Early development of neuronal hypothalamic thermosensitivity in birds: influence of epigenetic temperature adaptation

The aim of the study was to investigate the prenatal influence of different incubation temperatures on the early postnatal development of neuronal hypothalamic thermosensitivity in birds. The experiments were carried out in brain slices of 1-, 5- and 10-days-old Muscovy ducklings incubated at 35, 37.5 (control) or 38.5 degrees C during the last week of incubation. Firing rate of neuronal activity was recorded extracellularly during sinusoidal temperature changes. The results show that the temperature experienced prenatally has a clear influence on postnatal neuronal hypothalamic thermosensitivity. For instance, at the 10th day post-hatching, exposure to the cooler prenatal incubation temperature resulted in elevated neuronal hypothalamic warm sensitivity through an increased proportion of warm sensitive neurons and a reduced proportion of cold sensitive neurons in comparison with the control group. Exposure to the warmer prenatal incubation temperature induced the opposite effect. In these age group changes in neuronal hypothalamic thermosensitivity occur in relation to the prenatal temperature experienced (proximate adaptive). During the first days of life, prenatal temperature load induced a significant change in the thermosensitivity of hypothalamic neurons which was independent of the direction of change in incubation temperature in comparison with control conditions (proximate non-adaptive). Changes in the thermosensitivity of hypothalamic neurons after prenatal temperature experiences observed in all age groups may be the result of epigenetic temperature adaptation.     

Reliability of the method of levels for determining cutaneous temperature sensitivity

Determination of the thermal thresholds is used clinically for evaluation of peripheral nervous system function. The aim of this study was to evaluate reliability of the method of levels performed with a new, low cost device for determining cutaneous temperature sensitivity. Nineteen male subjects were included in the study. Thermal thresholds were tested on the right side at the volar surface of mid-forearm, lateral surface of mid-upper arm and front area of mid-thigh. Thermal testing was carried out by the method of levels with an initial temperature step of 2°C. Variability of thermal thresholds was expressed by means of the ratio between the second and the first testing, coefficient of variation (CV), coefficient of repeatability (CR), intraclass correlation coefficient (ICC), mean difference between sessions (S1-S2diff), standard error of measurement (SEM) and minimally detectable change (MDC). There were no statistically significant changes between sessions for warm or cold thresholds, or between warm and cold thresholds. Within-subject CVs were acceptable. The CR estimates for warm thresholds ranged from 0.74°C to 1.06°C and from 0.67°C to 1.07°C for cold thresholds. The ICC values for intra-rater reliability ranged from 0.41 to 0.72 for warm thresholds and from 0.67 to 0.84 for cold thresholds. S1-S2diff ranged from -0.15°C to 0.07°C for warm thresholds, and from -0.08°C to 0.07°C for cold thresholds. SEM ranged from 0.26°C to 0.38°C for warm thresholds, and from 0.23°C to 0.38°C for cold thresholds. Estimated MDC values were between 0.60°C and 0.88°C for warm thresholds, and 0.53°C and 0.88°C for cold thresholds. The method of levels for determining cutaneous temperature sensitivity has acceptable reliability.     

Depression of sublingual temperature by cold saliva.

Sublingual and oesophageal temperatures were compared at various air temperatures in 16 subjects. In warm air (25-44 degrees C) sublingual temperatures stabilized within plus or minus 0-45 degrees C of oesophageal temperatures, but in air at room temperature (18-24 degrees C) they were sometimes as much as 1-1 degrees C below and in cold air (5-10 degrees C) as much as 4-4 degrees C below oesophageal readings. The sublingual-oesophageal temperature difference in cold air was greatly reduced by keeping the face warm, but it was not reduced in two patients breathing through tracheostomies and thereby eliminating cold air flow from the nose and pharynx. Parotid saliva temperature was low and saliva flow high during exposure, and cold saliva seemed to be mainly responsible for the erratic depression of sublingual temperature in the cold. These results indicate hazards in the casual use of sublingual temperatures, and indicate that external heat may have to be supplied to enable them to give reliable clinical assessments of body temperature.     

