Brainstem ADCYAP1+ neurons control multiple aspects of sickness behaviour

Bidirectional regulation of the brain-gut-microbiota axis following traumatic brain injury

JOURNAL/nrgr/04.03/01300535-202508000-00002/figure1/v/2024-09-30T120553Z/r/image-tiff Traumatic brain injury is a prevalent disorder of the central nervous system. In addition to primary brain parenchymal damage, the enduring biological consequences of traumatic brain injury pose long-term risks for patients with traumatic brain injury; however, the underlying pathogenesis remains unclear, and effective intervention methods are lacking. Intestinal dysfunction is a significant consequence of traumatic brain injury. Being the most densely innervated peripheral tissue in the body, the gut possesses multiple pathways for the establishment of a bidirectional "brain-gut axis" with the central nervous system. The gut harbors a vast microbial community, and alterations of the gut niche contribute to the progression of traumatic brain injury and its unfavorable prognosis through neuronal, hormonal, and immune pathways. A comprehensive understanding of microbiota-mediated peripheral neuroimmunomodulation mechanisms is needed to enhance treatment strategies for traumatic brain injury and its associated complications. We comprehensively reviewed alterations in the gut microecological environment following traumatic brain injury, with a specific focus on the complex biological processes of peripheral nerves, immunity, and microbes triggered by traumatic brain injury, encompassing autonomic dysfunction, neuroendocrine disturbances, peripheral immunosuppression, increased intestinal barrier permeability, compromised responses of sensory nerves to microorganisms, and potential effector nuclei in the central nervous system influenced by gut microbiota. Additionally, we reviewed the mechanisms underlying secondary biological injury and the dynamic pathological responses that occur following injury to enhance our current understanding of how peripheral pathways impact the outcome of patients with traumatic brain injury. This review aimed to propose a conceptual model for future risk assessment of central nervous system-related diseases while elucidating novel insights into the bidirectional effects of the "brain-gut-microbiota axis."

Non-neuronal brain biology and its relevance to animal welfare

Non-neuronal cells constitute a significant portion of brain tissue and are seen as having key roles in brain homeostasis and responses to challenges. This review illustrates how non-neuronal biology can bring new perspectives to animal welfare through understanding mechanisms that determine welfare outcomes and highlighting interventions to improve welfare. Most obvious in this respect is the largely unrecognised relevance of neuroinflammation to animal welfare which is increasingly found to have roles in determining how animals respond to challenges. We start by introducing non-neuronal cells and review their involvement in affective states and cognition often seen as core psychological elements of animal welfare. We find that the evidence for a causal involvement of glia in cognition is currently more advanced than the corresponding evidence for affective states. We propose that translational research on affective disorders could usefully apply welfare science derived approaches for assessing affective states. Using evidence from translational research, we illustrate the involvement of non-neuronal cells and neuroinflammatory processes as mechanisms modulating resilience to welfare challenges including disease, pain, and social stress. We review research on impoverished environments and environmental enrichment which suggests that environmental conditions which improve animal welfare also improve resilience to challenges through balancing pro- and anti-inflammatory non-neuronal processes. We speculate that non-neuronal biology has relevance to animal welfare beyond neuro-inflammation including facilitating positive affective states. We acknowledge the relevance of neuronal biology to animal welfare whilst proposing that non-neuronal biology provides additional and relevant insights to improve animals' lives.

Sleep and the recovery from stress

The relationship between stress and sleep is multifaceted, with stress capable of both disrupting and promoting sleep depending on the nature, intensity, and duration of the stressor. While stress commonly leads to sleep fragmentation and arousal in both humans and animals, certain selective stressors, such as immune challenges and psychosocial stress, promote sleep in rodent models. Specific neural circuits, such as those involving the ventral tegmental area and lateral habenula, mediate this stress-induced sleep. Post-stress sleep may facilitate recovery, reduce anxiety, and enhance stress resilience, but the extent to which sleep versus wakefulness post-stress aids long-term adaptation is unclear. Both human and animal studies highlight a bidirectional relationship, where stress-induced changes in sleep architecture may have adaptive or maladaptive consequences. Here, we propose that post-stress sleep contributes to resilience and discuss potential mechanisms underlying this process. A deeper understanding of these pathways may provide new strategies for enhancing stress recovery and improving mental health outcomes.

Semaglutide effects on energy balance are mediated by Adcyap1+ neurons in the dorsal vagal complex

The use of the GLP-1R agonist semaglutide is revolutionizing the treatment of obesity, yet its mechanistic effects on energy balance remain elusive. Here, we demonstrate that reactivation of semaglutide-responsive dorsal vagal complex neurons mimics the drug's effects of reducing food intake and body weight and promoting fat utilization and conditioned taste aversion. We observe that many of the semaglutide-activated area postrema (AP) and nucleus of the solitary tract (NTS) neurons express Adcyap1 mRNA, and ablation of AP/NTS Adcyap1+ neurons largely reverses semaglutide's effects on energy balance acutely in lean mice and in subchronically treated obese mice. Semaglutide-activated AP/NTS Adcyap1+ neurons promote the loss of fat rather than lean mass, with only a modest effect on conditioned taste aversion. Furthermore, NTS Adcyap1+ neurons are engaged by GLP-1R-expressing AP neurons and are necessary for semaglutide-induced activation of several downstream satiety-related structures. Selective targeting of semaglutide-responsive Adcyap1+ neurons holds potential for improved future anti-obesity treatments.

Interoceptive modulation of emotions

The metaphorical use of the heart to represent emotions has been documented since our earliest known writings, which reflects a historical recognition of the deep connection between bodily sensations and emotions. However, it remains an active topic of investigation to determine the degree to which bodily physiology modulates emotion states. Recent advances in the neuroscience of interoception-the process by which we sense, interpret, and integrate internal bodily signals and physiology-are uncovering neurobiological mechanisms by which visceral signals can influence emotions. Here we review interoceptive pathways that relay visceral signals to the brain and discuss how these signals influence emotion states as well as challenges and opportunities to better understand interoceptive modulation of emotions.

Microglial TAK1 promotes neurotoxic astrocytes and cognitive impairment in LPS-induced hippocampal neuroinflammation

The peripheral immune system has a strong effect on the central nervous system (CNS). Systemic lipopolysaccharides (LPS) administration triggers robust microglial activation and induces significant inflammatory responses in the hippocampus. This study investigates the role of Transforming Growth Factor-β-Activated Kinase 1 (TAK1) in mediating LPS-induced hippocampal neuroinflammation and cognitive impairment. Our findings reveal that LPS induces activation of microglial TAK1, which in turn actives downstream effector NF-κB/p65 to release pro-inflammatory cytokines. The activated microglia also promote astrocytes to polarize into a neurotoxic phenotype (A1-like phenotype), and cause the loss of newborn neurons in the hippocampal dentate gyrus (DG). However, TAK1 reduction inhibits microglial responses, limits neurotoxic astrocytes, rescues newborn neurons, and subsequently improves LPS-induced cognitive deficits, suggesting that targeting TAK1 may be an effective strategy for alleviating neuroinflammation. The interaction between TAK1 activation, microglial responses, and the transition of neurotoxic astrocytes enhances our understanding of the cellular dynamics driving LPS-induced neuroinflammation, suggesting that TAK1 may be a therapeutic target for treating cognitive impairment.

