Sex difference in thermal preference of adult mice does not depend on presence of the gonads

Sex differences in metabolic regulation by Gi/o-coupled receptor modulation of exocytosis

Background

Presynaptic Gi/o coupled GPCRs can act as negative feedback regulators of neurotransmitter release via Gβγ effector modulation through two mechanisms: decreased calcium influx and direct inhibition of membrane fusion by soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE). Previously, we discovered that truncation of the last three C-terminal amino acids of SNAP25 (SNAP25Δ3) prevents Gβγ-SNARE interaction, effectively removing the braking mechanism on neurotransmitter release. We have demonstrated enhanced metabolic protection in male SNAP25Δ3/Δ3 mice housed at room temperature (22°C), including increased adipose tissue beiging and glucose uptake and enhanced insulin sensitivity, rendering them resistant to diet-induced obesity (DIO). When male SNAP25Δ3/Δ3 mice were housed at thermoneutrality (30°C), all metabolic protection was abolished, suggesting sympathetic tone is important for the phenotypes.

Methods

We housed male and female mice at either standard room temperature (21°C) or at thermoneutrality (30°C) and fed them a high fat diet (HFD) for 8 weeks. Glucose tolerance tests were performed before and after the 8 weeks of HFD along with body composition analyses. Organs were then dissected for mass analysis as well as immunohistochemistry. Additionally, we ovariectomized female mice to investigate the role of sex hormones in our phenotypes. Finally, we housed mice in Sable Promethion chambers at various environmental temperatures to investigate the effect of environmental temperature on basal metabolic rates.

Results

We found SNAP25Δ3/Δ3 female mice exhibited the same metabolic protection at RT (22°C) and displayed enhanced metabolic protection from DIO compared to standard chow just as males did. However, female SNAP25Δ3/Δ3 mice display persistent metabolic protection even when housed at thermoneutrality. In this study, we investigate the mechanisms behind this sex dependent persistent phenotype. Thermoneutral set point did not differ between sexes nor genotype, suggesting that metabolic protection is not due to a difference in hypothalamic temperature regulation. Metabolic protection in SNAP25Δ3/Δ3 persisted in ovariectomized mice despite increased weight gain compared to mice receiving sham operations.

Conclusion

This study has identified that there is not a sex-dependent difference for thermoneutral set point in mice. Additionally, there is a sex hormone independent mechanism driving the persistent metabolic protection of female SNAP25Δ3/Δ3 mice housed in thermoneutrality.

Effect of Painful Stimuli on PVNCRH Neurons: Implications for States of Consciousness Under Isoflurane Anesthesia

BACKGROUND

Many patients undergoing surgery experience accompanying pain symptoms preoperatively. The impact of painful stimuli on general anesthesia remains largely unknown. Corticotrophin-releasing hormone neurons in the paraventricular nucleus of the hypothalamus (PVNCRH neurons) are crucial central stress hubs that respond to painful stimuli. These neurons also participate in regulating processes such as sleep and anesthesia. Natural reward can inhibit PVNCRH neurons to relieve stress-induced behavioral changes, but the effect of natural reward on the anesthesia process in patients with pain is not clear. In this study, we assessed the impact of painful stimuli on isoflurane anesthesia and its potential neural mechanism. We also investigated the potential of natural reward therapy for alleviating the impact of painful stimuli on isoflurane anesthesia.

METHODS

The righting reflex test and cortical electroencephalography (EEG) were used as measures of consciousness in complete Freund's adjuvant (CFA)-injected mice during isoflurane anesthesia. EEG and burst-suppression ratios (BSR) were used to assess the depth of anesthesia. The expression of c-Fos, fiber photometry recording, and brain slice electrophysiology were used to determine neuronal activity changes in PVNCRH neurons after CFA injection or 10% sucrose treatment. Finally, chemogenetic technology was used to specifically manipulate PVNCRH neurons.

RESULTS

Compared to the saline-injected mice, the CFA-injected mice exhibited an increased the mean[SD] induction time of isoflurane anesthesia (354[48] s vs 258[30] s, P = .0001) and a reduced BSR of isoflurane anesthesia (60.1[10.3] % vs 81.5[9.76] %, P = .002). CFA injection increased PVN c-Fos expression (3667[706] vs 1735[407], P = .0002) and enhanced the population activity of PVNCRH neurons (33.4[13.6] % vs 1.23[3.57] %, P = .0009). Chemogenetic suppression of PVNCRH neurons reversed the anesthesia abnormalities in CFA-injected mice. Natural reward accelerated the induction time of isoflurane anesthesia (252[24] s vs 324[36] s, P = .003) and increased the BSR of isoflurane anesthesia (84.8[5.36] % vs 57.7[14.3] %, P = .0005). Chemogenetic activation of PVNCRH neurons reversed the effect of natural reward on isoflurane anesthesia in CFA-injected mice.