Developmental arrest during embryonic development of the common chameleon (Chamaeleo chamaeleon) in Spain

Embryonic development of the common chameleon, Chamaeleo chamaeleon, was monitored from oviposition to hatching at a field site in southwestern Spain and in the laboratory under five experimental temperature regimes. Embryos were diapausing gastrulae at the time of oviposition; developmental arrest in the field continued as cold torpor during winter. Postarrest development in the field commenced in April, and hatching occurred in August, for a total incubation period of 10.5 mo. In the laboratory, one group of eggs was incubated at a constant warm (26 degrees C) temperature. The remaining treatments simulated field conditions and consisted of initial periods of warm temperature of 0, 27, 46, and 71 d, a subsequent 4-mo period of cold winter (16 degrees C) temperature, and a final period of warm (26 degrees C) temperature. Embryos in the constant warm temperature treatment were in diapause an average of 3 mo, with clutch means ranging from 2 to 4 mo. Hatching among clutches occurred over 2 mo. In contrast, for field and experimental eggs that experienced cold winter conditions, hatching within treatments occurred over 2-14 d; "winter" conditions synchronized development. The length of time between the end of cold conditions and hatching did not differ among treatments; development thus resumed as soon as temperature was suitable regardless of the initial period of warm temperature. Diapause in nature thus insures that embryos remain gastrulae after oviposition despite nest temperatures that may be warm enough to support development.     

Core temperature is regulated, although at a lower temperature, in rats exposed to hypergravic fields

1. In rats acclimated to 23 degrees C (RT rats) or 5 degrees C (CA rats), core temperature (Tc), tail temperature (Tt) and oxygen consumption (VO2) were measured during exposure to a hypergravic field. 2. Rats were exposed for 5.5 h to a 3 g field while ambient temperature (Ta) was varied. For the first 2 h, Ta was 25 degrees C; then Ta was raised to 34 degrees C for 1.5 h. During this period of warm exposure, Tc increased 4 degrees C in both RT and CA rats. Finally, Ta was returned to 25 degrees C for 2 h, and Tc decreased toward the levels measured prior to warm exposure. 3. In a second experiment at 3 g, RT and CA rats were exposed to cold (12 degrees C) after two hours at 25 degrees C. During the one hour cold exposure, Tc fell 1.5 degrees C in RT and 0.5 degree C in CA rats. After cold exposure, when ambient temperature was again 25 degrees C, Tc of RT and CA rats returned toward the levels measured prior to the thermal disturbance. 4. Rats appear to regulate their temperature, albeit at a lower level, in a 3 g field.     

Synthetic heat at mild temperatures

"Synthetic heat", also known as the heat grill illusion, occurs when contact with spatially adjacent warm and cold stimuli produce a sensation of "heat". This phenomenon has been explained as a painful perception that occurs when warm stimulation inhibits cold-sensitive neurons in the spinothalamic tract (STT), which in turn unmasks activity in the pain pathway caused by stimulation of C-polymodal nociceptors (CPNs). The "unmasking model" was tested in experiment 1 by combining warm (35-40 degrees C) and cool (> or = 27 degrees C) stimuli that were too mild to stimulate CPNs. After discovering that these temperatures produced nonpainful heat, experiment 2 was designed to determine whether heat could be induced when near-threshold cooling was paired with mild warmth, and whether lowering the base temperature for cooling would increase the noxious (burning, stinging) components of heat for fixed cooling steps of 1-3 degrees C. Cooling by just 1 degrees C from a base temperature of 33 degrees C led to reports of heat on more than 1/3 of trials, and cooling by just 3 degrees C evoked heat on 75% of trials. Lowering the base temperature to 31 or 29 degrees C increased reports of heat and burning but did not produce significant reports of pain. Perception of nonpainful heat at such mild temperatures indicates either that cold-sensitive nociceptors with thresholds very similar to cold fibers innervate hairy skin in humans, or that heat can result from integration of warm fiber and cold fiber activity, perhaps via convergence on nonspecific (e.g., WDR) neurons in the STT.     

Different roles of intrahypothalamic and nigrostriatal dopaminergic systems in thermoregulatory responses of the rat

Classically, two neurotransmitters in the brain have been implicated in thermoregulation: 5-hydroxytryptamine and norepinephrine. A dopamine action is less well-known and usually has been studied by means of pharmacological rather than physiological procedures. In the present work using a physiological approach to the problem, the role of different central dopaminergic systems in the thermoregulatory response of rats exposed to cold (4 degrees C) or warm (45 degrees C) environments has been studied. Rostral incertohypothalamic neurons in the medial preoptic area synthesized and released more dopamine in response to a warm but not to a cold environment. On the other hand DA and DOPAC levels in nigrostriatal systems were decreased by cold but not warm environments. The dopaminergic neurons projecting to nucleus accumbens or hypothalamus do not appear to be related to the thermoregulatory response in the rat.     

