Role of the Preoptic Area in Sleep and Thermoregulation

Vertebrate behavioral thermoregulation: knowledge and future directions

Thermoregulation is critical for survival across species. In animals, the nervous system detects external and internal temperatures, integrates this information with internal states, and ultimately forms a decision on appropriate thermoregulatory actions. Recent work has identified critical molecules and sensory and motor pathways controlling thermoregulation. However, especially with regard to behavioral thermoregulation, many open questions remain. Here, we aim to both summarize the current state of research, the "knowledge," as well as what in our mind is still largely missing, the "future directions." Given the host of circuit entry points that have been discovered, we specifically see that the time is ripe for a neuro-computational perspective on thermoregulation. Such a perspective is largely lacking but is increasingly fueled and made possible by the development of advanced tools and modeling strategies.

Understanding the role of temperature in seasonal timing: Effects on behavioural, physiological and molecular phenotypes

Organisms adapt to daily and seasonal environmental changes to maximise their metabolic and reproductive fitness. For seasonally breeding animals, photoperiod is considered the most robust cue to drive these changes. It, however, does not explain the interannual variations in different seasonal phenotypes. Several studies have repeatedly shown the influence of ambient temperature on the timing of different seasonal physiologies including the timing of migration, reproduction and its associated behaviours, etc. In the present review, we have discussed the effects of changes in ambient temperature on different seasonal events in endotherms with a focus on migratory birds as they have evolved to draw benefits from distinct but largely predictable seasonal patterns of natural resources. We have further discussed the physiological and molecular mechanisms by which temperature affects seasonal timings. The primary brain area involved in detecting temperature changes is the hypothalamic preoptic area. This area receives thermal inputs via sensory neurons in the peripheral ganglia that measure changes in thermoregulatory tissues such as the skin and spinal cord. For the input signals, several thermal sensory TRP (transient receptor potential ion channels) channels have been identified across different classes of vertebrates. These channels are activated at specific thermal ranges. Once perceived, this information should activate an effector function. However, the link between temperature sensation and the effector pathways is not properly understood yet. Here, we have summarised the available information that may help us understand how temperature information is translated into seasonal timing.

Chronic Astrocytic TNFα Production in the Preoptic-Basal Forebrain Causes Aging-like Sleep-Wake Disturbances in Young Mice

Sleep disruption is a frequent problem of advancing age, often accompanied by low-grade chronic central and peripheral inflammation. We examined whether chronic neuroinflammation in the preoptic and basal forebrain area (POA-BF), a critical sleep-wake regulatory structure, contributes to this disruption. We developed a targeted viral vector designed to overexpress tumor necrosis factor-alpha (TNFα), specifically in astrocytes (AAV5-GFAP-TNFα-mCherry), and injected it into the POA of young mice to induce heightened neuroinflammation within the POA-BF. Compared to the control (treated with AAV5-GFAP-mCherry), mice with astrocytic TNFα overproduction within the POA-BF exhibited signs of increased microglia activation, indicating a heightened local inflammatory milieu. These mice also exhibited aging-like changes in sleep-wake organization and physical performance, including (a) impaired sleep-wake functions characterized by disruptions in sleep and waking during light and dark phases, respectively, and a reduced ability to compensate for sleep loss; (b) dysfunctional VLPO sleep-active neurons, indicated by fewer neurons expressing c-fos after suvorexant-induced sleep; and (c) compromised physical performance as demonstrated by a decline in grip strength. These findings suggest that inflammation-induced dysfunction of sleep- and wake-regulatory mechanisms within the POA-BF may be a critical component of sleep-wake disturbances in aging.

Hypothalamic Subunit Volumes in Schizophrenia and Bipolar Spectrum Disorders

BACKGROUND

The hypothalamus is central to many hormonal and autonomous nervous system pathways. Emerging evidence indicates that these pathways may be disrupted in schizophrenia and bipolar disorder. Yet, few studies have examined the volumes of hypothalamic subunits in these patient groups. We compared hypothalamic subunit volumes in individuals with psychotic disorders to healthy controls.

STUDY DESIGN

We included 344 patients with schizophrenia spectrum disorders (SCZ), 340 patients with bipolar disorders (BPD), and 684 age- and-sex-matched healthy controls (CTR). Total hypothalamus and five hypothalamic subunit volumes were extracted from T1-weighted magnetic resonance imaging (MRI) using an automated Bayesian segmentation method. Regression models, corrected for age, age2, sex, and segmentation-based intracranial volume (sbTIV), were used to examine diagnostic group differences, interactions with sex, and associations with clinical symptoms, antipsychotic medication, antidepressants and mood stabilizers.

STUDY RESULTS

SCZ had larger volumes in the left inferior tubular subunit and smaller right anterior-inferior, right anterior-superior, and right posterior hypothalamic subunits compared to CTR. BPD did not differ significantly from CTR for any hypothalamic subunit volume, however, there was a significant sex-by-diagnosis interaction. Analyses stratified by sex showed smaller right hypothalamus and right posterior subunit volumes in male patients, but not female patients, relative to same-sex controls. There was a significant association between BPD currently taking antipsychotic medication and the left inferior tubular subunits volumes.

CONCLUSIONS

Our results show regional-specific alterations in hypothalamus subunit volumes in individuals with SCZ, with relevance to HPA-axis dysregulation, circadian rhythm disruption, and cognition impairment.

