The thermoregulation system and how it works

Review of wearable technologies and machine learning methodologies for systematic detection of mild traumatic brain injuries

Mild traumatic brain injuries (mTBIs) are the most common type of brain injury. Timely diagnosis of mTBI is crucial in making 'go/no-go' decision in order to prevent repeated injury, avoid strenuous activities which may prolong recovery, and assure capabilities of high-level performance of the subject. If undiagnosed, mTBI may lead to various short- and long-term abnormalities, which include, but are not limited to impaired cognitive function, fatigue, depression, irritability, and headaches. Existing screening and diagnostic tools to detect acute andearly-stagemTBIs have insufficient sensitivity and specificity. This results in uncertainty in clinical decision-making regarding diagnosis and returning to activity or requiring further medical treatment. Therefore, it is important to identify relevant physiological biomarkers that can be integrated into a mutually complementary set and provide a combination of data modalities for improved on-site diagnostic sensitivity of mTBI. In recent years, the processing power, signal fidelity, and the number of recording channels and modalities of wearable healthcare devices have improved tremendously and generated an enormous amount of data. During the same period, there have been incredible advances in machine learning tools and data processing methodologies. These achievements are enabling clinicians and engineers to develop and implement multiparametric high-precision diagnostic tools for mTBI. In this review, we first assess clinical challenges in the diagnosis of acute mTBI, and then consider recording modalities and hardware implementation of various sensing technologies used to assess physiological biomarkers that may be related to mTBI. Finally, we discuss the state of the art in machine learning-based detection of mTBI and consider how a more diverse list of quantitative physiological biomarker features may improve current data-driven approaches in providing mTBI patients timely diagnosis and treatment.

A Conformable Two-Dimensional Resistance Temperature Detector for Measuring Average Skin Temperature

Thermoregulation research and various medical procedures are accomplished by manipulating skin temperature in a nonuniform pattern. Skin temperature monitoring is essential to assess conformance to protocol specifications and to prevent thermal injury. Existing solutions for skin temperature monitoring include single point sensors, such as thermocouples, and two-dimensional methods of sensing surface temperature, such as infrared thermography, and wearable technology. Single point sensors cannot detect the average temperature and consequently their measurements cannot be representative of average surface temperature in a nonuniform temperature field. Infrared thermography requires optical access, and existing ambulatory sensors may require complex manufacturing processes and impede the heat exchange with a source by including a structural substrate layer. Our solution is a two-dimensional resistance temperature detector (two-dimensional (2D) RTD) created by knitting copper magnet wire into custom shapes. The 2D RTDs were calibrated, compared to one-dimensional sensors and wearable sensors, and analyzed for hysteresis, repeatability, and surface area conformation. Resistance and temperature were correlated with an R² of 0.99. The 2D RTD proved to be a superior device for measuring average skin temperature over a defined area exposed to a nonuniform temperature boundary in the absence of optical access such as when a full body thermal control garment is worn.

Naturally occurring hypothermia promotes survival in severe anaphylaxis

Although hypothermia has received substantial attention as an indicator of severity in anaphylaxis, it has been neglected from the perspective of whether it could act as a disease-modifying factor in this condition. Here, the impact of naturally occurring (spontaneous) hypothermia on anaphylaxis was evaluated in a murine model of ovalbumin (OVA)-induced allergy. Nonextreme changes in the ambient temperature (T_a) were used to modulate the magnitude of spontaneous hypothermia. At a T_a of 24°C, challenge with OVA intraperitoneally or intravenously resulted in a rapid, transient fall in body core temperature, which reached its nadir 4-6°C below baseline in 30 min. This hypothermic response was largely attenuated when the mice were kept at a T_a of 34°C. The T_a-dependent attenuation of hypothermia resulted in a survival rate of only 30%, as opposed to survival of 100% in the condition that favored the development of hypothermia. The protective effect of hypothermia did not involve changes in the rate of mast cell degranulation, as assessed by the concentration of mast cell protease-1 in bodily fluids. On the other hand, hypothermia improved oxygenation of the brain and kidneys, as indicated by higher NAD⁺/NADH ratios. Therefore, it is plausible to propose that naturally occurring hypothermia makes organs more resistant to the anaphylactic insult.

High Temperature Drives Topoisomerase Mediated Chromosomal Break Repair Pathway Choice

Simple Summary

Targeting topoisomerases has been widely used as anticancer therapeutics. Exposure to high temperature (hyperthermia) protects cells from the cytotoxic effect of topoisomerase-targeting therapeutics, yet the mechanism remains unknown. Here, we report that hyperthermia inhibits the nucleolytic processing of topoisomerase-induced DNA damage and drives repair to a more faithful pathway mediated by TDP1 and TDP2. We further show that hyperthermia suppresses topoisomerase-induced chromosomal translocation and hallmarks of inflammation, which has broad implications in cancer development and therapy.

