Thermosensitive Neurons Research Articles

Molecular and cellular changes underlying plasticity and regeneration of intact, injured and aged cold corneal nerves

The peripheral nerve endings from trigeminal neurons that innervate the cornea are key neural structures to detect and encode the features of the physical and chemical external stimuli at the ocular surface. These neurons are functionally diverse and have been classified into polymodal nociceptors, mechano‐nociceptors and cold thermoreceptors. Each functional type evokes qualitative different conscious sensations. The sensory modality that is generated from a nerve ending is determined by the type and specific characteristics of the ion channels involved in stimulus transduction and encoding. Among them, TRPM8 channels transduce both cold and osmotic stimuli in corneal cold nerve terminals. These cold thermoreceptors mediate sensations of ocular surface cooling and dryness, and play an important role in the regulation of basal tearing and blinking. Morphologically, cold thermosensitive neurons display a more complex branching of their peripheral nerve endings innervating the cornea in comparison to the other functional classes of sensory neurons.With aging, TRPM8‐expressing cold sensory neurons innervating the mouse cornea experience morphological and functional alterations. These changes occur earlier and are more prominent at the nerve terminal than at the neuron cell body. A drastic reduction of the nerve terminal branching complexity in addition to lower background impulse activity is observed in cold nerves of aged mice. Similarly, after performing photorefractive keratectomy (PRK) in the adult mouse cornea, both the nerve terminal branching and background activity are reduced in a fraction of the cold nerve terminals. An altered morphological configuration along with an aberrant transducing and coding ion channels expression at corneal cold nerve terminals are likely to contribute to the discomfort sensations experienced after corneal surgery and to the age‐related abnormal tearing in the elderly.(Supported by PID2021‐124460OB‐I00 from DOI: MCIN/AEI/ 10.13039/501100011033, and CIPROM/2021/48 from the Generalitat Valenciana, Spain)

Naturally occurring compounds in relieving symptoms and reducing perimenopausal risks

Metabolic disorders that are progressive in nature most significantly influence the health of postmenopausal women. Osteoporosis and cardiovascular diseases are the most important long-term consequences and seriously affect the menopausal women’s quality of life. Hot flashes, a sudden feeling of heat or burning that begins in the face, neck, upper chest or back regions, is a common reason to see a doctor. Sometimes, hot flashes are accompanied by redness of the skin, red blotches, or rapid heartbeat. In some cases, rises in local skin temperature are observed. The above symptoms are the result of impaired functioning of thermosensitive neurons in the hypothalamic region. Menopausal hormone therapy is the gold standard for pharmacotherapy of various menopausal symptoms. However, it has different absolute and relative contraindications, as well as patients’ refusal of treatment mainly due to hormone phobia, that have resulted in a situation where 30% of menopausal women take hormone replacement therapy and only 15% continue to take it for a long period. Patients often insist on a natural approach to symptom relief and need evidence-based information about different hormonal and non-hormonal treatment options. Concerns about potential side effects of the hormone replacement therapy resulted in increased interest rates for phytoestrogens to manage menopausal symptoms. A rational fixed dose combination of phytoestrogens and micronutrients is a well-tolerated alternative preparation to support the health of perimenopausal women, which can be used with virtually no restrictions.

Transient receptor potential M2 channel in the hypothalamic preoptic area and its impact on thermoregulation during menopause

