Preferred Ambient Temperature Research Articles

Abstract 51: Targeted Apoptosis of the Angiotensin AT 1 R-Expressing Subtype of Agouti-Related Peptide Neurons Increases Resting Metabolism and Blood Pressure

Agouti-related peptide (AgRP) neurons in the hypothalamic arcuate nucleus (ARC) control feeding and resting metabolic rate (RMR) and may also contribute to blood pressure (BP) and heart rate (HR) control. Our recent studies demonstrate that three subtypes of ARC AgRP neurons can be distinguished by differential expression of angiotensin II (ANG) receptors and differential electrophysiological responses to ANG. The "Type 1" subtype of AgRP neurons in the ARC express the ANG type 1 receptor (AT 1 R), and application of ANG inhibits these cells via a Gi cascade, ultimately causing increased RMR. Other published data suggest that AT 1 R action in AgRP neurons may also stimulate BP. Thus, we hypothesized that cell-specific ablation of Type 1 AgRP neurons would disinhibit (increase) RMR and BP. Within the ARC, only Type 1 AgRP neurons express AT 1 R. Thus, cell-specific ablation of Type 1 AgRP neurons was achieved by injecting an Adeno-associated virus (AAV) encoding Cre-activatable Caspase3 into the ARC of adult AT 1 R CRE mice that express Cre-recombinase via the AT 1 R locus (n=10m+6f). Cre-deficient mice receiving AAV-Casp3 injection, mice receiving anesthesia but no virus, and AT 1 R CRE mice receiving an AAV vector encoding GFP were used as controls (n=21m+10f). Multiplexed metabolic phenotyping demonstrated that two weeks after injection, ablation of Type 1 cells grossly stimulated RMR (+11%: 0.331±0.007 vs. 0.366±0.008 kcal/h, p<0.01) without affecting activity-dependent expenditure; and paradoxically increased meal initiations (+10%, p<0.05) but reduced meal size (-14%, p<0.05), yielding no net change in total food intake after correction for body size and composition (+7%, p=0.24). Ablation of Type 1 neurons also increased preferred ambient temperature in a thermal gradient (29.4±0.3 vs 30.9±0.1 °C, p<0.01). In a separate cohort instrumented with radiotelemetric BP transducers (n=6m), HR progressively decreased (24h avg: -58±9 bpm, p<0.01) as systolic BP tended toward an increase (24h avg: +6±3 mmHg, p=0.10) through 5-7 weeks after ablation. We conclude that AT 1 R-expressing AgRP Type 1 neurons critically contribute to RMR control and appear to also influence BP/HR and feeding control. Therefore, we posit that altered function of these cells may mechanistically contribute to changes in RMR, BP/HR, and feeding control associated with obesity.

Greater severity of depressive symptoms is associated with changes to perceived sweating, preferred ambient temperature, and warmth-seeking behavior

ABSTRACT The thermosensory system is relevant to both the conceptualization and treatment of depression. There is evidence that depression is associated with changes in thermoregulatory functioning, and that thermosensory pathways can be recruited to influence affect and reduce depressive symptoms. In this study, we investigated the relationship between severity of depressive symptoms and changes to measures of subjective experiences associated with thermoregulatory processes as well as the relationship between severity of depressive symptoms and affective responses to warm stimuli, specifically frequency of warmth-seeking behavior. Participants (N = 529) completed measures of depressive symptoms, subjective experiences associated with thermoregulatory processes (i.e., perceived sweating and preferred ambient temperature) and frequency of warmth-seeking behavior (e.g., long hot baths, saunas, etc.). We demonstrate that, controlling for age and gender, greater severity of depressive symptoms is associated with greater perceived sweating and lower preferred ambient temperature. Furthermore, we demonstrate that greater severity of depressive symptoms is associated with more frequent warmth-seeking behavior, and that something other than thermal preference (i.e., stated preference for warmer temperature) is driving this behavior. These data highlight the importance of incorporating the thermoregulatory system in our conceptualization of the pathophysiology of depression and support the potential to recruit thermosensory pathways to target depressive symptoms.