Abstract

Cancer-causing mutations often arise from inappropriate DNA repair, yet acute exposure to DNA damage is widely used to treat cancer. The challenge remains in how to specifically induce excessive DNA damage in cancer cells while minimizing the undesirable effects of genomic instability in noncancerous cells. One approach is the acute exposure to hyperthermia, which suppresses DNA repair and synergizes with radiotherapy and chemotherapy. An exception, however, is the protective effect of hyperthermia on topoisomerase targeting therapeutics. The molecular explanation for this conundrum remains unclear. Here, we show that hyperthermia suppresses the level of topoisomerase mediated single- and double-strand breaks induced by exposure to topoisomerase poisons. We further uncover that, hyperthermia suppresses hallmarks of genomic instability induced by topoisomerase targeting therapeutics by inhibiting nuclease activities, thereby channeling repair to error-free pathways driven by tyrosyl-DNA phosphodiesterases. These findings provide an explanation for the protective effect of hyperthermia from topoisomerase-induced DNA damage and may help to explain the inverse relationship between cancer incidence and temperature. They also pave the way for the use of controlled heat as a therapeutic adjunct to topoisomerase targeting therapeutics.

Intramuscular Temperature Changes in the Quadriceps Femoris Muscle After Post-Exercise Cold-Water Immersion (10°C for 10 min): A Systematic Review With Meta-Analysis

Post-exercise cold-water immersion (CWI) is a widely accepted recovery strategy for maintaining physical performance output. However, existing review articles about the effects of CWI commonly pool data from very heterogenous study designs and thus, do rarely differentiate between different muscles, different CWI-protocols (duration, temperature, etc.), different forms of activating the muscles before CWI, and different thickness of the subcutaneous adipose tissue. This systematic review therefore aimed to investigate the effects of one particular post-exercise CWI protocol (10°C for 10 min) on intramuscular temperature changes in the quadriceps femoris muscle while accounting for skinfold thickness. An electronic search was conducted on PubMed, LIVIVO, Cochrane Library, and PEDro databases. Pooled data on intramuscular temperature changes were plotted with respect to intramuscular depth to visualize the influence of skinfold thickness. Spearman's rho (r_s) was used to assess a possible linear association between skinfold thickness and intramuscular temperature changes. A meta-analysis was performed to investigate the effect of CWI on pre-post intramuscular temperature for each measurement depth. A total of six articles met the inclusion criteria. Maximum intramuscular temperature reduction was 6.40°C with skinfold thickness of 6.50 mm at a depth of 1 cm, 4.50°C with skinfold thickness of 11.00 mm at a depth of 2 cm, and only 1.61°C with skinfold thickness of 10.79 mm at a depth of 3 cm. However, no significant correlations between skinfold thickness and intramuscular temperature reductions were observed at a depth of 1 cm (r _s = 0.0), at 2 cm (r _s = -0.8) and at 3 cm (r _s = -0.5; all p > 0.05). The CWI protocol resulted in significant temperature reductions in the muscle tissue layers at 1 cm (d = -1.92 [95% CI: -3.01 to -0.83] and 2 cm (d = -1.63 [95% CI: -2.20 to -1.06]) but not at 3 cm (p < 0.05). Skinfold thickness and thus, subcutaneous adipose tissue, seems to influence temperature reductions in the muscle tissue only to a small degree. These findings might be useful for practitioners as they demonstrate different intramuscular temperature reductions after a specific post-exercise CWI protocol (10°C for 10 min) in the quadriceps femoris muscle.

Non-contact infrared assessment of human body temperature: The journal Temperature toolbox

The assessment of human internal/core temperature (T core) is relevant in many scientific disciplines, but also for public health authorities when attempting to identify individuals with fever. Direct assessment of T core is often invasive, impractical on a large scale, and typically requires close contact between the observer and the target subject. Non-contact infrared thermometry (NCIT) represents a practical solution in which T core can potentially be assessed from a safe distance and in mass screening scenarios, by measuring skin temperature at specific anatomical locations. However, the COVID-19 pandemic has clearly demonstrated that these devices are not being used correctly, despite expert guided specifications available in International Standard Organization (ISO) documents. In this review, we provide an overview of the most pertinent factors that should be considered by users of NCIT. This includes the most pertinent methodological and physiological factors, as well as an overview on the ability of NCIT to track human T core. For practical use, we provide a checklist based on relevant ISO standards which are simple to follow and should be consulted prior to using NCIT for assessment of human T core. Our intention is for users of NCIT to adopt this checklist, which may improve the performance of NCIT for its ability to track T core.

