The contribution of the mouse tail to thermoregulation is modest

Involvement of the gut microbiota in the metabolic phenotypes of two sympatric gerbils

Temporal niche partitioning is a crucial strategy for sympatric species to avoid predation and competition for habitat space and food resources. This study investigated the effect of the gut microbiota on the metabolic rhythms of two sympatric gerbil species (Meriones unguiculatus and Meriones meridianus) to test the hypothesis that the oscillatory patterns of microbiota may not fully mirror those of the host's metabolism. Experiment 1 compared the circadian metabolic and gut microbiota rhythms of M. unguiculatus (n = 12) and M. meridianus (n = 12) and measured the subjects' body temperatures and environmental temperature preferences. In Experiment 2.1, six M. meridianus gerbils were treated with antibiotics, and in Experiment 2.2, 21 M. unguiculatus gerbils (seven per treatment) were randomly gavaged with saline or a gut microbiota suspension from either M. unguiculatus or M. meridianus; their metabolic rhythms were subsequently measured. The results showed that the two gerbils had different metabolic phenotypes that determined activity heterogeneity and contributed to their coexistence. The relative abundances of Bacteroidetes, Actinobacteria, and Cyanobacteria in M. meridianus varied rhythmically in parallel with the daily metabolic rate, which was significantly higher at night than during the day. The rhythm of the metabolic rate was not noticeable in M. unguiculatus. However, in M.unguiculatus, the relative abundances of Firmicutes, Bacteroidetes, Proteobacteria, and Verrucomicrobia were significantly higher during the day than at night, while Cyanobacteria exhibited the opposite pattern. Antibiotic treatment significantly weakened the metabolic rhythms of M. meridianus, and the circadian rhythms slowly recovered after stopping antibiotic gavage. However, after transplanting M. meridianus' gut microbiota into M. unguiculatus, the metabolic rate of M. unguiculatus was not significantly different from that of the control groups. Our hypothesis was partly supported: the microbiota was only partially involved in regulating the metabolic rhythms of gerbils, and other factors could compensate for the effect of the gut microbiota on host metabolic rhythms. This finding underscores the complexity of host-microbiota interactions and highlights the need for further exploration into the multifaceted mechanisms governing host metabolic regulation.

Aging is associated with impaired triggering of TRPV3-mediated cutaneous vasodilation: a crucial process for local heat exposure

Sensing temperature is vitally important to adapt our body to environmental changes. Local warm detection is required to initiate regulation of cutaneous blood flow, which is part of the peripheral thermoregulatory mechanisms, and thus avoid damage to surrounding tissues. The mechanisms mediating cutaneous vasodilation during local heat stress are impaired with aging. However, the impact of aging on the ability of the skin to detect subtle thermal changes is unknown. Among heat-activated cation channels, transient receptor potential vanilloid 3 (TRPV3) is a thermo-sensor predominantly expressed on keratinocytes and involved in local vascular thermoregulatory mechanisms of the skin in young mice. In the present study, using a murine in vivo model of local heat exposure of the skin, we showed that heat-induced vasodilation was reduced in old mice associated with reduced expression of TRPV3 channels. We also found a decrease in expression and activity of TRPV3 channel, as well as reduced TRPV3-dependent adenosine tri-phosphate release in human primary keratinocytes from old donors. This study shows that aging alters the epidermal TRPV3 channels, which might delay the detection of changes in skin temperature, thereby limiting the mechanisms triggered for local vascular thermoregulation in the old skin.

Beyond day and night: The importance of ultradian rhythms in mouse physiology

Our circadian world shapes much of metabolic physiology. In mice ∼40% of the light and ∼80% of the dark phase time is characterized by bouts of increased energy expenditure (EE). These ultradian bouts have a higher body temperature (Tb) and thermal conductance and contain virtually all of the physical activity and awake time. Bout status is a better classifier of mouse physiology than photoperiod, with ultradian bouts superimposed on top of the circadian light/dark cycle. We suggest that the primary driver of ultradian bouts is a brain-initiated transition to a higher defended Tb of the active/awake state. Increased energy expenditure from brown adipose tissue, physical activity, and cardiac work combine to raise Tb from the lower defended Tb of the resting/sleeping state. Thus, unlike humans, much of mouse metabolic physiology is episodic with large ultradian increases in EE and Tb that correlate with the active/awake state and are poorly aligned with circadian cycling.

