Nasal inhalation of l-menthol reduces respiratory discomfort associated with loaded breathing

Dyspnoea relief as an inherent benefit of high flow nasal cannula therapy: A laboratory randomized trial in healthy humans

BACKGROUND AND OBJECTIVE

Persistent dyspnoea is a public health issue for which the therapeutic arsenal is limited. This study tested high-flow nasal cannula therapy (HFNT) as a means to alleviate experimental dyspnoea.

METHODS

Thirty-two healthy subjects underwent an experimental dyspnoea induced by thoracoabdominal elastic loading. HFNT was administered with alternately FiO2 of 100% (HFNT100) or 21% (HFNT21). The sensory (S-VAS) and affective (A-VAS) components of dyspnoea, transcutaneous CO2 pressure (PtcCO2 ), pulse-oximetry oxygen saturation (SpO2 ), heart rate, respiratory rate and skin galvanometry were monitored continuously. Three experimental sessions of 8 min were conducted: the first session consisted in familiarization with the experimental dyspnoea and the next two sessions tested the effects of HFNT100 and HFNT21 alternatively in a randomized order.

RESULTS

HFNT21 and HFNT100 significantly reduced dyspnoea, respectively of ∆A-VAS = 0.80 cm [-0.02-1.5]; p = 0.007 and ∆A-VAS = 1.00 cm [0.08-1.75]; p < 0.0001; ∆S-VAS = 0.70 cm [-0.15-1.98]), p < 0.0001 and ∆S-VAS = 0.70 cm [0.08-1.95]), p = 0.0002) with no significant difference between HFNT21 and HFNT100. HFNT did not significantly alter the respiratory rate or the heart rate, reduced PtcCO2 only on room air and GSR under both experimental conditions.

CONCLUSION

HFNT was associated with a statistically significant reduction in the intensity of the sensory and affective components of dyspnoea, independent of oxygen addition. This relief of laboratory dyspnoea could result from a reduction of afferent-reafferent mismatch.

Heterogeneous deposition of regular and mentholated little cigar smoke in the lungs of Sprague-Dawley rats

BACKGROUND

Quantifying the dose and distribution of tobacco smoke in the respiratory system is critical for understanding its toxicity, addiction potential, and health impacts. Epidemiologic studies indicate that the incidence of lung tumors varies across different lung regions, suggesting there may be a heterogeneous deposition of smoke particles leading to greater health risks in specific regions. Despite this, few studies have examined the lobar spatial distribution of inhaled particles from tobacco smoke. This gap in knowledge, coupled with the growing popularity of little cigars among youth, underscores the need for additional research with little cigars.

RESULTS

In our study, we analyzed the lobar deposition in rat lungs of smoke particles from combusted regular and mentholated Swisher Sweets little cigars. Twelve-week-old male and female Sprague-Dawley rats were exposed to smoke particles at a concentration of 84 ± 5 mg/m3 for 2 h, after which individual lung lobes were examined. We utilized Inductively Coupled Plasma Mass Spectrometry to quantify lobar chromium concentrations, serving as a smoke particle tracer. Our findings demonstrated an overall higher particle deposition from regular little cigars than from the mentholated ones. Higher particle deposition fraction was observed in the left and caudal lobes than other lobes. We also observed sex-based differences in the normalized deposition fractions among lobes. Animal study results were compared with the multi-path particle dosimetry (MPPD) model predictions, which showed that the model overestimated particle deposition in certain lung regions.

CONCLUSIONS

Our findings revealed that the particle deposition varied between different little cigar products. The results demonstrated a heterogenous deposition pattern, with higher particle deposition observed in the left and caudal lobes, especially with the mentholated little cigars. Additionally, we identified disparities between our measurements and the MPPD model. This discrepancy highlights the need to enhance the accuracy of models before extrapolating animal study results to human lung deposition. Overall, our study provides valuable insights for estimating the dose of little cigars during smoking for toxicity research.

L-menthol administration facilitates breathing comfort during exhaustive endurance running and improves running capacity in well-trained runners: A randomized crossover study

ABSTRACTThis study aimed to clarify the contribution of L-menthol administration to endurande exercise capacity. Thirteen male runners (age, 35.8 ± 7.8 years; peak oxygen uptake, 62.7 ± 6.8 mL kg-1 min-1) ran on treadmills at fixed intensities of their anaerobic thresholds to exhaustion. All participants underwent three trials-water ingestion (W-IG), L-menthol mouth rinsing (M-MR), and L-menthol ingestion (M-IG)- in a random order every 5 min while running. Breathing comfort (BC) was measured immediately after fluid intake. Dyspnea threshold against external inspiratory resistance was examined before and after the running test. The running time with M-IG (1683.9 ± 520.3 s) was longer than that with W-IG (1410.2 ± 465.9 s, effect size [ES] = 0.55). BC with M-IG (2.00 ± 0.74) was higher than that with W-IG (0.42 ± 0.79) at exhaustion (ES > 2.00). The dyspnea threshold after running decreased to 19.2 ± 7.6 cm H₂O L-1 s-1 with W-IG, whereas that with M-MR (26.2 ± 6.5 cm H₂O L-1 s-1) and M-IG (29.2 ± 2.8 cm H₂O L-1 s-1) remained high (p for interaction < 0.001). M-IG facilitated BC during running, improved endurance capacity, and prevented decreases in the dyspnea threshold against external inspiratory resistance after exhaustive running.HighlightsL-menthol ingestion facilitated breathing comfort during high intensity endurance running and improved exhaustive endurance running capacity.Even after exhaustion, L-menthol solution relieved dyspnea sensitivity against external inspiratory resistance.L-menthol ingestion might help athletes improve their endurance running capacity.

Distinguishing science from pseudoscience in commercial respiratory interventions: an evidence-based guide for health and exercise professionals

Respiratory function has become a global health priority. Not only is chronic respiratory disease a leading cause of worldwide morbidity and mortality, but the COVID-19 pandemic has heightened attention on respiratory health and the means of enhancing it. Subsequently, and inevitably, the respiratory system has become a target of the multi-trillion-dollar health and wellness industry. Numerous commercial, respiratory-related interventions are now coupled to therapeutic and/or ergogenic claims that vary in their plausibility: from the reasonable to the absurd. Moreover, legitimate and illegitimate claims are often conflated in a wellness space that lacks regulation. The abundance of interventions, the range of potential therapeutic targets in the respiratory system, and the wealth of research that varies in quality, all confound the ability for health and exercise professionals to make informed risk-to-benefit assessments with their patients and clients. This review focuses on numerous commercial interventions that purport to improve respiratory health, including nasal dilators, nasal breathing, and systematized breathing interventions (such as pursed-lips breathing), respiratory muscle training, canned oxygen, nutritional supplements, and inhaled L-menthol. For each intervention we describe the premise, examine the plausibility, and systematically contrast commercial claims against the published literature. The overarching aim is to assist health and exercise professionals to distinguish science from pseudoscience and make pragmatic and safe risk-to-benefit decisions.

