Area Postrema Cell Types that Mediate Nausea-Associated Behaviors

Neuropathological links between T2DM and LOAD: systematic review and meta-analysis

Recent decades have described parallel neuropathological mechanisms increasing the risk for developing late-onset Alzheimer's dementia (LOAD) in type 2 diabetes mellitus (T2DM); however, still little is known of the role of diabetic encephalopathy and brain atrophy in LOAD. The aim of this systematic review is to provide a comprehensive view on diabetic encephalopathy/cerebral atrophy, taking into account neuroimaging data, neuropathology, metabolic and endocrine mechanisms, amyloid formation, brain perfusion impairments, neuroimmunology, and inflammasome activation. Key switches were identified, to further meta-analyze genomic candidate loci and epigenetic modifications. For the qualitative meta-analysis of genomic bases extracted, human linkage studies were examined; for epigenetic mechanisms, data from both human and animal studies are described. For the systematic review of pathophysiological mechanisms, 1,259 publications were evaluated and 93 gene loci extracted for candidate risk linkages. Sixty-six publications were evaluated for genomic association and descriptions of epigenomic modifications. Overall accumulated results highlight the insulin signaling system, vascular markers, inflammation and inflammasome pathways, amylin interactions, and glycosylation mechanisms. The protocol was registered with PROSPERO (ID: CRD42023440535).

Circadian rhythms and gastrointestinal hormone-related appetite regulation

PURPOSE OF REVIEW

Circadian biology influences the gastrointestinal system as exemplified by hormonal patterns that modulate appetite. Indeed, people tend to get hungrier towards the later parts of the day. How misalignment of our circadian biology with behavioral factors (i.e. diet, exercise, sleep, etc.) influences obesity related disease has been an area of intense recent investigation.

RECENT FINDINGS

The gastrointestinal hormones (e.g. ghrelin, glucagon-like polypeptide-1, glucose dependent insulinotrophic peptide, peptide tyrosine-tyrosine, and insulin) play unique roles across the 24-h cycle in fostering anticipatory responses that promote desires to eat while concurrently responding to environmental stimuli. A persons chronotype has emerged as a target area since it provides a metric of circadian biology interacting with environmental factors and affects all people. In fact, later chronotypes tend to be at higher risk for obesity, due to in part, alterations in gastrointestinal hormones (e.g. GIP, insulin) that align with behavioral observations of greater food intake and desires to eat fatty/sweet foods later in the day.

SUMMARY

Changes in gastrointestinal hormones across the 24-h cycle impact obesity risk when misalignment of our circadian biology occurs with behavioral cycles. Better understanding how chronotype modulates appetite may enable personalized prescription of exercise, diet and/or medication to foster reduced chronic disease risk.

Oxyntomodulin - past, present and future

Almost since its discovery, glucagon was suspected to be formed in the gastrointestinal tract, and the L-cells were shown to contain glucagon-like immunoreactivity. This was due to the presence of two peptides that both contained the full glucagon sequence:glicentin of 69 amino acids and oxyntomodulin of 37 amino acids. While glicentin is a part of the glucagon precursor, proglucagon, and probably is inactive, oxyntomodulin, a fragment of glicentin, interacts although weakly with the glucagon as well as the GLP-1 receptor. However, in agreement with these activities, oxyntomodulin inhibited appetite and food intake in humans and inspired development of long acting, potent glucagon-GLP-1 co-agonists. Several such co-agonists are currently in clinical development and show promise because they combine GLP-1 like activities with those of glucagon agonism: additive weight loss and a stimulation of hepatic lipid metabolism with unique effectiveness on hepatic steatosis. They may therefore be effective in the treatment of metabolic dysfunction-associated steatotic liver disease (MASLD).

Specific loss of GIPR signaling in GABAergic neurons enhances GLP-1R agonist-induced body weight loss

OBJECTIVES

Dual incretin agonists are among the most effective pharmaceutical treatments for obesity and type 2 diabetes to date. Such therapeutics can target two receptors, such as the glucagon-like peptide-1 (GLP-1) receptor and the glucose-dependent insulinotropic polypeptide (GIP) receptor in the case of tirzepatide, to improve glycemia and reduce body weight. Regarding body weight effects, GIPR signaling is thought to involve at least two relevant mechanisms: the enhancement of food intake reduction and the attenuation of aversive effects caused by GLP-1R agonists. Although it is known that dual GLP-1R-GIPR agonism produces greater weight loss than GLP-1R agonism alone, the precise mechanism is unknown.

METHODS

To address this question, we used mice lacking GIPR in the whole body, GABAergic neurons, or glutamatergic neurons. These mice were given various combinations of GLP-1R and GIPR agonist drugs with subsequent food intake and conditioned taste aversion measurements.

RESULTS

A GIPR knockout in either the whole body or selectively in inhibitory GABAergic neurons protects against diet-induced obesity, whereas a knockout in excitatory glutamatergic neurons had a negligible effect. Furthermore, we found that GIPR in GABAergic neurons is essential for the enhanced weight loss efficacy of dual incretin agonism, yet, surprisingly, its removal enhances the effect of GLP-1R agonism alone. Finally, GIPR knockout in GABAergic neurons prevents the anti-aversive effects of GIPR agonism.

CONCLUSIONS

Our findings are consistent with GIPR research at large in that both enhancement and removal of GIPR signaling are metabolically beneficial. Notably, however, our findings suggest that future obesity therapies designed to modulate GIPR signaling, whether by agonism or antagonism, would be best targeted towards GABAergic neurons.

Glucose-dependent insulinotropic polypeptide (GIP)

BACKGROUND

Glucose-dependent insulinotropic polypeptide (GIP) was the first incretin identified and plays an essential role in the maintenance of glucose tolerance in healthy humans. Until recently GIP had not been developed as a therapeutic and thus has been overshadowed by the other incretin, glucagon-like peptide 1 (GLP-1), which is the basis for several successful drugs to treat diabetes and obesity. However, there has been a rekindling of interest in GIP biology in recent years, in great part due to pharmacology demonstrating that both GIPR agonism and antagonism may be beneficial in treating obesity and diabetes. This apparent paradox has reinvigorated the field, led to new lines of investigation, and deeper understanding of GIP.

SCOPE OF REVIEW

In this review, we provide a detailed overview on the multifaceted nature of GIP biology and discuss the therapeutic implications of GIPR signal modification on various diseases.

MAJOR CONCLUSIONS

Following its classification as an incretin hormone, GIP has emerged as a pleiotropic hormone with a variety of metabolic effects outside the endocrine pancreas. The numerous beneficial effects of GIPR signal modification render the peptide an interesting candidate for the development of pharmacotherapies to treat obesity, diabetes, drug-induced nausea and both bone and neurodegenerative disorders.

