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.

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.

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.

Heat stress and age: Skin blood flow and body temperature

1. 1. The ability to increase skin blood flow is an important mechanism for transferring heat from the body core to the skin for dissipation.

2. 2. During exercise, skin blood flow is typically 20–40% lower in men and women aged 55 and over (compared with 20–30 years old) at a given body core temperature. Yet criterion measures of heat tolerance (changes in core temperature, heat storage) often show minimal or no age-related alterations. From a series of studies conducted in our laboratory over the past 5 years, the following conclusions can be drawn.

3. 3. When fit healthy older subjects are matched with younger subjects of the same gender, size and body composition, V_O2max, acclimation state, and hydration level, age-related differences in skin blood flow are evident. However, these differences often do not translate into “poorer” heat tolerance or higher core temperatures.

4. 4. The larger core-to-skin thermal gradient maintained by the older individuals allows for effective heat transfer at lower skin blood flows.

5. 5. Furthermore, there is an increased coefficient of variation for thermoregulatory response variables with increasing age.

6. 6. Despite differences in the mechanisms underlying thermoregulation, true thermal tolerance is less a function of chronological age than of functional capacity and physiological health status.

7. 7. While this conclusion is based primarily on cross-sectional studies, it is supported by the results of more recent studies using multiple regression analyses.

8. 8. Implicit in this conclusion is the notion that thermal tolerance, at any age, is a modifiable individual characteristic.

Cellular mechanisms of neuronal thermosensitivity

1. There are differences between warm sensitive and temperature insensitive neurons in the rostral hypothalamus.

2. In warm sensitive neurons, temperature affects the rate of depolarization in prepotentials that precede action potentials. Warming increases the depolarization rate, which shortens the interspike interval and increases firing rate.

3. Inactivation of the potassium A current is temperature sensitive and contributes to the depolarizing prepotential.

4. In addition to intrinsic mechanisms, neuronal warm-sensitivity is affected by inhibitory synaptic input. Since cooling increases neuronal resistance, temperature affects the amplitude of postsynaptic inhibitory potentials, and this enhances neuronal thermosensitivity.

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.

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.

The effects of wind and thermal radiation on thermal responses during rest and exercise in a cold environment

1. 1. The purpose of this study was to investigate the effects of thermal radiation and wind on thermal responses at rest and during exercise in a cold environment.

2. 2. The experimental conditions were radiation and wind (R + W), no radiation and wind (W), radiation and no wind (R), no radiation and no wind (C).

3. 3. The air temperature was −5°C. Thermal radiation was 360 W/m². Air velocities were 0.76, 1.73 and 2.8 m/s. Rectal and skin temperatures, heart rate and oxygen consumption were recorded. Thermal and comfort sensations were questioned.

4. 4. There are no significant effects of thermal radiation and wind on the physiological responses except the mean skin temperature. There are significant effects on the mean skin temperature (P < 0.01) and thermal sensation (P < 0.05).

Thermal responses and temperature tolerance of a dessert ant-lion larva

1. 1.Cueta trivirgata larvae construct pits in the dry Kuiseb River bed in the Namib Desert.

2. 2.An art, Ocymyrmex robustior comprises 65.4% of the biomass of prey consumed by the ant-lions.

3. 3.O. robustior is active between surface temperatures of 27–68°C.

4. 4.Ant-lions tolerate high body temperatures (LD₅₀ = 53.4°C).

5. 5.By exploiting the pit microclimate and by digging below the surface during extreme thermal loads, ant-lions can capture prey at surface temperatures of 13–63°C.

6. 6.These behavioural and physiological adaptations enable ant-lions to maximize the duration of vigilance and hence prey capture success.

Threshold temperature responses of thermosensitive neurons in guinea-pig hypothalamic slices

1. 1.|Neuronal activity in slices of the preoptic and anterior hypothalamic area of guinea-pigs during slow low-amplitude temperature changes analogous to temperature changes in the brain of endothermic animals, was extracellularly recorded.

2. 2.|42% of neurons showed threshold temperature responses. The threshold of response averaged 37.4°C for warm-sensitive neurons during warming and 37.0°C for cold-sensitive neurons during cooling.

3. 3.|The thresholds differed, on average, by 0.1°C in the same neuron at repeated temperature changes.

4. 4.|With temperatures 0.8°C above threshold on average (0.2°C in some units) neuronal activity reached a new high level that did not change either during a further exceeding of the threshold or prolonged maintenance of suprathreshold temperature.

5. 5.|The characteristics of the threshold temperature response of a hypothalamic neuron meet the criteria of thermoinduced structural rearrangements of cell membranes, caused by phase transitions of lipids, changes in protein conformation and cytoskeletal activity.

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.

Effect of fiber type and fabric moisture content on the hydration state of human stratum corneum

1. 1. The purpose of this study was to determine the effect of fiber type and fabric moisture content on SC hydration.

2. 2. Using three similarly constructed fabrics, six fabric type/moisture content combinations were selected.

3. 3. Fabric swatches were placed on both “normal” and “hydrated” volar forearm skin of five subjects for a specified period, then removed.

4. 4. Two minutes after removal, evaporative water loss (EWL) and skin temperature were measured.

5. 5. Data were analyzed using analyses of variance and Bonferroni t-tests.

6. 6. For normal skin, SC hydration generally increased as fabric moisture content increased. SC was significantly drier after being in contact with cotton swatches at regain than at the two moisture content levels above regain, and also under polyester swatches.

7. 7. For hydrated skin, hydration state was significantly lower under the cotton swatch at regain than at 38.6% moisture content or at saturation, but was not significantly different under the polyester swatch at regain or at saturation.

