Physiology of temperature regulation: comparative aspects

Commentary: The microbial dependence continuum: Towards a comparative physiology approach to understand host reliance on microbes

Comparative physiologists often compare physiological traits across organisms to understand the selective pressures influencing their evolution in different environments. Traditionally focused on the organisms themselves, comparative physiology has more recently incorporated studies of the microbiome-the communities of microbes living in and on animals that influence host physiology. In this commentary, we describe the utility of applying a comparative framework to study the microbiome, particularly in understanding how hosts vary in their dependence on microbial communities for physiological function, a concept we term the "microbial dependence continuum". This hypothesis suggests that hosts exist on a spectrum ranging from high to low reliance on their microbiota. Certain physiological traits may be highly dependent on microbes for proper function in some species but microbially independent in others. Comparative physiology can elucidate the selective pressures driving species along this continuum. Here, we discuss the microbial dependence continuum in detail and how comparative physiology can be useful to study it. Then, we discuss two example traits, herbivory and flight, where comparative physiology has helped reveal the selective pressures influencing host dependence on microbial communities. Lastly, we discuss useful experimental approaches for studying the microbial dependence continuum in a comparative physiology context.

Temperature-dependent exercise recovery is not associated with behavioral thermoregulation in a salmonid fish

The relationship between behavioral thermoregulation and physiological recovery following exhaustive exercise is not well understood. Behavioral thermoregulation could be beneficial for exercise recovery; for example, selection of cooler temperatures could reduce maintenance metabolic cost to preserve aerobic scope for recovery cost, or selection of warmer temperatures could accelerate recovery of exercise metabolites. While post-exercise behavioral thermoregulation has been observed in lizards and frogs, little is known about its importance in fish. We examined the influence of post-exercise recovery temperature on metabolic rate, thermal preference, and metabolite concentrations in juvenile brook char (Salvelinus fontinalis). Fish were acclimated to and exercised at 15 °C, then recovered at either 15 °C or 10 °C while their metabolic rate was measured via respirometry. Metabolite concentrations were measured in fish after exercise at 15 °C and recovery under one of three thermal treatments (to simulate various behavioral thermoregulation scenarios): (i) 6 h recovery at 15 °C, (ii) 6 h recovery at 10 °C, or (iii) 3 h recovery at 10 °C followed by 3 h recovery at 15 °C. Thermal preference was quantified using a static temperature preference system (15 °C vs. 10 °C). Metabolic rates returned to resting faster at 10 °C compared with 15 °C, although at 10 °C there was a tradeoff of delayed metabolite recovery. Specifically, post-exercise plasma osmolality, plasma lactate, and muscle lactate remained elevated for the entire period in fish recovering at 10 °C, whereas these parameters returned to resting levels by 6 h in fish from the other two recovery groups. Regardless, fish did not exhibit clear behavioral thermoregulation (i.e., fish overall did not consistently prefer one temperature) to prioritize either physiological recovery process. The advantage of metabolic rate recovery at cooler temperatures may balance against the advantage of metabolite recovery at warmer temperatures, lessening the usefulness of behavioral thermoregulation as a post-exercise recovery strategy in fish.

Thermal tolerance for the tropical clawed frog, Xenopus tropicalis with comments on comparative methods for amphibian studies

Thermal tolerance data are important for identifying the potential range of non-native species following introduction and establishment. Such data are particularly important for understanding invasion risks of tropical species introduced to temperate climates and identifying whether they can survive outside tropical regions. A breeding population of the tropical clawed frog (Xenopus tropicalis) was recently discovered in west-central Florida, U.S.A. This fully aquatic species is native to the rainforest belt of west Africa and has not been documented outside its native range. Because of the lack of invasion history, data are sparse on the thermal limits for this species. We used chronic lethal and critical thermal methodologies to investigate thermal tolerance on adult stages and critical thermal methods on tadpoles. Because of our use of both chronic and critical methodologies, we also examined the literature to reveal common methods used to investigate thermal minimum and maximum temperature in amphibians, which were found to be dominated by the critical maximum. Chronic lethal temperatures for adult X. tropicalis were 9.73 °C and 36.68 °C. Critical temperatures were affected by acclimation temperature and life stage; adults were more tolerant of extreme temperatures. Based on these critical thermal data and the fact that breeding tends to occur when temperatures are suitable for survival, tadpole stages are unlikely to be affected by extreme temperatures. Instead, range expansion in Florida will likely be limited by the adult stages. Our findings indicate that the tropical clawed frog could occupy much of southern Peninsular Florida and other tropical and subtropical regions worldwide.

Mitochondrial function in skeletal muscle contributes to reproductive endothermy in tegu lizards (Salvator merianae)

AIM

In cyclic climate variations, including seasonal changes, many animals regulate their energy demands to overcome critical transitory moments, restricting their high-demand activities to phases of resource abundance, enabling rapid growth and reproduction. Tegu lizards (Salvator merianae) are ectotherms with a robust annual cycle, being active during summer, hibernating during winter, and presenting a remarkable endothermy during reproduction in spring. Here, we evaluated whether changes in mitochondrial respiratory physiology in skeletal muscle could serve as a mechanism for the increased thermogenesis observed during the tegu's reproductive endothermy.

METHODS

We performed high-resolution respirometry and calorimetry in permeabilized red and white muscle fibers, sampled during summer (activity) and spring (high activity and reproduction), in association with citrate synthase measurements.

RESULTS

During spring, the muscle fibers exhibited increased oxidative phosphorylation. They also enhanced uncoupled respiration and heat production via adenine nucleotide translocase (ANT), but not via uncoupling proteins (UCP). Citrate synthase activity was higher during the spring, suggesting greater mitochondrial density compared to the summer. These findings were consistent across both sexes and muscle types (red and white).

CONCLUSION

The current results highlight potential cellular thermogenic mechanisms in an ectothermic reptile that contribute to transient endothermy. Our study indicates that the unique feature of transitioning to endothermy through nonshivering thermogenesis during the reproductive phase may be facilitated by higher mitochondrial density, function, and uncoupling within the skeletal muscle. This knowledge contributes significant elements to the broader picture of models for the evolution of endothermy, particularly in relation to the enhancement of aerobic capacity.

Behavioral responses during sickness in amphibians and reptiles: Concepts, experimental design, and implications for field studies

In ectothermic vertebrates, behavioral fever, where an individual actively seeks warmer areas, seems to be a primary response to pathogens. This is considered a broad and evolutionarily conserved response among vertebrates. Recent population declines in amphibians are associated with an increase of infectious disease driven largely by climate change, habitat degradation, and pollution. Immediate action through research is required to better understand and inform conservation efforts. The literature available, does not provide unifying concepts that can guide adequate experimental protocols and interpretation of data, especially when studying animals in the field. The aim of this review is to promote common understanding of terminology and facilitating improved comprehension and application of key concepts about the occurrence of both sickness behavior or behavioral fever in ectothermic vertebrates. We start with a conceptual synthesis of sickness behavior and behavioral fever, with examples in different taxa. Through this discussion we present possible paths to standardize terminology, starting from original use in endothermic tetrapods which was expanded to ectothermic vertebrates, particularly amphibians and reptiles. This conceptual expansion from humans (endothermic vertebrates) and then to ectothermic counterparts, gravitates around the concept of 'normality'. Thus, following this discussion, we highlight caveats with experimental protocols and state the need of a reference value considered normal (RVCN), which is different from experimental control and make recommendations regarding experimental procedures and stress the value of detailed documentation of behavioral responses. We also propose some future directions that could enhance interaction among disciplines, emphasizing relationships at different levels of biological organization. This is crucial given the increasing convergence of fields such as thermal physiology, immunology, and animal behavior due to emerging diseases and other global crises impacting biodiversity.