Exertional heat stroke causes long-term skeletal muscle epigenetic reprogramming, altered gene expression, and impaired satellite cell function in mice

The effect of exertional heat stroke (EHS) exposure on skeletal muscles is incompletely understood. Muscle weakness is an early symptom of EHS but is not considered a major target of multiorgan injury. Previously, in a preclinical mouse model of EHS, we observed the vulnerability of limb muscles to a second EHS exposure, suggesting hidden processes contributing to declines in muscle resilience. Here, we evaluated the possible molecular origins of EHS-induced declines in muscle resilience. Female C57BL/6 mice [total n = 56; 28/condition, i.e., EHS and exercise control (EXC)] underwent forced wheel running at 37.5°C/40% relative humidity until symptom limitation (unconsciousness). EXC mice exercised identically at room temperature (22-23°C). After 1 mo of recovery, the following were assessed: 1) specific force and caffeine-induced contracture in soleus (SOL) and extensor digitorum longus (EDL) muscles; 2) transcriptome and DNA methylome responses in gastrocnemius (GAST); and 3) primary satellite cell function (proliferation and differentiation). There were no differences in specific force in either SOL or EDL from EXC. Only EHS solei exhibited lower caffeine sensitivity. EHS GAST exhibited higher RNA expression of genes encoding structural proteins of slow fibers, heat shock proteins, and myogenesis. A total of ∼2,500 differentially methylated regions of DNA that could potentially affect many cell functions were identified. Primary satellite cells exhibited suppressed proliferation rates but normal differentiation responses. Results demonstrate long-term changes in skeletal muscles 1 mo after EHS that could contribute to declines in muscle resilience. Skeletal muscle may join other, more recognized tissues considered vulnerable to long-term effects of EHS.NEW & NOTEWORTHY Exertional heat stroke (EHS) in mice induces long-term molecular and functional changes in limb muscle that could reflect a loss of "resilience" to further stress. The phenotype was characterized by altered caffeine sensitivity and suppressed satellite cell proliferative potential. This was accompanied by changes in gene expression and DNA methylation consistent with ongoing muscle remodeling and stress adaptation. We propose that EHS may induce a prolonged vulnerability of skeletal muscle to further stress or injury.

Traumatic brain injury extending to the striatum alters autonomic thermoregulation and hypothalamic monoamines in recovering rats

The brain cortex is the structure that is typically injured in traumatic brain injury (TBI) and is anatomically connected with other brain regions, including the striatum and hypothalamus, which are associated in part with motor function and the regulation of body temperature, respectively. We investigated whether a TBI extending to the striatum could affect peripheral and core temperatures as an indicator of autonomic thermoregulatory function. Moreover, it is unknown whether thermal modulation is accompanied by hypothalamic and cortical monoamine changes in rats with motor function recovery. The animals were allocated into three groups: the sham group (sham), a TBI group with a cortical contusion alone (TBI alone), and a TBI group with an injury extending to the dorsal striatum (TBI + striatal injury). Body temperature and motor deficits were evaluated for 20 days post-injury. On the 3rd and 20th days, rats were euthanized to measure the serotonin (5-HT), noradrenaline (NA), and dopamine (DA) levels using high-performance liquid chromatography (HPLC). We observed that TBI with an injury extending to the dorsal striatum increased core and peripheral temperatures. These changes were accompanied by a sustained motor deficit lasting for 14 days. Furthermore, there were notable increases in NA and 5-HT levels in the brain cortex and hypothalamus both 3 and 20 days after injury. In contrast, rats with TBI alone showed no changes in peripheral temperatures and achieved motor function recovery by the 7th day post-injury. In conclusion, our results suggest that TBI with an injury extending to the dorsal striatum elevates both core and peripheral temperatures, causing a delay in functional recovery and increasing hypothalamic monoamine levels. The aftereffects can be attributed to the injury site and changes to the autonomic thermoregulatory functions.

