Prostaglandin EP3 receptor-expressing preoptic neurons bidirectionally control body temperature via tonic GABAergic signaling

Exploring the influence of moon phases and weather on mortality in a palliative care unit over a ten year period

Despite a common belief among public and sometimes medical professionals that moon phases affect mortality rates, studies do not confirm generally higher mortality rates. However, periods of extreme heat or cold have been shown to cause fluctuations in mortality, especially in vulnerable patients. This study aimed to examine whether mortality rates in a 10-bed palliative care unit were influenced by moon phases or weather conditions (temperature, barometric pressure, humidity). Data were gathered from records of the Wuerzburg University Hospital palliative care unit, the Wuerzburg weather station, and the NASA lunar calendar. Daily death rates were calculated over a 10-year period (2010-2019). Bivariate analyses and linear multivariate regression analyses were used to explore potential relationships between moon phases, weather, and mortality. Linear associations, a prerequisite for regression analysis, were ensured using Box-Tidwell tests. Over 3652 days, 3120 patients were treated, with 1508 (48.4%) deaths recorded. The average daily death rate was 0.41 (SD = 0.65), with a maximum of five deaths per day. No deaths occurred on 2411 days (66%). The average death rates were similar across the moon phases: 0.40 (SD = 0.71) for the full moon, 0.42 (SD = 0.66) for the new moon, 0.40 (SD = 0.62) for the waxing moon, and 0.43 (SD = 0.66) for the waning moon, with no significant association (ANOVA: F(3, 3648) = 0.51, p = 0.67). Weather variations were not significantly associated with death rates. The multivariate linear regression analysis confirmed that no combined effects, e.g., of different weather aspects, were found (F(6, 3643) = 0.41, p = 0.87). Our findings align with those of previous studies, which revealed no associations between the moon phases and mortality rates. Unlike general mortality trends, temperature did not significantly impact death rates in the palliative care unit, possibly because of controlled environmental factors. Limitations included a low incidence of extreme weather, which may have reduced the statistical power. Trial registration This study did not involve any health care interventions for human participants and, therefore, did not require registration.

Development of the thermoregulatory mechanism - Raising the possibility that it is acquired at birth

Whether the human thermoregulation mechanism in response to environmental temperature stimuli originates from learning or evolution remains an intriguing research question. Body temperature regulation depends not only on innate temperature sensation but also on acquired conditioning. Maintaining body temperature is essential for homeostasis, and the brain coordinates this process through a network of interconnected regulatory systems. In this review, we discuss how humans perceive temperature and establish thermoregulatory mechanisms at birth. We also propose an acquired connectivity structure perspective for the development of neonatal thermoregulatory mechanisms, particularly for brown adipose tissue thermogenesis. This perspective will enhance our understanding of the various acquired mechanisms of thermoregulation and adaptation to environmental temperature. Ultimately, this knowledge may contribute to the development of effective interventions for thermal balance disruptions, such as neonatal hypothermia.

Elucidation of the antipyretic and anti-inflammatory effect of 8-O-Acetyl Shanzhiside methyl ester based on intestinal flora and metabolomics analysis

Introduction

Phlomoides rotata (Benth. ex Hook.f.) Mathiesen (syn. Lamiophlomis rotata (Benth. ex Hook.f.) Kudô) (P. rotate) is a traditional Tibetan medicine known for its hemostatic, analgesic, and anti-inflammatory effects, as well as its high content of 8-O-Acetyl Shanzhiside methyl ester (8-OaS). Clinical and experimental studies have reported gastrointestinal side effects, such as diarrhea, loose stools, even to black stools, associated with P. rotata. Given the bitter taste characteristic, laxative and antipyretic effects of iridoid glycosides, this study aims to investigate the antipyretic and anti-inflammatory effects of 8-OaS (the primary iridoid glycosides of P. rotate) on yeast-induced pyrexia in rats. Additionally, the role 8-OaS in modulating the intestinal flora composition and metabolome profile is explored.