BackgroundDecreased estrogen levels can cause abnormal thermosensitivity of the preoptic area (POA) in the hypothalamus during menopause, which may cause hot flashes. Thermosensitive transient receptors (ThermoTRPs) affect the thermosensitivity of neurons. It is worth exploring whether ThermoTRPs change under low estrogen state and participate in the abnormal thermoregulation of POA. MethodsAdult female Sprague–Dawley rats were randomly divided into sham operation (SHAM), ovariectomy (OVX) and estrogen treatment after ovariectomy (OVX+E) groups. Under 10 ℃, 18 ℃, 25 ℃, 37 ℃ and 45 ℃ incubations, their skin temperature was monitored and the expression of TRPA1, TRPM8, TRPM2, and TRPV1 in POA were investigated. ResultsThe skin temperature of ovariectomized rats changed faster and more dramatically under different incubation temperatures. The results at mRNA level show that only the expression of TRPM2 decreased in POA of OVX group compared with the other two groups at 25 ℃, TRPA1 expression in POA of the three groups increased at 10 ℃, TRPM8 increased at 10 ℃ and 18 ℃, TRPV1 increased at 10 ℃ and 45 ℃, while the expression of TRPM2 decreased at 10 ℃ and 18 ℃ and increased at 37 ℃ and 45 ℃. In all these cases, the magnitudes of the changes were less in the OVX group relative to the other two groups. The further immunohistochemical and Western blot results of TRPM2 and the activated TRPM2 positive cells labeled by c-Fos were consistent with the results of mRNA level. ConclusionsThe expression and thermosensitivity of TRPM2 in POA changed greatly under different incubation temperatures, but the changes in ovariectomized rats were less. This may be the key factor triggering thermoregulation dysfunction under low estrogen and may cause hot flashes.

Arginine vasopressin effects on membrane potentials of preoptic area temperature-sensitive and -insensitive neurons in rat hypothalamic tissue slices

Arginine vasopressin (AVP) plays a hypothermic regulatory role in thermoregulation and is an important endogenous mediator in this mechanism. In the preoptic area (POA), AVP increases the spontaneous firing and thermosensitivity of warm-sensitive neurons and decreases those of cold-sensitive and temperature-insensitive neurons. Because POA neurons play a crucial role in precise thermoregulatory responses, these findings indicate that there is an association between the hypothermia and changes in the firing activity of AVP-induced POA neurons. However, the electrophysiological mechanisms by which AVP controls this firing activity remain unclear. Therefore, in the present study, using in vitro hypothalamic brain slices and whole-cell recordings, we elucidated the membrane potential responses of temperature-sensitive and –insensitive POA neurons to identify the applications of AVP or V1a vasopressin receptor antagonists. By monitoring changes in the resting potential and membrane potential thermosensitivity of the neurons before and during experimental perfusion, we observed that AVP increased the changes in the resting potential of 50% of temperature-insensitive neurons but reduced them in others. These changes are because AVP enhances the membrane potential thermosensitivity of nearly 50% of the temperature-insensitive neurons. On the other hand, AVP changes both the resting potential and membrane potential thermosensitivity of temperature-sensitive neurons, with no differences between the warm- and cold-sensitive neurons. Before and during AVP or V1a vasopressin receptor antagonist perfusion, no correlation was observed between changes in the thermosensitivity and membrane potential of all neurons. Furthermore, no correlation was observed between the thermosensitivity and membrane potential thermosensitivity of the neurons during experimental perfusion. In the present study, we found that AVP induction did not result in any changes in resting potential, which is unique to temperature-sensitive neurons. The study results suggest that AVP-induced changes in the firing activity and firing rate thermosensitivity of POA neurons are not controlled by resting potentials.

Artificial homeostatic temperature regulation via bio-inspired feedback mechanisms

Homeostasis comprises one of the main features of living organisms that enables their robust functioning by adapting to environmental changes. In particular, thermoregulation, as an instance of homeostatic behavior, allows mammals to maintain stable internal temperature with tightly controlled self-regulation independent of external temperatures. This is made by a proper reaction of the thermoeffectors (like skin blood vessels, brown adipose tissue (BAT), etc.) on a wide range of temperature perturbations that reflect themselves in the thermosensitive neurons’ activity. This activity is being delivered to the respective actuation points and translated into thermoeffectors’ actions, which bring the temperature of the organism to the desired level, called a set-point. However, it is still an open question whether these mechanisms can be implemented in an analog electronic device: both on a system theoretical and a hardware level. In this paper, we transfer this control loop into a real electric circuit by designing an analog electronic device for temperature regulation that works following bio-inspired principles. In particular, we construct a simplified single-effector regulation system and show how spiking trains of thermosensitive artificial neurons can be processed to realize an efficient feedback mechanism for the stabilization of the a priori unknown but system-inherent set-point. We also demonstrate that particular values of the set-point and its stability properties result from the interplay between the feedback control gain and activity patterns of thermosensitive artificial neurons, for which, on the one hand, the neuronal interconnections are generally not necessary. On the other hand, we show that such connections can be beneficial for the set-point regulation and hypothesize that the synaptic plasticity in real thermosensitive neuronal ensembles can play a role of an additional control layer empowering the robustness of thermoregulation. The electronic realization of temperature regulation proposed in this paper might be of interest for neuromorphic circuits which are bioinspired by taking the basal principle of homeostasis on board. In this way, a fundamental building block of life would be transferred to electronics and become a milestone for the future of neuromorphic engineering.

