Influence of skin temperature distribution on thermal sensation in a cool environment

Thermal sensation and distribution of skin temperatures in persons exercising at 36.5 W on a bicycle ergometer and resting in a cool environment (10 degrees C) in two different clothings, one with the insulation mainly over the trunk (1.22 clo), and one with well insulated limbs (1.67 clo), were studied. Their general thermal sensations varied from slightly warm to slightly cool. The placing of the insulation had a decisive influence on skin temperature distribution, so that skin temperature was always high in well-insulated areas. When the insulation was placed over the limbs, a greater amount of heat was lost than if a similar insulation was placed on the trunk. Neither Tsk nor skin temperature distribution correlated with general thermal sensation. Instead, mean body temperature seemed to be the determinant of general thermal sensation in these conditions. The best prediction of general thermal sensation was obtained by adding Tre with a weighting factor of 0.8-0.9 and Tsk with a weighting factor of 0.1-0.2.     

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

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

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

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

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

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

Probit analysis of thermal sensation assessments

The probit technique for analysis of subjective assessments of thermal sensation is described. It enables transition temperatures from any selected thermal sensation to the adjacent thermal sensation (e.g. from neutral to warm) to be identified. A transition temperature is defined as that temperature at which the maximum number of people would change their assessment from one thermal sensation to the next. Thus if a seven-point scale of thermal sensation is used, six transition temperatures are possible. Increments between them will not necessarily be identical, as would be assumed in a linear regression analysis. The method has been applied in three studies: laboratory studies by the Kansas State University, field studies in Port Moresby, and field studies in Melbourne. In the first it is shown that men are more thermally tolerant than women, in the second it is shown that in Port Moresby the preferred temperatures of Melanesians are 2°C higher than those of Caucasians and in the third it is suggested that subjects in Melbourne have a slightly lower preferred temperature than predicted by Fanger (1972).     

Modeling the thermal responses of the skin surface during hand-object interactions

The objective of this research is to analyze and model the decreases in skin temperature when the hand makes contact with an object at room temperature so that thermal feedback can be incorporated into haptic displays. A thermal model is proposed that predicts the thermal responses of the skin and object surface as well as the heat flux exchanged during hand-object interactions. The model was evaluated by comparing the theoretical predictions of temperature changes to those experimentally measured using an infrared thermal measurement system. The thermal measurement system was designed to overcome the limitations imposed by contact thermal sensors, and was able to measure skin temperature during contact, together with the contact area and contact force. The experimental results indicated that over the pressure range of 0.73-10.98 kPa, changes in skin temperature were well localized to the contact area and were affected by contact pressure. The pressure in turn influenced both thermal contact resistance and blood flow. Over the range of contact forces typically used in manual exploration, blood perfusion and metabolic heat generation do not appear to have a significant effect on the skin's thermal responses. The theoretical predictions and the measured data were consistent in characterizing the time course and amplitude of the skin temperature change during contact with differences typically being less than 1 degrees C between the two for pressures greater than 4 kPa. These findings indicate that the proposed thermal model is able to characterize and predict the skin temperature responses during hand-object interactions and could be used in a thermal display that simulates the properties of different materials.     

Discrimination of thermal sensation in unhomogeneous thermal environments using theory of quantification II

1. 1. One hundred and forty-five thermal-sensation tests by subjects were performed in unhomogeneous thermal environments and the whole body and the lower leg thermal-sensations were discriminated with physical data of the thermal environments using the discrimination analysis and the expanded theory of quantification II which is able to deal with data including quantitative continuous-variables and qualitative category-variables simultaneously.

2. 2. The discrimination of the whole-body thermal-sensations on the basis of the local-body thermal sensations was also done.

3. 3. As a result, it is shown that the discrimination analysis and the expanded theory of quantification II are able to discriminate the thermal sensation in unhomogeneous environments.

