Thermoregulatory Mechanisms Research Articles

Pathophysiology of Fever and Application of Infrared Thermography (IRT) in the Detection of Sick Domestic Animals: Recent Advances.

Simple SummaryThe current immune, metabolic, and neural pathways and the structures involved in developing the febrile response and, in return, to thermal homeostasis are known. There is still much information to be revealed about the underlying mechanisms that participate in the febrile process and the control of energy balance. This review analyzes the recent advances in pathophysiological mechanisms of the febrile process, the heat loss in an animal with fever, thermoregulation, the adverse effects of fever, and recent scientific findings related to different pathologies in farm animals through the use of infrared thermography, a fast, reliable, and non-invasive tool that is useful in the early detection of pathologies of clinical importance.Body-temperature elevations are multifactorial in origin and classified as hyperthermia as a rise in temperature due to alterations in the thermoregulation mechanism; the body loses the ability to control or regulate body temperature. In contrast, fever is a controlled state, since the body adjusts its stable temperature range to increase body temperature without losing the thermoregulation capacity. Fever refers to an acute phase response that confers a survival benefit on the body, raising core body temperature during infection or systemic inflammation processes to reduce the survival and proliferation of infectious pathogens by altering temperature, restriction of essential nutrients, and the activation of an immune reaction. However, once the infection resolves, the febrile response must be tightly regulated to avoid excessive tissue damage. During fever, neurological, endocrine, immunological, and metabolic changes occur that cause an increase in the stable temperature range, which allows the core body temperature to be considerably increased to stop the invasion of the offending agent and restrict the damage to the organism. There are different metabolic mechanisms of thermoregulation in the febrile response at the central and peripheral levels and cellular events. In response to cold or heat, the brain triggers thermoregulatory responses to coping with changes in body temperature, including autonomic effectors, such as thermogenesis, vasodilation, sweating, and behavioral mechanisms, that trigger flexible, goal-oriented actions, such as seeking heat or cold, nest building, and postural extension. Infrared thermography (IRT) has proven to be a reliable method for the early detection of pathologies affecting animal health and welfare that represent economic losses for farmers. However, the standardization of protocols for IRT use is still needed. Together with the complete understanding of the physiological and behavioral responses involved in the febrile process, it is possible to have timely solutions to serious problem situations. For this reason, the present review aims to analyze the new findings in pathophysiological mechanisms of the febrile process, the heat-loss mechanisms in an animal with fever, thermoregulation, the adverse effects of fever, and recent scientific findings related to different pathologies in farm animals through the use of IRT.

Evaporative Water Loss and Stopover Behavior in Three Passerine Bird Species During Autumn Migration

Migratory birds are often not specifically adapted to arid conditions, yet several species travel across deserts during their journeys, and often have more or less short stopovers there. We investigated whether differences in thermoregulatory mechanisms, specifically evaporative cooling, explain the different behavior of three passerine species while stopping over in the Negev desert, Israel. We measured cutaneous water loss (CWL) under ambient conditions and the temperature of panting onset in an experimental setup. In addition, we performed behavioral observations of birds at a stopover site where we manipulated water availability. Blackcaps had slightly higher CWL at relatively low temperatures than Willow Warblers and Lesser Whitethroats. When considered relative to total body mass, however, Willow Warblers had the highest CWL of the three species. Blackcaps started panting at lower ambient temperature than the other two species. Taken together, these results suggest that Willow Warblers are the most efficient in cooling their body, possibly with the cost of needing to regain water by actively foraging during their staging. Lesser Whitethroats had a similar pattern, which was reflected in their slightly higher levels of activity and drinking behavior when water was available. However, in general the behavior of migratory species was not affected by the availability of water, and they were observed drinking rather rarely. Our results indicate that differences in thermoregulatory mechanisms might be at the basis of the evolution of different stopover strategies of migratory birds while crossing arid areas such as deserts.