Thermal sensations during simultaneous warming and cooling at theh forearm: A human psychophysical study

1. 1.The forearm of 5 female subjects ws thermally stimulated by 2 sets of interposed servo-thermodes that respectively drove skin temperature at ±0.1°C.s⁻¹ for 25 s and then held it constant. Mean skin temperature remained constant. The sequence was repeated at adapting temperatures between 22.5 and 37.5°C.

2. 2.Thermal sensations, continuously reported by the position of a dial, were warmer for heterogeneous thermal stimuli than for homogeneous stimuli when mean skin temperature was greater than 30°C and cooler when less than 27.5°C.

3. 3.This phenomenon is inconsistent with a single additive contribution of “warm” and “cold” information to thermal sensations.

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.

Cardiac output and oxygen uptake kinetics at the onset and offset of exercise

1. 1. The aim of the present study is to assess the relationship between rapidity of oxygen uptake (V_O2 and cardiac output (Q) kinetics at the transient phase of the onset and offset of exercise.

2. 2. Five healthy male subjects performed multiple rest-exercise-recovery transitions on an electrically braked ergometer, work rate was 50, 75, or 100 W for 6 min, respectively.

3. 3. V_O2 was obtained by a breath-by-breath method, and Q was measured by an impedance method during normal breath, using an ensemble averaged method.

4. 4. On transition from rest to exercise, V_O2 rapidly increased as phase I with a time constant of 7.0–7.8 s. Q also showed a similar rapid increment with a time constant of 6.3–6.8 s in phase I.

5. 5. In this phase I, V_O2 increased approx. 42–68% of steady state value and Q increased 71–84%. Thereafter, V_O2 and Q increased monoexponentially up to steady state with a time constant of 26.7–32.3 and 23.7–34.4 s, respectively.

6. 6. During recovery, V_O2 (with a time constant of 35.7–38.1 s and time delay (TD) of −1 to −2 s), while Q remained to sustain the value of steady state exercise with a couple of time delay (TD = 2–7 s), and thereafter decreased monoexponentially (with a time constant of 18.9–31.6 s).

7. 7. The stroke volume showed the similar behavior to the Q kinetics after exercise, while heart rate rapidly decreased (time constant = 10.6–21.2 s).

8. 8. It is suggested that the delayed Q kinetics after exercise might be attributable to the sustained level of venous return and that Q kinetics is not linked with V_O2 kinetics after exercise.

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.

Cyclic temperature effects on growing-finishing swine

1. 1.|Growing swine (average 15.8 kg) had increased rate of feed intake and feed required per unit of gain and rate of gain decreased at 5 compared to 20°C, while feed intake and feed conversion were not affected by cycling temperatures.

2. 2.|Rate of gain and feed conversion of finishing swine (65–100 kg) were negatively affected both by 5°C and by cycles of ± 12°C during the initial 4-wk period but not during the final 3 wk.

3. 3.|Evaluations of immune function through total leukocyte count, cell differentiation, skinfold response to mitogen injection and antibody formation to a foreign protein in the finishing swine displaced mixed response to temperature and cyclicity.

Expression of NADPH-diaphorase in nucleus tractus solitarius after peripheral injection of E. coli endotoxin in rats

1. The possibility that peripheral exogenous pyrogens can activate brainstem nuclei by abdominal viscera afferents was studied using the NADPH-diaphorase method in E. coli lipopolysaccharide treated rats with and without ibuprofen pre-treatment.

2. NADPH-d staining revealed: (i) a significant increase in the number of NADPH-d labeled neurons in the subpostremal area of the nucleus tractus solitarius lipopolysaccharide treated rats compared with control animals (p<0.05), and (ii) an almost similar number of NADPH-d positive neurons in both control and ibuprofen pre-treated rats (p=0.091).

3. These data indicate that peripheral administration of an exogenous pyrogen stimulates the synthesis of nitric oxide in the nucleus tractus solitarius, and are consistent with the hypothesis of a direct neural link between the periphery and the hypothalamus.

Central thermosensitivity and the integrative responses of hypothalamic neurons

1. Hypothalamic thermosensitive neurons are important in the integrative regulation of body temperature. In addition to receiving afferent thermal input, their activity correlates with the stimulation of thermoregulatory mechanisms.

2. While cold sensitivity is synaptically mediated, warm sensitivity depends on inherent cellular responses. Warm sensitive neurons may also respond to other homeostatic variations, hormones, and endogenous mediators.

3. In contrast to peripheral thermoresponsiveness, which depends on conductance changes that regulate membrane potential, hypothalamic warm sensitivity relies on regulating the prepotential phase of the action potential.

4. Additionally, the recent morphologic characterization of these neurons supports the criterion for warm sensitivity.

Study of function of fingers by physiological tremor

1. 1. Physiological tremor is invisible mechanical vibration of body parts.

2. 2. It has two peak frequencies in the p ower spectrum. The origin of the peaks has not been well elucidated. Therefore, the mechanism and its application to labor science is studied in the paper.

3. 3. The effect of immersion of fingers in water and of loading weights on fingers are performed to elucidate the mechanism involved.

4. 4. It is found that the power spectrum output has two bands from the lower frequency band (1.5–18 Hz) from the CNS and the higher frequency band (18–50 Hz).

5. 5. These results are applied to the evaluation of fatigue of fingers in tapping and typing work.

6. 6. The total power, which is the sum of power spectrum in frequency range between 1.5 and 50 Hz, is employed as evaluational index. The change of total power explains finger fatigue during tapping and typing loads.

7. 7. Physiological tremor is an effective way of evaluating the function of fingers in human work.