Autonomic thermoregulatory effects of electrical stimulation of the hypothalamus in the sheep (Ovis aries)

1. 1.|The effects of electrical stimulation of the preoptic region, on autonomic thermoregulatory responses, were studied in conscious sheep at ambient temperatures of 5, 20, and 40°C.

2. 2.|Stimulation of the dorsal preoptic region elicited co-ordinated thermoregulatory responses characterized by increased respiratory frequency (RF), vasodilation of the ears and lowered body temperature. Stimulation inhibited shivering in cold environments.

3. 3.|The thermoregulatory responses were greater at 5°C in unshorn than in shorn sheep. Increased RF, induced at 20 and 40°C, persisted several minutes after stimulation ceased.

4. 4.|Intraventricular injection of noradrenaline reduced both normal and electrically-induced panting.

5. 5.|Sheep would press panels to electrically stimulate the preoptic region and this “self-stimulation” activated heat-loss mechanisms.

Cardiovascular and thermoregulatory responses to repeated anticholinesterase administration

1. 1.|Pyridostigmine administration decreased resting heart rate by 11 ± 7 beats/min and resting oesophageal temperature by 0.23 ± 12°C after 50 h (P < 0.05). In addition, red blood cell cholinesterase activity was decreased an average of 43 ± 7% after 50 h of pyridostigmine treatment.

2. 2.|The lower heart rates and core temperatures at rest were continued during high intensity exercise in a 35°C environment. Whole body sweating was 12 ± 18% higher (P = 0.20) during exercise in the heat after 50 h of pyridostigmine treatment.

3. 3.|Repeated anticholinesterase administration had little effect on cardiovascular and thermoregulatory responses during high intensity exercise.

Thermal responses of the fresh water turtle Mauremys caspica to step-function changes in the ambient temperature

1. 1.|The turtle Mauremys caspica cools significantly faster than it heats in air. The heating/cooling ratio is 0.49.

2. 2.|The variation of body temperature in relation to time-course in response to a step-function change of environmental temperature, fitted to a second-order system improves that of a first-order system.

3. 3.|The gradient between ambient temperature (T_a) and equilibrium body temperature (T_b) increases significantly and progressively when ambient temperature rises over 25°C.

4. 4.|At 40°C thermoregulatory hyperventilation was detected, implying an increase in air convection requirement (ventilation relative to O₂ consumption, ).

Skin temperatures, thermosensory and pleasantness estimates in case of heterogeneity in the thermal environment

1. 1. Seven thermal conditions were imposed on male sitting subjects (slightly clothed: 0.6 clo).

2. 2. A thermal mannikin was also used to determine the exact operative temperature, T₀.

3. 3. Conditions were: uniform (UN: all parameters at 24.5°C, air velocity at 0.15 ms⁻¹), heated ceiling (HC at 45°C), heated floor (HF at 34°C), cold floor (CF at 14°C), two conditions of one cold wall at 6°C (CW1 and CW2 respectively with and without air temperature compensation) and increased air velocity (AV at 0.4 ms⁻¹).

4. 4. Local skin temperatures and answers to questionnaires were obtained.

5. 5. Skin temperature variations were affected by conditions and slight T₀ changes.

6. 6. Comfort judgments were fairly well related to T₀, especially when expressed as differences between actual non-uniform environment and the uniform one.

7. 7. It is concluded that, in case of non-uniform environments close to thermoneutral zone, thermal comfort or discomfort reflects the climate alterations better than the thermal sensation does.

Thermoregulatory responses of old men to gradual changes in ambient temperature

1. 1. Thermoregulatory respones to gradual rise and fall in the ambient temperature (T_a) were compared between 8 old (68–78 years) and 8 younger (20–25 years) male subjects.

2. 2. Starting at T_a of 31.5°C (r.h. 40%), T_a was raised to 39.5°C, then lowered to 21.5°C, and raised back to 31.5°C at a constant rate of 0.3°C/min.

3. 3. Noticeable differences in responses between the age groups were as follows: decline of sweating rate and reduction of acral blood flow during room cooling were retarded in the aged group, with wider variations among individuals, compared with those in the younger group; the tympanic and oesophageal temperatures fell considerably during cooling in the elderly group, failing to return to the level at start during the rewarming of the room, in contrast to the younger group.

4. 4. Such sluggish responses may be attributed largely to reduced cutaneous thermal perception with advancing age.