Prostaglandin synthesis mediates the suppression of arcuate Kiss1 neuron activation and pulsatile luteinizing hormone secretion during immune/inflammatory stress in female mice

Stress induces a series of compensatory mechanisms with the objective of restoration or adaptation of physiological function. A common casualty of the response to stress is impaired reproduction via the inhibition of pulsatile luteinizing hormone (LH) secretion; however, how stressors convey LH inhibition remains unclear and may be dependent on stress type. Immune/inflammatory stress, modeled with peripheral lipopolysaccharide (LPS) exposure, induces a systemic inflammatory response which may contrast with the neural mechanisms employed by psychosocial stressors. We examined the suppressive effect of LPS versus psychosocial stress, modeled with restraint, on pulsatile LH secretion and investigated the neural mechanisms underlying LPS-induced LH suppression in ovariectomized (OVX) female mice. We observed that both LPS and restraint significantly suppressed mean LH concentrations; however, the dynamics of pulse suppression displayed stress-type dependency. LPS induced a reduction in both LH pulse frequency and amplitude, whereas restraint suppressed LH pulse frequency without compromising pulse amplitude. Next, we investigated the mediatory role of immune/inflammatory signaling for LPS to impair LH secretion and upstream arcuate Kiss1 cell function. Peripheral administration of flurbiprofen, a prostaglandin synthesis inhibitor, blocked the suppressive effect of LPS on LH pulse frequency and amplitude. Interestingly, flurbiprofen only partially prevented the suppressive effect of LPS on arcuate Kiss1 cell activity, as measured by c-Fos expression. These data demonstrate that immune/inflammatory stress inhibits the activity of the LH pulse generator, in part, via a prostaglandin-dependent pathway and supports the role of differential neural mechanisms mediating LH pulse suppression during stress.

Neural representation of cytokines by vagal sensory neurons

The nervous system coordinates with the immune system to detect and respond to harmful stimuli. Inflammation is a universal response to injury and infection that involves the release of cytokines. While it is known that information about cytokines is transmitted from the body to the brain, how the nervous system encodes specific cytokines in the form of neural activity is not well understood. Using in vivo calcium imaging, we show that vagal sensory neurons within the nodose ganglia exhibit distinct real-time neuronal responses to inflammatory cytokines. Some neurons respond selectively to individual cytokines, while others encode multiple cytokines with distinct activity patterns. In male mice with induced colitis, inflammation increased the baseline activity of these neurons but decreased responsiveness to specific cytokines, reflecting altered neural excitability. Transcriptomic analysis of vagal ganglia from colitis mice revealed downregulation of cytokine signaling pathways, while neuronal activity pathways were upregulated. Thus, nodose ganglia neurons perform real-time encoding of cytokines at the first neural station in a body-brain axis, providing a new framework for studying the dynamic nature of neuroimmune communication.

Brain-wide mapping of immune receptors uncovers a neuromodulatory role of IL-17E and the receptor IL-17RB

Cytokines interact with their receptor complexes to orchestrate diverse processes-from immune responses to behavioral modulation. Interleukin-17A (IL-17A) mediates protective immune responses by binding to IL-17 receptor A (IL-17RA) and IL-17RC subunits. IL-17A also modulates social interaction, yet the role of cytokine receptors in this process and their expression in the brain remains poorly characterized. Here, we mapped the brain-region-specific expression of all major IL-17R subunits and found that in addition to IL-17RA, IL-17RB-but not IL-17RC-plays a role in social behaviors through its expression in the cortex. We further showed that IL-17E, expressed in cortical neurons, enhances social interaction by acting on IL-17RA- and IL-17RB-expressing neurons. These findings highlight an IL-17 circuit within the cortex that modulates social behaviors. Thus, characterizing spatially restricted cytokine receptor expression can be leveraged to elucidate how cytokines function as critical messengers mediating neuroimmune interactions to shape animal behaviors.

Interoceptive processing in the nucleus of the solitary tract

The interoceptive nervous system continuously monitors the status of visceral organs to synthesize internal perceptions and regulate behavioral and physiological responses. The nucleus of the solitary tract (NTS) in the brainstem serves as a central interoceptive hub and the initial site where sensory information from internal organs is processed in the brain. Here we review the neurobiological underpinnings of interoceptive processing in the NTS, focusing on recent progress enabled by modern genetic and optical tools for neural circuit dissection and neuronal recordings. Sensory information from internal organs is organized into a topographic map within the NTS, computed locally, modulated by descending inputs from higher brain regions, and distributed to downstream targets via projection neurons to control behavior and physiology. We present a sensory processing perspective on interoceptive coding within this brain structure.

Pathogen infection induces sickness behaviors through neuromodulators linked to stress and satiety in C. elegans

When animals are infected by a pathogen, peripheral sensors of infection signal to the brain to induce adaptive behavioral changes known as sickness behaviors. While the pathways that signal from the periphery to the brain have been intensively studied, how central circuits are reconfigured to elicit these behavioral changes is not well understood. Here we find that neuromodulatory systems linked to stress and satiety are recruited during chronic pathogen infection to alter the behavior of Caenorhabditis elegans. Upon infection by the bacterium Pseudomonas aeruginosa PA14, C. elegans decrease feeding, then display reversible bouts of quiescence, and eventually die. The ALA neuron and its neuropeptides FLP-7, FLP-24, and NLP-8, which control stress-induced sleep in uninfected animals, promote the PA14-induced feeding reduction. However, the ALA neuropeptide FLP-13 instead delays quiescence and death in infected animals. Cell-specific genetic perturbations show that the neurons that release FLP-13 to delay quiescence in infected animals are distinct from ALA. A brain-wide imaging screen reveals that infection-induced quiescence involves ASI and DAF-7/TGF-beta, which control satiety-induced quiescence in uninfected animals. Our results suggest that a common set of neuromodulators are recruited across different physiological states, acting from distinct neural sources and in distinct combinations to drive state-dependent behaviors.

Comprehensive insights into emerging advances in the Neurobiology of anorexia

BACKGROUND

Anorexia is a complex eating disorder influenced by genetic, environmental, psychological, and socio-cultural factors. Research into its molecular mechanisms and neural circuits has deepened our understanding of its pathogenesis. Recent advances in neuroscience, molecular biology, and genetics have revealed key molecular and neural circuit mechanisms underlying anorexia.

AIM OF REVIEW

Clarify the peripheral and central molecular mechanisms regulating various types of anorexia, identify key cytokines and neural circuits, and propose new strategies for its treatment. Key scientific concepts of review: Anorexia animal models, including activity-induced, genetic mutation, and inflammation-induced types, are explored for their relevance to studying the disorder. Anorexic behavior is regulated by cytokines, hormones (like GDF15, GLP-1, and leptin), and neural circuits such as AgRP, serotonergic, dopaminergic, and glutamatergic pathways. Disruptions in these pathways, including GABAergic signaling in AgRP neurons and 5-HT2C and D2 receptors, contribute to anorexia. Potential therapies target neurotransmitter receptors, ghrelin receptors, and the GDF15-GFRAL pathway, offering insights for treating anorexia, immune responses, and obesity.