CONCLUSIONS

Painful stimuli affect the process of isoflurane anesthesia by activating PVNCRH neurons, which implies that these neurons modulate isoflurane anesthesia. Additionally, natural reward alleviates the impact of painful stimuli on isoflurane anesthesia by inhibiting PVNCRH neurons.

Characterization of Reusable and Recyclable Plastic Bedding Materials for Laboratory Mice

The scientific community has placed increasing importance on sustainability, leading to the exploration of alternative bedding materials to the widely used aspen wood chips. Bedding plays a critical role in ensuring the wellbeing of animals and the validity of experimental outcomes. Compared to the frequently evaluated biological materials, such as corncobs or spelts, synthetic materials such as plastic granules have been less investigated. We characterized two thermostable plastic materials as an alternative bedding material in C57BL/6J and BALB/c mice. We examined the impact of those bedding alternatives on physiological parameters, behavior, health status, and cage climate in static and digitally ventilated cages as well as the possibility of a reuse cycle after reprocessing. The mouse lines showed different locomotor activity, feeding, and nestbuilding behavior on plastic granules. While ammonia levels were constantly higher in static cages than in ventilated cages, blood parameters were unaltered, and health status was maintained during the reuse procedure. We show the use of plastic granulate as bedding material for mice that has the potential for processing and recycling. Further, we show that the material is accepted differently by the lines in the preference choice test without affecting their health or hygiene status.

Anxiety-Like Behaviors in Mice Unmasked: Revealing Sex Differences in Anxiety Using a Novel Light-Heat Conflict Test

Anxiety and chronic pain afflict hundreds of millions worldwide. Anxiety and pain are more prevalent in females compared to males. Unfortunately, robust sex differences in human anxiety are not recapitulated in rodent tests, and results from rodent pain studies frequently fail to translate clinically. Therefore, there is a need to develop tests that reflect the differential salience of anxiety or pain-related stimuli between the sexes. Accordingly, here we introduce the Thermal Increments Dark-Light (TIDAL) conflict test. The TIDAL test places an anxiety-relevant stimulus (dark vs. illuminated chamber) in conflict with a heat-related stimulus (incrementally heated vs. isothermic chamber); mice freely explore both apparatus chambers. Here, we aim to determine whether the TIDAL conflict test reveals in mice underappreciated sex differences in anxiety and/or heat sensitivity. We establish in four distinct experiments that females on the TIDAL conflict test persist substantially longer on the dark-heated plate, suggesting that female mice exhibit elevated anxiety-like behavior. Mice more strongly prefer the heated-dark plate on the TIDAL conflict test compared to control thermal place preference with both chambers illuminated. We also reveal that an anxiety-relieving drug, paroxetine, reduces mouse preference for the heating dark plate, supporting the validity of the TIDAL test. Therefore, our new TIDAL conflict test reliably unmasks the relative salience of anxiety (vs. heat sensitivity): mice that are female exhibit robust anxiety-like behaviors not consistently observed in classical tests. Future studies should incorporate TIDAL and other conflict tests to better understand rodent behavior and to identify mechanisms underlying anxiety and pain.

Thermotherapy has sexually dimorphic responses in APP/PS1 mice

A thermoregulatory decline occurs with age due to changes in muscle mass, vasoconstriction, and metabolism that lowers core body temperature (Tc). Although lower Tc is a biomarker of successful aging, we have previously shown this worsens cognitive performance in the APP/PS1 mouse model of Alzheimer's disease (AD). We hypothesized that elevating Tc with thermotherapy would improve metabolism and cognition in APP/PS1 mice. From 6-12 months of age, male and female APP/PS1 and C57BL/6 mice were chronically housed at 23 or 30°C. At 12 months of age, mice were assayed for insulin sensitivity, glucose tolerance, and spatial cognition. Plasma, hippocampal, and peripheral (adipose, hepatic, and skeletal muscle) samples were procured postmortem and tissue-specific markers of amyloid accumulation, metabolism, and inflammation were assayed. Chronic 30°C exposure increased Tc in all groups except female APP/PS1 mice. All mice receiving thermotherapy had either improved glucose tolerance or insulin sensitivity, but the underlying processes responsible for these effects varied across sexes. In males, glucose regulation was influenced predominantly by hormonal signaling in plasma and skeletal muscle glucose transporter 4 expression, whereas in females, this was modulated at the tissue level. Thermotherapy improved spatial navigation in male C57BL/6 and APP/PS1 mice, with the later attributed to reduced hippocampal soluble amyloid-β (Aβ)42. Female APP/PS1 mice exhibited worse spatial memory recall after chronic thermotherapy. Together, the data highlights the metabolic benefits of passive thermotherapy, but future studies are needed to determine therapeutic benefits for those with AD.

