Effect of 2450 MHz microwave exposure on behavioural thermoregulation in mice

1. 1.|The purpose of this study was to determine the threshold specific absorption rate (SAR) during exposure to 2450 MHz continuous wave (CW) microwaves that affected thermoregulatory behaviour in mice.

2. 2.|A Plexiglas shuttle box was placed inside a waveguide imposed with a temperature gradient. The temperature gradient allowed the mice to select a particular section of the shuttle box which was, presumably, related to their state of thermal comfort. Exposing the mice to 2450 MHz inside the waveguide at SARs of 0–5.3 W kg⁻¹ for 1 h caused no significant change in their preferred ambient temperature.

3. 3.|Increasing SAR from 5.3 to 18.1 W kg⁻¹ caused the animals to shift their position to the cooler end of the shuttle box.

4. 4.|Following termination of microwave exposure animals that had selected a cool ambient temperature returned to the warm side of the shuttle box.

5. 5.|It is concluded that for mice exposed to radiation at 2450 MHz the thermoregulatory behaviour is significantly affected at SARs of 5.3 to 9.9 W kg⁻¹.

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.

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, ).

A central excitatory serotonergic or serotonergic-like synapse on the pathway to heat production in the sheep

1. 1.|Intraventricular injections of serotonergic agonists and receptor blockers were given to sheep to determine whether the central nervous pathway mediating the drive to heat production involves serotonergic synapses.

2. 2.|At 15°C ambient temperature (T_a), 5-hydroxytryptamine (5-HT) at all doses tested, and norfenfluramine (NF) in low doses increased heat loss and decreased rectal temperature (T_re); lysergic acid diethylamide (LSD-25) and methysergide prevented these effects.

3. 3.|AT 0°C T_a, 5-HT, even in high doses failed to increase heat production but NF increased heat production and T_re.

4. 4.|The results suggest the effects of NF and LSD-25 on heat production may be related to synapses activated by an indoleamine other than 5-HT.

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.

Polar bear thermoregulation: Effect of oil on the insulative properties of fur

1. 1.|Oil caused a substantial decrease in the insulative value of polar bear (Ursus maritimus) pelts measured in vitro.

2. 2.|Following oil contamination the calm air heat transfer coefficient increased by a factor of 2 to 5: the wind coefficient averaged 290% greater and the solar utilization increased by 55%.

3. 3.|Conductance through oil-covered furs remained high at winter temperatures (T_a = 0.6°C) but decreased with time at summer temperatures (T_a = 24.7°C).

4. 4.|The most viscous of the three oils tested had a more consistently negative effect on insulation.

Development of thermoregulation in Hawaiian brown noddies (Anous stolidus pileatus)

1. 1.|Oxygen consumption ( ) and body temperture (T_b) of Hawaiian brown noddies (Anous stolidus pileatus [Aves: Laridae]) during late incubation and in the first 24 h after hatching were measured at ambient temperatures (T_a) between 28 and 38°C and between 15 and 43°C, respectively. Evaporative cooling by hatchings at T_a of 36–43°C was also measured.

2. 2.|Throughout the late incubation stages studied, and T_b both varied directly with T_a in an ectothermic pattern.

3. 3.|The hatchlings successfully regulated T_b at T_a between ca. 29 and 43°C.

4. 4.|The functional basis of the abrupt increase in thermoregulatory capacity with hatching is discussed.

Perinatal epigenetic temperature adaptation in avian species: comparison of turkey and Muscovy duck

1. Heat production (HP) and body core temperature (CT) where measured in 1- to 10-day old Muscovy ducklings and turkey chick, incubated during the last week before hatching at a lower (34.5 °C, LT-group) or at higher (38.5 °C, HT-group), than the normal temperature of 37.5 °C (control C-group).

2. In Muscovy ducklings, on the 1st day post-hatching HP was affected by exposure to low T_a of 10 °C T_a 28.2±3.9 W kg⁻¹ in the LT-group vs. 18.1±2.4 W kg⁻¹ in normal controls. On the same day, CT was higher (39.5±1.1 °C) in the HT- than in the CT-group (37.5±2.9 °C).

