Endogenous Glucagon-like Peptide-1 Suppresses High-Fat Food Intake by Reducing Synaptic Drive onto Mesolimbic Dopamine Neurons

Time-restricted feeding promotes glucagon-like peptide-1 secretion and regulates appetite via tryptophan metabolism of gut Lactobacillus in pigs

Previous clinical trials have shown that time-restricted feeding can be involved in regulating the metabolic health of humans and animals. However, the underlying mechanism has not been fully explored. In this study, the pig model was employed to simulate four prevalent human eating habits, with the aim of investigating the impact of gut microbiota and microbial metabolites on gut hormone secretion and appetite regulation. Compared to the ad libitum feeding (ALF) pattern, three time-restricted feeding patterns reduced total food intake and eating time. Meanwhile, three time-restricted feeding patterns induced elevated levels of serum and hypothalamic glucagon-like peptide-1 (GLP-1), while suppressing reward-related circuits in the hypothalamus. It is noteworthy that the early time-restricted feeding (eTRF) pattern increased the number of intestinal enteroendocrine cells (EECs) compared to ALF. Metagenomic and metabonomic analyses revealed that three time-restricted feeding patterns induced colonization of Lactobacillus and significantly increased the levels of its metabolite, indole-3-lactic acid (ILA). Dietary supplementation with ILA exhibited an increasing trend in fasting serum GLP-1 level of piglets. In vitro studies with pig intestinal organoids showed the Lactobacillus metabolite ILA enhanced GLP-1 secretion through the promotion of intestinal stem cell differentiation into EECs, rather than activating the ability of EECs to secrete GLP-1. Overall, time-restricted feeding promoted GLP-1 secretion and affected long-term appetite regulation by promoting the colonization of Lactobacillus and modulating microbial tryptophan metabolism.

The Enteric Neuronal Circuitry: A Key Ignored Player in Nutrient Sensing Along the Gut-Brain Axis

The role of the gut-to-brain axis in the regulation of nutrient sensing has been studied extensively for decades. Research has mainly centered on vagal afferent and efferent neurotransmission along the gastrointestinal tract, followed by the integration of luminal information in the nodose ganglia and transmission to vagal integral sites in the brain. The physiological and cellular mechanisms of nutrient sensing by enterocytes and enteroendocrine cells have been well established; however, the roles of the enteric nervous system (ENS) remain elusive. Recent advances in targeting specific neuronal subpopulations and imaging techniques unravel the plausible roles of the ENS in nutrient sensing. In this review, we highlight physiological, cellular, and molecular insights that direct toward direct and indirect roles of the ENS in luminal nutrient sensing and vagal neurotransmission along the gut-brain axis and discuss functional maladaptations observed during metabolic insults, as observed during obesity and associated comorbidities, including type 2 diabetes.

The Interplay Between Psychological and Neurobiological Predictors of Weight Regain: A Narrative Review

Introduction: Obesity is a global health problem requiring effective interventions to achieve weight loss and maintain it in the long term. A major challenge for clinicians is weight regain (WR), defined as progressive weight gain following successful weight loss. WR is affected by multiple factors, including psychological traits linked to specific brain alterations. Understanding these mechanisms is crucial in developing strategies to prevent WR and to ensure effective weight control. Objectives: This narrative review aims to gather current findings on the psychological and neurobiological determinants of WR and to discuss the interplay between these factors. Methods: A literature search was conducted on PubMed, Medline, and Web of Science for English-language studies published between December 1990 and November 2024. Results: WR is driven by interconnected psychological and neurobiological factors that influence eating behavior and the regulation of body weight. Certain personality traits and emotional patterns are associated with specific changes in brain activity, which together affect vulnerability to WR. Although distinct mechanisms can be identified, the complexity of homeostatic and nonhomeostatic appetite control suggests that no single factor predominates. Conclusions: This review highlights the dynamic interplay between psychological and neurobiological predictors of WR. However, due to the narrative nature of this review, the focus on selected determinants, and the limited quality and size of the available studies, further research is needed to comprehensively understand causality and to improve relapse prevention strategies.

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.

Activation of GLP-1R modulates the spontaneous discharge of nigral dopaminergic neurons and motor behavior in mice with chronic MPTP Parkinson's disease

The gradual decline of nigral dopaminergic neurons is the main cause of Parkinson's disease (PD), yet as of now, there exists no conclusive therapeutic intervention. Glucagon-like peptide-1 (GLP-1) is an incretin, which is also a key substance regulating neuronal activity and synaptic transmission. GLP-1 receptors (GLP-1Rs) are widely expressed in the central nervous system. Chronic administration of low doses of 1-methyl-4-phenyl, 1,2,3,6-tetrahydropiridine (MPTP) mitigates mortality in mice during the modeling phase, thereby more closely mirroring the progression of PD. This study aims to observe the effects of GLP-1 receptor agonists (GLP-1RAs) on the firing activity of nigral dopaminergic neurons and motor behaviors in MPTP-induced chronic PD mice. Our findings revealed that peripheral administration of GLP-1RAs exendin-4 significantly alleviated motor impairments in MPTP-induced chronic PD mice. Concurrently, peripheral administration of exendin-4 increased the number of active dopaminergic neurons, improved the spontaneous firing activity, as well as alleviated MPTP-induced dopaminergic neuron loss in MPTP-induced PD mice. Furthermore, local administration of exendin-4 directly increased the firing rate of nigral dopaminergic neurons via GLP-1Rs, suggesting that peripheral administration of exendin-4 may exert neuroprotection through its mild excitation on dopaminergic neurons. These findings collectively imply that peripheral administration of GLP-1RAs may hold potential in the treatment of PD.