Methods

The pyretic rat model was established by injected subcutaneously with 20% dry yeast suspension. Serum, hypothalamic tissues and colon content were collected for the assessment of relevant indicators. The peripheral inflammatory factors and central thermoregulatory mediators were assessed using enzyme-linked immunosorbent assay (ELISA). The expressions of mRNA and protein in hypothalamic tissue were evaluated through polymerase chain reaction (PCR), immunohistochemistry, and western blotting. 16S rDNA sequencing and LC-MS/MS were performed to determine the alteration and correlation of the intestinal flora and neurotransmitters in the colonic contents and hypothalamus.

Results and discussion

Results show that 8-OaS treatment reduced pyrogenic cytokines (such as IL-6, IL-1β), and down-regulated the level of central thermoregulatory mediators (PGE2), via multiply involved in TLR4/NF-κB and HSP70/NF-κB signaling pathways. Crucially, 8-OaS treatment significantly reduced the relative abundance of Alistipes (P < 0.01), Odoribacter (P < 0.05) and Alistipes_finegoldii (P < 0.05) in the intestinal flora. The correlation analysis demonstrated that 8-OaS treatment significantly correlated with the increasing on the abundance of Alistipes and levels of 5-hydroxytryptamine (P < 0.01), and tryptamine (P < 0.01). Our findings indicate that 8-OaS exhibits significant antipyretic and anti-inflammatory properties, potentially mediated by intestinal flora and metabolites of neurotransmitters. The results of this study may help to elucidate the antipyretic and anti-inflammatory mechanism of 8-OaS based on intestinal flora and metabolomics analysis.

Hypothalamic GABAergic neurons: their roles in health and metabolic diseases

Hypothalamic GABAergic neurons are important in regulating metabolic homeostasis and energy balance. Serving as critical integrators of catabolic and anabolic processes, these neurons orchestrate a broad spectrum of metabolic functions, including feeding, nutrient metabolism, fluid homeostasis, basal metabolism, thermoregulation, and circadian rhythms. Recent advances in neuroscience have facilitated a deeper exploration of the role of hypothalamic GABAergic neurons in metabolic regulation. Emerging research has uncovered key mechanisms through which these neurons modulate energy balance and maintain metabolic balance. These findings not only enhance our understanding of obesity and related metabolic disorders but also underscore the link between hypothalamic dysfunction and prevalent metabolic diseases such as obesity and type 2 diabetes. This review summarizes the latest advancements in our understanding of the role of hypothalamic GABAergic neurons in metabolic regulation. It aims to elucidate the neural and molecular mechanisms underlying hypothalamic control of metabolism, offering new perspectives for the diagnosis and treatment of metabolic disorders.

Inhibition of the hypothalamic ventromedial periventricular area activates a dynorphin pathway-dependent thermoregulatory inversion in rats

To maintain core body temperature in mammals, CNS thermoregulatory networks respond to cold exposure by increasing brown adipose tissue and shivering thermogenesis. However, in hibernation or torpor, this canonical thermoregulatory response is replaced by a new, emerging paradigm, thermoregulatory inversion (TI), an alternative homeostatic state in which cold exposure inhibits thermogenesis and warm exposure stimulates thermogenesis. Here, we demonstrate that in the non-torpid rat, either exclusion of the canonical thermoregulatory integrator in the preoptic hypothalamus or inhibition of neurons in the ventromedial periventricular area (VMPeA) induces the TI state through an alternative thermoregulatory pathway. Within this pathway, we have identified a dynorphinergic input to the dorsomedial hypothalamus from the dorsolateral parabrachial nucleus that plays a critical role in mediating the cold-evoked inhibition of thermogenesis during TI. Our results reveal a novel thermosensory reflex circuit within the mammalian CNS thermoregulatory pathways and support the potential for pharmacologically inducing the TI state to elicit therapeutic hypothermia in non-hibernating species, including humans.

The short term impact of radiofrequency ablative techniques and peripheral nerve block on thermoregulation in mouse models

This study investigated the impact of multiple nerve block methods (local anesthesia, conventional radiofrequency thermocoagulation [CRF], and pulsed radiofrequency [PRF]) on thermoregulation. Focusing on hypothalamic function, the effects of local anesthesia, CRF, and PRF on central and peripheral temperatures were analyzed and compared. Our findings revealed that all three nerve block groups cause a decrease in central temperature, with the CRF group exhibiting the most pronounced effect. Furthermore, immunostaining analysis showed decreased neural activity in the preoptic area, suggesting that nerve blocks may influence central thermoregulatory mechanisms. This study provides valuable insights into the effects of peripheral nerve blocks on thermoregulation and may contribute to the development of therapeutic strategies to managing perioperative hypothermia and enhancing pain management, especially in patients undergoing surgeries with high risks of thermoregulatory complications, such as on-pump surgery and laparoscopic surgery.

