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PubMed1991

Significance of skin temperature changes in surface electromyography.

Differing results have been reported concerning the direction and quantity of the electromyogram (EMG) amplitude response to changes in tissue temperature. The EMG signals from the soleus muscle of six healthy human subjects were therefore recorded during dynamic exercise (concentric contractions) at ambient temperatures of 30 degrees C and 14 degrees C. The mean skin temperature (Tsk) above the muscle investigated was 32.9 degrees C and 21.7 degrees C, respectively. The core temperature, estimated by rectal temperature, was unchanged. The cooling of the superficial tissues caused approximately a doubling of the EMG amplitude. For the probability level 0.9 in the amplitude probability distribution function, the average signal level increased from 73 microV to 135 microV (P = 0.02). The average mean power frequency of the EMG signal was reduced from 142 Hz to 83 Hz (P = 0.004). The amplitude increase was not due to shivering but other possible explanations are presented. As the changes in Tsk investigated were within the range which may occur normally during the working hours, it was concluded that Tsk should be carefully controlled in vocational EMG studies.

Adult↗
PubMed1994

Effect of unilateral surgical denervation of brown adipose tissue on uncoupling protein mRNA level and cytochrom-c-oxidase activity in the Djungarian hamster.

The bilateral lobe of interscapular brown adipose tissue of the Djungarian hamster was unilaterally denervated in order to study the role of the sympathetic innervation for maintenance and cold-induced increase of non-shivering thermogenesis. Denervation decreased the noradrenaline content of brown adipose tissue to less than 9% of the intact contralateral pad. This low noradrenaline level was maintained for 1-14 days after denervation. First, to study the role of the sympathetic innervation of brown adipose tissue in the maintenance of the high thermogenic capacity characteristic of the cold acclimated state, brown adipose tissue was denervated in hamsters either kept at thermoneutrality or acclimated to 5 degrees C ambient temperature for 4 weeks. Cold-acclimated hamsters had elevated levels of uncoupling protein messenger ribonucleic acid (8.1-fold) and cytochrom-c oxidase-activity (3-fold). Denervation of brown adipose tissue decreased uncoupling protein-messenger ribonucleic acid level and cytochrom-c-oxidase-activity as compared to the intact pad in thermoneutral and in cold-acclimated hamsters. However, in cold-acclimated hamsters uncoupling protein-messenger ribonucleic acid level and cytochrom-c-oxidase-activity in denervated brown adipose tissue both were maintained on an elevated 6-fold higher level as compared to thermoneutral controls. Second, to study the role of the sympathetic innervation of brown adipose tissue in the cold-induced increase in thermogenic capacity, hamsters were denervated prior to cold acclimation and responses were measured after 3 and 14 days of cold exposure. Uncoupling protein-messenger ribonucleic acid level and cytochrom-c-oxidase-activity of intact brown adipose tissue increased after 14 days cold acclimation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue, Brown↗
PubMed1991

Threshold and slope of selective brain cooling.

Experiments (n = 50) in three conscious goats were performed in a thermoneutral environment to determine the threshold (i.e. the point at which the brain temperature is equal to the carotid blood temperature) and slope (i.e. the difference between brain and carotid blood temperatures as a function of carotid blood temperature) of selective brain cooling (SBC) and analyse the thermal inputs affecting them. Prior to the experiments the animals received carotid loops and an arteriovenous shunt to manipulate head and trunk temperatures independently of each other. The mean SBC threshold was 38.75 degrees C T(carotis) and independent of T(trunk). When body core temperature was increased from a hypo- to a moderately hyperthermic level, the SBC threshold was passed before metabolic rate had reached its minimum and before cutaneous vasodilation occurred. The mean SBC slope was 0.78 and rose with increasing Ttrunk. The degree of SBC was principally independent of respiratory heat loss: high levels of heat loss were found without SBC, and large degrees of SBC were observed at low levels of heat loss. The effect of SBC in and around normothermia is to smooth the onset of shivering or panting and to establish a range of internal temperature within which metabolic rate and respiratory heat loss are simultaneously at low levels.

Animals↗
PubMed1981

Combined effects of cold and somatostatin on glucose kinetics in dogs.