Integrating behavioural thermoregulatory strategy into the animal personality framework using the common lizard, Zootoca vivipara as a model

The study of consistent between-individual behavioural variation in single (animal personality) and across two or more behavioural traits (behavioural syndrome) is a central topic of behavioural ecology. Besides behavioural type (individual mean behaviour), behavioural predictability (environment-independent within-individual behavioural variation) is now also seen as an important component of individual behavioural strategy. Research focus is still on the 'Big Five' traits (activity, exploration, risk-taking, sociability and aggression), but another prime candidate to integrate to the personality framework is behavioural thermoregulation in small-bodied poikilotherms. Here, we found animal personality in thermoregulatory strategy (selected body temperature, voluntary thermal maximum, setpoint range) and 'classic' behavioural traits (activity, sheltering, risk-taking) in common lizards (Zootoca vivipara). Individual state did not explain the between-individual variation. There was a positive behavioural type-behavioural predictability correlation in selected body temperature. Besides an activity-risk-taking syndrome, we also found a risk-taking-selected body temperature syndrome. Our results suggest that animal personality and behavioural syndrome are present in common lizards, both including thermoregulatory and 'classic' behavioural traits, and selecting high body temperature with high predictability is part of the risk-prone behavioural strategy. We propose that thermoregulatory behaviour should be considered with equal weight to the 'classic' traits in animal personality studies of poikilotherms employing active behavioural thermoregulation.

Flight or fight: different strategies of intertidal periwinkle Littoraria sinensis coping with high temperature across populations

Intertidal organisms usually live near their upper thermal limits, and are vulnerable to future global warming. As a vital response to thermal stress, thermoregulatory strategy in physiological and behavioral performance is essential for organisms coping with thermal stress and surviving the changing world. To investigate the relationship between the thermoregulatory strategy and habitat temperature, in the present study, we comparatively investigated the thermal responsive strategy among different geographic populations of the supralittoral snail Littoraria sinensis by determining snails' cardiac function and behavioral performance. Our results indicated that populations inhabiting high ambient temperatures had higher sublethal temperatures (i.e. Arrhenius breakpoint temperatures, ABTs, the temperature at which the heart rate shapely decreases with further heating) and lethal temperatures (i.e. Flatline temperatures, FLTs, the temperature at which heart rate ceases), and behaved less actively (e.g. shorter moving distances and shorter moving time) in the face of high and rising temperatures-a physiological fight strategy. On the other hand, populations at relatively low ambient temperatures had relatively lower physiological upper thermal limits with lower ABTs and FLTs and moved more actively in the face of high and rising temperatures-a behavioral flight strategy. These results demonstrate that the thermoregulatory strategies of the snails are closely related to their habitat temperatures and are different among populations surviving divergent thermal environments.

INTERPLAY BETWEEN BRAIN OXYGENATION AND THE DEVELOPMENT OF HYPOTHERMIA IN ENDOTOXIC SHOCK

ABSTRACT

There is evidence to suggest that the hypothermia observed in the most severe cases of systemic inflammation or sepsis is a regulated response with potential adaptive value, but the mechanisms involved are poorly understood. Here, we investigated the interplay between brain oxygenation (assessed by tissue P o2 ) and the development of hypothermia in unanesthetized rats challenged with a hypotension-inducing dose of bacterial LPS (1 mg/kg i.v.). At an ambient temperature of 22°C, oxygen consumption (V̇O 2 ) began to fall only a few minutes after the LPS injection, and this suppression in metabolic rate preceded the decrease in core temperature. No reduction in brain P o2 was observed prior to the development of the hypometabolic, hypothermic response, ruling out the possibility that brain hypoxia served as a trigger for hypothermia in this model. Brain P o2 was even increased. Such an improvement in brain oxygenation could reflect either an increased O 2 delivery or a decreased O 2 consumption. The former explanation seems unlikely because blood flow (cardiac output) was being progressively decreased during the recording period. On the other hand, the decrease in V̇O 2 usually preceded the rise in P o2 , and an inverse correlation between V̇O 2 and brain P o2 was consistently observed. These findings do not support the existence of a closed-loop feedback relationship between brain oxygenation and hypothermia in systemic inflammation. The data are consistent with a feedforward mechanism in which hypothermia is triggered (possibly by cryogenic inflammatory mediators) in anticipation of changes in brain oxygenation to prevent the development of tissue hypoxia.

Exercise derived myokine irisin as mediator of cardiorespiratory, metabolic and thermal adjustments during central and peripheral chemoreflex activation

Exercise elicits physiological adaptations, including hyperpnea. However, the mechanisms underlying exercise-induced hyperpnea remain unresolved. Skeletal muscle acts as a secretory organ, releasing irisin (IR) during exercise. Irisin can cross the blood-brain barrier, influencing muscle and tissue metabolism, as well as signaling in the central nervous system (CNS). We evaluated the effect of intracerebroventricular or intraperitoneal injection of IR in adult male rats on the cardiorespiratory and metabolic function during sleep-wake cycle under room air, hypercapnia and hypoxia. Central IR injection caused an inhibition on ventilation (VE) during wakefulness under normoxia, while peripheral IR reduced VE during sleep. Additionally, central IR exacerbates hypercapnic hyperventilation by increasing VE and reducing oxygen consumption. As to cardiovascular regulation, central IR caused an increase in heart rate (HR) across all conditions, while no change was observed following peripheral administration. Finally, central IR attenuated the hypoxia-induced regulated hypothermia and increase sleep episodes, while peripheral IR augmented CO2-induced hypothermia, during wakefulness. Overall, our results suggest that IR act mostly on CNS exerting an inhibitory effect on breathing under resting conditions, while stimulating the hypercapnic ventilatory response and increasing HR. Therefore, IR seems not to be responsible for the exercise-induced hyperpnea, but contributes to the increase in HR.

Sublingual Misoprostol-Induced Rhabdomyolysis and Convulsions in Postpartum Hemorrhage: A Case Report and Literature Review

Postpartum hemorrhage (PPH) remains the leading cause of maternal mortality, primarily attributed to uterine atony. Both the World Health Organization (WHO) and the International Federation of Gynecology and Obstetrics (FIGO) endorse the use of misoprostol not only for the prevention but also for the treatment of PPH. However, the administration of misoprostol is commonly associated with transient pyrexia, attributed to a shift in the hypothalamic set point observed in certain animal studies. Misoprostol-induced hyperpyrexia can occasionally manifest with a prodrome of shivering, particularly when administered via the sublingual route, which achieves a higher and faster maximum plasma concentration compared to vaginal and rectal routes. General management strategies to reduce fever involve removing clothing and blankets, applying cool compresses, administering oral acetaminophen, and ensuring adequate hydration. While some cases have reported misoprostol-induced convulsions, hyperpyrexia leading to convulsions and subsequent rhabdomyolysis is a rare and potentially lethal side effect. In this case presentation, we emphasize a scenario where misoprostol was employed for the treatment of PPH but led to rhabdomyolysis. Our goal is to highlight the side effects of misoprostol and the significance of considering the initial combination of misoprostol with anti-pyretic management to minimize the risk of hyperthermia-related side effects and prevent additional severe complications.

Lectin binding to pectoral fin of neonate little skates reared under ambient and projected-end-of-century temperature regimes

The glycosylation of macromolecules can vary both among tissue structural components and by adverse conditions, potentially providing an alternative marker of stress in organisms. Lectins are proteins that bind carbohydrate moieties and lectin histochemistry is a common method to visualize microstructures in biological specimens and diagnose pathophysiological states in human tissues known to alter glycan profiles. However, this technique is not commonly used to assess broad-spectrum changes in cellular glycosylation in response to environmental stressors. In addition, the binding of various lectins has not been studied in elasmobranchs (sharks, skates, and rays). We surveyed the binding tissue structure specificity of 14 plant-derived lectins, using both immunoblotting and immunofluorescence, in the pectoral fins of neonate little skates (Leucoraja erinacea). Skates were reared under present-day or elevated (+5°C above ambient) temperature regimes and evaluated for lectin binding as an indicator of changing cellular glycosylation and tissue structure. Lectin labeling was highly tissue and microstructure specific. Dot blots revealed no significant changes in lectin binding between temperature regimes. In addition, lectins only detected in the elevated temperature treatment were Canavalia ensiformis lectin (Concanavalin A) in spindle cells of muscle and Ricinus communis agglutinin in muscle capillaries. These results provide a reference for lectin labeling in elasmobranch tissue that may aid future investigations.