Impact of trigeminal and/or olfactory nerve stimulation on measures of inspiratory neural drive: Implications for breathlessness

The perception of breathlessness is mechanistically linked to the awareness of increased inspiratory neural drive (IND). Stimulation of upper airway cold receptors on the trigeminal nerve (TGN) with TGN agonists such as menthol or cool air to the face/nose has been hypothesized to reduce breathlessness by decreasing IND. The aim of this systematic scoping review was to identify and summarize the results of studies in animals and humans reporting on the impact of TGN stimulation or blockade on measures of IND. Thirty-one studies were identified, including 19 in laboratory animals and 12 in human participants. Studies in laboratory animals consistently reported that as TGN activity increased, measures of IND decreased (e.g., phrenic nerve activity). In humans, stimulation of the TGN with a stream of cool air to the face/nose decreased the sensitivity of the ventilatory chemoreflex response to hypercapnia. Otherwise, TGN stimulation with menthol or cool air to the face/note had no effect on measures of IND in humans. This review provides new insight into a potential neural mechanism of breathlessness relief with selected TGN agonists.

Impact of trigeminal nerve and/or olfactory nerve stimulation on activity of human brain regions involved in the perception of breathlessness

Breathlessness is a centrally processed symptom, as evidenced by activation of distinct brain regions such as the insular cortex and amygdala, during the anticipation and/or perception of breathlessness. Inhaled L-menthol or blowing cool air to the face/nose, both selective trigeminal nerve (TGN) stimulants, relieve breathlessness without concurrent improvements in physiological outcomes (e.g., breathing pattern), suggesting a possible but hitherto unexplored central mechanism of action. Four databases were searched to identify published reports supporting a link between TGN stimulation and activation of brain regions involved in the anticipation and/or perception of breathlessness. The collective results of the 29 studies demonstrated that TGN stimulation activated 12 brain regions widely implicated in the anticipation and/or perception of breathlessness, including the insular cortex and amygdala. Inhaled L-menthol or cool air to the face activated 75% and 33% of these 12 brain regions, respectively. Our findings support the hypothesis that TGN stimulation contributes to breathlessness relief by altering the activity of brain regions involved in its central neural processing.

Modulation of transient receptor potential (TRP) channels by plant derived substances used in over-the-counter cough and cold remedies

BACKGROUND

Upper respiratory tract infections (URTIs) impact all age groups and have a significant economic and social burden on society, worldwide. Most URTIs are mild and self-limiting, but due to the wide range of possible causative agents, including Rhinovirus (hRV), Adenovirus, Respiratory Syncytial Virus (RSV), Coronavirus and Influenza, there is no single and effective treatment. Over-the-counter (OTC) remedies, including traditional medicines and those containing plant derived substances, help to alleviate symptoms including inflammation, pain, fever and cough.

PURPOSE

This systematic review focuses on the role of the major plant derived substances in several OTC remedies used to treat cold symptoms, with a particular focus on the transient receptor potential (TRP) channels involved in pain and cough.

METHODS

Literature searches were done using Pubmed and Web of Science, with no date limitations, using the principles of the PRISMA statement. The search terms used were 'TRP channel AND plant compound', 'cough AND plant compound', 'cough AND TRP channels AND plant compound', 'cough AND P2X3 AND plant compound' and 'P2X3 AND plant compound' where plant compound represents menthol or camphor or eucalyptus or turpentine or thymol.

RESULTS

The literature reviewed showed that menthol activates TRPM8 and may inhibit respiratory reflexes reducing irritation and cough. Menthol has a bimodal action on TRPA1, but inhibition may have an analgesic effect. Eucalyptus also activates TRPM8 and inhibits TRPA1 whilst down regulating P2X3, aiding in the reduction of cough, pain and airway irritation. Camphor inhibits TRPA1 and the activation of TRPM8 may add to the effects of menthol. Activation of TRPV1 by camphor, may also have an analgesic effect.

CONCLUSIONS

The literature suggests that these plant derived substances have multifaceted actions and can interact with the TRP 'cough' receptors. The plant derived substances used in cough and cold medicines have the potential to target multiple symptoms experienced during a cold.

The Severity of Acute Kidney and Lung Injuries Induced by Cecal Ligation and Puncture Is Attenuated by Menthol: Role of Proliferating Cell Nuclear Antigen and Apoptotic Markers

Objective

Sepsis-induced acute lung injury (ALI) and acute kidney injury (AKI) are major causes of mortality. Menthol is a natural compound that has anti-inflammatory and antioxidative actions. Since exaggerated inflammatory and oxidative stress are characteristics of sepsis, the aim of this study was to evaluate the effect of menthol against sepsis-induced mortality, ALI, and AKI.

Methods

The cecal ligation and puncture (CLP) procedure was employed as a model of sepsis. Rats were grouped into sham, sham-Menthol, CLP, and CLP-Menthol (100 mg/kg, p.o).

Key Findings

A survival study showed that menthol enhanced the survival after sepsis from 0% in septic group to 30%. Septic rats developed histological evidence of ALI and AKI. Menthol markedly suppressed sepsis induced elevation of tissue TNF-a, ameliorated sepsis-induced cleavage of caspase-3 and restored the antiapoptotic marker Bcl2.

Significance

We introduced a role of the proliferating cell nuclear antigen (PCNA) in these tissues with a possible link to the damage induced by sepsis. PCNA level was markedly reduced in septic animals and menthol ameliorated this effect. Our data provide novel evidence that menthol protects against organ damage and decreases mortality in experimental sepsis.

Breathing control, brain, and bodily self-consciousness: Toward immersive digiceuticals to alleviate respiratory suffering

Breathing is peculiar among autonomic functions through several characteristics. It generates a very rich afferent traffic from an array of structures belonging to the respiratory system to various areas of the brain. It is intimately associated with bodily movements. It bears particular relationships with consciousness as its efferent motor control can be automatic or voluntary. In this review within the scope of "respiratory neurophysiology" or "respiratory neuroscience", we describe the physiological organisation of breathing control. We then review findings linking breathing and bodily self-consciousness through respiratory manipulations using virtual reality (VR). After discussing the currently admitted neurophysiological model for dyspnea, as well as a new Bayesian model applied to breathing control, we propose that visuo-respiratory paradigms -as developed in cognitive neuroscience- will foster insights into some of the basic mechanisms of the human respiratory system and will also lead to the development of immersive VR-based digital health tools (i.e. digiceuticals).