An accumbal microcircuit for the transition from acute to chronic pain

Persistent nociceptive inputs arising from peripheral tissues or/and nerve injuries cause maladaptive changes in neurons or neural circuits in the central nervous system, which further confer acute injury into chronic pain transitions (pain chronification) even after the injury is resolved. However, the critical brain regions and their neural mechanisms involved in this transition have not yet been elucidated. Here, we reveal an accumbal microcircuit that is essential for pain chronification. Notably, the increase of neuronal activity in the nucleus accumbens shell (NAcS) in the acute phase (<7 days) and in core (NAcC) in the chronic phase (14-21 days) was detected in a neuropathic pain mouse model. Importantly, we demonstrated that the NAcS neuronal activation in the acute phase of injury was necessary and sufficient for the development of chronic neuropathic pain. This process was mediated by the accumbal dopamine D2 receptor-expressing neuronal microcircuit from NAcS to NAcC. Thus, our findings reveal an accumbal microcircuit mechanism for pain chronification and suggest that the early intervention targeting this microcircuit may provide a therapeutic approach to pain chronification.

On the Pleiotropic Actions of Glucagon-like Peptide-1 in Its Regulation of Homeostatic and Hedonic Feeding

We examined the neuroanatomical substrates and signaling mechanisms underlying the suppressive effect of GLP1 on homeostatic and hedonic feeding. Electrophysiological and behavioral studies were conducted in agouti-related peptide (AgRP)-cre and tyrosine hydroxylase (TH)-cre mice, and AgRP-cre/pituitary adenylyl cyclase-activating polypeptide (PACAP) type I receptor (PAC1R)fl/fl animals. GLP1 (30 pmol) delivered directly into the arcuate nucleus (ARC) decreased homeostatic feeding and diminished the rate of consumption. This anorexigenic effect was associated with an inhibitory outward current in orexigenic neuropeptide Y (NPY)/AgRP neurons. GLP1 injected into the ventral tegmental area reduced binge feeding, coupled with decrements in the rate of consumption and the percent daily caloric consumption during the binge interval. These reductions were associated with a GLP1-induced outward current in mesolimbic (A10) dopamine neurons. GLP1 administered into the ventromedial nucleus (VMN) reduced homeostatic feeding that again was associated with a diminished rate of consumption and abrogated by the GLP1 receptor antagonist exendin 9-39 and in AgRP-cre/PAC1Rfl/fl mice. This suppressive effect was linked with a GLP-induced inward current in VMN PACAP neurons, and further supported by the fact that GLP1 neurons in the nucleus tractus solitarius project to the VMN. Conversely, intra-VMN GLP1 had modest effects on binge feeding behavior. Finally, apoptotic ablation of VMN PACAP neurons obliterated the anorexigenic effect of intra-VMN GLP1 on homeostatic feeding in PACAP-cre mice but not their wildtype counterparts. Collectively, these data demonstrate that GLP1 acts within the homeostatic and hedonic circuits to curb appetitive behavior by exciting PACAP neurons, and inhibiting NPY/AgRP and A10 dopamine neurons.

The neurobiology of overeating

Food intake serves to maintain energy homeostasis; however, overeating can result in obesity, which is associated with serious health complications. In this review, we explore the intricate relationship between overeating, obesity, and the underlying neurobiological mechanisms. We review the homeostatic and hedonic feeding systems, highlighting the role of the hypothalamus and reward systems in controlling food intake and energy balance. Dysregulation in both these systems leads to overeating, as seen in genetic syndromes and environmental models affecting appetite regulation when consuming highly palatable food. The concept of "food addiction" is examined, drawing parallels to drug addiction. We discuss the cellular substrate for addiction-related behavior and current pharmacological obesity treatments-in particular, GLP-1 receptor agonists-showcasing synaptic plasticity in the context of overeating and palatable food exposure. A comprehensive model integrating insights from addiction research is proposed to guide effective interventions for maladaptive feeding behaviors. Ultimately, unraveling the neurobiological basis of overeating holds promise for addressing the pressing public health issue of obesity.

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.

Comparison of Effects of Glucagon-Like Peptide-1 Receptor Agonists Compared to Long-Acting Insulin, Added to Oral Anti-Diabetic Agents on Self-Management Behaviors, Anxiety, and Sleep Quality in Patients with Type 2 Diabetes

AIM

This study aimed to investigate the impact of glucagon-like peptide-1 receptor agonists (GLP-1RAs) on individuals with type 2 diabetes (T2DM) by comparing self-management behaviors, anxiety, and sleep quality in T2DM patients.

METHODS

This is a single-center prospective study. During the patients' hospitalization, we collected their clinical data, and three months after discharge, we conducted follow-up by phone to record weight changes, blood glucose levels, self-management behaviors, anxiety levels, and sleep quality.

RESULTS

A total of 271 patients were included in this study. Among them, 177 (65.31%) were classified into the oral drug combined with long-acting insulin group, and 94 (34.69%) were classified into the oral drug combined with GLP-1RAs group. No statistically significant differences were found between the two groups in age, duration of diabetes, comorbidities, complications, or types of oral medications (P> 0.05). However, significant differences were observed between the groups in postprandial blood glucose, glycated hemoglobin, dietary control, medication adherence, actual anxiety, and sleep time (P<0.05). Notably, the oral medication combined with GLP-1RAs group demonstrated improved dietary control, medication adherence, anxiety and actual sleep time compared to the oral medication combined with long-acting insulin group.

CONCLUSION

In this 3-month study, there were statistically significant differences in HbA1c, post-prandial glucose, weight, for self-management behaviors, for dietary control, medication adherence, anxiety, and actual sleep time in T2DM patients. The findings suggest that GLP-1 RA may contribute to the improvement of dietary behaviors, medication adherence, anxiety, and sleep quality in addition to weight and glycemic control in T2DM patients.

An endogenous GLP-1 circuit engages VTA GABA neurons to regulate mesolimbic dopamine neurons and attenuate cocaine seeking

Recent studies show that systemic administration of a glucagon-like peptide-1 receptor (GLP-1R) agonist is sufficient to attenuate cocaine seeking. However, the neural mechanisms mediating these effects and the role of endogenous central GLP-1 signaling in cocaine seeking remain unknown. Here, we show that voluntary cocaine taking decreased plasma GLP-1 levels in rats and that chemogenetic activation of GLP-1-producing neurons in the nucleus tractus solitarius that project to the ventral tegmental area (VTA) decreased cocaine seeking. Single-nuclei transcriptomics and FISH studies revealed that GLP-1Rs are expressed primarily on GABA neurons in the VTA. Using in vivo fiber photometry, we found that the efficacy of a systemic GLP-1R agonist to attenuate cocaine seeking was associated with increased activity of VTA GABA neurons and decreased activity of VTA dopamine neurons. Together, these findings suggest that targeting central GLP-1 circuits may be an effective strategy toward reducing cocaine relapse and highlight a functional role of GABAergic GLP-1R-expressing midbrain neurons in drug seeking.

