Chronic Heat Exposure Research Articles

Passive Heat Therapy as a Novel Approach for Inducing Angiogenesis in Humans: Roles of Nitric Oxide

Chronic passive heat therapy is a novel health intervention which may have widespread cardiovascular benefits. Studies in animals suggest chronic heat exposure promotes angiogenesis via NO, independently of VEGF. We sought to determine whether the same occurs in humans using an endothelial tubule formation assay to quantify serum angiogenic balance.METHODSSerum was collected from ten young (23±2 years), healthy human subjects before and after 8 weeks of passive heat therapy (36 sessions of hot water immersion sufficient to maintain rectal temperature ≥38.5°C for 60min per session; post‐heat therapy serum was collected at least 36h after the last session). All analyses were performed in duplicate using human sera collected pre and post heat therapy. To assess serum angiogenic balance, human umbilical vein endothelial cells (HUVECs) were plated onto serum‐free Matrigel, exposed to human sera, and incubated for 10h, after which total tubule length per frame was determined by two blinded investigators. To investigate whether potential improvements in serum angiogenic balance following heat therapy were NOS‐dependent, angiogenesis experiments were repeated in which HUVECs were additionally treated with 1mM L‐NNA, a competitive inhibitor of NOS. In separate experiments, HUVECs were exposed to human sera for 24h and eNOS protein was determined using Western blot, normalized to vinculin loading control. Lastly, serum VEGF concentration was determined by ELISA.RESULTSSerum angiogenic balance was improved following 8 weeks of heat therapy (total tubule length: 71.8±1.0 to 74.3±1.1mm, p=0.03) and this improvement was prevented by L‐NNA (73.1±1.7 to 73.9±1.1, p=0.56). eNOS protein expression increased by 18.6±3.4% (p=0.05) in endothelial cells exposed to human sera following heat therapy relative to pre‐heat therapy. Heat therapy decreased serum VEGF concentration (370±77 to 331±69 pg/ml, p=0.05).CONCLUSIONSChronic passive heat therapy in humans upregulates circulating factor(s) which promote angiogenesis in a NOS‐dependent and VEGF‐independent manner, possibly through increasing eNOS expression. These results are consistent with those reported in animal studies and suggest chronic passive heat therapy could be a viable treatment option for improving vascularization in at‐risk populations.Support or Funding InformationSupported by AHA Grant #14PRE20380300 and the Eugene and Clarissa Evonuk Memorial Foundation

Changes of brain monoamine levels and physiological indexes during heat acclimation in rats

Brain monoamines, such as noradrenaline (NA), dopamine (DA), and serotonin (5-HT), regulate many important physiological functions including thermoregulation. The purpose of this study was to clarify changes in NA, DA, and 5-HT levels in several brain regions in response to heat acclimation while also recording body temperature (Tb), heart rate (HR), and locomotor activity (Act). Rats were exposed to a heated environment (32°C) for 3h (3H), 1 day (1D), 7 days, 14 days (14D), 21 days, or 28 days (28D). After heat exposure, each of the following brain regions were immediately extracted and homogenized: the caudate putamen (CPu), preoptic area (PO), dorsomedial hypothalamus (DMH), frontal cortex (FC), and hippocampus (Hip). NA, DA, and 5-HT levels in the extract were measured by high performance liquid chromatography. Although Tb increased immediately after heat exposure, it decreased about 14D later. HR was maintained at a low level throughout heat exposure, and Act tended to increase near the end of heat exposure. After 3H, we observed a marked increase in NA level in the CPu. Although this response vanished after 1D, the level increased again after 28D. DA level in the CPu decreased significantly from 1D to 28D. 5-HT level in the PO and DMH decreased from 1D to 14D. It returned to control levels after 28D with increment of DA level. 5-HT level in the FC decreased at the start of heat exposure, but recovered after 28D; a time point at which DA level also increased. Monoamine levels in the Hip were unchanged after early heat exposure, but both 5-HT and DA levels increased after 28D. These results provide definitive evidence of changes in monoamines in individual brain regions involved in thermoregulation and behavioral, cognitive, and memory function during both acute and chronic heat exposure.