Glucagon-Like Peptide-1 and Hypothalamic Regulation of Satiation: Cognitive and Neural Insights from Human and Animal Studies

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) have emerged as blockbuster drugs for treating metabolic diseases. Glucagon-like peptide-1 (GLP-1) plays a pivotal role in glucose homeostasis by enhancing insulin secretion, suppressing glucagon release, delaying gastric emptying, and acting on the central nervous system to regulate satiation and satiety. This review summarizes the discovery of GLP-1 and the development of GLP-1RAs, with a particular focus on their central mechanisms of action. Human neuroimaging studies demonstrate that GLP-1RAs influence brain activity during food cognition, supporting a role in pre-ingestive satiation. Animal studies on hypothalamic feed-forward regulation of hunger suggest that cognitive hypothalamic mechanisms may also contribute to satiation control. We highlight the brain mechanisms of GLP-1RA-induced satiation and satiety, including cognitive impacts, with an emphasis on animal studies of hypothalamic glucagon-like peptide-1 receptor (GLP-1R) and GLP-1R-expressing neurons. Actions in non-hypothalamic regions are also discussed. Additionally, we review emerging combination drugs and oral GLP-1RA formulations aimed at improving efficacy and patient adherence. In conclusion, the dorsomedial hypothalamus (DMH)-a key GLP-1RA target-mediates pre-ingestive cognitive satiation, while other hypothalamic GLP-1R neurons regulate diverse aspects of feeding behavior, offering potential therapeutic targets for obesity treatment.

GLP-1 receptor agonist exendin-4 suppresses food intake by inhibiting hindbrain orexigenic NPY neurons

Peripherally delivered glucagon-like peptide-1 (GLP-1)-based drugs suppress eating through their action in the brain. However, the specific neuronal mechanisms, especially their impacts on the orexigenic circuit, remain largely elusive. Neuropeptide Y (NPY) neurons in the nucleus tractus solitarius (NTS) are newly identified as orexigenic neurons with a potent eating-stimulating effect, but their responses to GLP-1 drugs are unknown. Through ex vivo electrophysiological recordings, we study the impacts of GLP-1 receptor (GLP-1R) agonist exendin-4 on NTSNPY neurons. We discovered that the GLP-1R agonist exendin-4 inhibits NTSNPY neuronal activity via GABAb receptors by augmenting presynaptic GABA release. We also explored the contribution of NTSNPY neurons to exendin-4-mediated eating suppression. Interestingly, chemogenetic activation of NTSNPY neurons effectively counteracted exendin-4-induced anorexigenic effect. Moreover, chemogenetic inhibition of NTSNPY neurons mimicked the eating-suppressing effect of exendin-4. Collectively, our findings highlight a population of orexigenic NTSNPY neurons that may be targeted by a GLP-1R agonist to suppress food intake, suggesting that this neuronal population has translational importance as a potential therapeutic target for obesity treatment.NEW & NOTEWORTHY This study discovers that the glucagon-like peptide-1 (GLP-1) receptor agonist exendin-4 indirectly inhibits the majority of orexigenic hindbrain NPY neurons via GABAb receptors by augmenting presynaptic GABA release. Chemogenetic activation of these NPY neurons effectively counteracts exendin-4 (Exn-4)-induced anorexigenic effect, whereas chemogenetic inhibition of them mimics the eating-suppressing effect of exendin-4. This study uncovers a mechanism by which Exn-4 inhibits orexigenic hindbrain NPY neurons, thereby providing new insights into how GLP-1 drugs suppress food intake.

GIPR-Ab/GLP-1 peptide-antibody conjugate requires brain GIPR and GLP-1R for additive weight loss in obese mice

Glucose-dependent insulinotropic polypeptide receptor (GIPR) and glucagon-like peptide 1 receptor (GLP-1R) are expressed in the central nervous system (CNS) and regulate food intake. Here, we demonstrate that a peptide-antibody conjugate that blocks GIPR while simultaneously activating GLP-1R (GIPR-Ab/GLP-1) requires both CNS GIPR and CNS GLP-1R for maximal weight loss in obese, primarily male, mice. Moreover, dulaglutide produces greater weight loss in CNS GIPR knockout (KO) mice, and the weight loss achieved with dulaglutide + GIPR-Ab is attenuated in CNS GIPR KO mice. Wild-type mice treated with GIPR-Ab/GLP-1 and CNS GIPR KO mice exhibit similar changes in gene expression related to tissue remodelling, lipid metabolism and inflammation in white adipose tissue and liver. Moreover, GIPR-Ab/GLP-1 is detected in circumventricular organs in the brain and activates c-FOS in downstream neural substrates involved in appetite regulation. Hence, both CNS GIPR and GLP-1R signalling are required for the full weight loss effect of a GIPR-Ab/GLP-1 peptide-antibody conjugate.

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.

Vestibular neurons link motion sickness, behavioural thermoregulation and metabolic balance in mice

Motion sickness is associated with thermoregulation and metabolic control, but the underlying neural circuitry remains largely unknown. Here we show that neurons in the medial vestibular nuclei parvocellular part (MVePC) mediate the hypothermic responses induced by motion. Reactivation of motion-sensitive MVePC neurons recapitulates motion sickness in mice. We show that motion-activated neurons in the MVePC are glutamatergic (MVePCGlu), and that optogenetic stimulation of MVePCGlu neurons mimics motion-induced hypothermia by signalling to the lateral parabrachial nucleus (LPBN). Acute inhibition of MVePC-LPBN circuitry abrogates motion-induced hypothermia. Finally, we show that chronic inhibition of MVePCGlu neurons prevents diet-induced obesity and improves glucose homeostasis without suppressing food intake. Overall, these findings highlight MVePCGlu neurons as a potential target for motion-sickness treatment and obesity control.

Targeting central pathway of Glucose-Dependent Insulinotropic Polypeptide, Glucagon and Glucagon-like Peptide-1 for metabolic regulation in obesity and type 2 diabetes

Obesity and type 2 diabetes are significant public health challenges that greatly impact global well-being. The development of effective therapeutic strategies has become more and more concentrated on the central nervous system and metabolic regulation. The primary pharmaceutical interventions for the treatment of obesity and uncontrolled hyperglycemia are now generally considered to be incretin-based anti-diabetic treatments, particularly glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide receptor agonists. This is a result of their substantial influence on the central nervous system and the consequent effects on energy balance and glucose regulation. It is increasingly crucial to understand the neural pathways of these pharmaceuticals. The purpose of this review is to compile and present the most recent central pathways regarding glucagon-like peptide-1, glucose-dependent insulinotropic polypeptide and glucagon receptors, with a particular emphasis on central metabolic regulation.