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.

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.

Mechanisms and pharmacotherapy of cancer cachexia-associated anorexia

Cachexia is a multifactorial metabolic syndrome characterized by weight and skeletal muscle loss caused by underlying illnesses such as cancer, heart failure, and renal failure. Inflammation, insulin resistance, increased muscle protein degradation, decreased food intake, and anorexia are the primary pathophysiological drivers of cachexia. Cachexia causes physical deterioration and functional impairment, loss of quality of life, lower response to active treatment, and ultimately morbidity and mortality, while the difficulties in tackling cachexia in its advanced phases and the heterogeneity of the syndrome among patients require an individualized and multidisciplinary approach from an early stage. Specifically, strategies combining nutritional and exercise interventions as well as pharmacotherapy that directly affect the pathogenesis of cachexia, such as anti-inflammatory, metabolism-improving, and appetite-stimulating agents, have been proposed, but none of which have demonstrated sufficient evidence to date. Nevertheless, several agents have recently emerged, including anamorelin, a ghrelin receptor agonist, growth differentiation factor 15 neutralization therapy, and melanocortin receptor antagonist, as candidates for ameliorating anorexia associated with cancer cachexia. Therefore, in this review, we outline cancer cachexia-associated anorexia and its pharmacotherapy, including corticosteroids, progesterone analogs, cannabinoids, anti-psychotics, and thalidomide which have been previously explored for their efficacy, in addition to the aforementioned novel agents, along with their mechanisms.

Glucagon-Like Peptide-1 Links Ingestion, Homeostasis, and the Heart

Glucagon-like peptide-1 (GLP-1), a hormone released from enteroendocrine cells in the distal small and large intestines in response to nutrients and other stimuli, not only controls eating and insulin release, but is also involved in drinking control as well as renal and cardiovascular functions. Moreover, GLP-1 functions as a central nervous system peptide transmitter, produced by preproglucagon (PPG) neurons in the hindbrain. Intestinal GLP-1 inhibits eating by activating vagal sensory neurons directly, via GLP-1 receptors (GLP-1Rs), but presumably also indirectly, by triggering the release of serotonin from enterochromaffin cells. GLP-1 enhances glucose-dependent insulin release via a vago-vagal reflex and by direct action on beta cells. Finally, intestinal GLP-1 acts on the kidneys to modulate electrolyte and water movements, and on the heart, where it provides numerous benefits, including anti-inflammatory, antiatherogenic, and vasodilatory effects, as well as protection against ischemia/reperfusion injury and arrhythmias. Hindbrain PPG neurons receive multiple inputs and project to many GLP-1R-expressing brain areas involved in reward, autonomic functions, and stress. PPG neuron-derived GLP-1 is involved in the termination of large meals and is implicated in the inhibition of water intake. This review details GLP-1's roles in these interconnected systems, highlighting recent findings and unresolved issues, and integrating them to discuss the physiological and pathological relevance of endogenous GLP-1 in coordinating these functions. As eating poses significant threats to metabolic, fluid, and immune homeostasis, the body needs mechanisms to mitigate these challenges while sustaining essential nutrient intake. Endogenous GLP-1 plays a crucial role in this "ingestive homeostasis."

Neuroendocrine gut-brain signaling in obesity

The past decades have witnessed the rise and fall of several, largely unsuccessful, therapeutic attempts to bring the escalating obesity pandemic to a halt. Looking back to look ahead, the field has now put its highest hopes in translating insights from how the gastrointestinal (GI) tract communicates with the brain to calibrate behavior, physiology, and metabolism. A major focus of this review is to summarize the latest advances in comprehending the neuroendocrine aspects of this so-called 'gut-brain axis' and to explore novel concepts, cutting-edge technologies, and recent paradigm-shifting experiments. These exciting insights continue to refine our understanding of gut-brain crosstalk and are poised to promote the development of additional therapeutic avenues at the dawn of a new era of antiobesity therapeutics.

Modulation of stress-related behaviour by preproglucagon neurons and hypothalamic projections to the nucleus of the solitary tract

Stress-induced behaviours are driven by complex neural circuits and some neuronal populations concurrently modulate diverse behavioural and physiological responses to stress. Glucagon-like peptide-1 (GLP-1)-producing preproglucagon (PPG) neurons within the lower brainstem caudal nucleus of the solitary tract (cNTS) are particularly sensitive to stressful stimuli and are implicated in multiple physiological and behavioural responses to interoceptive and psychogenic threats. However, the afferent inputs driving stress-induced activation of PPG neurons are largely unknown, and the role of PPG neurons in anxiety-like behaviour is controversial. Through chemogenetic manipulations we reveal that cNTS PPG neurons have the ability to moderately increase anxiety-like behaviours in mice in a sex-dependent manner. Using an intersectional approach, we show that input from the paraventricular nucleus of the hypothalamus (PVN) drives activation of both the cNTS as a whole and PPG neurons in particular in response to acute restraint stress, but that while this input is rich in corticotropin-releasing hormone (CRH), PPG neurons do not express significant levels of receptors for CRH and are not activated following lateral ventricle delivery of CRH. Finally, we demonstrate that cNTS-projecting PVN neurons are necessary for the ability of restraint stress to suppress food intake in male mice. Our findings reveal sex differences in behavioural responses to PPG neural activation and highlight a hypothalamic-brainstem pathway in stress-induced hypophagia.

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.

Potential role of glucagon-like peptide-1 (GLP-1) receptor agonists in substance use disorder: A systematic review of randomized trials

BACKGROUND

Increasing evidence suggests that GLP-1 receptor agonists (GLP-1RA) have a potential use in addiction treatment. Few studies have assessed the impact of GLP-1RA on substance use disorder (SUD), particularly in humans. The study aimed to do systematic review of clinical trials to assess GLP-1RA's effect on reducing SUD in patients.