Dipeptidyl peptidase-4 inhibitors may lower body temperature: A case-control study

AIMS

Dipeptidyl peptidase-4 inhibitors (DPP4i) enhance GABAergic transmission via the glucagon-like peptide-1 (GLP-1)/GLP-1 receptor pathway. Oral γ-aminobutyric acid (GABA) administration reduces body temperature in humans; thus, DPP4i may reduce body temperature in humans. Therefore, this study aimed to determine the effects of DPP4i administration on the body temperature of patients with type 2 diabetes (T2D).

METHODS

This study included 128 outpatients with T2D who visited the hospital monthly from May to July 2022. The DPP4i group included 64 patients treated with DPP4i while the non-DPP4i group included 64 patients not treated with DPP4i. Body temperature was measured at the axilla point upon entry to the hospital and was compared between the two groups.

RESULTS

The means of age, body mass index, T2D duration, systolic blood pressure, diastolic blood pressure, serum creatinine level, casual triglyceride level, high-density lipoprotein cholesterol level, low-density lipoprotein cholesterol level, casual plasma glucose level, and glycated hemoglobin level were not significantly different between the two groups. The mean body temperatures (°C) were 36.1 ± 0.2 and 36.4 ± 0.17 in the DPP4i and non-DPP4i groups, respectively (p = 1.123 E-05).

CONCLUSIONS

DPP4i reduced the body temperature of patients with T2D.

Prostaglandin E2 production in the brainstem parabrachial nucleus facilitates the febrile response

Our body temperature is normally kept within a narrow range of 1°C. For example, if our body temperature rises, such as in a hot environment or due to strenuous exercise, our thermoregulatory system will trigger a powerful heat defense response with vasodilation, sweating, and lowered metabolism. During fever, which often involves body temperatures of up to 41°C, this heat defense mechanism is apparently inhibited; otherwise, the rising body temperature would be immediately combated, and fever would not be allowed to develop. New evidence suggests how and where this inhibition takes place. In two consecutive studies from Cheng et al. and Xu et al., it has been shown that prostaglandin E2, which generates fever by acting on thermosensory neurons in the preoptic hypothalamus, also acts on neurons in the brainstem parabrachial nucleus, which receive temperature information from temperature-activated spinal cord neurons and relay this information to the thermoregulatory center in the hypothalamus to either induce cold or heat defenses. By acting on the same type of prostaglandin E2 receptor that is critical for fever generation in the preoptic hypothalamus, the EP3 receptor, prostaglandin E2 inhibits the signaling of the heat-responsive parabrachial neurons, while stimulating the cold-responsive neurons. These novel findings thus show that prostaglandin E2, by binding to the same receptor subtype in the parabrachial nucleus as in the preoptic hypothalamus, adjusts the sensitivity of the thermosensory system in a coordinated manner to allow the development of febrile body temperatures.

Thermoregulatory pathway underlying the pyrogenic effects of prostaglandin E2 in the lateral parabrachial nucleus of male rats