神经生长因子在痛感受过程中的生物作用

神经生长因子（ＮＧＦ）地神经系统的生长发育具有十分重要的作用,为神经元增殖、分化和存活以及功能维持所必需,并能促进神经损伤后的修复和再生。新近研究表明ＮＧＦ是炎症致痛的重要中介物质参与对伤害性热刺激和机械性刺激的痛过敏,成为引人注目与富有挑战意义的痛觉研究前沿,为临床镇痛药物的开发提供了新的思路。     

Parallel "pain" pathways arise from subpopulations of primary afferent nociceptor

A major unanswered question concerning "pain" circuitry is the extent to which different populations of primary afferent nociceptor engage the same or different ascending pathways. In the present study, we followed the transneuronal transport of a genetically expressed lectin tracer, wheat germ agglutinin, in Na(V)1.8-expressing nociceptors of the nonpeptide class. We found that interneurons of lamina II are at the origin of the major ascending circuits targeted by the nonpeptide nociceptors. These interneurons contact lamina V projection neurons, which in turn predominantly target fourth-order neurons in the amygdala, hypothalamus, bed nucleus of the stria terminalis, and to a remarkable extent, the globus pallidus. These circuits differ greatly from the lamina I-based projection that is targeted by the peptide class of nociceptors. Our results indicate that parallel, perhaps independent pain pathways arise from different nociceptor classes and that motor as well as limbic targets predominate in the circuits that originate from the nonpeptide population.     

Seasonal variations of physiological characteristics and thermal sensation under identical thermal conditions

Seasonal variations of human thermal characteristics were inspected in thermal comfort and when constantly indoors. Metabolic rate, tympanic temperature, skin temperature, body fat, body weight and thermal sensation were measured under identical thermal conditions in a chamber over the course of one year. Experiments were carried out for each subject in both summer and winter. Six subjects were measured 35 times in summer and 45 times in winter. one subject was measured weekly for 14 months. Measurements for analyses were taken 40-60 min after entrance into the chamber. Results revealed the following. 1) For all subjects, the metabolic rate, tympanic temperature and body fat were lower in summer than in winter; thigh skin temperatures were higher in summer than in winter. The averaged individual ratio of seasonal difference was 11.9% for metabolic rate, 14.9% for body fat, 1.8% for thigh temperature and 0.53% for tympanic temperature. Seasonal differences of about 10% in metabolic rate were maintained in this study. 2) Seasonal variations of the variables were examined for phase relationships against the outdoor temperature. 2-1) Metabolic rate, thermal sensation, body weight and body fat changed in reverse phase, whereas skin temperature was in-phase. 2-2) Skin temperature lagged by about one month in both summer and winter. Body fat also lagged by about one month in summer, but corresponded to the phase in winter. Metabolic rates were also in-phase in winter but led about three months in summer. Thermal sensations lagged by about three months in winter but were in-phase in summer. Body weight was in-phase in summer and winter. 2-3) Summer disorders were observed particularly in seasonal variations of metabolic rates, tympanic temperature, skin temperatures, and thermal sensation, thereby suggesting that the effect of temperature exposure was altered by air-conditioner use.     

The role of activin in neuropeptide induction and pain sensation

Signals from target tissues play critical roles in the functional differentiation of neuronal cells, and in their subsequent adaptations to peripheral changes in the adult. Sensory neurons in the dorsal root ganglia (DRG) provide an excellent model system for the study of signals that regulate the development of neuronal diversity. DRG have been well characterized and contain both neurons that convey information from muscles about limb position, as well as other neurons that provide sensations from skin about pain information. Sensory neurons involved in pain sensation can be distinguished physiologically and antigenically, and one hallmark characteristic is that these neurons contain neuropeptides important for their functions. The transforming growth factor (TGF) beta family member activin A has recently been implicated in neural development and response to injury. During sensory neuron development, peripheral target tissues containing activin or activin itself can regulate pain neuropeptide expression. Long after development has ceased, skin target tissues retain the capacity to signal neurons about changes or injury, to functionally refine synapses. This review focuses on the role of activin as a target-derived differentiative factor in neural development that has additional roles in response to cutaneous injuries in the adult.     

Regional differences in temperature sensation and thermal comfort in humans

Sensations evoked by thermal stimulation (temperature-related sensations) can be divided into two categories, "temperature sensation" and "thermal comfort." Although several studies have investigated regional differences in temperature sensation, less is known about the sensitivity differences in thermal comfort for the various body regions. In the present study, we examined regional differences in temperature-related sensations with special attention to thermal comfort. Healthy male subjects sitting in an environment of mild heat or cold were locally cooled or warmed with water-perfused stimulators. Areas stimulated were the face, chest, abdomen, and thigh. Temperature sensation and thermal comfort of the stimulated areas were reported by the subjects, as was whole body thermal comfort. During mild heat exposure, facial cooling was most comfortable and facial warming was most uncomfortable. On the other hand, during mild cold exposure, neither warming nor cooling of the face had a major effect. The chest and abdomen had characteristics opposite to those of the face. Local warming of the chest and abdomen did produce a strong comfort sensation during whole body cold exposure. The thermal comfort seen in this study suggests that if given the chance, humans would preferentially cool the head in the heat, and they would maintain the warmth of the trunk areas in the cold. The qualitative differences seen in thermal comfort for the various areas cannot be explained solely by the density or properties of the peripheral thermal receptors and thus must reflect processing mechanisms in the central nervous system.     