Delayed metabolic disturbances in the myocardium after exertional heat stroke: contrasting effects of exertion and thermal load

Epidemiological studies report higher risks of cardiovascular disease in humans exposed to heat stroke earlier in life. Previously, we explored mechanistic links between heat stroke and developing cardiac abnormalities using a preclinical mouse model of exertional heat stroke (EHS). Profound metabolic abnormalities developed in the ventricles of females but not males after 2 wk of recovery. Here we tested whether this lack of response in males could be attributed to the lower exercise performances or reduced thermal loads they experienced with the same running protocol. We systematically altered environmental temperature (Te) during EHS to manipulate heat exposure and exercise performance in the males. Three groups of adult C57BL/6 male mice were studied: "EHS-34" (Te = 34°C), "EHS-41" (Te = 41°C), and "EHS-39.5" (Te = 39.5°C). Mice ran until symptom limitation (unconsciousness), reaching max core temperature (Tc,max). After a 2-wk recovery, the mice were euthanized, and the ventricles were removed for untargeted metabolomics. Results were compared against age-matched nonexercise controls. The EHS-34 mice greatly elevated their exercise performance but reached lower Tc,max and lower thermal loads. The EHS-41 mice exhibited equivalent thermal loads, exercise times, and Tc,max compared with EHS-39.5. The ventricles from EHS-34 mice exhibited the greatest metabolic disturbances in the heart, characterized by shifts toward glucose metabolism, reductions in acylcarnitines, increased amino acid metabolites, elevations in antioxidants, altered TCA cycle flux, and increased xenobiotics. In conclusion, delayed metabolic disturbances following EHS in male myocardium appear to be greatly amplified by higher levels of exertion in the heat, even with lower thermal loads and max core temperatures.NEW & NOTEWORTHY Epidemiological data demonstrate greater cardiovascular risk in patients with previous heat stroke exposure. Using a preclinical mouse model of exertional heat stroke, male mice were exposed to one of three environmental temperatures (Te) during exercise. Paradoxically, after 2 wk, the mice in the lowest Te, exhibiting the largest exercise response and lowest heat load, had the greatest ventricular metabolic disturbances. Metabolic outcomes resemble developing left ventricular hypertrophy or stress-induced heart disease.

Inhibition of adipose tissue angiogenesis prevents rebound weight gain after caloric restriction in mice fed a high-fat diet

AIMS

We investigated whether modulation of white adipose tissue (WAT) vasculature regulates rebound weight gain (RWG) after caloric restriction (CR) in mice fed a high-fat diet (HFD).

MAIN METHODS

We compared changes in energy balance, hypothalamic neuropeptide gene expression, and characteristics of WAT by RT-qPCR, ELISA, immunohistochemistry, and adipose-derived stromal vascular fraction spheroid sprouting assay in obese mice fed a HFD ad libitum (HFD-AL), mice under 40 % CR for 3 or 4 weeks, mice fed HFD-AL for 3 days after CR (CRAL), and CRAL mice treated with TNP-470, an angiogenic inhibitor.

KEY FINDINGS

WAT angiogenic genes were expressed at low levels, but WAT vascular density was maintained in the CR group compared to that in the HFD-AL group. The CRAL group showed RWG, fat regain, and hyperphagia with higher expression of angiogenic genes and reduced pericyte coverage of the endothelium in WAT on day 3 after CR compared to the CR group, indicating rapidly increased angiogenic activity after CR. Administration of TNP-470 suppressed RWG, fat regain, and hyperphagia only after CR compared to the CRAL group. Changes in circulating leptin levels and hypothalamic neuropeptide gene expression were correlated with changes in weight and fat mass, suggesting that TNP-470 suppressed hyperphagia independently of the hypothalamic melanocortin system. Additionally, TNP-470 increased gene expression related to thermogenesis, fuel utilization, and browning in brown adipose tissue (BAT) and WAT, indicating TNP-470-induced increase in thermogenesis.

SIGNIFICANCE

Modulation of the WAT vasculature attenuates RWG after CR by suppressing hyperphagia and increasing BAT thermogenesis and WAT browning.

