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Notley SR, Mitchell D, Taylor NAS. A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 3: Heat and cold tolerance during exercise. Eur J Appl Physiol 2024; 124:1-145. [PMID: 37796292 DOI: 10.1007/s00421-023-05276-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Accepted: 07/04/2023] [Indexed: 10/06/2023]
Abstract
In this third installment of our four-part historical series, we evaluate contributions that shaped our understanding of heat and cold stress during occupational and athletic pursuits. Our first topic concerns how we tolerate, and sometimes fail to tolerate, exercise-heat stress. By 1900, physical activity with clothing- and climate-induced evaporative impediments led to an extraordinarily high incidence of heat stroke within the military. Fortunately, deep-body temperatures > 40 °C were not always fatal. Thirty years later, water immersion and patient treatments mimicking sweat evaporation were found to be effective, with the adage of cool first, transport later being adopted. We gradually acquired an understanding of thermoeffector function during heat storage, and learned about challenges to other regulatory mechanisms. In our second topic, we explore cold tolerance and intolerance. By the 1930s, hypothermia was known to reduce cutaneous circulation, particularly at the extremities, conserving body heat. Cold-induced vasodilatation hindered heat conservation, but it was protective. Increased metabolic heat production followed, driven by shivering and non-shivering thermogenesis, even during exercise and work. Physical endurance and shivering could both be compromised by hypoglycaemia. Later, treatments for hypothermia and cold injuries were refined, and the thermal after-drop was explained. In our final topic, we critique the numerous indices developed in attempts to numerically rate hot and cold stresses. The criteria for an effective thermal stress index were established by the 1930s. However, few indices satisfied those requirements, either then or now, and the surviving indices, including the unvalidated Wet-Bulb Globe-Thermometer index, do not fully predict thermal strain.
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Affiliation(s)
- Sean R Notley
- Defence Science and Technology Group, Department of Defence, Melbourne, Australia
- School of Human Kinetics, University of Ottawa, Ottawa, Canada
| | - Duncan Mitchell
- Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa
- School of Human Sciences, University of Western Australia, Crawley, Australia
| | - Nigel A S Taylor
- Research Institute of Human Ecology, College of Human Ecology, Seoul National University, Seoul, Republic of Korea.
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Notley SR, Mitchell D, Taylor NAS. A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 2: physiological measurements. Eur J Appl Physiol 2023; 123:2587-2685. [PMID: 37796291 DOI: 10.1007/s00421-023-05284-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2023] [Accepted: 07/14/2023] [Indexed: 10/06/2023]
Abstract
In this, the second of four historical reviews on human thermoregulation during exercise, we examine the research techniques developed by our forebears. We emphasise calorimetry and thermometry, and measurements of vasomotor and sudomotor function. Since its first human use (1899), direct calorimetry has provided the foundation for modern respirometric methods for quantifying metabolic rate, and remains the most precise index of whole-body heat exchange and storage. Its alternative, biophysical modelling, relies upon many, often dubious assumptions. Thermometry, used for >300 y to assess deep-body temperatures, provides only an instantaneous snapshot of the thermal status of tissues in contact with any thermometer. Seemingly unbeknownst to some, thermal time delays at some surrogate sites preclude valid measurements during non-steady state conditions. To assess cutaneous blood flow, immersion plethysmography was introduced (1875), followed by strain-gauge plethysmography (1949) and then laser-Doppler velocimetry (1964). Those techniques allow only local flow measurements, which may not reflect whole-body blood flows. Sudomotor function has been estimated from body-mass losses since the 1600s, but using mass losses to assess evaporation rates requires precise measures of non-evaporated sweat, which are rarely obtained. Hygrometric methods provide data for local sweat rates, but not local evaporation rates, and most local sweat rates cannot be extrapolated to reflect whole-body sweating. The objective of these methodological overviews and critiques is to provide a deeper understanding of how modern measurement techniques were developed, their underlying assumptions, and the strengths and weaknesses of the measurements used for humans exercising and working in thermally challenging conditions.
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Affiliation(s)
- Sean R Notley
- Defence Science and Technology Group, Department of Defence, Melbourne, Australia
- School of Human Kinetics, University of Ottawa, Ottawa, Canada
| | - Duncan Mitchell
- Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa
- School of Human Sciences, University of Western Australia, Crawley, Australia
| | - Nigel A S Taylor
- College of Human Ecology, Research Institute of Human Ecology, Seoul National University, Seoul, Republic of Korea.
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Vizin RC, Almeida MC, Soriano RN, Romanovsky AA. Selection of preferred thermal environment and cold-avoidance responses in rats rely on signals transduced by the dorsal portion of the lateral funiculus of the spinal cord. Temperature (Austin) 2023; 10:121-135. [PMID: 37187830 PMCID: PMC10177698 DOI: 10.1080/23328940.2023.2191378] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2023] [Revised: 03/05/2023] [Accepted: 03/09/2023] [Indexed: 05/17/2023] Open
Abstract
Thermoregulatory behaviors are powerful effectors for core body temperature (Tc) regulation. We evaluated the involvement of afferent fibers ascending through the dorsal portion of the lateral funiculus (DLF) of the spinal cord in "spontaneous" thermal preference and thermoregulatory behaviors induced by thermal and pharmacological stimuli in a thermogradient apparatus. In adult Wistar rats, the DLF was surgically severed at the first cervical vertebra bilaterally. The functional effectiveness of funiculotomy was verified by the increased latency of tail-flick responses to noxious cold (-18°C) and heat (50°C). In the thermogradient apparatus, funiculotomized rats showed a higher variability of their preferred ambient temperature (Tpr) and, consequently, increased Tc fluctuations, as compared to sham-operated rats. The cold-avoidance (warmth-seeking) response to moderate cold (whole-body exposure to ~17°C) or epidermal menthol (an agonist of the cold-sensitive TRPM8 channel) was attenuated in funiculotomized rats, as compared to sham-operated rats, and so was the Tc (hyperthermic) response to menthol. In contrast, the warmth-avoidance (cold-seeking) and Tc responses of funiculotomized rats to mild heat (exposure to ~28°C) or intravenous RN-1747 (an agonist of the warmth-sensitive TRPV4; 100 μg/kg) were unaffected. We conclude that DLF-mediated signals contribute to driving spontaneous thermal preference, and that attenuation of these signals is associated with decreased precision of Tc regulation. We further conclude that thermally and pharmacologically induced changes in thermal preference rely on neural, presumably afferent, signals that travel in the spinal cord within the DLF. Signals conveyed by the DLF are important for cold-avoidance behaviors but make little contribution to heat-avoidance responses.