The role of GIPR in food intake control

Glucose-dependent insulinotropic polypeptide (GIP) is one of two incretin hormones playing key roles in the control of food intake, nutrient assimilation, insulin secretion and whole-body metabolism. Recent pharmacological advances and clinical trials show that unimolecular co-agonists that target the receptors for the incretins - GIP and glucagon-like peptide 1 (GLP-1) - offer more effective treatment strategies for obesity and type 2 diabetes mellitus (T2D) compared with GLP-1 receptor (GLP1R) agonists alone, suggesting previously underappreciated roles of GIP in regulating food intake and body weight. The mechanisms by which GIP regulates energy balance remain controversial as both agonism and antagonism of the GIP receptor (GIPR) produce weight loss and improve metabolic outcomes in preclinical models. Recent studies have shown that GIPR signalling in the central nervous system (CNS), especially in regions of the brain that regulate energy balance, is essential for its action on appetite regulation. This finding has sparked interest in understanding the mechanisms by which GIP engages brain circuits to reduce food intake and body weight. In this review, we present key knowledge around the actions of GIP on food intake regulation and the potential mechanisms by which GIPR and GIPR/GLP1R agonists may regulate energy balance.

On the causes of obesity and its treatment: The end of the beginning

Over the last 30 years, our understanding of the causes of obesity has been transformed, and new, highly effective medicines for reducing weight have been developed. This remarkable progress marks an end and a beginning. By establishing that obesity is a biologic disorder amenable to scientific inquiry and rational drug development, simplistic notions about its causes and treatment should be laid to rest. The future holds the promise that additional therapeutic approaches for inducing or maintaining weight loss will be developed, and that these treatments will be tailored to different subgroups to potentially address the pathogenic mechanisms.

Central mechanisms of emesis: A role for GDF15

BACKGROUND

Nausea and emesis are ubiquitously reported medical conditions and often present as treatment side effects along with polymorbidities contributing to detrimental life-threatening outcomes, such as poor nutrition, lower quality of life, and unfavorable patient prognosis. Growth differentiation factor 15 (GDF15) is a stress response cytokine secreted by a wide variety of cell types in response to a broad range of stressors. Circulating GDF15 levels are elevated in a range of medical conditions characterized by cachexia and malaise. In recent years, GDF15 has gained scientific and translational prominence with the discovery that its receptor, GDNF family receptor α-like (GFRAL), is expressed exclusively in the hindbrain. GFRAL activation may results in profound anorexia and body weight loss, effects which have attracted interest for the pharmacological treatment of obesity.

PURPOSE

This review highlights compelling emerging evidence indicating that GDF15 causes anorexia through the induction of nausea, emesis, and food aversions, which encourage a perspective on GDF15 system function in physiology and behavior beyond homeostatic energy regulation contexts. This highlights the potential role of GDF15 in the central mediation of nausea and emesis following a variety of physiological, and pathophysiological conditions such as chemotherapy-induced emesis, hyperemesis gravidarum, and cyclic vomiting syndrome.

Insights into the neurobiology of weight loss after bariatric surgery and GLP-1R agonists

Obesity and its related complications are growing in prevalence worldwide, with increasing impact to individuals and healthcare systems alike. Currently, the leading treatment approaches for effective and sustained weight loss are bariatric surgery and gut peptide therapeutics. At a high level, both treatment strategies work by hijacking gut-brain axis signaling to reduce food intake. However, we predict that each modality has distinct neuronal mechanisms that are responsible for their success and complications. This review compares the neurobiology of feeding behavior between these two weight loss strategies via a discussion of both clinical and pre-clinical data. The most compelling evidence points to signaling within the hindbrain, hypothalamus, and reward circuits contributing to weight loss. Considerations for treatment, including differing complications between the two treatment approaches, will also be discussed. Based on the data, we pose the hypothesis that these two interventions are acting via distinct mechanisms to induce weight loss. Both interventions have variable degrees of weight loss across the patient population, thus, understanding these distinct mechanisms could help drive individualized medicine to optimize weight loss. This article is part of the Special Issue on "Food intake and feeding states".

GLP-1 receptor agonists and the risk of postoperative nausea and vomiting after laparoscopic sleeve gastrectomy: a single-center, retrospective cohort study

BACKGROUND

Whether preoperative exposure to glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are associated with postoperative nausea and vomiting (PONV) after laparoscopic sleeve gastrectomy (LSG) remains unclear.

OBJECTIVES

To investigate the association between preoperative GLP-1RAs exposure and PONV after LSG.

SETTING

University Hospital, China.

METHODS

We reviewed a retrospective cohort of patients underwent LSG between January 1, 2017, and December 30, 2021 at Nanjing Drum Tower Hospital, dividing the patients into 2 groups on the basis of whether they were exposed to GLP-1RAs preoperatively. A 1:1 propensity score matching was performed to balance the characteristics between the groups. Associations between GLP-1RAs exposure and PONV were determined by logistic regressions.

RESULTS

A total of 564 eligible patients underwent LSG, 351 (62.2%, 95% CI 58.2-66.1) of whom had PONV. In total cohort, PONV occurred in 72(84.7%) patients exposed to GLP-1RAs preoperatively and 279 (58.2%) patients not exposed to GLP-1RAs (adjusted odds ratio 6.782, 95% confidence interval 3.307-13.907, P < .001). In the 158 matched patients, PONV occurred in 66 (83.5%) patients exposed to GLP-1RAs preoperatively and 48 (60.8%) matched patients not exposed to GLP-1RAs (adjusted odds ratio 3.830, 95% confidence interval 1.461-10.036, P = .006). Subgroup analysis by dosage forms and doses revealed a positive association between greater doses and an increased risk of PONV after LSG for both once-daily and once-weekly formulations.

CONCLUSIONS

Preoperative exposure to GLP-1RAs is associated with an increased risk of PONV in patients undergoing LSG, particularly at higher doses of exposure.

A Growth Differentiation Factor 15 Receptor Agonist in Randomized Placebo-Controlled Trials in Healthy or Obese Persons

BACKGROUND

Growth differentiation factor 15 (GDF15), a divergent member of the TGF-β superfamily, signals via the hindbrain glial-derived neurotrophic factor receptor alpha-like and rearranged during transfection receptor co-receptor (GFRAL-RET) complex. In nonclinical species, GDF15 is a potent anorexigen leading to substantial weight loss. MBL949 is a half-life extended recombinant human GDF15 dimer.