The IgLON family of cell adhesion molecules expressed in developing neural circuits ensure the proper functioning of the sensory system in mice

Deletions and malfunctions of the IgLON family of cell adhesion molecules are associated with anatomical, behavioral, and metabolic manifestations of neuropsychiatric disorders. We have previously shown that IgLON genes are expressed in sensory nuclei/pathways and that IgLON proteins modulate sensory processing. Here, we examined the expression of IgLON alternative promoter-specific isoforms during embryonic development and studied the sensory consequences of the anatomical changes when one of the IgLON genes, Negr1, is knocked out. At the embryonal age of E12.5 and E13.5, various IgLONs were distributed differentially and dynamically in the developing sensory areas within the central and peripheral nervous system, as well as in limbs and mammary glands. Sensory tests showed that Negr1 deficiency causes differences in vestibular function and temperature sensitivity in the knockout mice. Sex-specific differences were noted across olfaction, vestibular functioning, temperature regulation, and mechanical sensitivity. Our findings highlight the involvement of IgLON molecules during sensory circuit formation and suggest Negr1's critical role in somatosensory processing.

Dim light at night unmasks sex-specific differences in circadian and autonomic regulation of cardiovascular physiology

Shift work and artificial light at night disrupt the entrainment of endogenous circadian rhythms in physiology and behavior to the day-night cycle. We hypothesized that exposure to dim light at night (dLAN) disrupts feeding rhythms, leading to sex-specific changes in autonomic signaling and day-night heart rate and blood pressure rhythms. Compared to mice housed in 12-hour light/12-hour dark cycles, mice exposed to dLAN showed reduced amplitudes in day-night feeding, heart rate, and blood pressure rhythms. In female mice, dLAN reduced the amplitude of day-night cardiovascular rhythms by decreasing the relative sympathetic regulation at night, while in male mice, it did so by increasing the relative sympathetic regulation during the daytime. Time-restricted feeding to the dim light cycle reversed these autonomic changes in both sexes. We conclude that dLAN induces sex-specific changes in autonomic regulation of heart rate and blood pressure, and time-restricted feeding may represent a chronotherapeutic strategy to mitigate the cardiovascular impact of light at night.

Thermotherapy has Sexually Dimorphic Responses in APP/PS1 Mice

A thermoregulatory decline occurs with age due to changes in muscle mass, vasoconstriction, and metabolism that lowers core body temperature (Tc). Although lower Tc is a biomarker of successful aging, we have previously shown this worsens cognitive performance in the APP/PS1 mouse model of Alzheimer's disease (AD) [1]. We hypothesized that elevating Tc with thermotherapy would improve metabolism and cognition in APP/PS1 mice. From 6-12 months of age, male and female APP/PS1 and C57BL/6 mice were chronically housed at 23 or 30°C. At 12 months of age, mice were assayed for insulin sensitivity, glucose tolerance, and spatial cognition. Plasma, hippocampal, and peripheral (adipose, hepatic, and skeletal muscle) samples were procured postmortem and tissue-specific markers of amyloid accumulation, metabolism, and inflammation were assayed. Chronic 30°C exposure increased Tc in all groups except female APP/PS1 mice. All mice receiving thermotherapy had either improved glucose tolerance or insulin sensitivity, but the underlying processes responsible for these effects varied across sexes. In males, glucose regulation was influenced predominantly by hormonal signaling in plasma and skeletal muscle glucose transporter 4 expression, whereas in females, this was modulated at the tissue level. Thermotherapy improved spatial navigation in male C57BL/6 and APP/PS1 mice, with the later attributed to reduced hippocampal soluble amyloid-β (Aβ)42. Female APP/PS1 mice exhibited worse spatial memory recall after chronic thermotherapy. Together, the data highlights the metabolic benefits of passive thermotherapy, but future studies are needed to determine therapeutic benefits for those with AD.