Role of Zhiqiao Chuanlian decoction in the treatment of food accumulation fever: Network pharmacology and animal experiments

Objective

Food accumulation fever (FAF), a common clinical disease in children, is generally induced by the excessive intake of high-calorie or high-fat foods. Zhiqiao Chuanlian decoction (ZQCLD) is a classical traditional Chinese medicine (TCM) that may have therapeutic effects on FAF.

Methods

Network pharmacological analyses of ZQCLD and FAF were conducted. Animal experiments lasted for 14 days. Rats in the model, positive control, and low-, medium-, and high-dose groups were fed a high-calorie diet. On days 11-14, the positive group was given a domperidone solution. The low-, medium-, and high-dose groups were administered different concentrations of ZQCLD. The body temperature, gastric emptying rate, and intestinal propulsion rate were measured. Relevant indicators were determined by ELISA.

Results

The main target proteins included IL-1β, C-C motif chemokine 2 (CCL2), prostaglandin G/H synthase 2 (PTGS2), transcription factor AP-1 (JUN), haem oxygenase 1 (HMOX1), interferon-gamma (IFN-γ), peroxisome proliferator-activated receptor-gamma (PPAR-γ), and inducible nitric oxide synthase (NOS2/iNOS). Compared with those in the control group, body weight, gastric emptying rate, intestinal propulsion rate, and neuronal nitric oxide synthase (NOS1/nNOS) levels were significantly lower in the model group, whereas body temperature and endotoxin, interleukin-1β (IL-1β), PGE2, and iNOS levels were increased. In each treatment group, body temperature and PGE2 levels returned to normal levels. Compared with those in the model group, the gastric emptying rates in the positive group and the low- and medium-dose groups increased; the intestinal propulsion rates were higher in the medium- and high-dose groups, whereas the endotoxin and IL-1β levels were lower; and the nNOS level was higher in the high-dose group, whereas the iNOS level was lower.

Conclusions

ZQCLD may treat FAF by regulating jejunal IL-1β and nNOS, serum endotoxin, and hypothalamic PGE2 and iNOS levels.

How seasonality influences the thermal biology of lizards with different thermoregulatory strategies: a meta-analysis

Ectotherms that maintain thermal balance in the face of varying climates should be able to colonise a wide range of habitats. In lizards, thermoregulation usually appears as a variety of behaviours that buffer external influences over physiology. Basking species rely on solar radiation to raise body temperatures and usually show high thermoregulatory precision. By contrast, species that do not bask are often constrained by climatic conditions in their habitats, thus having lower thermoregulatory precision. While much focus has been given to the effects of mean habitat temperatures, relatively less is known about how seasonality affects the thermal biology of lizards on a macroecological scale. Considering the current climate crisis, assessing how lizards cope with temporal variations in environmental temperature is essential to understand better how these organisms will fare under climate change. Activity body temperatures (Tb ) represent the internal temperature of an animal measured in nature during its active period (i.e. realised thermal niche), and preferred body temperatures (Tpref ) are those selected by an animal in a laboratory thermal gradient that lacks thermoregulatory costs (i.e. fundamental thermal niche). Both traits form the bulk of thermal ecology research and are often studied in the context of seasonality. In this study, we used a meta-analysis to test how environmental temperature seasonality influences the seasonal variation in the Tb and Tpref of lizards that differ in thermoregulatory strategy (basking versus non-basking). Based on 333 effect sizes from 137 species, we found that Tb varied over a greater magnitude than Tpref across seasons. Variations in Tb were not influenced by environmental temperature seasonality; however, body size and thermoregulatory strategy mediated Tb responses. Specifically, larger species were subjected to greater seasonal variations in Tb , and basking species endured greater seasonal variations in Tb compared to non-basking species. On the other hand, the seasonal variation in Tpref increased with environmental temperature seasonality regardless of body size. Thermoregulatory strategy also influenced Tpref , suggesting that behaviour has an important role in mediating Tpref responses to seasonal variations in the thermal landscape. After controlling for phylogenetic effects, we showed that Tb and Tpref varied significantly across lizard families. Taken together, our results support the notion that the relationship between thermal biology responses and climatic parameters can be taxon and trait dependent. Our results also showcase the importance of considering ecological and behavioural aspects in macroecological studies. We further highlight current systematic, geographical, and knowledge gaps in thermal ecology research. Our work should benefit those who aim to understand more fully how seasonality shapes thermal biology in lizards, ultimately contributing to the goal of elucidating the evolution of temperature-sensitive traits in ectotherms.

Spatiotemporal Niche Separation among Passeriformes in the Halla Mountain Wetland of Jeju, Republic of Korea: Insights from Camera Trap Data

This study analyzed 5322 camera trap photographs from Halla Mountain Wetland, documenting 1427 independent bird sightings of 26 families and 49 species of Passeriformes. Key observations include morning activities in Cyanoptila cyanomelana and Horornis canturians and afternoon activity in Muscicapa dauurica and Phoenicurus auroreus. Wetlands were significantly preferred (P_i = 0.398) despite their smaller area, contrasting with underutilized grasslands (P_i = 0.181). Seasonal activity variations were notable, with overlap coefficients ranging from 0.08 to 0.81 across species, indicating diverse strategies in resource utilization and thermoregulation. Population density was found to be a critical factor in habitat usage, with high-density species showing more consistent activity patterns. The study's results demonstrate the ecological adaptability of Passeriformes in the Halla Mountain Wetland while highlighting the limitations of camera trapping methods. These limitations include their fixed field of view and intermittent recording capability, which may not fully capture the spectrum of complex avian behaviors. This research underlines the need for future studies integrating various methodologies, such as direct observation and acoustic monitoring, to gain a more comprehensive understanding of avian ecology.

Thermosensation and Temperature Preference: From Molecules to Neuronal Circuits in Drosophila

Temperature has a significant effect on all physiological processes of animals. Suitable temperatures promote responsiveness, movement, metabolism, growth, and reproduction in animals, whereas extreme temperatures can cause injury or even death. Thus, thermosensation is important for survival in all animals. However, mechanisms regulating thermosensation remain unexplored, mostly because of the complexity of mammalian neural circuits. The fruit fly Drosophila melanogaster achieves a desirable body temperature through ambient temperature fluctuations, sunlight exposure, and behavioral strategies. The availability of extensive genetic tools and resources for studying Drosophila have enabled scientists to unravel the mechanisms underlying their temperature preference. Over the past 20 years, Drosophila has become an ideal model for studying temperature-related genes and circuits. This review provides a comprehensive overview of our current understanding of thermosensation and temperature preference in Drosophila. It encompasses various aspects, such as the mechanisms by which flies sense temperature, the effects of internal and external factors on temperature preference, and the adaptive strategies employed by flies in extreme-temperature environments. Understanding the regulating mechanisms of thermosensation and temperature preference in Drosophila can provide fundamental insights into the underlying molecular and neural mechanisms that control body temperature and temperature-related behavioral changes in other animals.

Seasonal Variation in the Thermoregulation Pattern of an Insular Agamid Lizard

Ectotherms, including lizards, rely on behavioral thermoregulation to maintain their body temperature within an optimal range. The benign climate of islands is expected to favor the thermoregulation efficiency of reptiles throughout their activity period. In this study, we investigated the seasonal variation in thermoregulation in an insular population of the roughtail rock agama (Laudakia stellio) on Naxos Island, Greece. We measured body, operative, and preferred temperatures across three seasons (spring, summer, and autumn), and we evaluated the effectiveness of thermoregulation, using the Hertz index (E). Our results revealed that the effectiveness of thermoregulation was significantly influenced by seasonality. E was quite high in summer (0.97) and spring (0.92), and lowest in autumn (0.81). Accordingly, the quality of the thermal environment was significantly low during autumn, and maximum during summer. However, despite the environmental temperature fluctuations, lizards exhibited remarkable stability in body temperatures. They also adjusted their preferred temperatures seasonally and doubled the thermal niche breadth they occupied during summer, thus enhancing thermoregulation efficiency. Whether or not these adjustments are plastic or fixed local adaptations remains to be explored in further research across multiple years and seasons, including additional insular populations.