Physical exercise-induced thermoregulatory responses in trained rats: Effects of manipulating the duration and intensity of aerobic training sessions

This study investigated the effects of increasing the intensity and/or duration of aerobic training sessions on thermoregulatory responses in rats subjected to exercises in temperate and warm environments. Thirty-two adult male Wistar rats were divided into four groups: a control (CON) group and three groups that were subjected to an 8-week aerobic training, during which the physical overload was achieved by predominantly increasing the exercise intensity (INT), duration (DUR) or by increasing both in an alternate manner (ID). During the last week of training, the rats received an abdominal sensor implant to measure their core body temperature (TCORE) by telemetry. After the training protocol, the 32 rats were subjected to incremental speed-exercises in temperate (23 °C) and warm (32 °C) environments. The rats had their TCORE recorded while running on a treadmill, and the ratio between the increase in TCORE and distance traveled was calculated to estimate thermoregulatory efficiency. All training protocols increased the rats' thermoregulatory efficiency during the incremental-speed exercise at 23 °C; i.e., trained rats attained faster running speeds but unchanged TCORE at fatigue compared to CON rats. However, none of the load components of training sessions - intensity or duration - was more effective than the other in improving this efficiency. At 32 °C, the aerobic training protocols did not influence the exercise-induced thermoregulatory responses. Our data indicate that different progressions in aerobic training performed at temperate conditions improved thermoregulatory efficiency during incremental exercise in the same environment; this training-induced adaptation was not clearly observed when running in warmer conditions.

Adrenergic Tone as an Intermediary in the Temperament Syndrome Associated With Flight Speed in Beef Cattle

The temperament of farm animals can influence their resilience to everyday variations within the managed production environment and has been under strong direct and indirect selection during the course of domestication. A prominent objective measure used for assessing temperament in beef cattle is the behavioral flight response to release from confinement in a crush or chute. This behavioral measure, termed flight speed (also known as escape velocity) is associated with physiological processes including body temperature, feeding behavior, growth rate, carcass composition, immune function, and health outcomes. This review examines the functional links between this suite of traits and adrenergic activity of the sympathetic nervous system and the adrenomedullary hormonal system. It is suggested that flight speed is the behavioral aspect of an underlying “flightiness” temperament syndrome, and that elevated adrenergic tone in animals with a high level of flightiness (i.e., flighty animals) tunes physiological activities toward a sustained “fight or flight” defense profile that reduces productivity and the capacity to flourish within the production environment. Nonetheless, despite a common influence of adrenergic tone on this suite of traits, variation in each trait is also influenced by other regulatory pathways and by the capacity of tissues to respond to a range of modulators in addition to adrenergic stimuli. It is suggested that tuning by adrenergic tone is an example of homeorhetic regulation that can help account for the persistent expression of behavioral and somatic traits associated with the flight speed temperament syndrome across the life of the animal. At a population level, temperament may modulate ecological fit within and across generations in the face of environmental variability and change. Associations of flight speed with the psychological affective state of the animal, and implications for welfare are also considered. The review will help advance understanding of the developmental biology and physiological regulation of temperament syndromes.

Noncontact Body Temperature Measurement: Uncertainty Evaluation and Screening Decision Rule to Prevent the Spread of COVID-19

The need to measure body temperature contactless and quickly during the COVID-19 pandemic emergency has led to the widespread use of infrared thermometers, thermal imaging cameras and thermal scanners as an alternative to the traditional contact clinical thermometers. However, limits and issues of noncontact temperature measurement devices are not well known and technical–scientific literature itself sometimes provides conflicting reference values on the body and skin temperature of healthy subjects. To limit the risk of contagion, national authorities have set the obligation to measure body temperature of workers at the entrance to the workplace. In this paper, the authors analyze noncontact body temperature measurement issues from both clinical and metrological points of view with the aim to (i) improve body temperature measurements accuracy; (ii) estimate the uncertainty of body temperature measurement on the field; (iii) propose a screening decision rule for the prevention of the spread of COVID-19. The approach adopted in this paper takes into account both the traditional instrumental uncertainty sources and clinical–medical ones related to the subjectivity of the measurand. A proper screening protocol for body temperature measurement considering the role of uncertainty is essential to correctly choose the threshold temperature value and measurement method to access critical places during COVID-19 pandemic emergency.

Environmental neurology in the tropics

We address the impact of the tropical environment on the human nervous system using the multifaceted approach characteristic of environmental neurology. First, environmental factors are examined according to their nature (physical, chemical and biological) and in relation to human activity and behavior. Some factors are specific to the tropics (climate and infections), while others are non-specific (chemicals, human communities and their way of life). Second, we examine the major role of human adaptation to the success of Homo sapiens, with emphasis on the linkage between thermoregulation and sleep-wake regulation. Third, we examine the performance of environmental neurology as a clinical discipline in tropical climates, with focus on the diagnostic and therapeutic challenges posed by human African trypanosomiasis. Finally, the prevention, early detection and monitoring of environmental neurological diseases is examined, as well as links with political and economic factors. In conclusion, practitioners of environmental neurology seek a global, multidisciplinary and holistic approach to understanding, preventing and treating neurological disorders within their purview. Environmental neurology integrates an expanded One Health concept by linking health and wellness to the interaction of plants, animals, humans and the ecosystem. Recent epidemics and the current COVID-19 pandemic exemplify the need for worldwide action to protect human health and biodiversity.