KCNQ1 is an essential mediator of the sex-dependent perception of moderate cold temperatures

Low temperatures and cooling agents like menthol induce cold sensation by activating the peripheral cold receptors TRPM8 and TRPA1, cation channels belonging to the TRP channel family, while the reduction of potassium currents provides an additional and/or synergistic mechanism of cold sensation. Despite extensive studies over the past decades to identify the molecular receptors that mediate thermosensation, cold sensation is still not fully understood and many cold-sensitive peripheral neurons do not express the well-established cold sensor TRPM8. We found that the voltage-gated potassium channel KCNQ1 (Kv7.1), which is defective in cardiac LQT1 syndrome, is, in addition to its known function in the heart, a highly relevant and sex-specific sensor of moderately cold temperatures. We found that KCNQ1 is expressed in skin and dorsal root ganglion neurons, is sensitive to menthol and cooling agents, and is highly sensitive to moderately cold temperatures, in a temperature range at which TRPM8 is not thermosensitive. C-fiber recordings from KCNQ1-/- mice displayed altered action potential firing properties. Strikingly, only male KCNQ1-/- mice showed substantial deficits in cold avoidance at moderately cold temperatures, with a strength of the phenotype similar to that observed in TRPM8-/- animals. While sex-dependent differences in thermal sensitivity have been well documented in humans and mice, KCNQ1 is the first gene reported to play a role in sex-specific temperature sensation. Moreover, we propose that KCNQ1, together with TRPM8, is a key instrumentalist that orchestrates the range and intensity of cold sensation.

Role of thermosensitive transient receptor potential (TRP) channels in thermal preference of male and female mice

Transient Receptor Potential (TRP) ion channels are important for sensing environmental temperature. In rodents, TRPV4 senses warmth (25-34 °C), TRPV1 senses heat (>42 °C), TRPA1 putatively senses cold (<17 °C), and TRPM8 senses cool-cold (18-26 °C). We investigated if knockout (KO) mice lacking these TRP channels exhibited changes in thermal preference. Thermal preference was tested using a dual hot-cold plate with one thermoelectric surface set at 30 °C and the adjacent surface at a temperature of 15-45 °C in 5 °C increments. Blinded observers counted the number of times mice crossed through an opening between plates and the percentage of time spent on the 30 °C plate. In a separate experiment, observers blinded as to genotype also assessed the temperature at the location on a thermal gradient (1.83 m, 4-50 °C) occupied by the mouse at 5- or 10-min intervals over 2 h. Male and female wildtype mice preferred 30 °C and significantly avoided colder (15-20 °C) and hotter (40-45 °C) temperatures. Male TRPV1KOs and TRPA1KOs, and TRPV4KOs of both sexes, were similar, while female WTs, TRPV1KOs, TRPA1KOs and TRPM8KOs did not show significant thermal preferences across the temperature range. Male and female TRPM8KOs did not significantly avoid the coldest temperatures. Male mice (except for TRPM8KOs) exhibited significantly fewer plate crossings at hot and cold temperatures and more crossings at thermoneutral temperatures, while females exhibited a similar but non-significant trend. Occupancy temperatures along the thermal gradient exhibited a broad distribution that shrank somewhat over time. Mean occupancy temperatures (recorded at 90-120 min) were significantly higher for females (30-34 °C) compared to males (26-27 °C) of all genotypes, except for TRPA1KOs which exhibited no sex difference. The results indicate (1) sex differences with females (except TRPA1KOs) preferring warmer temperatures, (2) reduced thermosensitivity in female TRPV1KOs, and (3) reduced sensitivity to cold and innocuous warmth in male and female TRPM8KOs consistent with previous studies.

Esketamine accelerates emergence from isoflurane general anaesthesia by activating the paraventricular thalamus glutamatergic neurones in mice

BACKGROUND

Delayed emergence from general anaesthesia poses a significant perioperative safety hazard. Subanaesthetic doses of ketamine not only deepen anaesthesia but also accelerate recovery from isoflurane anaesthesia; however, the mechanisms underlying this phenomenon remain elusive. Esketamine exhibits a more potent receptor affinity and fewer adverse effects than ketamine and exhibits shorter recovery times after brief periods of anaesthesia. As the paraventricular thalamus (PVT) plays a pivotal role in regulating wakefulness, we studied its role in the emergence process during combined esketamine and isoflurane anaesthesia.

METHODS

The righting reflex and cortical electroencephalography were used as measures of consciousness in mice during isoflurane anaesthesia with coadministration of esketamine. The expression of c-Fos was used to determine neuronal activity changes in PVT neurones after esketamine administration. The effect of esketamine combined with isoflurane anaesthesia on PVT glutamatergic (PVTGlu) neuronal activity was monitored by fibre photometry, and chemogenetic technology was used to manipulate PVTGlu neuronal activity.