METHODS

MBL949 was evaluated in multiple nonclinical species, and then in humans, in 2 randomized and placebo-controlled clinical trials. In the phase 1, first-in-human, single ascending dose trial, MBL949 or placebo was injected subcutaneously to overweight and obese healthy volunteers (n = 65) at doses ranging from 0.03 to 20 mg. In phase 2, MBL949 or placebo was administered subcutaneously every other week for a total of 8 doses to obese participants (n = 126) in 5 different dose regimens predicted to be efficacious based on data from the phase 1 trial.

RESULTS

In nonclinical species, MBL949 was generally safe and effective with reduced food intake and body weight in mice, rats, dogs, and monkeys. Weight loss was primarily from reduced fat, and metabolic endpoints improved. A single ascending dose study in overweight or obese healthy adults demonstrated mean terminal half-life of 18 to 22 days and evidence of weight loss at the higher doses. In the phase 2, weight loss was minimal following biweekly dosing of MBL949 for 14 weeks. MBL949 was safe and generally tolerated in humans over the dose range tested, adverse events of the gastrointestinal system were the most frequent observed.

CONCLUSION

The prolonged half-life of MBL949 supports biweekly dosing in patients. MBL949 had an acceptable safety profile. The robust weight loss observed in nonclinical species did not translate to weight loss efficacy in humans.

Integration of Glucagon-Like Peptide 1 Receptor Actions Through the Central Amygdala

Understanding the detailed mechanism of action of glucagon-like peptide 1 receptor (GLP-1R) agonists on distinct topographic and genetically defined brain circuits is critical for improving the efficacy and mitigating adverse side effects of these compounds. In this mini-review, we propose that the central nucleus of the amygdala (CeA) is a critical mediator of GLP-1R agonist-driven hypophagia. Here, we review the extant literature demonstrating CeA activation via GLP-1R agonists across multiple species and through multiple routes of administration. The precise role of GLP-1Rs within the CeA is unclear but the site-specific GLP-1Rs may mediate distinct behavioral and physiological hallmarks of GLP-1R agonists on food intake. Thus, we propose important novel directions and methods to test the role of the CeA in mediating GLP-1R actions.

Neural pathways of nausea and roles in energy balance

Our internal sensory systems encode various gut-related sensations, such as hunger, feelings of fullness, and nausea. These internal feelings influence our eating behaviors and play a vital role in regulating energy balance. Among them, the neurological basis for nausea has been the least well characterized, which has hindered comprehension of the connection between these sensations. Single-cell sequencing, along with functional mapping, has brought clarity to the neural pathways of nausea involving the brainstem area postrema. In addition, the newly discovered nausea sensory signals have deepened our understanding of the area postrema in regulating feeding behaviors. Nausea has significant clinical implications, especially in developing drugs for weight loss and metabolism. This review summarizes recent research on the neural pathways of nausea, particularly highlighting their contribution to energy balance.

Novel neural pathways targeted by GLP-1R agonists and bariatric surgery

The glucagon-like peptide 1 receptor (GLP-1R) agonist semaglutide has revolutionized the treatment of obesity, with other gut hormone-based drugs lined up that show even greater weight-lowering ability in obese patients. Nevertheless, bariatric surgery remains the mainstay treatment for severe obesity and achieves unparalleled weight loss that generally stands the test of time. While their underlying mechanisms of action remain incompletely understood, it is clear that the common denominator between GLP-1R agonists and bariatric surgery is that they suppress food intake by targeting the brain. In this Review, we highlight recent preclinical studies using contemporary neuroscientific techniques that provide novel concepts in the neural control of food intake and body weight with reference to endogenous GLP-1, GLP-1R agonists, and bariatric surgery. We start in the periphery with vagal, intestinofugal, and spinal sensory nerves and then progress through the brainstem up to the hypothalamus and finish at non-canonical brain feeding centers such as the zona incerta and lateral septum. Further defining the commonalities and differences between GLP-1R agonists and bariatric surgery in terms of how they target the brain may not only help bridge the gap between pharmacological and surgical interventions for weight loss but also provide a neural basis for their combined use when each individually fails.

Roles for Prlhr/GPR10 and Npffr2/GPR74 in feeding responses to PrRP

OBJECTIVE

Several groups of neurons in the NTS suppress food intake, including Prlh-expressing neurons (NTSPrlh cells). Not only does the artificial activation of NTSPrlh cells decrease feeding, but also the expression of Prlh (which encodes the neuropeptide PrRP) and neurotransmission by NTSPrlh neurons contributes to the restraint of food intake and body weight, especially in animals fed a high fat diet (HFD). We set out to determine roles for putative PrRP receptors in the response to NTS PrRP and exogenous PrRP-related peptides.

METHODS

We used animals lacking PrRP receptors GPR10 and/or GPR74 (encoded by Prlhr and Npffr2, respectively) to determine roles for each in the restraint of food intake and body weight by the increased expression of Prlh in NTSPrlh neurons (NTSPrlhOX mice) and in response to the anorectic PrRP analog, p52.

RESULTS

Although Prlhr played a crucial role in the restraint of food intake and body weight in HFD-fed control animals, the combined absence of Prlhr and Npffr2 was required to abrogate the restraint of food intake in NTSPrlhOX mice. p52 suppressed feeding independently of both receptors, however.

CONCLUSIONS

Hence, each receptor can participate in the NTSPrlh-mediated suppression of food intake and body weight gain, while PrRP analog treatment can mediate its effects via distinct systems. While Prlhr plays a crucial role in the physiologic restraint of weight gain, the action of either receptor is capable of ameliorating obesity in response to enhanced NTSPrlh signaling.

Mechanosensation of the heart and gut elicits hypometabolism and vigilance in mice

Interoception broadly refers to awareness of one's internal milieu. Although the importance of the body-to-brain communication that underlies interoception is implicit, the vagal afferent signalling and corresponding brain circuits that shape perception of the viscera are not entirely clear. Here, we use mice to parse neural circuits subserving interoception of the heart and gut. We determine that vagal sensory neurons expressing the oxytocin receptor (Oxtr), referred to as NGOxtr, send projections to cardiovascular or gastrointestinal tissues and exhibit molecular and structural features indicative of mechanosensation. Chemogenetic excitation of NGOxtr decreases food and water consumption, and remarkably, produces a torpor-like phenotype characterized by reductions in cardiac output, body temperature and energy expenditure. Chemogenetic excitation of NGOxtr also creates patterns of brain activity associated with augmented hypothalamic-pituitary-adrenal axis activity and behavioural indices of vigilance. Recurrent excitation of NGOxtr suppresses food intake and lowers body mass, indicating that mechanosensation of the heart and gut can exert enduring effects on energy balance. These findings suggest that the sensation of vascular stretch and gastrointestinal distention may have profound effects on whole-body metabolism and, possibly, mental health.