Vagal sensory circuits of the lower airway in respiratory physiology: Insights from neuronal diversity

Sensory neurons innervating the lower airway provide essential feedback information that regulates respiratory physiology. These neurons synapse with second-order neurons in the central nervous system, which project directly or indirectly to the respiratory and autonomic centers. Both primary sensory neurons and second-order neurons within these circuits exhibit significant heterogeneity, and the precise roles of individual neuronal subtypes in coding the airway's internal states and modulating respiratory and autonomic outputs remain incompletely understood. In this review, we summarize recent advances in understanding the neuronal diversity along sensory circuits of the lower airway and their physiological functions. We also highlight the challenges in elucidating the roles of specific neuronal subtypes due to the extensive molecular and anatomical diversity among these neurons. Improving targeting specificity for neuronal manipulation, combined with the development of a comprehensive connectivity map, will be critical for revealing the coding and wiring logics that underlie the precise control of respiratory physiology.

Single-Cell Resolution of Individual Variation in Hypothalamic Neurons Allows Targeted Manipulation Affecting Social Motivation

Despite decades of research, connecting molecular and cellular phenotypes to complex behavioral traits remains an elusive goal1. Social motivation exhibits individual trait variation2, which we hypothesize is mediated by molecular and cellular variability across hypothalamic neurons. To test this, we generated single-nucleus RNA-sequencing profiles3,4 of >120,000 neurons from tuberal hypothalamus and adjacent thalamus in 36 mice, balanced across sex and autism-associated mutation5, with all mice assessed for social motivation2. First, we show that molecular activation patterns predict behavior across individuals: specifically, activation of paraventricular Agtr1a+ (angiotensin receptor 1a) neurons predicted reduced social behavior. Subsequent inhibition of AGTR1A with telmisartan-an FDA-approved antihypertensive6-improved social orienting. Second, we show natural variation in neuronal proportions-likely arising from stochastic developmental events7-is sufficient to shape adult behavior even among genetically-identical individuals: we identified multiple neuronal populations whose relative abundance predicted social reward-seeking behavior. Chemogenetic inhibition of one such population, Nxph4+ neurons of the postero-lateral hypothalamus8, suppressed multiple aspects of social motivation. This work establishes proof-of-principle for an approach where single-cell genomics precisely maps neural substrates governing behavior. This approach revealed that stochastic variations in neuronal architecture deterministically influence social motivation, and enabled identification of therapeutically-actionable targets with immediate translational potential for disorders with social deficits.

Parallel gut-to-brain pathways orchestrate feeding behaviors

The caudal nucleus of the solitary tract (cNTS) in the brainstem serves as a hub for integrating interoceptive cues from diverse sensory pathways. However, the mechanisms by which cNTS neurons transform these signals into behaviors remain debated. We analyzed 18 cNTS-Cre mouse lines and cataloged the dynamics of nine cNTS cell types during feeding. We show that Th+ cNTS neurons encode esophageal mechanical distension and transient gulp size via vagal afferent inputs, providing quick feedback regulation of ingestion speed. By contrast, Gcg+ cNTS neurons monitor intestinal nutrients and cumulative ingested calories and have long-term effects on food satiation and preference. These nutritive signals are conveyed through a portal vein-spinal ascending pathway rather than vagal sensory neurons. Our findings underscore distinctions among cNTS subtypes marked by differences in temporal dynamics, sensory modalities, associated visceral organs and ascending sensory pathways, all of which contribute to specific functions in coordinated feeding regulation.

The neuroimmune connectome in health and disease

The nervous and immune systems have complementary roles in the adaptation of organisms to environmental changes. However, the mechanisms that mediate cross-talk between the nervous and immune systems, called neuroimmune interactions, are poorly understood. In this Review, we summarize advances in the understanding of neuroimmune communication, with a principal focus on the central nervous system (CNS): its response to immune signals and the immunological consequences of CNS activity. We highlight these themes primarily as they relate to neurological diseases, the control of immunity, and the regulation of complex behaviours. We also consider the importance and challenges linked to the study of the neuroimmune connectome, which is defined as the totality of neuroimmune interactions in the body, because this provides a conceptual framework to identify mechanisms of disease pathogenesis and therapeutic approaches. Finally, we discuss how the latest techniques can advance our understanding of the neuroimmune connectome, and highlight the outstanding questions in the field.

Immune control of brain physiology

The peripheral immune system communicates with the brain through complex anatomical routes involving the skull, the brain borders, circumventricular organs and peripheral nerves. These immune-brain communication pathways were classically considered to be dormant under physiological conditions and active only in cases of infection or damage. Yet, peripheral immune cells and signals are key in brain development, function and maintenance. In this Perspective, we propose an alternative framework for understanding the mechanisms of immune-brain communication. During brain development and in homeostasis, these anatomical structures allow selected elements of the peripheral immune system to affect the brain directly or indirectly, within physiological limits. By contrast, in ageing and pathological settings, detrimental peripheral immune signals hijack the existing communication routes or alter their structure. We discuss why a diversity of communication channels is needed and how they work in relation to one another to maintain homeostasis of the brain.

The parasubthalamic nucleus: A novel eating center in the brain

Eating behavior stands as a fundamental determinant of animal survival and growth, intricately regulated by an amalgamation of internal and external stimuli. Coordinated movements of facial muscles and the mandible orchestrate prey capture and food processing, propelled by the allure of taste and rewarding food properties. Conversely, satiation, pain, aversion, negative emotion or perceived threats can precipitate the cessation or avoidance of eating activities. In recent years, the parasubthalamic nucleus (PSTN), located in the lateral hypothalamic area, has emerged as a focal point in feeding research. PSTN neurons assume pivotal roles within multiple feeding circuits, bridging central feeding centers with peripheral organs. They intricately modulate regulation of oral sensorimotor functions, hedonic feeding, appetite motivation and the processing of satiation and aversive signals, thereby orchestrating the initiation or termination of feeding behaviors. This review delves into the distinctive neuronal subpopulations within the PSTN and their associated neural networks, aiming to refine our comprehension of the neural underpinnings of feeding while also seeking to unearth more efficacious therapeutic avenues for feeding and eating disorders.

Leptin reduces LPS-induced A1 reactive astrocyte activation and inflammation via inhibiting p38-MAPK signaling pathway

Neurotoxic A1 reactive astrocytes are induced by inflammatory stimuli. Leptin has been confirmed to have neuroprotective properties. However, its effect on the activation of A1 astrocytes in infectious inflammation is unclear. In the current study, astrocytes cultured from postnatal day 1 Sprague-Dawley rats were stimulated with lipopolysaccharide (LPS) to induce an acute in vitro inflammatory response. Leptin was applied 6 h later to observe its protective effects. The viability of the astrocytes was assessed. A1 astrocyte activation was determined by analyzing the gene expression of C3, H2-D1, H2-T23, and Serping 1 and secretion of pro-inflammatory cytokines IL-6 and TNF-α. The levels of phospho-p38 (pp38) and nuclear factor-κB (NF-κB) phosphor-p65 (pp65) were measured to explore the possible signaling pathways. Additionally, an LPS-induced inflammatory animal model was established to investigate the in vivo effects of leptin on A1 astrocytic activation. Results showed that in the in vitro culture system, LPS stimulation caused elevated expression of A1 astrocyte-specific genes and the secretion of pro-inflammatory cytokines, indicating the activation of A1 astrocytes. Leptin treatment significantly reversed the LPS induced upregulation in a dose-dependent manner. Similarly, LPS upregulated pp38, NF-κB pp65 protein and inflammatory cytokines were successfully reduced by leptin. In the LPS-induced animal model, the amelioratory effect of leptin on A1 astrocyte activation and inflammation was further confirmed, showed by the reduced sickness behaviors, A1 astrocyte genesis and inflammatory cytokines in vivo. Our results demonstrate that leptin efficiently inhibits LPS-induced neurotoxic activation of A1 astrocytes and neuroinflammation by suppressing p38-MAPK signaling pathway.