Therapeutic hyperthermia for the treatment of infection-a narrative review

Modulating body temperature, mostly through the use of antipyretics, is a commonly employed therapeutic intervention in medical practice. However, emerging evidence suggests that hyperthermia could serve as an adjuvant therapy for patients with infection. We performed a narrative review to explore the application of therapeutic hyperthermia in the treatment of infection. A number of studies have been performed in the pre-antibiotic era, enrolling patients with neurosyphilis and gonococcal infections, with reported cure rates at around 60%-80%. We have outlined the potential molecular and immunological mechanisms explaining the possible beneficial effects of therapeutic hyperthermia. For some pathogens increased temperature exerts a direct negative effect on virulence; however, it is presumed that temperature driven activation of the immune system is probably the most important factor affecting microbial viability. Lastly, we performed a review of modern-era studies where modulation of body temperature has been used as a treatment strategy. In trials of therapeutic hypothermia in patients with infection worse outcomes have been observed in the hypothermia group. Use of antipyretics has not been associated with any improvement in clinical outcomes. In modern-era therapeutic hyperthermia achieved by physical warming has been studied in one pilot trial, and better survival was observed in the hyperthermia group. To conclude, currently there is not enough data to support the use of therapeutic hyperthermia outside clinical trials; however, available studies are in favor of at least a temperature tolerance strategy for non-neurocritical patients.

Selection of preferred thermal environment and cold-avoidance responses in rats rely on signals transduced by the dorsal portion of the lateral funiculus of the spinal cord

Thermoregulatory behaviors are powerful effectors for core body temperature (Tc) regulation. We evaluated the involvement of afferent fibers ascending through the dorsal portion of the lateral funiculus (DLF) of the spinal cord in "spontaneous" thermal preference and thermoregulatory behaviors induced by thermal and pharmacological stimuli in a thermogradient apparatus. In adult Wistar rats, the DLF was surgically severed at the first cervical vertebra bilaterally. The functional effectiveness of funiculotomy was verified by the increased latency of tail-flick responses to noxious cold (-18°C) and heat (50°C). In the thermogradient apparatus, funiculotomized rats showed a higher variability of their preferred ambient temperature (Tpr) and, consequently, increased Tc fluctuations, as compared to sham-operated rats. The cold-avoidance (warmth-seeking) response to moderate cold (whole-body exposure to ~17°C) or epidermal menthol (an agonist of the cold-sensitive TRPM8 channel) was attenuated in funiculotomized rats, as compared to sham-operated rats, and so was the Tc (hyperthermic) response to menthol. In contrast, the warmth-avoidance (cold-seeking) and Tc responses of funiculotomized rats to mild heat (exposure to ~28°C) or intravenous RN-1747 (an agonist of the warmth-sensitive TRPV4; 100 μg/kg) were unaffected. We conclude that DLF-mediated signals contribute to driving spontaneous thermal preference, and that attenuation of these signals is associated with decreased precision of Tc regulation. We further conclude that thermally and pharmacologically induced changes in thermal preference rely on neural, presumably afferent, signals that travel in the spinal cord within the DLF. Signals conveyed by the DLF are important for cold-avoidance behaviors but make little contribution to heat-avoidance responses.

Circadian rhythm of preferred temperature in fish: Behavioural thermoregulation linked to daily photocycles in zebrafish and Nile tilapia

Ectothermic vertebrates, e.g. fish, maintain their body temperature within a specific physiological range mainly through behavioural thermoregulation. Here, we characterise the presence of daily rhythms of thermal preference in two phylogenetically distant and well-studied fish species: the zebrafish (Danio rerio), an experimental model, and the Nile tilapia (Oreochromis niloticus), an aquaculture species. We created a non-continuous temperature gradient using multichambered tanks according to the natural environmental range for each species. Each species was allowed to freely choose their preferred temperature during the 24h cycle over a long-term period. Both species displayed strikingly consistent temporal daily rhythms of thermal preference with higher temperatures being selected during the second half of the light phase and lower temperatures at the end of the dark phase, with mean acrophases at Zeitgeber Time (ZT) 5.37 h (zebrafish) and ZT 12.5 h (tilapia). Interestingly, when moved to the experimental tank, only tilapia displayed consistent preference for higher temperatures and took longer time to establish the thermal rhythms. Our findings highlight the importance of integrating both light-driven daily rhythm and thermal choice to refine our understanding of fish biology and improve the management and welfare of the diversity of fish species used in research and food production.

Effects of an immune challenge on the thermal preferences of adult and newborn Liolaemus lizards from Patagonia, Argentina

Body temperature has relevant effects on the immune response. Here, we characterized the thermal biology and health condition of the viviparous lizard Liolaemus kingii from Patagonia (Argentina), by studying field body temperatures, presence of injuries or ectoparasites, body condition (BC), and individual immune response capacity with the phytohemagglutinin (PHA) skin-swelling assay. In addition, we analyzed the effects of injections of a bacterial endotoxin (lipopolysaccharide; LPS) on the preferred temperature (Tp) and BC of adult males and newborns. The PHA treatment caused detectable thickening at 2 and 20 hours post-assay in males, indicating a significant immune response related to an increase in cellular activity. LPS-challenged lizards thermoregulated accurately and at stable body temperatures within the 50% interquartile of Tp (Tset) over the 72-hour period while the control group showed a more variable and lower Tp. Exposure to LPS negatively affected the BC of newborns, whereas it did not affect the BC of adult males. LPS challenges, used as a proxy of pathogen exposures to study lizard behavioral thermoregulation, constitute a practical approach to assess the immunological constraints lizards from high-latitude regions may face due to global warming and anthropogenic disturbances.

A functional study of the role of Turandot genes in Drosophila melanogaster: An emerging candidate mechanism for inducible heat tolerance

Plastic responses to heat stress have been shown to temporarily increase heat stress tolerance in many small ectotherms. Heat shock proteins (Hsps) have previously been shown to play a role in this induced heat stress tolerance. The heat shock response is fast but short lived, with the cellular Hsp concentration peaking within a few hours after induction. Induced heat stress tolerance, on the other hand, peaks 16-32 h after induction. Therefore, the inducible heat stress response must depend on additional mechanisms. The Turandot gene family has been suggested as a candidate. It contains eight genes that are all upregulated to some degree following heat stress in Drosophila melanogaster. Previously, Turandot A (totA) and Turandot X (totX) have been linked to induced heat stress tolerance. The study presented here aimed to investigate the temporal dynamics of Turandot expression and the functional role of totA and totC for heat stress tolerance. This was done by assaying the temporal heat tolerance and Turandot gene expression after a heat insult, and by exposing Turandot gene knock down flies to a range of heat hardening treatments, and evaluating the effects on heat tolerance. Successful gene knock down was verified by gene expression assays. In addition, expression of hsp70A was included. Both totA, totC, and hsp70A expression increased following a heat hardening treatment, while the results for totX were less clear. The expression of totC temporally co-occurred with and was functionally linked to increased heat tolerance. Expression of totA did not have a significant effect on heat stress tolerance. The complexity of inducible heat tolerance was underlined by the result that knock down of Turandot genes led to increased expression of hsp70. The results suggest that heat tolerance is determined by the interaction between several mechanisms, of which Turandot genes constitute one such mechanism.

Evolved reductions in body temperature and the metabolic costs of thermoregulation in deer mice native to high altitude

The evolution of endothermy was instrumental to the diversification of birds and mammals, but the energetic demands of maintaining high body temperature could offset the advantages of endothermy in some environments. We hypothesized that reductions in body temperature help high-altitude natives overcome the metabolic challenges of cold and hypoxia in their native environment. Deer mice (Peromyscus maniculatus) from high-altitude and low-altitude populations were bred in captivity to the second generation and were acclimated as adults to warm normoxia or cold hypoxia. Subcutaneous temperature (Tsub, used as a proxy for body temperature) and cardiovascular function were then measured throughout the diel cycle using biotelemetry. Cold hypoxia increased metabolic demands, as reflected by increased food consumption and heart rate (associated with reduced vagal tone). These increased metabolic demands were offset by plastic reductions in Tsub (approx. 2°C) in response to cold hypoxia, and highlanders had lower Tsub (approx. 1°C) than lowlanders in both environmental treatments. Empirical and theoretical evidence suggested that these reductions could together reduce metabolic demands by approximately 10-30%. Therefore, plastic and evolved reductions in body temperature can help mammals overcome the metabolic challenges at high altitude and may be a valuable energy-saving strategy in some non-hibernating endotherms in extreme environments.