METHODS

The scientific literature was reviewed using the MEDLINE, Scopus and Cochrane Library databases, following PRISMA guidelines. Studies including patients with a diagnosis of SU who were treated with GLP-1RA were selected. The primary outcome was GLP-1RA's therapeutic effect on SUD, and the secondary outcomes were therapeutic effects of GLP-1RA on weight, BMI and HbA1c.

RESULTS

1218 studies were retrieved, resulting in 507 papers after title and abstract screening. Following full-text review, only 5 articles met inclusion criteria. We incorporated a total of 630 participants utilizing Exenatide (n=3) and Dulaglutide (n=2) as GLP-1RAs. Therapeutic effect of GLP-1RA on SUD was assessed in 5 studies, with 3 demonstrating a significant decrease in SUD (alcohol and nicotine). GLP-1RA's impact on body weight, BMI, and HbA1c, was reported in 3 studies. These revealed a notable reduction in these parameters among the GLP-1RA treated group.

CONCLUSION

This review will give an overview of current new findings in human studies; we suggest that the effects of GLP-1RA in SUD is a possible new option of therapy in addiction medicine.

Oral Trehalose Intake Modulates the Microbiota-Gut-Brain Axis and Is Neuroprotective in a Synucleinopathy Mouse Model

Parkinson's disease (PD) is a neurodegenerative disease affecting dopaminergic neurons in the nigrostriatal and gastrointestinal tracts, causing both motor and non-motor symptoms. This study examined the neuroprotective effects of trehalose. This sugar is confined in the gut due to the absence of transporters, so we hypothesized that trehalose might exert neuroprotective effects on PD through its action on the gut microbiota. We used a transgenic mouse model of PD (PrP-A53T G2-3) overexpressing human α-synuclein and developing GI dysfunctions. Mice were given water with trehalose, maltose, or sucrose (2% w/v) for 6.5 m. Trehalose administration prevented a reduction in tyrosine hydroxylase immunoreactivity in the substantia nigra (-25%), striatum (-38%), and gut (-18%) in PrP-A53T mice. It also modulated the gut microbiota, reducing the loss of diversity seen in PrP-A53T mice and promoting bacteria negatively correlated with PD in patients. Additionally, trehalose treatment increased the intestinal secretion of glucagon-like peptide 1 (GLP-1) by 29%. Maltose and sucrose, which break down into glucose, did not show neuroprotective effects, suggesting glucose is not involved in trehalose-mediated neuroprotection. Since trehalose is unlikely to cross the intestinal barrier at the given dose, the results suggest its effects are mediated indirectly through the gut microbiota and GLP-1.

Glucagon-like peptide 1 agonist and effects on reward behaviour: A systematic review

INTRODUCTION

The roles of metabolic signals, including Glucagon-like peptide 1 (GLP-1), have been implicated in multiple domains outside metabolic regulation. There is a growing interest in repurposing Glucagon-like peptide 1 receptor agonists (GLP-1RAs) as therapeutics for motivation and reward-related behavioural disturbances. Herein, we aim to systematically review the extant evidence on the potential effects of GLP-1RAs on the reward system.

METHODS

The study followed PRISMA guidelines using databases such as OVID, PubMed, Scopus, and Google Scholar. The search focused on "Reward Behavior" and "Glucagon Like Peptide 1 Receptor Agonists" and was restricted to human studies. Quality assessment achieved by the NIH's Quality Assessment of Controlled Intervention Studies RESULTS: GLP-1RAs consistently reduced energy intake and influenced reward-related behaviour. These agents have been associated with decreased neurocortical activation in response to higher rewards and food cues, particularly high-calorie foods, and lowered caloric intake and hunger levels.

DISCUSSION

GLP-1RAs show promise in addressing reward dysfunction linked to food stimuli, obesity, and T2DM. They normalize insulin resistance, and might also modulate dopaminergic signalling and reduce anhedonia. Their effects on glycemic variability and cravings suggest potential applications in addiction disorders.

The GLP-1 receptor agonist exendin-4 reduces taurine and glycine in nucleus accumbens of male rats, an effect tentatively involving the nucleus tractus solitarius

The physiological effects of glucagon-like peptide-1 (GLP-1) are mainly centered on its ability to decrease blood glucose levels and facilitate satiety. Additional physiological functions have been identified by means of GLP-1 agonists such as exenatide (exendin-4; Ex4). In particular, Ex4 reduces the intake of natural and artificial rewards, effects that to some extent involve activation of GLP-1 receptors in the nucleus tractus solitarius (NTS). Although Ex4 acts in the brain, the neurochemical mechanisms underlying this activation are not fully elucidated. Investigating Ex4-induced neurochemical alterations in the nucleus accumbens (NAc) would be valuable for understanding its impact on reward-related behaviors. The aim of the present exploratory in vivo microdialysis study was therefore to study how Ex4, administered either systemically or locally into the NTS, influences classical neurotransmitters like dopamine, serotonin, noradrenaline, glutamate and GABA as well as additional players such as glycine, taurine and serine in NAc of male rats. We showed that Ex4 reduced extracellular levels of serine, taurine and glycine, where the latter two declines appear to involve activation of GLP-1R in the NTS. Besides, after systemic Ex4 injection the metabolites DOPAC, HVA, and 5HIAA are elevated. Where the increase in metabolites related to dopamine, but not serotonin, involves GLP-1 receptors in other areas than the NTS. Although the descriptive nature of the present data does not provide causality, it may however serve as an indication of mechanisms underlying how Ex4 may modulate reward-related behaviors.