The role of the endocrine pancreas in glucose production (Ra), utilization (Rd), and metabolic clearance (R'd) was investigated during acute exposure to cold in normal normothermic dogs. Two ambient temperatures (TaN = +25 degrees C and TaC = -21 degrees C) were selected. At TaC, metabolic rate and glucose turnover of the shivering dogs were 4.3 and 2.4 times, respectively, higher than in dogs resting at TaN. As compared with the pre-experimental period, somatostatin infusion at TaN induced a 25% (arterial) and 34% (portal) glucagon deficiency, while insulin concentration dropped by 59% (arterial) and 74% (portal). Similar values were obtained at TaC for glucagon (39% arterial and 47% portal) and for insulin (52% arterial and 56% portal). At TaN, these simultaneous hormonal alterations provoked a slight reduction in plasma glucose concentration which levelled down to 4.4 mM. This reduction was due to a decrease in Ra, followed by a parallel decrease in Rd whereas R'd remained unchanged. At TaC, plasma glucose concentration dropped to the same level but quickly rose again during somatostatin infusion. This rise was due to a larger reduction in Rd than in Ra, accompanied by an abrupt fall in R'd. This reduction in R'd appears to be an important mechanism able to restore euglycemia during global pancreatic hormone deficiency in cold exposed dogs.

Animals↗
PubMed1985

Muscle glycogen depletion during exercise at 9 degrees C and 21 degrees C.

This study compared glycogen depletion in active skeletal muscle after light and moderate exercise in both cold and comfortable ambient conditions. Twelve male subjects (Ss) were divided into two groups equally matched for the submaximal exercise intensity corresponding to a blood lactate concentration of 4 mM (W4) during cycle exercise. On two separate days Ss rested for 30 min at ambient temperatures of either 9 degrees C or 21 degrees C, with the order of temperature exposure being counter-balanced among Ss. Following rest a tissue specimen was obtained from the m. vastus lateralis with the needle biopsy technique. Six Ss then exercised on a cycle ergometer for 30 min at 30% W4 (range = 50 - 65 W) while the remaining group exercised at 60% W4 (range = 85 - 120 W). Another biopsy was taken immediately after exercise and both samples were assayed for glycogen content. Identical procedures were repeated for the second environmental exposure. No significant glycogen depletion was observed in the Ss exercising at 30% W4 in 21 degrees C, but a 23% decrease (p = 0.04) was observed when the same exercise was performed at 9 degrees C. A 22% decrease (p = 0.002) in glycogen occurred in the 60% W4 group at 21 degrees C, which was not significantly different from that observed during the same exercise at 9 degrees C. The results suggest that muscle substrate utilization is increased during light exercise in a cold environment as compared to similar exercise at a comfortable temperature, probably due to shivering thermogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1982

Central thermal adaptation of lower brain stem units in the guinea-pig.

Cold adaptive changes were found in single units responding to thermal skin stimulation. All units were located in the subcoeruleus region of the lower brain stem. In cold-adapted guinea-pigs (five weeks in ambient temperature of 4 degrees C), the maximum activity of cold-responsive neurones was reduced markedly in comparison with that of cold-responsive neurones in animals adapted to room temperature (ca. 21 degrees C). This decrease may be a neuronal correlate to long-term downward shifts of shivering threshold temperature known to occur within adaptation periods of several weeks in man, as well as in animals.

Acclimatization↗
PubMed1979

Mammalian-like thermosensitivity in the lower brainstem of the Pekin duck.

In Pekin ducks the brainstem between the preoptic region and the medulla oblongata was probed with chronically implanted bilateral thermodes to evaluate its thermosensory function in temperature regulation. Cooling of the lower mesencephalic and rostral rhombencephalic region in conscious animals elicited cutaneous vasoconstriction and increased metabolic heat production by shivering. This finding contrasts to the observation of a paradoxical inhibition of cold defence activities by cooling the preoptic/anterior hypothalamic region in the same species.

Animals↗
PubMed1980

Maximum oxygen consumption in dogs during muscular exercise and cold exposure.