Thermal escape box: A cost-benefit evaluation paradigm for investigating thermosensation and thermal pain

Thermosensation, the ability to detect and estimate temperature, is an evolutionarily conserved process that is essential for survival. Thermosensing is impaired in various pain syndromes, resulting in thermal allodynia, the perception of an innocuous temperature as painful, or thermal hyperalgesia, an exacerbated perception of a painful thermal stimulus. Several behavioral assays exist to study thermosensation and thermal pain in rodents, however, most rely on reflexive withdrawal responses or the subjective quantification of spontaneous nocifensive behaviors. Here, we created a new apparatus, the thermal escape box, which can be attached to temperature-controlled plates and used to assess temperature-dependent effort-based decision-making. The apparatus consists of a light chamber with an opening that fits around temperature-controlled plates, and a small entryway into a dark chamber. A mouse must choose to stay in a brightly lit aversive area or traverse the plates to escape to the enclosed dark chamber. We quantified escape latencies of adult C57Bl/6 mice at different plate temperatures from video recordings and found they were significantly longer at 5 °C, 18 °C, and 52 °C, compared to 30 °C, a mouse’s preferred ambient temperature. Differences in escape latencies were abolished in male Trpm8−/− mice and in male Trpv1−/− animals. Finally, we show that chronic constriction injury procedures or oxaliplatin treatement significantly increased escape latencies at cold temperatures compared to controls, the later of which was prevented by the analgesic meloxicam. This demonstrates the utility of this assay in detecting cold pain. Collectively, our study has identified a new and effective tool that uses cost-benefit valuations to study thermosensation and thermal pain.

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

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

Behavioural thermoregulation by montane ungulates under climate warming

AbstractAimGlobal warming is threatening species survival worldwide. Cold‐adapted montane ungulates may be among the first species to be affected by global warming. Here, we investigate the behavioural thermoregulation hypothesis that montane ungulates buffer the effects of warming climate through behavioural adjustment.LocationFoping National Nature Reserve (FNNR) on the southern slopes of the Qinling Mountains, Shaanxi, China.MethodsWe used infrared camera traps over six consecutive years to monitor behavioural responses of montane ungulates to seasonal and diurnal changes in ambient temperature. We evaluated how seasonal altitudinal migration and changes to their daily activity budget may mitigate the effect of warming on montane ungulates.ResultsAll four montane ungulate species examined here preferred ambient temperatures <22°C in summer. On this basis, we estimate that 27.9% (+2°C) and 46.7% (+3°C) of suitable summer habitats will become unsuitable under climate change. Chinese muntjac and tufted deer displayed behavioural changes to daily activity budgets, which may help them overcome global climate warming to a certain extent. By contrast, golden takin and wild boar did not display similar behavioural changes, and it may be because they are not affected by current shifts in climate due to larger body size and thus lower thermal stress.Main ConclusionsThese analyses demonstrate different species responses to warming are likely and are determined by specific tolerances to ambient temperature thresholds. However, it remains to be seen whether species interactions caused by behavioural shifts may affect species ability to respond to climate.

Effects of late incubation temperature and moment of first post-hatch feed access on neonatal broiler development, temperature preference, and stress response

Early life experiences are known to be of great importance for later life. For instance, exposure to stress during early life can increase fearfulness at later age. In broilers, delayed feeding after hatch may cause metabolic stress. Besides, delayed feeding after hatch may affect neonatal broiler development and thermogenesis and consequently preferred ambient temperature. Moreover, these effects of feeding strategy may be dependent on late incubation temperature. To study this, eggs (n = 1,338) from a 54-wk-old Ross broiler breeder flock were incubated at 37.8°C (control) or 36.7°C (lower) eggshell temperature (EST) during late incubation (≥ embryonic d 17). At hatch, two feeding strategies were applied (direct access (early feeding) or 51 to 54 h delayed access (delayed feeding)). Broilers (n = 960) were equally divided over 32 pens and grown for 3 wk. Stress was assessed by determination of corticosterone in blood at 0 h, 48 h, 96 h and d 21 after hatch. Fearfulness was assessed by tonic immobility at d 13. Temperature preference was assessed at d 2 and d 12. Broiler development was determined at 0 h, 48 h, and 96 h after hatch. There was no EST × feeding strategy interaction for any parameter (P ≥ 0.07). Early feeding resulted in a 2.5× lower plasma corticosterone concentration at 48 h (P < 0.01) and a 2.2°C and 2.0°C lower preference temperature for d 2 and d 12 respectively (P = 0.01) compared to delayed feeding. Tonic immobility was not affected. In conclusion, early feeding reduces exposure to stress in the short term and stimulates thermoregulatory ability of broilers in the longer term.