Mapping the 5-HTergic neural pathways in perimenopausal mice and elucidating the role of oestrogen receptors in 5-HT neurotransmission

Perimenopausal syndrome (PMS) encompasses neuropsychiatric symptoms, such as hot flashes and depression, which are associated with alterations in the 5-HTergic neural pathway in the brain. However, the specific changes and mechanisms underlying these alterations remain unclear. In this study, ovariectomized mice were used to successfully establish a perimenopause model, and the changes in the expression of 5-HT and its receptors (5-HT1AR and 5-HT2AR) across 72 brain regions in these ovariectomized mice were assessed by immunohistochemistry. Although both 5-HT and 5-HT1AR were widely expressed throughout the brain, only a limited number of regions expressed 5-HT2AR. Notably, decreased expression of 5-HT was observed across almost all brain regions in the ovariectomy (OVX) group compared with the Sham group. Altered expression of both receptors was found within areas related to hot flashes (the preoptic area) or mood disorders (the amygdala). Additionally, reduced oestrogen receptor (ER)α/β expression was detected in cells in the raphe nucleus (RN), an area known to regulate body temperature. Results showed that ERα/β positively regulate the transcriptional activity of the enzymes TPH2/MAOA, which are involved in serotonin metabolism during perimenopause. This study revealed the changes in 5-HT neuropathways (5-HT, 5-HT1AR and 5-HT2AR) in perimenopausal mice, mainly in brain regions related to regulation of the body temperature, mood, sleep and memory. This study clarified that the expression of oestrogen receptor decreased in perimenopause, which regulated the transcription levels of TPH2 and MAOA, and ultimately led to the reduction of 5-HT content, providing a new target for clinical diagnosis and treatment of perimenopausal diseases.

Sleep: How stress keeps you up at night

Stress disrupts sleep, but the neural mechanisms underlying this relationship remain unclear. Novel findings in mice reveal a hypothalamic circuit that fragments sleep and promotes arousal after stress.

Neuroanatomy of the Cetacean Sensory Systems

Cetaceans have undergone profound sensory adaptations in response to their aquatic environment during evolution. These adaptations are characterised by anatomo-functional changes in the classically defined sensory systems, shaping their neuroanatomy accordingly. This review offers a concise and up-to-date overview of our current understanding of the neuroanatomy associated with cetacean sensory systems. It encompasses a wide spectrum, ranging from the peripheral sensory cells responsible for detecting environmental cues, to the intricate structures within the central nervous system that process and interpret sensory information. Despite considerable progress in this field, numerous knowledge gaps persist, impeding a comprehensive and integrated understanding of their sensory adaptations, and through them, of their sensory perspective. By synthesising recent advances in neuroanatomical research, this review aims to shed light on the intricate sensory alterations that differentiate cetaceans from other mammals and allow them to thrive in the marine environment. Furthermore, it highlights pertinent knowledge gaps and invites future investigations to deepen our understanding of the complex processes in cetacean sensory ecology and anatomy, physiology and pathology in the scope of conservation biology.

TNFR1 signaling converging on FGF14 controls neuronal hyperactivity and sickness behavior in experimental cerebral malaria

BACKGROUND

Excess tumor necrosis factor (TNF) is implicated in the pathogenesis of hyperinflammatory experimental cerebral malaria (eCM), including gliosis, increased levels of fibrin(ogen) in the brain, behavioral changes, and mortality. However, the role of TNF in eCM within the brain parenchyma, particularly directly on neurons, remains underdefined. Here, we investigate electrophysiological consequences of eCM on neuronal excitability and cell signaling mechanisms that contribute to observed phenotypes.

METHODS

The split-luciferase complementation assay (LCA) was used to investigate cell signaling mechanisms downstream of tumor necrosis factor receptor 1 (TNFR1) that could contribute to changes in neuronal excitability in eCM. Whole-cell patch-clamp electrophysiology was performed in brain slices from eCM mice to elucidate consequences of infection on CA1 pyramidal neuron excitability and cell signaling mechanisms that contribute to observed phenotypes. Involvement of identified signaling molecules in mediating behavioral changes and sickness behavior observed in eCM were investigated in vivo using genetic silencing.

RESULTS

Exploring signaling mechanisms that underlie TNF-induced effects on neuronal excitability, we found that the complex assembly of fibroblast growth factor 14 (FGF14) and the voltage-gated Na+ (Nav) channel 1.6 (Nav1.6) is increased upon tumor necrosis factor receptor 1 (TNFR1) stimulation via Janus Kinase 2 (JAK2). On account of the dependency of hyperinflammatory experimental cerebral malaria (eCM) on TNF, we performed patch-clamp studies in slices from eCM mice and showed that Plasmodium chabaudi infection augments Nav1.6 channel conductance of CA1 pyramidal neurons through the TNFR1-JAK2-FGF14-Nav1.6 signaling network, which leads to hyperexcitability. Hyperexcitability of CA1 pyramidal neurons caused by infection was mitigated via an anti-TNF antibody and genetic silencing of FGF14 in CA1. Furthermore, knockdown of FGF14 in CA1 reduced sickness behavior caused by infection.

CONCLUSIONS

FGF14 may represent a therapeutic target for mitigating consequences of TNF-mediated neuroinflammation.