Scrotal thermographic profile and seminal characteristics of Mangalarga Marchador stallions bred in the Atlantic Rainforest biome

ABSTRACT The objective of this study was to determine the scrotal thermographic profile and to verify the influence of temperature and humidity of the humid tropical climate on testicular temperature and seminal quality of Mangalarga Marchador stallions. The thermal profiles of the proximal, middle, and distal zones of the testicles and total surface temperature (TSTT) were recorded using an FLIR E60bx thermal imager. The average air temperature (°C) and relative humidity (%) were obtained 1, 5, 9, 33, and 66 days before semen collection and showed a mean value of 26.5±2.4 and 80.4±6.0 respectively. The scrotal surface temperature was close to 34°C and there was no variation with the age of the stallion, reproductive activity, and characteristics of the ejaculate (P>0.05). The only significant correlations obtained were between TSTT and minor defects (R = 0.41; P<0.05), between TSTT and total defects (R = 0.46; P<0.01), and between TSTT and percentage of morphologically normal sperm (R = -0.46; P<0.05). It was concluded that the Mangalarga Marchador stallions maintained the testicular temperature within favorable conditions for spermatogenesis, demonstrating the efficiency of testicular thermoregulation mechanisms in the Atlantic Forest biome.

Clinical Applications and Factors Involved in Validating Thermal Windows Used in Infrared Thermography in Cattle and River Buffalo to Assess Health and Productivity.

Simple SummaryInfrared thermography is a clinically useful method for detecting physiopathological alterations in animals through microvascular changes. It has been adapted for applications with large species, as a support tool in evaluating animal welfare, and can also contribute to productive and reproductive evaluations. This review discusses the thermal windows currently in use and characterizes their differences and limitations as resources for early detection and diagnosis in cattle and river buffaloes.Infrared thermography (IRT) is a non-ionizing, non-invasive technique that permits evaluating the comfort levels of animals, a topic of concern due to the growing interest in determining the state of health and welfare of production animals. The operating principle of IRT is detecting the heat irradiated in anatomical regions characterized by a high density of near-surface blood vessels that can regulate temperature gain or loss from/to the environment by modifying blood flow. This is essential for understanding the various vascular thermoregulation mechanisms of different species, such as rodents and ruminants’ tails. The usefulness of ocular, nasal, and vulvar thermal windows in the orbital (regio orbitalis), nasal (regio nasalis), and urogenital (regio urogenitalis) regions, respectively, has been demonstrated in cattle. However, recent evidence for the river buffalo has detected discrepancies in the data gathered from distinct thermal regions in these large ruminants, suggesting a limited sensitivity and specificity when used with this species due to various factors: the presence of hair, ambient temperature, and anatomical features, such as skin thickness and variations in blood supplies to different regions. In this review, a literature search was conducted in Scopus, Web of Science, ScienceDirect, and PubMed, using keyword combinations that included “infrared thermography”, “water buffalo”, “river buffalo” “thermoregulation”, “microvascular changes”, “lacrimal caruncle”, “udder”, “mastitis”, and “nostril”. We discuss recent findings on four thermal windows—the orbital and nasal regions, mammary gland in the udder region (regio uberis), and vulvar in the urogenital region (regio urogenitalis)—to elucidate the factors that modulate and intervene in validating thermal windows and interpreting the information they provide, as it relates to the clinical usefulness of IRT for cattle (Bos) and the river buffalo (Bubalus bubalis).

The Effect of Backplate Design for Mountain Bike Backpacks on Thermoregulation Mechanisms

Using infrared thermography, we assess how a new backpack design for mountain bikers can contribute to their thermoregulation process and perceived comfort during a cycling activity in a controlled environment. We gathered qualitative and quantitative data of heat concentration areas on skin temperature and thermal comfort perception by comparing two types of backpacks: a conventional backpack and a novel backpack design. Our results show that a guaranteeing airflow due to distance between the user’s back and the backpack with a rigid backplate and an arc radius morphology improves heat dissipation and thermal comfort for mountain bikers.