Cyclic variations in incubation conditions induce adaptive responses to later heat exposure in chickens: a review

Selection programs have enabled broiler chickens to gain muscle mass without similar enlargement of the cardiovascular and respiratory systems that are essential for thermoregulatory efficiency. Meat-type chickens cope with high ambient temperature by reducing feed intake and growth during chronic and moderate heat exposure. In case of acute heat exposure, a dramatic increase in morbidity and mortality can occur. In order to alleviate heat stress in the long term, research has recently focused on early thermal manipulation. Aimed at stimulation of long-term thermotolerance, the thermal manipulation of embryos is a method based on fine tuning of incubation conditions, taking into account the level and duration of increases in temperature and relative humidity during a critical period of embryogenesis. The consequences of thermal manipulation on the performance and meat quality of broiler chickens have been explored to ensure the potential application of this strategy. The physiological basis of the method is the induction of epigenetic and metabolic mechanisms that control body temperature in the long term. Early thermal manipulation can enhance poultry resistance to environmental changes without much effect on growth performance. This review presents the main strategies of early heat exposure and the physiological concepts on which these methods were based. The cellular mechanisms potentially underlying the adaptive response are discussed as well as the potential interest of thermal manipulation of embryos for poultry production.

Dermatoses due to Indian cultural practices.

A wide prevalence of socio-religious and cultural practices in the Asian subcontinent often leads to multitude of skin diseases which may be missed by the dermatologists because of a lack of awareness. ‘Henna’ use causes IgE-mediated hypersensitivity reactions and contact dermatitis. ‘Kumkum’ application can result in pigmented contact dermatitis and lichen planus pigmentosus. Sticker ‘bindis’ and ‘alta’ induce contact leukoderma. Irritant and allergic contact dermatitis occurs after playing with ‘Holi’ colors. Threading and drawstring dermatitis lead to koebnerization of pre-existing dermatoses, infections and even squamous cell carcinoma of skin. Mild irritant reactions and contact sensitization occur secondary to balm and hair oil use. ‘Mudichood’ represents the comedogenic effect of hair oils combined with occlusion and humidity. Aromatherapy oils can cause contact dermatitis and photosensitive reactions. Heavy metal and steroid toxicity along with severe cutaneous adverse effects like erythroderma can occur as a consequent to the use of alternative medicines. Squamous cell carcinoma due to chronic heat exposure from the heating device “kangri” is seen in Kashmiris. Prayer nodules in Muslims and traction alopecia in Sikhs illustrate how religious practices can negatively affect the skin. With increasing globalization and migration, the practice of indigenous customs and traditions is no longer limited to regional territories, making it imperative for the dermatologists to be acquainted with the cutaneous side effects they can cause.

Effects of Tannic Acid on Performance and Fatty Acid Composition of Breast Muscle in Broiler Chickens Under Heat Stress

One hundred twenty day-old broiler chicks (Cobb 500) were randomly assigned into 4 treatment groups to investigate the effects of tannic acid supplementation (TA) on fatty acid composition in breast muscle of broilers under chronic heat exposure conditions. Five pen replicates of 6 chicks each were assigned to each of the following 4 dietary treatments: i) basal diet containing no TA at 25°C (CL); ii) basal diet containing no TA at 35°C (CH); iii) basal diet supplemented with 1% TA at 25°C (TL); and iv) basal diet supplemented with 1% TA at 35°C (TH). At the end of the 5-week experiment, breast muscle samples were collected to examine the fatty acid composition. Results showed that temperature, TA and their interaction effect significantly decreased body weight gain and feed intake. In addition, feed conversion ratio (FCR) significantly increased under high temperature, and addition of TA under high temperature did not improve the FCR. The effects of temperature, TA and their interaction on the saturated and unsaturated fatty acids were not significant (P<0.05). However, monounsaturated fatty acids significantly reduced by adding TA to the diet. Generally, TA improved the fatty acid profile of breast muscle of broilers under heat stress in comparison to the heat stressed chickens, which did not receive TA. Hence, it seems that dietary TA supplementation can be applied as a biological antioxidant for poultry nutrition in hot climatic conditions.