Comparison of thermal responses with and without cold protective clothing in a warm environment after severe cold exposures

1. 1. Ten male students remained in a severely cold room (-25°C) for 20 min. thereafter, they transferred in a warm room (25°C) for 20 min.

2. 2. This pattern was repeated three times, total cold exposure time amounting to 60 min.

3. 3. In the warm room, the subjects removed their cold-protective jackets, or wore them continously.

4. 4. Rectal temperature, skin temperatures, manual performance and thermal comfort were measured during the experiment.

5. 5. Removing cold-protective jackets after severe cold exposure increased peripheral skin temperatures and reduced the discomfort in the warm room.

6. 6. However, these results were accompanied by a greater decrease in rectal temperature and manual performance.

7. 7. It is recommended that workers continue to wear cold-protective clothing in the warm areas outside of the cold storage to prevent decreases in deep body temperature and work efficiency caused by repated cold exposures.

The effect of temperature on caecal fermentation processes in a poikilothermic mammal, Heterocephalus glaber

1. 1.|The effect of temperature on caecal function was examined in the naked mole-rat Heterocephalus glaber, a poikilothermic mammal, which consumes a high proportion of fibre in its natural diet.

2. 2.|The temperature of optimal caecal function was determined from fermentation data measure at three specifically chosen temperatures (28, 33 and 40°C).

3. 3.|There was no significant difference between gas production at 33 and 40°C, however, gas production was significantly lower at 28°C.

4. 4.|The relative proportions of the gases produced were markedly different at 33 and 40°C (P ≤ 0.01). More methane and hydrogen were produced at 33°C than at 40°C.

5. 5.|These data suggest that microbial organisms within the caecum were active and functioning more effectively at 33°C (the preferred body temperature of the naked mole-rat) than at the other two temperatures.

Some effects of thyroidectomy on growth, heat production and the thermoregulatory ability of the immature fowl (Gallus domesticus)

1. 1.|The effect of thyroidectomy at 12 days of age on weight gain, and on heat production and thermoregulatory ability of 4- to 5-week-old chickens at temperatures within and below the thermo-neutral zone was investigated.

2. 2.|Despit the absence of thyroid tissue, as demonstrated with radioiodine, a small amount of thyroxine was found in the plasma of some thyroidectomized (TX) birds.

3. 3.|Thyroidectomy depressed weight gain; pair-fed controls grew significantly faster than TX birds.

4. 4.|Resting heat production of TX birds at thermoneutrality (30°C) was depressed by 18% (P < 0.001) and body temperature by 0.4°C (P < 0.001).

5. 5.|At 12°C heat production of TX birds was similar to that of controls but the body temperature of TX birds was 0.7°C lower (P < 0.001).

6. 6.|Thyroidectomized birds were unable to regulate body temperature at 5°C even if thyroxine was provided on the day before and at the time of cold-exposure. This inability to thermoregulate was probably due to inadequate insulation and poor nutritional status.

Physiological and psychological thermal response to local cooling of human body

1. 1. In order to investigate the thermoregulatory responses to the non-uniform thermal environment of the human body, the effects of cooling 10 different body regions were compared by circulating cool water to the neck, breast, back, loin, upper-arms, lower-arms, hands, thighs, legs and feet, respectively. Tympanic temperature, regional (11 sites) and mean skin temperature, and the thermal sensations were measured during experiment in which 30 min local coolings were applied on 5 female students in a climatic chamber controlled at 30°C and 50% r.h.

2. 2. The skin temperature beneath the cooling pad decreased in the order of arms, legs, hands and feet, and trunk.

3. 3. The temperature drop was significantly correlated with the thermal sensation of the region itself.

4. 4. On the other hand, the tympanic temperature increased once by any local cooling. The increase of it was correlated with the change of the general thermal sensation.

5. 5. Results of principal component analysis of skin temperature showed that the peripheral cooling affected the skin temperature in the limited peripheral regions, while the effects of cooling of the breast and the back extended to both the central and peripheral.

Electrical skin resistance and rectal temperature changes in resting human subjects exposed to heat

1. 1.|Fourteen male volunteers were examined under passive heating.

2. 2.|Electrical skin resistance (ESR) and rectal temperature (T_re) were measured during the whole period of exposure.

3. 3.|It was found that:

• —|ESR decreases rapidly with increasing air temperature. Assuming an exponential curve yields a mean time constant of 14 min.

• —|There is a correlation between the individual ESR time constants and T_re increases (r = 0.695, P < 0.005).