Comparative Analysis of Thermovision Images of Healthy Young Men with Different Terms of Adaptation to Conditions of the North

Introduction. The correlation between skin temperature and cutaneous blood flow is a factor that influences thermal imaging of the body in response to thermoregulation. The objective of our study was to identify features of thermal images of young male permanent residents of the Russian North belonging to different generations. Materials and methods. Thermography was carried out using a thermal imaging camera (FLIR SC620 thermal imager, Sweden), providing long-wave (7.5–13 μm) imaging with a thermal sensitivity of 0.1 °С. Quantitative analysis of thermovision images was performed for eight sites of the body captured from the front and back in a sitting position. We examined 90 young healthy men aged 17 to 21 years, permanently residing in the Magadan Region. Depending on the duration of adaptation to extreme conditions of the North, all subjects were divided into four groups: adapting migrants (“zero generation”) and those born in the North in the first, second and third generations. Results. We established a significant increase in skin temperature at all measured body sites in the series from adapting migrants (“zero generation”) to the natives in the first to third generation. The maximum differences were observed for the average temperature of the forehead, abdomen, and lower back, reaching 0.97, 1.04, and 0.98 °C, respectively. It should be noted that the young men of the city of Magadan had a higher average skin temperature than those living in optimal climatic and geographical conditions of Central Russia and Eastern Europe. The smallest difference (0.43 °С) was registered for breast temperature between the migrants and representatives of the third generation. Conclusions. Our findings prove compensatory and adaptive physiological changes occurring in the body over time to reduce adverse effects of the cold environment. This reorganization of the body is achieved through optimization of the thermoregulatory mechanism and changes in vegetative skin vasomotor responses.

Physiological and Behavioral Mechanisms of Thermoregulation in Mammals.

Simple SummaryThe study of the hypothalamic neuromodulation of thermoregulation offers broad areas of opportunity with practical applications that are currently being strengthened by the availability of efficacious tools like infrared thermography (IRT). This review analyzes the effect of climate change on behavior and productivity; and the effects of exercise on animals involved in sporting activities; identifies the microvascular changes that occur in response to fear, pleasure, pain, and other situations that induce stress in animals; and examines thermoregulating behaviors.This review analyzes the main anatomical structures and neural pathways that allow the generation of autonomous and behavioral mechanisms that regulate body heat in mammals. The study of the hypothalamic neuromodulation of thermoregulation offers broad areas of opportunity with practical applications that are currently being strengthened by the availability of efficacious tools like infrared thermography (IRT). These areas could include the following: understanding the effect of climate change on behavior and productivity; analyzing the effects of exercise on animals involved in sporting activities; identifying the microvascular changes that occur in response to fear, pleasure, pain, and other situations that induce stress in animals; and examining thermoregulating behaviors. This research could contribute substantially to understanding the drastic modification of environments that have severe consequences for animals, such as loss of appetite, low productivity, neonatal hypothermia, and thermal shock, among others. Current knowledge of these physiological processes and complex anatomical structures, like the nervous systems and their close relation to mechanisms of thermoregulation, is still limited. The results of studies in fields like evolutionary neuroscience of thermoregulation show that we cannot yet objectively explain even processes that on the surface seem simple, including behavioral changes and the pathways and connections that trigger mechanisms like vasodilatation and panting. In addition, there is a need to clarify the connection between emotions and thermoregulation that increases the chances of survival of some organisms. An increasingly precise understanding of thermoregulation will allow us to design and apply practical methods in fields like animal science and clinical medicine without compromising levels of animal welfare. The results obtained should not only increase the chances of survival but also improve quality of life and animal production.

A 3-D virtual human thermoregulatory model to predict whole-body and organ-specific heat-stress responses

ObjectiveThis study aimed at assessing the risks associated with human exposure to heat-stress conditions by predicting organ- and tissue-level heat-stress responses under different exertional activities, environmental conditions, and clothing.MethodsIn this study, we developed an anatomically detailed three-dimensional thermoregulatory finite element model of a 50th percentile U.S. male, to predict the spatiotemporal temperature distribution throughout the body. The model accounts for the major heat transfer and thermoregulatory mechanisms, and circadian-rhythm effects. We validated our model by comparing its temperature predictions of various organs (brain, liver, stomach, bladder, and esophagus), and muscles (vastus medialis and triceps brachii) under normal resting conditions (errors between 0.0 and 0.5 °C), and of rectum under different heat-stress conditions (errors between 0.1 and 0.3 °C), with experimental measurements from multiple studies.ResultsOur simulations showed that the rise in the rectal temperature was primarily driven by the activity level (~ 94%) and, to a much lesser extent, environmental conditions or clothing considered in our study. The peak temperature in the heart, liver, and kidney were consistently higher than in the rectum (by ~ 0.6 °C), and the entire heart and liver recorded higher temperatures than in the rectum, indicating that these organs may be more susceptible to heat injury.ConclusionOur model can help assess the impact of exertional and environmental heat stressors at the organ level and, in the future, evaluate the efficacy of different whole-body or localized cooling strategies in preserving organ integrity.