Is the “Preferred” Color Temperature Transferable from Near-Vision to Ambient Home Lighting? An Exploratory Study with People Who Have Central Visual Field Loss

Introduction: The literature supports the importance of adequate lighting for people with visual impairments, but little is known regarding ambient color temperature at home, and the evaluation process is not standardized. Thus, this study aimed to test a method for evaluating the preferred ambient color temperature, established with a near-vision assessment in clinic, and by using standardized tools to evaluate the effects at home for people with central visual field loss. Methods: An exploratory quasi-experimental study was conducted with three interventions and six observation times. A convenience sample of eight women and two men with central visual field loss, aged 64–91 years with visual acuity between 6/21 (20/69) and 6/48 (20/158), was recruited. Two certified low vision therapists realized evaluations with Minnesota Low-Vision Reading Test, International Reading Speed Texts, a Visual Comfort Scale, a Digital Light Meter LX1330B, and Home Environment Lighting Assessment. The LuxIQ and various illuminated magnifiers were used for clinical interventions. Home lighting interventions were individualized and aimed to apply participants’ preferred color temperature in a selected room. Results: The use of the LuxIQ and illuminated magnifiers showed positive effects in near-vision for all participants by increasing reading speed and visual comfort. Home lighting interventions in participants’ kitchen ( n = 4), living room ( n = 4), or office ( n = 2) also had beneficial effects on their visual comfort and ability to perform activities of daily living. The choice of preferred color temperature was transferable from near-vision to ambient lighting for all participants but one and varied widely. Discussion: Innovative preliminary data support the importance of ambient color temperature for people with visual impairments and suggest an efficient standardized evaluation method. Further research is needed to obtain statistically significant empirical evidence in this field. Implications for practitioners: It could be beneficial for low vision therapists to evaluate the individual ambient color temperature preferences of people with visual impairments by using standardized tools.

Impact of ambient temperature on inflammation-induced encephalopathy in endotoxemic mice\u2014role of phosphoinositide 3-kinase gamma

BackgroundSepsis-associated encephalopathy (SAE) is an early and frequent event of infection-induced systemic inflammatory response syndrome. Phosphoinositide 3-kinase γ (PI3Kγ) is linked to neuroinflammation and inflammation-related microglial activity. In homeotherms, variations in ambient temperature (Ta) outside the thermoneutral zone lead to thermoregulatory responses, mainly driven by a gradually increasing sympathetic activity, and may affect disease severity. We hypothesized that thermoregulatory response to hypothermia (reduced Ta) aggravates SAE in PI3Kγ-dependent manner.MethodsExperiments were performed in wild-type, PI3Kγ knockout, and PI3Kγ kinase-dead mice, which were kept at neutral (30 ± 0.5 °C) or moderately lowered (26 ± 0.5 °C) Ta. Mice were exposed to lipopolysaccharide (LPS, 10 μg/g, from Escherichia coli serotype 055:B5, single intraperitoneal injection)—evoked systemic inflammatory response (SIR) and monitored 24 h for thermoregulatory response and blood–brain barrier integrity. Primary microglial cells and brain tissue derived from treated mice were analyzed for inflammatory responses and related cell functions. Comparisons between groups were made with one-way or two-way analysis of variance, as appropriate. Post hoc comparisons were made with the Holm–Sidak test or t tests with Bonferroni’s correction for adjustments of multiple comparisons. Data not following normal distribution was tested with Kruskal-Wallis test followed by Dunn’s multiple comparisons test.ResultsWe show that a moderate reduction of ambient temperature triggers enhanced hypothermia of mice undergoing LPS-induced systemic inflammation by aggravated SAE. PI3Kγ deficiency enhances blood–brain barrier injury and upregulation of matrix metalloproteinases (MMPs) as well as an impaired microglial phagocytic activity.ConclusionsThermoregulatory adaptation in response to ambient temperatures below the thermoneutral range exacerbates LPS-induced blood–brain barrier injury and neuroinflammation. PI3Kγ serves a protective role in suppressing release of MMPs, maintaining microglial motility and reinforcing phagocytosis leading to improved brain tissue integrity. Thus, preclinical research targeting severe brain inflammation responses is seriously biased when basic physiological prerequisites of mammal species such as preferred ambient temperature are ignored.