A single dorsal vagal complex circuit mediates the aversive and anorectic responses to GLP1R agonists

GLP-1 receptor agonists (GLP1RAs) effectively reduce feeding to treat obesity, although nausea and other aversive side effects of these drugs can limit their use. Brainstem circuits that promote satiation and that mediate the physiologic control of body weight can be distinguished from those that cause aversion. It remains unclear whether brainstem Glp1r neurons contribute to the normal regulation of energy balance and whether GLP1RAs control appetite via circuits distinct from those that mediate aversive responses, however. Hence, we defined roles for AP and NTS Glp1r-expressing neurons (APGlp1r and NTSGlp1r neurons, respectively) in the physiologic control of body weight, the GLP1RA-dependent suppression of food intake, and the GLP1RA-mediated stimulation of aversive responses. While silencing non-aversive NTSGlp1r neurons interfered with the physiologic restraint of feeding and body weight, restoring NTSGlp1r neuron Glp1r expression on an otherwise Glp1r-null background failed to enable long-term body weight suppression by GLP1RAs. In contrast, selective Glp1r expression in APGlp1r neurons restored both aversive responses and long-term body weight suppression by GLP1RAs. Thus, while non-aversive NTSGlp1r neurons control physiologic feeding, aversive APGlp1r neurons mediate both the anorectic and weight loss effects of GLP1RAs, dictating the functional inseparability of these pharmacologic GLP1RA responses at a circuit level.

A Cross-Species Atlas of the Dorsal Vagal Complex Reveals Neural Mediators of Cagrilintide's Effects on Energy Balance

Amylin analogs, including potential anti-obesity therapies like cagrilintide, act on neurons in the brainstem dorsal vagal complex (DVC) that express calcitonin receptors (CALCR). These receptors, often combined with receptor activity-modifying proteins (RAMPs), mediate the suppression of food intake and body weight. To understand the molecular and neural mechanisms of cagrilintide action, we used single-nucleus RNA sequencing to define 89 cell populations across the rat, mouse, and non-human primate caudal brainstem. We then integrated spatial profiling to reveal neuron distribution in the rat DVC. Furthermore, we compared the acute and long-term transcriptional responses to cagrilintide across DVC neurons of rats, which exhibit strong cagrilintide responsiveness, and mice, which respond poorly to cagrilintide over the long term. We found that cagrilintide promoted long-term transcriptional changes, including increased prolactin releasing hormone (Prlh) expression, in the nucleus of the solitary tract (NTS) Calcr/Prlh cells in rats, but not in mice, suggesting the importance of NTS Calcr/Prlh cells for sustained weight loss. Indeed, activating rat area postrema Calcr cells briefly reduced food intake but failed to decrease food intake or body weight over the long term. Overall, these results not only provide a cross-species and spatial atlas of DVC cell populations but also define the molecular and neural mediators of acute and long-term cagrilintide action.

GLP-1 and the Neurobiology of Eating Control: Recent Advances

Obesity is now considered a chronic relapsing progressive disease, associated with increased all-cause mortality that scales with body weight, affecting more than 1 billion people worldwide. Excess body fat is strongly associated with excess energy intake, and most successful anti-obesity medications (AOMs) counter this positive energy balance through the suppression of eating to drive weight loss. Historically, AOMs have been characterized by modest weight loss and side effects which are compliance-limiting, and in some cases life-threatening. However, the field of obesity pharmacotherapy has now entered a new era of AOMs based on analogues of the gut hormone and neuropeptide glucagon-like peptide-1 (GLP-1). The latest versions of these drugs elicit unprecedented levels of weight loss in clinical trials, which are now starting to be substantiated in real-world usage. Notably, these drugs reduce weight primarily by reducing energy intake, via activation of the GLP-1 receptor on multiple sites of action primarily in the central nervous system, although the most relevant sites of action, and the neural circuits recruited remain contentious. Here we provide a targeted synthesis of recent developments in the field of GLP-1 neurobiology, highlighting studies which have advanced our understanding of how GLP-1 signaling modulates eating, and identify open questions and future challenges we believe still need to be addressed to aid the prevention and/or treatment of obesity.

Brainstem BDNF neurons are downstream of GFRAL/GLP1R signalling

Growth differentiation factor 15, GDF15, and glucagon-like peptide-1 (GLP-1) analogues act through brainstem neurons that co-localise their receptors, GDNF-family receptor α-like (GFRAL) and GLP1R, to reduce food intake and body weight. However, their use as clinical treatments is partially hampered since both can also induce sickness-like behaviours, including aversion, that are mediated through a well-characterised pathway via the exterolateral parabrachial nucleus. Here, in mice, we describe a separate pathway downstream of GFRAL/GLP1R neurons that involves a distinct population of brain-derived neurotrophic factor (BDNF) cells in the medial nucleus of the tractus solitarius. Thus, BDNFmNTS neurons are required for the weight-reducing actions of both GDF15 and the GLP1RA, Exendin-4. Moreover, acute activation of BDNFmNTS neurons is sufficient to reduce food intake and drive fatty acid oxidation and might provide a route for longer-term weight loss.

Systematic druggable genome-wide Mendelian randomization identifies therapeutic targets for hyperemesis gravidarum

BACKGROUND

Hyperemesis gravidarum (HG), excessive vomiting in pregnancy, occurs in 0.3-10.8% of pregnancies and is associated with maternal and fetal morbidity. Despite the existence of several off-label treatment options that have shown clinical effectiveness in managing HG symptoms, the variability in treatment response highlights the need for more effective therapies. Our study aims to identify novel therapeutic targets that could lead to the development of additional, more effective treatment options.

METHODS

A two-sample Mendelian randomization (MR) analysis was performed to estimate the causal effects of blood-druggable genes on HG. Summary statistics for HG were obtained from the FinnGen study and UK Biobank. Cis-expression quantitative trait loci (cis-eQTL) for blood druggable genes were obtained from the eQTLGen Consortium and used as genetic instrumental variables. Another MR method, summary level mendelian randomization (SMR), was used to further confirm our results. We also used eQTL data of other vomiting-related tissues, brain regions, and esophagus, to validate our MR results. Finally, the potential side effects of the druggable genes for HG treatment were assessed using a phenome-wide MR.