Heat stress in dairy cows

This review includes an analysis of the literature on various influencing factors influencing heat stress in lactating dairy cows and the way it affects milk production. Signs and symptoms of heat stress in cows are reduced feed consumption and decreased milk yield, elevated breathing rate, increased body temperature and reduced reproductive overall performance. There are other problems for example, a seasonal growth in bulk tank somatic cell counts. The birth weight is decreased in cows which have been exposed to heat stress throughout the dry length. It is established that the most critical is the heat accumulated via direct radiation from the solar. It was found out that high feed consumption results in raised metabolic heat increment. High metabolic warmness increment requires powerful thermoregulatory mechanisms to maintain body temperature in a thermoneutral area and in physiological homeostasis. It is confirmed that heat stress is complicated because the responses to heat stress have an effect on not best the energy stability, but also water, sodium, potassium and chlorine metabolism. Plasma progesterone degrees may be elevated or reduced depending on whether or not the heat pressure is acute or chronic. Water, sodium, potassium and chlorine are vital constituents of sweat, and sweating is a chief, if not the most important, thermoregulatory mechanism used to burn up extra body heat. Strategies to reduce heat stress must be evolved to enable cows to express their full genetic ability. Key words: dairy cows, heat stress, thermoregulatory mechanism, water, feed consumption, mineral elements.

Posterior subthalamic nucleus (PSTh) mediates innate fear-associated hypothermia in mice

The neural mechanisms of fear-associated thermoregulation remain unclear. Innate fear odor 2-methyl-2-thiazoline (2MT) elicits rapid hypothermia and elevated tail temperature, indicative of vasodilation-induced heat dissipation, in wild-type mice, but not in mice lacking Trpa1–the chemosensor for 2MT. Here we report that Trpa1−/− mice show diminished 2MT-evoked c-fos expression in the posterior subthalamic nucleus (PSTh), external lateral parabrachial subnucleus (PBel) and nucleus of the solitary tract (NTS). Whereas tetanus toxin light chain-mediated inactivation of NTS-projecting PSTh neurons suppress, optogenetic activation of direct PSTh-rostral NTS pathway induces hypothermia and tail vasodilation. Furthermore, selective opto-stimulation of 2MT-activated, PSTh-projecting PBel neurons by capturing activated neuronal ensembles (CANE) causes hypothermia. Conversely, chemogenetic suppression of vGlut2+ neurons in PBel or PSTh, or PSTh-projecting PBel neurons attenuates 2MT-evoked hypothermia and tail vasodilation. These studies identify PSTh as a major thermoregulatory hub that connects PBel to NTS to mediate 2MT-evoked innate fear-associated hypothermia and tail vasodilation.

In Ovo Injection of GABA Can Help Body Weight Gain at Hatch, Increase Chick Weight to Egg Weight Ratio, and Improve Broiler Heat Resistance.