A rich component of Fructus Aurantii, meranzin hydrate, exerts antidepressant effects via suppressing caspase4 to regulate glial cell and neuronal functions in the hippocampus

Fructus Aurantii, a Chinese herbal medicine, has been indicated to have antidepressant effects in our previous study. However, the main component and specific mechanisms of the antidepressant effects of Fructus Aurantii still need to be further revealed. This study aimed to explore the main antidepressant component of Fructus Aurantii and the underlying mechanisms of its antidepressant effects in the hippocampus. The results showed that the component of meranzin hydrate (MH) was enrichment in Fructus Aurantii. MH could alleviate depressive phenotypes in LPS-induced mice after a single administration 1 day later. High genetic and proteinic levels of caspase4 in the hippocampus in LPS-induced mice were reversed by MH after a single administration 1 day later. Moreover, MH was capable of relieving inflammatory factors (TNF-a and IL-1β) and LPS in the serum in LPS-induced mice. Subsequently, activation of hippocampal caspase4 blocked MH's antidepressant effects and its effects on suppression of microglia and improvement of astrocyte in the hippocampus. Furthermore, MH could increase long-term potential (LTP) in the hippocampal dentate gyrus (DG) and activation of hippocampal caspase4 blocked MH's enhancement on neuronal activities and synaptic plasticity in the hippocampal DG. To sum up, the antidepressant effects of a rich component MH in Fructus Aurantii suppressed the activation of caspase4 by maintaining glial cells function to promote neuronal activities and synaptic plasticity in the hippocampus.

Molecular Ontology of the Nucleus of Solitary Tract

The nucleus of the solitary tract (NTS) receives visceral information and regulates appetitive, digestive, and cardiorespiratory systems. Within the NTS, diverse processes operate in parallel to sustain life, but our understanding of their cellular composition is incomplete. Here, we integrate histologic and transcriptomic analysis to identify and compare molecular features that distinguish neurons in this brain region. Most glutamatergic neurons in the NTS and area postrema co-express the transcription factors Lmx1b and Phox2b, except for a ventral band of neurons in the far-caudal NTS, which include the Gcg-expressing neurons that produce glucagon-like peptide 1 (GLP-1). GABAergic interneurons intermingle through the Lmx1b+Phox2b macropopulation, and dense clusters of GABAergic neurons surround the NTS. The Lmx1b+Phox2b macropopulation includes subpopulations with distinct distributions expressing Grp, Hsd11b2, Npff, Pdyn, Pou3f1, Sctr, Th, and other markers. These findings highlight Lmx1b-Phox2b co-expression as a common feature of glutamatergic neurons in the NTS and improve our understanding of the organization and distribution of neurons in this critical brain region.

Delivery and kinetics of immersion optical clearing agents in tissues: Optical imaging from ex vivo to in vivo

Advanced optical imaging provides a powerful tool for the structural and functional analysis of tissues with high resolution and contrast, but the imaging performance decreases as light propagates deeper into the tissue. Tissue optical clearing technique demonstrates an innovative way to realize deep-tissue imaging and have emerged substantially in the last two decades. Here, we briefly reviewed the basic principles of tissue optical clearing techniques in the view of delivery strategies via either free diffusion or external forces-driven advection, and the commonly-used optical techniques for monitoring kinetics of clearing agents in tissue, as well as their ex vivo to in vivo applications in multiple biomedical research fields. With future efforts on the even distribution of both clearing agents and probes, excavation of more effective clearing agents, and automation of tissue clearing processes, tissue optical clearing should provide more insights into the fundamental questions in biological events clinical diagnostics.

Projections from subfornical organ to bed nucleus of the stria terminalis modulate inflammation-induced anxiety-like behaviors in mice

Peripheral inflammation is closely related to the pathogenesis of sickness behaviors and psychiatric disorders such as anxiety and depression. The circumventricular organs (CVOs) are important brain sites to perceive peripheral inflammatory signals, but few studies have reported their role in inflammation-induced anxiety or depression. Using a mouse model of lipopolysaccharide (LPS)-induced inflammation, we identified a previously unreported role of the subfornical organ (SFO), one of the CVOs, in combating inflammation-induced anxiety. LPS treatment induced anxiety-like and sickness behaviors in mice. Although both the SFO and the organum vasculosum of the lamina terminalis (a CVO) neurons were activated after LPS treatment, only manipulating SFO neurons modulated LPS-induced anxiety-like behaviors. Activating or inhibiting SFO neurons alleviated or aggravated LPS-induced anxiety-like behaviors. In addition, SFO exerted this effect through glutamatergic projections to the bed nucleus of the stria terminalis. Manipulating SFO neurons did not affect LPS-induced sickness behaviors. Thus, we uncovered an active role of SFO neurons in counteracting peripheral inflammation-induced anxiety.

Neuronal regeneration in the area postrema of adult mouse medulla oblongata following glutamate-induced neuronal elimination

Neural stem cells and/or progenitor cells (NSCs/NPCs) in the subventricular and subgranular zones of the adult mammal forebrain generate new neurons and are involved in partial repair after injury. Recently, NSCs/NPCs were identified in the area postrema (AP) of the medulla oblongata of the hindbrain. In this study, we used the properties of fenestrate capillaries to observe specific neuronal elimination in the AP of adult mice and investigated subsequent neuronal regeneration by neurogenesis. Subcutaneous administration of monosodium glutamate (MSG) induced prominent Fos expression in HuC/D+ neurons in the AP 2 h after administration. MSG administration caused a marked decrease in HuC/D+ neuronal density by neuronal death 3 to 21 days after administration, which recovered to the control level 35 days later. After MSG administration, the density of TUNEL+ dying neurons and phagocytic microglia surrounding or engulfing neurons increased. Within 7 days of MSG administration, the number of BrdU+　Sox2+ and BrdU+ Math1+ cells increased markedly, and at least the BrdU+ Math1+ cells similarly increased for the next following 7 days. A remarkable number of HuC/D+ neurons with BrdU+ nuclei were observed 35 days after MSG administration. This study reveals that neurogenesis occurs in the AP of adult mice, recovering and maintaining normal neuronal density after neuronal death.

