[Why 37 degrees C? Evolutionary fundamentals of thermoregulation]

Possible spread of SARS-CoV-2 in domestic and wild animals and body temperature role

The COVID-19 pandemic was officially announced in March 2020 and is still moving around the world. Virus strains, their pathogenicity and infectivity are changing, but the ability is fast to spread and harm people's health remained, despite the seasonality seasons and other circumstances. Most likely, humanity is doomed for a long time to coexistence with this emergent pathogen, since it is already circulating not only among the human population, but and among fauna, especially among wild animals in different regions of the planet. Thus, the range the virus has expanded, the material and conditions for its evolution are more than enough. The detection of SARS-CoV-2 in known infected fauna species is analyzed and possible spread and ongoing circulation of the virus in domestic and wild animals are discussed. One of the main focus of the article is the role of animal body temperature, its fluctuations and the presence of entry receptors in the susceptibility of different animal species to SARS-CoV-2 infection and virus spreading in possible new ecological niches. The possibility of long-term circulation of the pathogen among susceptible organisms is discussed.

Noble gas and neuroprotection: From bench to bedside

In recent years, inert gases such as helium, argon, and xenon have gained considerable attention for their medical value. Noble gases present an intriguing scientific paradox: although extremely chemically inert, they display a remarkable spectrum of clinically useful biological properties. Despite a relative paucity of knowledge about their mechanisms of action, some noble gases have been used successfully in clinical practice. The neuroprotection elicited by these noble gases has been investigated in experimental animal models of various types of brain injuries, such as traumatic brain injury, stroke, subarachnoid hemorrhage, cerebral ischemic/reperfusion injury, and neurodegenerative diseases. Collectively, these central nervous system injuries are a leading cause of morbidity and mortality every year worldwide. Treatment options are presently limited to thrombolytic drugs and clot removal for ischemic stroke, or therapeutic cooling for other brain injuries before the application of noble gas. Currently, there is increasing interest in noble gases as novel treatments for various brain injuries. In recent years, neuroprotection elicited by particular noble gases, xenon, for example, has been reported under different conditions. In this article, we have reviewed the latest in vitro and in vivo experimental and clinical studies of the actions of xenon, argon, and helium, and discuss their potential use as neuroprotective agents.

Pediatric Hypothermia: An Ambiguous Issue

Hypothermia in pediatrics is mainly about small body size. The key thermal factor here is the large surface-to-volume ratio. Although small mammals, including human infants and children, are adapted to higher heat losses through their elevated metabolic rate and thermogenic capacity, they are still at risk of hypothermia because of a small regulatory range and an impending metabolic exhaustion. However, some small mammalian species (hibernators) use reduced metabolic rates and lowered body temperatures as adaptations to impaired energy supply. Similar to nature, hypothermia has contradictory effects in clinical pediatrics as well: In neonates, it is a serious risk factor affecting respiratory adaptation in term and developmental outcome in preterm infants. On the other hand, it is an important self-protective response to neonatal hypoxia and an evidence-based treatment option for asphyxiated babies. In children, hypothermia first enabled the surgical repair of congenital heart defects and promotes favorable outcome after ice water drowning. Yet, it is also a major threat in various prehospital and clinical settings and has no proven therapeutic benefit in pediatric critical care. All in all, pediatric hypothermia is an ambiguous issue whose harmful or beneficial effects strongly depend on the particular circumstances.

Neuroprotective effect of helium after neonatal hypoxic ischemia: a narrative review

Neonatal hypoxic ischemia is one of the leading causes of permanent morbidity and mortality in newborns, which is caused by difficulty in supplying blood and oxygen to brain tissue and is often associated with epilepsy, cerebral palsy, death, short-term or long-term neurological and cognitive impairment. In recent years, the clinical therapeutic effects of noble gases have been gradually discovered and recognized. Numerous studies have shown that noble gases have unique neuroprotective effects to restore damaged nerve and relieve symptoms in patients. Although research on the neuroprotective mechanisms of xenon and argon has yielded a lot of results, studies on helium have stalled. Helium is a colorless, odorless, monoatomic inert gas. The helium has no hemodynamic or neurocognitive side effects and can be used as an ideal pre-adaptor for future clinical applications. In recent years, studies have shown that heliox (a mixture of helium and oxygen) pretreatment can protect the heart, brain, liver and intestine from damage in several animal models, where a variety of signaling pathways have been proved to be involved. There are numerous studies on it even though the mechanism of helium for protecting newborns has not been fully elucidated. It is urgent to find an effective treatment due to the high death rate and disability rate of neonatal hypoxic ischemia. It is believed that helium will be approved safely and effectively for clinical use in the near future.