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Affiliation(s)
- Robson C.L. Vizin
- Thermoregulation and Systemic Inflammation Laboratory (FeverLab), St. Joseph’s Hospital and Medical Center, Dignity Health, Phoenix, AZ, USA
- Center for Natural and Human Sciences, Federal University of ABC, São Bernardo do Campo, SP, Brazil
| | - Maria C. Almeida
- Thermoregulation and Systemic Inflammation Laboratory (FeverLab), St. Joseph’s Hospital and Medical Center, Dignity Health, Phoenix, AZ, USA
- Center for Natural and Human Sciences, Federal University of ABC, São Bernardo do Campo, SP, Brazil
| | - Renato N. Soriano
- Thermoregulation and Systemic Inflammation Laboratory (FeverLab), St. Joseph’s Hospital and Medical Center, Dignity Health, Phoenix, AZ, USA
- Department of Basic Life Sciences, Federal University of Juiz de Fora, Governador Valadares, MG, Brazil
| | - Andrej A. Romanovsky
- Thermoregulation and Systemic Inflammation Laboratory (FeverLab), St. Joseph’s Hospital and Medical Center, Dignity Health, Phoenix, AZ, USA
- School of Molecular Sciences, University of Arizona, Tempe, AZ, USA
- Zharko Pharma, Inc, Olympia, WA, USA
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Hyperthermia and dehydration: their independent and combined influences on physiological function during rest and exercise. Eur J Appl Physiol 2020; 120:2813-2834. [DOI: 10.1007/s00421-020-04493-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Accepted: 09/03/2020] [Indexed: 10/23/2022]
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Frei R, Notley SR, Taylor EA, Burdon CA, Ohnishi N, Taylor NAS. Revisiting the dermatomal recruitment of, and pressure-dependent influences on, human eccrine sweating. J Therm Biol 2019; 82:52-62. [PMID: 31128659 DOI: 10.1016/j.jtherbio.2019.03.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Revised: 03/10/2019] [Accepted: 03/18/2019] [Indexed: 10/27/2022]
Abstract
Herein we describe two experiments in which the recruitment and pressure-induced modifications of human eccrine sweating were investigated. In one experiment, the longstanding belief that glandular recruitment follows a gradual, caudal-to-rostral (dermatomal) recruitment pattern was re-evaluated. The onset of sweating was simultaneously determined (ventilated capsules) from four spinal (dermatomal) segments (forehead, dorsal hand, lower chest and dorsal foot) during the passive heating of supine participants (N = 8). No evidence was found to support either dermatomal or simultaneous glandular recruitment patterns. Instead, the results were more consistent with individualised (random) patterns of regional activation (P > 0.05), with significant time delays among sites. Such delays in the appearance of discharged sweat may reflect differences in neurotransmitter sensitivity, precursor sweat production or ductal reabsorption. In the second experiment, the pressure-induced hemihidrotic reflex (contralateral sudomotor enhancement) was revisited, using pressures applied over 10 cm2 areas of the chest (left side: 6 N cm-2) and left heel (3 N cm-2) during both supine and seated postures (N = 12). Participants were passively heated and thermally clamped before pressure application. Hemihidrosis was not observed from the contralateral surfaces within the same (chest) or lower spinal segments (abdomen; both P > 0.05) during chest pressure, but a generalised enhancement followed heel pressure when supine. We suggest that previous observations of hemihidrosis possibly resulted from elevated heat storage, rather than a neural reflex. Chest pressure significantly inhibited ipsilateral sweating (forehead, hand, chest; all P < 0.05), and that influence is hypothesised to result from interactions between ascending mechanoreceptor afferents and the descending sudomotor pathways.
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Affiliation(s)
- Remo Frei
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Sean R Notley
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Elizabeth A Taylor
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Catriona A Burdon
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Norikazu Ohnishi
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia; Faculty of Nursing, Mie Prefectural College of Nursing, Mie, 514-0116, Japan
| | - Nigel A S Taylor
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia.
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Abstract
Heat exchange processes between the body and the environment are introduced. The definition of the thermoneutral zone as the ambient temperature range within which body temperature (Tb) regulation is achieved only by nonevaporative processes is explained. Thermoreceptors, thermoregulatory effectors (both physiologic and behavioral), and neural pathways and Tb signals that connect receptors and effectors into a thermoregulation system are reviewed. A classification of thermoeffectors is proposed. A consensus concept is presented, according to which the thermoregulation system is organized as a dynamic federation of independent thermoeffector loops. While the activity of each effector is driven by a unique combination of deep (core) and superficial (shell) Tbs, the regulated variable of the system can be viewed as a spatially distributed Tb with a heavily represented core and a lightly represented shell. Core Tb is the main feedback; it is always negative. Shell Tbs (mostly of the hairy skin) represent the auxiliary feedback, which can be negative or positive, and which decreases the system's response time and load error. Signals from the glabrous (nonhairy) skin about the temperature of objects in the environment serve as feedforward signals for various behaviors. Physiologic effectors do not use feedforward signals. The system interacts with other homeostatic systems by "meshing" with their loops. Coordination between different thermoeffectors is achieved through the common controlled variable, Tb. The term balance point (not set point) is used for a regulated level of Tb. The term interthreshold zone is used for a Tb range in which no effectors are activated. Thermoregulatory states are classified, based on whether: Tb is increased (hyperthermia) or decreased (hypothermia); the interthreshold zone is narrow (homeothermic type of regulation) or wide (poikilothermic type); and the balance point is increased (fever) or decreased (anapyrexia). During fever, thermoregulation can be either homeothermic or poikilothermic; anapyrexia is always a poikilothermic state. The biologic significance of poikilothermic states is discussed. As an example of practical applications of the concept presented, thermopharmacology is reviewed. Thermopharmacology uses drugs to modulate specific temperature signals at the level of a thermoreceptor (transient receptor potential channel).