TACI: An ImageJ Plugin for 3D Calcium Imaging Analysis.

Research in neuroscience has evolved to use complex imaging and computational tools to extract comprehensive information from data sets. Calcium imaging is a widely used technique that requires sophisticated software to obtain reliable results, but many laboratories struggle to adopt computational methods when updating protocols to meet modern standards. Difficulties arise due to a lack of programming knowledge and paywalls for software. In addition, cells of interest display movements in all directions during calcium imaging. Many approaches have been developed to correct the motion in the lateral (x/y) direction. This paper describes a workflow using a new ImageJ plugin, TrackMate Analysis of Calcium Imaging (TACI), to examine motion on the z-axis in 3D calcium imaging. This software identifies the maximum fluorescence value from all the z-positions a neuron appears in and uses it to represent the neuron's intensity at the corresponding t-position. Therefore, this tool can separate neurons overlapping in the lateral (x/y) direction but appearingon distinct z-planes. As an ImageJ plugin, TACI is a user-friendly, open-source computational tool for 3D calcium imaging analysis. We validated this workflow using fly larval thermosensitive neurons that displayed movements in all directions during temperature fluctuation and a 3D calcium imaging dataset acquired from the fly brain.

Regulation of thermoregulatory behavior by commensal bacteria in Drosophila.

Commensal bacteria affect many aspects of host physiology. In this study, we focused on the role of commensal bacteria in the thermoregulatory behavior of Drosophila melanogaster. We demonstrated that the elimination of commensal bacteria caused an increase in the preferred temperature of Drosophila third-instar larvae without affecting the activity of transient receptor potential ankyrin 1 (TRPA1)-expressing thermosensitive neurons. We isolated eight bacterial strains from the gut and culture medium of conventionally reared larvae and found that the preferred temperature of the larvae was decreased by mono-association with Lactobacillus plantarum or Corynebacterium nuruki. Mono-association with these bacteria did not affect the indices of energy metabolism such as ATP and glucose levels of larvae, which are closely linked to thermoregulation in animals. Thus, we show a novel role for commensal bacteria in host thermoregulation and identify two bacterial species that affect thermoregulatory behavior in Drosophila.

Desynchronization of thermosensitive neurons by using energy pumping

A temperature-dependent nonlinear circuit can be mapped into an equivalent thermosensitive neuron model and then the main dynamical properties of neural activities can be reproduced. A thermistor is connected to different branch circuits of the FHN (FitzHugh–Nagumo) neural circuit, and different thermosensitive neuron models are obtained by applying scale transformation on the parameters and physical variables. The dynamics of the thermosensitive neurons is dependent on the temperature greatly, and synchronization stability between these neurons is investigated by selecting different kinds coupling channels. The reliability of this coupling scheme is mainly controlled by the physical properties of the electronic components in the coupling channels. A capacitor (and induction coil) can be used to connect nonlinear circuits and field coupling is activated to pump field energy for realizing synchronization. This kind of field coupling shows some advantage than the known voltage coupling via resistor connection because of no consumption of Joule heat and the coupling channel is adjustable. The results confirmed that two identical temperature-sensitive neurons can be coupled to reach complete synchronization by regulating the physical parameters in the coupling channel, and energy pumping along the coupling channel is decreased to zero under complete synchronization. For two thermosensitive neurons with parameter mismatch and diversity in temperature, synchronization approach becomes difficult and the energy pumping in the coupling channel is continued under phase lock. Its biophysical significance is that diversity in excitability and difference in channels makes thermosensitive neurons become much different, and the occurrence of bursting synchronization and seizure can be prevented completely.