Thermoregulatory reflex control of cutaneous vasodilation in healthy aging

Reflex cutaneous vasodilation during heating is attenuated in healthy human aging secondary to blunted increases in efferent skin sympathetic nervous system activity (SSNA) and reductions in end-organ sensitivity. Whether age-related alterations in the mean body temperature ( T - _b) threshold for increasing SSNA and/or the sensitivity of responses are evident with aging have not been examined. We tested the hypotheses that the T_b threshold for SSNA and cutaneous vascular conductance (CVC) would be increased, but the sensitivity would be reduced, with aging. Reflex vasodilation was induced in 13 young (23 ± 3 y) and 13 older (67 ± 7 y) adults using a water-perfused suit to systematically increase mean skin and esophageal temperatures. SSNA (peroneal microneurography) and red cell flux (laser Doppler flowmetry) in the innervated dermatome were continuously measured. SSNA was normalized to baseline; CVC was normalized as a percentage of maximal CVC. Baseline T - _b was lower in older adults (36.0 ± 0.4°C vs 36.4 ± 0.3°C; p = 0.005). During passive heating, the ∆ T - _b thresholds for increasing SSNA and CVC were greater (1.3 ± 0.4°C vs 0.9 ± 0.3°C; p = 0.007 and 1.3 ± 0.4°C vs 0.8 ± 0.3°C; p = 0.002, respectively) in older adults. The slope of the relation between both SSNA (0.31 ± 0.23 vs 0.13 ± 0.10 V⋅s⋅°C ^-1; p = 0.01) and CVC (87.5 ± 50.1 vs 32.4 ± 18.1%max⋅°C^-1; p = 0.002) vs T - _b was lower in older adults. The relative T - _b threshold for activation of SSNA and the initiation of reflex cutaneous vasodilation is higher in older adults, and once activated, the sensitivity of both responses is diminished, supporting the concept that the efferent component of the thermoregulatory reflex arc is impaired in healthy aging. Abbreviations: CI: confidence interval; CVC: cutaneous vascular conductance; SSNA: skin sympathetic nervous system activity; T - _b: mean body temperature; T_es: esophageal temperature; T - _sk: mean skin temperature.

Inhibition of type 4 cAMP-phosphodiesterases (PDE4s) in mice induces hypothermia via effects on behavioral and central autonomous thermoregulation

Inhibitors of Type 4 cAMP-phosphodiesterases (PDE4s) exert a number of promising therapeutic benefits, including potent anti-inflammatory, memory- and cognition-enhancing, metabolic, and antineoplastic effects. We report here that treatment with a number of distinct PDE4 inhibitors, including Rolipram, Piclamilast, Roflumilast and RS25344, but not treatment with the PDE3-selective inhibitor Cilostamide, induces a rapid (10-30 min), substantial (-5 °C) and long-lasting (up to 5 h) decrease in core body temperature of C57BL/6 mice; thus, identifying a critical role of PDE4 also in the regulation of body temperature. As little as 0.04 mg/kg of the archetypal PDE4 inhibitor Rolipram induces hypothermia. As similar or higher doses of Rolipram were used in a majority of published animal studies, most of the reported findings are likely paralleled by, or potentially impacted by hypothermia induced by these drugs. We further show that PDE4 inhibition affects central body temperature regulation and acts by lowering the cold-defense balance point of behavioral (including posture and locomotion) and autonomous (including cutaneous tail vasodilation) cold-defense mechanisms. In line with the idea of an effect on central body temperature regulation, hypothermia is induced by moderate doses of various brain-penetrant PDE4 inhibitors, but not by similar doses of YM976, a PDE4 inhibitor that does not efficiently cross the blood-brain barrier. Finally, to begin delineating the mechanism of drug-induced hypothermia, we show that blockade of D2/3-type dopaminergic, but not β-adrenergic, H1-histaminergic or opiate receptors, can alleviate PDE4 inhibitor-induced hypothermia. We thus propose that increased D2/3-type dopaminergic signaling, triggered by PDE4 inhibitor-induced and cAMP-mediated dopamine release in the thermoregulatory centers of the hypothalamus, is a significant contributor to PDE4 inhibitor-induced hypothermia.