Limitations of a 6-minute-walk test to assess the efficacy of menthol for breathlessness

Walking is a vital component of physical activity in patients with chronic obstructive pulmonary disease (COPD). Exertional multidimensional breathlessness in daily life can reduce walking speed and time in patients with established COPD [1]. Improvement in breathlessness beyond a minimal clinically significant difference brought about by pulmonary rehabilitation, pharmaceutical bronchodilators and opioids has been reported [2–4]. However, despite guideline-directed disease-specific therapy, some patients with COPD experience residual breathlessness. Therefore, the application of a novel symptom-based treatment that is widely available will benefit patients with long-term breathlessness.

l-Menthol is a novel treatment option for breathlessness in patients with COPD. However, the clinical application of menthol for the treatment of exertional breathlessness in these patients warrants further research.https://bit.ly/3D6rLiJ

Dyspnea

The clinical term dyspnea (a.k.a. breathlessness or shortness of breath) encompasses at least three qualitatively distinct sensations that warn of threats to breathing: air hunger, effort to breathe, and chest tightness. Air hunger is a primal homeostatic warning signal of insufficient alveolar ventilation that can produce fear and anxiety and severely impacts the lives of patients with cardiopulmonary, neuromuscular, psychological, and end-stage disease. The sense of effort to breathe informs of increased respiratory muscle activity and warns of potential impediments to breathing. Most frequently associated with bronchoconstriction, chest tightness may warn of airway inflammation and constriction through activation of airway sensory nerves. This chapter reviews human and functional brain imaging studies with comparison to pertinent neurorespiratory studies in animals to propose the interoceptive networks underlying each sensation. The neural origins of their distinct sensory and affective dimensions are discussed, and areas for future research are proposed. Despite dyspnea's clinical prevalence and impact, management of dyspnea languishes decades behind the treatment of pain. The neurophysiological bases of current therapeutic approaches are reviewed; however, a better understanding of the neural mechanisms of dyspnea may lead to development of novel therapies and improved patient care.

l-Menthol - a new treatment for breathlessness?

PURPOSE OF REVIEW

In patients with advanced chronic obstructive pulmonary disease (COPD), it is challenging to treat breathlessness. In addition, novel palliative interventions are required for multiple perspectives of breathlessness that may still be present after disease-specific therapies. This review provides an overview of the mechanisms and effects of l-menthol on breathlessness by covering the latest relevant papers.

RECENT FINDINGS

A literature review identified one randomized controlled trial assessing the effect of l-menthol on relieving breathlessness in patients with COPD. It has been reported that the mechanism of relieving breathlessness partly involves stimulation of the trigeminal nerve by the cooling sensation of l-menthol, which gives a cognitive illusion of inspiratory flow perception. The effect of l-menthol on breathlessness caused by exertion has been reported in healthy subjects but not yet in patients with breathlessness.

SUMMARY

The effect of l-menthol on the sensory-emotional dimensions of laboratory-induced breathlessness in patients with COPD has been described in a clinical trial. Further studies are warranted to investigate its application to inspiratory muscle training and its effects in combination with exercise training.

Medical aromatherapy in geriatric syndrome

Geriatric syndromes are symptoms and signs, such as falls, incontinence, delirium, pressure ulcers, dysphagia and so on, that often threaten the independence of older adults, rather than the disease itself. Although the syndromes are very common in older people, it is difficult to treat those by modern medicine due to their complexity. To mitigate the intractable geriatric symptoms, we review the efficacy of aromatherapy, especially for dysphagia, dyspnea, cognitive dysfunction and falls in geriatric syndrome. Olfactory stimulation using a volatile black pepper oil on institutional residents improved the swallowing reflex, which is a crucial risk factor of aspiration pneumonia. Brain imaging study showed that olfactory stimulation using volatile black pepper oil activated cerebral regions of the anterior cingulate and the insular cortex, which play a role in controlling appetite and swallowing. Also, aromatherapy with volatile l-menthol decreased the sense of dyspnea and improved the efficacy of exercise therapy. The fragrance of the combination of rosemary and lemon oils in the morning, and the combination of lavender and orange oils in the night-time were reported to improve cognition and behavioural and psychological symptoms of dementia, respectively. Also, the combination of lavender and lemon balm oils was reported to be effective for irritability-related agitation in older adults. Furthermore, aromatherapy with lavender fragrance could improve both static and dynamic balance, resulting in a reduction in the number of fallers and the incidence rate in older people. Thus, aromatherapy is a promising remedy for geriatric syndrome. Geriatr Gerontol Int 2021; 21: 377-385.

Mechanisms underlying the sensation of dyspnea

Dyspnea is defined as a subjective experience of breathing discomfort that consists of qualitatively distinct sensations that vary in intensity. It is a common symptom among patients with respiratory diseases that reduces daily activities, induces deconditioning, and is self-perpetuating. Although clinical interventions are needed to reduce dyspnea, its underlying mechanism is poorly understood depending on the intertwined peripheral and central neural mechanisms as well as emotional factors. Nonetheless, experimental and clinical observations suggest that dyspnea results from dissociation or a mismatch between the intended respiratory motor output set caused by the respiratory neuronal network in the lower brainstem and the ventilatory output accomplished. The brain regions responsible for detecting the mismatch between the two are not established. The mechanism underlying the transmission of neural signals for dyspnea to higher sensory brain centers is not known. Further, information from central and peripheral chemoreceptors that control the milieu of body fluids is summated at higher brain centers, which modify dyspneic sensations. The mental status also affects the sensitivity to and the threshold of dyspnea perception. The currently used methods for relieving dyspnea are not necessarily fully effective. The search for more effective therapy requires further insights into the pathophysiology of dyspnea.

Updates in opioid and nonopioid treatment for chronic breathlessness

PURPOSE OF REVIEW

Chronic breathlessness is a troublesome symptom experienced by people with advanced malignant and nonmalignant disease. Disease-directed therapies are often insufficient in the management of chronic breathlessness. Therefore, pharmacological and nonpharmacological breathlessness-specific interventions should be considered for select patients.

RECENT FINDINGS

There is some evidence to support the use of low-dose opioids (≤30 mg morphine equivalents per day) for the relief of breathlessness in the short term. However, additional studies are needed to understand the efficacy of opioids for chronic breathlessness in the long term.Nonopioid therapies, including inspiratory muscle training, fan-to-face therapy, L-menthol and inhaled nebulized furosemide show some promise for the relief of breathlessness in advanced disease. There is insufficient evidence to support the use of anxiolytics and benzodiazepines and cannabis for chronic breathlessness.

SUMMARY

More research is needed to identify therapies for the management of chronic breathlessness.