Maximum oxygen consumption for a short exhaustive work (Ex VO2 max) and for a severe cold stress (C VO2 max) were investigated in 8 dogs. Heart rate, plasma catecholamines and substrate concentrations were measured under both conditions. Mean C VO2 max was lower than mean Ex VO2 max. Heart rate and plasma lactate were also lower during cold exposure than during exercise. Average plasma epinephrine concentrations were not significantly different and average plasma norepinephrine concentrations were similar under C VO2 max and Ex VO2 max conditions. A positive correlation was found between plasma lactate and epinephrine concentrations measured under both conditions. It may be assumed that maximum oxygen consumption during muscular exercise is higher than during shivering thermogenesis. This difference does not seem to be due to differences in the involvement of the sympathico-adreno-medullary system.

Animals↗
PubMed1980

Effect of the adrenocorticostatic agent, metopirone, on thermoregulatory heat production in the European hedgehog*.

1. Non-shivering thermogenesis (NST) was studied in 8 hedgehogs before and after a single injection of metopirone ditartrate (150-450 mg/kg, i.p.) at a thermoneutral chamber temperature (Ta) of 28C and during cold exposure (Ta = 8 degrees C for 20 min). 2. An average metabolic increase of 149% of the standard metabolic rate (SMR) was observed 12-26 min after an injection of metopirone ditartrate at thermoneutral chamber temperature. Average temperatures simultaneously increased by 2.1C in the brown adipose tissue (BAT) and 2.0C in the deep colon. This initial effect lasted for 40 plus or minus 8 min. 3. In a period of 3-48 h after injection of metopirone ditartrate, cold-induced NST was reduced by 89% of SMR (av.). Concomitant exposure to cold caused average temperatures to decrease by 1.0C in the BAT and 1.1 C in the colon relative to control experiments. 4. Our results suggest the participation of corticosteroids in the control of NST in the hedgehog. As metopirone blocks enzymatic 11 beta-hydroxylation in the steroid ring, there is a pronounced increase of endogenous 11-deoxycorticosteroids, such as deoxycorticoterone (DOC). An injection of DOC (3 mg/kg, i.m.) increases NST at hermoneutrality similar to the initial metabolic effect elicited by metopirone ditartrate. The reduced response to cold exposure after several hours may be explained by competitive inhibition of glucocorticoid receptors since there is also an increased production of other 11-deoxycorticosteroids.

Animals↗
PubMed1975

Carbon dioxide response curves during hypothermia.

The responsiveness of the medullary chemoreceptors, measured by the ventilatory response to hypercapnia given in an hyperoxic gas mixture in intact anesthetized dogs has been evaluated during normothermia and at two levels of hypothermia. The response was studied in: 1) 20 dogs during normothermia, 2) 10 of these dogs at a blood temperature of 32-33 degrees C, and 3) in the other 10 dogs during deeper hypothermia (28-29 degrees C). The ventilatory response to CO2 decreased while blood temperature was lowered until the response became absent during deep hypothermia. For normothermia and both levels of hypothermia a similar oxygen drive of ventilation was found which was equivalent to approximately one fourth of the spontaneous ventilation. It is suggested, that in the deeply hypothermic animal the normal respiratory drive is apparently of peripheral (arterial) chemoreceptor origin and when this drive is nullified or significantly decreased, gentle shivering could be responsible for stimulating the respiratory center.

Animals↗
PubMed1987

Changes in cold- and heat-defence following electrolytic lesions of raphe nuclei in the guinea-pig.

In conscious guinea-pigs the effects of electrolytic lesions of the nucleus raphe magnus (NRM) and of adjacent areas in the lower brainstem on cold- and heat-defence were studied. Changes in core temperature, heat production and heat loss effectors as well as their threshold temperatures were compared in the same animals before and after lesioning. As an additional index of heat loss, ear skin temperature and a derived parameter--vasomotor index--were also measured. Three days after NRM lesion the fall in core temperature evoked by an exposure to 14-15 degrees C was smaller than before lesion, furthermore the body temperature threshold for shivering increased. Cold-induced heat production was also higher following NRM lesions. Lesions outside the NRM or sham-operation did not influence cold-defence. After NRM lesion heat-defence was also improved; the rise in core temperature elicited by an exposure to 36-37 degrees C was smaller and the body temperature threshold for ear skin vasoconstriction during recovery from hyperthermia decreased. No change in respiratory evaporative heat loss could be observed after NRM lesion. Lesions outside the NRM or sham-operation did not influence heat-defence. An attempt has been made to explain the observed improvements in cold- and heat-defence by discussing relevant data on mechanisms in central temperature control.