Thermal Sensation in Older People with and without Dementia Living in Residential Care: New Assessment Approaches to Thermal Comfort Using Infrared Thermography

The temperature of the indoor environment is important for health and wellbeing, especially at the extremes of age. The study aim was to understand the relationship between self-reported thermal sensation and extremity skin temperature in care home residents with and without dementia. The Abbreviated Mental Test (AMT) was used to discriminate residents to two categories, those with, and those without, dementia. After residents settled and further explanation of the study given (approximately 15 min), measurements included: tympanic membrane temperature, thermal sensation rating and infrared thermal mapping of non-dominant hand and forearm. Sixty-nine afebrile adults (60-101 years of age) were studied in groups of two to five, in mean ambient temperatures of 21.4-26.6 °C (median 23.6 °C). Significant differences were observed between groups; thermal sensation rating (p = 0.02), tympanic temperature (p = 0.01), fingertip skin temperature (p = 0.01) and temperature gradients; fingertip-wrist p = 0.001 and fingertip-distal forearm, p = 0.001. Residents with dementia were in significantly lower air temperatures (p = 0.001). Although equal numbers of residents per group rated the environment as 'neutral' (comfortable), resident ratings for 'cool/cold' were more frequent amongst those with dementia compared with no dementia. In parallel, extremity (hand) thermograms revealed visual temperature demarcation, variously across fingertip, wrist, and forearm commensurate with peripheral vasoconstriction. Infrared thermography provided a quantitative and qualitative method to measure and observe hand skin temperature across multiple regions of interest alongside thermal sensation self-report. As an imaging modality, infrared thermography has potential as an additional assessment technology with clinical utility to identify vulnerable residents who may be unable to communicate verbally, or reliably, their satisfaction with indoor environmental conditions.

Individual Responses to Heat Stress: Implications for Hyperthermia and Physical Work Capacity

Background

Extreme heat events are increasing in frequency, severity, and duration. It is well known that heat stress can have a negative impact on occupational health and productivity, particularly during physical work. However, there are no up-to-date reviews on how vulnerability to heat changes as a function of individual characteristics in relation to the risk of hyperthermia and work capacity loss. The objective of this narrative review is to examine the role of individual characteristics on the human heat stress response, specifically in relation to hyperthermia risk and productivity loss in hot workplaces. Finally, we aim to generate practical guidance for industrial hygienists considering our findings. Factors included in the analysis were body mass, body surface area to mass ratio, body fat, aerobic fitness and training, heat adaptation, aging, sex, and chronic health conditions.

Findings

We found the relevance of any factor to be dynamic, based on the work-type (fixed pace or relative to fitness level), work intensity (low, moderate, or heavy work), climate type (humidity, clothing vapor resistance), and variable of interest (risk of hyperthermia or likelihood of productivity loss). Heat adaptation, high aerobic fitness, and having a large body mass are the most protective factors during heat exposure. Primary detrimental factors include low fitness, low body mass, and lack of heat adaptation. Aging beyond 50 years, being female, and diabetes are less impactful negative factors, since their independent effect is quite small in well matched participants. Skin surface area to mass ratio, body composition, hypertension, and cardiovascular disease are not strong independent predictors of the heat stress response.

Conclusion

Understanding how individual factors impact responses to heat stress is necessary for the prediction of heat wave impacts on occupational health and work capacity. The recommendations provided in this report could be utilized to help curtail hyperthermia risk and productivity losses induced by heat.

Menthol can be safely applied to improve thermal perception during physical exercise: a meta-analysis of randomized controlled trials

Menthol is often used as a cold-mimicking substance to allegedly enhance performance during physical activity, however menthol-induced activation of cold-defence responses during exercise can intensify heat accumulation in the body. This meta-analysis aimed at studying the effects of menthol on thermal perception and thermophysiological homeostasis during exercise. PubMed, EMBASE, Cochrane Library, and Google Scholar databases were searched until May 2020. Menthol caused cooler thermal sensation by weighted mean difference (WMD) of - 1.65 (95% CI, - 2.96 to - 0.33) and tended to improve thermal comfort (WMD = 1.42; 95% CI, - 0.13 to 2.96) during physical exercise. However, there was no meaningful difference in sweat production (WMD = - 24.10 ml; 95% CI, - 139.59 to 91.39 ml), deep body temperature (WMD = 0.02 °C; 95% CI, - 0.11 to 0.15 °C), and heart rate (WMD = 2.67 bpm; 95% CI - 0.74 to 6.09 bpm) between the treatment groups. Menthol improved the performance time in certain subgroups, which are discussed. Our findings suggest that different factors, viz., external application, warmer environment, and higher body mass index can improve menthol's effects on endurance performance, however menthol does not compromise warmth-defence responses during exercise, thus it can be safely applied by athletes from the thermoregulation point of view.