Oceanographic preferences of yellowfin tuna (Thunnus albacares) in warm stratified oceans: A remote sensing approach

ABSTRACT Yellowfin tuna (Thunnus albacares, Bonnaterre, 1788; YFT) face extensive exploitation pressure worldwide owing to the attractive economics of these fisheries. A better understanding of how oceanography influences the distribution of YFT (or highly migratory species more generally) will improve the ability for fisheries management policies to achieve conservation (e.g., maintain a stocks reproductive capacity), economic (e.g., maximize gross domestic product), and social (e.g., optimize successful fishing opportunities) objectives. Such ecosystem-based linkages, when combined with real-time remote sensing data, provide the predictive framework for enhancing favourable fishing opportunities and limiting excessive harvest. We examined factors influencing YFT distribution and behaviour using pop-up satellite archival tags and remotely sensed oceanographic data from two regions in the northern Indian Ocean. Tagged individuals did not exhibit significant deep diving or diurnal behaviour, and preferred ambient temperatures of 26–30°C and 25–29°C in the Arabian Sea (AS) and the Bay of Bengal (BoB), respectively. In general, tagged YFT were found to be in waters with sea surface temperatures of 26–29°C, 60% of the time and within a sea surface height-anomaly of ±6 cm 70% of the time. YFT avoided moving below the relatively shallow oxycline depth, which is indicative of the stratified waters of the AS and the BoB. Low dissolved oxygen levels are likely a limiting factor for tuna movement given their high oxygen demand. The northern Indian Ocean provides an opportunity to study climate impacts on fish distribution and movement, and our findings provide a basis for understanding how habitat and migratory patterns may be altered under climate change.

Hypothalamic TRPV4 channels participate in the medial preoptic activation of warmth-defence responses in Wistar male rats.

Recently, we have described, in non-genetically modified rats, that peripheral transient receptor potential vanilloid-4 (TRPV4) channels are activated and trigger warmth-defence responses at ambient temperatures of 26-30°C. Evidence points to the presence of TRPV4 in the medial preoptic area, a region described to be involved in the activation of thermoeffector pathways, including those involved in heat loss. Thus, we tested the hypothesis that TRPV4 in the medial preoptic area modulates thermoregulation under warm conditions. To this end, under two ambient temperatures (21 and 28°C), body temperature was measured in rats following blockade of preoptic TRPV4 with two antagonists, HC-067047 and GSK 2193874. Oxygen consumption, heat loss index and preferred ambient temperature were also determined in order to assess thermoeffector activity. Antagonism of central TRPV4 caused an increase in body temperature in rats exposed to 28°C, but not in those exposed to 21°C. The body temperature increase at 28°C was accompanied by an increase in oxygen consumption and an earlier reduction of the heat loss index. In behavioural experiments, control animals previously exposed to warm ambient temperatures (28-30°C) for 2h selected colder temperatures in a thermogradient compared to those injected with HC-067047. Our results support the idea that preoptic TRPV4 modulates thermoregulation in a warm environment by activating both autonomic and behavioural heat loss responses. Thus, according to the present study and to that published recently by our group, the activation of warmth-defence responses by TRPV4 seems to be dependent on the activity of both peripheral and central channels.

Early maternal separation promotes alterations in the thermoregulatory profile of adult Wistar rats

Stressful lifelong events may influence psychiatric diseases, like depression and anxiety. Interestingly, depressed patients have dysfunction of thermoregulatory cooling mechanisms. Thus, understanding the mechanisms related to the thermoregulatory changes in stress-related pathologies is important to better understand the symptoms and treatments for those diseases. However, the influence of early-life stress on the thermoregulatory profile of adults is unknown. In this study, we aimed to evaluate the thermoregulatory profile of adult male Wistar rats submitted to early-life stress by maternal separation (MS). On postnatal days 2–14, rats were submitted daily to MS for 3 h per day. At 3–4 months of age, anxiety-like behavior was evaluated using the open field test and elevated plus maze, depression-like behavior was evaluated using the forced swim test and thermoregulatory profile were also evaluated. In the behavioral tests, MS animals exhibited anxiety- and depression-like behaviors, and had higher core body temperatures during dark period of the circadian cycle, when compared to controls. In addition, MS animals presented higher hyperthermic and vasoconstriction responses than control animals when exposed to the warmth environment, and engaged in cold-seeking behavior whenever possible to select their preferred ambient temperature. The results suggest that, besides emotional alterations, MS induces a change in the thermoregulatory profile of rats that persists into adulthood.