RESULTS

Overall, 2499 unique druggable genes were gathered. Two blood drug targets (OVGP1 and LGALS1) showed significant MR results in two independent datasets. No significant heterogeneity of instrumental variables or pleiotropy was detected. In addition, SMR analysis further confirmed the significance of these two prior druggable genes in the brain and esophagus tissues. Further phenome-wide MR analysis revealed no association between genetic proxies of OVGP1, and LGALS1 has been detected in increasing the risk of adverse pregnancy outcomes and other common diseases.

CONCLUSIONS

This study provides genetic evidence that targeting two druggable genes for HG has potential therapeutic advantages. This information is of considerable value in guiding and prioritizing the development of more effective therapies for HG.

Growth hormone secretagogue receptor and cannabinoid receptor type 1 intersection in the mouse brain

The growth hormone secretagogue receptor (GHSR) and the cannabinoid receptor type 1 (CB1R) are G-protein coupled receptors highly expressed in the brain and involved in critical regulatory processes, such as energy homeostasis, appetite control, reward, and stress responses. GHSR mediates the effects of both ghrelin and liver-expressed antimicrobial peptide 2, while CB1R is targeted by cannabinoids. Strikingly, both receptors mediate their effects by acting on common brain areas and their individual roles have been well characterized. However, the potential for their co-expression in the same neuronal subsets remains largely unexplored. Here, we aim to map the cell populations where GHSR and CB1R might converge, hypothesizing that their co-expression in specific brain circuits could mediate integrated physiological responses. By utilizing two complementary labeling techniques-GHSR-eGFP mice and Fr-ghrelin labeling of GHSR+ cells-along with specific CB1R immunostaining, we sought to visualize and quantify potential areas of overlap. Also, we analyzed several cell RNA sequencing datasets to estimate the fraction of brain cells expressing both GPCRs and their phenotype. Our neuroanatomical studies revealed evident overlap of GHSR+ and CB1R+ signals in specific neuronal subsets mainly located in the cerebral cortex, hippocampus and the amygdala. Transcriptomic analysis revealed specific subsets of Ghsr+/Cnr1+ glutamatergic neurons in the hippocampus and amygdala, as well as different subtypes of Ghsr+/Cnr1+ neurons in the midbrain, hypothalamus, pons, and medulla. Thus, we revealed that GHSR and CB1R interact differentially across specific regions of the mouse brain, providing new insights into how these receptors' actions are integrated. Current findings may open new avenues for dual therapeutic interventions in metabolic disorders, obesity, and psychiatric conditions.

Beyond classical immunity: Mast cells as signal converters between tissues and neurons

Mast cells are regarded as effectors in immune defense against parasites and venoms and play an essential role in the pathology of allergic diseases. More recently, mast cells have been shown to receive stimuli derived from type 2 immunity, tissue damage, stress, and inflammation. Mast cells then rapidly convert these diverse signals into appropriate, organ-specific protective reflexes that can limit inflammation or reduce tissue damage. In this review, we consider functions of mast cells in sensations-such as pain, itch, and nausea-arising from tissue insults and inflammation and the ensuing protective responses. In light of emerging data highlighting the involvement of mast cells in neuroimmune communication, we also propose that mast cells are "signal converters" linking immunological and tissue states with nervous system responses.

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.

From Mammals to Insects: Exploring the Genetic and Neural Basis of Eating Behavior

Obesity and anorexia are life-threatening diseases that are still poorly understood at the genetic and neuronal levels. Patients suffering from these conditions experience disrupted regulation of food consumption, leading to extreme weight gain or loss and, in severe situations, death from metabolic dysfunction. Despite the development of various behavioral and pharmacological interventions, current treatments often yield limited and short-lived success. To address this, a deeper understanding of the genetic and neural mechanisms underlying food perception and appetite regulation is essential for identifying new drug targets and developing more effective treatment methods. This review summarizes the progress of past research in understanding the genetic and neural mechanisms controlling food consumption and appetite regulation, focusing on two key model organisms: the fruit fly Drosophila melanogaster and the mouse Mus musculus. These studies investigate how the brain senses energy and nutrient deficiency, how sensory signals trigger appetitive behaviors, and how food intake is regulated through interconnected neural circuits in the brain.

Loss of Calcitonin Gene Related Receptor component protein (RCP) in nervous system can bias "gepant" antagonism

We examined calcitonin gene-related peptide (CGRP)'s effects on behavioral surrogates for motion-induced nausea and static imbalance in the nestinRCP (-/-), a novel mouse model that loses expression of receptor component protein (RCP) in the nervous system after tamoxifen induction. The assays used were the motion-induced thermoregulation and center of pressure (CoP) assays. Findings suggest CGRP's affects behavioral measures in the nestinRCP (-/-) similarly to littermate controls, since CGRP was observed to increase female sway and diminishes tail vasodilations to provocative motion in both sexes. However, the CGRP-receptor antagonist olcegepant did not antagonize CGRP's effects in the nestinRCP (-/-), whereas it was effective in littermate controls. Findings suggest RCP loss may change the sensitivity of the CGRP receptor and affect the efficacy of receptor antagonists.

Significance Statement

Research in calcitonin gene-related peptide (CGRP) has primarily focused on ligand- receptor interactions at the calcitonin-like receptor (CLR) and receptor activity-modifying unit 1 (RAMP1) subunits. However, the role of receptor component protein (RCP), which mediates signaling via the Gα-stimulatory pathway, is less understood. A novel tamoxifen-inducible mouse model, nestinRCP (-/-), was generated to study loss of RCP in CGRP signaling in the nervous system, and behavioral changes to motion-induced nausea and postural sway were studied after systemic injections of CGRP or CGRP co-delivered with migraine drugs. Findings from this study suggest the loss of CGRP-RCP can bias "gepant" antagonists like olcegepant, and may promote development of therapies to inhibit the RCP-CLR interactions.

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.

GLP-1 physiology in obesity and development of incretin-based drugs for chronic weight management

The introduction of the highly potent incretin receptor agonists semaglutide and tirzepatide has marked a new era in the treatment of type 2 diabetes and obesity. With normalisation of glycated haemoglobin levels and weight losses around 15-25%, therapeutic goals that were previously unrealistic are now within reach, and clinical trials have documented that these effects are associated with reduced risk of cardiovascular events and premature mortality. Here, I review this remarkable development from the earliest observations of glucose lowering and modest weight losses with native glucagon-like peptide (GLP)-1 and short acting compounds, to the recent development of highly active formulations and new molecules. I will classify these agents as GLP-1-based therapies in the understanding that these compounds or combinations may have actions on other receptors as well. The physiology of GLP-1 is discussed as well as its mechanisms of actions in obesity, in particular, the role of sensory afferents and GLP-1 receptors in the brain. I provide details regarding the development of GLP-1 receptor agonists for anti-obesity therapy and discuss the possible mechanism behind their beneficial effects on adverse cardiovascular events. Finally, I highlight new pharmacological developments, including oral agents, and discuss important questions regarding maintenance therapy.