Clinicopathological Studies on Broiler Exposed to High Environmental Temperature

The present study was performed to investigate the clinicopathological changes associated with exposure to heat stress in chickens. One hundred Hubbard chickens were used in this study. Experimental chicks were divided into five equal groups each containing 20 chickens. The first gp. chickens were kept as negative control (non treated non heat treated), gp. 2 chickens were exposed to 42±1°C for 3 hrs. with RH. 45-60% at 45 days old, gp. 3 chickens were administrated with No Heat-S with a dose 1 gm/liter in drinking water 24hrs. before heat exposure and exposed to 42±1°C for 3hrs with RH. 45-60%. at 45 days old, gp. 4 chickens were exposed to 39±1°C for 6 hrs. for 3 successive days with RH. 45-60% at 43, 44 and 45 days old while gp. 5 chickens were administrated with No Heat-S with a dose 1 gm/liter in drinking 24hrs. before heat exposure and exposed to 39±1°C for 6 hrs. for 3 successive days with RH. 45-60%. at 43, 44 and 45 days old. Blood gases, acid/base balance and electrolytes revealed respiratory alkalosis and hyper capnia in heat treated chickens with disturbance in electrolyte immediately after exposure. After 12 hrs., the alkalosis persisted in acute heat treated group only with increase the bicarbonate level in all groups. Hypo capnia occur in all heat treated gps. The hyper kalemia disappeared. After 36 hrs., no changes in blood PH and blood gases were persisted. Regarding the biochemical changes, Serum and liver ascorbic acid decreased significantly in case of acute and chronic non treated groups retuned to normal levels 36 after exposure. Serum AST and CK activities were significantly increased in birds exposed to acute and chronic heat exposure which persisted 12 hrs. after exposure and returned to normal 36 hrs. after exposure, hyperuricemia, hypocalcimia and increased creatinine level occurred in birds exposed to acute and chronic heat exposure which persisted 12 hrs. past exposure and returned to normal 36 hrs. after exposure.

Some Like It Hot: Erythema Ab Igne due to Cannabinoid Hyperemesis

A 42-year-old man with cyclical vomiting due to chronic cannabis use was admitted for intractable nausea and vomiting. He stated that he took 5–6 hot showers daily for nausea relief. On exam, a reticular, red to brown pigmented rash was seen on his trunk and upper extremities, areas chronically exposed to hot water. His rash was consistent with erythema ab igne (EAI) or thermal keratosis. EAI occurs after chronic heat exposure and has historically been found on the shins of those working by open fires or coal stoves, areas of chronic pain exposed to heating pads, and recently on the thighs of portable computer users. EAI lesions are often asymptomatic, but may exhibit mild pruritus. Treatment consists of eliminating the heat exposure. While mild lesions may remit, many persist and have been associated with an increased risk of squamous cell carcinoma due to underlying damage from infrared radiation as heat. Cannabinoid hyperemesis, a syndrome of cyclical vomiting from chronic marijuana use, has been associated with compulsive bathing, which ameliorates the nausea. The linkage of cannabinoid hyperemesis and EAI due to compulsive bathing is a new association of this classic heatassociated skin lesion. The patient was discharged without complication.

Elastolytic giant cell granuloma: clinic-pathologic review of twenty cases

O'Brien described four histopathological patterns of actinic granuloma (AG). Since then, only single cases and a few series have been reported in the literature, most corresponding to cases of the giant cell type. We reviewed all the cases diagnosed as AG or elastolytic giant cell granuloma (EGCG) in our department from 1988 until 2010. The biopsies were classified into the four patterns previously described. Giant cell pattern was found to be the most frequent (70% of the cases). In four cases, the biopsies showed more than one histopathologic pattern. All the lesions were located on sun-exposed areas or were related to chronic heat exposure. Diabetes mellitus was associated in 40 % of the cases. The giant cell pattern of EGCG is the most frequent. Some cases may share histopathologic features of more than one variant and thus, we consider they may be categorized as mixed patterns. Diabetes mellitus is the most common associated disease and should always be ruled out.