Pattern formation in a thermosensitive neural network

Pattern formation and synchronization stability in the network are dependent on cooperation between nodes and the local kinetics as well. Temperature has a significant effect on the membrane potential by regulating the channel conductance and excitability of neurons. Thermistor is a smart sensor and its resistance value changes with temperature. A nonlinear circuit composed of thermistors is effective to detect the changes in surroundings temperature. In this paper, a temperature-induced pattern formation in a two-dimensional regular lattice network composed of thermosensitive neurons is studied. Numerical simulations are performed to research the effect of parameters (coupling amplitude) and temperature spatial gradient distribution of neural network on pattern formation and synchronization stability. The bifurcation analysis of the membrane potential reveals the conversion in electrical activity and pattern selection. The results show that neural membrane potential can present distinct firing patterns with the change of temperature. The electrical synapse coupling between neurons promotes effective signals propagation in the network. It is found that the collective dynamic behavior of the network is changed by taming the coupling intensity. The Hamilton energy is estimated to predict the mode selection in neural activities. The energy can be ordered in the network under the temperature gradient distribution. Our results confirm that electrical synapse coupling and temperature spatial gradient distribution can be controlled to affect the neural activities in nervous system.

Effect of astrocyte on synchronization of thermosensitive neuron-astrocyte minimum system

Astrocytes have a regulatory function on the central nervous system (CNS), especially in the temperature-sensitive hippocampal region. In order to explore the thermosensitive dynamic mechanism of astrocytes in the CNS, we establish a neuron–astrocyte minimum system to analyze the synchronization change characteristics based on the Hodgkin–Huxley model, in which a pyramidal cell and an interneuron are connected by an astrocyte. The temperature range is set as 0 °C–40 °C to juggle between theoretical calculation and the reality of a brain environment. It is shown that the synchronization of thermosensitive neurons exhibits nonlinear behavior with changes in astrocyte parameters. At a temperature range of 0 °C–18 °C, the effects of the astrocyte can provide a tremendous influence on neurons in synchronization. We find the existence of a value for inositol triphosphate (IP3) production rate and feedback intensities of astrocytes to neurons, which can ensure the weak synchronization of two neurons. In addition, it is revealed that the regulation of astrocytes to pyramidal cells is more sensitive than that to interneurons. Finally, it is shown that the synchronization and phase transition of neurons depend on the change in Ca2+ concentration at the temperature of weak synchronization. The results in this paper provide some enlightenment on the mechanism of cognitive dysfunction and neurological disorders with astrocytes.

Unknown Input Reconstruction from Temporal Activity Patterns of Thermosensitive Neuronal Ensembles using Reservoir Computing*

The paper addresses the problem of the unknown temperature reconstruction from the neuronal signal generated by networks of thermosensitive neurons modeled by the Hodgkin-Huxley formalism. We show that the instantaneous frequencies of the neurons do not provide sufficient information for the precise temperature reconstruction and that the temporal patterns of the instantaneous frequencies should be taken into account. For this purpose, we augment the considered network of thermosensitive neurons with a multi-layered artificial neural network (ANN) and train it to reconstruct the unknown piecewise-constant input temperature using a supervised learning technique. The input layer of the ANN receives the discretized (in time) trajectories of the instantaneous frequencies of neurons over a certain time interval. Interestingly more rich information containing the time evolution of membrane potentials in the input layer does not lead to any improvement of the unknown input reconstruction. This observation is in accordance with one of the fundamental principles of neuroscience stating that, except for a few highly specific contexts, information in neural systems is encoded in the temporal rather than voltage characteristics of action potentials. Finally, we benchmark the performance of the proposed reconstruction scheme against different types of input signals.