It has been shown that prostaglandin (PG) E2 synthesized in the lateral parabrachial nucleus (LPBN) is involved in lipopolysaccharide-induced fever. But the neural mechanisms of how intra-LPBN PGE2 induces fever remain unclear. In this study, we investigated whether the LPBN-preoptic area (POA) pathway, the thermoafferent pathway for feed-forward thermoregulatory responses, mediates fever induced by intra-LPBN PGE2 in male rats. The core temperature (Tcore) was monitored using a temperature radiotelemetry transponder implanted in rat abdomen. We showed that microinjection of PGE2 (0.28 nmol) into the LPBN significantly enhanced the density of c-Fos-positive neurons in the median preoptic area (MnPO). The chemical lesioning of MnPO with ibotenate or selective genetic lesioning or inhibition of the LPBN-MnPO pathway significantly attenuated fever induced by intra-LPBN injection of PGE2. We demonstrated that EP3 receptor was a pivotal receptor for PGE2-induced fever, since microinjection of EP3 receptor agonist sulprostone (0.2 nmol) or EP3 receptor antagonist L-798106 (2 nmol) into the LPBN mimicked or weakened the pyrogenic action of LPBN PGE2, respectively, but this was not the case for EP4 and EP1 receptors. Whole-cell recording from acute LPBN slices revealed that the majority of MnPO-projecting neurons originating from the external lateral (el) and dorsal (d) LPBN were excited and inhibited, respectively, by PGE2 perfusion, initiating heat-gain and heat-loss mechanisms. The amplitude but not the frequency of spontaneous and miniature glutamatergic excitatory postsynaptic currents (sEPSCs and mEPSCs) in MnPO-projecting LPBel neurons increased after perfusion with PGE2; whereas the frequency and amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs) and the A-type potassium (IA) current density did not change. In MnPO-projecting LPBd neurons, neither sEPSCs nor sIPSCs responded to PGE2; however, the IA current density was significantly increased by PGE2 perfusion. These electrophysiological responses and the thermoeffector reactions to intra-LPBN PGE2 injection, including increased brown adipose tissue thermogenesis, shivering, and decreased heat dissipation, were all abolished by L-798106, and mimicked by sulprostone. These results suggest that the pyrogenic effects of intra-LPBN PGE2 are mediated by both the inhibition of the LPBd-POA pathway through the EP3 receptor-mediated activation of IA currents and the activation of the LPBel-POA pathway through the selective enhancement of glutamatergic synaptic transmission via EP3 receptors.

Opposing actions of co-released GABA and neurotensin on the activity of preoptic neurons and on body temperature

Neurotensin (Nts) is a neuropeptide acting as a neuromodulator in the brain. Pharmacological studies have identified Nts as a potent hypothermic agent. The medial preoptic area, a region that plays an important role in the control of thermoregulation, contains a high density of neurotensinergic neurons and Nts receptors. The conditions in which neurotensinergic neurons play a role in thermoregulation are not known. In this study, optogenetic stimulation of preoptic Nts neurons induced a small hyperthermia. In vitro, optogenetic stimulation of preoptic Nts neurons resulted in synaptic release of GABA and net inhibition of the preoptic pituitary adenylate cyclase-activating polypeptide (Adcyap1) neurons firing activity. GABA-A receptor antagonist or genetic deletion of Slc32a1 (VGAT) in Nts neurons unmasked also an excitatory effect that was blocked by a Nts receptor 1 antagonist. Stimulation of preoptic Nts neurons lacking Slc32a1 resulted in excitation of Adcyap1 neurons and hypothermia. Mice lacking Slc32a1 expression in Nts neurons presented changes in the fever response and in the responses to heat or cold exposure as well as an altered circadian rhythm of body temperature. Chemogenetic activation of all Nts neurons in the brain induced a 4-5°C hypothermia, which could be blocked by Nts receptor antagonists in the preoptic area. Chemogenetic activation of preoptic neurotensinergic projections resulted in robust excitation of preoptic Adcyap1 neurons. Taken together, our data demonstrate that endogenously released Nts can induce potent hypothermia and that excitation of preoptic Adcyap1 neurons is the cellular mechanism that triggers this response.

Hypothalamic neural circuits regulating energy expenditure

The hypothalamus plays a central role in regulating energy expenditure and maintaining energy homeostasis, crucial for an organism's survival. Located in the ventral diencephalon, it is a dynamic and adaptable brain region capable of rapid responses to environmental changes, exhibiting high anatomical and cellular plasticity and integrates a myriad of sensory information, internal physiological cues, and humoral factors to accurately interpret the nutritional state and adjust food intake, thermogenesis, and energy homeostasis. Key hypothalamic nuclei contain distinct neuron populations that respond to hormonal, nutrient, and neural inputs and communicate extensively with peripheral organs like the gastrointestinal tract, liver, pancreas, and adipose tissues to regulate energy production, storage, mobilization, and utilization. The hypothalamus has evolved to enhance energy storage for survival in famine and scarce environments but contribute to obesity in modern contexts of caloric abundance. It acts as a master regulator of whole-body energy homeostasis, rapidly adapting to ensure energy supplies for cellular functions. Understanding hypothalamic function, pertaining to energy expenditure, is crucial for developing targeted interventions to address metabolic disorders, offering new insights into the neural control of metabolic states and potential therapeutic strategies.