Acclimation of entomopathogenic nematodes to novel temperatures: trehalose accumulation and the acquisition of thermotolerance

The effect of thermal acclimation on trehalose accumulation and the acquisition of thermotolerance was studied in three species of entomopathogenic nematodes adapted to either cold or warm temperatures. All three Steinernema species accumulated trehalose when acclimated at either 5 or 35 degrees C, but the amount of trehalose accumulation differed by species and temperature. The trehalose content of the cold adapted Steinernema feltiae increased by 350 and 182%, of intermediate Steinernema carpocapsae by 146 and 122% and of warm adapted Steinernema riobrave by 30 and 87% over the initial level (18.25, 27.24 and 23.97 microg trehalose/mg dry weight, respectively) during acclimation at 5 and 35 degrees C, respectively. Warm and cold acclimation enhanced heat (40 degrees C for 8h) and freezing (-20 degrees C for 4h) tolerance of S. carpocapsae and the enhanced tolerance was positively correlated with the increased trehalose levels. Warm and cold acclimation also enhanced heat but not freezing tolerance of S. feltiae and the enhanced heat tolerance was positively correlated with the increased trehalose levels. In contrast, warm and cold acclimation enhanced the freezing but not heat tolerance of S. riobrave, and increased freezing tolerance of only warm acclimated S. riobrave was positively correlated with the increased trehalose levels. The effect of acclimation on maintenance of original virulence by either heat or freeze stressed nematodes against the wax moth Galleria mellonella larvae was temperature dependent and differed among species. During freezing stress, both cold and warm acclimated S. carpocapsae (84%) and during heat stress, only warm acclimated S. carpocapsae (95%) maintained significantly higher original virulence than the non-acclimated (36 and 47%, respectively) nematodes. Both cold and warm acclimated S. feltiae maintained significantly higher original virulence (69%) than the non-acclimated S. feltiae (0%) during heat but not freezing stress. In contrast, both warm and cold acclimated S. riobrave maintained significantly higher virulence (41%) than the non-acclimated (14%) nematodes during freezing, but not during heat stress. Our data indicate that trehalose accumulation is not only a cold associated phenomenon but is a general response of nematodes to thermal stress. However, the extent of enhanced thermal stress tolerance conferred by the accumulated trehalose differs with nematode species.     

Perception of foot temperature in young women with cold constitution: analysis of skin temperature and warm and cold sensation thresholds

To examine the disease state of cold constitution, physiological measurements of the foot were conducted by investigating thermal sensations under an environmental condition of 25 degrees C-26 degrees C (neutral temperature) in 29 young women with and without cold constitution. The subjects were classified into 3 groups according to their experiences with cold constitution: cold constitution, intermediate, and normal groups. Foot skin temperature was measured by thermography. Thermal sensations were measured on the dorsum of the left foot using a thermal stimulator. Cold and warm spots on the dorsum of the right foot were ascertained. Thermal stimulation was delivered by a copper probe. No significant differences in foot skin temperature among these 3 groups were identified as measured in a laboratory under neutral temperature conditions. However, the mean warm sensation threshold was +6.3+/-1.09 degrees C (mean+/-SEM) for the cold constitution group (n=14), +3.4+/-2.10 degrees C (mean+/-SEM) for the intermediate group (n=7), and -0.25+/-1.96 degrees C (mean+/-SEM) for the normal group (n=6). The difference was significant between the cold constitution and normal groups. No significant differences among the 3 groups were found in the cold sensation threshold. This may be attributable to the distribution of thermal receptors and to chronically reduced blood flow in subcutaneous tissues, where the skin temperature receptors responsible for temperature sensation are located.     

A second postcooling afterdrop: more evidence for a convective mechanism.