Licking microstructure in response to novel rewards, reward devaluation and dopamine antagonists: Possible role of D1 and D2 medium spiny neurons in the nucleus accumbens

Evidence on the effect of dopamine D1 and D2-like antagonists and of manipulations of reward value on licking microstructure is reanalysed considering recent findings on the role of nucleus accumbens (NAc) medium spiny neurons (MSNs) in the control of sugar intake. The results of this analysis suggest that D1 MSN activation, which is involved in the emission of licking bursts, might play a crucial role in response to novel rewards. D2 MSN activation, which results in reduction of burst size and suppression of licking, might mediate the response to reward devaluation. Elucidating the neural mechanisms underlying the licking response might lead to a better definition of its microstructural measures in behaviourally and psychologically meaningful functional terms. This could further support its use as a behavioural substrate in the study of the neural mechanisms of ingestive behaviour and motivation, as well as in animal models of pathological conditions such as eating disorders and obesity.

A neural mechanism for learning from delayed postingestive feedback

Animals learn the value of foods based on their postingestive effects and thereby develop aversions to foods that are toxic1-6 and preferences to those that are nutritious7-14. However, it remains unclear how the brain is able to assign credit to flavors experienced during a meal with postingestive feedback signals that can arise after a substantial delay. Here, we reveal an unexpected role for postingestive reactivation of neural flavor representations in this temporal credit assignment process. To begin, we leverage the fact that mice learn to associate novel15-18, but not familiar, flavors with delayed gastric malaise signals to investigate how the brain represents flavors that support aversive postingestive learning. Surveying cellular resolution brainwide activation patterns reveals that a network of amygdala regions is unique in being preferentially activated by novel flavors across every stage of the learning process: the initial meal, delayed malaise, and memory retrieval. By combining high-density recordings in the amygdala with optogenetic stimulation of genetically defined hindbrain malaise cells, we find that postingestive malaise signals potently and specifically reactivate amygdalar novel flavor representations from a recent meal. The degree of malaise-driven reactivation of individual neurons predicts strengthening of flavor responses upon memory retrieval, leading to stabilization of the population-level representation of the recently consumed flavor. In contrast, meals without postingestive consequences degrade neural flavor representations as flavors become familiar and safe. Thus, our findings demonstrate that interoceptive reactivation of amygdalar flavor representations provides a neural mechanism to resolve the temporal credit assignment problem inherent to postingestive learning.

Refractory singultus and area postrema syndrome as a presentation of neurocysticercosis

Neurocysticercosis (NCC) is the most common parasitic infection of the central nervous system, caused by the pork tapeworm, Taenia solium Common presenting features are seizures, headaches and focal neurodeficits. The present report details the anecdote of a middle-aged Asian man, who presented with subacute onset of persistent nausea, vomiting and hiccups. Following unsuccessful trials with numerous prokinetic, antipsychotic, muscle relaxant and anticonvulsant medications, as well as an uneventful battery of gastrointestinal tests, he was referred for neurological evaluation. The constellation of symptoms was congruent with the diagnosis of area postrema syndrome. Although initial CT scan of brain was normal, MRI with contrast evaluation revealed a circumscribed, ring-enhancing lesion of the dorsal medulla oblongata, reminiscent of colloid vesicular stage of NCC. The patient was successfully treated with steroids and albendazole. The association of refractory singultus, nausea and vomiting and NCC is thus far, not reported in the literature.

Sensory sentinels: Neuroimmune detection and food allergy

Food allergy is classically characterized by an inappropriate type-2 immune response to allergenic food antigens. However, how allergens are detected and how that detection leads to the initiation of allergic immunity is poorly understood. In addition to the gastrointestinal tract, the barrier epithelium of the skin may also act as a site of food allergen sensitization. These barrier epithelia are densely innervated by sensory neurons, which respond to diverse physical environmental stimuli. Recent findings suggest that sensory neurons can directly detect a broad array of immunogens, including allergens, triggering sensory responses and the release of neuropeptides that influence immune cell function. Reciprocally, immune mediators modulate the activation or responsiveness of sensory neurons, forming neuroimmune feedback loops that may impact allergic immune responses. By utilizing cutaneous allergen exposure as a model, this review explores the pivotal role of sensory neurons in allergen detection and their dynamic bidirectional communication with the immune system, which ultimately orchestrates the type-2 immune response. Furthermore, it sheds light on how peripheral signals are integrated within the central nervous system to coordinate hallmark features of allergic reactions. Drawing from this emerging evidence, we propose that atopy arises from a dysregulated neuroimmune circuit.

Parabrachial neurons promote nociplastic pain

The parabrachial nucleus (PBN) in the dorsal pons responds to bodily threats and transmits alarm signals to the forebrain. Parabrachial neuron activity is enhanced during chronic pain, and inactivation of PBN neurons in mice prevents the establishment of neuropathic, chronic pain symptoms. Chemogenetic or optogenetic activation of all glutamatergic neurons in the PBN, or just the subpopulation that expresses the Calca gene, is sufficient to establish pain phenotypes, including long-lasting tactile allodynia, that scale with the extent of stimulation, thereby promoting nociplastic pain, defined as diffuse pain without tissue inflammation or nerve injury. This review focuses on the role(s) of molecularly defined PBN neurons and the downstream nodes in the brain that contribute to establishing nociplastic pain.

Regulation of Energy and Glucose Homeostasis by the Nucleus of the Solitary Tract and the Area Postrema

The central nervous system regulates feeding, weight and glucose homeostasis in rodents and humans, but the site-specific mechanisms remain unclear. The dorsal vagal complex in the brainstem that contains the nucleus of the solitary tract (NTS) and area postrema (AP) emerges as a regulatory center that impacts energy and glucose balance by monitoring hormonal and nutrient changes. However, the specific mechanistic metabolic roles of the NTS and AP remain elusive. This mini-review highlights methods to study their distinct roles and recent findings on their metabolic differences and similarities of growth differentiation factor 15 (GDF15) action and glucose sensing in the NTS and AP. In summary, future research aims to characterize hormonal and glucose sensing mechanisms in the AP and/or NTS carries potential to unveil novel targets that lower weight and glucose levels in obesity and diabetes.