An endogenous GLP-1 circuit engages VTA GABA neurons to regulate mesolimbic dopamine neurons and attenuate cocaine seeking

Recent studies show that systemic administration of a glucagon-like peptide-1 receptor (GLP-1R) agonist is sufficient to attenuate the reinstatement of cocaine-seeking behavior, an animal model of relapse. However, the neural mechanisms mediating these effects and the role of endogenous central GLP-1 signaling in cocaine seeking remain unknown. Here, we show that voluntary cocaine taking decreased plasma GLP-1 levels in rats and that chemogenetic activation of GLP-1-producing neurons in the nucleus tractus solitarius (NTS) that project to the ventral tegmental area (VTA) decreased cocaine reinstatement. Single nuclei transcriptomics and FISH studies revealed GLP-1Rs are expressed primarily on GABA neurons in the VTA. Using in vivo fiber photometry, we found that the efficacy of a systemic GLP-1R agonist to attenuate cocaine seeking was associated with increased activity of VTA GABA neurons and decreased activity of VTA dopamine neurons. Together, these findings suggest that targeting central GLP-1 circuits may be an effective strategy toward reducing cocaine relapse and highlight a novel functional role of GABAergic GLP-1R-expressing midbrain neurons in drug seeking.

The interplay between leptin, glucocorticoids, and GLP1 regulates food intake and feeding behaviour

Nutritional, endocrine, and neurological signals converge in multiple brain centres to control feeding behaviour and food intake as part of the allostatic regulation of energy balance. Among the several neuroendocrine systems involved, the leptin, glucocorticoid, and glucagon-like peptide 1 (GLP1) systems have been extensively researched. Leptin is at the top hierarchical level since its complete absence is sufficient to trigger severe hyperphagia. Glucocorticoids are key regulators of the energy balance adaptation to stress and their sustained excess leads to excessive adiposity and metabolic perturbations. GLP1 participates in metabolic adaptation to food intake, regulating insulin secretion and satiety by parallel central and peripheral signalling systems. Herein, we review the brain and peripheral targets of these three hormone systems that integrate to regulate food intake, feeding behaviour, and metabolic homeostasis. We examine the functional relationships between leptin, glucocorticoids, and GLP1 at the central and peripheral levels, including the cross-regulation of their circulating levels and their cooperative or antagonistic actions at different brain centres. The pathophysiological roles of these neuroendocrine systems in dysregulated intake are explored in the two extremes of body adiposity - obesity and lipodystrophy - and eating behaviour disorders.

A Comprehensive Review on Weight Gain following Discontinuation of Glucagon-Like Peptide-1 Receptor Agonists for Obesity

Obesity is considered the leading public health problem in the medical sector. The phenotype includes overweight conditions that lead to several other comorbidities that drastically decrease health. Glucagon-like receptor agonists (GLP-1RAs) initially designed for treating type 2 diabetes mellitus (T2DM) had demonstrated weight loss benefits in several clinical trials. In vivo studies showed that GLP-1RA encourages reduced food consumption and consequent weight reduction by stimulating brown fat and enhancing energy outlay through the action of the sympathetic nervous system (SNS) pathways. Additionally, GLP-1RAs were found to regulate food intake through stimulation of sensory neurons in the vagus, interaction with the hypothalamus and hindbrain, and through inflammation and intestinal microbiota. However, the main concern with the use of GLP-1RA treatment was weight gain after withdrawal or discontinuation. We could identify three different ways that could lead to weight gain. Potential factors might include temporary hormonal adjustment in response to weight reduction, the central nervous system's (CNS) incompetence in regulating weight augmentation owing to the lack of GLP-1RA, and β-cell malfunction due to sustained exposure to GLP-1RA. Here, we also review the data from clinical studies that reported withdrawal symptoms. Although the use of GLP-1RA could be beneficial in multiple ways, withdrawal after years has the symptoms reversed. Clinical studies should emphasize the downside of these views we highlighted, and mechanistic studies must be carried out for a better outcome with GLP-1RA from the laboratory to the bedside.

Dopamine neuron activity evoked by sucrose and sucrose-predictive cues is augmented by peripheral and central manipulations of glucose availability

Food deprivation drives eating through multiple signals and circuits. Decreased glucose availability (i.e., cytoglucopenia) drives eating and also increases the value of sucrose. Ventral tegmental area (VTA) dopamine neurons (DANs) contribute to the evaluation of taste stimuli, but their role in integrating glucoprivic signals remains unknown. We monitored VTA DAN activity via Cre-dependent expression of a calcium indicator with in vivo fibre photometry. In ad libitum fed rats, intraoral sucrose evoked a phasic increase in DAN activity. To manipulate glucose availability, we administered (intraperitoneal, lateral or fourth ventricular) the antiglycolytic agent 5-thio-D-glucose (5TG), which significantly augmented the phasic DAN activity to sucrose. 5TG failed to alter DAN activity to water or saccharin, suggesting the response was selective for caloric stimuli. 5TG enhancement of sucrose-evoked DAN activity was stronger after fourth ventricular administration, suggesting a critical node of action within the hindbrain. As 5TG also increases blood glucose, in a separate study, we used peripheral insulin, which stimulates eating, to decrease blood glucose-which was associated with increased DAN activity to intraoral sucrose. DAN activity developed to a cue predictive of intraoral sucrose. While 5TG augmented cue-evoked DAN activity, its action was most potent when delivered to the lateral ventricle. Together, the studies point to central glucose availability as a key modulator of phasic DAN activity to food and food-cues. As glucose sensing neurons are known to populate the hypothalamus and brainstem, results suggest differential modulation of cue-evoked and sucrose-evoked DAN activity.

Metformin and the Liver: Unlocking the Full Therapeutic Potential

Metformin is a highly effective medication for managing type 2 diabetes mellitus. Recent studies have shown that it has significant therapeutic benefits in various organ systems, particularly the liver. Although the effects of metformin on metabolic dysfunction-associated steatotic liver disease and metabolic dysfunction-associated steatohepatitis are still being debated, it has positive effects on cirrhosis and anti-tumoral properties, which can help prevent the development of hepatocellular carcinoma. Furthermore, it has been proven to improve insulin resistance and dyslipidaemia, commonly associated with liver diseases. While more studies are needed to fully determine the safety and effectiveness of metformin use in liver diseases, the results are highly promising. Indeed, metformin has a terrific potential for extending its full therapeutic properties beyond its traditional use in managing diabetes.