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Muzik O, Diwadkar VA. Regulation of Brown Adipose Tissue Activity by Interoceptive CNS Pathways: The interaction between Brain and Periphery. Front Neurosci 2017; 11:640. [PMID: 29200996 PMCID: PMC5696740 DOI: 10.3389/fnins.2017.00640] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2017] [Accepted: 11/03/2017] [Indexed: 12/31/2022] Open
Abstract
To maintain thermal homeostasis, specific thermogenic tissues are under the control of central thermoregulatory networks that regulate the body's response to thermal challenges. One of these mechanisms involves non-shivering thermogenesis in brown adipose tissue (BAT), which is activated in cold environments in order to defend the body against physical damage as a result of hypothermia. The objective of our study was to assess the interaction between CNS thermoregulatory pathways and sympathetic innervation in BAT during a cold exposure paradigm. Our results show that an innocuous whole-body cooling paradigm induces significant differences in fMRI BOLD signal at the location of the right anterior insula and the red nucleus/substantia nigra region, between lean subjects with high levels of sympathetic innervation in supraclavicular BAT (BAT+ group), and subjects with low levels of sympathetic innervation (BAT− group). Specifically, results indicate significantly larger fMRI BOLD signal changes between periods of cooling and warming of the skin in the BAT+ (as compared to BAT−) group at the location of the right anterior insula. In contrast, the BAT+ group showed significantly smaller fMRI BOLD signal changes in the midbrain between periods of skin cooling and warming. Our findings are consistent with a hierarchical thermoregulatory control system that involves the initiation of inhibitory signals from the right anterior insula toward midbrain areas that normally exert tonic inhibition on the medullary raphe, from where BAT is directly innervated. Our data suggests that exposure to cold elicits differential neuronal activity in interoceptive regulatory centers of subjects with high and low level of sympathetic innervation. As a result, the variability of cold-activated BAT mass observed in humans might be, in part, yoked to different sensitivities of interoceptive cortical brain areas to skin temperature changes.
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Affiliation(s)
- Otto Muzik
- Departments of Pediatrics, Wayne State University School of Medicine, Detroit, MI, United States.,Radiology, Wayne State University School of Medicine, Detroit, MI, United States
| | - Vaibhav A Diwadkar
- Psychiatry and Behavioral Neurosciences, Wayne State University School of Medicine, Detroit, MI, United States
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Indirect hand and forearm vasomotion: Regional variations in cutaneous thermosensitivity during normothermia and mild hyperthermia. J Therm Biol 2017; 65:95-104. [DOI: 10.1016/j.jtherbio.2017.02.015] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Revised: 02/24/2017] [Accepted: 02/24/2017] [Indexed: 11/21/2022]
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Notley SR, Park J, Tagami K, Ohnishi N, Taylor NAS. Variations in body morphology explain sex differences in thermoeffector function during compensable heat stress. Exp Physiol 2017; 102:545-562. [PMID: 28231604 DOI: 10.1113/ep086112] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Accepted: 02/08/2017] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the central question of this study? Can sex-related differences in cutaneous vascular and sudomotor responses be explained primarily by variations in the ratio between body surface area and mass during compensable exercise that elicits equivalent heat-loss requirements and mean body temperature changes across participants? What is the main finding and its importance? Mass-specific surface area was a significant determinant of vasomotor and sudomotor responses in men and women, explaining 10-48% of the individual thermoeffector variance. Nonetheless, after accounting for changes in mean body temperature and morphological differences, sex explained only 5% of that inter-individual variability. It was concluded that sex differences in thermoeffector function are morphologically dependent, but not sex dependent. Sex is sometimes thought to be an independent modulator of cutaneous vasomotor and sudomotor function during heat exposure. Nevertheless, it was hypothesized that, when assessed during compensable exercise that evoked equal heat-loss requirements across participants, sex differences in those thermoeffectors would be explained by variations in the ratio between body surface area and mass (specific surface area). To evaluate that possibility, vasomotor and sudomotor functions were assessed in 60 individuals (36 men and 24 women) with widely varying (overlapping) specific surface areas (range, 232.3-292.7 and 241.2-303.1 cm2 kg-1 , respectively). Subjects completed two trials in compensable conditions (28°C, 36% relative humidity) involving rest (20 min) and steady-state cycling (45 min) at fixed, area-specific metabolic heat-production rates (light, ∼135 W m-2 ; moderate, ∼200 W m-2 ). Equivalent heat-loss requirements and mean body temperature changes were evoked across participants. Forearm blood flow and vascular conductance were positively related to specific surface area during light work in men (r = 0.67 and r = 0.66, respectively; both P < 0.05) and during both exercise intensities in women (light, r = 0.57 and r = 0.69; and moderate, r = 0.64 and r = 0.68; all P < 0.05). Whole-body and local sweat rates were negatively related to that ratio (correlation coefficient range, -0.33 to -0.62; all P < 0.05) during both work rates in men and women. Those relationships accounted for 10-48% of inter-individual thermoeffector variance (P < 0.05). Furthermore, after accounting for morphological differences, sex explained no more than 5% of that variability (P < 0.05). It was concluded that, when assessed during compensable exercise, sex differences in thermoeffector function were largely determined morphologically, rather than being sex dependent.
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Affiliation(s)
- Sean R Notley
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Joonhee Park
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Kyoko Tagami
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Norikazu Ohnishi
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia.,Faculty of Nursing, Mie Prefectural College of Nursing, Mie, 514-0116, Japan
| | - Nigel A S Taylor
- Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia
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Muzik O, Diwadkar VA. In vivo correlates of thermoregulatory defense in humans: Temporal course of sub-cortical and cortical responses assessed with fMRI. Hum Brain Mapp 2016; 37:3188-202. [PMID: 27220041 DOI: 10.1002/hbm.23233] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2015] [Revised: 04/18/2016] [Accepted: 04/18/2016] [Indexed: 01/28/2023] Open
Abstract
Extensive studies in rodents have established the role of neural pathways that are activated during thermoregulation. However, few studies have been conducted in humans to assess the complex, hierarchically organized thermoregulatory network in the CNS that maintains thermal homeostasis, especially as it pertains to cold exposure. To study the human thermoregulatory network during whole body cold exposure, we have used functional MRI to characterize changes in the BOLD signal within the constituents of the thermoregulatory network in 20 young adult controls during non-noxious cooling and rewarming of the skin by a water-perfused body suit. Our results indicate significant decreases of BOLD signal during innocuous whole body cooling stimuli in the midbrain, the right anterior insula, the right anterior cingulate, and the right inferior parietal lobe. Whereas brain activation in these areas decreased during cold exposure, brain activation increased significantly in the bilateral orbitofrontal cortex during this period. The BOLD signal time series derived from significant activation sites in the orbitofrontal cortex showed opposed phase to those observed in the other brain regions, suggesting complementary processing mechanisms during mild hypothermia. The significance of our findings lies in the recognition that whole body cooling evokes a response in a hierarchically organized thermoregulatory network that distinguishes between cold and warm stimuli. This network seems to generate a highly resolved interoceptive representation of the body's condition that provides input to the orbitofrontal cortex, where higher-order integration takes place and invests internal states with emotional significance that motivate behavior. Hum Brain Mapp 37:3188-3202, 2016. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Otto Muzik