Pattern selection in thermosensitive neuron network induced by noise

It is well known that the firing modes of biological neurons are sensitive to slight temperature changes in their environments. In this paper, a type of noise, which is dependent on temperature changes, is introduced to describe the effect of varying external environments. The effect of this type of noise on the mode transition of the collective dynamical behaviors of coupled thermosensitive neurons in a regular network is investigated. In the simulation, noise is imposed on the network in two ways: on the center area and on the boundary of the network. The results show that the target waves could be induced with noise being imposed on the center area of the network, and traveling waves could be generated with noise imposed on the boundary region of the network. All these results verify that noise could regulate the modes’ transitions of the collective electrical activities in the network, transforming them from synchronization to another ordered collective dynamics type (target wave or traveling wave). Furthermore, the synchronization factors for two cases are calculated, and the results confirm that noise could make network become from high order to low order, but it cannot transform it from low to high order.

Transient Receptor Potential Melastatin 2 Thermosensitive Neurons in the Preoptic Area Involved in Menopausal Hot Flashes in Ovariectomized Mice

Introduction: Menopausal hot flashes are related to hypothalamic preoptic area (POA) dysfunction. Thermosensitive transient receptor potential channels (ThermoTRPs) are involved in temperature sensing and regulation of thermosensitive neurons (TSNs) in the POA. Whether ThermoTRP-TSNs in the POA, particularly the non-noxious thermoreceptor, transient receptor potential melastatin 2 (TRPM2), are involved in the occurrence of hot flashes is still unclear. Methods: Twenty wild-type and 50 Trpm2-Cre adult female mice were randomly divided into sham (SHAM) and ovariectomy (OVX) groups. In the POA, ERα, ERβ, GPR30, TRPA1, TRPM8, TRPM2, and TRPV1 expression was detected by Western blot or/and quantitative real-time polymerase chain reaction and the number of TSNs expressing TRPM2 (TRPM2-TSNs) by immunofluorescence. Before and after TRPM2-TSN activation/inhibition, back (BST) and tail skin temperature (TST) and the proportion of glutamatergic and GABAergic neurons among TRPM2-TSNs were recorded. Results: Compared with SHAM, the expression of ERα, ERβ, TRPM2, and TRPM8 in the POA of the OVX group decreased, with a significantly larger change range for TRPM2 than TRPM8. In addition, the number of TRPM2-TSNs showing TRPA1, TRPM8, and TRPV1 expression in the OVX group decreased, and the proportion of glutamatergic and GABAergic neurons in TRPM2-TSNs decreased and increased, respectively. Meanwhile, BST and TST increased. After activating or inhibiting TRPM2-TSNs, the proportions of glutamatergic and GABAergic neurons in TRPM2-TSNs changed, along with the BST and TST. Conclusion: In menopause, the abnormal quantity and function of TRPM2-TSNs in the POA is key for the development of hot flashes, characterized by an imbalance in heat dissipation and production due to the corresponding imbalance in glutamatergic and GABAergic neurons.

Phase-locking intermittency induced by dynamical heterogeneity in networks of thermosensitive neurons.

In this work, we study the phase synchronization of a neural network and explore how the heterogeneity in the neurons' dynamics can lead their phases to intermittently phase-lock and unlock. The neurons are connected through chemical excitatory connections in a sparse random topology, feel no noise or external inputs, and have identical parameters except for different in-degrees. They follow a modification of the Hodgkin-Huxley model, which adds details like temperature dependence, and can burst either periodically or chaotically when uncoupled. Coupling makes them chaotic in all cases but each individual mode leads to different transitions to phase synchronization in the networks due to increasing synaptic strength. In almost all cases, neurons' inter-burst intervals differ among themselves, which indicates their dynamical heterogeneity and leads to their intermittent phase-locking. We argue then that this behavior occurs here because of their chaotic dynamics and their differing initial conditions. We also investigate how this intermittency affects the formation of clusters of neurons in the network and show that the clusters' compositions change at a rate following the degree of intermittency. Finally, we discuss how these results relate to studies in the neuroscience literature, especially regarding metastability.