Chronic urinary tract infections cause persistent microglial changes in a humanized ɑ-synuclein mouse model

BACKGROUND

Urinary tract infections (UTIs) have recently been linked to the onset of multiple synucleinopathies including Parkinson's disease (PD) and multiple system atrophy (MSA). UTIs are more common in people with PD or MSA, than in the general population and within these patient groups the incidence of UTIs is evenly distributed between men and women. UTIs are especially common during disease, but also in the years before clinical diagnosis.

OBJECTIVE

The mechanisms by which UTIs may contribute to the development and progression of PD or MSA are not well understood. In this work, we evaluate the neuroinflammatory effects of recurrent UTIs on the brain.

METHODS

In a humanized mouse model of ɑ-synuclein, we find that repeated administration of uropathogenic E. coli result in sustained UTIs, or a non-resolving chronic UTI phenotype with persistent bacteriuria. Using this model, we investigate the effects of repeated chronic UTIs on neuroinflammation and synucleinopathy in the brain.

RESULTS

Recurrent UTIs lead to behavioral motor changes and are accompanied by persistent neuroinflammatory changes in multiple brain areas. Affected regions with microglial changes involve multiple lower brainstem areas responsible for sickness behavior, including the dorsal vagal complex, and the cingulate cortex.

CONCLUSIONS

These results suggests that recurrent UTIs can have lasting impact on the brain, and it warrants further investigation of the potential role of UTIs in the disease progression of synucleinopathies and related neurological disorders.

Brain-body physiology: Local, reflex, and central communication

Behavior is tightly synchronized with bodily physiology. Internal needs from the body drive behavior selection, while optimal behavior performance requires a coordinated physiological response. Internal state is dynamically represented by the nervous system to influence mood and emotion, and body-brain signals also direct responses to external sensory cues, enabling the organism to adapt and pursue its goals within an ever-changing environment. In this review, we examine the anatomy and function of the brain-body connection, manifested across local, reflex, and central regulation levels. We explore these hierarchical loops in the context of the immune system, specifically through the lens of immunoception, and discuss the impact of its dysregulation on human health.

The area postrema: a critical mediator of brain-body interactions

The dorsal vagal complex contains three structures: the area postrema, the nucleus tractus solitarii, and the dorsal motor nucleus of the vagus. These structures are tightly linked, both anatomically and functionally, and have important yet distinct roles in not only conveying peripheral bodily signals to the rest of the brain but in the generation of behavioral and physiological responses. Reports on the new discoveries in these structures were highlights of the symposium. In this outlook, we focus on the roles of the area postrema in mediating brain-body interactions and its potential utility as a therapeutic target, especially in cancer cachexia.

Suppressed testicular macrophage M1 polarization by HDAC5 enforces insensitivity to LPS-elicited blood-testis barrier damage

Infertility caused by lipopolysaccharide (LPS) exposure due to infection is endangering male fertility worldwide, but the mechanism remains unclear. The blood-testis barrier (BTB) is essential for maintaining spermatogenesis and male fertility. In the present study, we showed that LPS (5.0 mg/kg) treatment markedly down-regulated the expression of BTB-related proteins, expanded the biotin penetration distance and caused histopathological injury in seminiferous tubules in mouse testes. Notably, testicular macrophage M1 polarization induced by LPS seems to be related to BTB damage, which was well confirmed by co-culture of RAW264.7 and TM4 cells in vitro. Interestingly, a low-dose LPS (0.1 mg/kg) pretreatment attenuated down-regulation of BTB-related proteins expression and histopathological injury and shorten biotin penetration distance in seminiferous tubules caused by LPS. Correspondingly, a low-dose LPS pretreatment suppresses testicular macrophage M1 polarization induced by LPS in mouse testes. Further experiments revealed that histone deacetylase 5 (HDAC5) was markedly down-regulated at 2 h and slightly down-regulated at 8 h, but up-regulated at 24 h in mouse testes after LPS treatment. Additionally, low-dose LPS pretreatment against the down-regulation of HDAC5 protein caused by LPS treatment. Notably, the suppressed testicular macrophage M1 polarization by low-dose LPS pretreatment was broken by BRD4354, a specific inhibitor of HDAC5 in vitro. These results suggest suppressed testicular macrophage M1 polarization by HDAC5 enforces insensitivity to LPS-elicited BTB damage.

Noninvasive closed-loop acoustic brain-computer interface for seizure control

Rationale: The brain-computer interface (BCI) is core tasks in comprehensively understanding the brain, and is one of the most significant challenges in neuroscience. The development of novel non-invasive neuromodulation technique will drive major innovations and breakthroughs in the field of BCI. Methods: We develop a new noninvasive closed-loop acoustic brain-computer interface (aBCI) for decoding the seizure onset based on the electroencephalography and triggering ultrasound stimulation of the vagus nerve to terminate seizures. Firstly, we create the aBCI system and decode the onset of seizure via a multi-level threshold model based on the analysis of wireless-collected electroencephalogram (EEG) signals recorded from above the hippocampus. Then, the different acoustic parameters induced acoustic radiation force were used to stimulate the vagus nerve in a rat model of epilepsy-induced by pentylenetetrazole. Finally, the results of epileptic EEG signal triggering ultrasound stimulation of the vagus nerve to control seizures. In addition, the mechanism of aBCI control seizures were investigated by real-time quantitative polymerase chain reaction (RT-qPCR). Results: In a rat model of epilepsy, the aBCI system selectively actives mechanosensitive neurons in the nodose ganglion while suppressing neuronal excitability in the hippocampus and amygdala, and stops seizures rapidly upon ultrasound stimulation of the vagus nerve. Physical transection or chemical blockade of the vagus nerve pathway abolish the antiepileptic effects of aBCI. In addition, aBCI shows significant antiepileptic effects compared to conventional vagus nerve electrical stimulation in an acute experiment. Conclusions: Closed-loop aBCI provides a novel, safe and effective tool for on-demand stimulation to treat abnormal neuronal discharges, opening the door to next generation non-invasive BCI.

An arginine-rich nuclear localization signal (ArgiNLS) strategy for streamlined image segmentation of single cells

High-throughput volumetric fluorescent microscopy pipelines can spatially integrate whole-brain structure and function at the foundational level of single cells. However, conventional fluorescent protein (FP) modifications used to discriminate single cells possess limited efficacy or are detrimental to cellular health. Here, we introduce a synthetic and nondeleterious nuclear localization signal (NLS) tag strategy, called "Arginine-rich NLS" (ArgiNLS), that optimizes genetic labeling and downstream image segmentation of single cells by restricting FP localization near-exclusively in the nucleus through a poly-arginine mechanism. A single N-terminal ArgiNLS tag provides modular nuclear restriction consistently across spectrally separate FP variants. ArgiNLS performance in vivo displays functional conservation across major cortical cell classes and in response to both local and systemic brain-wide AAV administration. Crucially, the high signal-to-noise ratio afforded by ArgiNLS enhances machine learning-automated segmentation of single cells due to rapid classifier training and enrichment of labeled cell detection within 2D brain sections or 3D volumetric whole-brain image datasets, derived from both staining-amplified and native signal. This genetic strategy provides a simple and flexible basis for precise image segmentation of genetically labeled single cells at scale and paired with behavioral procedures.