- Department of Pediatrics, Wayne State University School of Medicine, Detroit, Michigan, 48201.,Department of Radiology, Wayne State University School of Medicine, Detroit, Michigan, 48201
| | - Vaibhav A Diwadkar
- Department of Psychiatry and Behavioral Neurosciences, Wayne State University School of Medicine, Detroit, Michigan, 48201
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Caldwell JN, Matsuda-Nakamura M, Taylor NAS. Three-dimensional interactions of mean body and local skin temperatures in the control of hand and foot blood flows. Eur J Appl Physiol 2014; 114:1679-89. [DOI: 10.1007/s00421-014-2894-x] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2013] [Accepted: 04/15/2014] [Indexed: 11/29/2022]
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Three-dimensional interactions of mean body and local skin temperatures in the control of hand and foot blood flows. Eur J Appl Physiol 2014. [PMID: 24819447 DOI: 10.1007/s00421‐014‐2894‐x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/29/2022]
Abstract
PURPOSE Much is known about the control of blood flow, yet gaps remain concerning the interactions of deep-body and peripheral thermal feedback. In this experiment, changes in the vascular tone of the hands and feet were mapped to demonstrate the separate and combined influences of mean body and local skin temperature changes. METHODS Eight males participated in three trials. Three pre-experimental conditions were established via water immersion (oesophageal temperatures: 36.1, 37.0, 38.5 °C), with core and mean skin temperatures then clamped (water-perfusion garment) whilst five thermal treatments were applied to the right hand and left foot (5, 15, 25, 33, 40 °C). This yielded 15 thermal combinations under which hand and foot blood flows were measured (displacement plethysmography). RESULTS Lower volume-specific blood flows were observed at the foot for almost all temperature combinations. When thermoneutral and moderately hyperthermic, the cutaneous thermosensitivity of the hand was significantly greater: thermoneutral: 0.2 vs. 0.1 (foot) mL 100 mL(-1) min(-1) °C(-1) (P < 0.05); moderate hyperthermia: 0.4 vs. 0.2 (foot) mL 100 mL(-1) min(-1) °C(-1) (P < 0.05). The hand was 13 times more responsive to core temperature elevations than an equivalent local skin temperature change. For the foot, this thermosensitivity differed by a factor of 26. CONCLUSION These observations identified the hands as heat radiators, with the feet resisting heat loss, and reinforce the dominance of central thermal feedback, particularly in controlling foot blood flow. However, thermosensitivity to local skin temperature changes was highly plastic, site-specific and dictated by thermal and regional variations in vaso- and venoconstrictor tone.
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Abstract
This review analyses whether skin temperature represents ambient temperature and serves as a feedforward signal for the thermoregulation system, or whether it is one of the body's temperatures and provides feedback. The body is covered mostly by hairy (non-glabrous) skin, which is typically insulated from the environment (with clothes in humans and with fur in non-human mammals). Thermal signals from hairy skin represent a temperature of the insulated superficial layer of the body and provide feedback to the thermoregulation system. It is explained that this feedback is auxiliary, both negative and positive, and that it reduces the system's response time and load error. Non-hairy (glabrous) skin covers specialized heat-exchange organs (e.g. the hand), which are also used to explore the environment. In thermoregulation, these organs are primarily effectors. Their main thermosensory-related role is to assess local temperatures of objects explored; these local temperatures are feedforward signals for various behaviours. Non-hairy skin also contributes to the feedback for thermoregulation, but this contribution is limited. Autonomic (physiological) thermoregulation does not use feedforward signals. Thermoregulatory behaviours use both feedback and feedforward signals. Implications of these principles to thermopharmacology, a new approach to achieving biological effects by blocking temperature signals with drugs, are discussed.
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Affiliation(s)
- A. A. Romanovsky
- Trauma Research Systemic Inflammation Laboratory (FeverLab) St. Joseph's Hospital and Medical Center Phoenix AZUSA
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Imbeault MA, Mantha OL, Haman F. Shivering modulation in humans: Effects of rapid changes in environmental temperature. J Therm Biol 2013. [DOI: 10.1016/j.jtherbio.2013.10.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Calorie restricted rats do not increase metabolic rate post-LPS, but do seek out warmer ambient temperatures to behaviourally induce a fever. Physiol Behav 2012; 107:762-72. [DOI: 10.1016/j.physbeh.2012.06.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2012] [Revised: 06/01/2012] [Accepted: 06/12/2012] [Indexed: 11/17/2022]
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Pharmacological blockade of the cold receptor TRPM8 attenuates autonomic and behavioral cold defenses and decreases deep body temperature. J Neurosci 2012; 32:2086-99. [PMID: 22323721 DOI: 10.1523/jneurosci.5606-11.2012] [Citation(s) in RCA: 176] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
We studied N-(2-aminoethyl)-N-(4-(benzyloxy)-3-methoxybenzyl)thiophene-2-carboxamide hydrochloride (M8-B), a selective and potent antagonist of the transient receptor potential melastatin-8 (TRPM8) channel. In vitro, M8-B blocked cold-induced and TRPM8-agonist-induced activation of rat, human, and murine TRPM8 channels, including those on primary sensory neurons. In vivo, M8-B decreased deep body temperature (T(b)) in Trpm8(+/+) mice and rats, but not in Trpm8(-/-) mice, thus suggesting an on-target action. Intravenous administration of M8-B was more effective in decreasing T(b) in rats than intrathecal or intracerebroventricular administration, indicating a peripheral action. M8-B attenuated cold-induced c-Fos expression in the lateral parabrachial nucleus, thus indicating a site of action within the cutaneous cooling neural pathway to thermoeffectors, presumably on sensory neurons. A low intravenous dose of M8-B did not affect T(b) at either a constantly high or a constantly low ambient temperature (T(a)), but the same dose readily decreased T(b) if rats were kept at a high T(a) during the M8-B infusion and transferred to a low T(a) immediately thereafter. These data suggest that both a successful delivery of M8-B to the skin (high cutaneous perfusion) and the activation of cutaneous TRPM8 channels (by cold) are required for the hypothermic action of M8-B. At tail-skin temperatures <23°C, the magnitude of the M8-B-induced decrease in T(b) was inversely related to skin temperature, thus suggesting that M8-B blocks thermal (cold) activation of TRPM8. M8-B affected all thermoeffectors studied (thermopreferendum, tail-skin vasoconstriction, and brown fat thermogenesis), thus suggesting that TRPM8 is a universal cold receptor in the thermoregulation system.
