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Thermoregulation in patients suffering from multiple sclerosis (MS) is impaired and may result in either increases or decreases in body temperature. We have found that rat experimental autoimmune encephalitis (EAE), being a model of MS, is associated with body temperature disturbances as well. The purpose of the current study was to examine whether the altered body temperature in EAE-induced rats is due to either a deficit in thermoregulation or a controlled change in its set point. Subcutaneous injection of encephalitogenic emulsion into both pads of hind feet of the Lewis rats provoked EAE symptoms. Body temperature (Tb) of 6 rats was measured using biotelemetry system, and ambient temperature (Ta) preferred by 6 rats of another group was analyzed using thermal gradient system. Symptoms of EAE started 11 days postinjection and progressed quickly, culminating in a complete paralysis in rats placed in the gradient, which was associated with behavioural fever (accordingly, selected Ta raised to as much as 32.8 ± 0.5 °C vs 27.2 ± 0.6 °C in control rats). On the other hand, EAE rats, placed at a constant Ta of 24 °C, were able to generate fever (Tb of 37.8 ± 0.1 °C) at the start of the illness and then paralysis compromised fever (most likely due to an impairment of thermogenesis), which, surprisingly, resulted in recovery. We conclude that EAE onset in rats is associated with fever and its behavioural supporting leads to aggravation of the autoimmune neurotoxicity., (Copyright © 2020 Nicolaus Copernicus University, ToruD, Poland. Published by Elsevier Ltd.. All rights reserved.)

To study the relationship between the individual and social thermoregulatory behaviour, we used honeybee workers and American cockroaches. Single insects or groups of 10-20 individuals were placed in a temperature gradient chamber, and their thermal preference was recorded for 48 h under natural summer photoperiod. Single bees showed diurnal changes in selected ambient temperature, which culminated at 14:00 reaching 34+/-2 degrees C, and then slowly decreased, reaching a nocturnal minimum of 28+/-2 degrees C at 04:00. In contrast, the zenith of temperature selected by groups of bees (31+/-1 degrees C) was reached at 04:00 and the nadir (29+/-2 degrees C) was recorded at 14:00. Groups of bees clustered together during the night time, and dispersed during intense day time activity. Such changes were absent in groups of cockroaches. Cockroaches selected an ambient temperature of 30+/-1 degrees C both during day and night. In conclusion, there is a striking analogy in the diurnal thermal behaviour between a colony of bees and mammals. During their nychthemeral rest phase, both of them select higher temperatures than during the activity phase and, simultaneously, they reduce their overall surface area of heat loss to conserve metabolic heat. Therefore, the colony behaves as a homeothermic superorganism. In contrast, a single bee, isolated from the colony, utilizes a heterothermic strategy to save energy for a morning warm up.

Hypothermia may limit asphyxic damages to the brain, and many small homeotherms have been shown to use anapyrexic strategies when exposed to asphyxic conditions. Larger homeotherms do not seem to use the same strategy, but could save oxygen and prevent hypoxic brain damage by employing selective brain cooling (SBC) in connection with asphyxia. To test the hypothesis that selective brain cooling may take place in connection with asphyxia, we have recorded brain [hypothalamic (THyp)] and body [colonic (TC)] temperatures and heart rates in four Pekin ducks during 5-min simulated (head submersion) diving in cold water (10 degrees C). Diving resulted in a drop in THyp (3.1 +/- 1.4 degrees C) that continued into the recovery period (P < 0.001). Restricting heat loss from the buccal cavity and eyes during diving compromised brain cooling in an additive manner. TC was not influenced by diving. Control cooling of the head with crushed ice during a 5-min period of undisturbed breathing had no effect on THyp. Warm water (35 degrees C) markedly reduced brain cooling, and dive capacity was reduced by approximately 14% (P < 0.05) compared with diving in water at 10 degrees C. The data suggest that SBC is used in ducks during diving, and we propose that this mechanism may enable the bird to save oxygen for prolonged aerobic submergence and to protect the brain from asphyxic damages.