Burning Question: How Does Our Brain Process Positive and Negative Cues Associated with Thermosensation?

Whether it is the dramatic suffocating sensation from a heat wave in the summer or the positive reinforcement arising from a hot drink on a cold day; we can certainly agree that our thermal environment underlies our daily rhythms of sensation. Extensive research has focused on deciphering the central circuits responsible for conveying the impact of thermogenesis on mammalian behavior. Here, we revise the recent literature responsible for defining the behavioral correlates that arise from thermogenic fluctuations in mammals. We transition from the physiological significance of thermosensation to the circuitry responsible for the autonomic or behavioral responses associated with it. Subsequently, we delve into the positive and negative valence encoded by thermoregulatory processes. Importantly, we emphasize the crucial junctures where reward, pain, and thermoregulation intersect, unveiling a complex interplay within these neural circuits. Finally, we briefly outline fundamental questions that are pending to be addressed in the field. Fully deciphering the thermoregulatory circuitry in mammals will have far-reaching medical implications. For instance, it may lead to the identification of novel targets to overcome thermal pain or allow the maintenance of our core temperature in prolonged surgeries.

Hypothalamic Neuromodulation and Control of the Dermal Surface Temperature of Livestock during Hyperthermia

Hyperthermia elicits several physiological and behavioral responses in livestock to restore thermal neutrality. Among these responses, vasodilation and sweating help to reduce core body temperature by increasing heat dissipation by radiation and evaporation. Thermoregulatory behaviors such as increasing standing time, reducing feed intake, shade-seeking, and limiting locomotor activity also increase heat loss. These mechanisms are elicited by the connection between peripheral thermoreceptors and cerebral centers, such as the preoptic area of the hypothalamus. Considering the importance of this thermoregulatory pathway, this review aims to discuss the hypothalamic control of hyperthermia in livestock, including the main physiological and behavioral changes that animals adopt to maintain their thermal stability.

Neural cell-types and circuits linking thermoregulation and social behavior

Understanding how social and affective behavioral states are controlled by neural circuits is a fundamental challenge in neurobiology. Despite increasing understanding of central circuits governing prosocial and agonistic interactions, how bodily autonomic processes regulate these behaviors is less resolved. Thermoregulation is vital for maintaining homeostasis, but also associated with cognitive, physical, affective, and behavioral states. Here, we posit that adjusting body temperature may be integral to the appropriate expression of social behavior and argue that understanding neural links between behavior and thermoregulation is timely. First, changes in behavioral states-including social interaction-often accompany changes in body temperature. Second, recent work has uncovered neural populations controlling both thermoregulatory and social behavioral pathways. We identify additional neural populations that, in separate studies, control social behavior and thermoregulation, and highlight their relevance to human and animal studies. Third, dysregulation of body temperature is linked to human neuropsychiatric disorders. Although body temperature is a "hidden state" in many neurobiological studies, it likely plays an underappreciated role in regulating social and affective states.

Age-related ciliopathy: Obesogenic shortening of melanocortin-4 receptor-bearing neuronal primary cilia

Obesity is often associated with aging. However, the mechanism of age-related obesity is unknown. The melanocortin-4 receptor (MC4R) mediates leptin-melanocortin anti-obesity signaling in the hypothalamus. Here, we discovered that MC4R-bearing primary cilia of hypothalamic neurons progressively shorten with age in rats, correlating with age-dependent metabolic decline and increased adiposity. This "age-related ciliopathy" is promoted by overnutrition-induced upregulation of leptin-melanocortin signaling and inhibited or reversed by dietary restriction or the knockdown of ciliogenesis-associated kinase 1 (CILK1). Forced shortening of MC4R-bearing cilia in hypothalamic neurons by genetic approaches impaired neuronal sensitivity to melanocortin and resulted in decreased brown fat thermogenesis and energy expenditure and increased appetite, finally developing obesity and leptin resistance. Therefore, despite its acute anti-obesity effect, chronic leptin-melanocortin signaling increases susceptibility to obesity by promoting the age-related shortening of MC4R-bearing cilia. This study provides a crucial mechanism for age-related obesity, which increases the risk of metabolic syndrome.