Depth and hierarchies in the predictive brain: From reaction to action

The human brain is a prediction device, a view widely accepted in neuroscience. Prediction is a rational and efficient response that relies on the brain's ability to create and employ generative models to optimize actions over unpredictable time horizons. We argue that extant predictive frameworks while compelling, have not explicitly accounted for the following: (a) The brain's generative models must incorporate predictive depth (i.e., rely on degrees of abstraction to enable predictions over different time horizons); (b) The brain's implementation scheme to account for varying predictive depth relies on dynamic predictive hierarchies formed using the brain's functional networks. We show that these hierarchies incorporate the ascending processes (driven by reaction), and the descending processes (related to prediction), eventually driving action. Because they are dynamically formed, predictive hierarchies allow the brain to address predictive challenges in virtually any domain. By way of application, we explain how this framework can be applied to heretofore poorly understood processes of human behavioral thermoregulation. Although mammalian thermoregulation has been closely tied to deep brain structures engaged in autonomic control such as the hypothalamus, this narrow conception does not translate well to humans. In addition to profound differences in evolutionary history, the human brain is bestowed with substantially increased functional complexity (that itself emerged from evolutionary differences). We argue that behavioral thermoregulation in humans is possible because, (a) ascending signals shaped by homeostatic sub-networks, interject with (b) descending signals related to prediction (implemented in interoceptive and executive sub-networks) and action (implemented in executive sub-networks). These sub-networks cumulatively form a predictive hierarchy for human thermoregulation, potentiating a range of viable responses to known and unknown thermoregulatory challenges. We suggest that our proposed extensions to the predictive framework provide a set of generalizable principles that can further illuminate the many facets of the predictive brain. This article is categorized under: Neuroscience > Behavior Philosophy > Action Psychology > Prediction.

Leptin signaling and its central role in energy homeostasis

Leptin plays a critical role in regulating appetite, energy expenditure and body weight, making it a key factor in maintaining a healthy balance. Despite numerous efforts to develop therapeutic interventions targeting leptin signaling, their effectiveness has been limited, underscoring the importance of gaining a better understanding of the mechanisms through which leptin exerts its functions. While the hypothalamus is widely recognized as the primary site responsible for the appetite-suppressing and weight-reducing effects of leptin, other brain regions have also been increasingly investigated for their involvement in mediating leptin's action. In this review, we summarize leptin signaling pathways and the neural networks that mediate the effects of leptin, with a specific emphasis on energy homeostasis.

Sleep and the hypothalamus

Neural substrates of wakefulness, rapid eye movement sleep (REMS), and non-REMS (NREMS) in the mammalian hypothalamus overlap both anatomically and functionally with cellular networks that support physiological and behavioral homeostasis. Here, we review the roles of sleep neurons of the hypothalamus in the homeostatic control of thermoregulation or goal-oriented behaviors during wakefulness. We address how hypothalamic circuits involved in opposing behaviors such as core body temperature and sleep compute conflicting information and provide a coherent vigilance state. Finally, we highlight some of the key unresolved questions and challenges, and the promise of a more granular view of the cellular and molecular diversity underlying the integrative role of the hypothalamus in physiological and behavioral homeostasis.

Evaluation of cellular activity in response to sleep deprivation by a comprehensive analysis of the whole mouse brain

Sleep deprivation (SD) causes several adverse functional outcomes, and understanding the associated processes can improve quality of life. Although the effects of SD on neuronal activity in several brain regions have been identified, a comprehensive evaluation of the whole brain is still lacking. Hence, we performed SD using two different methods, gentle handling and a dedicated chamber, in targeted recombination in active populations 2 (TRAP2) mice crossed with Rosa-ZsGreen reporter mice and visualized cellular activity in the whole brain. Using the semi-automated post-imaging analysis tool Slice Histology Alignment, Registration, and Cell Quantification (SHARCQ), the number of activated cells was quantified. From the analysis of 14 brain regions, cellular activity was significantly increased in the olfactory areas and decreased in the medulla by the two SD methods. From the analysis of the further subdivided 348 regions, cellular activity was significantly increased in the vascular organ of the lamina terminalis, lateral hypothalamic area, parabigeminal nucleus, ventral tegmental area, and magnocellular reticular nucleus, and decreased in the anterior part of the basolateral amygdalar nucleus, nucleus accumbens, septohippocampal nucleus, reticular nucleus of the thalamus, preoptic part of the periventricular hypothalamic nucleus, ventromedial preoptic nucleus, rostral linear nucleus raphe, facial motor nucleus, vestibular nuclei, and some fiber tracts (oculomotor nerve, genu of corpus callosum, and rubrospinal tract) by the two SD methods. Two subdivided regions of the striatum (caudoputamen and other striatum), epithalamus, vascular organ of the lamina terminalis, anteroventral preoptic nucleus, superior colliculus optic layer, medial terminal nucleus of the accessory optic tract, pontine gray, and fiber tracts (medial lemniscus, columns of the fornix, brachium of the inferior colliculus, and mammillary peduncle) were differentially affected by the two SD methods. Most brain regions detected from these analyses have been reported to be involved in regulating sleep/wake regulatory circuits. Moreover, the results from the connectivity analysis indicated that the connectivity of cellular activity among brain regions was altered by SD. Together, such a comprehensive analysis of the whole brain is useful for understanding the mechanisms by which SD and/or sleep disruption affects brain function.

In Vitro and In Vivo Evaluation of Pellotine: A Hypnotic Lophophora Alkaloid

Quality of life is often reduced in patients with sleep-wake disorders. Insomnia is commonly treated with benzodiazepines, despite their well-known side effects. Pellotine (1), a Lophophora alkaloid, has been reported to have short-acting sleep-inducing properties in humans. In this study, we set out to evaluate various in vitro and in vivo properties of 1. We demonstrate that 1 undergoes slow metabolism; e.g. in mouse liver microsomes 65% remained, and in human liver microsomes virtually no metabolism was observed after 4 h. In mouse liver microsomes, two phase I metabolites were identified: 7-desmethylpellotine and pellotine-N-oxide. In mice, the two diastereomers of pellotine-O-glucuronide were additionally identified as phase II metabolites. Furthermore, we demonstrated by DESI-MSI that 1 readily enters the central nervous system of rodents. Furthermore, radioligand-displacement assays showed that 1 is selective for the serotonergic system and in particular the serotonin (5-HT)1D, 5-HT6, and 5-HT7 receptors, where it binds with affinities in the nanomolar range (117, 170, and 394 nM, respectively). Additionally, 1 was functionally characterized at 5-HT6 and 5-HT7, where it was found to be an agonist at the former (EC50 = 94 nM, Emax = 32%) and an inverse agonist at the latter (EC50 = 291 nM, Emax = -98.6). Finally, we demonstrated that 1 dose-dependently decreases locomotion in mice, inhibits REM sleep, and promotes sleep fragmentation. Thus, we suggest that pellotine itself, and not an active metabolite, is responsible for the hypnotic effects and that these effects are possibly mediated through modulation of serotonergic receptors.