Cutaneous TRPV4 Channels Activate Warmth-Defense Responses in Young and Adult Birds

Transient receptor potential vanilloid 4 (TRPV4) channels are sensitive to warm ambient temperatures (Tas), triggering heat loss responses in adult rats in a Tas range of ∼26–30°C. In birds, however, the thermoregulatory role of TRPV4 has never been shown. Here, we hypothesized that stimulation of TRPV4 induces thermolytic responses for body temperature (Tb) maintenance in birds, and that this function is already present in early life, when the Ta range for TRPV4 activation does not represent a warm condition for these animals. We first demonstrated the presence of TRPV4 in the dorsal and ventral skin of chickens (Gallus gallus domesticus) by immunohistochemistry. Then, we evaluated the effects of the TRPV4 agonist, RN1747, and the TRPV4 antagonists, HC067047 and GSK2193874, on Tb and thermoeffectors at different Tas in 5-day-old chicks and 60-day-old adult chickens. For the chicks, RN1747 transiently reduced Tb both in thermoneutrality (31°C) and in a cold Ta for this phase (26°C), which relied on huddling behavior inhibition. The TRPV4 antagonists alone did not affect Tb or thermoeffectors but blocked the Tb decrease and huddling inhibition promoted by RN1747. For the adults, TRPV4 antagonism increased Tb when animals were exposed to 28°C (suprathermoneutral condition for adults), but not to 19°C. In contrast, RN1747 decreased Tb by reducing metabolic rate and activating thermal tachypnea at 19°C, a Ta below the activation range of TRPV4. Our results indicate that peripheral TRPV4 receptors are functional in early life, but may be inhibited at that time when the range of activation (∼26–30°C) represents cold Ta for chicks, and become physiologically relevant for Tb maintenance when the activation Ta range for TRPV4 becomes suprathermoneutral for adult chickens.

The Birth of the Mammalian Sleep

Simple Summary

Mammals evolved from reptiles as a consequence of an evolutionary bottleneck. Some diurnal reptiles extended their activity, first to twilight and then to the entire dark time. This forced the change of the visual system. Pursuing maximal sensitivity, they abandoned the filters protecting the eyes against the dangerous diurnal light, which, in turn, forced immobility in lightproof burrows during light time. This was the birth of the mammalian sleep. Then, the Cretacic-Paleogene extinction of dinosaurs leaved free the diurnal niche and allowed the expansion of a few early mammals to diurnal life and the high variability of sleep traits. On the other hand, we propose that the idling rest is a state showing homeostatic regulation. Therefore, the difference between behavioral rest and wakeful idling is rather low: both show quiescence, raised sensory thresholds, reversibility, specific sleeping-resting sites and body positions, it is a pleasing state, and both are dependent of circadian and homeostatic regulation. Indeed, the most important difference is the unconsciousness of sleep and the consciousness of wakeful idling. Thus, we propose that sleep is a mere upgrade of the wakeful rest, and both may have the same function: guaranteeing rest during a part of the daily cycle.

Abstract

Mammals evolved from small-sized reptiles that developed endothermic metabolism. This allowed filling the nocturnal niche. They traded-off visual acuity for sensitivity but became defenseless against the dangerous daylight. To avoid such danger, they rested with closed eyes in lightproof burrows during light-time. This was the birth of the mammalian sleep, the main finding of this report. Improved audition and olfaction counterweighed the visual impairments and facilitated the cortical development. This process is called “The Nocturnal Evolutionary Bottleneck”. Pre-mammals were nocturnal until the Cretacic-Paleogene extinction of dinosaurs. Some early mammals returned to diurnal activity, and this allowed the high variability in sleeping patterns observed today. The traits of Waking Idleness are almost identical to those of behavioral sleep, including homeostatic regulation. This is another important finding of this report. In summary, behavioral sleep seems to be an upgrade of Waking Idleness Indeed, the trait that never fails to show is quiescence. We conclude that the main function of sleep consists in guaranteeing it during a part of the daily cycle.

Metabolite Profiling of the Social Spider Stegodyphus dumicola Along a Climate Gradient

Animals experience climatic variation in their natural habitats, which may lead to variation in phenotypic responses among populations through local adaptation or phenotypic plasticity. In ectotherm arthropods, the expression of thermoprotective metabolites such as free amino acids, sugars, and polyols, in response to temperature stress, may facilitate temperature tolerance by regulating cellular homeostasis. If populations experience differences in temperatures, individuals may exhibit population-specific metabolite profiles through differential accumulation of metabolites that facilitate thermal tolerance. Such thermoprotective metabolites may originate from the animals themselves or from their associated microbiome, and hence microbial symbionts may contribute to shape the thermal niche of their host. The social spider Stegodyphus dumicola has extremely low genetic diversity, yet it occupies a relatively broad temperature range occurring across multiple climate zones in Southern Africa. We investigated whether the metabolome, including thermoprotective metabolites, differs between populations, and whether population genetic structure or the spider microbiome may explain potential differences. To address these questions, we assessed metabolite profiles, phylogenetic relationships, and microbiomes in three natural populations along a temperature gradient. The spider microbiomes in three genetically distinct populations of S. dumicola showed no significant population-specific pattern, and none of its dominating genera (Borrelia, Diplorickettsia, and Mycoplasma) are known to facilitate thermal tolerance in hosts. These results do not support a role of the microbiome in shaping the thermal niche of S. dumicola. Metabolite profiles of the three spider populations were significantly different. The variation was driven by multiple metabolites that can be linked to temperature stress (e.g., lactate, succinate, or xanthine) and thermal tolerance (e.g., polyols, trehalose, or glycerol): these metabolites had higher relative abundance in spiders from the hottest geographic region. These distinct metabolite profiles are consistent with a potential role of the metabolome in temperature response.

Post-exercise Hypothermia Varies Between High- and Low-Altitude Populations in the Asiatic Toad (Bufo gargarizans)

Whether and how poikilothermic animals change their thermal performance to cope with global warming are crucial questions to predict the future of biodiversity. Intraspecific comparison among populations that occur in different climatic zones can provide insight into how poikilotherms may alter their thermal performance under a particular climatic event. We compared populations of the Asiatic toad (Bufo gargarizans) from two altitudinal zones (3239 and 926 m above sea level) to explore variations of post-exercise hypothermia, which can lead to lower temperature preference than normal conditions. Common garden experiment was also employed to test plasticity of hypothermic performance in adult toads. As results, exhaustive exercise induced measurable reduction in body temperature for both populations. Furthermore, high-altitude population experienced larger reduction in body temperature than low-altitude conspecifics in both original habitat and common garden conditions. Therefore, low-altitude toads may to enhance their hypothermic reaction if they shift their ranges to higher altitudes to survive warming climate; However, the relatively limited plasticity of hypothermic performance may constraint their adaptative process.

Metabolic trade-offs favor regulated hypothermia and inhibit fever in immune-challenged chicks

The febrile response to resist a pathogen is energetically expensive while regulated hypothermia seems to preserve energy for vital functions. We hypothesized here that immune challenged birds under metabolic trade-offs (reduced energy supply / increased energy demand) favor a regulated hypothermic response at the expense of fever. To test this hypothesis, we compared 5-days old broiler chicks exposed to fasting, cold (25oC), and fasting combined with cold to a control group fed at thermoneutral condition (30oC). The chicks were injected with saline or with a high dose of endotoxin known to induce a biphasic thermal response composed of body temperature (Tb) drop followed by fever. Then Tb, oxygen consumption (metabolic rate), peripheral vasomotion (cutaneous heat exchange), breathing frequency (respiratory heat exchange), and huddling behavior (heat conservation indicator) were analyzed. Irrespective of metabolic trade-offs, chicks presented a transient regulated hypothermia in the first hour, which relied on a suppressed metabolic rate for all groups, increased breathing frequency for chicks fed/fasted at 30oC, and peripheral vasodilation in fed/fasted chicks at 25oC. Fever was observed only in chicks kept at thermoneutrality and was supported by peripheral vasoconstriction and huddling behavior. Fed and fasted chicks at 25oC completely eliminated fever despite the ability to increase metabolic rate for thermogenesis in the phase correspondent to fever when it was pharmacologically induced by 2.4-Dinitrophenol. Our data suggest that increased competing demands affect chicks’ response to an immune challenge favoring regulated hypothermia to preserve energy while the high costs of fever to resist a pathogen are avoided.