Impaired pain sensation in mice lacking Aquaporin-1 water channels

Aquaporin-1 (AQP1), a membrane water channel, is expressed in choroid plexus where it contributes to cerebrospinal fluid production. Here, we show that AQP1 is also expressed in the dorsal horn of the spinal cord and the trigeminal nucleus caudalis, regions that process pain information. Within the dorsal root and trigeminal sensory ganglia, AQP1 is concentrated in small diameter cell bodies, most of which give rise to unmyelinated C-fibers. To study the role of AQP1 in pain signaling, we compared acute pain responses in wild-type mice and in mice lacking AQP1. AQP1^−/− mice had reduced responsiveness to thermal and capsaicin chemical stimuli, but not to mechanical stimuli or formalin. These results provide evidence for AQP1 expression in nociceptive neurons and suggest that AQP1 may play a role in pain signal transduction.     

Modification of neuropathic pain sensation through microglial ATP receptors

Neuropathic pain that typically develops when peripheral nerves are damaged through surgery, bone compression in cancer, diabetes, or infection is a major factor causing impaired quality of life in millions of people worldwide. Recently, there has been a rapidly growing body of evidence indicating that spinal glia play a critical role in the pathogenesis of neuropathic pain. Accumulating findings also indicate that nucleotides play an important role in neuron-glia communication through P2 purinoceptors. Damaged neurons release or leak nucleotides including ATP and UTP to stimulate microglia through P2 purinoceptors expressing on microglia. It was shown in an animal model of neuropathic pain that microglial P2X₄ and P2X₇ receptors are crucial in pain signaling after peripheral nerve lesion. In this review, we describe the modification of neuropathic pain sensation through microglial P2X₄ and P2X₇, with the possibility of P2Y₆ and P2Y₁₂ involvement.     

Purinergic mechanosensory transduction and visceral pain

Background

Little is known about whether peripheral nerve injury during the early postnatal period modulates synaptic efficacy in the immature superficial dorsal horn (SDH) of the spinal cord, or whether the neonatal SDH network is sensitive to the proinflammatory cytokine TNFα under neuropathic conditions. Thus we examined the effects of TNFα on synaptic transmission and intrinsic membrane excitability in developing rat SDH neurons in the absence or presence of sciatic nerve damage.

Results

The spared nerve injury (SNI) model of peripheral neuropathy at postnatal day (P)6 failed to significantly alter miniature excitatory (mEPSCs) or inhibitory (mIPSCs) postsynaptic currents in SDH neurons at P9-11. However, SNI did alter the sensitivity of excitatory synapses in the immature SDH to TNFα. While TNFα failed to influence mEPSCs or mIPSCs in slices from sham-operated controls, it significantly increased mEPSC frequency and amplitude following SNI without modulating synaptic inhibition onto the same neurons. This was accompanied by a significant decrease in the paired-pulse ratio of evoked EPSCs, suggesting TNFα increases the probability of glutamate release in the SDH under neuropathic conditions. Similarly, while SNI alone did not alter action potential (AP) threshold or rheobase in SDH neurons at this age, TNFα significantly decreased AP threshold and rheobase in the SNI group but not in sham-operated littermates. However, unlike the adult, the expression of TNFα in the immature dorsal horn was not significantly elevated during the first week following the SNI.

Conclusion

Developing SDH neurons become susceptible to regulation by TNFα following peripheral nerve injury in the neonate. This may include both a greater efficacy of glutamatergic synapses as well as an increase in the intrinsic excitability of immature dorsal horn neurons. However, neonatal sciatic nerve damage alone did not significantly modulate synaptic transmission or neuronal excitability in the SDH, which could reflect a relatively weak expression of TNFα in the injured spinal cord at early ages. The above data suggest that although the sensitivity of the SDH network to proinflammatory cytokines after nerve injury is present from the first days of life, the profile of spinal cytokine expression under neuropathic conditions may be highly age-dependent.     