Natural product P57 induces hypothermia through targeting pyridoxal kinase

Induction of hypothermia during hibernation/torpor enables certain mammals to survive under extreme environmental conditions. However, pharmacological induction of hypothermia in most mammals remains a huge challenge. Here we show that a natural product P57 promptly induces hypothermia and decreases energy expenditure in mice. Mechanistically, P57 inhibits the kinase activity of pyridoxal kinase (PDXK), a key metabolic enzyme of vitamin B6 catalyzing phosphorylation of pyridoxal (PL), resulting in the accumulation of PL in hypothalamus to cause hypothermia. The hypothermia induced by P57 is significantly blunted in the mice with knockout of PDXK in the preoptic area (POA) of hypothalamus. We further found that P57 and PL have consistent effects on gene expression regulation in hypothalamus, and they may activate medial preoptic area (MPA) neurons in POA to induce hypothermia. Taken together, our findings demonstrate that P57 has a potential application in therapeutic hypothermia through regulation of vitamin B6 metabolism and PDXK serves as a previously unknown target of P57 in thermoregulation. In addition, P57 may serve as a chemical probe for exploring the neuron circuitry related to hypothermia state in mice.

Hypothalamus volumes in adolescent Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): impact of self-reported fatigue and illness duration

Adolescent Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a complex illness of unknown aetiology. Emerging theories suggest ME/CFS may reflect a progressive, aberrant state of homeostasis caused by disturbances within the hypothalamus, yet few studies have investigated this using magnetic resonance imaging in adolescents with ME/CFS. We conducted a volumetric analysis to investigate whether whole and regional hypothalamus volumes in adolescents with ME/CFS differed compared to healthy controls, and whether these volumes were associated with fatigue severity and illness duration. 48 adolescents (25 ME/CFS, 23 controls) were recruited. Lateralised whole and regional hypothalamus volumes, including the anterior-superior, superior tubular, posterior, anterior-inferior and inferior tubular subregions, were calculated from T1-weighted images. When controlling for age, sex and intracranial volume, Bayesian linear regression models revealed no evidence for differences in hypothalamus volumes between groups. However, in the ME/CFS group, a weak linear relationship between increased right anterior-superior volumes and fatigue severity was identified, which was absent in controls. In addition, Bayesian quantile regression revealed a likely-positive association between illness duration and right superior tubular volumes in the ME/CFS group. While these findings suggest overall comparability in regional and whole hypothalamus volumes between adolescents with ME/CFS and controls, preliminary evidence was identified to suggest greater fatigue severity and longer illness duration were associated with greater right anterior-superior and superior-tubular volumes, respectively. These regions contain the anterior and superior divisions of the paraventricular nucleus, involved in the neuroendocrine response to stress, suggesting involvement in ME/CFS pathophysiology. However, replication in a larger, longitudinal cohort is required.

Disease-associated astrocytes and microglia markers are upregulated in mice fed high fat diet

High-fat diet (HFD) is associated with Alzheimer's disease (AD) and type 2 diabetes risk, which share features such as insulin resistance and amylin deposition. We examined gene expression associated with astrocytes and microglia since dysfunction of these cell types is implicated in AD pathogenesis. We hypothesize gene expression changes in disease-associated astrocytes (DAA), disease-associated microglia and human Alzheimer's microglia exist in diabetic and obese individuals before AD development. By analyzing bulk RNA-sequencing (RNA-seq) data generated from brains of mice fed HFD and humans with AD, 11 overlapping AD-associated differentially expressed genes were identified, including Kcnj2, C4b and Ddr1, which are upregulated in response to both HFD and AD. Analysis of single cell RNA-seq (scRNA-seq) data indicated C4b is astrocyte specific. Spatial transcriptomics (ST) revealed C4b colocalizes with Gfad, a known astrocyte marker, and the colocalization of C4b expressing cells with Gad2 expressing cells, i.e., GABAergic neurons, in mouse brain. There also exists a positive correlation between C4b and Gad2 expression in ST indicating a potential interaction between DAA and GABAergic neurons. These findings provide novel links between the pathogenesis of obesity, diabetes and AD and identify C4b as a potential early marker for AD in obese or diabetic individuals.

From Infection to Death: An Overview of the Pathogenesis of Visceral Leishmaniasis

Kala-azar, also known as visceral leishmaniasis (VL), is a disease caused by Leishmania infantum and L. donovani. Patients experience symptoms such as fever, weight loss, paleness, and enlarged liver and spleen. The disease also affects immunosuppressed individuals and has an overall mortality rate of up to 10%. This overview explores the literature on the pathogenesis of preclinical and clinical stages, including studies in vitro and in animal models, as well as complications and death. Asymptomatic infection can result in long-lasting immunity. VL develops in a minority of infected individuals when parasites overcome host defenses and multiply in tissues such as the spleen, liver, and bone marrow. Hepatosplenomegaly occurs due to hyperplasia, resulting from parasite proliferation. A systemic inflammation mediated by cytokines develops, triggering acute phase reactants from the liver. These cytokines can reach the brain, causing fever, cachexia and vomiting. Similar to sepsis, disseminated intravascular coagulation (DIC) occurs due to tissue factor overexpression. Anemia, hypergammaglobulinemia, and edema result from the acute phase response. A regulatory response and lymphocyte depletion increase the risk of bacterial superinfections, which, combined with DIC, are thought to cause death. Our understanding of VL's pathogenesis is limited, and further research is needed to elucidate the preclinical events and clinical manifestations in humans.