A subset of dopamine receptor-expressing neurons in the nucleus accumbens controls feeding and energy homeostasis

Orchestrating complex behaviors, such as approaching and consuming food, is critical for survival. In addition to hypothalamus neuronal circuits, the nucleus accumbens (NAc) also controls appetite and satiety. However, specific neuronal subtypes of the NAc that are involved and how the humoral and neuronal signals coordinate to regulate feeding remain incompletely understood. Here we decipher the spatial diversity of neuron subtypes of the NAc shell (NAcSh) and define a dopamine receptor D1-expressing and Serpinb2-expressing subtype controlling food consumption in male mice. Chemogenetics and optogenetics-mediated regulation of Serpinb2+ neurons bidirectionally regulate food seeking and consumption specifically. Circuitry stimulation reveals that the NAcShSerpinb2→LHLepR projection controls refeeding and can overcome leptin-mediated feeding suppression. Furthermore, NAcSh Serpinb2+ neuron ablation reduces food intake and upregulates energy expenditure, resulting in reduced bodyweight gain. Our study reveals a neural circuit consisting of a molecularly distinct neuronal subtype that bidirectionally regulates energy homeostasis, providing a potential therapeutic target for eating disorders.

Dissociable hindbrain GLP1R circuits for satiety and aversion

The most successful obesity therapeutics, glucagon-like peptide-1 receptor (GLP1R) agonists, cause aversive responses such as nausea and vomiting1,2, effects that may contribute to their efficacy. Here, we investigated the brain circuits that link satiety to aversion, and unexpectedly discovered that the neural circuits mediating these effects are functionally separable. Systematic investigation across drug-accessible GLP1R populations revealed that only hindbrain neurons are required for the efficacy of GLP1-based obesity drugs. In vivo two-photon imaging of hindbrain GLP1R neurons demonstrated that most neurons are tuned to either nutritive or aversive stimuli, but not both. Furthermore, simultaneous imaging of hindbrain subregions indicated that area postrema (AP) GLP1R neurons are broadly responsive, whereas nucleus of the solitary tract (NTS) GLP1R neurons are biased towards nutritive stimuli. Strikingly, separate manipulation of these populations demonstrated that activation of NTSGLP1R neurons triggers satiety in the absence of aversion, whereas activation of APGLP1R neurons triggers strong aversion with food intake reduction. Anatomical and behavioural analyses revealed that NTSGLP1R and APGLP1R neurons send projections to different downstream brain regions to drive satiety and aversion, respectively. Importantly, GLP1R agonists reduce food intake even when the aversion pathway is inhibited. Overall, these findings highlight NTSGLP1R neurons as a population that could be selectively targeted to promote weight loss while avoiding the adverse side effects that limit treatment adherence.

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.

Brainstem Dbh+ neurons control allergen-induced airway hyperreactivity

Exaggerated airway constriction triggered by repeated exposure to allergen, also called hyperreactivity, is a hallmark of asthma. Whereas vagal sensory neurons are known to function in allergen-induced hyperreactivity1-3, the identity of downstream nodes remains poorly understood. Here we mapped a full allergen circuit from the lung to the brainstem and back to the lung. Repeated exposure of mice to inhaled allergen activated the nuclei of solitary tract (nTS) neurons in a mast cell-, interleukin-4 (IL-4)- and vagal nerve-dependent manner. Single-nucleus RNA sequencing, followed by RNAscope assay at baseline and allergen challenges, showed that a Dbh+ nTS population is preferentially activated. Ablation or chemogenetic inactivation of Dbh+ nTS neurons blunted hyperreactivity whereas chemogenetic activation promoted it. Viral tracing indicated that Dbh+ nTS neurons project to the nucleus ambiguus (NA) and that NA neurons are necessary and sufficient to relay allergen signals to postganglionic neurons that directly drive airway constriction. Delivery of noradrenaline antagonists to the NA blunted hyperreactivity, suggesting noradrenaline as the transmitter between Dbh+ nTS and NA. Together, these findings provide molecular, anatomical and functional definitions of key nodes of a canonical allergen response circuit. This knowledge informs how neural modulation could be used to control allergen-induced airway hyperreactivity.

Area postrema neurons mediate interleukin-6 function in cancer cachexia

Interleukin-6 (IL-6) has been long considered a key player in cancer cachexia. It is believed that sustained elevation of IL-6 production during cancer progression causes brain dysfunctions, which ultimately result in cachexia. However, how peripheral IL-6 influences the brain remains poorly understood. Here we show that neurons in the area postrema (AP), a circumventricular structure in the hindbrain, is a critical mediator of IL-6 function in cancer cachexia in male mice. We find that circulating IL-6 can rapidly enter the AP and activate neurons in the AP and its associated network. Peripheral tumor, known to increase circulating IL-6, leads to elevated IL-6 in the AP, and causes potentiated excitatory synaptic transmission onto AP neurons and AP network hyperactivity. Remarkably, neutralization of IL-6 in the brain of tumor-bearing mice with an anti-IL-6 antibody attenuates cachexia and the hyperactivity in the AP network, and markedly prolongs lifespan. Furthermore, suppression of Il6ra, the gene encoding IL-6 receptor, specifically in AP neurons with CRISPR/dCas9 interference achieves similar effects. Silencing Gfral-expressing AP neurons also attenuates cancer cachectic phenotypes and AP network hyperactivity. Our study identifies a central mechanism underlying the function of peripheral IL-6, which may serve as a target for treating cancer cachexia.

A body-brain circuit that regulates body inflammatory responses

The body-brain axis is emerging as a principal conductor of organismal physiology. It senses and controls organ function1,2, metabolism3 and nutritional state4-6. Here we show that a peripheral immune insult strongly activates the body-brain axis to regulate immune responses. We demonstrate that pro-inflammatory and anti-inflammatory cytokines communicate with distinct populations of vagal neurons to inform the brain of an emerging inflammatory response. In turn, the brain tightly modulates the course of the peripheral immune response. Genetic silencing of this body-brain circuit produced unregulated and out-of-control inflammatory responses. By contrast, activating, rather than silencing, this circuit affords neural control of immune responses. We used single-cell RNA sequencing, combined with functional imaging, to identify the circuit components of this neuroimmune axis, and showed that its selective manipulation can effectively suppress the pro-inflammatory response while enhancing an anti-inflammatory state. The brain-evoked transformation of the course of an immune response offers new possibilities in the modulation of a wide range of immune disorders, from autoimmune diseases to cytokine storm and shock.

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.

Neuroimmune modulation by tryptophan derivatives in neurological and inflammatory disorders

The nervous and immune systems are highly developed, and each performs specialized physiological functions. However, they work together, and their dysfunction is associated with various diseases. Specialized molecules, such as neurotransmitters, cytokines, and more general metabolites, are essential for the appropriate regulation of both systems. Tryptophan, an essential amino acid, is converted into functional molecules such as serotonin and kynurenine, both of which play important roles in the nervous and immune systems. The role of kynurenine metabolites in neurodegenerative and psychiatric diseases has recently received particular attention. Recently, we found that hyperactivity of the kynurenine pathway is a critical risk factor for septic shock. In this review, we first outline neuroimmune interactions and tryptophan derivatives and then summarized the changes in tryptophan metabolism in neurological disorders. Finally, we discuss the potential of tryptophan derivatives as therapeutic targets for neuroimmune disorders.