Pharmacokinetics behaviors of l-menthol after inhalation and intravenous injection in rats and its inhibition effects on CYP450 enzymes in rat liver microsomes

1. l-Menthol, as a kind of monocyclic terpene, is widely used in inhalation formulations, food and tobacco. The purpose of this study was to investigate the pharmacokinetic behavior of l-menthol as well as its influence on the activities of cytochrome P450 enzymes. 2. The pharmacokinetic behaviors of l-menthol after inhalation (50 mg/kg) and intravenous injection (10 mg/kg) were investigated. A rat liver microsomal model was adopted to elucidate the inhibitory effect of l-menthol on CYP1A2, CYP2C11, CYP2D1/2, CYP2D4, CYP2E1 and CYP3A1 using phenacetin, tolbutamide, omeprazole, dextromethorphan, chlorzoxazone and testosterone as probe drugs, respectively. 3. The plasma concentration reached the C_max within 1.0 h (inhalation) and descended with the T_1/2 of 8.53 and 6.69 h for inhalation and i.v. administration, respectively. IC₅₀ for inhibition of l-menthol on CYP 450 enzymes were 4.35 μM for 2D4, 8.67 μM for 1A2, 13.02 μM for 3A1, 14.78 μM for 2D1/2, 234.9 μM for 2C11 and 525.4 μM for 2E1, respectively. 4. The results illustrate the pharmacokinetic process of l-menthol in rats and provide information for further rational applications. l-Menthol had moderate inhibitions on CYP2D4 and 1A2, which might affect the disposition of medicines primarily dependent on these pathways.

Menthol: A Fresh Ergogenic Aid for Athletic Performance

The application of menthol has recently been researched as a performance-enhancing aid for various aspects of athletic performance including endurance, speed, strength and joint range of motion. A range of application methods has been used including a mouth rinse, ingestion of a beverage containing menthol or external application to the skin or clothing via a gel or spray. The majority of research has focussed on the use of menthol to impart a cooling sensation on athletes performing endurance exercise in the heat. In this situation, menthol appears to have the greatest beneficial effect on performance when applied internally. In contrast, the majority of investigations into the external application of menthol demonstrated no performance benefit. While studies are limited in number, menthol has not yet proven to be beneficial for speed or strength, and only effective at increasing joint range of motion following exercise that induced delayed-onset muscle soreness. Internal application of menthol may provoke such performance-enhancing effects via mechanisms related to its thermal, ventilatory, analgesic and arousing properties. Future research should focus on well-trained subjects and investigate the addition of menthol to nutritional sports products.

Effects of "trigeminal training" on trigeminal sensitivity and self-rated nasal patency

Purpose

Patients with the feeling of a congested nose not always suffer from an anatomical obstruction but might just have a low trigeminal sensibility, which prevents them from perceiving the nasal airstream. We examined whether intermittent trigeminal stimulation increases sensitivity of the nasal trigeminal nerve and whether this effect is accompanied by subjective improvement of nasal breathing.

Method

Thirty-five patients (M_age = 58.4 years; SD = 14.8; Min_age = 21 years; Max_age = 79 years; 43% females) and 30 healthy controls (M_age = 36.7 years, SD = 14.5; Min_age = 20 years; Max_age = 73 years; 60% females) participated in a study comprised of two sessions separated by “trigeminal training”. During each session, trigeminal sensitivity towards CO₂, trigeminal lateralization abilities and ratings of nasal patency were assessed. Age and training compliance were controlled.

Results

“Trigeminal training” had a positive effect on trigeminal sensitivity in both groups, (p = .027) and this effect depended on the training compliance (p < .001). “Trigeminal training” had no effect on lateralization abilities of the subjects (p > .05). Ratings of nasal patency increased in patients (p = .03), but not in controls.

Conclusions

“Trigeminal training” consisting of intermittent presentation of diverse stimulants leads to an increase of trigeminal sensitivity, but this effect depended on the training compliance. Importantly, in patients, this training is also associated with an increase in self-rated nasal patency.

l-Menthol alleviates cigarette smoke extract induced lung injury in rats by inhibiting oxidative stress and inflammation via nuclear factor kappa B, p38 MAPK and Nrf2 signalling pathways

l-Menthol is the main ingredient of peppermint which affects various pharmacological effects such as anti-inflammation and anti-oxidative activity.

Fooling the brain to alleviate dyspnoea

Dyspnoea affects a multitude of patients with a multitude of diseases, and therefore concerns a multitude of physicians and other healthcare professionals. In view of the physical and psychological distress associated with dyspnoea, and in view of the pervasive impact of dyspnoea on the patient's psychological state and social life [1, 2], relieving dyspnoea should constitute a leading and universal clinical goal. Some have even proposed that failing to provide a patient with dyspnoea with “state of the art” management of this symptom would constitute an infringement of human rights [3, 4].

The application of a stream of air onto the face by a hand-held fan has a real place in the treatment of dyspnoea http://ow.ly/tKJk30dJ5Pv

Oral L-menthol reduces thermal sensation, increases work-rate and extends time to exhaustion, in the heat at a fixed rating of perceived exertion

PURPOSE

The study investigated the effect of a non-thermal cooling agent, L-menthol, on exercise at a fixed subjective rating of perceived exertion (RPE) in a hot environment.

METHOD

Eight male participants completed two trials at an exercise intensity between 'hard' and 'very hard', equating to 16 on the RPE scale at ~35 °C. Participants were instructed to continually adjust their power output to maintain an RPE of 16 throughout the exercise trial, stopping once power output had fallen by 30%. In a randomized crossover design, either L-menthol or placebo mouthwash was administered prior to exercise and at 10 min intervals. Power output, [Formula: see text]O₂, heart rate, core and skin temperature was monitored, alongside thermal sensation and thermal comfort. Isokinetic peak power sprints were conducted prior to and immediately after the fixed RPE trial.

RESULTS

Exercise time was greater (23:23 ± 3:36 vs. 21:44 ± 2:32 min; P = 0.049) and average power output increased (173 ± 24 vs. 167 ± 24 W; P = 0.044) in the L-menthol condition. Peak isokinetic sprint power declined from pre-post trial in the L-menthol l (9.0%; P = 0.015) but not in the placebo condition (3.4%; P = 0.275). Thermal sensation was lower in the L-menthol condition (P = 0.036), despite no changes in skin or core temperature (P > 0.05).

CONCLUSION

These results indicate that a non-thermal cooling mouth rinse lowered thermal sensation, resulting in an elevated work rate, which extended exercise time in the heat at a fixed RPE.

Identification of the cold receptor TRPM8 in the nasal mucosa

BACKGROUND

The transient receptor potential channel melastatin 8 (TRPM8) has been proposed to be a cold receptor. However, its distribution and physiologic role in the nose is not yet fully explored.

OBJECTIVE

We investigated the expression of TRPM8 in human nasal mucosa and its function when using the TRPM8 agonist.