Arteries are finely tuned thermosensors regulating myogenic tone and blood flow

In response to changing blood pressure, arteries adjust their caliber to control perfusion. This vital autoregulatory property, termed vascular myogenic tone, stabilizes downstream capillary pressure. We discovered that tissue temperature critically determines myogenic tone. Heating steeply activates tone in skeletal muscle, gut, brain and skin arteries with temperature coefficients ( Q ₁₀ ) of ∼11-20. Further, arterial thermosensitivity is tuned to resting tissue temperatures, making myogenic tone sensitive to small thermal fluctuations. Interestingly, temperature and intraluminal pressure are sensed largely independently and integrated to trigger myogenic tone. We show that TRPV1 and TRPM4 mediate heat-induced tone in skeletal muscle arteries. Variations in tissue temperature are known to alter vascular conductance; remarkably, thermosensitive tone counterbalances this effect, thus protecting capillary integrity and fluid balance. In conclusion, thermosensitive myogenic tone is a fundamental homeostatic mechanism regulating tissue perfusion.

One-Sentence Summary

Arterial blood pressure and temperature are integrated via thermosensitve ion channels to produce myogenic tone.

A mast cell-thermoregulatory neuron circuit axis regulates hypothermia in anaphylaxis

IgE-mediated anaphylaxis is an acute life-threatening systemic reaction to allergens, including certain foods and venoms. Anaphylaxis is triggered when blood-borne allergens activate IgE-bound perivascular mast cells (MCs) throughout the body, causing an extensive systemic release of MC mediators. Through precipitating vasodilatation and vascular leakage, these mediators are believed to trigger a sharp drop in blood pressure in humans and in core body temperature in animals. We report that the IgE/MC-mediated drop in body temperature in mice associated with anaphylaxis also requires the body's thermoregulatory neural circuit. This circuit is activated when granule-borne chymase from MCs is deposited on proximal TRPV1+ sensory neurons and stimulates them via protease-activated receptor-1. This triggers the activation of the body's thermoregulatory neural network, which rapidly attenuates brown adipose tissue thermogenesis to cause hypothermia. Mice deficient in either chymase or TRPV1 exhibited limited IgE-mediated anaphylaxis, and, in wild-type mice, anaphylaxis could be recapitulated simply by systemically activating TRPV1+ sensory neurons. Thus, in addition to their well-known effects on the vasculature, MC products, especially chymase, promote IgE-mediated anaphylaxis by activating the thermoregulatory neural circuit.

Individual variation in heat substitution: is activity in the cold energetically cheaper for some individuals than others?

In many endotherms, a potentially important yet often overlooked mechanism to save energy is the use of the heat generated by active skeletal muscles to replace heat that would have been generated by thermogenesis (i.e., "activity-thermoregulatory heat substitution"). While substitution has been documented numerous times, the extent of individual variation in substitution has never been quantified. Here, we used a home-cage respirometry system to repeatedly measure substitution through the concomitant monitoring of metabolic rate (MR) and locomotor activity in 46 female white-footed mice (Peromyscus leucopus). A total of 117 measures of substitution were taken by quantifying the difference in the slope of the relationship between MR and locomotor activity speed at two different ambient temperatures. Consistency repeatability (±se) of substitution was 0.313±0.131 - hence, about a third of the variation in substitution occurs at the among-individual level. Body length and heart mass were positively correlated with substitution whereas surface area was negatively correlated with substitution. These two sub-organismal traits accounted for the majority of the among-individual variation (i.e., individual differences in substitution were not significant after accounting for these traits). Overall, our results imply that the energetic cost of activity below the thermoneutral zone is consistently cheaper from some individuals than others, and that the energy saved from substitution might be available to invest in fitness-enhancing activities.