Tolerance for chronic heat exposure is greater in female than male mice

Purpose: Chronic heat exposure in mice has cellular and physiological effects that improve thermal tolerance [1], but also modifies innate immune responses with potential adverse consequences [2]. While male and female mice are known to respond differently to acute exposure to severe hyperthermia, sex-based differences in responses to chronic moderate heat exposure have not been reported. The major objective of this study was to compare the tolerance of male and female mice for chronic heat exposure.Materials and methods: We used a mouse model of 5-day moderate heat exposure (ambient temperature ∼37°C) to compare the physiological and cellular heat shock response in male and female mice. Core temperature, heart rate, and activity were monitored telemetrically and heat shock protein levels were measured in brain and lung by western blotting.Results: Adult CD-1 female mice maintained a 1.2°C lower core temperature (38.31 ± 0.64 versus 39.51 ± 0.72°C; p = 0.002), experienced less weight loss (1.54 ± 0.45 versus 4.54 ± 1.97 g; p = 0.0007), and had improved survival (16/16 survived versus 13/21, p < 0.006) than male mice of the same age. After 5 days of moderate heat exposure Hsp72 levels in brain and lung increased 2.1-fold (p = 0.007) and 5-fold (p = 0.048) in male mice compared with 1.3- (p = 0.054) and 1.5-fold (p = 0.134) in female mice.Conclusions: This study reveals previously unknown and potentially important differences between male and female mice in physiological and cellular responses to chronic heat exposure, which had consequences for survival. Future studies may identify biomarkers of differential heat tolerance and treatments to improve heat tolerance in humans.

Skin surface temperature of broiler chickens is correlated to body core temperature and is indicative of their thermoregulatory status

Extreme thermal conditions may dramatically affect the performance of broilers and other domestic animals, thereby impairing animal welfare and causing economic losses. Although body core temperature is the parameter that best reflects a bird's thermal status, practical and physiological obstacles make it irrelevant as a source of information on the thermal status of commercial flocks. Advances in the technology of infrared thermal imaging have enabled highly accurate, noncontact, and noninvasive measurements of skin surface temperature. Providing that skin surface temperature correlates with body temperature, this technology could enable acquisition of reliable information on the thermal status of animals, thereby improving diagnoses of environmental stress in a flock. This study of broiler chickens found a strong positive correlation between body core temperature and facial surface temperature, as recorded by infrared thermal imaging. The correlation was equally strong at all ages from 8 to 36 d during exposure to acute heat stress with or without proper ventilation and after acclimation to chronic heat exposure. A similar correlation was found by measurements in commercial flocks of broilers. Measurements of blood plasma concentrations of corticosterone, thyroid hormones, and arginine vasotocin confirmed that metabolic activity was low after acclimation to chronic exposure to heat, whereas ventilation was at least as efficient as acclimation in reducing thermal stress but did not impair metabolism. In light of these novel results, commercial benefits of infrared thermal imaging technology are suggested, especially in climate control for commercial poultry flocks. The application of this technique to other domestic animals should be investigated in future experiments.

Effects of dietary supplementation of methionine and its hydroxy analog dl-2-hydroxy-4-methylthiobutanoic acid on growth performance, plasma hormone levels, and the redox status of broiler chickens exposed to high temperatures

Heat stress is known to impair performance and to induce oxidative stress in poultry. The aim of the present study was to compare the effects of dietary supplementation of dl-methionine (dl-M) or the synthetic analog 2-hydroxy-4-methylthiobutanoic acid (dl-HMTBA) on broiler growth performance, plasma hormone levels, and some oxidative stress-related parameters under conditions of chronic exposure to high temperatures (HT). From 2 to 6 wk of age, male broiler chickens were reared under either a constant temperature of 32°C until 6 wk of age or a normal temperature scheme (gradual decrease to 18°C at 5 wk of age). Chicks in both the normal and HT treatments were provided with a commercial grower diet supplemented with either 1.0 or 1.2 g/kg of dl-M or 1.0 or 1.2 g/kg of dl-HMTBA. Because there were no effects of supplement dose, data were pooled over both doses within each temperature treatment. The chronic HT treatment impaired feed intake and BW gain, but these negative effects were less pronounced when the chickens received dl-HMTBA. Exposure to HT was also associated with decreased (P < 0.001) plasma thyroid hormones and increased (P < 0.0001) plasma corticosterone levels. At 4 wk of age, and irrespective of the supplemental source, chickens subjected to HT were characterized by significantly lower plasma TBA-reactive substance levels. In contrast, at 6 wk of age, plasma TBA-reactive substance levels were significantly increased by HT, but this effect was observed only for the chickens receiving dl-M and not for those receiving dl-HMTBA. High temperatures induced a significant increase in hepatic total glutathione (GSH) and oxidized GSH levels, regardless of the supplemental source. However, the hepatic ratios of reduced GSH to total GSH and reduced GSH to oxidized GSH were highest in chickens supplemented with dl-HMTBA. In conclusion, dl-HMTBA supplementation partially prevented the growth-depressing effects of chronic heat exposure compared with dl-M supplementation. It can be inferred that dl-HMTBA is more efficient in alleviating HT-induced oxidative damage because of a more favorable reduced GSH-to-total GSH ratio.