Physiologic disruption and metabolic reprogramming in infection and sepsis

Effective responses against severe systemic infection require coordination between two complementary defense strategies that minimize the negative impact of infection on the host: resistance, aimed at pathogen elimination, and disease tolerance, which limits tissue damage and preserves organ function. Resistance and disease tolerance mostly rely on divergent metabolic programs that may not operate simultaneously in time and space. Due to evolutionary reasons, the host initially prioritizes the elimination of the pathogen, leading to dominant resistance mechanisms at the potential expense of disease tolerance, which can contribute to organ failure. Here, we summarize our current understanding of the role of physiological perturbations resulting from infection in immune response dynamics and the metabolic program requirements associated with resistance and disease tolerance mechanisms. We then discuss how insight into the interplay of these mechanisms could inform future research aimed at improving sepsis outcomes and the potential for therapeutic interventions.

Effects of systemic inflammation on the network oscillation in the anterior cingulate cortex and cognitive behavior

Network oscillation in the anterior cingulate cortex (ACC) plays a key role in attention, novelty detection and anxiety; however, its involvement in cognitive impairment caused by acute systemic inflammation is unclear. To investigate the acute effects of systemic inflammation on ACC network oscillation and cognitive function, we analyzed cytokine level and cognitive performance as well as network oscillation in the mouse ACC Cg1 region, within 4 hours after lipopolysaccharide (LPS, 30 μg/kg) administration. While the interleukin-6 concentration in the serum was evidently higher in LPS-treated mice, the increases in the cerebral cortex interleukin-6 did not reach statistical significance. The power of kainic acid (KA)-induced network oscillation in the ACC Cg1 region slice preparation increased in LPS-treated mice. Notably, histamine, which was added in vitro, increased the oscillation power in the brain slices from LPS-untreated mice; for the LPS-treated mice, however, the effect of histamine was suppressive. In the open field test, frequency of entries into the center area showed a negative correlation with the power of network oscillation (0.3 μM of KA, theta band (3-8 Hz); 3.0 μM of KA, high-gamma band (50-80 Hz)). These results suggest that LPS-induced systemic inflammation results in increased network oscillation and a drastic change in histamine sensitivity in the ACC, accompanied by the robust production of systemic pro-inflammatory cytokines in the periphery, and that these alterations in the network oscillation and animal behavior as an acute phase reaction relate with each other. We suggest that our experimental setting has a distinct advantage in obtaining mechanistic insights into inflammatory cognitive impairment through comprehensive analyses of hormonal molecules and neuronal functions.

Antagonism between neuropeptides and monoamines in a distributed circuit for pathogen avoidance

Pathogenic infection elicits behaviors that promote recovery and survival of the host. After exposure to the pathogenic bacterium Pseudomonas aeruginosa PA14, the nematode Caenorhabditis elegans modifies its sensory preferences to avoid the pathogen. Here, we identify antagonistic neuromodulators that shape this acquired avoidance behavior. Using an unbiased cell-directed neuropeptide screen, we show that AVK neurons upregulate and release RF/RYamide FLP-1 neuropeptides during infection to drive pathogen avoidance. Manipulations that increase or decrease AVK activity accelerate or delay pathogen avoidance, respectively, implicating AVK in the dynamics of avoidance behavior. FLP-1 neuropeptides drive pathogen avoidance through the G protein-coupled receptor DMSR-7, as well as other receptors. DMSR-7 in turn acts in multiple neurons, including tyraminergic/octopaminergic neurons that receive convergent avoidance signals from the cytokine DAF-7/transforming growth factor β. Neuromodulators shape pathogen avoidance through multiple mechanisms and targets, in agreement with the distributed neuromodulatory connectome of C. elegans.

Activation of GFRAL+ neurons induces hypothermia and glucoregulatory responses associated with nausea and torpor

GFRAL-expressing neurons actuate aversion and nausea, are targets for obesity treatment, and may mediate metformin effects by long-term GDF15-GFRAL agonism. Whether GFRAL+ neurons acutely regulate glucose and energy homeostasis is, however, underexplored. Here, we report that cell-specific activation of GFRAL+ neurons using a variety of techniques causes a torpor-like state, including hypothermia, the release of stress hormones, a shift from glucose to lipid oxidation, and impaired insulin sensitivity, glucose tolerance, and skeletal muscle glucose uptake but augmented glucose uptake in visceral fat. Metabolomic analysis of blood and transcriptomics of muscle and fat indicate alterations in ketogenesis, insulin signaling, adipose tissue differentiation and mitogenesis, and energy fluxes. Our findings indicate that acute GFRAL+ neuron activation induces endocrine and gluco- and thermoregulatory responses associated with nausea and torpor. While chronic activation of GFRAL signaling promotes weight loss in obesity, these results show that acute activation of GFRAL+ neurons causes hypothermia and hyperglycemia.

Biofilm exopolysaccharides alter sensory-neuron-mediated sickness during lung infection

Infections of the lung cause observable sickness thought to be secondary to inflammation. Signs of sickness are crucial to alert others via behavioral-immune responses to limit contact with contagious individuals. Gram-negative bacteria produce exopolysaccharide (EPS) that provides microbial protection; however, the impact of EPS on sickness remains uncertain. Using genome-engineered Pseudomonas aeruginosa (P. aeruginosa) strains, we compared EPS-producers versus non-producers and a virulent Escherichia coli (E. coli) lung infection model in male and female mice. EPS-negative P. aeruginosa and virulent E. coli infection caused severe sickness, behavioral alterations, inflammation, and hypothermia mediated by TLR4 detection of the exposed lipopolysaccharide (LPS) in lung TRPV1+ sensory neurons. However, inflammation did not account for sickness. Stimulation of lung nociceptors induced acute stress responses in the paraventricular hypothalamic nuclei by activating corticotropin-releasing hormone neurons responsible for sickness behavior and hypothermia. Thus, EPS-producing biofilm pathogens evade initiating a lung-brain sensory neuronal response that results in sickness.

Evidence for vagal sensory neural involvement in influenza pathogenesis and disease

Influenza A virus (IAV) is a common respiratory pathogen and a global cause of significant and often severe morbidity. Although inflammatory immune responses to IAV infections are well described, little is known about how neuroimmune processes contribute to IAV pathogenesis. In the present study, we employed surgical, genetic, and pharmacological approaches to manipulate pulmonary vagal sensory neuron innervation and activity in the lungs to explore potential crosstalk between pulmonary sensory neurons and immune processes. Intranasal inoculation of mice with H1N1 strains of IAV resulted in stereotypical antiviral lung inflammation and tissue pathology, changes in breathing, loss of body weight and other clinical signs of severe IAV disease. Unilateral cervical vagotomy and genetic ablation of pulmonary vagal sensory neurons had a moderate effect on the pulmonary inflammation induced by IAV infection, but significantly worsened clinical disease presentation. Inhibition of pulmonary vagal sensory neuron activity via inhalation of the charged sodium channel blocker, QX-314, resulted in a moderate decrease in lung pathology, but again this was accompanied by a paradoxical worsening of clinical signs. Notably, vagal sensory ganglia neuroinflammation was induced by IAV infection and this was significantly potentiated by QX-314 administration. This vagal ganglia hyperinflammation was characterized by alterations in IAV-induced host defense gene expression, increased neuropeptide gene and protein expression, and an increase in the number of inflammatory cells present within the ganglia. These data suggest that pulmonary vagal sensory neurons play a role in the regulation of the inflammatory process during IAV infection and suggest that vagal neuroinflammation may be an important contributor to IAV pathogenesis and clinical presentation. Targeting these pathways could offer therapeutic opportunities to treat IAV-induced morbidity and mortality.