Opposing actions of co-released GABA and neurotensin on the activity of preoptic neurons and on body temperature

Neurotensin (Nts) is a neuropeptide acting as a neuromodulator in the brain. Pharmacological studies have identified Nts as a potent hypothermic agent. The medial preoptic area, a region that plays an important role in the control of thermoregulation, contains a high density of neurotensinergic neurons and Nts receptors. The conditions in which neurotensinergic neurons play a role in thermoregulation are not known. In this study optogenetic stimulation of preoptic Nts neurons induced a small hyperthermia. In vitro, optogenetic stimulation of preoptic Nts neurons resulted in synaptic release of GABA and net inhibition of the preoptic pituitary adenylate cyclase-activating polypeptide (PACAP) neurons firing activity. GABA-A receptor antagonist or genetic deletion of VGAT in Nts neurons unmasked also an excitatory effect that was blocked by a Nts receptor 1 antagonist. Stimulation of preoptic Nts neurons lacking VGAT resulted in excitation of PACAP neurons and hypothermia. Mice lacking VGAT expression in Nts neurons presented changes in the fever response and in the responses to heat or cold exposure as well as an altered circadian rhythm of body temperature. Chemogenetic activation of all Nts neurons in the brain induced a 4-5 °C hypothermia, which could be blocked by Nts receptor antagonists in the preoptic area. Chemogenetic activation of preoptic neurotensinergic projections resulted in robust excitation of preoptic PACAP neurons. Taken together our data demonstrate that endogenously released Nts can induce potent hypothermia and that excitation of preoptic PACAP neurons is the cellular mechanism that triggers this response.

Central Mechanisms of Thermoregulation and Fever in Mammals

Thermoregulation is a fundamental homeostatic function in mammals mediated by the central nervous system. The framework of the central circuitry for thermoregulation lies in the hypothalamus and brainstem. The preoptic area (POA) of the hypothalamus integrates cutaneous and central thermosensory information into efferent control signals that regulate excitatory descending pathways through the dorsomedial hypothalamus (DMH) and rostral medullary raphe region (rMR). The cutaneous thermosensory feedforward signals are delivered to the POA by afferent pathways through the lateral parabrachial nucleus, while the central monitoring of body core temperature is primarily mediated by warm-sensitive neurons in the POA for negative feedback regulation. Prostaglandin E2, a pyrogenic mediator produced in response to infection, acts on the POA to trigger fever. Recent studies have revealed that this circuitry also functions for physiological responses to psychological stress and starvation. Master psychological stress signaling from the medial prefrontal cortex to the DMH has been discovered to drive a variety of physiological responses for stress coping, including hyperthermia. During starvation, hunger signaling from the hypothalamus was found to activate medullary reticular neurons, which then suppress thermogenic sympathetic outflows from the rMR for energy saving. This thermoregulatory circuit represents a fundamental mechanism of the central regulation for homeostasis.

Advanced neurobiological tools to interrogate metabolism

Engineered neurobiological tools for the manipulation of cellular activity, such as chemogenetics and optogenetics, have become a cornerstone of modern neuroscience research. These tools are invaluable for the interrogation of the central control of metabolism as they provide a direct means to establish a causal relationship between brain activity and biological processes at the cellular, tissue and organismal levels. The utility of these methods has grown substantially due to advances in cellular-targeting strategies, alongside improvements in the resolution and potency of such tools. Furthermore, the potential to recapitulate endogenous cellular signalling has been enriched by insights into the molecular signatures and activity dynamics of discrete brain cell types. However, each modulatory tool has a specific set of advantages and limitations; therefore, tool selection and suitability are of paramount importance to optimally interrogate the cellular and circuit-based underpinnings of metabolic outcomes within the organism. Here, we describe the key principles and uses of engineered neurobiological tools. We also highlight inspiring applications and outline critical considerations to be made when using these tools within the field of metabolism research. We contend that the appropriate application of these biotechnological advances will enable the delineation of the central circuitry regulating systemic metabolism with unprecedented potential.