The contribution of the mouse tail to thermoregulation is modest

Understanding mouse thermal physiology informs the usefulness of mice as models of human disease. It is widely assumed that the mouse tail contributes greatly to heat loss (as it does in rat), but this has not been quantitated. We studied C57BL/6J mice after tail amputation. Tailless mice housed at 22°C did not differ from littermate controls in body weight, lean or fat content, or energy expenditure. With acute changes in ambient temperature from 19 to 39°C, tailless and control mice demonstrated similar body temperatures (Tb), metabolic rates, and heat conductances and no difference in thermoneutral point. Treatment with prazosin, an α1-adrenergic antagonist and vasodilator, increased tail temperature in control mice by up to 4.8 ± 0.8°C. Comparing prazosin treatment in tailless and control mice suggested that the tail's contribution to total heat loss was a nonsignificant 3.4%. Major heat stress produced by treatment at 30°C with CL316243, a β3-adrenergic agonist, increased metabolic rate and Tb and, at a matched increase in metabolic rate, the tailless mice showed a 0.72 ± 0.14°C greater Tb increase and 7.6% lower whole body heat conductance. Thus, the mouse tail is a useful biomarker of vasodilation and thermoregulation, but in our experiments contributes only 5-8% of whole body heat dissipation, less than the 17% reported for rat. Heat dissipation through the tail is important under extreme scenarios such as pharmacological activation of brown adipose tissue; however, non-tail contributions to heat loss may have been underestimated in the mouse.

Mouse Thermoregulation: Introducing the Concept of the Thermoneutral Point

Human and mouse thermal physiology differ due to dissimilar body sizes. Unexpectedly, in mice we found no ambient temperature zone where both metabolic rate and body temperature were constant. Body temperature began increasing once cold-induced thermogenesis was no longer required. This result reproduced in male, female, C57BL/6J, 129, chow-fed, diet-induced obese, and ob/ob mice as well as Trpv1-/-;Trpm8-/-;Trpa1-/- mice lacking thermal sensory channels. During the resting-light phase, the energy expenditure minimum spanned ∼4°C of ambient temperature, whereas in the active-dark phase it approximated a point. We propose the concept of a thermoneutral point (TNP), a discrete ambient temperature below which energy expenditure increases and above which body temperature increases. Humans do not have a TNP. As studied, the mouse TNP is ∼29°C in light phase and ∼33°C in dark phase. These observations inform how thermoneutrality is defined and how mice are used to model human energy physiology and drug development.

An experimental study on effects of radiofrequency electromagnetic fields on sleep in healthy elderly males and females: Gender matters!

BACKGROUND

Results from human experimental studies investigating possible effects of radiofrequency electromagnetic fields (RF-EMF) on sleep are heterogeneous. So far, there is no study on possible sex-differences in RF-EMF effects.

OBJECTIVES

The present study aimed at analyzing differences in RF-EMF effects on the macrostructure of sleep between healthy elderly males and females.

METHODS

With a double-blind, randomized, sham-controlled cross-over design effects of two RF-EMF exposures (GSM900 and TETRA) on sleep were investigated in samples of 30 elderly healthy male and 30 healthy elderly female volunteers. Participants underwent each of the three exposure conditions on three occassions following an individually randomized order resulting in a total of nine study nights per participant. Exposure was delivered for 30 min prior to sleep and for the whole night (7.5 h) by a head worn antenna specifically designed for the projects. The peak spatial absorption rate averaged over time in head tissues (psSAR10g) was 6 W/kg for TETRA and 2 W/kg for GSM900. Thirty variables characterising the macrostructure of sleep and arousals as well as four subjective sleep variables were considered for statistical analyses.

RESULTS

Multivariate analyses revealed that exposure to GSM900 and/or TETRA resulted in a significant reduction in arousals, a shorter latency to sleep stage N3, and a shorter self-reported time awake after sleep in both males and females. Exposure effects depending on sex (significant interactions) were observed. Latency to sleep stage R was shorter in females and tended to be longer in males under both exposures. Latency to stage N3 was shorter in females under TETRA exposure and almost not affected in males. The time awake within the sleep period under TETRA exposure was shorter in females and only slightly longer in males. Under GSM exposure, the self-rated total sleep time tended to be longer in females and to be shorter in males. Finally, the number of awakenings was lower only in females and tended to be higher in males under GSM exposure.

DISCUSSION

With regard to RF-EMF effects on human sleep it seems that gender matters since GSM900 and TETRA led to significantly more exposure effects in females. Regardless of gender, none of the observed changes is indicative of a sleep disturbing effect of RF-EMF exposure. Observed effects might be mediated by skin related thermoregulatory mechanisms.