Strategies and Mechanisms of Thermal Compensation in Newborn Water Buffaloes

Hypothermia is one of the principal causes of perinatal mortality in water buffaloes and can range from 3% to 17.9%. In ruminants, factors affecting hypothermia in newborns may be of intrinsic (e.g., level of neurodevelopment, birth weight, vitality score, amount of brown fat, skin features) or extrinsic origin (e.g., maternal care, environmental conditions, colostrum consumption). When newborn buffaloes are exposed to cold stress, thermoregulatory mechanisms such as peripheral vasoconstriction and shivering and non-shivering thermogenesis are activated to prevent hypothermia. Due to the properties of infrared thermography (IRT), as a technique that detects vasomotor changes triggered by a reduction in body temperature, evaluating the central and peripheral regions in newborn buffaloes is possible. This review aims to analyze behavioral, physiological, and morphological strategies and colostrum consumption as thermal compensation mechanisms in newborn water buffalo to cope with environmental changes affecting thermoneutrality. In addition, the importance of monitoring by IRT to identify hypothermia states will be highlighted. Going deeper into these topics related to the water buffalo is essential because, in recent years, this species has become more popular and is being bred in more geographic areas.

Energy metabolism and thermoregulation during sleep in young and old females

Core body temperature (CBT) shows a diurnal rhythm, and the nocturnal decrease in CBT is blunted in older people. The physiological mechanisms responsible for the blunted nocturnal decrease in CBT in older people remain to be revealed. The aim of this study was to compare heat production and heat dissipation in young and old subjects during sleep, as assessed by indirect calorimetry and the distal-proximal temperature gradient (DPG) of skin temperature. A complete dataset of 9 young (23.3 ± 1.1 years) and 8 old (72.1 ± 2.5 years) females was analyzed. CBT and energy metabolism were monitored during sleep using an ingestible temperature sensor in a metabolic chamber maintained at 25 °C. Skin temperature was measured at proximal and distal parts of the body. CBT, distal skin temperature, and DPG in older subjects were higher than in young subjects. Protein oxidation was similar between the two groups, but fat oxidation was lower and carbohydrate oxidation was higher in old subjects compared to young subjects. On the other hand, energy expenditure was similar between the two age groups. Thus, the elevated CBT in older subjects was not attributed to deteriorated heat dissipation or enhanced heat production, suggesting an alternative explanation such as deteriorated evaporative heat loss in old subjects.

Hierarchical fluctuation shapes a dynamic flow linked to states of consciousness

Consciousness arises from the spatiotemporal neural dynamics, however, its relationship with neural flexibility and regional specialization remains elusive. We identified a consciousness-related signature marked by shifting spontaneous fluctuations along a unimodal-transmodal cortical axis. This simple signature is sensitive to altered states of consciousness in single individuals, exhibiting abnormal elevation under psychedelics and in psychosis. The hierarchical dynamic reflects brain state changes in global integration and connectome diversity under task-free conditions. Quasi-periodic pattern detection revealed that hierarchical heterogeneity as spatiotemporally propagating waves linking to arousal. A similar pattern can be observed in macaque electrocorticography. Furthermore, the spatial distribution of principal cortical gradient preferentially recapitulated the genetic transcription levels of the histaminergic system and that of the functional connectome mapping of the tuberomammillary nucleus, which promotes wakefulness. Combining behavioral, neuroimaging, electrophysiological, and transcriptomic evidence, we propose that global consciousness is supported by efficient hierarchical processing constrained along a low-dimensional macroscale gradient.

Calcium Dynamics of the Ventrolateral Preoptic GABAergic Neurons during Spontaneous Sleep-Waking and in Response to Homeostatic Sleep Demands

The ventrolateral preoptic area (VLPO) contains GABAergic sleep-active neurons. However, the extent to which these neurons are involved in expressing spontaneous sleep and homeostatic sleep regulatory demands is not fully understood. We used calcium (Ca2+) imaging to characterize the activity dynamics of VLPO neurons, especially those expressing the vesicular GABA transporter (VGAT) across spontaneous sleep-waking and in response to homeostatic sleep demands. The VLPOs of wild-type and VGAT-Cre mice were transfected with GCaMP6, and the Ca2+ fluorescence of unidentified (UNID) and VGAT cells was recorded during spontaneous sleep-waking and 3 h of sleep deprivation (SD) followed by 1 h of recovery sleep. Although both VGAT and UNID neurons exhibited heterogeneous Ca2+ fluorescence across sleep-waking, the majority of VLPO neurons displayed increased activity during nonREM/REM (VGAT, 120/303; UNID, 39/106) and REM sleep (VGAT, 32/303; UNID, 19/106). Compared to the baseline waking, VLPO sleep-active neurons (n = 91) exhibited higher activity with increasing SD that remained elevated during the recovery period. These neurons also exhibited increased Ca2+ fluorescence during nonREM sleep, marked by increased slow-wave activity and REM sleep during recovery after SD. These findings support the notion that VLPO sleep-active neurons, including GABAergic neurons, are components of neuronal circuitry that mediate spontaneous sleep and homeostatic responses to sustained wakefulness.

Volumetric changes in hypothalamic subunits in patients with relapsing remitting multiple sclerosis

PURPOSE

Studies on hypothalamic changes in patients with relapsing remitting multiple sclerosis (RRMS) are very scarce, despite the fact that the relationship with the hypothalamus is frequently reported. The aim of the study was to determine the volume of the hypothalamic subunits and the total hypothalamus and its relationship with the total demyelinating lesion volume (TLV) and expanded disability status scale (EDSS) in RRMS patients.