The purpose of our study was a comparison of pyrogenic and behavioural effects of Escherichia coli (E.coli) and Salmonella abortus (S.abortus) endotoxins in unrestrained, freely moving Wistar rats, placed in a thermal gradient and having an easy access to ambient temperatures within a range 5-40 degrees C. Hypothalamic and chosen by the rats ambient temperatures as well as locomotor activity were recorded before and after intraperitoneal injection of 1 mg/kg lipopolysaccharide from E. coli or from S. abortus. Control animals were injected with pyrogen-free saline. Both endotoxins induced warm-seeking behaviour which was accompanied by biphasic fever. Locomotor activity of LPS-injected rats was reduced. S. abortus-induced fever peaked at 100th minute (reaching 37.5 +/- 0.2 degrees C) and at 250th minute (reaching 38.1 +/- 0.1 degrees C). Respective data for E. coli fever were: 170th minute (when hypothalamic temperature reached 37.6 +/- 0.3 degrees C) and 430th minute (with hypothalamic temperature of 38.6 +/- 0.1 degrees C). Comparing to S. abortus-generated fever both peaks of E. coli LPS-induced fever were significantly delayed (p < 0.05). A limited structural variability of lipid A from both bacteria is likely to be responsible for the difference in fever timing recorded in this study.

The effects of early (postnatal), long-term warm exposure on thermoregulatory system of rats were compared with those resulting from warm acclimation induced in adult animals. To obtain warm-reared (wr) rats pregnant females 7 days before term were permanently exposed to a constant ambient temperature of 35 degrees C and their offsprings were housed under these conditions for at least 6 months. Wr rats differed from both control and warm acclimated (wa) animals morphologically as well as functionally. They were leaner and lighter but their tails and feet grew relatively bigger. Moreover, warm rearing led to a marked and highly significant elevation in mass of salivary gland (the main source of water for evaporative cooling). Core temperature in wr rats was regulated at a significantly higher level during the day and at night. Moreover, hyperthermia reduced the exercise performance less in wr than in wa rats. In conclusion, early exposure to high environmental temperature modifies the development of temperature regulation in a way different from that occurring during thermal acclimation in the adult. Changes occurring in wr rats might mimic genetical adaptations of a population to variety of thermal environments.

1. The technique of perceptual rating of thermal stimuli was used, in eight human subjects immersed in warm water, in order to appreciate whether they were hypo-, normo- or hyperthermic. Oesophageal, tympanic and forehead skin temperatures were recorded, as also was the temperature of the skin above the angularis oculi vein. Once the subjects gave clearly hyperthermic ratings, one arm was exposed to a 6 m/s wind. After 5--10 min the arm was re-immersed and the face was fanned. 2. Fanning of the arm resulted in lowering of body core temperature. However ratings of thermal stimuli remained hyperthermic. 3. Face fanning decreased forehead skin, angularis oculi vein and tympanic temperatures. Hyperthermic ratings were replaced by normothermic ratings, although oesophageal temperature continued to rise. 4. The upper limit of oesophageal temperature for normothermic ratings was 37.o6 +/- 0.09 degrees C during the control period without fanning. This temperature rose to 37.91 +/- 0.09 degrees C during facial ventilation. 5. These results suggest a selective cerebral cooling due to venous blood returning from facial skin via the ophthalmic vein to the cavernous sinus, where a cooling of arterial blood ascending to the brain can take place.

Human subjects were placed on a bicycle ergometer and left to pedal ad lib. for 43 min to warm themselves and thereby attain thermal comfort at an ambient temperature of 10 degrees C. Esophageal (Tes), tympanic (Tty), forehead, and hand skin temperatures were recorded. In addition, the work of pedaling was noted for each 2-min period. In some experiments sweating rate was also recorded. Two series of experiments were performed, the first with face fanning and the second with thermal insulation of the head. Face fanning resulted in decreased Tty, but in substantially increased Tes, which was 1.5 degrees C higher than Tty after an intense pedaling effort of 46-50 W. In experiments with head covering, a mild increase of both Tes and Tty was observed toward a position halfway between the extreme values obtained during face fanning. Simultaneously, pedaling intensity decreased to 16.7 W and the rate of sweating increased. In general, pedaling work was inversely proportional to intracranial temperature (Tty) and independent of trunk temperature (Tes). Therefore, motivation for muscular activity in humans exposed to cold appears to be goverened chiefly by the brain temperature.

An influence of brain and trunk temperatures controlled independently of each other by means of artificial heat exchangers, on the intensity of natural selective brain cooling (SBC) was studied in 6 conscious goats. Intensity of SBC was markedly enhanced by increasing brain temperature. On the other hand, a rise of trunk temperature with the cerebral temperature clamped at 39 degrees C or 40 degrees C, reduced SBC intensity in spite of a simultaneous increase in the respiratory evaporative heat loss. When brain temperature was clamped at 41 degrees C, the magnitude of SBC was essentially independent of trunk temperature. These results suggest that during hyperthermia a competition exists between trunk and brain for cool nasal blood.