Individual variation in the compromise between social group membership and exposure to preferred temperatures

Group living is widespread among animal species, and comes with a number of costs and benefits associated with foraging, predator avoidance and reproduction. It is largely unknown, however, whether individuals sacrifice exposure to their own preferred or optimal environmental conditions so they can remain part of a social group. Here, we demonstrate that individual three-spine sticklebacks vary in the degree to which they forego exposure to their preferred ambient temperature so they can associate with a group of conspecifics. Individual fish varied widely in preferred temperature when tested in isolation. When the same individuals were presented with a choice of a warm or cold thermal regime in the presence of a social group in one of the environments, fish spent more time with the group if it was close to their own individually preferred temperature. When a group was in a relatively cool environment, focal individuals that were more social deviated most strongly from their preferred temperature to associate with the group. Standard and maximum metabolic rate were not related to temperature preference or thermal compromise. However, individuals with a higher standard metabolic rate were less social, and so energetic demand may indirectly influence the environmental costs experienced by group members. The reduced tendency to engage with a social group when there is a large difference between the group temperature and the individual's preferred temperature suggests a role for temperature in group formation and cohesion that is mediated by individual physiology and behaviour. Together, these data highlight exposure to non-preferred temperatures as a potential cost of group membership that probably has important but to date unrecognized implications for metabolic demand, energy allocation, locomotor performance and overall group functioning.

Preferred temperature with standing and treadmill workstations

Prolonged sedentary behavior has been shown to increase chronic diseases. Using standing and treadmill desk reduces sitting time, increases metabolic rate and thus has potential to improve health. There is little existing guidance on how to keep thermal comfort when using standing and treadmill desk. It is unknown what are the suitable ambient temperatures for occupants at elevated office activity levels. This experiment investigated thermal sensation and preferred temperature at elevated office activity levels, including sitting (SED), standing (STD), and two slow-walk speeds: walking at 1.2 km/h (TRD1) and walking at 2.4 km/h (TRD2). Comfort votes were obtained from 20 subjects under personal controlled ambient temperature. The active workstation significantly increased human metabolic level and reduced preferred temperature. The measured metabolic rates were 1.0, 1.1, 1.9 and 2.5 met for SED, STD, TRD 1 and TRD 2. The preferred ambient temperature reduced from 25.85 °C for SED, to 25.0, 24.1 and 23.2 °C for STD, TRD 1 and TRD 2 respectively. All subjects were comfortable at their preferred temperatures. PMV model was found to predict too cool temperature than needed for higher metabolic rates.

Oviposition activity of Drosophila suzukii as mediated by ambient and fruit temperature.

The invasive pest Drosophila suzukii was introduced to southern Europe in 2008 and spread throughout Central Europe in the following years. Precise reliable data on the temperature-dependent behavior of D. suzukii are scarce but will help forecasting and cultivation techniques. Depending on physico-chemical properties, surface temperature of objects may differ from ambient temperatures, determining physical activity, and affect oviposition on or into substrate, determining preimaginal development later. Therefore, the preferred ambient temperatures of D. suzukii and fruit temperature for oviposition were examined on a linear temperature gradient device. Thirty adults (15 ♀; 15 ♂) were adapted to different temperatures (10, 20, 30°C) for six days and then exposed to different temperature gradients (10–25, 20–35, 25–40°C). D. suzukii adapted to 10°C remained in cooler regions and suffered from a significantly higher mortality at the 25–40°C gradient. Animals adapted to warmer temperatures had a wider temperature preference on the gradient device. Acclimation to lower temperatures and the resulting lower temperature preferences may allow the flies to disperse better in spring to search for oviposition sites. The oviposition activity decreased continuously at a fruit temperature above 28°C and below 15°C, with highest oviposition activity in fruits with temperatures between 19.7°C and 24.8°C. The preferred fruit temperature is in accordance with the temperature optimum of reproduction biology and preimaginal development of D. suzukii reported in the literature.