Lipopolysaccharide (LPS) attenuates the primary conditioning of lithium chloride (LiCl)-induced context aversion but not the secondary conditioning of context aversion or taste avoidance

A first-order association can be formed between toxin-induced nausea and a context, as well as nausea and a taste cue. However, comparatively little is understood about second-order associations. The present study examined if the bacterial endotoxin, LPS, could impair the first- and second-order conditioning of context aversion (anticipatory nausea paradigm) and subsequent conditioned taste avoidance (two-bottle task). Adult male Long Evans rats were treated with LiCl (127 mg/kg, intraperitoneal [i.p.]) or vehicle control (NaCl) and then exposed to a distinct context for 4 first-order conditioning trials. LPS (200 μg/kg, i.p.) or NaCl were administered 24 h after each trial. Seventy-two h after the final first-order conditioning trial, rats underwent 2 second-order conditioning trials where they were treated with 2% saccharin (i.p.) and then exposed to the same context. Twenty-four h after the final second-order conditioning trial, rats were tested in a two-bottle task (2 trials), where they were given a choice between water and a palatable 0.2% saccharin solution. LiCl-treated rats demonstrated a context aversion by the 3rd conditioning trial in the anticipatory nausea paradigm. Rats previously exposed to LiCl also displayed a conditioned taste avoidance of saccharin within the two-bottle task. LPS attenuated first-order context aversion but did not alter either second-order context aversion or conditioned taste avoidance in the two-bottle task. This study demonstrated that a secondary association formed within an aversive context could result in a conditioned taste avoidance. Further, LPS may be able to attenuate primary conditioning, but not secondary conditioning.

A molecularly defined NAcSh D1 subtype controls feeding and energy homeostasis

Orchestrating complex behavioral states, such as approach and consumption of food, is critical for survival. In addition to hypothalamus neuronal circuits, the nucleus accumbens (NAc) also plays an important role in controlling appetite and satiety in responses to changing external stimuli. However, the specific neuronal subtypes of NAc involved as well as how the humoral and neuronal signals coordinate to regulate feeding remain incompletely understood. Here, we deciphered the spatial diversity of neuron subtypes of the NAc shell (NAcSh) and defined a dopamine receptor D1(Drd1)- and Serpinb2-expressing subtype located in NAcSh encoding food consumption. Chemogenetics- and optogenetics-mediated regulation of Serpinb2 + neurons bidirectionally regulates food seeking and consumption specifically. Circuitry stimulation revealed the NAcSh Serpinb2 →LH LepR projection controls refeeding and can overcome leptin-mediated feeding suppression. Furthermore, NAcSh Serpinb2 + neuron ablation reduces food intake and upregulates energy expenditure resulting in body weight loss. Together, our study reveals a neural circuit consisted of molecularly distinct neuronal subtype that bidirectionally regulates energy homeostasis, which can serve as a potential therapeutic target for eating disorders.

The Coding Logic of Interoception

Interoception, the ability to precisely and timely sense internal body signals, is critical for life. The interoceptive system monitors a large variety of mechanical, chemical, hormonal, and pathological cues using specialized organ cells, organ innervating neurons, and brain sensory neurons. It is important for maintaining body homeostasis, providing motivational drives, and regulating autonomic, cognitive, and behavioral functions. However, compared to external sensory systems, our knowledge about how diverse body signals are coded at a system level is quite limited. In this review, we focus on the unique features of interoceptive signals and the organization of the interoceptive system, with the goal of better understanding the coding logic of interoception.

Post-COVID dysautonomias: what we know and (mainly) what we don't know

Following on from the COVID-19 pandemic is another worldwide public health challenge that is referred to variously as long COVID, post-COVID syndrome or post-acute sequelae of SARS-CoV-2 infection (PASC). PASC comes in many forms and affects all body organs. This heterogeneous presentation suggests involvement of the autonomic nervous system (ANS), which has numerous roles in the maintenance of homeostasis and coordination of responses to various stressors. Thus far, studies of ANS dysregulation in people with PASC have been largely observational and descriptive, based on symptom inventories or objective but indirect measures of cardiovascular function, and have paid little attention to the adrenomedullary, hormonal and enteric nervous components of the ANS. Such investigations do not consider the syndromic nature of autonomic dysfunction. This Review provides an update on the literature relating to ANS abnormalities in people with post-COVID syndrome and presents a theoretical perspective on how the ANS might participate in common features of PASC.

The gut microbiome in disorders of gut-brain interaction

Functional gastrointestinal disorders (FGIDs), chronic disorders characterized by either abdominal pain, altered intestinal motility, or their combination, have a worldwide prevalence of more than 40% and impose a high socioeconomic burden with a significant decline in quality of life. Recently, FGIDs have been reclassified as disorders of gut-brain interaction (DGBI), reflecting the key role of the gut-brain bidirectional communication in these disorders and their impact on psychological comorbidities. Although, during the past decades, the field of DGBIs has advanced significantly, the molecular mechanisms underlying DGBIs pathogenesis and pathophysiology, and the role of the gut microbiome in these processes are not fully understood. This review aims to discuss the latest body of literature on the complex microbiota-gut-brain interactions and their implications in the pathogenesis of DGBIs. A better understanding of the existing communication pathways between the gut microbiome and the brain holds promise in developing effective therapeutic interventions for DGBIs.

Molecular and immunological origins of catatonia

Catatonia occurs secondary to both primary psychiatric and neuromedical etiologies. Emerging evidence suggests possible linkages between causes of catatonia and neuroinflammation. These include obvious infectious and inflammatory etiologies, common neuromedical illnesses such as delirium, and psychiatric entities such as depression and autism-spectrum disorders. Symptoms of sickness behavior, thought to be a downstream effect of the cytokine response, are common in many of these etiologies and overlap significantly with symptoms of catatonia. Furthermore, there are syndromes that overlap with catatonia that some would consider variants, including neuroleptic malignant syndrome (NMS) and akinetic mutism, which may also have neuroinflammatory underpinnings. Low serum iron, a common finding in NMS and malignant catatonia, may be caused by the acute phase response. Cellular hits involving either pathogen-associated molecular patterns (PAMP) danger signals or the damage-associated molecular patterns (DAMP) danger signals of severe psychosocial stress may set the stage for a common pathway immunoactivation state that could lower the threshold for a catatonic state in susceptible individuals. Immunoactivation leading to dysfunction in the anterior cingulate cortex (ACC)/mid-cingulate cortex (MCC)/medial prefrontal cortex (mPFC)/paralimbic cortico-striato-thalamo-cortical (CSTC) circuit, involved in motivation and movement, may be particularly important in generating the motor and behavioral symptoms of catatonia.