Acute and Chronic Exposure to Linagliptin, a Selective Inhibitor of Dipeptidyl Peptidase-4 (DPP-4), Has an Effect on Dopamine, Serotonin and Noradrenaline Level in the Striatum and Hippocampus of Rats

Linagliptin is a selective dipeptidyl peptidase-4 (DPP-4) inhibitor that indirectly elevates the glucagon-like peptide-1 (GLP-1) level. The aim of the present study was to check whether linagliptin has an influence on neurotransmission in rat brain. Rats were acutely and chronically exposed to linagliptin (10 and 20 mg/kg, intraperitoneally (i.p.)). Twenty-four hours later, the striatum and hippocampus were selected for further studies. In neurochemical experiments, using high-performance liquid chromatography with electrochemical detection (HPLC-ED), the concentrations of three major neurotransmitters-dopamine, serotonin and noradrenaline-and their metabolites were measured. The analysis of mRNA expression of dopamine (D1 and D2), serotonin (5-HT-1 and 5-HT-2) and noradrenaline (α1 and α2a) receptors was also investigated using real-time quantitative reverse transcription polymerase chain reaction (RQ-PCR) in the same brain areas. Linagliptin has the ability to influence the dopaminergic system. In the striatum, the elevation of dopamine and its metabolites was observed after repeated administration of that linagliptin, and in the hippocampus, a reduction in dopamine metabolism was demonstrated. Acute linagliptin exposure increases the serotonin level in both areas, while after chronic linagliptin administration a tendency for the mRNA expression of serotoninergic receptors (5-HT1A and 5-HT2A) to increase was observed. A single instance of exposure to linagliptin significantly modified the noradrenaline level in the striatum and intensified noradrenaline turnover in the hippocampus. The recognition of the interactions in the brain between DPP-4 inhibitors and neurotransmitters and/or receptors is a crucial step for finding novel discoveries in the pharmacology of DPP-4 inhibitors and raises hope for further applications of DPP-4 inhibitors in clinical practices.

Acupuncture for obesity and related diseases: Insight for regulating neural circuit

Obesity is defined as abnormal or excessive fat accumulation that may impair health. Obesity is associated with numerous pathological changes including insulin resistance, fatty liver, hyperlipidemias, and other obesity-related diseases. These comorbidities comprise a significant public health threat. Existing anti-obesity drugs have been limited by side effects that include depression, suicidal thoughts, cardiovascular complications and stroke. Acupuncture treatment has been shown to be effective for treating obesity and obesity-related conditions, while avoiding side effects. However, the mechanisms of acupuncture in treating obesity-related diseases, especially its effect on neural circuits, are not well understood. A growing body of research has studied acupuncture's effects on the endocrine system and other mechanisms related to the regulation of neural circuits. In this article, recent research that was relevant to the use of acupuncture to treat obesity and obesity-related diseases through the neuroendocrine system, as well as some neural circuits involved, was summarized. Based on this, acupuncture's potential ability to regulate neural circuits and its mechanisms of action in the endocrine system were reviewed, leading to a deeper mechanistic understanding of acupuncture's effects and providing insight and direction for future research about obesity. Please cite this article as: Jiang LY, Tian J, Yang YN, Jia SH, Shu Q. Acupuncture for obesity and related diseases: insight for regulating neural circuit. J Integr Med. 2024; 22(2): 93-101.

Exendin-4 increases the firing activity of hippocampal CA1 neurons through TRPC4/5 channels

The central neuropeptide GLP-1 is synthesized by preproglucagon (PPG) neurons in the brain. GLP-1 receptors are widely distributed in central nervous system. Hippocampus is a key component of the limbic system which is involved in learning, memory, and cognition. Previous studies have shown that overexpression of GLP-1 receptors in the hippocampus could improve the process of learning and memory. However, up to now, the direct electrophysiological effects and possible molecular mechanisms of GLP-1 in hippocampal CAl neurons remain unexplored. The present study aims to evaluate the effects and mechanisms of GLP-1 on the spontaneous firing activity of hippocampal CAl neurons. Employing multibarrel single-unit extracellular recordings, the present study showed that micro-pressure administration of GLP-1 receptor agonist, exendin-4, significantly increased the spontaneous firing rate of hippocampal CA1 neurons in rats. Furthermore, application of the specific GLP-1 receptor antagonist, exendin(9-39), alone significantly decreased the firing rate of CA1 neurons, suggesting that endogenous GLP-1 modulates the firing activity of CA1 neurons. Co-application of exendin(9-39) completely blocked exendin-4-induced excitation of hippocampal CA1 neurons. Finally, the present study demonstrated for the first time that the transient receptor potential canonical 4 (TRPC4)/TRPC5 channels may be involved in exendin-4-induced excitation. The present studies may provide a rationale for further investigation of the modulation of GLP-1 on learning and memory as well as its possible involvement in Alzheimer's disease.

A putative loop connection between VTA dopamine neurons and nucleus accumbens encodes positive valence to compensate for hunger

Dopamine (DA) signal play pivotal roles in regulating motivated behaviors, including feeding behavior, but the role of midbrain DA neurons in modulating food intake and neural circuitry mechanisms remain largely unknown. Here, we found that activating but not inhibiting ventral tegmental area (VTA) DA neurons reduces mouse food intake. Furthermore, DA neurons in ventral VTA, especially neurons projecting to the medial nucleus accumbens (NAc), are activated by refeeding in the 24 h fasted mice. Combing neural circuitry tracing, optogenetic, chemogenetic, and pharmacological manipulations, we established that the VTA→medial NAc→VTA loop circuit is critical for the VTA DA neurons activation-induced food intake reduction. Moreover, activating either VTA DA neurons or dopaminergic axons in medial NAc elevates positive valence, which will compensate for the hungry-induced food intake. Thus, our study identifies a subset of positive valence-encoded VTA DA neurons forming possible loop connections with medial NAc that are anorexigenic.