RESULTS

A low dose of esketamine (5 mg kg-1) accelerated emergence from isoflurane general anaesthesia (474 [30] s vs 544 [39] s, P=0.001). Esketamine (5 mg kg-1) increased PVT c-Fos expression (508 [198] vs 258 [87], P=0.009) and enhanced the population activity of PVTGlu neurones (0.03 [1.7]% vs 6.9 [3.4]%, P=0.002) during isoflurane anaesthesia (1.9 [5.7]% vs -5.1 [5.3]%, P=0.016) and emergence (6.1 [6.2]% vs -1.1 [5.0]%, P=0.022). Chemogenetic suppression of PVTGlu neurones abolished the arousal-promoting effects of esketamine (459 [33] s vs 596 [33] s, P<0.001).

CONCLUSIONS

Our results suggest that esketamine promotes recovery from isoflurane anaesthesia by activating PVTGlu neurones. This mechanism could explain the rapid arousability exhibited upon treatment with a low dose of esketamine.

Consideration of the importance of measuring thermal discomfort in biomedical research

Core temperature stability is the result of a dynamically regulated balance of heat loss and gain, which is not reflected by a simple thermometer reading. One way in which these changes manifest is in perceived thermal comfort, 'feeling too cold' or 'feeling too hot', which can activate stress pathways. Unfortunately, there is surprisingly little preclinical research that tracks changes in perceived thermal comfort in response to either disease progression or various treatments. Without measuring this endpoint, there may be missed opportunities to evaluate disease and therapy outcomes in murine models of human disease. Here, we discuss the possibility that changes in thermal comfort in mice could be a useful and physiologically relevant measure of energy trade-offs required under various physiological or pathological conditions.

Spinal cord injury in mice amplifies anxiety: A novel light-heat conflict test exposes increased salience of anxiety over heat

Spinal cord injury (SCI) predisposes individuals to anxiety and chronic pain. Anxiety- and pain-like behavior after SCI can be tested in rodents, yet commonly used tests assess one variable and may not replicate effects of SCI or sex differences seen in humans. Thus, novel preclinical tests should be optimized to better evaluate behaviors relating to anxiety and pain. Here, we use our newly developed conflict test - the Thermal Increments Dark-Light (TIDAL) test - to explore how SCI affects anxiety- vs. pain-like behavior, and whether sex affects post-SCI behavior. The TIDAL conflict test consists of two plates connected by a walkway; one plate remains illuminated and at an isothermic temperature, whereas the other plate is dark but is heated incrementally to aversive temperatures. A control mice thermal place preference test was also performed in which both plates are illuminated. Female and male mice received moderate T9 contusion SCI or remained uninjured. At 7 days post-operative (dpo), mice with SCI increased dark plate preference throughout the TIDAL conflict test compared to uninjured mice. SCI increased dark plate preference for both sexes, although female (vs. male) mice remained on the heated-dark plate to higher temperatures. Mice with SCI that repeated TIDAL at 7 and 21 dpo showed reduced preference for the dark-heated plate at 21 dpo. Overall, in female and male mice, SCI enhances the salience of anxiety (vs. heat sensitivity). The TIDAL conflict test meets a need for preclinical anxiety- and pain-related tests that recapitulate the human condition; thus, future rodent behavioral studies should incorporate TIDAL or other conflict tests to help understand and treat neurologic disorders.

Sex differences in thermoregulation in mammals: Implications for energy homeostasis

Thermal homeostasis is a fundamental process in mammals, which allows the maintenance of a constant internal body temperature to ensure an efficient function of cells despite changes in ambient temperature. Increasing evidence has revealed the great impact of thermoregulation on energy homeostasis. Homeothermy requires a fine regulation of food intake, heat production, conservation and dissipation and energy expenditure. A great interest on this field of research has re-emerged following the discovery of thermogenic brown adipose tissue and browning of white fat in adult humans, with a potential clinical relevance on obesity and metabolic comorbidities. However, most of our knowledge comes from male animal models or men, which introduces unwanted biases on the findings. In this review, we discuss how differences in sex-dependent characteristics (anthropometry, body composition, hormonal regulation, and other sexual factors) influence numerous aspects of thermal regulation, which impact on energy homeostasis. Individuals of both sexes should be used in the experimental paradigms, considering the ovarian cycles and sexual hormonal regulation as influential factors in these studies. Only by collecting data in both sexes on molecular, functional, and clinical aspects, we will be able to establish in a rigorous way the real impact of thermoregulation on energy homeostasis, opening new avenues in the understanding and treatment of obesity and metabolic associated diseases.