Simple SummaryHeat stress is a vital issue that causes severe losses to the poultry industry. A partly developed thermoregulatory mechanism during the embryonic phase is emphasized to manipulate embryos for achieving thermotolerance during rearing. The present study was conducted firstly to standardize the dosage for an in ovo manipulation, and the selective dose was used to evaluate its effects on early-age heat-stressed (HS) broilers. HS induces cholesterol while an antioxidant acts as a first line of defense under stress. However, 5% GABA supplementation had a higher hatchling weight and chick weight to egg weight ratio (CWEWR). We selected a 10% GABA dosage for HS studies due to its higher antioxidants and lower cholesterol values in hatchlings. In ovo, 10% GABA supplementation significantly increased total antioxidant capacity and reduced malondialdehyde levels, hepatic mRNA levels of HSP70, FAS, and L-FABP in broilers when subjected to HS (38 ± 1 °C; 3 h) at ten days of age. This indicates that an in ovo GABA injection improves CWEWR and antioxidant status at hatch, and creates thermotolerance by increasing antioxidant production and downregulating the expression of HSP70 and fatty acid metabolism genes in HS chicks.The aim of this study was to explore the outcomes of an in ovo GABA injection in broilers challenged with HS. In Experiment 1, 210 Arbor Acres eggs were allocated to five treatments: no-injection, and in ovo injection of 0.6 mL of 0%, 5%, 10%, or 20% of GABA. Hatchling weight and CWEWR were significantly increased in the 5% GABA group. In ovo, injection of 10% GABA solution caused a significant decrease in plasma cholesterol and increased plasma total antioxidant capacity of hatchlings. Experiment 2 was conducted with 126 fertile Arbor Acres eggs distributed into one of two groups. At 17.5 days of incubation, one received no injection, and the other was fed 0.6 mL of 10% GABA. On day 10, one subgroup (4 replicates * 3 birds) from each treatment was submitted to HS (38 ± 1 °C for 3 h) while the other was kept at a thermoneutral temperature (29 ± 1 °C). An in ovo injection of GABA significantly increased total antioxidant capacity, but reduced malondialdehyde levels, hepatic mRNA levels of HSP70, FAS, and L-FABP with HS. In conclusion, an in ovo GABA injection improves CWEWR and antioxidant status at hatch, and enhances antioxidant status while downregulating the expression of HSP70 and fatty acid metabolism-related genes in young chicks under HS.

Thermoregulatory strategies of three reclusive lizards (genus Xantusia) from the Baja California peninsula, Mexico, under current and future microenvironmental temperatures.

The thermal quality of the habitat is key for the regulation of body temperature in terrestrial ectotherms and, therefore, permits them to carry out their fundamental biological activities. In thermally heterogeneous environments, ectotherms might follow different behavioral or physiological strategies to maintain their body temperature within biologically adequate boundaries, for which they depend on microhabitat selection. These aspects are, thus, relevant in the context of habitat degradation and land-use change. In this study, we characterized the thermal ecology of three lizard species (genus Xantusia) that differ in microhabitat use along the Baja California peninsula, Mexico. We made three predictions: (1) the three species will follow different thermoregulatory strategies according to habitat thermal quality; (2) the thermal requirements and tolerances of these species will match the environmental or microenvironmental thermal conditions; and (3) due to their habitat and range restriction, the species studied will be highly vulnerable to climate change. Our results indicate the existence of thermoregulatory mechanisms in Xantusia to face thermal heterogeneity, including behavioral thermoregulation by choosing different microhabitats, shifts in activity periods, and adaptation to particular high thermal quality microhabitats. Furthermore, despite their association to specific microhabitats and specialized physiology, the studied species will not be adversely affected by climate change, as the increased microenvironmental temperatures will lead to a higher habitat thermal quality and lower costs of thermoregulation. However, we do not discard other indirect adverse effects of climate change not considered in this study.

Reproducibility and Effect of Sampling Depth on Laser Doppler Flowmetry Measures During the Reflex Cutaneous Vasoconstriction Response