An attempt was made to demonstrate the importance of increased perfusion of cold tissue in core temperature afterdrop. Five male subjects were cooled twice in water (8 degrees C) for 53-80 min. They were then rewarmed by one of two methods (shivering thermogenesis or treadmill exercise) for another 40-65 min, after which they entered a warm bath (40 degrees C). Esophageal temperature (Tes) as well as thigh and calf muscle temperatures at three depths (1.5, 3.0, and 4.5 cm) were measured. Cold water immersion was terminated at Tes varying between 33.0 and 34.5 degrees C. For each subject this temperature was similar in both trials. The initial core temperature afterdrop was 58% greater during exercise (mean +/- SE, 0.65 +/- 0.10 degrees C) than shivering (0.41 +/- 0.06 degrees C) (P < 0.005). Within the first 5 min after subjects entered the warm bath the initial rate of rewarming (previously established during shivering or exercise, approximately 0.07 degrees C/min) decreased. The attenuation was 0.088 +/- 0.03 degrees C/min (P < 0.025) after shivering and 0.062 +/- 0.022 degrees C/min (P < 0.025) after exercise. In 4 of 10 trials (2 after shivering and 2 after exercise) a second afterdrop occurred during this period. We suggest that increased perfusion of cold tissue is one probable mechanism responsible for attenuation or reversal of the initial rewarming rate. These results have important implications for treatment of hypothermia victims, even when treatment commences long after removal from cold water.     

Body temperature regulation in the rat

In loosely-restrained adult conscious rats exposed to stepwise changes in ambient temperature (T(a)) from 25 to 5 degrees C or from 20 to 35 degrees C, we have recorded body and tail temperatures, metabolic rate (VO(2)), shivering and ventilation (V). It was found that VO(2) and V vary with T(a) and show a nadir for a T(a) of 30 degrees C whereas shivering starts at 20 degrees C and increases progressively with cold exposure. T(tail) follows changes in T(a) whereas T(body) decreases slightly in cold and increases markedly in warm exposure. These results suggest that the control of T(body) interacts with the control of breathing in order to increase VO(2) during cold exposure and to facilitate evaporative respiratory heat dissipation during warm exposure.     

Cold tolerance in Drosophila: adaptive variations revealed by the analysis of starvation survival reaction norms

Three species of Drosophila were investigated for their capacity to survive without food (starvation tolerance) at seven different temperatures ranging from 0 to 25 degrees C. In all cases biphasic response curves (reaction norms) were observed, corresponding either to special deleterious effects of cold or to a progressive exhaustion of reserves proportional to metabolic rate. The temperature at which survival was longest was called the threshold temperature. The position of the threshold exhibited adaptive changes, either due to acclimation in the same species, or to genetic variations evidenced between species. In D. melanogaster, adults grown at lower temperature (12 degrees C) were more tolerant to cold than adults grown at higher temperatures (21, 25 or 30 degrees C). This acclimation process shifted, in an adaptive way, the position of the threshold temperature from 6.2 to 7.5 degrees C. A comparison of three different species grown at a single developmental temperature (21 degrees C) revealed similar but greater adaptive differences in their threshold temperature: 4.8 degrees C in the temperate D. subobscura, 7 degrees C in the cosmopolitan D. melanogaster and 14.6 degrees C in the tropical D. ananassae.     

Increased air temperature during simulated autumn conditions does not increase photosynthetic carbon gain but affects the dissipation of excess energy in seedlings of the evergreen conifer Jack pine

Temperature and daylength act as environmental signals that determine the length of the growing season in boreal evergreen conifers. Climate change might affect the seasonal development of these trees, as they will experience naturally decreasing daylength during autumn, while at the same time warmer air temperature will maintain photosynthesis and respiration. We characterized the down-regulation of photosynthetic gas exchange and the mechanisms involved in the dissipation of energy in Jack pine (Pinus banksiana) in controlled environments during a simulated summer-autumn transition under natural conditions and conditions with altered air temperature and photoperiod. Using a factorial design, we dissected the effects of daylength and temperature. Control plants were grown at either warm summer conditions with 16-h photoperiod and 22 degrees C or conditions representing a cool autumn with 8 h/7 degrees C. To assess the impact of photoperiod and temperature on photosynthesis and energy dissipation, plants were also grown under either cold summer (16-h photoperiod/7 degrees C) or warm autumn conditions (8-h photoperiod/22 degrees C). Photosynthetic gas exchange was affected by both daylength and temperature. Assimilation and respiration rates under warm autumn conditions were only about one-half of the summer values but were similar to values obtained for cold summer and natural autumn treatments. In contrast, photosynthetic efficiency was largely determined by temperature but not by daylength. Plants of different treatments followed different strategies for dissipating excess energy. Whereas in the warm summer treatment safe dissipation of excess energy was facilitated via zeaxanthin, in all other treatments dissipation of excess energy was facilitated predominantly via increased aggregation of the light-harvesting complex of photosystem II. These differences were accompanied by a lower deepoxidation state and larger amounts of beta-carotene in the warm autumn treatment as well as by changes in the abundance of thylakoid membrane proteins compared to the summer condition. We conclude that photoperiod control of dormancy in Jack pine appears to negate any potential for an increased carbon gain associated with higher temperatures during the autumn season.     