Physiological responses to chronic heat exposure in an aging non-human primate species, the gray mouse lemur ( Microcebus murinus)

Epidemiological evidence related to increased death from hyperthermia suggests higher frailty in the elderly when exposed to high ambient temperatures. Despite the recent awareness of such public health problems, integrative studies investigating the effects of age on the physiological responses to heat wave thermal conditions remain scarce. Daily rhythmicity of core temperature (T c) and locomotor activity (LA), as well as parameters representative of energy balance and IGF-1 levels which are involved in the aging process and stress resistance, were monitored in a non-human primate species, the gray mouse lemur ( Microcebus murinus). Adult and aged animals, acclimated to long days (LD) or short days (SD), were monitored during 8-day periods of exposure to 25 °C and 34 °C. Adult animals displayed efficient coping with heat exposure, regardless of the photoperiod. Hence, efficient responses resulted in decrease of energy intake, energy expenditure, IGF-1 levels and LA levels, promoting hyperthermia avoidance. Positive energy balance was maintained and water turnover did not change significantly after heat exposure. In contrast, while aged animals acclimated to LD responded similarly to adults, aged mouse lemurs acclimated to SD showed great difficulties coping with heat exposure. Indeed, in this group, normothermia impairment was associated with increased T c levels, alterations in daily rhythmicity, negative energy balance and increased IGF-1 levels. Impaired responses to heat exposure were seen in aged mouse lemurs acclimated to SD only. The main effects were observed during diurnal resting periods, suggesting decreased capacities with age to dissipate excess body heat. Taken together, these data highlight daily rhythmicity and IGF-1 pathway as main targets in the impaired response to heat exposure in the elderly.

Expression analysis of global gene response to chronic heat exposure in broiler chickens (Gallus gallus) reveals new reactive genes

The process of heat regulation is complex and the exact molecular mechanism is not fully understood. To investigate the global gene response to chronic heat exposure, a breast muscle cDNA library and a liver tissue cDNA library from Silkie fowl were constructed and analyzed in bioinformatics. A total of 8,935 nonredundant EST were identified from and used for gene expression analysis. Microarray assay revealed that in breast muscle of broiler chickens (Gallus gallus), 110 genes changed expression levels after 3 wk of cycling heat stress. Ubiquitin B (UBB); ubiquitin C (UBC); tumor necrosis factor receptor-associated factor 3-interacting Jun amino-terminal kinase activating modulator (TRAF3IP3); eukaryotic translation initiation factor 3, subunit 6 (EIF3S6); poly(A) binding protein, cytoplasmic 1 (PABPC1); and F-box only protein 11 (FBXO11) were the only genes that have been reported to be involved in heat regulation; the majority of the other genes were shown to be related for the first time. The finding of new heat-reactive genes [mitogen-activated protein kinase activating protein PM20/PM21; suppressors of cytokine signaling (SOCS) box-containing protein 2 (ASB2); ubiquitin-specific proteinase 45 (USP45); and TRK-fused gene (TFG)] suggests that the mitogen-activated protein kinase pathways as well as the ubiquitin-proteasome pathways and the nuclear factor κB pathways play important roles in heat regulation. This study provides new information on the regulation of heat stress, though the mechanism is far from being understood. Further in-depth research on the newly discovered heat-reactive genes is required to fully understand their molecular functions in thermoregulation.

Effects of chronic heat exposure on drug metabolism in the rat.

Effects of chronic heat exposure on drug metabolism in the rat.