During cold exposure, reflex cutaneous vasoconstriction is an important thermoregulatory mechanism that minimizes heat loss. Laser Doppler flowmetry (LDF) is a widely used, non-invasive method of assessing cutaneous microvascular blood flow. However, data on the reproducibility of LDF during a cooling stimulus is limited. Furthermore, various sampling depths of skin measurement are available depending on the type of LDF probe used; however, a comparison of different depths to the same cooling stimulus has not been determined. We hypothesized that LDF probes, particularly those sampling at deeper skin depths, would provide a reproducible measurement of cutaneous microvascular blood flow during whole-body cooling. Fourteen healthy, young adults completed two whole-body cooling bouts, each bout separated by 3-7 days. Participants wore a water-perfused whole-body suit to reduce skin temperature (Tsk) from 34°C to 30.5°C over 30 minutes, and held at 30.5°C for an additional 10 minutes. LDF flux was measured continuously at five forearm sites using 1 VP1-HP Doppler probe, 2 VP7b integrated probes, and 2 VP12 single point Dopplers (Moor Instruments, Axminster, UK) measuring at depths of 4.0 mm, 0.66 mm, and 0.33 mm, respectively. Cutaneous vascular conductance (CVC) was calculated as flux/mean arterial pressure at each 0.5°C reduction in Tsk and at plateau. CVC values were expressed as percent changes from baseline (%ᐃCVCBASELINE). A greater vasoconstriction response was recorded using the VP1-HP Doppler at plateau (34.7 ± 0.6%) compared to the VP7b (31.9 ± 0.5%, p < 0.001) and VP12 (30.3 ± 0.6%, p < 0.001) LDF probes. Additionally, test-retest reproducibility between visits displayed good reproducibility (coefficient of variation <9%) among all three Doppler probes. These data indicate that LDF provides reproducible measurements during reflex cutaneous vasoconstriction at different depths. However, deeper Dopplers, which analyze a greater area of skin, are more likely to discriminate differences in cutaneous microvascular blood flow than those at shallower depths.

Cholinergic nerve contribution to cutaneous active vasodilation in response to exercise heat‐loading is similar to passive whole‐body heat‐loading

Introduction Twenty-five years ago, Dean Kellogg and colleagues established the sympathetic cholinergic nerve co-transmitter theory for cutaneous active vasodilation (CAVD) during passive heating in humans. In this seminal study, pretreatment of the skin with botulinum toxin type-A (BOTOX), a presynaptic cholinergic nerve blocker, abolished CAVD during passive whole-body heat stress in six subjects. To date, these findings have not been confirmed. More recently, a clear role for NO in CAVD has been established, where NO accounts for up to 50% of CAVD. The specific isoform of NO-synthase has been reported to differ between CAVD in response to different thermal loading modalities (passive heating vs. exercise). These findings suggest that there may be mechanistic differences in the skin blood flow responses (SkBF) to hyperthermic challenge that are dependent on how thermal loading is accomplished. With this in mind, it is unknown if the cholinergic co-transmitter theory of CAVD applies to other thermal loading modalities such as exercise heat-loading. Therefore, this study sought to confirm the role of cholinergic nerve activation in CAVD during passive whole-body heat-loading and expand these findings to exercise heat-loading using a cross-over study design. It was hypothesized that CAVD during exercise and passive whole-body heating would both be abolished by BOTOX administration. Methods Eight young (18-30 years) recreationally-active individuals participated in both an exercise heat-loading study day (40% VO2peak, 1 hour; seated cycle ergometer) and a passive whole-body heat-loading study day (mean skin temperature clamp @ 39°C, ~1 hour; water-perfused suit, seated), in a randomized order. Cholinergic nerve blockade was achieved through BOTOX administration ~2 weeks prior to study days. Throughout heat-loading trials, SkBF was assessed at BOTOX treated and untreated sites using laser-doppler flowmetry. Results At rest, there were no differences in SkBF expressed as % CVCmax by site (BOTOX treated vs. untreated) or by modality (Exercise heat-loading vs. passive whole body heat-loading). The SkBF response, as a function of increasing internal temperature, was similar between heat-loading modalities at BOTOX treated and untreated sites. At the end of heat-loading (@ 0.7 °C increase in internal temperature), % CVCmax at the BOTOX treated sites (Exercise: 19 ± 2 and Passive whole-body heating: 15 ± 5 % CVCmax), were significantly less (P<0.001) than at the untreated sites (Exercise: 35 ± 4 and Passive whole-body heating: 38 ± 2 % CVCmax). Additionally, there were no differences in %CVCMax between thermal loading modalities (modality, P = 0.909; modality-by-microdialysis site interaction, P=0.230) at the end of heat-loading. Conclusions We conclude that CAVD in response to exercise heat-loading and passive whole-body heat-loading are both mediated by cholinergic nerve transmission, a critical thermoregulatory mechanism whose function appears to be independent of the thermal loading modality.