Thermoregulation of Eremias argus alters temperature-dependent toxicity of beta-cyfluthrin: Ecotoxicological effects considering ectotherm behavior traits

Risk assessments of the ecotoxicological effects insecticides impose on ectotherms have increasingly considered temperature. However, the changes toxicants induce in thermoregulatory behavioral traits may lead to a divergence of thermal selection and temperature-dependent changes of contaminant toxicity. This study demonstrated the interaction of behavioral thermoregulation and temperature-dependent toxicity of beta-cyfluthrin (BC) in the lizard Eremias argus. Based on the negative relationship between temperature and BC toxicity, seeking a warming environment was assumed to represent a self-rescue behavior (and vice versa). The results showed that BC-treated lizards (0-20 μg/g body weight (bw)) showed such self-rescue behavior, while lizards exposed to an extremely high BC dose (200 μg/g bw) sought a cooler environment. Biochemical assays showed that BC affected neurotransmitter systems, caused oxidative stress, and interfered with ion-transport in the central nervous system. Biomarkers of the cholinergic and glutamatergic system, ion-transport function, and oxidative stress were identified as potential biochemical variables related to thermoregulatory behavior. Apparently, seeking a warmer environment is a survival strategy with the aim to neutralize BC toxicity, while seeking a cooler environment aims to attenuate the harmful effects of metabolic and oxidative stress, and to decelerate internal BC diffusion. This phenomenon could be also explained by the concept of the "cooling trap", i.e., a behavior where cooler temperatures are sought. This impairs survival after exposure to BC at it has a negative temperature coefficient, derived from a dysfunction of the central nervous system regarding thermoregulation caused by the high dosage of neurotoxicant and resulting temperature maladaptation. Implications of the interaction between thermoregulatory behavior and temperature-dependent toxicity are presented, which may aid further temperature-dependent risk assessments.

Sensitivity of marine fish thermal habitat models to fishery data sources

Statistical models built using different data sources and methods can exhibit conflicting patterns. We used the northern stock of black sea bass (Centropristis striata) as a case study to assess the impacts of using different fisheries data sources and laboratory-derived physiological metrics in the development of thermal habitat models for marine fishes. We constructed thermal habitat models using generalized additive models (GAMs) based on various fisheries datasets as input, including the NOAA Northeast Fisheries Science Center (NEFSC) bottom trawl surveys, various inshore fisheries-independent trawl surveys (state waters), NEFSC fisheries-dependent observer data, and laboratory-based physiological metrics. We compared each model's GAM response curve and coupled them to historical ocean conditions in the U.S. Northeast Shelf using bias-corrected ocean temperature output from a regional ocean model. Thermal habitat models based on shelf-wide data (NEFSC fisheries-dependent observer data and fisheries-independent spring and fall surveys) explained the most variation in black sea bass presence/absence data at ~15% deviance explained. Models based on a narrower range of sampled thermal habitat from inshore survey data in the Northeast Area Monitoring and Assessment Program (NEAMAP) and the geographically isolated Long Island Sound data performed poorly. All models had similar lower thermal limits around 8.5℃, but thermal optima, when present, ranged from 16.7 to 24.8℃. The GAMs could reliably predict habitat from years excluded from model training, but due to strong seasonal temperature fluctuations in the region, could not be used to predict habitat in seasons excluded from training. We conclude that survey data source can greatly impact development and interpretation of thermal habitat models for marine fishes. We suggest that model development be based on data sources that sample the widest range of ocean temperature and physical habitat throughout multiple seasons when possible, and encourage thorough consideration of how data gaps may influence model uncertainty.

Individual quality and phenology mediate the effect of radioactive contamination on body temperature in Chernobyl barn swallows

Anthropogenic stressors, such as radioactive contaminants released from the Chernobyl and Fukushima Daiichi accidents, deteriorate ecological and evolutionary processes, as evidence for damaging effects of radioactive contamination on wildlife is accumulating. Yet little is known about physiological traits of animals inhabiting contaminated areas, and how those are affected by individual quality and phenology. We investigated variation in body temperature of wild barn swallows, Hirundo rustica, exposed to radioactive contamination from the Chernobyl accident in Ukraine and Belarus. We tested whether exposure to variable levels of radioactive contamination modified core body temperature of birds, and whether individual and phenological characteristics modulated radiosensitivity of body temperature. We showed that barn swallow body temperature varied with exposure to environmental radioactive contamination and that individual characteristics and phenology affected radioactive exposure. Increased radiosensitivity and up-regulation of body temperature were detected in birds of low body condition, high risk of capture, and in animals captured late during the day but early during the season. These results highlight the complex ways that the body temperature of a wild bird is impacted by exposure to increased radioactive contamination in natural habitats. By impacting body temperature, increased radioactive contamination may compromise energetic balance, jeopardize responsiveness to global warming, and increase risk of overheating.

Regulated hypothermia in response to endotoxin in birds

KEY POINTS

The costs associated with immune and thermal responses may exceed the benefits to the host during severe inflammation. In this case, regulated hypothermia instead of fever can occur in rodents as a beneficial strategy to conserve energy for vital functions with consequent tissue protection and hypoxia prevention. We tested the hypothesis that this phenomenon is not exclusive to mammals, but extends to the other endothermic group, birds. A decrease in metabolic rate without any failure in mitochondrial respiration, nor oxygen delivery, is the main evidence supporting the regulated nature of endotoxin-induced hypothermia in chicks. Thermolytic mechanisms such as tachypnea and cutaneous vasodilatation can also be recruited to facilitate body temperature decrease under lipopolysaccharide treatment, especially in the cold. Our findings bring a new perspective for evolutionary medicine studies on energy trade-off in host defence because regulated hypothermia may be a phenomenon spread among vertebrates facing a severe immune challenge.

ABSTRACT

A switch from fever to regulated hypothermia can occur in mammals under circumstances of reduced physiological fitness (e.g. sepsis) to direct energy to defend vital systems. Birds in which the cost to resist a pathogen is additive to the highest metabolic rate and body temperature (T_b ) among vertebrates may also benefit from regulated hypothermia during systemic inflammation. Here, we show that the decrease in T_b observed during an immune challenge in birds is a regulated hypothermia, and not a result of metabolic failure. We investigated O₂ consumption (thermogenesis index), ventilation (respiratory heat loss), skin temperature (sensible heat loss) and muscle mitochondrial respiration (thermogenic tissue) during T_b fall in chicken chicks challenged with endotoxin [lipopolysaccharide (LPS)]. Chicks injected with LPS were also tested regarding the capacity to raise O₂ consumption to meet an increased demand driven by 2,4-dinitrophenol. LPS decreased T_b and the metabolic rate of chicks without affecting muscle uncoupled, coupled and non-coupled mitochondrial respiration. LPS-challenged chicks were indeed capable of increasing metabolic rate in response to 2,4-dinitrophenol, indicating no O₂ delivery limitation. Additionally, chicks did not attempt to prevent T_b from falling during hypothermia but, instead, activated cutaneous and respiratory thermolytic mechanisms, providing an additional cooling force. These data provide the first evidence of the regulated nature of the hypothermic response to endotoxin in birds. Therefore, it changes the current understanding of bird's thermoregulation during severe inflammation, indicating that regulated hypothermia is either a convergent trait for endotherms or a conserved response among vertebrates, which adds a new perspective for evolutionary medicine research.