Chimera states in a thermosensitive FitzHugh-Nagumo neuronal network

Temperature can affect the action potential of a neuron such that the firing pattern is changed under its variation. To incorporate the effects of the temperature, recently, a thermosensitive neuron was proposed in which a thermistor was added to a simple FitzHugh-Nagumo neuron model. Here, thermosensitive neurons are studied to realize the consequence of the thermistor on the neurons’ collective behavior. For specific coupling strengths, the chimera state is developed. The parameter region of the occurrence of the chimera state is obtained by computing the strength of incoherence and shows that the occurrence of the chimera is highly dependent on the coefficient of temperature change in the thermistor. Since, in reality, the neurons are not identical and also the thermistors are not precisely the same, the network is further considered with non-identical neurons. For this purpose, the coefficient of temperature changes in thermistors is not fixed and selected randomly from a normal distribution. The results show that for distributions with a small standard deviation, the behavior of the network changes slightly. While with increasing the standard deviation, the synchronization is achieved for higher coupling strengths, and the region of chimera is extended. Furthermore, although in the asynchronous network the neurons have different attractors, by the appearance of coherent groups and creation of the chimera, the attractors become identical.

Hot-water bathing before bedtime and shorter sleep onset latency are accompanied by a higher distal-proximal skin temperature gradient in older adults.

Passive body heating in controlled settings could shorten sleep onset latency (SOL). The hypothesized mechanism is vasodilation-induced heat loss before bedtime. However, this evidence is based on small sample-sized studies in specific populations. Thus, we analyzed the association of hot-water bathing and its before-bedtime timing with SOL and heat loss in a large study population of older adults. We conducted a longitudinal analysis using repeated measurements of hot-water bathing and sleep among 1,094 older adults (mean age, 72.0 years). SOL was recorded using actigraphy and self-reported sleep estimates and was categorized into conditions (intervals of 1-60, 61-120, 121-180, and > 181 minutes between hot bath and bedtime) and compared with the control condition of no bathing. The heat-loss indicator, distal-proximal skin temperature gradient, was examined in the same categorization. Mixed-effects linear regression models suggested that the bathing conditions of 61-120 minutes and 121-180 minutes showed significantly shorter log-transformed actigraphic SOL by 0.23 log-minutes (95% confidence interval (CI), 0.03-0.42) and 0.32 log-minutes (95% CI, 0.09-0.56), shorter self-reported SOL by 0.16 log-minutes (95% CI, 0.02-0.30) and 0.18 log-minutes (95% CI, 0.01-0.35), and higher distal-proximal skin temperature gradient for 30 minutes before bedtime by 0.49°C (95% CI, 0.22-0.75) and 0.51°C (95% CI, 0.20-0.83), respectively, independent of potential confounders. Hot-water bathing before bedtime is significantly associated with shorter SOL and higher distal-proximal skin temperature gradient among the large-scale older population. This finding could enhance the generalizability of hot-water bathing habits for ameliorating sleep initiation difficulty.

Development of a "Cooling" Menthol Energy Gel for Endurance Athletes: Effect of Menthol Concentration on Acceptability and Preferences.

Menthol is effective at stimulating thermosensitive neurons that evoke pleasant cooling sensations. Internal application of menthol can be ergogenic for athletes, and hence, addition of menthol to sports nutrition products may be beneficial for athletes. The aim of this study was to develop a menthol energy gel for consumption during exercise and to determine acceptability and preferences for gels with different menthol concentrations. With a randomized, crossover, and double-blind placebo-controlled design, 40 endurance athletes (20 females) ingested an energy gel with a menthol additive at a high (0.5%; HIGH) or low concentration (0.1%; LOW), or a mint-flavored placebo (CON), on separate occasions during outdoor endurance training sessions. The athletes rated the gels for cooling sensation, mint flavor intensity, sweetness, and overall experience and provided feedback. Results are reported as median (interquartile range). Both menthol gels successfully delivered a cooling sensation, with a significantly greater response for HIGH (5.0 [4.0-5.0]) compared with LOW (3.5 [3.0-4.0]; p = .022) and CON (1.0 [1.0-2.0]; p < .0005), and LOW compared with CON (p < .0005). Ratings of mint flavor intensity followed the same trend as cooling sensation, while ratings of overall experience were significantly worse for HIGH (2.0 [1.0-3.0]) compared with LOW (4.0 [2.0-4.0]; p = .001) and CON (4.0 [3.0-4.0]; p < .0005). An energy gel with the addition of menthol at 0.1-0.5% provides a cooling sensation for athletes with a dose-response when ingested during exercise. The 0.1% concentration is recommended to maximize the overall experience of the gel.