The Role of Nonshivering Thermogenesis Genes on Leptin Levels Regulation in Residents of the Coldest Region of Siberia.

Leptin plays an important role in thermoregulation and is possibly associated with the microevolutionary processes of human adaptation to a cold climate. In this study, based on the Yakut population (n = 281 individuals) living in the coldest region of Siberia (t°minimum −71.2 °C), we analyze the serum leptin levels and data of 14 single nucleotide polymorphisms (SNPs) of 10 genes (UCP1, UCP2, UCP3, FNDC5, PPARGC1A, CIDEA, PTGS2, TRPV1, LEPR, BDNF) that are possibly involved in nonshivering thermogenesis processes. Our results demonstrate that from 14 studied SNPs of 10 genes, 2 SNPs (the TT rs3811787 genotype of the UCP1 gene and the GG rs6265 genotype of the BDNF gene) were associated with the elevated leptin levels in Yakut females (p < 0.05). Furthermore, of these two SNPs, the rs3811787 of the UCP1 gene demonstrated more indications of natural selection for cold climate adaptation. The prevalence gradient of the T-allele (rs3811787) of UCP1 increased from the south to the north across Eurasia, along the shore of the Arctic Ocean. Thereby, our study suggests the potential involvement of the UCP1 gene in the leptin-mediated thermoregulation mechanism, while the distribution of its allelic variants is probably related to human adaptation to a cold climate.

The multilevel responses of Acipenser baerii and its hybrids (A. baerii ♀ × A. schrenckii ♂) to chronic heat stress

The global warming profoundly impacts on fishes' survival by imposing a chronic heat stress condition, but the thermoregulation mechanism of fishes, especially for cold-water fishes, against chronic heat stress remains to be explored. In this study, we evaluated the thermal resistance of Acipenser baerii and its hybrids (A. baerii ♀ × A. schrenckii♂). In the analysis of cumulative survival rate (CSR) and histologic section, the hybrids showed higher survival rate and lower gill damage than A. baerii. Under the chronic heat stress, plasma cortisol and glucose levels were increased at different degrees in A. baerii and the hybrids. At the same time, oxidative stress markers (LPO, SOD, CAT, GSH-Px and GSH) levels, and the mRNA expression levels of heat shock proteins (HSP70, HSP90, GRP75 and HSC70) and inflammation factors (IL-1β and TGF-β) were also increased in A. baerii and the hybrids. Among these results, the increases were relatively higher in A. baerii at the early period (day 7) of heat stress, indicating that A. baerii is more susceptible to heat stress. In addition, the expression levels of HSP70 protein were greatly increased in A. baerii, in support of the low survival ability of A. baerii under chronic heat stress. Our study provides a direct evidence to prove the outstanding thermal resistance of the hybrids, and also contributes to understand the coping strategy of cold-water fishes to chronic heat stress.

Short-term sleep deprivation and human thermoregulatory function during thermal challenges.

What is the topic of this review? It is generally accepted that sleep deprivation constitutes a predisposing factor to the development of thermal injury. This review summarizes the available human-based evidence on the impact of sleep loss on autonomic and behavioural thermoeffectors during acute exposure to low and high ambient temperatures. What advances does it highlight? Limited to moderate evidence suggests that sleep deprivation per se impairs thermoregulatory defence mechanisms during exposure to thermal extremes. Future research is required to establish whether inadequate sleep enhances the risk for cold- and heat-related illnesses. Relatively short periods of inadequate sleep provoke physiological and psychological perturbations, typically leading to functional impairments and degradation in performance. It is commonly accepted that sleep deprivation also disturbs thermal homeostasis, plausibly enhancing susceptibility to cold- and heat-related illnesses. Herein, we summarize the current state of human-based evidence on the impact of short-term (i.e., ≤4nights) sleep deprivation on autonomic and behavioural thermoeffectors during acute exposure to low and high ambient temperatures. The purpose of this brief narrative review is to highlight knowledge gaps in the area and stimulate future research to investigate whether sleep deprivation constitutes a predisposing factor for the development of thermal injuries.