Sex-specific energy management strategies in response to training for increased foraging effort prior to reproduction in captive zebra finches

Free-living animals often engage in behaviour that involves high rates of workload and results in high daily energy expenditure (DEE), such as reproduction. However, the evidence for elevated DEE accompanying reproduction remains equivocal. In fact, many studies have found no difference in DEE between reproducing and non-reproducing females. One of the hypotheses explaining the lack of difference is the concept of an 'energetic ceiling'. However, it is unclear whether the lack of increase in energy expenditure is due to the existence of an energetic ceiling and/or compensation by males during parental care. To investigate whether an energetic ceiling exists, we experimentally manipulated foraging effort in captive zebra finches, Taeniopygia guttata, creating two groups with high and low foraging efforts followed by both groups breeding in the low foraging effort common garden condition. DEE was measured in both sexes throughout the experiment. We show sex-specific energy management strategies in response to training for increased foraging effort prior to reproduction. Specifically, males and females responded differently to the high foraging effort treatment and subsequently to chick rearing in terms of energy expenditure. Our results also suggest that there is an energetic ceiling in females and that energetic costs incurred prior to reproduction can be carried over into subsequent stages of reproduction in a sex-specific manner.

A thermoregulatory role of the medullary raphe in birds

The brainstem region medullary raphe modulates non-shivering and shivering thermogenesis and cutaneous vasomotion in rodents. Whether the same scenario occurs in the other endothermic group, i.e. birds, is still unknown. Therefore, we hypothesised that the medullary raphe modulates heat gain and loss thermoeffectors in birds. We investigated the effect of glutamatergic and GABAergic inhibitions in this specific region on body temperature (Tb), oxygen consumption (thermogenesis), ventilation (O2 supply in cold, thermal tachypnea in heat) and heat loss index (cutaneous vasomotion) in one-week-old chicken exposed to neutral (31°C), cold (26°C) and heat (36°C) conditions. Intra-medullary raphe antagonism of NMDA glutamate (AP5; 0.5, 5 mM) and GABAA (bicuculline; 0.05, 0.5 mM) receptors reduced Tb of chicks at 31°C and 26oC, due mainly to an O2 consumption decrease. AP5 transiently increased breathing frequency during cold exposure. At 31°C, heat loss index was higher in the bicuculline and AP5 groups (higher doses) than vehicle at the beginning of the Tb reduction. No treatment affected any variable tested at 36oC. The results suggest that glutamatergic and GABAergic excitatory influences on the medullary raphe of chicks modulate thermogenesis and glutamatergic stimulation prevents tachypnea, without having any role in warmth-defence responses. A double excitation influence on the medullary raphe may provide a protective neural mechanism for supporting thermogenesis during early life, when energy expenditure to support growth and homeothermy is high. This novel demonstration of a thermoregulatory role for the raphe in birds suggests a convergent brainstem neurochemical regulation of body temperature in endotherms.

Rest-Phase Hypothermia Reveals a Link Between Aging and Oxidative Stress: A Novel Hypothesis

In endotherms, growth, reproduction, and survival are highly depended on energy metabolism. Maintenance of constant body temperature can be challenging for endotherms under continuously changing environmental conditions, such as low or high ambient temperatures or limited food. Thus, many birds may drop body temperature below normothermic values during the night, known as rest-phase hypothermia, presumably to decrease energy metabolism. Under the assumption of the positive link between aerobic metabolism and reactive oxygen species, it is reasonable to suggest that low body temperature, a proxy of energy metabolism, will affect oxidative stress of the birds. Aging may considerably affect behavior, performance and physiology in birds and still requires further investigation to understand age-specific changes along the lifespan of the organism. Until today, age-specific rest-phase hypothermic responses and their effect on oxidant-antioxidant status have never been investigated. We exposed 25 zebra finches (Taeniopygia guttata) of three age classes, 12 young birds (1.1–1.3 years old), 8 middle-aged (2.4–2.8 years old), and 5 old birds (4.2–7.5 years old) to day-long food deprivation or provided them normal access to food under thermoneutral conditions. We compared night-time body temperature, measured through implanted data loggers, and quantified plasma oxidative status (uric acid, antioxidant capacity, and d-ROM assay) the following morning. We found age-related differences in night-time body temperature following a day-long food deprivation while all three age groups remained normothermic in the night following a day with access to food. The lowest minimum body temperature (LSM ± SE: 36.6 ± 0.2°C) was observed in old individuals during rest-phase hypothermia. Surprisingly, these old birds also revealed the highest levels of plasma oxidative damage, while young and middle-aged birds maintained higher night-time body temperature and showed lower values of oxidative damage. These results lead us to propose a novel hypothesis on how aging may lead to an accumulation of oxidative damage; the impaired physiological capacity to thermoregulate with advancing age does increase the risk of oxidative stress under challenging conditions. When energy is limited, the risk to encounter oxidative stress is increasing via a compensation to defend normothermic body temperatures.

Pharmacological Characterization of 4-Methylthioamphetamine Derivatives

Amphetamine derivatives have been used in a wide variety of pathologies because of their pharmacological properties as psychostimulants, entactogens, anorectics, and antidepressants. However, adverse cardiovascular effects (sympathomimetics) and substance abuse problems (psychotropic and hallucinogenic effects) have limited their use. 4-Methylthioamphetamine (MTA) is an amphetamine derivative that has shown to inhibit monoamine uptake and monoamine oxidase. However, the pharmacological characterization (neurochemical, behavioral, and safety) of its derivatives 4-ethylthioamphetamine (ETA) and 4-methylthio-phenil-2-butanamine (MT-But) have not been studied. In the current experiments, we show that ETA and MT-But do not increase locomotor activity and conditioned place preference with respect to MTA. At the neurochemical level, ETA and MT-But do not increase in vivo DA release in striatum, but ETA and MT-But affect the nucleus accumbens bioaccumulation of DA and DOPAC. Regarding cardiovascular effects, the administration of MTA and ETA increased the mean arterial pressure and only ETA significantly increases the heart rate. Our results show that the pharmacological and safety profiles of MTA are modulated by changing the methyl-thio group or the methyl group of the aminoethyl chain.

Neither altered incubation temperature during fetal development nor preferred rearing temperature improves leg bone characteristics of broilers

The present study evaluated whether broiler femoral and tibiotarsal characteristics (as assessed at slaughter age) could be improved if birds were reared under their preferred temperature and whether continuous high or low incubation temperature during the fetal period improves bone characteristics of broilers reared under heat stress or thermal preference. Broiler breeder eggs were incubated from day 13 until hatching under cold (36 °C), control (37.5 °C), or hot (39 °C) temperatures. Under these conditions, the eggshell temperatures were 37.4 ± 0.1°C, 37.8 ± 0.15°C, and 38.8 ± 0.3°C, respectively. Then, broiler chicks were reared under control, preferred (determined previously in thermal preference test), or high temperatures. At day 42 of age, the broilers were weighed and euthanized, and femora and tibiotarsi collected to measure weight, length, diaphysis perimeter, breaking strength, maximum flexion, rigidity, ash, phosphorus, and calcium. Rearing under the preferred temperature did not affect broiler body weight or femoral and tibiotarsal characteristics (P > 0.05). In contrast, high rearing temperature, decreased the body weight, mineral contents of both bones, femoral breaking strength, and tibiotarsal rigidity (P < 0.05). Regarding incubation temperature effects, egg exposure to cold and hot temperatures during the fetal period minimized or avoided a few effects of high rearing temperature, such as those on femoral and tibiotarsal morphological characteristics, mineral composition, and mechanical properties at slaughter age (P < 0.05), but not all. In conclusion, rearing under the preferred broiler temperature did not improve the bone characteristics, and the negative effects of high rearing temperature on bone development were minimized but not completely prevented by high or low temperature incubation during the fetal period.

Step-patterned survivorship curves: Mortality and loss of equilibrium responses to high temperature and food restriction in juvenile rainbow trout (Oncorhynchus mykiss)

While survivorship curves typically exhibit smooth declines over time, step-patterned curves can occur with multiple stressors within a life stage. To explore this process, we examined the effects of heat (24°C) and food restriction on juvenile rainbow trout (Oncorhynchus mykiss Walbaum) in challenge experiments. We observed step-patterned survivorship curves determined by mortality and loss of equilibrium (LOE) endpoints. To examine the cause of heterogeneity in the stress responses from early to late mortality and LOE, we measured indices of energetic reserves. The step transition in the survivorship curves, the peak mortality rates, and start of when individuals reached a critical energetic threshold (14% dry mass; 4.0 kJ·g-1 energy) all occurred at around days 10-15 of the challenge. The coherence in these temporal patterns suggest heterogeneity in the cohort stress responses, in which an early subgroup died from heat stress and a late subgroup died from starvation. Thus, their endpoint sensitivities resulted in step-patterned survivorship curves. We discuss the implications of the study for understanding effects of multiple stressors on population heterogeneity and note the possible significance of stress response selection under climate change in which heat stress and food limitations occur in concert.