3. In turkeys, the relationships between T_a and HP could be described by parabola-like functions. Apart from the first day of life, the HP of the LT-group and the HT-group was higher than of the CT-group.

4. The low prenatal temperature of incubation resulted in a decrease of the preferred temperature in the LH-group and in an increase in the HT-group.

5. It is concluded that changes in incubation temperature at the end of embryonic development may induce an epigenetic temperature adaptation, which results in a long-lasting cold- and warm-adaptation in ducks but not in turkeys.

Temperature effects on evoked potentials of hippocampal slices from noncold-acclimated, cold-acclimated and hibernating hamsters

1. 1.|Neural activity was recorded in hippocampal slices from noncold-acclimated, cold-acclimated and hibernating hamsters.

2. 2.|Action potentials from a population of hippocampal pyramidal neurons were evoked by stimulating an afferent fiber tract, the Schaffer collaterals. The temperature of the artificial cerebrospinal fluid bathing the slice was varied by controlling the temperature of a water chamber jacketing the recording chamber.

3. 3.|The temperature just below that at which a population spike could be evoked, T_t, was 15.8 ± 0.9°C (mean ± SEM) for noncold-acclimated hamsters, 13.9 ± 0.3°C for cold-acclimated hamsters and 12.3 ± 0.3°C for hibernating hamsters.

4. 4.|These thresholds for evoked activity were significantly different in noncold-acclimated, cold-acclimated and hibernating hamsters, and may reflect acclimation of hippocampal neurons to cold.

Muscle temperature and muscle metabolism during short-term exercise in the goat

1. 1.|External heat exchangers acting on lower aortal blood temperature were used to dissociate hindleg muscle temperature (T_hlm) from general internal temperature (T_int) during short-term exercise of moderate intensity.

2. 2.|In series 1 39°C T_hlm was combined with 40.6°C T_int, and in series II 42°C T_hlm was combined with 39.8°C T_int.

3. 3.|At constant work rates, the 3°C difference in muscle temperature did not result in significantly different concentrations of muscle metabolites.

4. 4.|It is concluded that high local muscle temperature without general hyperthermia does not influence muscle metabolism during short-term moderate excercise.

How are neuronal thermosensitivity and lack of thermoreception related in the duck's hypothalamus? A tentative answer

1. 1.|In 15 conscious Pekin ducks, 40 “warm sensitive” hypothalamic neurons were identified according to their discharge rates at 40°C T_hy (F₄₀), local temperature coefficients (Δ/ΔT) and Q₁₀.

2. 2.|Q₁₀ and either F₄₀ or ΔF/ΔT were little or not related.

3. 3.|A positive correlation between F₄₀ and ΔF/ΔT was observed which was particularly close (r = 0.94 and 0.96) when the neurons were classified according to their Q₁₀ of <2 and >2.

4. 4.|The results suggest that neurons with positive temperature coefficients in the duck's hypothalamus mostly exhibit linear to exponential temperature-discharge relationships.

5. 5.|This is an contrast to observations on mammalian hypothalamic thermosensitive neurons and may relate to the absence of the thermosensory function in the duck's rostral brainstem.

Effects of weather and feeding on body temperature and activity in the snake Masticophis flagellum

1. 1.|Body temperature (T_b) and activity of the snake Masticophis flagellum were studied by radiotelemetry in an outdoor enclosure.

2. 2.|Mean diurnal T_b varied little over a wide range of weather conditions, but weather variation was accompanied by major changes in sun exposure and in the timing and duration of activity.

3. 3.|Recently fed snakes reduced activity and exhibited neither a thermophilic response nor increased precision of thermoregulation compared to fasting snakes.

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.

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.

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.

The importance of microhabitat in thermoregulation and thermal conductance in two namib rodents—a crevice dweller, Aethomys namaquensis, and a burrow dweller, Gerbillurus paeba

1. 1.|Thermoregulatory measurements of two Nambi rodents; Gerbillurus paeba, a burrow dweller, and Aethomys namaquensis, a crevice dweller were compared. Both were similar to other small arid-adapted rodents in that basal metabolic rates were reduced, thermoneutral zones narrow and evaporative water losses low. Rates of conductance and thermal lability, however, at ambient temperatures (T_a) below thermoneutral zone, were significantly different (P 0.01).