Effect of Different Ambient Temperatures on Reproductive Outcome and Stress Level of Lactating Females in Two Mouse Strains

Simple Summary

The optimal temperature for laboratory mice has been under discussion for some time. Current standard temperature is 20 °C–24 °C but it has been suggested to elevate the standard to 30 °C, which is the thermoneutral zone for mice. In this study, the effect of different cage temperatures (20 °C, 25 °C, 30 °C) on reproduction and stress hormone metabolite excretion was evaluated in lactating females of two commonly used mouse strains. Pup loss was higher, and weights of mothers and pups were reduced at 30 °C compared to the lower temperatures. In addition, pups showed increased tail length at weaning under the high temperature (30 °C). There was no difference in stress hormone metabolite excretion in mice between temperature groups. We could not show any detrimental effects of the lower or higher cage temperature on stress hormone metabolite excretion, but found decreased reproductive outcome under the higher temperature.

Abstract

Ambient temperature is an important non-biotic environmental factor influencing immunological and oncological parameters in laboratory mice. It is under discussion which temperature is more appropriate and whether the commonly used room temperature in rodent facilities of about 21 °C represents a chronic cold stress or the 30 °C of the thermoneutral zone constitutes heat stress for the animals. In this study, we selected the physiological challenging period of lactation to investigate the influence of a cage temperature of 20 °C, 25 °C, and 30 °C, respectively, on reproductive performance and stress hormone levels in two frequently used mouse strains. We found that B6D2F1 hybrid mothers weaned more pups compared to C57BL/6N mothers, and that the number of weaned pups was reduced when mothers of both strains were kept at 30 °C. Furthermore, at 30 °C, mothers and pups showed reduced body weight at weaning and offspring had longer tails. Despite pronounced temperature effects on reproductive parameters, we did not find any temperature effects on adrenocortical activity in breeding and control mice. Independent of the ambient temperature, however, we found that females raising pups showed elevated levels of faecal corticosterone metabolites (FCMs) compared to controls. Peak levels of stress hormone metabolites were measured around birth and during the third week of lactation. Our results provide no evidence of an advantage for keeping lactating mice in ambient temperatures near the thermoneutral zone. In contrast, we found that a 30 °C cage temperature during lactation reduced body mass in females and their offspring and declined female reproductive performance.

TIGAR deficiency enhances skeletal muscle thermogenesis by increasing neuromuscular junction cholinergic signaling

Cholinergic and sympathetic counter-regulatory networks control numerous physiological functions, including learning/memory/cognition, stress responsiveness, blood pressure, heart rate, and energy balance. As neurons primarily utilize glucose as their primary metabolic energy source, we generated mice with increased glycolysis in cholinergic neurons by specific deletion of the fructose-2,6-phosphatase protein TIGAR. Steady-state and stable isotope flux analyses demonstrated increased rates of glycolysis, acetyl-CoA production, acetylcholine levels, and density of neuromuscular synaptic junction clusters with enhanced acetylcholine release. The increase in cholinergic signaling reduced blood pressure and heart rate with a remarkable resistance to cold-induced hypothermia. These data directly demonstrate that increased cholinergic signaling through the modulation of glycolysis has several metabolic benefits particularly to increase energy expenditure and heat production upon cold exposure.

Temperature, heat shock proteins and growth regulation of the bone tissue

Ambient heat modulates the elongation of bones in mammals, and the mechanism of such a plasticity has not been studied completely. The influence of heat on growth and development of bone depends on its values. Five zones of temperature influence on the bone tissue with different biological effects have been distinguished : a) under-threshold thermal zone < 36.6 ºС, insufficient amount of heat is a limiting factor for osteogenesis; b) normal temperature zone 36.6‒37.5 ºС, the processes of breakdown and development of bone in this temperature range is balanced; b) zone of mild thermal shock 39‒41 ºС, the processes of functioning of osteoblasts, osteocytes and formation of the bone tissue intensify; d) the zone of sublethal thermal shock > 42 ºС, growth of bone slows; e) zone of non-critical shock > 50 ºС, bone tissue cells die. We propose a model of the mechanism of influence of heat shock on bone growth. Mild heat shock is a type of stress to which membrane enzymes adenylyl cyclase and cAMP-protein kinase react. Protein kinase A phosphorylates the gene factors of thermal shock proteins, stress proteins and enzymes of energy-generating processes – glycolysis and lipolysis. Heat shock protein HSP70 activates alkaline phosphatase and promotes the process of mineralization of the bone tissue. In the cells, there is intensification in syntheses of insulin-like growth factor-I, factors of mitogenic action, signals of intensification of blood circulation (NO) and synthesis of somatotropin. The affinity between insulin-like growth factor I and its acid-labile subunit decreases, leading to increased free and active insulin-like growth factor I. Against the background of acceleration of the capillarization process, energy generation and the level of stimulators of growth of bone tissue, mitotic and functional activities of producer cells of the bone – osteoblasts and osteocytes – activate. The generally known Allen’s rule has been developed and expanded: “Warm-blooded animals of different species have longer distal body parts (tails) if after birth the young have developed in the conditions of higher temperature”. The indicated tendency is realized through increased biosynthesis of heat shock proteins and other stimulators of growth processes in the bone tissue.