Gender differences in narcolepsy: What are recent findings telling us?

Three papers currently published in SLEEP using two different mouse models of narcolepsy, including either Hcrt-tTa;TetO diptheria toxin-A (DTA) or Hypocretin knock-out (Hcrt-KO) mice, suggest important gender differences in narcolepsy expression. Specifically, these recent data corroborate previous findings in mice demonstrating that females show more cataplexy events and more total cataplexy expression than males. Moreover, in the neurotoxic DTA mouse model, females show earlier onset of cataplexy expression than males during active Hcrt cell loss. Finally, females show a doubling of cataplexy during estrous compared to other phases of the estrous cycle. These findings are reviewed in the broader context of prior published literature, including reported gender differences in Hcrt expression and hormonal influences on sleep and wakefulness. Although similar findings have not been reported in humans, a systematic evaluation of gender differences in human narcolepsy has yet to be performed. Taken together, these animal data suggest that more research exploring gender differences in human narcolepsy is warranted.

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.

Restoring VTA DA neurons excitability accelerates emergence from sevoflurane general anesthesia of anxiety state

Preoperative anxiety is common and often comes with a higher probability of worse recovery. However, the neurological mechanism of the effect of preoperative anxiety on general anesthesia and subsequent awakening remains unknown. In this study, we report an anxious state results in delayed awakening in anxiety model mice from sevoflurane general anesthesia. More profound inhibition of DA neurons in the VTA contributes to delayed awakening. Optogenetic stimulation of VTA DA neurons can reverse the delay. The results indicate that VTA DA neurons may be involved in the delay in awakening from general anesthesia caused by anxiety.

Thermal Preferences of Cowpea Seed Beetles (Callosobruchus maculatus): Effects of Sex and Nuptial Gift Transfers

Simple Summary

The thermal environment is crucial for organismal functioning, and many cold-blooded organisms, including insects, behaviorally regulate their body temperature. Why do insects inhabit given thermal conditions? We propose that access to water affects thermal preference and that insects with poor access to water inhabit colder environments, which reduces evaporation and preserves water. We studied the seed beetle Callosobruchus maculatus, which, as adults, do not drink or eat; however, males provide their mates with sperm, as well as nuptial gifts, including nutrients and water sources. We compared preferred temperatures between males and females that had access to mates or remained unmated and measured the sizes of the transferred gifts. We found that females preferred higher temperatures than males, but these preferences did not change due to mating or the transfer of larger or smaller gifts. It appears that males and females receive and lose certain amounts of water during mating, but they do not alter their thermal preferences according to the amount of water they receive or lose.

Abstract

The thermal environment influences insect performance, but the factors affecting insect thermal preferences are rarely studied. We studied Callosobruchus maculatus seed beetles and hypothesized that thermal preferences are influenced by water balance, with individuals with limited water reserves preferring cooler habitats to reduce evaporative water loss. Adult C. maculatus, in their flightless morph, do not consume food or water, but a copulating male provides a female with a nuptial gift of ejaculate containing nutrients and water. We hypothesized that gift recipients would prefer warmer habitats than gift donors and that both sexes would plastically adjust their thermal preferences according to the size of the transferred gift. We measured the thermal preference in each sex in individuals that were mated once or were unmated. In the mated group, we measured the sizes of the nuptial gifts and calculated proportional body mass changes in each mate during copulation. Supporting the role of water balance in thermal preference, females preferred warmer habitats than males. Nevertheless, thermal preferences in either sex were not affected by mating status or gift size. It is likely that high rates of mating and gift transfers in C. maculatus living under natural conditions promoted the evolution of constitutive sex-dependent thermal preferences.

The Impacts of Age and Sex in a Mouse Model of Childhood Narcolepsy

Narcolepsy is a sleep disorder caused by selective death of the orexin neurons that often begins in childhood. Orexin neuron loss disinhibits REM sleep during the active period and produces cataplexy, episodes of paralysis during wakefulness. Cataplexy is often worse when narcolepsy develops in children compared to adults, but the reason for this difference remains unknown. We used orexin-tTA; TetO DTA mice to model narcolepsy at different ages. When doxycycline is removed from the diet, the orexin neurons of these mice express diphtheria toxin A and die within 2-3 weeks. We removed doxycycline at 4 weeks (young-onset) or 14 weeks (adult-onset) of age in male and female mice. We implanted electroencephalography (EEG) and electromyography (EMG) electrodes for sleep recordings two weeks later and then recorded EEG/EMG/video for 24 h at 3 and 13 weeks after removal of doxycycline. Age-matched controls had access to doxycycline diet for the entire experiment. Three weeks after doxycycline removal, both young-onset and adult-onset mice developed severe cataplexy and the sleep-wake fragmentation characteristic of narcolepsy. Cataplexy and maintenance of wake were no worse in young-onset compared to adult-onset mice, but female mice had more bouts of cataplexy than males. Orexin neuron loss was similarly rapid in both young- and adult-onset mice. As age of orexin neuron loss does not impact the severity of narcolepsy symptoms in mice, the worse symptoms in children with narcolepsy may be due to more rapid orexin neuron loss than in adults.