2. 2.|The rock rat A. namaquensis, living in a microclimate characterized by a large diel range and low humidities, compensates for a reduced basal metabolic rate by having a low rate of conductance. In this way it maintains precise thermoregulatory control. G. paeba, on the other hand, living in a thermally-stable milieu, does not control body temperature precisely. This animal instead utilizes a high rate of conductance to remove metabolic heat produced within the body. This would be advantageous to an animal living in a plugged burrow where the high humidities encountered impede the rate of evaporative cooling.

3. 3.|The energetic responses of both species, above the thermoneutral zone, appear to reflect very closely the environmental conditions which occur in the microhabitat that they rest in during the day. G. paeba shows less tolerance to temperature fluctuations than A. namaquensis, but shows more marked increases in short-term cooling mechanisms at high T_as.

4. 4.|Despite the increased use of evaporative cooling through salivation and panting in addition to pulmocutaneous evaporation, exposure to T_as above 38°C is rapidly lethal to G. paeba.

Comparative aspects of the thermal biology of the short-tailed gerbil, Desmodillus auricularis, and the bushveld gerbil, Tatera leucogaster

1. 1. The response of oxygen consumption (VO₂), thermal conductance (C_d and C_min, body temperature (T_b), and evaporative water loss (EWL) of Tatera leucogaster and Desmodillus auricularis were measured over the range of ambient temperatures (T_a) from 5–35°C.

2. 2. Basal metabolic rate (BMR) of T. leucogaster was 0.841 ± 0.049 ml O₂ g⁻¹ h⁻¹ and lower than predicted, while that of D. auricularis was similar to the expected value (1.220 ± 0.058 ml O₂ g⁻¹ h⁻¹). D. auricularis had a high, narrow thermoneutral zone (TNZ) typical of nocturnal, xerophilic, burrowing rodents.

3. 3. D. auricularis and T. leucogaster regulated T_b over the range T_a = 5–35°C and kept EWL and dry thermal conductance at a minimum below the TNZ. However, the EWL of T. leucogaster increased rapidly above T_a = 30°C.

4. 4. After comparison with data from other species, it was concluded that there is an optimum size for xeric, nocturnal, burrowing rodents.

Thermal gradients in the oesophagus of man during exercise and passive warming

1. 1.|Oesophageal temperature (T_es) has been recorded at four vertical levels in the oesophagus of human subjects during exercise and during passive body heating.

2. 2.|The temperature increased with depth.

3. 3.|The rate of increase in T_es during exercise was greatest at the level of the diaphragm.

4. 4.|During passive heating of the body T_es increased most rapidly, and with shortest latency time, at the level adjacent to the left atrium of the heart.

5. 5.|During exercise, when breathing is deeper than at rest, T_es should be measured at a deeper level than that which is used during passive heating.

The effect of acclimation temperature and the removal of peripheral temperature receptors on body temperature preference in the cockroach, Periplaneta americana

1. 1.|Body temperature preferences were compared between cockroaches acclimated to different ambient temperatures and between 25°C acclimated cockroaches and cockroaches deprived of their peripheral temperature receptors.

2. 2.|Acclimation to 35°C resulted in a significantly higher mean body temperature and low body temperature selected compared with 25°C acclimated cockroaches.

3. 3.|Cockroaches deprived of their peripheral temperature receptors showed a significantly higher mean high body temperature selected when compared to normal 25°C acclimated cockroaches.

4. 4.|It is concluded that cockroach temperature regulation is more precise than expected and that central temperature receptors are the primary sensing elements for cockroach thermoregulation.

Effect of temperature on the electrical activity of the rat epididymis in vitro

1. 1.|Regional differences in the frequency of electrical activity in rat epididymis were maintained at all temperatures below 39°C.

2. 2.|The change in frequency per deg C increased with temperature and was highest in the temperature region of 34–39°C and the Arrhenius plots of the frequency were linear and parallel in all parts of the epididymis.

3. 3.|The Q₁₀ of the frequency varied between 2.2.–4.3.

4. 4.|The conduction velocity at the cauda epididymis was highest (2.8 mm/s) at 37°C. The Q₁₀ of the conduction velocity was 2.3 in the temperature region of 24–37°C.