Seasonal changes in energy expenditure, body temperature and activity patterns in llamas (Lama glama)

Mammals typically keep their body temperature (T_b) within a narrow limit with changing environmental conditions. There are indications that some wild ungulates can exhibit certain forms of energy saving mechanisms when ambient temperatures are low and/or food is scarce. Therefore, the aim of the study was to determine if the llama, one of the most extensively kept domestic livestock species, exhibits seasonal adjustment mechanisms in terms of energy expenditure, T_b and locomotion. For that purpose llamas (N = 7) were kept in a temperate habitat on pasture. Locomotor activity, T_b (measured in the rumen) and the location of each animal were recorded continuously for one year using a telemetry system. Daily energy expenditure was measured as field metabolic rate (FMR). FMR fluctuated considerably between seasons with the lowest values found in winter (17.48 ± 3.98 MJ d⁻¹, 402 kJ kg^−0.75 d⁻¹) and the highest in summer (25.87 ± 3.88 MJ d⁻¹, 586 kJ kg^−0.75 d⁻¹). Llamas adjusted their energy expenditure, T_b and locomotor activity according to season and also time of day. Thus, llamas seem to have maintained the ability to reduce their energy expenditure and adjust their T_b under adverse environmental conditions as has been reported for some wild ungulates.

Advances in molecular mechanism of cardioprotection induced by helium

Helium has been classified as a kind of inert gas that is not effortless to spark chemical reactions with other substances in the past decades. Nevertheless, the cognition of scientists has gradually changed accompanied with a variety of studies revealing the potential molecular mechanism underlying organ-protection induced by helium. Especially, as a non-anesthetic gas which is deficient of relevant cardiopulmonary side effects, helium conditioning is recognized as an emerging and promising approach to exert favorable effects by mimicking the cardioprotection of anesthetic gases or xenon. In this review we will summarize advances in the underlying biological mechanisms and clinical applicability with regards to the cardioprotective effects of helium.

Thyroid hormones correlate with field metabolic rate in ponies, Equus ferus caballus

During winter free living herbivores are often exposed to reduced energy supply at the same time that energy needs for thermoregulation increase. Several wild herbivores as well as robust horse breeds reduce their metabolism during times of low ambient temperature and food shortage. Thyroid hormones (TH) affect metabolic intensity and a positive effect of TH on basal metabolic rate (BMR) has been demonstrated in mammals and birds. As BMR and field metabolic rate (FMR) are often assumed to be intrinsically linked, TH may represent a reliable indicator for FMR. To test this hypothesis, ten Shetland pony mares were kept under semi-extensive central European conditions. During the winter month one group was fed 60% and one group 100% of their maintenance energy requirements. We measured FMR, locomotor activity, resting heart rate and TH levels in summer and winter. FMR, locomotor activity, resting heart rate and total T3 concentrations decreased substantially in winter compared to summer, whereas total T4 increased. Feed restriction led to a reduced FMR and resting heart rate, while TH and locomotor activity were not affected. Across both seasons FMR, resting heart and locomotor activity were positively correlated with total T3 but negatively and more weakly related with total T4.

Improved contractility with tepid modified full blood cardioplegia compared with cold crystalloid cardioplegia in a piglet model

OBJECTIVES

Experience regarding warm blood cardioplegia according to Calafiore results from its broad use in adult patients. In this experimental study, tepid (28°C) modified full blood cardioplegia (MBC) was adopted for paediatric use and compared with cold crystalloid cardioplegia (CCC).

METHODS

Twenty male piglets (mean weight: 11.1 ± 1.0 kg) were operated on cardiopulmonary bypass (CPB) in moderate hypothermia (28°C) and randomized to MBC (n = 8) or CCC (n = 12) for 60 min aortic cross-clamping. Blood levels of myocardial proteins [N-terminal pro-brain natriuretic peptide (NT-pro-BNP), myoglobin, creatine kinase type MB and troponin-I] were investigated at the beginning of the experiment and after CPB. Haemodynamic measurements included thermodilution and conductance-catheter technique inserted through the left ventricle-apex. Pressure-volume loop analysis was performed with dobutamine-stress test and inflow occlusion, enabling preload independent evaluation of myocardial performance. Changes of measured data post-CPB were calculated in relation to baseline-levels (%).