METHODS

Immunohistochemistry was used to study TRPM8 receptors in the nasal mucosa from patients with and those without allergic rhinitis (AR). By using isometric contraction studies, we also tested the effectiveness of the TRPM8 agonist menthol on nasal mucosa. Changes in nasal mucosal contractility in response to the application of the adrenergic agent methoxamine were also measured. We explored the effect of menthol on electrical field stimulation (EFS) induced nasal mucosal contractions.

RESULTS

TRPM8 immunoreactivity was present principally in the nasal cilia, epithelium, and subepithelium around the glands. Except for nerve fibers, no obvious TRPM8-immunoreactive cells were detected in connective tissues. The immunoreactivity revealed no significant difference between patients with AR and those without AR. Adding menthol had a negligible effect on the basal tension of the nasal mucosa, but higher doses of menthol had a significant spasmolytic effect on nasal mucosa precontracted with methoxamine. Menthol inhibited the spike contraction induced by EFS, even at low doses.

CONCLUSIONS

The finding of the TRPM8 immunoreactivity underlines the important physiologic role of the nose in temperature regulation, both in patients with allergy and those without allergy. Isometric contraction studies demonstrate the role of TRPM8 in regulating nasal patency and airway resistance. The antiadrenergic effect of menthol showed an effect apparently opposite that of clinical observations, that we usually feel decongested after menthol inhalation. The underlying mechanisms deserve further investigation, and the TRPM8 antagonists deserve consideration for treatment of rhinitis in a therapeutic trial.

Psychophysical and Vasomotor Responses of the Oral Tissues: A Nicotine Dose-Response and Menthol Interaction Study

INTRODUCTION

This study implemented an intra-oral test-platform to assess the sensory, psychophysical, and vasomotor responses to nicotine and menthol, alone or in combination.

METHODS

Two double-blinded, placebo-controlled, randomized, cross-over studies, including healthy nonsmoking participants were performed. Study I: A dose-response relationship (N = 20) between 0, 2, and 4 mg nicotine gum. Study II: An interaction response (N = 22) to 30 mg menthol and 4 mg nicotine alone or in combination. Heart rate, blood pressure, tactile and thermosensory thresholds, intra-oral blood flow and temperature, pain/irritation intensities/locations, McGill Pain Questionnaire, and taste experience were assessed before, during or after the completion of a standardized chewing regime.

RESULTS

A dose-response elevation in heart rate was attenuated when nicotine was combined with menthol. Blood flow, temperature, and warm-detection thresholds, as assessed on the tongue, similarly increased for all gums. Pain intensity and taste experiences were similar between nicotine doses. Nicotine attenuated the sweet, cooling, and freshening sensation of menthol. Within the first 4 minutes, menthol reduced the intensity but not the area of nicotine-induced pain and irritation. The 4-mg nicotine dose led to a continued increase in the intensity and area of irritation in the throat post-chewing. Moreover, one-half of participants responded to menthol as an irritant, and these individuals demonstrated larger areas of nicotine-induced irritation in the throat post-chewing.

CONCLUSIONS

The intra-oral test platform provides a basis to optimize the assessment of nicotine-related taste and sensory experiences and can be used in future studies for profiling nicotine gum.

The effect of inhaled menthol on upper airway resistance in humans: a randomized controlled crossover study

BACKGROUND

Menthol (l-menthol) is a naturally-occurring cold receptor agonist commonly used to provide symptomatic relief for upper airway congestion. Menthol can also reduce the sensation of dyspnea. It is unclear whether the physiological action of menthol in dyspnea reduction is through its cold receptor agonist effect or whether associated mechanical changes occur in the upper airway.

OBJECTIVE

To determine whether menthol inhalation alters upper airway resistance in humans.

METHODS

A randomized, sham-controlled, single-blinded crossover study of inhaled menthol on upper airway resistance during semirecumbent quiet breathing in healthy subjects was conducted. Ten healthy participants (eight female) with a mean (± SD) age of 21±1.6 years completed the study.

RESULTS

Nasal resistance before testing was similar on both occasions. No differences were found in respiratory frequency (mean ± SEM) (menthol 17.0±1.1 cmH2O⁄L⁄s; sham 16.9±0.9 cmH2O⁄L⁄s), minute ventilation (menthol 7.7±0.5 cmH2O⁄L⁄s; sham 7.9±0.5 cmH2O⁄L⁄s) or total inspiratory time⁄total breath time (menthol 0.4±0.1 cmH2O⁄L⁄s; sham 0.4±0.1 cmH2O⁄L⁄s). The upper airway resistance was similar during menthol (3.47±0.32 cmH2O⁄L⁄s) and sham (3.27±0.28 cmH2O⁄L⁄s) (P=0.33) inhalation.

CONCLUSION

Inhalation of menthol does not alter upper airway resistance in awake human subjects.

A physiological perspective for utility or futility of alcohol-based hand rub gel against nausea-vomiting: is it P-6 acupoint or transnasal aroma?

Nausea-vomiting is a common and unpleasant phenomenon with numerous underlying mechanisms and pathways that are not always well elucidated. In clinical practice, refractory nausea-vomiting is encountered in several settings. Antiemetic medications may reduce these symptoms but are not always effective in all patients. In the absence of a well-defined optimal strategy for management of nausea-vomiting, the search for better approaches to treat this distressing symptom continues. One of the alternative treatment approaches is a compounded formulation called ABHR gel that is comprised of multiple antiemetic medications and has been shown to be useful for symptomatic relief in some patients with refractory nausea-vomiting. It has been suggested that alternative mechanisms should be explored to explain the perceived efficacy of ABHR gel, because transdermal absorption leading to nil-to-minimal or subtherapeutic blood concentrations of active ingredients does not explain the role of ABHR gel in the treatment of nausea-vomiting. In the current paper, we discuss possible mechanisms that may explain ABHR transdermal gel's efficacy. Compounded ABHR transdermal gel formulation's efficacy in antagonizing nausea-vomiting that has been recently questioned may be explained by alternative mechanisms mediated through the P-6 acupoint stimulation and facial-nasal, cooling-related counterstimulation.

Laryngeal and tracheal afferent nerve stimulation evokes swallowing in anaesthetized guinea pigs

  We describe swallowing reflexes evoked by laryngeal and tracheal vagal afferent nerve stimulation in anaesthetized guinea pigs. The swallowing reflexes evoked by laryngeal citric acid challenges were abolished by recurrent laryngeal nerve (RLN) transection and mimicked by electrical stimulation of the central cut ends of an RLN. By contrast, the number of swallows evoked by upper airway/pharyngeal distensions was not significantly reduced by RLN transection but they were virtually abolished by superior laryngeal nerve transection. Laryngeal citric acid-evoked swallowing was mimicked by laryngeal capsaicin challenges, implicating transient receptor potential vanilloid 1 (TRPV1)-expressing laryngeal afferent nerves arising from the jugular ganglia. The swallowing evoked by citric acid and capsaicin and evoked by electrical stimulation of either the tracheal or the laryngeal mucosa occurred at stimulation intensities that were typically subthreshold for evoking cough in these animals. Swallowing evoked by airway afferent nerve stimulation also desensitized at a much slower rate than cough. We speculate that swallowing is an essential component of airway protection from aspiration associated with laryngeal and tracheal afferent nerve activation.