Role of TRPM8 in switching between fever and hypothermia in adult mice during endotoxin-induced inflammation

Transient receptor potential melastatin 8 (TRPM8) functions in the sensing of noxious and innocuous colds; however, its significance in pathogen-induced thermoregulation remains unclear. In the present study, we investigated the role of TRPM8 in the regulation of endotoxin-induced body temperature control. The peripheral administration of low-dose lipopolysaccharide (LPS) at 50 ​μg/kg generated fever in wild-type (WT) mice, whereas it caused hypothermia in TRPM8 knockout (KO) animals. LPS-induced sickness responses such as decrease in body weight, and food and water intake were not different between WT and TRPM8 KO mice. TRPM8 KO mice exhibited more severe hypothermia and lower locomotor activity following the peripheral administration of high-dose LPS at 5 ​mg/kg compared with WT ones. An intracerebroventricular (i.c.v.) injection of either LPS at 3.6 ​μg/kg or interleukin-1β at 400 ​ng/kg elicited hypothermia in TRPM8 KO mice, in contrast to fever in WT animals. The peripheral administration of zymosan at 3 ​mg/kg also induced hypothermia in contrast to fever in WT mice. An i.c.v. injection of prostaglandin E₂ at 16 or 160 ​nmol/kg induced normal fever in both WT and TRPM8 KO mice. Infrared thermography showed significant decline of the interscapular skin temperature that estimates temperature of the brown adipose tissue, regardless of no alteration of its temperature in WT animals. Fos immunohistochemistry showed stronger Fos activation of hypothalamic thermoregulation-associated nuclei in TRPM8 KO mice compared with WT animals following the peripheral administration of low-dose LPS. Therefore, the present study indicates that TRPM8 is necessary for switching between fever and hypothermia during endotoxin-induced inflammation.

The Hypothermic Effect of Hydrogen Sulfide Is Mediated by the Transient Receptor Potential Ankyrin-1 Channel in Mice

Hydrogen sulfide (H₂S) has been shown in previous studies to cause hypothermia and hypometabolism in mice, and its thermoregulatory effects were subsequently investigated. However, the molecular target through which H₂S triggers its effects on deep body temperature has remained unknown. We investigated the thermoregulatory response to fast-(Na₂S) and slow-releasing (GYY4137) H₂S donors in C57BL/6 mice, and then tested whether their effects depend on the transient receptor potential ankyrin-1 (TRPA1) channel in Trpa1 knockout (Trpa1^−/−) and wild-type (Trpa1^+/+) mice. Intracerebroventricular administration of Na₂S (0.5–1 mg/kg) caused hypothermia in C57BL/6 mice, which was mediated by cutaneous vasodilation and decreased thermogenesis. In contrast, intraperitoneal administration of Na₂S (5 mg/kg) did not cause any thermoregulatory effect. Central administration of GYY4137 (3 mg/kg) also caused hypothermia and hypometabolism. The hypothermic response to both H₂S donors was significantly (p < 0.001) attenuated in Trpa1^−/− mice compared to their Trpa1^+/+ littermates. Trpa1 mRNA transcripts could be detected with RNAscope in hypothalamic and other brain neurons within the autonomic thermoeffector pathways. In conclusion, slow- and fast-releasing H₂S donors induce hypothermia through hypometabolism and cutaneous vasodilation in mice that is mediated by TRPA1 channels located in the brain, presumably in hypothalamic neurons within the autonomic thermoeffector pathways.