TRPV1-lineage neurons are required for thermal sensation

The ion-channel TRPV1 is believed to be a major sensor of noxious heat, but surprisingly animals lacking TRPV1 still display marked responses to elevated temperature. In this study, we explored the role of TRPV1-expressing neurons in somatosensation by generating mice wherein this lineage of cells was selectively labelled or ablated. Our data show that TRPV1 is an embryonic marker of many nociceptors including all TRPV1- and TRPM8-neurons as well as many Mrg-expressing neurons. Mutant mice lacking these cells are completely insensitive to hot or cold but in marked contrast retain normal touch and mechanical pain sensation. These animals also exhibit defective body temperature control and lose both itch and pain reactions to potent chemical mediators. Together with previous cell ablation studies, our results define and delimit the roles of TRPV1- and TRPM8-neurons in thermosensation, thermoregulation and nociception, thus significantly extending the concept of labelled lines in somatosensory coding.     

DEG/ENaC but not TRP channels are the major mechanoelectrical transduction channels in a C. elegans nociceptor

Many nociceptors detect mechanical cues, but the ion channels responsible for mechanotransduction in these sensory neurons remain obscure. Using in?vivo recordings and genetic dissection, we identified the DEG/ENaC protein, DEG-1, as the major mechanotransduction channel in ASH, a polymodal nociceptor in Caenorhabditis elegans. But DEG-1 is not the only mechanotransduction channel in ASH: loss of deg-1 revealed a minor current whose properties differ from those expected of DEG/ENaC channels. This current was independent of two TRPV channels expressed in ASH. Although loss of these TRPV channels inhibits behavioral responses to noxious stimuli, we found that both mechanoreceptor currents and potentials were essentially wild-type in TRPV mutants. We propose that ASH nociceptors rely on two genetically distinct mechanotransduction channels and that TRPV channels contribute to encoding and transmitting information. Because mammalian and insect nociceptors also coexpress DEG/ENaCs and TRPVs, the cellular functions elaborated here for these ion channels may be conserved.     

Local thermal sensation and finger vasoconstriction in the locally heated hand

The effects of local heating on finger blood flow (BF) and local thermal sensation (Sensw) were studied. Finger BFs in both hands were measured simultaneously; one hand was immersed in water the temperature (Tw) of which was raised from 35 degrees C to 43 degrees C by steps of 2 degrees C every 10 min, while the other hand was kept at Tw 35 degrees C. Finger BF in the locally heated hand decreased at Tw 37 to 41 degrees C, while finger BF in the control hand did not alter. Sensw in the heated hand showed a dynamic response, initially increasing concomitantly with an increase in Tw, then gradually returning and adapting to a new level of Sensw. The dynamic response of Sensw was not perceived during mental calculation even when Tw was raised to 40 degrees C, and the reduction in finger blood flow was not observed. These results suggest that finger vasoconstriction caused by local heating closely relates to the dynamic response characteristic of local thermal sensation at Tw above core temperature, and that the perception of local thermal sensation in the central nervous system is involved in the mechanism of this vasoconstrictor response.     

Type III Nrg1 back signaling enhances functional TRPV1 along sensory axons contributing to basal and inflammatory thermal pain sensation

Type III Nrg1, a member of the Nrg1 family of signaling proteins, is expressed in sensory neurons, where it can signal in a bi-directional manner via interactions with the ErbB family of receptor tyrosine kinases (ErbB RTKs). Type III Nrg1 signaling as a receptor (Type III Nrg1 back signaling) can acutely activate phosphatidylinositol-3-kinase (PtdIns3K) signaling, as well as regulate levels of α7* nicotinic acetylcholine receptors, along sensory axons. Transient receptor potential vanilloid 1 (TRPV1) is a cation-permeable ion channel found in primary sensory neurons that is necessary for the detection of thermal pain and for the development of thermal hypersensitivity to pain under inflammatory conditions. Cell surface expression of TRPV1 can be enhanced by activation of PtdIns3K, making it a potential target for regulation by Type III Nrg1. We now show that Type III Nrg1 signaling in sensory neurons affects functional axonal TRPV1 in a PtdIns3K-dependent manner. Furthermore, mice heterozygous for Type III Nrg1 have specific deficits in their ability to respond to noxious thermal stimuli and to develop capsaicin-induced thermal hypersensitivity to pain. Cumulatively, these results implicate Type III Nrg1 as a novel regulator of TRPV1 and a molecular mediator of nociceptive function.