The role of trigeminal nasal TRPM8-expressing afferent neurons in the antitussive effects of menthol

The cold-sensitive cation channel TRPM8 is a target for menthol, which is used routinely as a cough suppressant and as an additive to tobacco and food products. Given that cold temperatures and menthol activate neurons through gating of TRPM8, it is unclear how menthol actively suppresses cough. In this study we describe the antitussive effects of (-)-menthol in conscious and anesthetized guinea pigs. In anesthetized guinea pigs, cough evoked by citric acid applied topically to the tracheal mucosa was suppressed by menthol only when it was selectively administered as vapors to the upper airways. Menthol applied topically to the tracheal mucosa prior to and during citric acid application or administered continuously as vapors or as an aerosol to the lower airways was without effect on cough. These actions of upper airway menthol treatment were mimicked by cold air delivered to the upper airways but not by (+)-menthol, the inactive isomer of menthol, or by the TRPM8/TRPA1 agonist icilin administered directly to the trachea. Subsequent molecular analyses confirmed the expression of TRPM8 in a subset of nasal trigeminal afferent neurons that do not coincidently express TRPA1 or TRPV1. We conclude that menthol suppresses cough evoked in the lower airways primarily through a reflex initiated from the nose.

Intranasal trigeminal sensitivity: measurements before and after nasal surgery

Nasal surgeries constitute an extensive manipulation of the nasal mucosa and therefore of structures related to trigeminal and olfactory sensitivity. While olfactory changes due to nasal surgery are relatively well investigated, there are only very few studies regarding trigeminal sensitivity. Aim of the present study was to investigate sensory changes after nasal surgery with special regard to the trigeminal sensitivity. In 38 patients prior to and around 12 weeks after nasal surgery the following psychophysical measures were performed: odor identification, odor discrimination, phenyl ethyl alcohol odor threshold, sensitivity to trigeminal stimuli, trigeminal detection thresholds and trigeminal pain thresholds. These results were compared to those of a control group (43 healthy volunteers). Psychophysical olfactory and trigeminal testing showed no major changes in patients after surgery compared to the control group. Independent from the time of measurement higher trigeminal detection thresholds were found in patients compared to healthy subjects, meaning that trigeminal thresholds were already increased before surgery. The present study revealed a decreased trigeminal sensitivity in patients already before surgery. It may be hypothesized that patients also exhibit a decreased sensitivity for nasal airflow, which may also contribute to the patients' impression of impaired nasal breathing.

Inhalation of menthol reduces capsaicin cough sensitivity and influences inspiratory flows in chronic cough

INTRODUCTION

Chronic cough is a common clinical problem and there is a shortage of effective treatments for it. Within the group of transient receptor potential ion channels a receptor for the cooling substance menthol has been identified. This study aimed to assess whether pre-inhalation of dissolved, nebulised menthol could increase capsaicin cough thresholds and influence spirometric values.

METHODS

Fourteen patients with chronic cough and airway sensitivity to environmental irritants and 15 control subjects were tested on three occasions. Each one inhaled a 1 mL of nebulised menthol solution of 0.5% or 1% or placebo (saline with 0.05% menthol) at each visit in a randomized and double-blind order. They were then provoked by capsaicin inhalation.

RESULTS

Patients' cough thresholds differed significantly from the controls' on all three provocations (P < 0.0001). After inhalation of 1% menthol, the patients' cough thresholds were significantly higher (P < 0.02) compared to after placebo inhalation and to after 0.5% menthol inhalation (P < 0.05). The patients' peak inspiratory flows were significantly reduced after inhalation of the placebo (saline) (P < 0.05) but not after inhalation of 0.5% or 1% menthol. Forced inspiratory flows 50% were lowered after inhalation of placebo and of 0.5% menthol (P < 0.05) but not after 1% menthol. Among the controls, forced inspiratory flows 50% were lowered after only placebo inhalation (P < 0.05).

CONCLUSIONS

In patients with chronic cough, pre-inhalation of menthol reduces cough sensitivity to inhaled capsaicin and influences inspiratory flows. The findings may provide scientific support for the common practice of using menthol as a reliever for variant airway discomfort. The use of menthol in different cigarette brands could be questioned since it could conceal the natural irritation following smoking.

TRPM8 and dyspnea: from the frigid and fascinating past to the cool future?

The transient receptor potential melastatin 8 (TRPM8) ion channel is gated by cool and noxious cold temperatures. The activation threshold is in the range of ≈25-28°C, which aligns well with the discharge of airway afferents. TRPM8 is widely expressed across species and evolutionary changes in the TRPM8 amino acid sequence may tune the temperatures at which it is gated. The discovery of TRPM8 and its molecular/biophysical characterization provides a robust candidate for airway afferents responding to cool/cold temperatures. TRPM8 may provide a mechanistic link for the manipulation of respiratory sensations such as dyspnea or mechanisms leading to cold-induced asthma and cough.

The health effects of menthol cigarettes as compared to non-menthol cigarettes

Since the 1920s, menthol has been added to cigarettes and used as a characterizing flavor. The health effects of cigarette smoking are well documented, however the health effects of menthol cigarettes as compared to non-menthol cigarettes is less well studied. This review discusses menthol’s effects on 1) biomarkers of tobacco smoke exposure, 2) toxicity and cellular effects, 3) lung function and respiration, 4) pulmonary and/or vascular function, 5) allergic reactions and inflammation, and 6) tobacco-related diseases. It is concluded that menthol is a biologically active compound that has effects by itself and in conjunction with nicotine, however much of the data on the other areas of interest are inconclusive and firm conclusions cannot be drawn.

Sensory properties of menthol and smoking topography

Although there is a great deal known about menthol as a flavoring agent in foods and confections, less is known about the particular sensory properties of menthol cigarette smoke. Similarly, although smoking topography (the unique way an individual smokes a cigarette) has been well studied using non-menthol cigarettes, there is relatively less known about how menthol affects smoking behavior. The objective of this review is to assess the sensory properties of menthol tobacco smoke, and smoking topography associated with menthol cigarettes. The cooling, analgesic, taste, and respiratory effects of menthol are well established, and studies have indicated that menthol’s sensory attributes can have an influence on the positive, or rewarding, properties associated smoking, including ratings of satisfaction, taste, perceived smoothness, and perceived irritation. Despite these sensory properties, the data regarding menthol’s effect on smoking topography are inconsistent. Many of the topography studies have limitations due to various methodological issues.