Electrophysiological properties of thermosensitive neurons in slices of rat lateral parabrachial nucleus.

Both warm- and cold-sensitive neurons are found in the lateral parabrachial nucleus (LPB), a crucial relay for skin temperature information from the spinal cord to the preoptic area. The aims of this study were to investigate the electrophysiological properties of temperature-sensitive and -insensitive neurons in brain slices, and elucidate the basic mechanisms underlying the thermosensitivity of rat LPB neurons. In warm-sensitive neurons, temperature exerted no significant effects on resting membrane potential (RMP), threshold potential, and amplitude of the afterhyperpolarizing potential. However, warming significantly increased the prepotential rates of depolarization and the inactivation rates of potassium A current (IA) in warm-sensitive neurons, which in turn shortened their interspike interval and elevated the firing rate. In contrast, temperature had no significant effects on the depolarizing prepotentials and inactivation rate of IA in temperature-insensitive neurons. Besides, in cold-sensitive neurons, cooling and warming produced membrane depolarization and hyperpolarization, respectively, and there was a strong correlation between firing rate and membrane potential thermosensitivity. Nevertheless, temperature exhibited no significant effect on the depolarizing prepotential of cold-sensitive neurons. These results suggest that LPB neuronal warm sensitivity may reside in the temperature-dependent prepotentials and IA, while neuronal cold sensitivity might be mainly due to heat-induced changes in RMP.

Link between elevated locomotor activity and the spike bursting of antennal thermosensitive neurons in the carabid beetle Pterostichus oblongopunctatus

Many aspects of ectothermic life are affected by external temperature conditions. Therefore, thermosensation and thermoregulation are crucial for survival of ground dwelling carabid beetles. Research in sensory physiology with Pterostichus oblongopunctatus has shown change in the reaction of antennal thermoreceptor neurons at temperatures above the P. oblongopunctatus’s preferred temperature. From 25 °C, these neurons in dome shaped sensilla start to change from regular impulse firing to firing in bursts. We hypothesized that temperature-dependent impulse bursts are involved in P. oblongopunctatus’s behavioural thermoregulation. Behavioural experiments were carried out on the arena inside an environmental test chamber, and in two different temperature conditions – one with linearly increasing temperature, and the other with constant temperature. The temperature was increased from 10 °C to 40 °C linearly during 50 min on first case and with 5 degree steps on second case with duration 50 min each step. Locomotion parameters (velocity and travelled distance) were measured using an automated video tracking system. We observed both low and high activity zones in P. oblongopunctatus. The threshold temperature for changing between zones occurred was at 25.8 °C. This indicates a link between spike burst of antennal thermoreceptor neurons and behavioural thermoregulation in P. oblongopunctatus.

Preoptic area cooling increases the sympathetic outflow to brown adipose tissue and brown adipose tissue thermogenesis.

Modest cold exposures are likely to activate autonomic thermogenic mechanisms due to activation of cutaneous thermal afferents, whereas central thermosensitive neurons set the background tone on which this afferent input is effective. In addition, more prolonged or severe cold exposures that overwhelm cold defense mechanisms would directly activate thermosensitive neurons within the central nervous system. Here, we examined the involvement of the canonical brown adipose tissue (BAT) sympathoexcitatory efferent pathway in the response to direct local cooling of the preoptic area (POA) in urethane-chloralose-anesthetized rats. With skin temperature and core body temperature maintained between 36 and 39°C, cooling POA temperature by ~1-4°C evoked increases in BAT sympathetic nerve activity (SNA), BAT temperature, expired CO2, and heart rate. POA cooling-evoked responses were inhibited by nanoinjections of ionotropic glutamate receptor antagonists or the GABAA receptor agonist muscimol into the median POA or by nanoinjections of ionotropic glutamate receptor antagonists into the dorsomedial hypothalamic nucleus (bilaterally) or into the raphe pallidus nucleus. These results demonstrate that direct cooling of the POA can increase BAT SNA and thermogenesis via the canonical BAT sympathoexcitatory efferent pathway, even in the face of warm thermal input from the skin and body core.