was observed at one hour post stress (p < 0.001). At 24 h the oxidative status had recovered significantly to below control values. Restraint stress, however, showed progressively increased oxidation which attained significance after 24 h (p < 0.005). It is postulated that stress may contribute to the higher oxidation status in AD patients.