The Thermoregulatory and Thermal Responses of Individuals With a Spinal Cord Injury During Exercise, Acclimation and by Using Cooling Strategies–A Systematic Review

Background: In individuals with a spinal cord injury thermoregulatory mechanisms are fully or partially interrupted. This could lead to exercise-induced hyperthermia in temperate conditions which can be even more distinct in hot conditions. Hyperthermia has been suggested to impair physiological mechanisms in athletes, which could negatively influence physical performance and subjective well-being or cause mild to severe health issues.Objective: The aim was to evaluate the literature on the thermoregulatory and thermal responses of individuals with a spinal cord injury during exercise in temperate and hot conditions taking the effects of cooling techniques and heat acclimation into account.Data sources: Two electronic databases, PubMed and Web of Science were searched. Studies were eligible if they observed the influence of exercise on various thermoregulatory parameters (e.g., core and skin temperature, sweat rate, thermal sensation) in individuals with a spinal cord injury.Results: In total 32 articles were included of which 26 were of strong, 3 of moderate and 3 of weak quality. Individuals with a high lesion level, especially those with a tetraplegia, reached a higher core and skin temperature with a lower sweat rate. The use of cooling techniques before and during exercise can positively affect the burden of the impaired thermoregulatory system in all individuals with a spinal cord injury.Conclusion: Due to the absence of normal thermoregulatory abilities, individuals with a high-level spinal cord injury need special attention when they are exercising in temperate and hot conditions to prevent them from potential heat related issues. The use of cooling techniques can reduce this risk.

Thermoregulation of the bovine scrotum 2: simulated acute and chronic heat waves reduces the scrotal thermoregulatory capability of Wagyu bulls.

The objective of this study was to investigate the effect of acute and chronic heat load events on scrotal temperature (ST), body temperature (BT) and bull behaviour, and to examine the interrelationship between these parameters; the underlying hypothesis was that adverse heat treatments delivered in a temperature controlled environment will lead to thermoregulatory dysfunction of the bull scrotum. Six sexually mature Wagyu bulls were used in this study with data loggers surgically implanted into the abdominal cavity and scrotum. Body temperate and ST were recorded at 30-min intervals for the duration of the study. There were two housing locations used throughout the study, outdoor pens and climate control rooms. The study was designed as a four-phase crossover design with two heat treatments: (1) a 5-day acute challenge, and (2) a 14-day chronic challenge. The study was also blocked by phase to control for systematic change between phases with a thermoneutral (TN) phase in outdoor pens between each heat challenge. Observations within the climate rooms were conducted at 1-h intervals and data on panting scores (PS), respiration rate (RR), posture (standing or lying) and general behaviours (feeding, drinking, ruminating) recorded. Ambient temperature (AT, °C) and relative humidity (RH, %) were obtained at 10-min intervals and used to calculate the temperature humidity index (THI). Multiple models were conducted using a linear mixed effects model that contained different permutations of date and time factors and interactions as well as inclusion of an autoregressive parameter. The strongest model based on Akaike's information criterion (AIC) was selected and further analysed. Ambient conditions during heat treatments were consistent with heat load and bulls showed typical physiological symptoms of the same. Maximum ST for acute and chronic treatments occurred once AT had exceeded 34 °C for at least 3 h (acute 35.59 °C at 1500 h; chronic 35.18 °C at 1400 h), whereas during TN conditions, maximum ST was at 2100 h. All phases showed variation in ST throughout the day. There were strong cross correlations between ST and RR during the heat treatments (acute r = 0.918, P < 0.0001; chronic r = 0.916, P < 0.0001), but not during TN (r = 0.411, P < 0.05). Our results confirmed that the ST of the bulls used in this study was not held at a constant temperature and that there was a possible connection between ST and RR. We have shown that during a period of heat load, the thermoregulatory mechanisms thought responsible for maintaining bovine ST appear to breakdown.

Vertebrate Life, 10th edition

Vertebrate Life, 10th edition