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MARLIN DJ, SCOTT CM, SCHROTER RC, MILLS PC, HARRIS RC, HARRIS PATRICIAA, ORME CE, ROBERTS CA, MARR CELIAM, DYSON SUEJ, BARRELET F. Physiological responses in nonheat acclimated horses performing treadmill exercise in cool (20°C/40%RH), hot dry (30°C/40%RH) and hot humid (30°C/80%RH) conditions. Equine Vet J 2010. [DOI: 10.1111/j.2042-3306.1996.tb05034.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Romanovsky AA, Almeida MC, Garami A, Steiner AA, Norman MH, Morrison SF, Nakamura K, Burmeister JJ, Nucci TB. The transient receptor potential vanilloid-1 channel in thermoregulation: a thermosensor it is not. Pharmacol Rev 2009; 61:228-61. [PMID: 19749171 PMCID: PMC2763780 DOI: 10.1124/pr.109.001263] [Citation(s) in RCA: 198] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The development of antagonists of the transient receptor potential vanilloid-1 (TRPV1) channel as pain therapeutics has revealed that these compounds cause hyperthermia in humans. This undesirable on-target side effect has triggered a surge of interest in the role of TRPV1 in thermoregulation and revived the hypothesis that TRPV1 channels serve as thermosensors. We review literature data on the distribution of TRPV1 channels in the body and on thermoregulatory responses to TRPV1 agonists and antagonists. We propose that two principal populations of TRPV1-expressing cells have connections with efferent thermoeffector pathways: 1) first-order sensory (polymodal), glutamatergic dorsal-root (and possibly nodose) ganglia neurons that innervate the abdominal viscera and 2) higher-order sensory, glutamatergic neurons presumably located in the median preoptic hypothalamic nucleus. We further hypothesize that all thermoregulatory responses to TRPV1 agonists and antagonists and thermoregulatory manifestations of TRPV1 desensitization stem from primary actions on these two neuronal populations. Agonists act primarily centrally on population 2; antagonists act primarily peripherally on population 1. We analyze what roles TRPV1 might play in thermoregulation and conclude that this channel does not serve as a thermosensor, at least not under physiological conditions. In the hypothalamus, TRPV1 channels are inactive at common brain temperatures. In the abdomen, TRPV1 channels are tonically activated, but not by temperature. However, tonic activation of visceral TRPV1 by nonthermal factors suppresses autonomic cold-defense effectors and, consequently, body temperature. Blockade of this activation by TRPV1 antagonists disinhibits thermoeffectors and causes hyperthermia. Strategies for creating hyperthermia-free TRPV1 antagonists are outlined. The potential physiological and pathological significance of TRPV1-mediated thermoregulatory effects is discussed.
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Affiliation(s)
- Andrej A Romanovsky
- Systemic Inflammation Laboratory, St. Joseph's Hospital and Medical Center, Phoenix, Arizona 85013, USA.
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A personal view of how ruminant animals control their intake and choice of food: minimal total discomfort. Nutr Res Rev 2007; 20:132-46. [DOI: 10.1017/s0954422407797834] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Voluntary food intake and the selection between foods are important subjects especially in ruminants in view of the economic importance of this class of animal and the complex digestive system with its attendant metabolic peculiarities. There is evidence that intake is limited by the capacity of the rumen as well as by metabolic factors; some theories assume that intake is controlled by the first limiting factor but this is not satisfying on physiological grounds and there is evidence that signals from feedback factors are integrated in an additive manner. It is now well established from research in which animals are given the chance to learn the metabolic consequences of eating food with a particular sensory profile, including a choice of foods, that animals including ruminants can adjust their diet, both quantitatively and qualitatively, to their nutrient requirements. It is proposed that they do this in order to minimise the total of the discomfort generated by the several signals from various body systems. The learning process is aided by the considerable day-to-day variation often seen in the intake of individual animals. An optimisation model is proposed and presented in a simple form, involving the addition of discomforts (calculated as the square of the deviation of the supply of metabolisable energy, crude protein and neutral-detergent fibre) and iterative elucidation of the intake at which total discomfort is minimal. With parameters appropriate for growing lambs the model provides reasonable agreement with observations, both in terms of daily intake and selection between foods of different protein contents. Manipulation of food composition and of nutrient requirements produces predictions broadly in agreement with reality except that protein deficiency has less severe consequences for the model than for real animals; it is proposed that protein deficiency be given more weighting than protein excess, and this may be true for other resources as well. This model is proposed as a philosophy and a starting point for further development and is not purveyed as a complete, working model. It nevertheless provides support for the concept of total minimal discomfort as a suitable base from which to view the control of intake and selection in all animals.
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Romanovsky AA. Thermoregulation: some concepts have changed. Functional architecture of the thermoregulatory system. Am J Physiol Regul Integr Comp Physiol 2007; 292:R37-46. [PMID: 17008453 DOI: 10.1152/ajpregu.00668.2006] [Citation(s) in RCA: 415] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
While summarizing the current understanding of how body temperature (Tb) is regulated, this review discusses the recent progress in the following areas: central and peripheral thermosensitivity and temperature-activated transient receptor potential (TRP) channels; afferent neuronal pathways from peripheral thermosensors; and efferent thermoeffector pathways. It is proposed that activation of temperature-sensitive TRP channels is a mechanism of peripheral thermosensitivity. Special attention is paid to the functional architecture of the thermoregulatory system. The notion that deep Tb is regulated by a unified system with a single controller is rejected. It is proposed that Tb is regulated by independent thermoeffector loops, each having its own afferent and efferent branches. The activity of each thermoeffector is triggered by a unique combination of shell and core Tbs. Temperature-dependent phase transitions in thermosensory neurons cause sequential activation of all neurons of the corresponding thermoeffector loop and eventually a thermoeffector response. No computation of an integrated Tb or its comparison with an obvious or hidden set point of a unified system is necessary. Coordination between thermoeffectors is achieved through their common controlled variable, Tb. The described model incorporates Kobayashi’s views, but Kobayashi’s proposal to eliminate the term sensor is rejected. A case against the term set point is also made. Because this term is historically associated with a unified control system, it is more misleading than informative. The term balance point is proposed to designate the regulated level of Tb and to attract attention to the multiple feedback, feedforward, and open-loop components that contribute to thermal balance.
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Affiliation(s)
- Andrej A Romanovsky
- Systemic Inflammation Laboratory, Trauma Research, St. Joseph's Hospital and Medical Center, Phoenix, AZ 85013, USA.