Temperature regulation in women: Effects of the menstrual cycle

Core body temperature changes across the ovulatory menstrual cycle, such that it is 0.3°C to 0.7°C higher in the post-ovulatory luteal phase when progesterone is high compared with the pre-ovulatory follicular phase. This temperature difference, which is most evident during sleep or immediately upon waking before any activity, is used by women as a retrospective indicator of an ovulatory cycle. Here, we review both historical and current literature aimed at characterizing changes in core body temperature across the menstrual cycle, considering the assessment of the circadian rhythm of core body temperature and thermoregulatory responses to challenges, including heat and cold exposure, exercise, and fever. We discuss potential mechanisms for the thermogenic effect of progesterone and the temperature-lowering effect of estrogen, and discuss effects on body temperature of exogenous formulations of these hormones as contained in oral contraceptives. We review new wearable temperature sensors aimed at tracking daily temperature changes of women across multiple menstrual cycles and highlight the need for future research on the validity and reliability of these devices. Despite the change in core body temperature across the menstrual cycle being so well identified, there remain gaps in our current understanding, particularly about the underlying mechanisms and microcircuitry involved in the temperature changes.

Neural correlates of non-specific skin conductance responses during resting state fMRI

Skin conductance responses (SCRs) reliably occur in the absence of external stimulation. However, the neural correlates of these non-specific SCRs have been less explored than brain activity associated with stimulus-elicited SCRs. This study modeled spontaneous skin conductance responses observed during an unstructured resting state fMRI scan in 58 adolescents. A Finite Impulse Response (FIR) fMRI model was used to detect any type of hemodynamic response shape time-locked to non-specific SCRs; the shape of these responses was then carefully characterized. The strongest evidence for signal change was found in several sub-regions of sensorimotor cortex. There also was evidence for engagement of discrete areas within the lateral surfaces of the parietal lobe, cingulate cortex, fronto-insular operculum, and both visual and auditory primary processing areas. The hemodynamic profile measured by FIR modeling clearly resembled an event-related response. However, it was a complex response, best explained by two quickly successive, but opposing neuronal impulses across all brain regions - a brief positive response that begins several seconds prior to the SCR with a much longer negative neuronal impulse beginning shortly after the SCR onset. Post hoc exploratory analyses linked these two hemodynamic response phases to different emotion-related individual differences. In conclusion, this study shows the neural correlates of non-specific SCRs are a widespread, cortical network of brain regions engaged in a complex, seemingly biphasic fashion. This bimodal response profile should be considered in replication studies that attempt to directly link brain activity to possible homeostatic mechanisms or seek evidence for alternative mechanisms.

No thermoregulatory or ergogenic effect of dietary nitrate among physically inactive males, exercising above gas exchange threshold in hot and dry conditions

The aim of this study was to determine the effect of five days dietary nitrate (NO₃^-) consumption on exercise tolerance and thermoregulation during cycling in hot, dry conditions. In a double-blind, randomised crossover design, 11 healthy males participated in an exercise tolerance test (T_lim) in the heat (35°C, 28% relative humidity), cycling above the thermoneutral gas exchange threshold, after five days of dietary supplementation, with either NO₃^-rich beetroot juice (BR; ∼ 9.2 mmol NO₃^-) or placebo (PLA). Changes in plasma [NO₃^-] and nitrite [NO₂^-], core and mean skin temperatures, mean local and whole-body sweat rates, heart rate, perceptual ratings and pulmonary gas exchange were measured during exercise, alongside calorimetric estimations of thermal balance. Mean arterial pressures (MAP) were recorded pre-T_lim. There were no differences in T_lim between conditions (BR = 22.8 ± 8.1 min; Placebo = 20.7 ± 7.9 min) (P = 0.184), despite increases in plasma [NO₃^-] and [NO₂^-] (P < 0.001) and a 3.8% reduction in resting MAP (P = 0.004) in the BR condition. There were no other differences in thermoregulatory, cardio-metabolic, perceptual or calorimetric responses to the T_lim between conditions (P > 0.05). Dietary NO₃^- supplementation had no effect on exercise tolerance or thermoregulation in hot, dry conditions, despite reductions in resting MAP and increases in plasma [NO₃^-] and [NO₂^-]. Healthy, yet physically inactive individuals with no known impairments in vasodilatory and sudomotor function do not appear to require BR for ergogenic or thermolytic effects during exercise in the heat.