Characterization of TRPM8-expressing neurons in the adult mouse hypothalamus

Transient receptor potential melastatin 8 (TRPM8) is a menthol receptor that detects cold temperatures and influences behaviors and autonomic functions under cold stimuli. Despite the well-documented peripheral roles of TRPM8, the evaluation of its central functions is still of great interest. The present study clarifies the nature of a subpopulation of TRPM8-expressing neurons in the adult mice. Combined in situ hybridization and immunohistochemistry revealed that TRPM8-expressing neurons are exclusively positive for glutamate decarboxylase 67 mRNA signals in the lateral septal nucleus (LS) and preoptic area (POA) but produced no positive signal for vesicular glutamate transporter 2. Double labeling immunohistochemistry showed the colocalization of TRPM8 with vesicular GABA transporter at axonal terminals. Immunohistochemistry further revealed that TRPM8-expressing neurons frequently expressed calbindin and calretinin in the LS, but not in the POA. TRPM8-expressing neurons in the POA expressed a prostaglandin E2 receptor, EP3, and neurotensin, whereas expression in the LS was minimal. These results indicate that hypothalamic TRPM8-expressing neurons are inhibitory GABAergic, while the expression profile of calcium-binding proteins, neurotensin, and EP3 differs between the POA and LS.

Two Ascending Thermosensory Pathways from the Lateral Parabrachial Nucleus That Mediate Behavioral and Autonomous Thermoregulation

Thermoregulatory behavior in homeothermic animals is an innate behavior to defend body core temperature from environmental thermal challenges in coordination with autonomous thermoregulatory responses. In contrast to the progress in understanding the central mechanisms of autonomous thermoregulation, those of behavioral thermoregulation remain poorly understood. We have previously shown that the lateral parabrachial nucleus (LPB) mediates cutaneous thermosensory afferent signaling for thermoregulation. To understand the thermosensory neural network for behavioral thermoregulation, in the present study, we investigated the roles of ascending thermosensory pathways from the LPB in avoidance behavior from innocuous heat and cold in male rats. Neuronal tracing revealed two segregated groups of LPB neurons projecting to the median preoptic nucleus (MnPO), a thermoregulatory center (LPB→MnPO neurons), and those projecting to the central amygdaloid nucleus (CeA), a limbic emotion center (LPB→CeA neurons). While LPB→MnPO neurons include separate subgroups activated by heat or cold exposure of rats, LPB→CeA neurons were only activated by cold exposure. By selectively inhibiting LPB→MnPO or LPB→CeA neurons using tetanus toxin light chain or chemogenetic or optogenetic techniques, we found that LPB→MnPO transmission mediates heat avoidance, whereas LPB→CeA transmission contributes to cold avoidance. In vivo electrophysiological experiments showed that skin cooling-evoked thermogenesis in brown adipose tissue requires not only LPB→MnPO neurons but also LPB→CeA neurons, providing a novel insight into the central mechanism of autonomous thermoregulation. Our findings reveal an important framework of central thermosensory afferent pathways to coordinate behavioral and autonomous thermoregulation and to generate the emotions of thermal comfort and discomfort that drive thermoregulatory behavior.SIGNIFICANCE STATEMENT Coordination of behavioral and autonomous thermoregulation is important for maintaining thermal homeostasis in homeothermic animals. However, the central mechanism of thermoregulatory behaviors remains poorly understood. We have previously shown that the lateral parabrachial nucleus (LPB) mediates ascending thermosensory signaling that drives thermoregulatory behavior. In this study, we found that one pathway from the LPB to the median preoptic nucleus mediates heat avoidance, whereas the other pathway from the LPB to the central amygdaloid nucleus is required for cold avoidance. Surprisingly, both pathways are required for skin cooling-evoked thermogenesis in brown adipose tissue, an autonomous thermoregulatory response. This study provides a central thermosensory network that coordinates behavioral and autonomous thermoregulation and generates thermal comfort and discomfort that drive thermoregulatory behavior.