Metabolic hormone action in the VTA: Reward-directed behavior and mechanistic insights

Dysfunctional signaling in midbrain reward circuits perpetuates diseases characterized by compulsive overconsumption of rewarding substances such as substance abuse, binge eating disorder, and obesity. Ventral tegmental area (VTA) dopaminergic activity serves as an index for how rewarding stimuli are perceived and triggers behaviors necessary to obtain future rewards. The evolutionary linking of reward with seeking and consuming palatable foods ensured an organism's survival, and hormone systems that regulate appetite concomitantly developed to regulate motivated behaviors. Today, these same mechanisms serve to regulate reward-directed behavior around food, drugs, alcohol, and social interactions. Understanding how hormonal regulation of VTA dopaminergic output alters motivated behaviors is essential to leveraging therapeutics that target these hormone systems to treat addiction and disordered eating. This review will outline our current understanding of the mechanisms underlying VTA action of the metabolic hormones ghrelin, glucagon-like peptide-1, amylin, leptin, and insulin to regulate behavior around food and drugs of abuse, highlighting commonalities and differences in how these five hormones ultimately modulate VTA dopamine signaling.

Liraglutide restores impaired associative learning in individuals with obesity

Survival under selective pressure is driven by the ability of our brain to use sensory information to our advantage to control physiological needs. To that end, neural circuits receive and integrate external environmental cues and internal metabolic signals to form learned sensory associations, consequently motivating and adapting our behaviour. The dopaminergic midbrain plays a crucial role in learning adaptive behaviour and is particularly sensitive to peripheral metabolic signals, including intestinal peptides, such as glucagon-like peptide 1 (GLP-1). In a single-blinded, randomized, controlled, crossover basic human functional magnetic resonance imaging study relying on a computational model of the adaptive learning process underlying behavioural responses, we show that adaptive learning is reduced when metabolic sensing is impaired in obesity, as indexed by reduced insulin sensitivity (participants: N = 30 with normal insulin sensitivity; N = 24 with impaired insulin sensitivity). Treatment with the GLP-1 receptor agonist liraglutide normalizes impaired learning of sensory associations in men and women with obesity. Collectively, our findings reveal that GLP-1 receptor activation modulates associative learning in people with obesity via its central effects within the mesoaccumbens pathway. These findings provide evidence for how metabolic signals can act as neuromodulators to adapt our behaviour to our body's internal state and how GLP-1 receptor agonists work in clinics.

Neuro-Vulnerability in Energy Metabolism Regulation: A Comprehensive Narrative Review

This comprehensive narrative review explores the concept of neuro-vulnerability in energy metabolism regulation and its implications for metabolic disorders. The review highlights the complex interactions among the neural, hormonal, and metabolic pathways involved in the regulation of energy metabolism. The key topics discussed include the role of organs, hormones, and neural circuits in maintaining metabolic balance. The review investigates the association between neuro-vulnerability and metabolic disorders, such as obesity, insulin resistance, and eating disorders, considering genetic, epigenetic, and environmental factors that influence neuro-vulnerability and subsequent metabolic dysregulation. Neuroendocrine interactions and the neural regulation of food intake and energy expenditure are examined, with a focus on the impact of neuro-vulnerability on appetite dysregulation and altered energy expenditure. The role of neuroinflammation in metabolic health and neuro-vulnerability is discussed, emphasizing the bidirectional relationship between metabolic dysregulation and neuroinflammatory processes. This review also evaluates the use of neuroimaging techniques in studying neuro-vulnerability and their potential applications in clinical settings. Furthermore, the association between neuro-vulnerability and eating disorders, as well as its contribution to obesity, is examined. Potential therapeutic interventions targeting neuro-vulnerability, including pharmacological treatments and lifestyle modifications, are reviewed. In conclusion, understanding the concept of neuro-vulnerability in energy metabolism regulation is crucial for addressing metabolic disorders. This review provides valuable insights into the underlying neurobiological mechanisms and their implications for metabolic health. Targeting neuro-vulnerability holds promise for developing innovative strategies in the prevention and treatment of metabolic disorders, ultimately improving metabolic health outcomes.

The glucagon-like peptide-1 (GLP-1) analogue semaglutide reduces alcohol drinking and modulates central GABA neurotransmission

Growing evidence indicates that the glucagon-like peptide-1 (GLP-1) system is involved in the neurobiology of addictive behaviors, and GLP-1 analogues may be used for the treatment of alcohol use disorder (AUD). Here, we examined the effects of semaglutide, a long-acting GLP-1 analogue, on biobehavioral correlates of alcohol use in rodents. A drinking-in-the-dark procedure was used to test the effects of semaglutide on binge-like drinking in male and female mice. We also tested the effects of semaglutide on binge-like and dependence-induced alcohol drinking in male and female rats, as well as acute effects of semaglutide on spontaneous inhibitory postsynaptic currents (sIPSCs) from central amygdala (CeA) and infralimbic cortex (ILC) neurons. Semaglutide dose-dependently reduced binge-like alcohol drinking in mice; a similar effect was observed on the intake of other caloric/noncaloric solutions. Semaglutide also reduced binge-like and dependence-induced alcohol drinking in rats. Semaglutide increased sIPSC frequency in CeA and ILC neurons from alcohol-naive rats, suggesting enhanced GABA release, but had no overall effect on GABA transmission in alcohol-dependent rats. In conclusion, the GLP-1 analogue semaglutide decreased alcohol intake across different drinking models and species and modulated central GABA neurotransmission, providing support for clinical testing of semaglutide as a potentially novel pharmacotherapy for AUD.

Chronic Semaglutide Treatment in Rats Leads to Daily Excessive Concentration-Dependent Sucrose Intake

Context

The glucagon-like peptide-1 receptor (GLP-1R) agonist semaglutide (SEMA) produces 15% weight loss when chronically administered to humans with obesity.

Methods

In 2 separate experiments, rats received daily injections of either vehicle (VEH) or SEMA starting at 7 µg/kg body weight (BW) and increasing over 10 days to the maintenance dose (70 µg/kg-BW), emulating clinical dose escalation strategies.

Results

During dose escalation and maintenance, SEMA rats reduced chow intake and bodyweight. Experiment 2 meal pattern analysis revealed that meal size, not number, mediated these SEMA-induced changes in chow intake. This suggests SEMA affects neural processes controlling meal termination and not meal initiation. Two-bottle preference tests (vs water) began after 10 to 16 days of maintenance dosing. Rats received either an ascending sucrose concentration series (0.03-1.0 M) and 1 fat solution (Experiment 1) or a 4% and 24% sucrose solution in a crossover design (Experiment 2). At lower sucrose concentrations, SEMA-treated rats in both experiments drank sometimes >2× the volume consumed by VEH controls; at higher sucrose concentrations (and 10% fat), intake was similar between treatment groups. Energy intake of SEMA rats became similar to VEH rats. This was unexpected because GLP-1R agonism is thought to decrease the reward and/or increase the satiating potency of palatable foods. Despite sucrose-driven increases in both groups, a significant bodyweight difference between SEMA- and VEH-treated rats remained.