Heterologous regulation of anion transporters by menthol in human airway epithelial cells

The present study concerns previously unreported effects of menthol, a cyclic terpene alcohol produced by the peppermint herb, on anion transporters in polarized human airway Calu-3 epithelia. Application of menthol (0.01-1mM) attenuated transepithelial anion transport, estimated as short-circuit currents (I(SC)), after stimulation by forskolin (10microM) but not before. In contrast, menthol potentiated forskolin-stimulated and -unstimulated apical Cl(-) conductance, which reflected the cystic fibrosis transmembrane conductance regulator (CFTR: the cAMP-regulated Cl(-) channel)-mediated conductance, without correlation to changes in cytosolic cAMP levels. These results indicate that menthol-induced attenuation of forskolin-induced I(SC) despite CFTR up-regulation was due to cAMP-independent inhibition of basolateral anion uptake, which is the rate-limiting step for transepithelial anion transport. Analyses of the responsible basolateral anion transporters revealed that forskolin increased both bumetanide (an inhibitor of the basolateral Na(+)-K(+)-2Cl(-) cotransporter [NKCC1])- and DNDS (an inhibitor of basolateral HCO(3)(-)-dependent anion transporters [NBC1/AE2])-sensitive I(SC) in the control whereas only the former was prevented by the application of menthol. Neither the bumetanide- nor DNDS-sensitive component was, however, reduced by menthol without forskolin. These heterologous effects of menthol were reproduced by latrunculin B, an inhibitor of actin polymerization. F-actin staining showed that menthol prevented forskolin-stimulated rearrangements of actin microfilaments without affecting the distribution of forskolin-unstimulated microfilaments. Collectively, menthol functions as an activator of CFTR and prevents activation of NKCC1 without affecting NBC1/AE although all of these transporters are commonly cAMP-dependent. The heterologous effects may be mediated by the actin cytoskeleton, which interacts with CFTR and NKCC1.

A review and assessment of menthol employed as a cigarette flavoring ingredient

Cigarette smoking is established as a substantial contributor to risks for cancer, cardiovascular and respiratory diseases. Less is known about the potential of cigarette composition to affect smoking risks. The use of cigarette flavoring ingredients such as menthol is currently of worldwide public health and regulatory interest. The unique conditions of menthol inhalation exposure that occur coincident with that of the complex cigarette smoke aerosol require specialized studies to support an assessment of its safety in cigarette flavoring applications. The present state of knowledge is sufficient to support an assessment of the safety of the use of menthol in cigarettes. Scientific, smoking behavioral and epidemiological data available through mid-2009 is critically reviewed and a broad convergence of findings supports a judgment that menthol employed as a cigarette tobacco flavoring ingredient does not meaningfully affect the inherent toxicity of cigarette smoke or the human risks that attend smoking. There remains a need for well-designed studies of the potential of menthol to affect smoking initiation, cessation and addiction in order to differentiate any independent effects of menthol in cigarettes from those imposed by socioeconomic, environmental and peer influences on these complex human behaviors.

Responses to trigeminal irritants at different locations of the human nasal mucosa

BACKGROUND

Previous work suggests differences in the distribution of human intranasal trigeminal receptors. The aim of this study was to investigate these topographic differences for different concentrations of different trigeminal irritants using an electrophysiologic measure of trigeminal activation, the negative mucosa potential (NMP).

MATERIALS AND METHODS

A total of 15 healthy volunteers participated. Presented by a computer-controlled olfactometer CO2 (30% and 40% v/v), ethyl acetate (5.5% and 9.3% v/v) and acetic acid (205 and 40% v/v) were used for stimulation. NMP was recorded at the middle septum, the middle turbinate, and the floor of the nasal cavity.

RESULTS

Maximum amplitudes of the NMP were found at the middle septum and were lowest at the nasal floor. Response amplitudes were related to stimulus concentrations. There was no significant difference between responses to the three different stimuli in relation to three recording sites.

CONCLUSIONS

In agreement with previous work, the present data suggest that there are topographic differences in the responsiveness of the mucosa to chemical irritants.

Possible effects on smokers of cigarette mentholation: a review of the evidence relating to key research questions

Menthol (2-isopropyl-5-methyl-cyclohexan-1-ol) is used in food, pharmaceutical, and tobacco products. Despite its long usage history and GRAS status, scientific literature on effects of cigarette mentholation is limited. Because African-American men have high lung cancer rates and predominantly smoke mentholated cigarettes, and because menthol's cooling effect might affect puffing and smoke inhalation, possible adverse effects of cigarette mentholation have been suggested. We review the evidence on the effects of mentholation on smokers, and we also identify areas for further study. Five large epidemiological studies provide no evidence that cigarette mentholation increases lung cancer risk. Mentholation cannot explain the higher risk for lung cancer in African-American male smokers, who also predominantly smoke mentholated cigarettes. Limited data on other cancers also suggest no risk from mentholation. The scientific literature suggests that cigarette mentholation does not increase puff number or puff volume of smoked cigarettes, and has little or no effect on heart rate, blood pressure, uptake of carbon monoxide, tar intake or retention, or blood cotinine concentration. Mentholation has little effect on other smoke constituents, and no apparent effect on nicotine absorption, airway patency and smoking initiation, dependency or cessation. Any toxicological effects of cigarette mentholation on adult smokers are probably quite limited.

A review of the bioactivity and potential health benefits of peppermint tea (Mentha piperita L.)

Peppermint (Mentha piperita L.) is one of the most widely consumed single ingredient herbal teas, or tisanes. Peppermint tea, brewed from the plant leaves, and the essential oil of peppermint are used in traditional medicines. Evidence-based research regarding the bioactivity of this herb is reviewed. The phenolic constituents of the leaves include rosmarinic acid and several flavonoids, primarily eriocitrin, luteolin and hesperidin. The main volatile components of the essential oil are menthol and menthone. In vitro, peppermint has significant antimicrobial and antiviral activities, strong antioxidant and antitumor actions, and some antiallergenic potential. Animal model studies demonstrate a relaxation effect on gastrointestinal (GI) tissue, analgesic and anesthetic effects in the central and peripheral nervous system, immunomodulating actions and chemopreventive potential. Human studies on the GI, respiratory tract and analgesic effects of peppermint oil and its constituents have been reported. Several clinical trials examining the effects of peppermint oil on irritable bowel syndrome (IBS) symptoms have been conducted. However, human studies of peppermint leaf are limited and clinical trials of peppermint tea are absent. Adverse reactions to peppermint tea have not been reported, although caution has been urged for peppermint oil therapy in patients with GI reflux, hiatal hernia or kidney stones.