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Nakamura K, Morrison SF. Central efferent pathways mediating skin cooling-evoked sympathetic thermogenesis in brown adipose tissue. Am J Physiol Regul Integr Comp Physiol 2006; 292:R127-36. [PMID: 16931649 PMCID: PMC2441894 DOI: 10.1152/ajpregu.00427.2006] [Citation(s) in RCA: 176] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Control of thermoregulatory effectors by the autonomic nervous system is a critical component of rapid cold-defense responses, which are triggered by thermal information from the skin. However, the central autonomic mechanism driving thermoregulatory effector responses to skin thermal signals remains to be determined. Here, we examined the involvement of several autonomic brain regions in sympathetic thermogenic responses in brown adipose tissue (BAT) to skin cooling in urethane-chloralose-anesthetized rats by monitoring thermogenic [BAT sympathetic nerve activity (SNA) and BAT temperature], metabolic (expired CO(2)), and cardiovascular (arterial pressure and heart rate) parameters. Acute skin cooling, which did not reduce either rectal (core) or brain temperature, evoked increases in BAT SNA, BAT temperature, expired CO(2), and heart rate. Skin cooling-evoked thermogenic, metabolic, and heart rate responses were inhibited by bilateral microinjections of bicuculline (GABA(A) receptor antagonist) into the preoptic area (POA), by bilateral microinjections of muscimol (GABA(A) receptor agonist) into the dorsomedial hypothalamic nucleus (DMH), or by microinjection of muscimol, glycine, 8-OH-DPAT (5-HT(1A) receptor agonist), or kynurenate (nonselective antagonist for ionotropic excitatory amino acid receptors) into the rostral raphe pallidus nucleus (rRPa) but not by bilateral muscimol injections into the lateral/dorsolateral part or ventrolateral part of the caudal periaqueductal gray. These results implicate the POA, DMH, and rRPa in the central efferent pathways for thermogenic, metabolic, and cardiac responses to skin cooling, and suggest that these pathways can be modulated by serotonergic inputs to the medullary raphe.
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Affiliation(s)
- Kazuhiro Nakamura
- Neurological Sciences Institute, Oregon Health and Science University, 505 NW 185th Ave., Beaverton, OR 97006, USA.
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22
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Cotter JD, Taylor NAS. The distribution of cutaneous sudomotor and alliesthesial thermosensitivity in mildly heat-stressed humans: an open-loop approach. J Physiol 2005; 565:335-45. [PMID: 15760945 PMCID: PMC1464483 DOI: 10.1113/jphysiol.2004.081562] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2004] [Accepted: 03/07/2005] [Indexed: 11/08/2022] Open
Abstract
The distribution of cutaneous thermosensitivity has not been determined in humans for the control of autonomic or behavioural thermoregulation under open-loop conditions. We therefore examined local cutaneous warm and cool sensitivities for sweating and whole-body thermal discomfort (as a measure of alliesthesia). Thirteen males rested supine during warming (+4 degrees C), and mild (-4 degrees C) and moderate (-11 degrees C) cooling of ten skin sites (274 cm2), whilst the core and remaining skin temperatures were clamped above the sweat threshold using a water-perfusion suit and climate chamber. Local thermosensitivities were calculated from changes in sweat rates (pooled from sweat capsules on all limbs) and thermal discomfort, relative to the changes in local skin temperature. Thermosensitivities were examined across local sites and body segments (e.g. torso, limbs). The face displayed stronger cold (-11 degrees C) sensitivity than the forearm, thigh, leg and foot (P = 0.01), and was 2-5 times more thermosensitive than any other segment for both sudomotor and discomfort responses (P = 0.01). The face also showed greater warmth sensitivity than the limbs for sudomotor control and discomfort (P = 0.01). The limb extremities ranked as the least thermosensitive segment for both responses during warming, and for discomfort responses during moderate cooling (-11 degrees C). Approximately 70% of the local variance in sudomotor sensitivity was common to the alliesthesial sensitivity. We believe these open-loop methods have provided the first clear evidence for a greater facial thermosensitivity for sweating and whole-body thermal discomfort.
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Affiliation(s)
- James D Cotter
- Department of Biomedical Science, University of Wollongong, NSW, Australia.
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Affiliation(s)
- A J Gunn
- Department of Paediatrics, University of Auckland, New Zealand.
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Frank SM, Raja SN, Bulcao CF, Goldstein DS. Relative contribution of core and cutaneous temperatures to thermal comfort and autonomic responses in humans. J Appl Physiol (1985) 1999; 86:1588-93. [PMID: 10233122 DOI: 10.1152/jappl.1999.86.5.1588] [Citation(s) in RCA: 188] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Subjective thermal comfort plays a critical role in body temperature regulation since this represents the primary stimulus for behavioral thermoregulation. Although both core (Tc) and skin-surface (Tsk) temperatures are known afferent inputs to the thermoregulatory system, the relative contributions of Tc and Tsk to thermal comfort are unknown. We independently altered Tc and Tsk in human subjects while measuring thermal comfort, vasomotor changes, metabolic heat production, and systemic catecholaminergic responses. Multiple linear regression was used to determine the relative Tc/Tsk contribution to thermal comfort and the autonomic thermoregulatory responses, by using the ratio of regression coefficients for Tc and Tsk. The Tc/Tsk contribution ratio was relatively lower for thermal comfort (1:1) than for vasomotor changes (3:1; P = 0.008), metabolic heat production (3.6:1; P = 0.001), norepinephrine (1.8:1; P = 0.03), and epinephrine (3:1; P = 0.006) responses. Thus Tc and Tsk contribute about equally toward thermal comfort, whereas Tc predominates in regulation of the autonomic and metabolic responses.
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Affiliation(s)
- S M Frank
- Department of Anesthesiology and Critical Care Medicine, The Johns Hopkins Medical Institutions, Baltimore, Maryland 21287, USA.
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Grahn D, Brock-Utne JG, Watenpaugh DE, Heller HC. Recovery from mild hypothermia can be accelerated by mechanically distending blood vessels in the hand. J Appl Physiol (1985) 1998; 85:1643-8. [PMID: 9804564 DOI: 10.1152/jappl.1998.85.5.1643] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Peripheral vasoconstriction decreases thermal conductance of hypothermic individuals, making it difficult to transfer externally applied heat to the body core. We hypothesized that increasing blood flow to the skin of a hypothermic individual would enhance the transfer of exogenous heat to the body core, thereby increasing the rate of rewarming. External auditory meatus temperature (TEAM) was monitored in hypothermic subjects during recovery from general anesthesia. In 10 subjects, heat (45-46 degreesC, water-perfused blanket) was applied to a single forearm and hand that had been placed in a subatmospheric pressure environment (-30 to -40 mmHg) to distend the blood vessels. Heat alone was applied to control subjects (n = 6). The application of subatmospheric pressure resulted in a 10-fold increase in rewarming rates as determined by changes in TEAM [13.6 +/- 2.1 (SE) degreesC/h in the experimental group vs. 1.4 +/- 0.1 degreesC/h in the control group; P < 0.001]. In the experimental subjects, the rate of change of TEAM decreased sharply as TEAM neared the normothermic range.