L’acclimatation embryonnaire : une technique innovante pour limiter les mortalités liées au stress thermique chez le poulet

Les poulets à croissance rapide sont sensibles à la chaleur en période de finition. En effet, leur sélection pour la croissance a favorisé la masse musculaire au détriment d’organes impliqués dans la thermorégulation. Ceci peut se traduire par des baisses de performances en cas de chaleur modérée et chronique,&amp;nbsp;mais également des problèmes de bien-être et des mortalités lors d’un coup de chaleur. Durant la dernière décennie les efforts ont porté sur l’acclimatation à la chaleur pendant la période périnatale, notamment pendant l’embryogenèse. Cette stratégie nécessite de mettre au point les conditions d’incubation (température, phase de l’embryogenèse, durée d’exposition…) qui favorisent la thermotolérance jusqu’en finition. Les conséquences sur les performances des poulets (croissance, qualité de viande…) sont évaluées. L’acclimatation périnatale met en jeu des mécanismes de régulation épigénétiques qui modulent à long terme la température interne des volailles. A terme, si cette technique se révélait applicable à grande échelle, elle pourrait favoriser la robustesse et le bien-être des volailles face aux variations de températures, tout en préservant leurs performances zootechniques. Dans cet article, sont rappelés les principales techniques d’exposition thermique embryonnaire et les fondements physiologiques de leur mise en œuvre. Sont évoquées ensuite les voies de recherche concernant la compréhension des mécanismes mis en jeu et l’intérêt potentiel de cette technique pour la filière avicole.

Time course of ROS production in skeletal muscle mitochondria from chronic heat-exposed broiler chicken

This study was designed to elucidate physiological changes of skeletal muscle mitochondria from broiler chickens ( Gallus gallus) during chronic heat exposure. Chickens (19-day-old) were exposed to either constant heat stress (34 °C) or kept at control temperature (24 °C) for 14 days. Mitochondrial ROS production for control group showed little changes during the experimental periods, whereas that for the heat-stressed group was increased after 3, 5 and 9 days of heat exposure and returned to original levels at day 14. Mitochondrial membrane potential in state 4 for heat-stressed birds was higher than those of control birds after 3 and 5 days, but was not at day 14. Mitochondrial oxygen consumption rate in state 3 was increased after 3 and 5 days, and also returned to original levels by day 14. These results suggest that chronic heat stress induces increased ROS production in skeletal muscle mitochondria, probably via elevation of the membrane potential in state 4, resulting from enhanced oxygen consumption in the initial stage of heat exposure. These physiological changes were no longer observed at day 14, possibly because the animals had acclimatized to environmental heat stress.

Metabolic characteristics and oxidative damage to skeletal muscle in broiler chickens exposed to chronic heat stress

Emerging evidence has shown that acute heat exposure affects metabolic characteristics and causes oxidative damage to skeletal muscle in birds. Little is known, however, about such phenomena under chronic heat stress conditions. To address this, we designed the present study to determine the influence of cyclic (32 to 24 to 32 °C: 32 °C for 8 h/d, 32–24–32HS ), and constant (32 and 34 °C, 32HS and 34HS, respectively) heat exposure on the metabolic and peroxide status in skeletal muscle of 4-wk-old male broiler chickens. Heat stress, particularly in the 32HS and 34HS groups, depressed feed intake and growth, while cyclic high temperature gave rise to a less severe stress response in performance terms. Malondialdehyde (MDA) levels in skeletal muscle were enhanced ( P < 0.05) by constant heat treatment; the degree of enhancement was not as large as the changes observed in our previous ‘acute’ heat stress model. The 3HADH (3-hydroxyacyl CoA dehydrogenase related to fatty acid oxidation) and CS (citrate synthase) enzyme activities were lowered ( P < 0.05) by both the cyclic and constant 34HS treatments, and constant 34HS group, respectively. These results suggest that chronic heat exposure decreases metabolic oxidation capacity in skeletal muscle of broiler chickens. On exposure to chronic heat stress, GPx activity remained relatively constant, though a temperature-dependent elevation in Cu/Zn-SOD activity was observed, implying that anti-oxidation ability was disturbed by the chronic stress condition. From these results it can be concluded that chronic heat stress did not induce oxidative damage to a major extent. This may probably be due to a decrease in metabolic oxidation capacity or due to a self-propagating scavenging system, though the system was not fully activated.