1. Five human subjects pedalled on a bicyle ergometer for at least two 74 min periods at 10 degrees C ambient temperature. During the first period the subjects cycled for 42 min with face fanning, followed by 32 min with the head thermally insulated. In the second period, this procedure was reversed. Oesophageal (tes), tympanic (Tty), forehead and hand skin temperatures were recorded. In addition, heart rate (H.R.) was counted throughout the experiments, and the technique of perceptual rating of cool and warm stimuli was used in order to appreciate whether the subjects were hypo-, normo-, or hyperthermic. 2. Face fanning resulted in decreased Tty, decreased H.R., mild skin vasoconstriction but increased Tes. 3. Head covering resulted in increased Tty and H.R., while Tes decreased slightly, due to peripheral vasodilatation. 4. When their faces were being fanned so that Tty was low and Tes was high, the subjects gave slightly hypothermic ratings. Ratings were clearly hyperthermic when their heads were covered and Tty was high and Tes was low. 5. The close correlation between vasomotor response and H.R. on the one hand and Tty on the other confirms that this variable is a better approximation of regulated core temperature than Tes. 6. Increase in Tes during face fanning and decrease in Tes during face insulation is new evidence for the possibility of the human brian being cooled during exercise by cool blood returning from the face. 7. We suggest that this selective brain cooling determines the apparent upper resetting of core temperature during exercise while brain temperature remains precisely regulated and constant.

Chronic experiments were conducted on five freely moving rabbits at ambient temperatures of 0-42 degrees Celsius. The influence of nasal mucosal thermal changes on the venous blood temperature inside the pterygoid plexus and on the temperatures at three intracerebral sites were investigated against the background of the carotid arterial blood temperature shifts. A correlation was found between: (i) the fluctuations in the nasal mucosal temperature reflecting its vasomotor responses, (ii) temperature shifts of the pterygoid plexus venous blood, and (iii) of the ventral brain. Mucosal vasodilatation caused parallel drops in both the plexal blood and brain temperatures. However, mucosal vasoconstriction was accompanied by increases in temperatures at those sites. Intracranial thermal shifts were independent of the arterial blood temperature changes. During motor activity in normothermia nasal mucosal vasoconstriction was present, and in that case brain temperatures exceeded arterial blood temperature. During rest, mucosal vasodilatation appeared and brain base cooled below the arterial blood temperature. During panting in dry heat, the brain base was cooler than the arterial blood by as much as 0.5 degree Celsius. The intensity of the selective brain cooling was directly proportional to deep body temperature. The blockade of the respiratory evaporation in heat elicited an increase of the plexal venous blood as well as brain temperatures above the arterial blood temperature. We conclude that the venous blood outflowing from the nasal mucosa exerts a cooling influence on the brain through the pterygoid plexus.

The hypothalamic-arterial blood temperature gradient (THpr-TAC difference) was studied on 10 freely moving rabbits at ambient temperatures between 0 and 42 degrees Celsius. In cold environment, below 10 degrees Celsius the THpt-TAC gradient varied considerably, but some distinct correlations were found between vasomotor responses of the nasal mucosa and fluctuations of brain temperature, as well as between vasomotor responses of the ear pinnas and changes of the arterial blood temperature. Vasodilatation of the nasal mucosa or the ear pinna caused respectively a drop in brain temperature or in arterial blood temperature. Opposite changes were induced by vasoconstriction in those areas. Variations in THpt-TAC gradient resulted from oppositely directed vasomotor responses in the nasal mucosa and in the ear pinnas. At high ambient temperatures above 35 degrees Celsius thermal panting was accompanied by selective brain cooling with respect to the arterial blood. Blocking the heat loss from the nasal mucosa caused an increase of the THpt-TAC difference, and under these conditions brain temperature was determined solely by arterial blood temperature. The assumed mechanism of the selective brain cooling in rabbits is the exchange of heat through the neurocranial bottom, between the ventral brain and the spacious splanchnocranial venous lakes supplied with blood from the nasal mucosa.

Three male humans were subjected repeatedly to 20 min exercise on a bicycle ergometer: twice when hydrated normally and twice when dehydrated. Tympanic (Tty) and oesophageal (Tes) temperatures were recorded and sweat rates on forehead and back were measured. Dehydration did not change the forehead sweat rate, but on the back it reduced significantly, resulting in an increase of Tes. However, Tty was decreased by dehydration. 20 min after the end of exercise subjects were allowed to drink water in order to trigger the potohidrotic response. A potohidrotic response was noted on the back of dehydrated subjects only. It is concluded that dehydration results in active inhibition of sweating on the body but not on the forehead, where evaporation is needed for selective cooling of the brain.