Comprehensive somatosensory and neurological phenotyping of NCS1 knockout mice

Neuronal calcium sensor 1 (NCS1) regulates a wide range of cellular functions throughout the mammalian nervous systems. Altered NCS1 expression is associated with neurodevelopmental and neurodegenerative diseases. Previous studies focused on affective and cognitive behaviors in NCS1 knockout (KO) mice, but little is known about the physiological and pathological states associated with the loss of NCS1 in the peripheral nervous system. We previously reported that NCS1 expression was reduced following paclitaxel-induced peripheral neuropathy. Here, we comprehensively investigated the phenotypes of NCS1-KO mice through a battery of behavioral tests examining both central and peripheral nervous systems. Generally, only mild differences were observed in thermal sensation and memory acquisition between NCS1-WT and -KO male mice, but not in female mice. No differences were observed in motor performance, affective behaviors, and hearing in both sexes. These results suggest that NCS1 plays a modulatory role in sensory perceptions and cognition, particularly in male mice. NCS1 has been proposed as a pharmacological target for various diseases. Therefore, the sex-specific effects of NCS1 loss may be of clinical interest. As we examined a constitutive KO model, future studies focusing on various conditional KO models will further elucidate the precise physiological significance of NCS1.

Differential modulation of thermal preference after sensitization by optogenetic or pharmacological activation of heat-sensitive nociceptors

Common approaches to studying mechanisms of chronic pain and sensory changes in pre-clinical animal models involve measurement of acute, reflexive withdrawal responses evoked by noxious stimuli. These methods typically do not capture more subtle changes in sensory processing nor report on the consequent behavioral changes. In addition, data collection and analysis protocols are often labour-intensive and require direct investigator interactions, potentially introducing bias. In this study, we develop and characterize a low-cost, easily assembled behavioral assay that yields self-reported temperature preference from mice that is responsive to peripheral sensitization. This system uses a partially automated and freely available analysis pipeline to streamline the data collection process and enable objective analysis. We found that after intraplantar administration of the TrpV1 agonist, capsaicin, mice preferred to stay in cooler temperatures than saline injected mice. We further observed that gabapentin, a non-opioid analgesic commonly prescribed to treat chronic pain, reversed this aversion to higher temperatures. In contrast, optogenetic activation of the central terminals of TrpV1+ primary afferents via in vivo spinal light delivery did not induce a similar change in thermal preference, indicating a possible role for peripheral nociceptor activity in the modulation of temperature preference. We conclude that this easily produced and robust sensory assay provides an alternative approach to investigate the contribution of central and peripheral mechanisms of sensory processing that does not rely on reflexive responses evoked by noxious stimuli.

Selection for lower residual feed intake in mice is accompanied by increased body fatness and lower activity but not lower metabolic rate

Context Mice bred to be genetically different in feed efficiency were used in this experiment designed to help improve our knowledge of the biological basis of variation in feed efficiency between individual animals. Aims This experiment used mice to explore the metabolic basis of genetic variation in feed efficiency in the growing animal. Methods Mice bred to differ in residual feed intake (RFI) recorded over a postweaning test were used. After 11 generations of divergent selection, mice in groups were tested for RFI from 6 to 8, 8 to 10, and 10 to 12 weeks of age, and measured for traits describing the ability to digest feed, body composition, protein turnover, basal and resting metabolic rate, and level of activity. Key results Compared with the low-RFI (high efficiency) line mice, high-RFI mice consumed 28% more feed per day over their RFI-test, were no heavier, were leaner (16% less total fat per unit of bodyweight), did not differ in the fractional synthesis rate of protein in skeletal muscle or in liver, and had similar basal metabolic rates at 33°C. On an energy basis, the selection lines did not differ in energy retained in body tissue gain, which represented only 1.8% of metabolisable energy intake. The remaining 98.2% was lost as heat. Of the processes measured contributing to the higher feed intake by the high-RFI mice, 47% of the extra feed consumed was lost in faeces and urine, activity was 84% higher and accounted for 24%, the cost of protein gain was 6% higher and accounted for 2%, and the energy cost of digesting and absorbing the extra feed consumed and basal heat production could have accounted for 11 and 15% each. Conclusions Selection for low RFI (high efficiency) in mice was accompanied by an increase in body fat, an improvement in the process of digestion, a lower rate of protein turnover and a much lower level of activity. Selection did not result in major change in basal metabolic rate. Implications This experiment with mice provided new information on the biological basis of genetic differences in feed efficiency. The experiment investigated the relative importance of major energy-consuming metabolic processes and was able to quantify the responses in protein turnover and level of activity, being responses in energy-consuming processes that have proven difficult to quantitatively demonstrate in large farm animals.