RESULTS

Baseline and operative data in both groups were similar. During the experiment, cardiac markers showed no significant variations between groups. Pressure-volume loop analysis during stress test revealed a significantly higher preload independent contractility (slope of end-systolic pressure-volume relation: Ees) with MBC compared with CCC (MBC: 123 ± 35% [confidence interval (CI95): 93-153] vs CCC: 78 ± 34% [CI95: 54-102]; P = 0.042), whereas cardiac output was not significantly different between groups {MBC: 122 ± 16% [95% confidence interval (CI95): 109-135] vs CCC: 105 ± 17% [CI95: 93-116]; P = 0.069}.

CONCLUSION

This randomized animal study proves feasibility and safety of MBC for paediatric use. Haemodynamic evaluation and cardiac markers did not show inferiority to standard CCC. Moreover, MBC seems to be associated with superior contractility post bypass, which encourages us to use MBC in paediatric patients in the near future.

Saving energy during hard times: energetic adaptations of Shetland pony mares

Recent results suggest that wild Northern herbivores reduce their metabolism during times of low ambient temperature and food shortage in order to reduce their energetic needs. It is, however, not known whether domesticated animals are also able to reduce their energy expenditure. We exposed 10 Shetland pony mares to different environmental conditions (summer and winter) and to two food quantities (60% and 100% of maintenance energy requirement) during low winter temperatures to examine energetic and behavioural responses. In summer, ponies showed a considerably higher field metabolic rate (FMR; 63.4±15.0 MJ day(-1)) compared with food-restricted and control animals in winter (24.6±7.8 and 15.0±1.1 MJ day(-1), respectively). During summer, locomotor activity, resting heart rate and total water turnover were considerably elevated (P<0.001) compared with winter. Animals on a restricted diet (N=5) compensated for the decreased energy supply by reducing their FMR by 26% compared with control animals (N=5). Furthermore, resting heart rate, body mass and body condition score were lower (29.2±2.7 beats min(-1), 140±22 kg and 3.0±1.0 points, respectively) than in control animals (36.8±41 beats min(-1), 165±31 kg, 4.4±0.7 points; P<0.05). While the observed behaviour did not change, nocturnal hypothermia was elevated. We conclude that ponies acclimatize to different climatic conditions by changing their metabolic rate, behaviour and some physiological parameters. When exposed to energy challenges, ponies, like wild herbivores, exhibited hypometabolism and nocturnal hypothermia.

The role of helium gas in medicine

The noble gas helium has many applications owing to its distinct physical and chemical characteristics, namely: its low density, low solubility, and high thermal conductivity. Chiefly, the abundance of studies in medicine relating to helium are concentrated in its possibility of being used as an adjunct therapy in a number of respiratory ailments such as asthma exacerbation, COPD, ARDS, croup, and bronchiolitis. Helium gas, once believed to be biologically inert, has been recently shown to be beneficial in protecting the myocardium from ischemia by various mechanisms. Though neuroprotection of brain tissue has been documented, the mechanism by which it does so has yet to be made clear. Surgeons are exploring using helium instead of carbon dioxide to insufflate the abdomen of patients undergoing laparoscopic abdominal procedures due to its superiority in preventing respiratory acidosis in patients with comorbid conditions that cause carbon dioxide retention. Newly discovered applications in Pulmonary MRI radiology and imaging of organs in very fine detail using Helium Ion Microscopy has opened exciting new possibilities for the use of helium gas in technologically advanced fields of medicine.