Hyperthermia induced by transient receptor potential vanilloid-1 (TRPV1) antagonists in human clinical trials: Insights from mathematical modeling and meta-analysis

Antagonists of the transient receptor potential vanilloid-1 (TRPV1) channel alter body temperature (T_b) in laboratory animals and humans: most cause hyperthermia; some produce hypothermia; and yet others have no effect. TRPV1 can be activated by capsaicin (CAP), protons (low pH), and heat. First-generation (polymodal) TRPV1 antagonists potently block all three TRPV1 activation modes. Second-generation (mode-selective) TRPV1 antagonists potently block channel activation by CAP, but exert different effects (e.g., potentiation, no effect, or low-potency inhibition) in the proton mode, heat mode, or both. Based on our earlier studies in rats, only one mode of TRPV1 activation - by protons - is involved in thermoregulatory responses to TRPV1 antagonists. In rats, compounds that potently block, potentiate, or have no effect on proton activation cause hyperthermia, hypothermia, or no effect on T_b, respectively. A T_b response occurs when a TRPV1 antagonist blocks (in case of hyperthermia) or potentiates (hypothermia) the tonic TRPV1 activation by protons somewhere in the trunk, perhaps in muscles, and - via the acido-antithermogenic and acido-antivasoconstrictor reflexes - modulates thermogenesis and skin vasoconstriction. In this work, we used a mathematical model to analyze T_b data from human clinical trials of TRPV1 antagonists. The analysis suggests that, in humans, the hyperthermic effect depends on the antagonist's potency to block TRPV1 activation not only by protons, but also by heat, while the CAP activation mode is uninvolved. Whereas in rats TRPV1 drives thermoeffectors by mediating pH signals from the trunk, but not T_b signals, our analysis suggests that TRPV1 mediates both pH and thermal signals driving thermoregulation in humans. Hence, in humans (but not in rats), TRPV1 is likely to serve as a thermosensor of the thermoregulation system. We also conducted a meta-analysis of T_b data from human trials and found that polymodal TRPV1 antagonists (ABT-102, AZD1386, and V116517) increase T_b, whereas the mode-selective blocker NEO6860 does not. Several strategies of harnessing the thermoregulatory effects of TRPV1 antagonists in humans are discussed.

Brain temperature and its role in physiology and pathophysiology: Lessons from 20 years of thermorecording

It is well known that temperature affects the dynamics of all physicochemical processes governing neural activity. It is also known that the brain has high levels of metabolic activity, and all energy used for brain metabolism is finally transformed into heat. However, the issue of brain temperature as a factor reflecting neural activity and affecting various neural functions remains in the shadow and is usually ignored by most physiologists and neuroscientists. Data presented in this review demonstrate that brain temperature is not stable, showing relatively large fluctuations (2-4°C) within the normal physiological and behavioral continuum. I consider the mechanisms underlying these fluctuations and discuss brain thermorecording as an important tool to assess basic changes in neural activity associated with different natural (sexual, drinking, eating) and drug-induced motivated behaviors. I also consider how naturally occurring changes in brain temperature affect neural activity, various homeostatic parameters, and the structural integrity of brain cells as well as the results of neurochemical evaluations conducted in awake animals. While physiological hyperthermia appears to be adaptive, enhancing the efficiency of neural functions, under specific environmental conditions and following exposure to certain psychoactive drugs, brain temperature could exceed its upper limits, resulting in multiple brain abnormalities and life-threatening health complications.

Energy Trade-offs in Host Defense: Immunology Meets Physiology

Host defense relies not only on microbicidal mechanisms (resistance), but also on management of collateral damage (tolerance). Here, we discuss how this immunology concept converges with a physiology-born theory on the dichotomy of thermometabolic responses in infection (fever versus hypothermia), yielding a model of immunity that transcends discipline barriers.

Camphor, Applied Epidermally to the Back, Causes Snout- and Chest-Grooming in Rats: A Response Mediated by Cutaneous TRP Channels

Thermoregulatory grooming, a behavioral defense against heat, is known to be driven by skin-temperature signals. Because at least some thermal cutaneous signals that drive heat defenses are likely to be generated by transient receptor potential (TRP) channels, we hypothesized that warmth-sensitive TRPs drive thermoregulatory grooming. Adult male Wistar rats were used. We showed that camphor, a nonselective agonist of several TRP channels, including vanilloid (V) 3, when applied epidermally to the back (500 mg/kg), caused a pronounced self-grooming response, including paw-licking and snout- and chest-“washing”. By the percentage of time spent grooming, the response was similar to the thermoregulatory grooming observed during exposure to ambient warmth (32 °C). Ruthenium red (a non-selective antagonist of TRP channels, including TRPV3), when administered intravenously at a dose of 0.1 mg/kg, attenuated the self-grooming behavior induced by either ambient warmth or epidermal camphor. Furthermore, the intravenous administration of AMG8432 (40 mg/kg), a relatively selective TRPV3 antagonist, also attenuated the self-grooming response to epidermal camphor. We conclude that camphor causes the self-grooming behavior by acting on TRP channels in the skin. We propose that cutaneous warmth signals mediated by TRP channels, possibly including TRPV3, drive thermoregulatory self-grooming in rats.