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Affiliation(s)
- D Grahn
- Department of Biological Sciences, School of Medicine, Stanford University, Stanford, California 94305, USA.
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Affiliation(s)
- F K Pierau
- Max-Planck-Institut für Physiologische und Klinische Forschung, Bad Nauheim, FRG
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Repeated exposures to cold and the relationship between skin and core temperatures in control of metabolic rate in the goat (Capra hircus). COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. A, COMPARATIVE PHYSIOLOGY 1990; 96:245-52. [PMID: 1976469 DOI: 10.1016/0300-9629(90)90687-n] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
1. After 10-12 experiments in each of three goats, in which skin or core temperatures were lowered while the other temperatures remained sufficiently high to prevent metabolic rate from increasing, the core temperature threshold of shivering was lowered by 0.35 degrees C. 2. After 10-15 experiments, in which skin and core temperatures were simultaneously lowered to induce major increases of metabolic rate, no further change of threshold was observed, while the slope of metabolic rate over core temperature was reduced. 3. It is concluded that repeated cold exposures without manifest shivering can induce tolerance adaptation to cold.
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Abstract
Experiments were done to assess that fraction of the metabolic response to external cold exposure, which is attributable to skin temperature. In 5 conscious and closely clipped goats the metabolic rate was determined at various stable levels of skin temperature in the range from 13 to 41 degrees C, while core temperature was kept constant at 38.8 degrees C. Skin temperature was manipulated by a rapidly circulating shower bath, while core temperature was controlled by means of heat exchangers acting on arterial blood temperature in a chronic arteriovenous shunt. The metabolic response to skin temperature fell into two clearly discernible sections: a first zone with skin temperatures above 25-30 degrees C, within which the metabolic rate rose at a rate of -0.34 +/- 0.07 W/kg.degrees C with decreasing skin temperature, and a second zone with skin temperatures below 25-30 degrees C, within which the metabolic rate either plateaued or even grew smaller with further decreasing skin temperature. It is concluded that the relationship between skin temperature and metabolic rate does not directly reproduce the temperature-response curve of cutaneous cold receptors but also reflects a complex interaction of several factors, including an unspecific temperature effect on muscle metabolism.
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Affiliation(s)
- G Kuhnen
- Physiologisches Institut der Universität, Giessen, Federal Republic of Germany
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30
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Abstract
1. Experiments were done in conscious goats to estimate the gain of brain temperature sensors and to evaluate that fraction of the thermosensitivity of the entire brain which can be determined by a thermode located in the hypothalamus. 2. The animals were implanted with local thermodes, carotid loops and intravascular heat exchangers permitting independent control of hypothalamic temperature, extrahypothalamic brain temperature and trunk core temperature. 3. Small and slow ramp-like displacements of hypothalamic temperature generated continuously increasing thermoregulatory responses without any dead band, if a negative feed-back from extrahypothalamic sources was suppressed. 4. The hypothalamic sensitivity determined by the metabolic response to slow ramp-like cooling of the thermode amounted to -1.4 W/(kg degrees C) and equalled approximately 30% of what had been found for total body core sensitivity in another series of experiments. 5. Total brain thermosensitivity was -1.6 W/(kg degrees C), which implies that a large thermode centred in the hypothalamus can detect approximately 85% of the thermosensitivity of the entire brain.
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Affiliation(s)
- M E Heath
- Physiologisches Institut der Universitaet, Giessen, F.R.G
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Feistkorn G, Kaciuba-Usciklko H, Kozklowski S, Jessen C. Muscle temperature and muscle metabolism during short-term exercise in the goat. J Therm Biol 1986. [DOI: 10.1016/0306-4565(86)90008-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Heath ME, Jessen C. Effects of skin temperature on cold defense after cutaneous denervation of the trunk. Pflugers Arch 1986; 407:175-7. [PMID: 3748778 DOI: 10.1007/bf00580672] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
In intact goats the core temperature threshold below which heat production increases with falling core temperature, is inversely related to the temperature of the water bath in which they stand and is therefore assumed to be indicative of the central integration of signals from skin and core temperature receptors. The present study shows that a difference in core temperature thresholds for bath temperatures of 35 degrees C and 40 degrees C persisted after denervation of about two-thirds of the skin of the trunk and limbs. Also, for a given combination of skin and core temperatures, heat production was as great or greater after cutaneous denervation as before. It is concluded that, following denervation of the trunk and upper limbs, intact temperature receptors in the non-denervated skin of the legs and tail, and/or also in tissues between the skin and core, provide important and significant inputs to the temperature regulating system. But these inputs cannot explain fully the thermoregulatory responses observed unless it is assumed that the thermosensitivity of these tissues increased.
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Nagel A, Herold W, Roos U, Jessen C. Skin and core temperatures as determinants of heat production and heat loss in the goat. Pflugers Arch 1986; 406:600-7. [PMID: 3714458 DOI: 10.1007/bf00584027] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
In 82 experiments on 10 goats body core temperature (Tcore) was altered between 35 degrees and 42 degrees C by external heat exchangers acting on blood temperature while skin temperature (Tskin) was maintained constant, by a circulating shower bath, at different levels between 32 degrees and 44 degrees C. At all skin temperatures at least fourfold increases of heat production (M) and respiratory evaporative heat loss (REHL) occurred when Tcore was lowered or raised, respectively. The lower Tskin was, the higher were the thresholds of Tcore, at which M or REHL exceeded resting levels. The lower Tskin was, the higher were the slopes, at which M or REHL changed per unit of Tcore. At a given Tskin, the slopes decreased with increasing M or REHL, and were dependent on the range of Tcore. The higher the range of Tcore, the steeper changed M and REHL with changing Tcore, if all other variables were held constant. The results support the concept that an exponential relationship between Tcore and the rate of core temperature signals is the primary cause of the effects exerted by Tskin on the slopes, at which M or REHL change per unit of Tcore.