Adaptation strategies to seasonal changes in environmental conditions of a domesticated horse breed, the Shetland pony (Equus ferus caballus)

Recent results suggest that the wild ancestor of the horse, the Przewalski horse, exhibits signs of a hypometabolism. However, there are speculations that domestic animals lost the ability to reduce energy expenditure during food shortage and adverse environmental conditions. Therefore, we investigated physiological and behavioural strategies employed by a robust domesticated horse breed, the Shetland pony, over the course of a year under temperate conditions by measuring ambient temperature (T(a)), subcutaneous temperature (T(s)), locomotor activity (LA), lying time, resting heart rate, body mass and body condition score. Ten animals were kept on pasture in summer and in open stables in winter; further, in winter the animals were allocated into one control and one feed-restricted group of five animals each to simulate natural seasonal food shortage. The annual course of the mean daily T(s) of all horses showed distinct fluctuations from a mean of 35.6±0.5°C, with higher variations in summer than in winter. Diurnal amplitudes in T(s) were highest (P<0.001) in April (12.6°C) and lowest in January (4.0°C), with a nadir around dawn and a peak around mid-day. The feed-restricted group had a significantly lower daily T(s) compared with the control group on cold winter days, with T(a) values below 0°C. Mean annual heart rate and LA followed T(a) closely. Heart rate of the feed-restricted animals significantly decreased from a mean of 52.8±8.1 beats min(-1) in summer to 29±3.9 beats min(-1) in winter and differed from the control group (P<0.001). Mean daily LA was lowest at the end of winter (7000 activity impulses day(-1)) and highest in summer (25,000 activity impulses day(-1)). Our results show that Shetland ponies exhibit signs of a winter hypometabolism indicated by reduced heart rate and T(s). Thus, domesticated horses seem to have maintained the capacity for seasonal adaptation to environmental conditions by seasonal fluctuations in their metabolic rate.

Single cell transcriptomics of hypothalamic warm sensitive neurons that control core body temperature and fever response Signaling asymmetry and an extension of chemical neuroanatomy

We report on an 'unbiased' molecular characterization of individual, adult neurons, active in a central, anterior hypothalamic neuronal circuit, by establishing cDNA libraries from each individual, electrophysiologically identified warm sensitive neuron (WSN). The cDNA libraries were analyzed by Affymetrix microarray. The presence and frequency of cDNAs were confirmed and enhanced with Illumina sequencing of each single cell cDNA library. cDNAs encoding the GABA biosynthetic enzyme Gad1 and of adrenomedullin, galanin, prodynorphin, somatostatin, and tachykinin were found in the WSNs. The functional cellular and in vivo studies on dozens of the more than 500 neurotransmitters, hormone receptors and ion channels, whose cDNA was identified and sequence confirmed, suggest little or no discrepancy between the transcriptional and functional data in WSNs; whenever agonists were available for a receptor whose cDNA was identified, a functional response was found. Sequencing single neuron libraries permitted identification of rarely expressed receptors like the insulin receptor, adiponectin receptor 2 and of receptor heterodimers; information that is lost when pooling cells leads to dilution of signals and mixing signals. Despite the common electrophysiological phenotype and uniform Gad1 expression, WSN transcriptomes show heterogeneity, suggesting strong epigenetic influence on the transcriptome. Our study suggests that it is well-worth interrogating the cDNA libraries of single neurons by sequencing and chipping.

Dry heat, moist heat and body fat: are heating modalities really effective in people who are overweight?

Surface heating modalities are commonly used in physical therapy and physical medicine for increasing circulation, especially in deep tissues, to promote healing. However, recent evidence seems to indicate that in people who are overweight, heat transfer is impaired by the subcutaneous fat layer. The present investigation was conducted on 10 subjects aged 22-54 years, whose body mass index averaged 25.8+/-4.6. Subcutaneous fat above the quadriceps muscle varied from 0.51 to 0.86 cm of thickness. Three heating modalities were examined: the application of dry heat with a commercial chemical heat pack, hydrocollator heat packs (providing a type of moist heat), and a whirlpool, where conductive heat loss through water contact would be very high. The temperature of the skin and the temperature in the muscle (25 mm below the skin surface) were assessed by thermocouples. The results of the experiments showed that for heating modalities that are maintained in skin contact for long periods of time, such as dry heat packs (in place for 6 hours), subcutaneous fat did not impair the change in deep muscle temperature. In contrast, when rapid heat modalities were used, such as the hydrocollator and the whirlpool (15 minutes of sustained skin contact), the transfer of heat from the skin to deep muscle was significantly impaired in people with thicker subcutaneous fat layers. We observed that the greater the impairment in heat transfer to muscle from skin covered by body fat, the warmer the skin temperature increase during the modality.