A comparison of the effectiveness of insecticides in constant and variable thermal conditions

ABSTRACTThe effectiveness of insecticides differs with changes in temperature, but insecticide toxicities are determined at constant temperatures. Constant thermal conditions do not occur in the field, where insects can change their behaviors to achieve a preferred temperature. The aim of this study was to assess whether the choice of ambient temperature affects the mortality rate of intoxicated firebugs and Colorado potato beetles. The insects’ mortality following insecticide exposure was monitored at constant temperatures (15, 25, and 35 °C) as well as in a thermal gradient system, where the insects could freely select their preferred ambient temperature. Firebugs treated with oxadiazine showed 58% higher mortality when held at a constant temperature post-treatment compared to mortality levels seen when able to choose a preferred temperature in a thermal gradient. Similar results were seen in Colorado potato beetles treated with oxadiazine (15%–33% higher mortality in constant vs. preferred temperature) or organophosphate (36% higher mortality in constant vs. preferred temperature). The insects’ ability to mitigate the impacts of pesticide exposure by selecting more beneficial thermal conditions is an important consideration for pest management. Therefore, the application rates of insecticides used under field conditions should be additionally analyzed to take this factor into account.

Incubation temperature alters thermal preference and response to heat stress of broiler chickens along the rearing phase

The current study aimed to investigate whether embryonic temperature manipulation may alter thermal preference throughout the rearing phase of broiler chickens and how this manipulation may affect response to thermal challenge, metabolism, growth rate and feed intake rate. Eggs were exposed to a constant incubation temperature [machine temperatures: 36°C (Low), 37.5°C (Control), and 39°C (High); eggshell temperature of 37.4 ± 0.08°C, 37.8 ± 0.15°C, and 38.8± 0.33°C, respectively] from d 13 till hatching. Low treatment chickens showed lower plasma T3 and GH levels at d 1 of age and lower T3 level at d 42 of age compared to the Control treatment. Preferred ambient, rectal temperature, T4 level, growth rate, food intake rate, and response to thermal challenge were not altered in these chickens. On the other hand, High-treatment chickens exhibited high preferred ambient temperature and rectal temperature during the first 2 wk post-hatch, lower plasma T3 level at d 21 and 42 and a delayed increase in respiratory movement in response to thermal challenge compared to the Control treatment. However, chickens subjected to the Control and High treatments did not differ in T4 and GH level and performance. We conclude that exposure to high temperature during late embryonic development has long-lasting effects on the thermoregulatory system of broiler chickens by affecting the heat tolerance of these chickens. Moreover, the preferred ambient temperature of the chickens from heat-treated eggs correspond to those recommended for the strain under study, whereas for the cold-treated and control-chickens it was 1°C below, indicating that incubation temperature might have consequences on the ambient temperature chickens require during the rearing phase.

Human thermoneutral zone and thermal comfort zone: effects of mild heat acclimation

Overheating of buildings is currently a hot topic in the Western World. A significant amount of energy is needed for air conditioning and ventilation of public and commercial buildings. Nevertheless, up to 80% of the occupants are dissatisfied with the thermal environment, even though buildings meet thermal comfort criteria as determined by the ASHRAE Standard 55 and ISO Standard 7730. Physiological parameters such as sex, age, body composition and metabolic rate can have a great effect on an individual's perception of the thermal environment. A study among young Europeans indicated that the preferred ambient temperature might vary as much as 10 °C between individuals. However, it is not yet clear how an individual's thermal comfort zone (TCZ) relates to the physiological thermo-neutral zone (TNZ). Moreover, unlike thermoregulatory adaptations to strong repetitive heat challenges, it is unknown to what extent humans adapt to more mild warm ambient conditions in terms of subjective perception and thermo-regulatory physiology. Therefore, the present study aimed to investigate the relationship of an individual's TNZ and TCZ as well as the influence of 7 days of mild heat acclimation on TNZ and TCZ. Since the study is still ongoing, preliminary data will be presented.