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Caputa M, Feistkorn G, Jessen C. Effects of brain and trunk temperatures on exercise performance in goats. Pflugers Arch 1986; 406:184-9. [PMID: 3960700 DOI: 10.1007/bf00586681] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
In 40 experiments on seven goats head and trunk temperatures were altered independently of each other and the effects on exercise performance on a treadmill (speed: 3 km/h, slope: 16%-20%) were observed. Brain temperature between 38.5 degrees C and 42.0 degrees C and trunk temperature between 39 degrees C and 43.5 degrees C did not reduce exercise performance or running time. Blood lactate concentration increased with rising brain and trunk temperatures, but did not exceed 13.1 mmol/l-1. Blood pressure and heart rate did not show any dependence on brain or trunk temperatures. Brain temperature between 42.0 degrees C and 42.9 degrees C shortened running time in 3 out of 12 experiments and reduced performance during shortlasting upward deviations of temperature. This suggests that in this species, the thermal safety limit to exercise is very close to that range of temperature which is likely to induce heat stroke.
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Caputa M, Feistkorn G, Jessen C. Competition for cool nasal blood between trunk and brain in hyperthermic goats. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. A, COMPARATIVE PHYSIOLOGY 1986; 85:423-7. [PMID: 2878769 DOI: 10.1016/0300-9629(86)90424-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
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.
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Werner J. Do black-box models of thermoregulation still have any research value? Contribution of system-theoretical models to the analysis of thermoregulation. THE YALE JOURNAL OF BIOLOGY AND MEDICINE 1986; 59:335-48. [PMID: 3751138 PMCID: PMC2590166] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The aims and the usefulness of modelling the thermoregulatory system are outlined by demonstrating applications and results of simulation on different levels of complexity. It is shown that both very simple one-loop models and complex models based on spatially distributed parameters have contributed to a better understanding of the system, but that current issues primarily require the latter type. However, mathematical modelling must be performed in conjunction with experimental studies and must be adapted to the amount of basic physiological data. Future fields of modelling are the adaptive mechanisms and the interactions of systems.
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Jessen C. Problems with neuronal models in temperature regulation. THE YALE JOURNAL OF BIOLOGY AND MEDICINE 1986; 59:361-8. [PMID: 3751140 PMCID: PMC2590165] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Neuronal models in temperature regulation are primarily considered explicit statements of assumptions and premises used in design of experiments and development of descriptive equations concerning the relationships between thermal inputs and control actions. Some of the premises of current multiplicative models are discussed in relation to presently available experimental evidence. The results of these experiments suggest that there is no skin temperature compatible with life which completely suppresses a rise of heat production in response to low internal temperature. The slope of heat production versus internal temperature at a given skin temperature is not constant but depends on internal temperature and the level of heat production. Therefore, a concept involving additive interaction of central and peripheral temperature signals appears more flexible in accepting data obtained even under extreme conditions.
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Heising M, Werner J. Differential heating of trunk and extremities. Effects on thermoregulation mechanisms. EUROPEAN JOURNAL OF APPLIED PHYSIOLOGY AND OCCUPATIONAL PHYSIOLOGY 1985; 54:79-83. [PMID: 4018060 DOI: 10.1007/bf00426303] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Experiments in which the whole human body was heated or cooled are compared with others in which one extremity (arm or leg) was simultaneously cooled or heated. With a warm load on the rest of the body resulting in general sweating, a cold load on one extremity did not evoke local shivering; with general body cooling, heating one limb did not stop the shivering. Skin temperatures of the other parts of the body were not influenced by warming or cooling one extremity. Evaporative heat loss was influenced by local, mean skin and core temperature, whereas shivering did not depend on local temperature, and vasomotor control seemed to be controlled predominantly by central temperatures. A cold load on an extremity during whole body heating in most cases induced an oscillatory behaviour of core temperature and of the evaporative heat loss from the body and the extremity. It is assumed that local, mean skin and core temperatures influence the three autonomous effector systems to very different degree.
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Mercer JB, Simon E. A comparison between total body thermosensitivity and local thermosensitivity in mammals and birds. Pflugers Arch 1984; 400:228-34. [PMID: 6728643 DOI: 10.1007/bf00581552] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
We have investigated how total body thermosensitivity in various mammalian and avian species (mouse, rat, golden hamster, guinea pig, rabbit, dog, goat, pigeon, duck, goose) is related to their respective local thermosensitivities in the hypothalamus, spinal cord and skin. Local and total thermosensitivities were determined by measuring the relationship between the response of one thermoregulatory effector, metabolic heat production, and the appropriate temperature. Local cooling was performed with chronically implanted, water perfused thermodes, and local thermosensitivities were estimated by relating the maximum activation of metabolic heat production to the induced decreases in local temperature. Total body cooling was achieved by means of chronically implanted intravascular heat exchangers or with thermodes inserted into the lower intestinal tract, and total body thermosensitivity was assessed by relating the rise in metabolic heat production to the induced fall in core temperature. These analyses plus previous estimations derived from the literature show total body thermosensitivity in the different species to range from -4.0 to -12.0 W X kg-1 . C-1. We also measured rabbit spinal cord thermosensitivity and guinea pig hypothalamic and spinal cord thermosensitivity; values for local thermosensitivity in other species were derived from the literature. In all species, local thermosensitivities determined as cold sensitivities in the described way were smaller than the corresponding total body core sensitivities. We conclude that thermosensitive structures outside of the investigated thermosensitive areas contribute a major input to the controller of body temperature, particularly in avian species in which hypothalamic thermosensitivity is lacking.(ABSTRACT TRUNCATED AT 250 WORDS)
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Graener R, Werner J, Buse M. Properties of central control of body temperature in the rabbit. BIOLOGICAL CYBERNETICS 1984; 50:437-445. [PMID: 6487681 DOI: 10.1007/bf00335201] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The structure of the central temperature controller in rabbits has been analysed. On the one hand, experiments were carried out to obtain the necessary data for system analysis; on the other hand, a mathematical model of the passive system was developed which describes the thermal characteristics of the body in accordance with the experimental results. In applying the model, different controller equations for the effector mechanisms involved were tested to fit the experimental data best. They are compared with already existing models of metabolic control. In addition, mechanisms of the effector coordination are discussed. It is shown that the three effectors make use of a similar controller structure that feeds core temperature as well as skin temperature back into the controller. The system is insensitive to variations of the controller gains, whereas a slight change in the controller reference temperature causes significant changes of the controlled core temperature. Furthermore it is shown that any mutual effector blockings are dispensible.
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Feistkorn G, Ritter P, Jessen C. Cardiovascular responses to thermal stress in conscious goats. J Therm Biol 1983. [DOI: 10.1016/0306-4565(83)90002-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Jessen C, Feistkorn G, Nagel A. Effects on heat loss of central-leg cooling in the conscious goat. J Therm Biol 1983. [DOI: 10.1016/0306-4565(83)90078-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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