Neural Progenitor Cells and the Hypothalamus

Neural progenitor cells (NPCs) are multipotent neural stem cells (NSCs) capable of self-renewing and differentiating into neurons, astrocytes and oligodendrocytes. In the postnatal/adult brain, NPCs are primarily located in the subventricular zone (SVZ) of the lateral ventricles (LVs) and subgranular zone (SGZ) of the hippocampal dentate gyrus (DG). There is evidence that NPCs are also present in the postnatal/adult hypothalamus, a highly conserved brain region involved in the regulation of core homeostatic processes, such as feeding, metabolism, reproduction, neuroendocrine integration and autonomic output. In the rodent postnatal/adult hypothalamus, NPCs mainly comprise different subtypes of tanycytes lining the wall of the 3^rd ventricle. In the postnatal/adult human hypothalamus, the neurogenic niche is constituted by tanycytes at the floor of the 3^rd ventricle, ependymal cells and ribbon cells (showing a gap-and-ribbon organization similar to that in the SVZ), as well as suprachiasmatic cells. We speculate that in the postnatal/adult human hypothalamus, neurogenesis occurs in a highly complex, exquisitely sophisticated neurogenic niche consisting of at least four subniches; this structure has a key role in the regulation of extrahypothalamic neurogenesis, and hypothalamic and extrahypothalamic neural circuits, partly through the release of neurotransmitters, neuropeptides, extracellular vesicles (EVs) and non-coding RNAs (ncRNAs).

Mediobasal hypothalamic neurons contribute to the control of brown adipose tissue sympathetic nerve activity and cutaneous vasoconstriction

The mediobasal hypothalamus (MBH) contains heterogeneous neuronal populations that regulate food intake and energy expenditure. However, the role of MBH neurons in the neural control of thermoeffector activity for thermoregulation is not known. This study sought to determine the effects of modulating the activity of MBH neurons on the sympathetic outflow to brown adipose tissue (BAT), BAT thermogenesis, and cutaneous vasomotion. Pharmacological inhibition of MBH neurons by local administration of muscimol, a GABAA receptor agonist, reduced skin cooling-evoked BAT thermogenesis, expired CO2, body temperature, heart rate, and mean arterial pressure, while blockade of GABAA receptors by nanoinjection of bicuculline in the MBH induced large increases in BAT sympathetic nerve activity (SNA), BAT temperature, body temperature, expired CO2, heart rate, and cutaneous vasoconstriction. Neurons in the MBH send projections to neurons in the dorsal hypothalamic area and dorsomedial hypothalamus (DMH), which excite sympathetic premotor neurons in the rostral raphe pallidus area (rRPa) that control sympathetic outflow to BAT. The increases in BAT SNA, BAT temperature, and expired CO2 elicited by blockade of GABAA receptors in the MBH were reversed by blocking excitatory amino acid receptors in the DMH or in the rRPa. Together, our data show that MBH neurons provide a modest contribution to BAT thermogenesis for cold defense, while GABAergic disinhibition of these neurons produces large increases in the sympathetic outflow to BAT, and cutaneous vasoconstriction. Activation of glutamate receptors on BAT thermogenesis-promoting neurons of the DMH and rRPa is necessary for the increased sympathetic outflow to BAT evoked by disinhibition of MBH neurons. These data demonstrate neural mechanisms that contribute to the control of thermoeffector activity, and may have important implications for regulating body temperature and energy expenditure.

Central circuit controlling thermoregulatory inversion and torpor-like state

To maintain core body temperature in mammals, the CNS thermoregulatory networks respond to cold exposure by increasing brown adipose tissue and shivering thermogenesis. However, in hibernation or torpor, this normal thermoregulatory response is supplanted by "thermoregulatory inversion", an altered homeostatic state in which cold exposure causes inhibition of thermogenesis and warm exposure stimulates thermogenesis. Here we demonstrate the existence of a novel, dynorphinergic thermoregulatory reflex pathway between the dorsolateral parabrachial nucleus and the dorsomedial hypothalamus that bypasses the normal thermoregulatory integrator in the hypothalamic preoptic area to play a critical role in mediating the inhibition of thermogenesis during thermoregulatory inversion. Our results indicate the existence of a neural circuit mechanism for thermoregulatory inversion within the CNS thermoregulatory pathways and support the potential for inducing a homeostatically-regulated, therapeutic hypothermia in non-hibernating species, including humans.