METHODS

In this cross-sectional study, anterior-superior, superior tubular, posterior hypothalamus, anterior-inferior, inferior tubular subunits of hypothalamus, and total hypothalamus volume were calculated, with fully automatic analysis methods using volumetric T1 images of 65 relapsed RRMS patients and 68 healthy controls (HC). Volume changes in the hypothalamus and its subunits in RRMS patients were examined using multivariate analysis of covariance (MANCOVA). The relationship of these volumes with EDSS and TLV was investigated by partial correlation analysis.

RESULTS

There is volume reduction in total hypothalamus (F = 13.87, p < 0.001), anterior-superior (F = 19.2, p < 0.001), superior tubular (F = 10.1, p = 0.002) subunits, and posterior hypothalamus (F = 19.2, p < 0.001) volume in RRMS patients. EDSS correlates negatively with anterior-superior (p = 0.017, r =  - 0.333), superior tubular subunits (p = 0.023, r =  - 0.439), posterior hypothalamus (p < 0.001, r =  - 0.511), and whole hypothalamus volume (p = 0.001, r =  - 0.439). TLV correlates negatively with anterior superior (p < 0.001, r =  - 0.565), anterior inferior (p = 0.002, r =  - 0.431), superior tubular subunits (p = 0.002, r =  - 0.432), posterior hypothalamus (p < 0.001, r =  - 0.703), and whole hypothalamus (p < 0.001, r =  - 0.627) volumes.

CONCLUSION

This study demonstrates a reduction in total hypothalamus volume, anterior-superior, superior tubular, and posterior hypothalamus in patients with RRMS. Anterior-superior and superior tubular subunit, posterior hypothalamus, and total hypothalamus volume were negatively correlated with TLV and EDSS scores.

Diurnal regulation of metabolism by Gs-alpha in hypothalamic QPLOT neurons

Neurons in the hypothalamic preoptic area (POA) regulate multiple homeostatic processes, including thermoregulation and sleep, by sensing afferent input and modulating sympathetic nervous system output. The POA has an autonomous circadian clock and may also receive circadian signals indirectly from the suprachiasmatic nucleus. We have previously defined a subset of neurons in the POA termed QPLOT neurons that are identified by the expression of molecular markers (Qrfp, Ptger3, LepR, Opn5, Tacr3) that suggest receptivity to multiple stimuli. Because Ptger3, Opn5, and Tacr3 encode G-protein coupled receptors (GPCRs), we hypothesized that elucidating the G-protein signaling in these neurons is essential to understanding the interplay of inputs in the regulation of metabolism. Here, we describe how the stimulatory Gs-alpha subunit (Gnas) in QPLOT neurons regulates metabolism in mice. We analyzed Opn5cre; Gnasfl/fl mice using indirect calorimetry at ambient temperatures of 22°C (a historical standard), 10°C (a cold challenge), and 28°C (thermoneutrality) to assess the ability of QPLOT neurons to regulate metabolism. We observed a marked decrease in nocturnal locomotion of Opn5cre; Gnasfl/fl mice at both 28°C and 22°C, but no overall differences in energy expenditure, respiratory exchange, or food and water consumption. To analyze daily rhythmic patterns of metabolism, we assessed circadian parameters including amplitude, phase, and MESOR. Loss-of-function GNAS in QPLOT neurons resulted in several subtle rhythmic changes in multiple metabolic parameters. We observed that Opn5cre; Gnasfl/fl mice show a higher rhythm-adjusted mean energy expenditure at 22°C and 10°C, and an exaggerated respiratory exchange shift with temperature. At 28°C, Opn5cre; Gnasfl/fl mice have a significant delay in the phase of energy expenditure and respiratory exchange. Rhythmic analysis also showed limited increases in rhythm-adjusted means of food and water intake at 22°C and 28°C. Together, these data advance our understanding of Gαs-signaling in preoptic QPLOT neurons in regulating daily patterns of metabolism.

Understanding Sleep Regulation in Normal and Pathological Conditions, and Why It Matters

Sleep occupies a peculiar place in our lives and in science, being both eminently familiar and profoundly enigmatic. Historically, philosophers, scientists and artists questioned the meaning and purpose of sleep. If Shakespeare's verses from MacBeth depicting "Sleep that soothes away all our worries" and "relieves the weary laborer and heals hurt minds" perfectly epitomize the alleviating benefits of sleep, it is only during the last two decades that the growing understanding of the sophisticated sleep regulatory mechanisms allows us to glimpse putative biological functions of sleep. Sleep control brings into play various brain-wide processes occurring at the molecular, cellular, circuit, and system levels, some of them overlapping with a number of disease-signaling pathways. Pathogenic processes, including mood disorders (e.g., major depression) and neurodegenerative illnesses such Huntington's or Alzheimer's diseases, can therefore affect sleep-modulating networks which disrupt the sleep-wake architecture, whereas sleep disturbances may also trigger various brain disorders. In this review, we describe the mechanisms underlying sleep regulation and the main hypotheses drawn about its functions. Comprehending sleep physiological orchestration and functions could ultimately help deliver better treatments for people living with neurodegenerative diseases.

Estradiol-dependent hypocretinergic/orexinergic behaviors throughout the estrous cycle

RATIONALE

The female menstrual or estrous cycle and its associated fluctuations in circulating estradiol (E2), progesterone, and other gonadal hormones alter orexin or hypocretin peptide production and receptor activity. Depending on the estrous cycle phase, the transcription of prepro-orexin mRNA, post-translational modification of orexin peptide, and abundance of orexin receptors change in a brain region-specific manner. The most dramatic changes occur in the hypothalamus, which is considered the starting point of the hypothalamic-pituitary-gonadal axis as well as the hub of orexin-producing neurons. Thus, hypothalamus-regulated behaviors, including arousal, feeding, reward processing, and the stress response depend on coordinated efforts between E2, progesterone, and the orexin system. Given the rise of orexin therapeutics for various neuropsychiatric conditions including insomnia and affective disorders, it is important to delineate the behavioral outcomes of this drug class in both sexes, as well as within different time points of the female reproductive cycle.