Neuropeptide Y Regulation of Energy Partitioning and Bone Mass During Cold Exposure

The maintenance of whole body energy homeostasis is critical to survival and mechanisms exist whereby an organism can adapt to its environment and the stresses placed upon it. Environmental temperature and thermogenesis are key components known to affect energy balance. However, little is known about how these processes are balanced against the overall energy balance. We show that even mild cold exposure has a significant effect on energy expenditure and UCP-1 levels which increase by 43% and 400%, respectively, when wild-type (WT) mice at thermoneutral (29 °C) were compared to mice at room temperature (22 °C) conditions. Interestingly, bone mass was lower in cold-stressed WT mice with significant reductions in femoral bone mineral content (- 19%) and bone volume (- 13%). Importantly, these cold-induced skeletal changes were absent in mice lacking NPY, one of the main controllers of energy homeostasis, highlighting the critical role of NPY in this process. However, energy expenditure was significantly greater in cold-exposed NPY null mice, indicating that suppression of non-thermogenic tissues, like bone, contributes to the adaptive responses to cold exposure. Altogether, this work identifies NPY as being crucial in coordinating energy and bone homeostasis where it suppresses energy expenditure, UCP-1 levels and lowers bone mass under conditions of cold exposure.

Sex difference in cold perception and shivering onset upon gradual cold exposure

To maintain a thermal balance when experiencing cold, humans reduce heat loss and enhance heat production. A potent and rapid mechanism for heat generation is shivering. Research has shown that women prefer a warmer environment and feel less comfortable than men in the same thermal condition. Using the Blanketrol^® III, a temperature management device commonly used to study brown adipose tissue activity, we tested whether the experimental temperature (T_E) at which men and women start to shiver differs. Twenty male and 23 female volunteers underwent a cooling protocol, starting at 24 °C and gradually decreasing by 1-2 °C every 5 min until an electromyogram detected the shivering or the temperature reached 9 °C. Women started shivering at a higher T_E than men (11.3 ± 1.8 °C for women vs 9.6 ± 1.8 °C for men, P = 0.003). In addition, women felt cool, scored by a visual analogue scale, at a higher T_E than men (18.3 ± 3.0 °C for women vs 14.6 ± 2.6 °C for men, P < 0.001). This study demonstrates a sex difference in response to cold exposure: women require shivering as a source of heat production earlier than men. This difference could be important and sex should be considered when using cooling protocols in physiological studies.

TRPM2 and warmth sensation

The abilities to detect warmth and heat are critical for the survival of all animals, both in order to be able to identify suitable thermal environments for the many different activities essential for life and to avoid damage caused by extremes of temperature. Several ion channels belonging to the TRP family are activated by non-noxious warmth or by heat and are therefore plausible candidates for thermal detectors, but identifying those that actually regulate warmth and heat detection in intact animals has proven problematic. TRPM2 has recently emerged as a likely candidate for the detector of non-noxious warmth, as it is expressed in sensory neurons, and mice show deficits in the detection of warmth when TRPM2 is genetically deleted. TRPM2 is a chanzyme, containing a thermally activated TRP ion channel domain attached to a C-terminal motif, derived from a mitochondrial ADP ribose pyrophosphatase, that confers on the channel sensitivity to ADP ribose and reactive oxygen species such as hydrogen peroxide. Several open questions remain. Male mammals prefer cooler environments than female, but the molecular basis of this sex difference is unknown. TRPM2 plays a role in regulating body temperature, but are other warmth-detecting mechanisms also involved? TRPM2 is expressed in autonomic neurons, but does it confer a sensory function in addition to the well-known motor functions of autonomic neurons? TRPM2 is thought to play important roles in the immune system, in pain and in insulin secretion, but the mechanisms are unclear. TRPM2 has to date received less attention than many other members of the TRP family but is rapidly assuming importance both in normal physiology and as a key target in disease pathology.