The effects of housing density on mouse thermal physiology depend on sex and ambient temperature

Objective

To improve understanding of mouse energy homeostasis and its applicability to humans, we quantitated the effects of housing density on mouse thermal physiology in both sexes.

Methods

Littermate wild type and Brs3-null mice were single- or group- (three per cage) housed and studied by indirect calorimetry with continuous measurement of core body temperature, energy expenditure, physical activity, and food intake.

Results

At 23 °C, below thermoneutrality, single-housed males had a lower body temperature and unchanged metabolic rate compared to group-housed controls. In contrast, single-housed females maintained a similar body temperature to group-housed controls by increasing their metabolic rate. With decreasing ambient temperature below 27 °C, only group-housed mice decreased their heat conductance, likely due to huddling, thus interfering with the energy expenditure vs ambient temperature relationship described by Scholander. In a hot environment (35 °C), the single-housed mice were less heat stressed. Upon fasting, single-housed mice had larger reductions in body temperature, with male mice having more torpor episodes of similar duration and female mice having a similar number of torpor episodes that lasted longer. Qualitatively, the effects of housing density on thermal physiology of Brs3-null mice generally mimicked the effects in controls.

Conclusions

Single housing is more sensitive than group housing for detecting thermal physiology phenotypes. Single housing increases heat loss and amplifies the effects of fasting or a cold environment. Male and female mice utilize different thermoregulatory strategies to respond to single housing.

• Changing housing density changes thermal physiology and metabolic rate.

• Singly housed mice are more affected by fasting and by cold temperatures.

• Single housing is more sensitive than group housing for detecting thermal phenotypes.

• Certain principles of thermal physiology are masked by group housing.

• Male and female mice respond differently to single housing.

Preoptic BRS3 neurons increase body temperature and heart rate via multiple pathways

The preoptic area (POA) is a key brain region for regulation of body temperature (Tb), dictating thermogenic, cardiovascular, and behavioral responses that control Tb. Previously characterized POA neuronal populations all reduced Tb when activated. Using mice, we now identify POA neurons expressing bombesin-like receptor 3 (POABRS3) as a population whose activation increased Tb; inversely, acute inhibition of these neurons reduced Tb. POABRS3 neurons that project to either the paraventricular nucleus of the hypothalamus or the dorsomedial hypothalamus increased Tb, heart rate, and blood pressure via the sympathetic nervous system. Long-term inactivation of POABRS3 neurons caused increased Tb variability, overshooting both increases and decreases in Tb set point, with RNA expression profiles suggesting multiple types of POABRS3 neurons. Thus, POABRS3 neuronal populations regulate Tb and heart rate, contribute to cold defense, and fine-tune feedback control of Tb. These findings advance understanding of homeothermy, a defining feature of mammalian biology.

A Neuroscientist's Guide to the Vole

Prairie voles have emerged as an important rodent model for understanding the neuroscience of social behavior. Prairie voles are well known for their capacity for pair bonding and alloparental care. These behavioral phenomena overlap with human social behavior but are not commonly observed in traditional rodent models. In this article, we highlight the many benefits of using prairie voles in neuroscience research. We begin by describing the advantages of using diverse and non-traditional study models. We then focus on social behaviors, including pair bonding, alloparental care, and peer interactions, that have brought voles to the forefront of social neuroscience. We describe many additional features of prairie vole biology and behavior that provide researchers with opportunities to address an array of research questions. We also survey neuroethological methods that have been used with prairie voles, from classic to modern techniques. Finally, we conclude with a discussion of other vole species, particularly meadow voles, and their own unique advantages for neuroscience studies. This article provides a foundation for researchers who are new to working with voles, as well as for experienced neuroscientists who want to expand their research scope. © 2021 Wiley Periodicals LLC.

Mice as experimental models for human physiology: when several degrees in housing temperature matter

Standfirst: Some “species differences” between mouse and human can be diminished simply by housing mice at warmer temperatures. Failure to strategically turn up the thermostat may undermine translation of findings in mice into insights on human metabolic diseases.