Hypothalamic temperature and thermogenesis of brown fat during desynchronized sleep in rats

The relationship between hypothalamic temperature and deep interscapular temperature measured just below the brown fat lobes has been studied during desynchronized sleep at two ambient temperatures (24 degrees C and 4 degrees C) before and after adaptation (9 days) to cold (4 degrees C). The results show that the increase in hypothalamic temperature during this stage of sleep occurs independently of a transfer of heat from interscapular brown fat.     

Effect of inspired air temperature on genioglossus activity during nose breathing in awake humans

Experimental data suggest the presence of sensory receptors specific to the nasopharynx that may reflexly influence respiratory activity. To investigate the effects of inspired air temperature on upper airway dilator muscle activity during nose breathing, we compared phasic genioglossus electromyograms (EMGgg) in eight normal awake adults breathing cold dry or warm humidified air through the nose. EMGgg was measured with peroral bipolar electrodes during successive trials of cold air (less than or equal to 15 degrees C) and warm air (greater than or equal to 34 degrees C) nasal breathing and quantified for each condition as percent activity at baseline (room temperature). In four of the subjects, the protocol was repeated after topical nasal anesthesia. For all eight subjects, mean EMGgg was greater during cold air breathing than during baseline (P less than 0.005) or warm air breathing (P less than 0.01); mean EMGgg during warm air breathing was not significantly changed from baseline. Nasal anesthesia significantly decreased the mean EMGgg response to cold air breathing. Nasal airway inspiratory resistance, measured by posterior rhinomanometry in six subjects under similar conditions, was no different for cold or warm air nose breathing [cold 1.4 +/- 0.7 vs. warm 1.4 +/- 1.1 (SD) cmH2O.l-1.s at 0.4 l/s flow]. These data suggest the presence of superficially located nasal cold receptors that may reflexly influence upper airway dilating muscle activity independently of pressure changes in awake normal humans.     

Effect of cold and warm dry air hyperventilation on canine airway blood flow

Tracheobronchial blood flow increases with cold air hyperventilation in the dog. The present study was designed to determine whether the cooling or the drying of the airway mucosa was the principal stimulus for this response. Six anesthetized dogs (group 1) were subjected to four periods of eucapnic hyperventilation for 30 min with warm humid air [100% relative humidity (rh)], cold dry air (-12 degrees C, 0% rh), warm humid air, and warm dry air (43 degrees C, 0% rh). Five minutes before the end of each period of hyperventilation, tracheal and central airway blood flow was determined using four differently labeled 15-micron diam radioactive microspheres. We studied another three dogs (group 2) in which 15- and 50-micron microspheres were injected simultaneously to determine whether there were any arteriovenous communications in the bronchovasculature greater than 15 micron diam. After the last measurements had been made, all dogs were killed, and the lungs, including the trachea, were excised and blood flow to the trachea, left lung bronchi, and parenchyma was calculated. Warm dry air hyperventilation produced a consistently greater increase in tracheobronchial blood flow (P less than 0.01) than cold dry air hyperventilation, despite the fact that there was a smaller fall (6 degrees C) in tracheal tissue temperature during warm dry air hyperventilation than during cold dry air hyperventilation (11 degrees C), suggesting that drying may be a more important stimulus than cold for increasing airway blood flow. In group 2, the 15-micron microspheres accurately reflected the distribution of airway blood flow but did not always give reliable measurements of parenchymal blood flow.     

Investigating the warming and cooling rates of human cadavers by development of a gel-filled model to validate core temperature