Animals↗
PubMed1981

Influence of noradrenaline on blood flow to brown adipose tissue in rats exhibiting diet-induced thermogenesis.

1. The influence of noradrenaline on regional blood flow was determined using radioactive microspheres in rats maintained on either stock diet or a palatable cafeteria diet. 2. Cardiac output and blood flow to brain, lungs, liver and skeletal muscle were similar for rats on the two diets. 3. Blood flow to total dissectable brown adipose tissue in control and cafeteria rats represented 1 and 2% of cardiac output respectively but these values rose to 7 and 15.5% during infusion of noradrenaline. 4. Arterial oxygen content was similar for all groups but the oxygen content of venous blood draining the interscapular brown adipose tissue fell to 6 ml O2/100 ml blood in control rats and 1 ml/100 ml in cafeteria rats after noradrenaline. 5. The total oxygen consumption of brown adipose tissue was calculated and found to account for 42% of the response to noradrenaline in control rats and 74% in cafeteria animals. The increments in the oxygen consumption of other tissues were almost identical in both groups and so all the diet-induced changes in thermogenic capacity can be attributed to increases in brown adipose tissue metabolism. 6. These findings demonstrate the quantitative importance of brown adipose tissue in diet-induced thermogenesis and confirm the similarities between diet and non-shivering thermogenesis.

Adipose Tissue, Brown↗
PubMed1976

Effects of acute cold exposure on the distribution of cardiac output in the sheep.

Conscious adult Merino sheep were studied in a thermoneutral environment and then during cold exposure. Microspheres labelled with 141Ce, 51Cr, 85Sr, and 46Sc were used to measure blood flow (Q) in most tissues of the body. (Microspheres labelled with 125I were found to be unsatisfactory.) Cold exposure which caused a marked decrease in skin surface temperature and mild, continuous shivering but no change in deep body temperature, was associated with mean increases in oxygen consumption, heart rate, and cardiac output (C.O.) of 100%, 62%, and 48%, respectively; blood pressure and total peripheral resistance were unchanged. There was approximately a 6-fold increase in Q in perirenal white adipose tissue, and a 3- to 4-fold increase in muscles of the upper foreleg and hindleg, and the intercostals; myocardial Q also increased significantly. There was a marked decrease in Q in skin of the legs and ears, in the maxillo turbinals and in the nasal mucosa, and a decrease in the total proportion of C.O. passing through arteriovenous anastomoses. Thus, not only did C.O. increase, but there was a redistribution appropriate to meet the challenge with which the animal was confronted.

Animals↗
PubMed1985

Comparison of the action of prostaglandin with endotoxin on thermoregulatory response thresholds.

Prostaglandin E2 (PGE2) and lipopolysaccharide (LPS) derived from E. coli were injected into the lateral cerebral ventricle of rabbits at 30 degrees C ambient temperature. The threshold core temperatures for ear cutaneous vasoconstriction (Thv) and shivering (Thsh) were determined by whole-body cooling with an intestinal thermode. Each threshold, as determined at the plateau phase of LPS fever and PGE2 hyperthermia respectively, were compared with the control values before LPS and PGE2 injection. Thsh was not changed by the injection of LPS, while Thv was increased. After PGE2 injection both Thsh and Thv were increased in comparison to their control levels. These changes paralleled the elevation of core temperature. The present study does not exclude prostaglandins as humoral mediators involved in some of the central processes generating fever, but suggest at the same time that there are additional properties of LPS fever for which prostaglandins do not account.

Animals↗
PubMed1983

Central short-term cold adaptation in the guinea-pig.