OBJECTIVES

Summarize how the menstrual or estrous cycle affects orexin system functionality in animal models in order to predict how orexin pharmacotherapies exert varying degrees of behavioral effects across the dynamic hormonal milieu.

Brain areas modulation in consciousness during sevoflurane anesthesia

Sevoflurane is presently one of the most used inhaled anesthetics worldwide. However, the mechanisms through which sevoflurane acts and the areas of the brain associated with changes in consciousness during anesthesia remain important and complex research questions. Sevoflurane is generally regarded as a volatile anesthetic that blindly targets neuronal (and sometimes astrocyte) GABAA receptors. This review focuses on the brain areas of sevoflurane action and their relation to changes in consciousness during anesthesia. We cover 20 years of history, from the bench to the bedside, and include perspectives on functional magnetic resonance, electroencephalogram, and pharmacological experiments. We review the interactions and neurotransmitters involved in brain circuits during sevoflurane anesthesia, improving the effectiveness and accuracy of sevoflurane's future application and shedding light on the mechanisms behind human consciousness.

Understanding the aging hypothalamus, one cell at a time

The hypothalamus is a brain region that integrates signals from the periphery and the environment to maintain organismal homeostasis. To do so, specialized hypothalamic neuropeptidergic neurons control a range of processes, such as sleep, feeding, the stress response, and hormone release. These processes are altered with age, which can affect longevity and contribute to disease status. Technological advances, such as single-cell RNA sequencing, are upending assumptions about the transcriptional identity of cell types in the hypothalamus and revealing how distinct cell types change with age. In this review, we summarize current knowledge about the contribution of hypothalamic functions to aging. We highlight recent single-cell studies interrogating distinct cell types of the mouse hypothalamus and suggest ways in which single-cell 'omics technologies can be used to further understand the aging hypothalamus and its role in longevity.

Hypothermia evoked by stimulation of medial preoptic nucleus protects the brain in a mouse model of ischaemia

Therapeutic hypothermia at 32-34 °C during or after cerebral ischaemia is neuroprotective. However, peripheral cold sensor-triggered hypothermia is ineffective and evokes vigorous counteractive shivering thermogenesis and complications that are difficult to tolerate in awake patients. Here, we show in mice that deep brain stimulation (DBS) of warm-sensitive neurones (WSNs) in the medial preoptic nucleus (MPN) produces tolerable hypothermia. In contrast to surface cooling-evoked hypothermia, DBS mice exhibit a torpor-like state without counteractive shivering. Like hypothermia evoked by chemogenetic activation of WSNs, DBS in free-moving mice elicits a rapid lowering of the core body temperature to 32-34 °C, which confers significant brain protection and motor function reservation. Mechanistically, activation of WSNs contributes to DBS-evoked hypothermia. Inhibition of WSNs prevents DBS-evoked hypothermia. Maintaining the core body temperature at normothermia during DBS abolishes DBS-mediated brain protection. Thus, the MPN is a DBS target to evoke tolerable therapeutic hypothermia for stroke treatment.

Hypothalamic GABAergic neurocircuitry in the regulation of energy homeostasis and sleep/wake control

Gamma-aminobutyric acid (GABAergic) neuron, as one of important cell types in synaptic transmission, has been widely involved in central nervous system (CNS) regulation of organismal physiologies including cognition, emotion, arousal and reward. However, upon their distribution in various brain regions, effects of GABAergic neurons in the brain are very diverse. In current report, we will present an overview of the role of GABAergic mediated inhibitory neurocircuitry in the hypothalamus, underlying mechanism of feeding and sleep homeostasis as well as the characteristics of latest transcriptome profile in order to call attention to the GABAergic system as potentially a promising pharmaceutical intervention or a deep brain stimulation target in eating and sleep disorders.

Circadian Oscillations in the Murine Preoptic Area Are Reset by Temperature, but Not Light

Mammals maintain their internal body temperature within a physiologically optimal range. This involves the regulation of core body temperature in response to changing environmental temperatures and a natural circadian oscillation of internal temperatures. The preoptic area (POA) of the hypothalamus coordinates body temperature by responding to both external temperature cues and internal brain temperature. Here we describe an autonomous circadian clock system in the murine ventromedial POA (VMPO) in close proximity to cells which express the atypical violet-light sensitive opsin, Opn5. We analyzed the light-sensitivity and thermal-sensitivity of the VMPO circadian clocks ex vivo. The phase of the VMPO circadian oscillations was not influenced by light. However, the VMPO clocks were reset by temperature changes within the physiological internal temperature range. This thermal-sensitivity of the VMPO circadian clock did not require functional Opn5 expression or a functional circadian clock within the Opn5-expressing cells. The presence of temperature-sensitive circadian clocks in the VMPO provides an advancement in the understanding of mechanisms involved in the dynamic regulation of core body temperature.

Effect of oral administration of GABA on thermoregulation in athletes during exercise in cold environments: A preliminary study

Background

γ-aminobutyric acid (GABA), a common ingredient in sports supplements and other health products, regulates body temperature in the preoptic area and anterior hypothalamus (PO/AH). To date, no study has examined the effect of GABA on thermoregulation during exercise in humans in a cold temperature environment (11 ± 0.3°C, 45% ± 2% relative humidity).