TRPV4 Induces Warm‐Defense Responses in Non‐Genetically Modified Rats

TRPV4 is a warmth sensitive channel, suggested to act as a thermosensor but with no thermoregulatory role described in vivo (sensitive to temperatures in vitro at the range of ~24 ‐ 34ºC). Thus, we aimed at investigating which thermoeffectors are affected by TRPV4 activation in rats. To this end, we measured core body temperature (Tc), oxygen consumption and heat loss index (HLI) in male rats (290‐320g) under different ambient temperatures (Ta) after the intravenous blockade of this channel with HC‐067047. Moreover the preferred ambient temperature was assessed: i) after thermal stimulation combined with the intravenous blockage of TRPV4 with HC‐067047; and ii) after topical application of agonist RN‐1747. HC‐067047 caused an increase on Tc at Ta of 26 and 30°C (~0.65°C; p&lt;0.05), but not at 22 and 32°C. At 26°C, HC‐067047‐induced hyperthermia was accompanied by increase in oxygen consumption (1.24 ± 0.2 mL O2 kg‐¹ min‐¹ more than the controls; p&lt; 0.05), but no difference on HLI was observed. Furthermore, rats chemically stimulated with TRPV4 agonist leaned towards colder Tas (29°C for controls and 21°C for agonist‐treated; p&lt; 0.05) and the cold‐seeking behaviour after thermal stimulation (28‐31°C) was inhibited by TRPV4 antagonist (24°C for controls and 28°C for antagonist‐treated; p&lt; 0.05). Our results suggest, for the first time, that TRPV4 channel is involved in the recruitment of behavioural and autonomic warmth defense responses in order to regulate Tc. Financial Support: FAPESP

TRPV4 activates autonomic and behavioural warmth-defence responses in Wistar rats.

In this study, we aimed at investigating the involvement of the warmth-sensitive channel - TRPV4 (in vitro sensitive to temperatures in the range of approx. 24-34 °C) - on the thermoregulatory mechanisms in rats. We treated rats with a chemical selective agonist (RN-1747) and two antagonists (RN-1734 and HC-067047) of the TRPV4 channel and measured core body temperature, metabolism, heat loss index and preferred ambient temperature. Our data revealed that chemical activation of TRPV4 channels by topical application of RN-1747 on the skin leads to hypothermia and this effect was blocked by the pre-treatment with the selective antagonist of this channel. Intracerebroventricular treatment with RN-1747 did not cause hypothermia, indicating that the observed response was indeed due to activation of TRPV4 channels in the periphery. Intravenous blockade of this channel with HC-067047 caused an increase in core body temperature at ambient temperature of 26 and 30 °C, but not at 22 and 32 °C. At 26 °C, HC-067047-induced hyperthermia was accompanied by increase in oxygen consumption (an index of thermogenesis), while chemical stimulation of TRPV4 increased tail heat loss, indicating that these two autonomic thermoeffectors in the rat are modulated through TRPV4 channels. Furthermore, rats chemically stimulated with TRPV4 agonist choose colder ambient temperatures and cold-seeking behaviour after thermal stimulation (28-31 °C) was inhibited by TRPV4 antagonist. Our results suggest, for the first time, that TRPV4 channel is involved in the recruitment of behavioural and autonomic warmth-defence responses to regulate core body temperature.

Chicken hatchlings prefer ambient temperatures lower than their thermoneutral zone

We investigated whether or not the preferred ambient temperature (Tapref) of the 1-day old chicken hatchling, a precocial neonate with excellent locomotory capacity, clearly identifiable thermogenesis and independence from maternal care, coincides with the lower critical temperature (LCT) of thermoneutrality and minimal oxygen consumption (V˙O2). Tapref of single chicks measured in a thermocline (N=16) averaged 33.5±0.3°C (mode, 33.3±0.4°C). The same value was obtained in hatchlings studied in pairs. LCT was computed from the ambient temperature (Ta)–V˙O2 relationship, constructed by slowly decreasing the Ta of a respirometer from 38 to 29°C over 2.5h, while continuously measuring V˙O2 by an open-flow methodology; LCT averaged 36.4°C±0.3 or 36.8°C±0.4, depending on the method of computation. In all hatchlings Tapref was lower than LCT (P<0.001), by a magnitude that depended on the method of computation of the two variables, 2.8°C±0.3 (P<0.001) or 3.9°C±0.5. The Tapref-LCT difference implied that, at Tapref, V˙O2 was higher than at thermoneutrality. We conclude that in the chicken hatchling thermal preference does not coincide with thermoneutrality, probably because during development what seems optimal from a thermoregulatory viewpoint may not necessarily be so for other regulatory functions.