Exercise on a vibratory platform increases blood perfusion on the stifle joint and rectal temperature in healthy dogs

ABSTRACT The effects of two vibration platform (VP) exercise protocols on stifle and rectal temperatures were evaluated. Eleven animals participated in two exercise protocols, different in duration in each exercise. Exercise protocol 1 (EP1) took 30 seconds and EP2, 60 seconds, with different vibratory levels in both cases (L1 = acceleration ≅ 1g, L4 = acceleration ≅ 2.5g, and L7 = acceleration ≅ 5g). The animals were evaluated before and 1 minute after the exercise, using infrared thermography to obtain stifle temperatures. The rectal temperature (RT) was also checked at each moment. The dogs had higher stifle temperatures in EP1 at all vibratory levels compared to the time before the exercise; EP2 resulted in higher temperature only at maximum vibration intensity (L7). Increase in TR was observed only in EP2. The results suggested that the short duration protocol (EP1) increased the muscular and peripheral vascular activities of the joint, regardless of the vibration intensity. The long duration protocol (EP2) with maximum vibration intensity increased the RT, demonstrating activity beyond the stifle muscle group. It is concluded that exercises on the VP can be used as complementary therapy for low-impact muscle activity in dogs and may be adequate for efficient energy consumption.

Neurons and astrocytes of the chicken hypothalamus directly respond to lipopolysaccharide and chicken interleukin-6

In 4-5-month-old chicken, intravenous injections of bacterial lipopolysaccharide (LPS) induced a dose-dependent fever response and a pronounced increase of circulating interleukin-6 (IL-6). To assess a possible role for IL-6 in the brain of birds, a hypothalamic neuro-glial primary culture from 1-day-old chicken was established. Each well of cultured hypothalamic cells contained some 615 neurons, 1350 astrocytes, and 580 microglial cells on average. Incubation of chicken hypothalamic primary cultures with 10 or 100 µg/ml LPS induced a dose-dependent release of bioactive IL-6 into the supernatant. Populations of hypothalamic neurons (4%) and astrocytes (12%) directly responded to superfusion with buffer containing 10 µg/ml LPS with a transient increase of intracellular calcium, a sign of direct cellular activation. Stimulation of hypothalamic cultures with buffer containing 50 ng/ml chicken IL-6 induced calcium signaling in 11% of neurons and 22% of astrocytes investigated. These results demonstrate that IL-6 is produced in the periphery and in the hypothalamus in response to LPS in chicken. The observed cellular responses of hypothalamic cells to chicken IL-6 indicate that this cytokine may readily be involved in the manifestation of fever in the avian hypothalamus.

Cardiovascular shunting in vertebrates: a practical integration of competing hypotheses

This review explores the long-standing question: 'Why do cardiovascular shunts occur?' An historical perspective is provided on previous research into cardiac shunts in vertebrates that continues to shape current views. Cardiac shunts and when they occur is then described for vertebrates. Nearly 20 different functional reasons have been proposed as specific causes of shunts, ranging from energy conservation to improved gas exchange, and including a plethora of functions related to thermoregulation, digestion and haemodynamics. It has even been suggested that shunts are merely an evolutionary or developmental relic. Having considered the various hypotheses involving cardiovascular shunting in vertebrates, this review then takes a non-traditional approach. Rather than attempting to identify the single 'correct' reason for the occurrence of shunts, we advance a more holistic, integrative approach that embraces multiple, non-exclusive suites of proposed causes for shunts, and indicates how these varied functions might at least co-exist, if not actually support each other as shunts serve multiple, concurrent physiological functions. It is argued that deposing the 'monolithic' view of shunting leads to a more nuanced view of vertebrate cardiovascular systems. This review concludes by suggesting new paradigms for testing the function(s) of shunts, including experimentally placing organ systems into conflict in terms of their perfusion needs, reducing sources of variation in physiological experiments, measuring possible compensatory responses to shunt ablation, moving experiments from the laboratory to the field, and using cladistics-related approaches in the choice of experimental animals.

An age- and sex-dependent role of catecholaminergic neurons in the control of breathing and hypoxic chemoreflex during postnatal development

The respiratory system undergoes significant development during the postnatal phase. Maturation of brainstem catecholaminergic (CA) neurons is important for the control and modulation of respiratory rhythmogenesis, as well as for chemoreception in early life. We demonstrated an inhibitory role for CA neurons in CO₂ chemosensitivity in neonatal and juvenile male and female rats, but information regarding their role in the hypoxic ventilatory response (HVR) is lacking. We evaluated the contribution of brainstem CA neurons in the HVR during postnatal (P) development (P7-8, P14-15 and P20-21) in male and female rats through chemical injury with conjugated saporin anti-dopamine beta-hydroxylase (DβH-SAP, 420 ng·μL^-1) injected in the fourth ventricle. Ventilation (V̇_E) and oxygen consumption were recorded one week after the lesion in unanesthetized rats during exposure to normoxia and hypoxia. Hypoxia reduced breathing variability in P7-8 control rats of both sexes. At P7-8, the HVR for lesioned males and females increased 27% and 24%, respectively. Additionally, the lesion reduced the normoxic breathing variability in both sexes at P7-8, but hypoxia partially reverted this effect. For P14-15, the increase in V̇_E during hypoxia was 30% higher for male and 24% higher for female lesioned animals. A sex-specific difference was detected at P20-21, as lesioned males exhibited a 24% decrease in the HVR, while lesioned females experienced a 22% increase. Furthermore, the hypoxia-induced body temperature reduction was attenuated in P20-21 lesioned females. We conclude that brainstem CA neurons modulate the HRV during the postnatal phase, and possibly thermoregulation during hypoxia.

Salinity affects growth but not thermal preference of adult mummichogs Fundulus heteroclitus

The effects of an ecologically relevant range of salinities (2, 12, 22, 32) on thermal preferences and growth of adult mummichogs Fundulus heteroclitus were determined for fish from a southern Chesapeake Bay population. Salinity did not affect the mean temperature selected by F. heteroclitus in a thermal gradient, which was identified as 26.6°C based on observations of 240 individuals. Salinity and temperature had significant and interacting effects on growth rates of F. heteroclitus measured over 12 weeks. Growth rates were highest overall and remained high over a broader range of temperatures at moderate salinities (12 and 22), while high growth rates were shifted toward lower temperatures for fish grown at a salinity of 2 and higher temperatures at a salinity of 32. Significant reductions in growth relative to the optimal conditions (28.6°C, salinity of 22) were observed at the coolest (19.6°C) and warmest (33.6°C) temperature tested at all salinities, as well as temperatures ≥ 26.6°C at a salinity of 2, ≥ 28.6°C at a salinity of 12 and ≤ 26.6°C at a salinity of 32. Growth rates provide a long-term, organismal measure of performance and results of this study indicate that performance may be reduced under conditions that the highly euryhaline F. heteroclitus can otherwise easily tolerate. The combination of reduced salinity and increased temperature that is predicted for temperate estuaries as a result of climate change may have negative effects on growth of this ecologically important species.

Estimation of the kidney metabolic heat generation rate

Thermogenesis results from the cellular metabolism and has a fundamental role for body thermoregulation in endothermic species. The motivation for this work is the analysis of the kidneys' contribution for thermoregulation. An inverse problem is solved for the estimation of the heat generation rate that results from the metabolic activities in the kidney, by using transient temperature measurements of the urine. The Markov chain Monte Carlo (MCMC) method is applied for the solution of the inverse problem, which presents inherent difficulties associated with low sensitivity of the parameters of main interest that represent the transient heat source term and strong correlation of the remaining model parameters. Such difficulties are dealt with in this work by using a version of the Metropolis-Hastings algorithm that samples the parameters in blocks. Simulated temperature measurements are used for the inverse problem solution, and the convergence of the Markov chains is verified with two different techniques.