Tissue Services (within NHS Blood and Transplant) plans to bring deceased donors to its state of the art retrieval suite at its new centre in Speke, Liverpool in air-conditioned transport at circa 20 degrees C but without dedicated active cooling. The aim of this study was to determine how quickly a refrigerated body would warm at different ambient temperatures using a gel-filled model. Two models of a human body were prepared consisting of neoprene wetsuits filled with approximately 7 or 18 l of a viscous solution, which once set has similar properties to ballistics gel. This gel consisted of 47.5% distilled water, 47.5% glycerol and 5% agar. Final "dummy" weights were 7.4 and 18.6 kg respectively, representing "virtual" weights of approximately 40 kg and 70 kg. A K-class thermocouple probe was then inserted into a "rectal" position within each model and the models were cooled to a series of different core temperatures: 5 degrees C, 10 degrees C and 15 degrees C and then were placed in an orbital incubator set at 20 degrees C or 30 degrees C ambient temperature. The rate of temperature increase, in the dummy, was measured, until the model's core temperature was close to the ambient temperature. This was done in triplicate for each size model and ambient temperature. Data indicate that increase in core temperature depends on the size of the model and the initial core temperature. For an equivalent donor weight of 70 kg and background temperature of 20 degrees C, core temperature rises from 5 degrees C to 9.2 degrees C; 10 degrees C to 13.3 degrees C and 15 degrees C to 15.5 degrees C after 2 h. The final core temperatures after 2 h are likely to retard bacterial growth, movement or contamination during transport. Cooling rate data indicated that a 70 kg donor equivalent cooled from 37 degrees C to 15 degrees C within 6 h in a cold room at 4 degrees C. This work has shown that a body can be transported without refrigeration and not cause further tissue deterioration as a result.     

Response characteristics of a spider warm cell: temperature sensitivities and structural properties

The sensitivity of a warm cell to temperature stimulation was examined electrophysiologically on the spider Cupiennius salei. The relationship between sensitivity and structure of the warm cell was assessed by comparing both the electrophysiological and electron-microscopic data with those described for insect cold cells. Stimulation of the spider warm cell with slowly oscillating temperature change and steady temperature elicited less sensitive responses than in insect cold cells. These characteristics are reflected in the size of the dendritic membrane area, which is smaller in the spider warm cell compared to the insect cold cells. Rapid step-like temperature change produced in the spider warm cell very sensitive responses when compared with data of insect cold cells. The dendritic tip of the spider warm cell is exposed at a pore on the tip of the sensillum but is covered by the cuticle of the sensillum in the insect cold cells.Dedicated to Richard Loftus on the occasion of his 70th birthday, who pioneered several of the questions addressed in this study     

Cold range edges of marine fishes track climate change better than warm edges

Species around the world are shifting their ranges in response to climate change. To make robust predictions about climate‐related colonizations and extinctions, it is vital to understand the dynamics of range edges. This study is among the first to examine annual dynamics of cold and warm range edges, as most global change studies average observational data over space or over time. We analyzed annual range edge dynamics of marine fishes—both at the individual species level and pooled into cold‐ and warm‐edge assemblages—in a multi‐decade time‐series of trawl surveys conducted on the Northeast US Shelf during a period of rapid warming. We tested whether cold edges show stronger evidence of climate tracking than warm edges (due to non‐climate processes or time lags at the warm edge; the biogeography hypothesis or extinction debt hypothesis), or whether they tracked temperature change equally (due to the influence of habitat suitability; the ecophysiology hypothesis). In addition to exploring correlations with regional temperature change, we calculated species‐ and assemblage‐specific sea bottom and sea surface temperature isotherms and used them to predict range edge position. Cold edges shifted further and tracked sea surface and bottom temperature isotherms to a greater degree than warm edges. Mixed‐effects models revealed that for a one‐degree latitude shift in isotherm position, cold edges shifted 0.47 degrees of latitude, and warm edges shifted only 0.28 degrees. Our results suggest that cold range edges are tracking climate change better than warm range edges, invalidating the ecophysiology hypothesis. We also found that even among highly mobile marine ectotherms in a global warming hotspot, few species are fully keeping pace with climate.     

Cortex senses environmental temperature earlier than the hypothalamus in awake rats

Simultaneous and direct recording of temperature from the body, hypothalamus, and cortex in animals exposed to acute thermal challenges lack evidence. This study was conducted to assess the usual concept, that brain temperature is rather stable when animals are exposed to different ambient temperatures. In this study, we report the characteristic changes in the body, hypothalamic, and cortical temperature, when the rats were acutely exposed to cold (6 °C) and hot (36 °C) ambient temperature. The results of our study show that the body temperature is robustly regulated while hypothalamic and cortical temperatures vary on challenges to ambient cold (6 °C) and warm (36 °C) exposure in awake rats. The onset of response was observed quickest in the cortex, indicating that the cortical thermal sensing may relay intracranial thermal input to the hypothalamus for the regulation of body temperature within narrow limits. The present findings contradict earlier evidence, which stated that the brain does not participate in thermal sensing.