• —|Additional changes of ESR were noted in 8 subjects at a constant air temperature of 42°C.

4. 4.|It is concluded that ESR may be a useful indicator of the sweating response of the human thermoregulatory system during exogenous heat load.

Development of autonomic and behavioural thermoregulation in turkeys (Meleagris gallopavo)

1. 1.|Heat production (HP) and body temperature (T_b) measurements were conducted at ambient temperatures (T_a) between 10 and 40°C. In addition preference temperatures (PT) were determined in a temperature channel and T_b was measured at preferred T_a

2. 2.|The influence of age on T_b at constant, as well as at PT, was proved. Increasing age was accompanied by an elevation of T_b whereas HP remained constant in the mid-range of T_a

3. 3.|The lower T_b in the first days of life is suggested to result from a lower thermoregulatory set point during the postnatal period.

4. 4.|The PT were different for the observed types of behaviour. The PT at rest was higher than the PT during locomotion, food intake and drinking.

Thermal avoidance and preference in Daphnia magna

1. Water fleas (Daphnia magna) bred at 23°C were non-responsive to temperatures between 13 and 25°C.

2. At the lower (11°C) and upper limits (30°C) their klinokinetic avoidance behaviour showed a larger intraindividual than interindividual variation.

3. Thermal sensitivity for avoidance responses in D. magna was about 1.5°C.

4. For D. magna bred for one parthenogenetic generation at 14°C heat avoidance temperature was about 8°C lower, and cold avoidance temperature was about 1°C higher than in D. magna from 23°C.

5. In group experiments the animals showed some preference for the acclimation temperature.

6. Cold induced stenothermy and warm induced eurythermy in D. magna were related to the mode of reproduction.

Exercise in the heat: Effects of dinitrophenol administration

1. 1.|Dinitrophenol (DNP) was administered to rats in two equal dosages (20 mg/kg, 30 min interval); the second injection was followed immediately by exercise (9.14 m/min) in the heat (30°C) or at room temperature (21°C).

2. 2.|At 21°C control (saline-treated) rats manifested a mean endurance of 94 min which was reduced to 32 min among DNP-treated animals.

3. 3.|At 30°C, control rats ran for 65 min (δT_re/min = 0.05°C) while DNP-treated animals had a mean endurance of only 12 min (δT_re/min = 0.22°C).

4. 4.|DNP-treated rats (30°C) manifested no decrements in tail-skin heat loss (δT_sk/min = 0.17°C vs 0.10°C) or saliva secretion (0.78 g/min, DNP vs. 0.19 g/min, control) for their brief treadmill duration.

5. 5.|The increased metabolic heat production of DNP severely reduced performance.

Exercise performance of normothermic and hyperthermic rats: Effect of warm rearing

1. 1.|Hypothalamic and rectal temperatures were recorded in 8 warm-reared (wr) and 12 control rats. Rats ran to exhaustion at a constant speed of 1.5 km h⁻¹ but at a variable ambient temperature adjusted to stabilize their hypothalamic temperature at 38.0°C (normothermia) or 41.0°C (hyperthermia). Blood lactate concentrations were determined before and after exercise.

2. 2.|Exercise caused exhaustion in normothermic control rats after 62.08 ± 5.43 min and in wr rats after 29.64 ± 2.09 min.

3. 3.|Hyperthermia shortened to one half (to 12.24 ± 1.36 min) and to one fourth (to 16.15 ± 1.20 min) the endurance time in wr and control rats, respectively.

4. 4.|There were no correlations between lactate concentraion and hyperthermia or endurance time.

5. 5.|In conclusion, in rats and other animals which have safe refuges, hyperthermia interferes with the ability to continue exercising.

Thermoregulatory effects of central injection of noradrenaline in the new-born columbian ground squirrel (Spermophilus columbianus)

1. 1.Effects of centrally injected noradrenaline (NA) into new-born (12–300 h. post-partum) Columbian ground squirrels (Spermophilus columbianus) were studied to provide comparative data on ontogeny of the thermoregulatory pathways in a hibernating species.

2. 2.At warm ambient temperatures (32–34°C, similar to nest temperature), NA increased heat production (47–92%). rectal temperature (0.27–1.73°C), and axillary temperature (0.59–1.92°C). Peak magnitudes of heat production increased with increasing age on a per unit weight basis.

3. 3.At lower temperatures (28–31°C), NA had no effect on heat production.