A Selected History of Exercise Thermoregulation: A Century of Discovery 1910‐2010

Exercise is a tremendous challenge for homeostasis. It was known that body temperature increases with exercise (Haldane and Hunt, 1905), but not appreciated until 1938 that core temperature is controlled (M. Nielsen), and at a level proportional to relative exertion (Astrand 1960). A debate ensued whether core or peripheral temperature regulated thermoregulatory responses. This was settled when Benzinger (1959) demonstrated that intracranial temperature most closely corresponds to sweating and skin blood flow during exercise. Lind (1963) identified a "prescriptive zone", where core temperature is not affected by ambient conditions. The importance of heat acclimation on work capacity was described by Dresoti (1935) and applied to soldiers by Robinson (1943) and miners by Wyndham (1966). The effect of hydration was studied by Pitts (1940's) and the cardiovascular and body fluid effects were graphically illustrated during desert walking by Adolf (1947) and Dill (1972). Recent studies have challenged the concept of Hunt (1912) that water ingestion is the best method to restore fluid balance during work in the heat. A new fascinating area is to understand cellular responses during acute (Salo 1991, Ryan 1991) and chronic (Horowitz 1997, Yamada 2007, McClung 2008) heat exposure and the consequences for tolerance to other environmental and disease stressors.

EEG power spectrum and neural network based sleep-hypnogram analysis for a model of heat stress

An effective application of back- propagation artificial neural network (ANN) in preparation of sleep-hypnogram based on electroencephalogram (EEG) power spectra under acute as well as chronic heat stress has been presented. Rats were divided in three groups (i) acute heat stress-subjected to a single exposure for four hours at 38 degrees C; (ii) chronic heat stress-exposed for 21 days daily for one hour at 38 degrees C, and (iii) handling control groups. The preprocessed EEG signals were fragmented in two-second artifact free epochs for calculation of power spectra, training and testing of ANN. The power spectrum analyses of EEG show that changes in higher frequency components (beta(2)) were significant in all sleep-wake states following both acute and chronic heat stress conditions. The power of beta(2) activity after acute heat exposure was significantly decreased during SWS (slow wave sleep) (P < 0.05) and REM (rapid eye movement) sleep (P < 0.05), while reverse was observed in AWA (awake state) (P < 0.05). Following chronic heat exposure, beta(2) activity was found increased in all three sleep-wake stages (P < 0.05). The ANN used for sleep-hypnogram preparation contains 64 nodes in input layer, weighted from power spectrum data from 0 to 32 Hz, 14 nodes in hidden layer and 3 output nodes. The results obtained from the study, suggest increased sleep efficiency following acute exposure to heat stress while fragmented sleep with decreased sleep efficiency following chronic heat stress. The ANN can be used for the analysis of stressful events by calculating the sleep-EEG alterations.

Acute cold‐ and chronic heat‐exposure upregulate hepatic leptin and muscle uncoupling protein (UCP) gene expression in broiler chickens

Emerging evidence showed that variations in environmental temperature affect both leptin and uncoupling protein (UCP) gene expression in mammals, whereas a little is known about such interactions in birds. Thus, we conducted the present study to investigate the influence of acute (2 hours) cold (4 degrees C) and chronic (10 days) heat (32 degrees C) exposure on hepatic leptin and muscle UCP gene expression in 5-wk-old broiler chickens. Both cold- and heat-exposure significantly (P < 0.05 to P < 0.001) upregulated hepatic leptin (by 35 and 46%, respectively) and muscle UCP mRNA levels (by 71 and 71%, respectively) compared to the thermoneutrality (22 degrees C). This result suggests that leptin and UCP may be involved in the thermoregulation response of chickens to extreme climate (cold and hot temperatures). The upregulation of hepatic leptin gene expression was accompanied by an increase in plasma leptin levels, indicating that leptin may be regulated at transcriptional level. The increase of leptin and UCP mRNA abundance, and leptinemia we report here were not related to plasma glucose or insulin levels. In conclusion, the exposure of broiler chickens to extreme ambient temperatures (cold and heat) increases hepatic leptin and muscle UCP gene expression.