The responses of seventeen single units to changes in skin temperature were recorded in fifteen guinea-pigs anaesthetized with urethane. All units were located in the subcoeruleus region which has been discussed as part of the thermoafferent system. Thermal stimuli were applied to different skin areas. The receptive fields of sixteen cold-responsive units were found to be parts of the abdominal and thoracic skin. The cold-responsive units could be subdivided into two groups. Ten units showed the known classic cold-responsive steady state response. A short-term thermal adaptation was seen in six units. These units had peak activities at skin temperatures between 22 degrees C and 29 degrees C and decreased their firing rates within 5 to 40 minutes when the temperature of the receptive skin area was kept constant in the range between 20 degrees C and 29 degrees C. This short-term cold-adaptive effect could be reversibly abolished by warming the corresponding skin area for a certain period of time. The short-term adapting neurones could be conceived of as the neurophysiological correlate to cold-adaptive changes in thermogenic responses seen in three guinea-pigs. Oxygen uptake and shivering activity were reduced in animals, which had reached approximately constant skin and core body temperature during sustained external cooling.

Adaptation, Physiological↗
PubMed1986

Absence of correlations between glutamine-synthetase activity and dysmyelination-associated modifications of astroglia in the brain of murine mutants.

Glutamine Synthetase (GS) activity was investigated in cerebellum (ce), cerebral cortex (cc), olfactory bulb (ob), and medulla oblongata (mo) of murine dysmyelinating mutants for correlations with modifications of astroglia associated with genetic dysmyelination. One of these mutants, jimpy, develops a strong gliosis throughout the CNS. The other three mutants: shiverer, mld, and quaking, exhibit various astrocytic responses to dysmyelination, but reduced gliosis if any. Comparison between CNS areas in control animals showed a higher GS activity in the olfactory bulb than in the cerebral cortex, medulla, and cerebellum. The developmental patterns of GS activity were similar in mutants and in controls in all four areas investigated. Data on Jimpy suggest that GS activity is not associated with reactive astrocytes.

Animals↗
PubMed1994

Contribution of transplantations to the understanding of the role of the PLP gene.

We present an overview of the results obtained in a cross-transplantation system using respectively controls, jimpy (jp), and shiverer mutant mice as donors and recipients. Homochronic transplantations (O days into O days) demonstrated that jp environment is non-toxic for non-jp cells and that, contrary to in vitro, jp oligodendrocytes phenotype cannot be modified by environmental factors at this age. Transplantations of embryonic fragments into the newborn brain demonstrated that in contrast to oligodendrocyte precursors contained in fragments of newborn tissue, jimpy embryonic stem cells are sensitive to environmental factors able to modulate the proportion of surviving oligodendrocytes. In addition, these series evidenced a disjunction between the surviving and the myelinating capacity of jp cells demonstrating a pleiotropic effect of the jp mutation on oligodendrocyte biology. Results are discussed with regards to the recent molecular biological finding on the role of the DM20/PLP gene.

Animals↗
PubMed1991

Seasonal energy requirements and thermoregulation of growing pouched mice, Saccostomus campestris (Cricetidae).

Pouched mice (Saccostomus campestris) were born in captivity during January and March and subsequently maintained under long photoperiod (14 h light: 10 h dark) at 25 degrees C. During their first winter (July) and the following summer (January) the pouched mice were exposed to natural photoperiod in an unheated laboratory for 3 weeks prior to measurement. The pouched mice continued to grow during the study, and were significantly heavier after summer exposure than after winter exposure 6 months earlier. Although this increase in body mass would result in a decline in their surface area to volume ratio there was no significant decline in minimal thermal conductance (Cm) and winter-exposed pouched mice had a relatively lower Cm than expected. Meanwhile the smaller, winter-exposed animals displayed a significantly higher capacity for non-shivering thermogenesis, together with higher levels of basal metabolism than summer individuals. These differences were not solely attributable to the contrasting body mass of each group and it is therefore clear that S. campestris can increase thermoregulatory heat production, and modify heat loss following exposure to short photoperiod and cold during their first winter. Despite the significant increase in metabolism, the overall energy requirements of small, winter-exposed animals were significantly lower than those for heavier pouched mice following exposure to summer conditions. These results suggest that growing pouched mice can effectively adapt to lower temperature conditions during their first winter, yet accrue considerable overall savings in total energy requirements as a result of their smaller body mass.

Animals↗