4. 4.The data indicate that metabolic and thermal responses to NA in neonates of hibernating species are comparable (e.g. rabbit. guinea pig) or different (e.g. lamb) from those observed in neonates of non-hibernating species.

Preferred temperature of the elderly after cold and heat exposures determined by individual self-selection of air temperature

1. 1. The purpose of the study was to investigate the preferred temperature of the elderly after cold and heat exposures.

2. 2. Eight elderly and 9 young females wearing the same type of clothing were exposed to cold (10°C), moderate (25°C) or hot (35°C) environments for 30 min in the exposure room.

3. 3. Then they moved to the self-control room in which the temperature was set at 25°C, and the room temperature increased or decreased continuously by 0.4°C every minute.

4. 4. The subjects were instructed to operate the switch when they felt uncomfortably warm or cool during a 90-min period.

5. 5. In operating the switch, the changing in room temperature shifted to the opposite direction.

6. 6. The ambient temperature was recorded continuously and analyzed as the preferred temperature, which was defined as the midpoint temperature of the crest and trough of temperature records.

7. 7. The preferred temperatures after the cold exposure were significantly higher than those of other exposure conditions in the elderly.

8. 8. On the other hand, in the young, there was no significant difference in the preferred temperature among the exposure conditions.

9. 9. Although the effect of exposure to cold or hot environments decreased in the latter parts of self-control, the elderly still preferred the higher temperature after cold exposure.

Muscle potentials and temperature acclimation and acclimatization in flight muscles of workers and drones of Apis mellifera

1. 1.Muscle potentials in fibrillar flight muscles of worker and drone honeybees were recorded extracellularly at thoracic temperatures from 30 to 10°C.

2. 2.Extinction temperatures for muscle potentials were higher in drones for all treatments.

3. 3.Cold acclimation (15°C) lowered extinction temperatures significantly in workers and drones. Acclimitization changed extinction temperatures significantly only in drones.

4. 4.Cold acclimitization had a bigger effect on the rate of muscle potential amplitude decline with decreasing temperature than acclimation.

5. 5.Acclimation and acclimitization had no effect on the increase of muscle potential duration with falling temperature.

6. 6.Muscle potential frequency during shivering was not much different between cold and warm treated bees.

Behavioural and autonomic thermoregulation in lean and genetically obese (ob/ob) mice

1. 1.|The capacity for behavioural thermoregulation has been assessed in lean and genetically obese (ob/ob) mice, using operant conditioning.

2. 2.|After 30 min at an initial air temperature (T_a) of 0°C, total thermal reinforcements and T_a were greater in ob/ob than lean mice; deep body temperature increased in both genotypes. Without a heater, body temperature in the ob/ob fell markedly in the cold.

3. 3.|Behavioural thermoregulation also depended on food intake and test temperature. i]4.|The capacity for behavioural thermoregulation is thus unimpaired in the ob/ob mouse, unlike that for autonomic thermoregulation, suggesting separate sets of central controls for the two thermoregulatory systems.

Effect of cerebro-ventricular administration of noradrenaline and carbachol on behavioural and autonomic thermoregulation in the monitor lizard Varanus albigularis albigularis

1. 1. When exposed to an ambient temperature of 45°C V. a. albigularis began to pant whne core temperature was between 35.4–38.6°C. The skin temperature, however, appeared to be more critical than the core temperature in determining onset of panting.

2. 2. Cerebro-ventricula injections of saline and moradrenaline had no effect on panting but carbachol inhibited pnting and disrupted normal thermoregulatory behaviour in a photothermal gradient. The significance of this is discussed in relation to comparable studies on mammals.

Responses of human skin temperature and thermal sensation to step change of air temperature

1. 1. The purpose of this paper is to clarify the non-linearity of the human physiological and psychological responses to step change of air temperature by impulse response analysis using Discrete Fourier Transformation.

2. 2. Experiments were conducted to investigate the effect of thermal transients on human responses.

3. 3. Experimental conditions were as follows: lowering air temperature from 30 to 20°C and raising air temperature from 20 to 30°C.

4. 4. The responses of local skin temperature on lowering air temperature from 30 to 20°C are not necessarily opposite to the responses found on raising air temperature from 20 to 30°C.

5. 5. From impulse response analysis using Discrete Fourier Transformation, skin temperature responses to the opposite air temperature change do not necessarily coincide with each other whenever the same temperature stimulus is occurred.