Methods

We performed a randomized, double-blind study. Ten trained male athletes consumed either a drink (3 ml/kg weight) containing GABA (1,000 mg, trial G) or an equivalent amount of placebo drink (trial C) before exercise. They rested for 20 min and then cycled at 60% of maximum output power for 40 min, pedaling at 60 rpm, and recovered for 20 min. Core temperature (T_c), skin temperature (upper arm, chest, thigh, calf), and heart rate (HR) were monitored at rest (T₀), exercise begins (T₂₀), 20 min of exercise (T₄₀), the exercise ends (T₆₀), and at recovery (T₈₀).

Results

Compared to T₀, T_c decreased significantly at T₂₀ and increased significantly at T₄₀, T₆₀ and T₈₀ (p < 0.01). From 35–80 min, the T_c was higher in trial G (peaked at 37.96 ± 0.25°C) than in trial C (37.89 ± 0.37°C), but it failed to reach significant difference (p > 0.05); T_sk continued to increase during exercise and was significantly higher than T₀ at T₄₀ (p < 0.05), T₆₀ and T₈₀ (p < 0.01). There was no significant difference in T_sk between the two trials (p > 0.05).

Conclusion

Our findings provide initial evidence that oral administration of GABA does not affect thermoregulation and has no adverse effects on the body as an ergogenic exercise supplement during exercise in cold environments.

The mitochondrial pyruvate carrier at the crossroads of intermediary metabolism

Pyruvate metabolism, a central nexus of carbon homeostasis, is an evolutionarily conserved process and aberrant pyruvate metabolism is associated with and contributes to numerous human metabolic disorders including diabetes, cancer, and heart disease. As a product of glycolysis, pyruvate is primarily generated in the cytosol before being transported into the mitochondrion for further metabolism. Pyruvate entry into the mitochondrial matrix is a critical step for efficient generation of reducing equivalents and ATP and for the biosynthesis of glucose, fatty acids, and amino acids from pyruvate. However, for many years, the identity of the carrier protein(s) that transported pyruvate into the mitochondrial matrix remained a mystery. In 2012, the molecular-genetic identification of the mitochondrial pyruvate carrier (MPC), a heterodimeric complex composed of protein subunits MPC1 and MPC2, enabled studies that shed light on the many metabolic and physiological processes regulated by pyruvate metabolism. A better understanding of the mechanisms regulating pyruvate transport and the processes affected by pyruvate metabolism may enable novel therapeutics to modulate mitochondrial pyruvate flux to treat a variety of disorders. Herein, we review our current knowledge of the MPC, discuss recent advances in the understanding of mitochondrial pyruvate metabolism in various tissue and cell types, and address some of the outstanding questions relevant to this field.

Cold-sensitive ventromedial hypothalamic neurons control homeostatic thermogenesis and social interaction-associated hyperthermia

Homeostatic thermogenesis is an essential protective feature of endotherms. However, the specific neuronal types involved in cold-induced thermogenesis remain largely unknown. Using functional magnetic resonance imaging and in situ hybridization, we screened for cold-sensitive neurons and found preprodynorphin (PDYN)-expressing cells in the dorsal medial region of the ventromedial hypothalamus (dmVMH) to be a candidate. Subsequent in vivo calcium recording showed that cold temperature activates dmVMH^Pdyn neurons, whereas hot temperature suppresses them. In addition, optogenetic activation of dmVMH^Pdyn neurons increases the brown adipose tissue and core body temperature, heart rate, and blood pressure, whereas optogenetic inhibition shows opposite effects, supporting their role in homeostatic thermogenesis. Furthermore, we found that dmVMH^Pdyn neurons are linked to known thermoregulatory circuits. Importantly, dmVMH^Pdyn neurons also show activation during mouse social interaction, and optogenetic inhibition suppresses social interaction and associated hyperthermia. Together, our study describes dual functions of dmVMH^Pdyn neurons that allow coordinated regulation of body temperature and social behaviors.

The Ventral Tegmental Area and Nucleus Accumbens as Circadian Oscillators: Implications for Drug Abuse and Substance Use Disorders

Circadian rhythms convergently evolved to allow for optimal synchronization of individuals’ physiological and behavioral processes with the Earth’s 24-h periodic cycling of environmental light and temperature. Whereas the suprachiasmatic nucleus (SCN) is considered the primary pacemaker of the mammalian circadian system, many extra-SCN oscillatory brain regions have been identified to not only exhibit sustainable rhythms in circadian molecular clock function, but also rhythms in overall region activity/function and mediated behaviors. In this review, we present the most recent evidence for the ventral tegmental area (VTA) and nucleus accumbens (NAc) to serve as extra-SCN oscillators and highlight studies that illustrate the functional significance of the VTA’s and NAc’s inherent circadian properties as they relate to reward-processing, drug abuse, and vulnerability to develop substance use disorders (SUDs).

The Sleep-Promoting Ventrolateral Preoptic Nucleus: What Have We Learned over the Past 25 Years?

For over a century, the role of the preoptic hypothalamus and adjacent basal forebrain in sleep-wake regulation has been recognized. However, for years, the identity and location of sleep- and wake-promoting neurons in this region remained largely unresolved. Twenty-five years ago, Saper and colleagues uncovered a small collection of sleep-active neurons in the ventrolateral preoptic nucleus (VLPO) of the preoptic hypothalamus, and since this seminal discovery the VLPO has been intensively investigated by labs around the world, including our own. Herein, we first review the history of the preoptic area, with an emphasis on the VLPO in sleep-wake control. We then attempt to synthesize our current understanding of the circuit, cellular and synaptic bases by which the VLPO both regulates and is itself regulated, in order to exert a powerful control over behavioral state, as well as examining data suggesting an involvement of the VLPO in other physiological processes.