Current perspectives on symptom perception in asthma: a biomedical and psychological review

Symptom perception in patients with asthma is often inadequate. Patients may fail to perceive serious airway obstruction or suffer from breathlessness without objective cause. These extremes are associated with fatal asthma and excessive use of medicines, respectively. This article covers symptom perception in a multidisciplinary perspective. A presentation of current definitions and methods for studying symptom perception in asthma is followed by a summary of theories on the origin of breathlessness. Next, biomedical and psychological factors influencing symptom perception are examined. Preliminary biomedical research emphasizes neural pathway impairment, but causal factors remain inconclusive, particularly regarding the overperception of symptoms. Psychological studies suggest that the accuracy of symptom perception is influenced by (a) competition between asthmatic and nonasthmatic sensory information, (b) negative emotions, and (c) acquired response tendencies (e.g. habituation to symptoms, repression of symptoms, selective perception, and false interpretation of symptoms). These factors may favor either blunted perception or overperception. Empirical data in support of psychological factors are still insufficient. Methodological problems and procedures to improve symptom perception are discussed.

Menthol: effects on nasal sensation of airflow and the drive to breathe

Menthol, in lozenges, nasal sprays, vapo-rubs, inhalers, and cough syrups, is widely used as a treatment for rhinitis that is associated with acute upper respiratory tract infection and allergy. Menthol as a plant extract has been used in traditional medicine in Asia for the treatment of respiratory diseases for hundreds of years, but it was only introduced to the West as a medicine at the end of the 19th century. With the recent discovery of a menthol receptor on the sensory nerves that modulate the cool sensation, menthol has graduated from the realms of herbal medicine into the field of molecular pharmacology. This review concerns the physiologic and pharmacologic mechanisms that underlie the widespread use of menthol as a treatment for the relief of nasal congestion associated with rhinitis and its effects on the drive to breathe and symptomatic relief of dyspnea.

Effect of aromatics on lung mucociliary clearance in patients with chronic airways obstruction

BACKGROUND

Complementary and alternative medicine have become an increasingly topical theme in respiratory medicine. Aromatics are a commonly used ingredient in a number of proprietary medicines. It is well established that lung mucus clearance is impaired in patients with chronic airways obstruction. This study investigated whether aromatics delivered by inunction could be objectively shown to enhance lung clearance.

METHODS

We studied 12 patients with chronic bronchitic with a mean standard error (SE) age of 67 (2) years (mean [SE] tobacco consumption history of 64 [12] pack-years). We used a randomized, single-blinded, placebo-controlled crossover trial within patient design assessing the effect of 7.5 g of aromatics inunction (compared to a "no-treatment baseline" and to a petrolatum "placebo") on lung mucus clearance measured by a standard radioaerosol technique.

RESULTS

Aromatic treatment significantly enhanced clearance at two time points 30 (p < 0.05) and 60 (p < 0.02) minutes postradioaerosol inhalation but had no demonstrable further effect over the following 5 hours despite further application of the inunction. The clearance improvement (relative to a baseline) observed during the first hour of testing was significantly correlated (p < 0.01) with the concentration level of aromatics.

CONCLUSION

Our data, thus, provide objective evidence of a positive effect of aromatics inunction on mucus clearance in chronic airways obstruction.

Ambulation-promoting effect of peppermint oil and identification of its active constituents

Various plant-derived essential oils (EOs) have traditionally been used in the treatment of mental disorders, despite a lack of scientific evidence. In a previous study, we demonstrated that certain EOs possess behavioral effects, a finding that supports our original hypotheses that EOs possess psychoactive actions. The present study was conducted in order to obtain further evidence to support our hypothesis. Peppermint oil, a type of EO, is believed to be effective for treating mental fatigue. When the oil was administered intraperitoneally to ICR mice, the ambulatory activity of mice increased dramatically. We identified alpha-pinene, beta-pinene, (R)-(+)-limonene, 1,8-cineol, isomenthone, menthone, menthol, (R)-(+)-pulegone, menthyl acetate and caryophyllene as constituent elements of peppermint oil by GC-MS analysis. We then examined the effect of each constituent element of peppermint oil on ambulatory activity in mice. Intraperitoneal administration of 1,8-cineol, menthone, isomenthone, menthol, (R)-(+)-pulegone, menthyl acetate and caryophyllene significantly increased ambulatory activity in mice, suggesting that these chemicals are the behaviorally active elements of peppermint oil. Intravenous administration of these substances to mice induced a significant increase in ambulatory activity at much lower doses. The present study provides further evidence demonstrating that EOs possess pharmacological actions on behavior. In addition, our finding revealed that the action of peppermint oil comes from its constituent elements.

Neural substrates for the perception of acutely induced dyspnea

Little is currently known about the brain regions involved in central processing of dyspnea. We performed a functional imaging study with positron emission tomography (PET) to assess brain activation associated with an important component of dyspnea, respiratory discomfort during loaded breathing. We induced respiratory discomfort in eight healthy volunteers by adding external resistive loads during inspiration and expiration. Brain activation was characterized by a significant increase in regional cerebral blood flow (rCBF) (Z score of peak activation > 3.09). As compared with the unloaded control condition, high loaded breathing was associated with neural activation in three distinct brain regions, the right anterior insula, the cerebellar vermis, and the medial pons (respective Z scores = 4.75, 4.44, 4.41). For these brain regions, we further identified a positive correlation between rCBF and the perceived intensity of respiratory discomfort (respective Z scores = 4.45, 4.75, 4.74) as well as between rCBF and the mean amplitude of mouth pressure swings (DeltaPm), the index of the main generating mechanism of the sensation (respective Z scores = 4.67, 4.36, 4.31), suggesting a common activation by these two parameters. Furthermore, we identified an area in the right posterior cingulate cortex where neural activation was specifically associated with perceived intensity of respiratory discomfort that is not related to DeltaPm (Z score = 4.25). Our results suggest that respiratory discomfort related to loaded breathing may be subserved by two distinct neural networks, the first being involved in the concomitant processing of the genesis and perception of respiratory discomfort and the second in the modulation of perceived intensity of the sensation by various factors other than its main generating mechanism, which may include emotional processing.

Role of cold receptors and menthol in thirst, the drive to breathe and arousal

Menthol is widely used in candy, chewing gum, toothpastes, cigarettes and common cold medications. Menthol has been shown to stimulate cold receptors in the mouth and nose. The present paper puts forward the hypothesis that menthol, by its effects on oral and nasal cold receptors, may influence thirst, the drive to breathe, and arousal. The satisfying effects of menthol on thirst and breathing, together with an effect on arousal, may explain the popularity of menthol and account for the very large amount of menthol-containing products that are consumed each day.