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.

Overview of growth differentiation factor 15 (GDF15) in metabolic diseases

GDF15 is a stress response cytokine and a distant member of the transforming growth factor beta (TGFβ) superfamily, its levels increase in response to cell stress and certain diseases in the serum. To exert its effects, GDF15 binds to glial-derived neurotrophic factor (GDNF) receptor alpha-like (GFRAL), which was firstly identified in 2017 and highly expressed in the brain stem. Many studies have demonstrated that elevated serum GDF15 is associated with anorexia and weight loss. Herein, we focus on the biology of GDF15, specifically how this circulating protein regulates appetite and metabolism in influencing energy homeostasis through its actions on hindbrain neurons to shed light on its impact on diseases such as obesity and anorexia/cachexia syndromes. It works as an endocrine factor and transmits metabolic signals leading to weight reduction effects by directly reducing appetite and indirectly affecting food intake through complex mechanisms, which could be a promising target for the treatment of energy-intake disorders.

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.

A neurofunctional signature of subjective disgust generalizes to oral distaste and socio-moral contexts

While disgust originates in the hard-wired mammalian distaste response, the conscious experience of disgust in humans strongly depends on subjective appraisal and may even extend to socio-moral contexts. Here, in a series of studies, we combined functional magnetic resonance imaging with machine-learning-based predictive modelling to establish a comprehensive neurobiological model of subjective disgust. The developed neurofunctional signature accurately predicted momentary self-reported subjective disgust across discovery (n = 78) and pre-registered validation (n = 30) cohorts and generalized across core disgust (n = 34 and n = 26), gustatory distaste (n = 30) and socio-moral (unfair offers; n = 43) contexts. Disgust experience was encoded in distributed cortical and subcortical systems, and exhibited distinct and shared neural representations with subjective fear or negative affect in interoceptive-emotional awareness and conscious appraisal systems, while the signatures most accurately predicted the respective target experience. We provide an accurate functional magnetic resonance imaging signature for disgust with a high potential to resolve ongoing evolutionary debates.

Whole-brain inputs and outputs of Phox2b and GABAergic neurons in the nucleus tractus solitarii

The nucleus tractus solitarii (NTS) plays a critical role in the homeostatic regulation of respiration, blood pressure, sodium consumption and metabolic processes. Despite their significance, the circuitry mechanisms facilitating these diverse physiological functions remain incompletely understood. In this study, we present a whole-brain mapping of both the afferent and efferent connections of Phox2b-expressing and GABAergic neurons within the NTS. Our findings reveal that these neuronal populations not only receive monosynaptic inputs primarily from the medulla oblongata, pons, midbrain, supra-midbrain and cortical areas, but also mutually project their axons to these same locales. Moreover, intense monosynaptic inputs are received from the central amygdala, the paraventricular nucleus of the hypothalamus, the parasubthalamic nucleus and the intermediate reticular nucleus, along with brainstem nuclei explicitly engaged in respiratory regulation. In contrast, both neuronal groups extensively innervate brainstem nuclei associated with respiratory functions, although their projections to regions above the midbrain are comparatively limited. These anatomical findings provide a foundational platform for delineating an anatomical framework essential for dissecting the specific functional mechanisms of these circuits.

Mapping of afferent and efferent connections of phenylethanolamine N-methyltransferase-expressing neurons in the nucleus tractus solitarii

OBJECTIVE

Phenylethanolamine N-methyltransferase (PNMT)-expressing neurons in the nucleus tractus solitarii (NTS) contribute to the regulation of autonomic functions. However, the neural circuits linking these neurons to other brain regions remain unclear. This study aims to investigate the connectivity mechanisms of the PNMT-expressing neurons in the NTS (NTSPNMT neurons).

METHODS

The methodologies employed in this study included a modified rabies virus-based retrograde neural tracing technique, conventional viral anterograde tracing, and immunohistochemical staining procedures.

RESULTS

A total of 43 upstream nuclei projecting to NTSPNMT neurons were identified, spanning several key brain regions including the medulla oblongata, pons, midbrain, cerebellum, diencephalon, and telencephalon. Notably, dense projections to the NTSPNMT neurons were observed from the central amygdaloid nucleus, paraventricular nucleus of the hypothalamus, area postrema, and the gigantocellular reticular nucleus. In contrast, the ventrolateral medulla, lateral parabrachial nucleus, and lateral hypothalamic area were identified as the primary destinations for axon terminals originating from NTSPNMT neurons. Additionally, reciprocal projections were evident among 21 nuclei, primarily situated within the medulla oblongata.

CONCLUSION

Our research findings demonstrate that NTSPNMT neurons form extensive connections with numerous nuclei, emphasizing their essential role in the homeostatic regulation of vital autonomic functions.

The role of glucagon-like peptide-1 receptor agonists in metabolic dysfunction-associated steatohepatitis

Despite its considerable and growing burden, there are currently no Food and Drug Administration-approved treatments for metabolic dysfunction-associated steatotic liver disease or its progressive form, metabolic dysfunction-associated steatohepatitis (MASH). Several glucagon-like peptide-1 receptor agonists (GLP-1RAs) and other agents are in various phases of clinical development for use in MASH; an ideal therapy should reduce liver fat content, improve chronic liver disease, help mitigate metabolic comorbidities and decrease all-cause mortality. Because of interconnected disease mechanisms, metabolic dysfunction-associated steatotic liver disease/MASH often coexists with type 2 diabetes (T2D), obesity and cardiovascular disease. Various GLP-1RAs are Food and Drug Administration-approved for use in T2D, and two, liraglutide and semaglutide, are approved for overweight and obesity. GLP-1RAs decrease glucose levels and body weight and improve cardiovascular outcomes in people with T2D who are at high risk of cardiovascular disease. In addition, GLP-1RAs have been reported to reduce liver fat content and liver enzymes, reduce oxidative stress and improve hepatic de novo lipogenesis and the histopathology of MASH. Weight loss may contribute to these effects; however, the exact mechanisms are unknown. Adverse events that are commonly associated with GLP-1RAs include vomiting, nausea and diarrhoea. There is a lack of evidence from meta-analyses regarding the increased risk of acute pancreatitis and various forms of cancer with GLP-1RAs. Large-scale, phase 3 trials, which will provide definitive data on GLP-1RAs and other potential therapies in MASH, are ongoing. Given the spectrum of modalities under investigation, it is hoped that these trials will support the identification of pharmacotherapies that provide clinical benefit for patients with MASH.

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.