Conclusion

The basis of the SEMA-induced overconsumption of sucrose at lower concentrations relative to VEH controls remains unclear, but the effects of chronic SEMA treatment on energy intake and BW appear to depend on the caloric sources available.

Glucagon-like peptide-1 receptors in nucleus accumbens, ventral hippocampus, and lateral septum reduce alcohol reinforcement in mice

Glucagon-like peptide 1 (GLP-1) receptor agonists can decrease alcohol intake by central mechanisms that are still poorly understood. The lateral septum (LS) and the ventral/caudal part of the hippocampus are enriched in GLP-1 receptors, and activity in these regions was shown to modulate reward-related behaviors. Using microinfusions of the GLP-1 receptor agonist exendin-4 in mice trained to self-administer oral alcohol in an operant assay, we tested whether pharmacological stimulation of GLP-1 receptors in hippocampus and LS decrease alcohol self-administration. We report that infusion of exendin-4 in the ventral hippocampus or LS was sufficient to reduce alcohol self-administration with as large effect sizes as we previously reported with systemic exendin-4 administration. Infusion of exendin-4 into the nucleus accumbens also reduced alcohol self-administration, as anticipated based on earlier reports, while infusion of exendin-4 into the caudate-putamen (dorsal striatum) had little effect, consistent with lack of GLP-1 receptor expression in this region. The distribution of exendin-4 after infusion into the LS or caudate putamen was visualized using a fluorescently labeled ligand. These findings add to our understanding of the circuit-level mechanisms underlying the ability of GLP-1 receptor agonists to reduce alcohol self-administration. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

G Protein-Coupled Receptors and the Rise of Type 2 Diabetes in Children

The human genome counts hundreds of GPCRs specialized to sense thousands of different extracellular cues, including light, odorants and nutrients in addition to hormones. Primordial GPCRs were likely glucose transporters that became sensors to monitor the abundance of nutrients and direct the cell to switch from aerobic metabolism to fermentation. Human β cells express multiple GPCRs that contribute to regulate glucose homeostasis, cooperating with many others expressed by a variety of cell types and tissues. These GPCRs are intensely studied as pharmacological targets to treat type 2 diabetes in adults. The dramatic rise of type 2 diabetes incidence in pediatric age is likely correlated to the rapidly evolving lifestyle of children and adolescents of the new century. Current pharmacological treatments are based on therapies designed for adults, while youth and puberty are characterized by a different hormonal balance related to glucose metabolism. This review focuses on GPCRs functional traits that are relevant for β cells function, with an emphasis on aspects that could help to differentiate new treatments specifically addressed to young type 2 diabetes patients.

Neuropeptides Modulate Feeding via the Dopamine Reward Pathway

Dopamine (DA) is a catecholamine neurotransmitter widely distributed in the central nervous system. It participates in various physiological functions, such as feeding, anxiety, fear, sleeping and arousal. The regulation of feeding is exceptionally complex, involving energy homeostasis and reward motivation. The reward system comprises the ventral tegmental area (VTA), nucleus accumbens (NAc), hypothalamus, and limbic system. This paper illustrates the detailed mechanisms of eight typical orexigenic and anorexic neuropeptides that regulate food intake through the reward system. According to recent literature, neuropeptides released from the hypothalamus and other brain regions regulate reward feeding predominantly through dopaminergic neurons projecting from the VTA to the NAc. In addition, their effect on the dopaminergic system is mediated by the prefrontal cortex, paraventricular thalamus, laterodorsal tegmental area, amygdala, and complex neural circuits. Research on neuropeptides involved in reward feeding can help identify more targets to treat diseases with metabolic disorders, such as obesity.

The therapeutic potential of glucagon-like peptide-1 for persons with addictions based on findings from preclinical and clinical studies

Although the multifaceted mechanisms underlying alcohol use disorder (AUD) have been partially defined, the neurobiological complexity of this disorder is yet to be unraveled. One of the systems that have gained attention in recent times is the gut–brain axis. Although numerous peptides participate in this axis, glucagon-like peptide-1 (GLP-1) plays a central role. GLP-1 is a crucial anorexigenic peptide, with potent abilities to reduce food intake and body weight. The physiological complexity of GLP-1 entails glucose homeostasis, gastrointestinal motility, and the release of insulin and glucagon. As reviewed in this study, acute or repeated treatment with GLP-1 receptor (GLP-1R) agonists decreases alcohol consumption in rodents. Moreover, the abilities of alcohol to promote hyperlocomotion, dopamine release in the nucleus accumbens, and reward in the conditioned place preference paradigm are all suppressed by GLP-1R ligands. Moreover, activation of GLP-1R suppresses the motivation to consume alcohol, alcohol-seeking behaviors, and relapse drinking in male rodents. Similarly, abstinence symptoms experienced during alcohol withdrawal are attenuated by activation of the GLP-1 pathway. On a similar note, the activation of GLP-1 receptors within areas of the brain that are processing reward modulates these alcohol-related responses. Another area that is crucial for this ability is the nucleus of the solitary tract, which is where GLP-1 is produced and from which GLP-1-containing neurons project to areas of reward. These findings may have clinical relevance as AUD is associated with polymorphisms in GLP-1-related genes. Although a GLP-1R agonist does not alter alcohol intake in AUD patients, it reduces this consumption in a sub-population of obese AUD individuals. Given the uncertainty of this outcome, additional clinical studies of obese AUD patients should explore the effects of the GLP-1R agonists on alcohol intake and body weight. Furthermore, GLP-1 receptors modulate the behavioral and neurochemical responses to addictive drugs. Taken together, these preclinical and clinical findings imply that the GLP-1 pathway plays a role in the complex mechanisms regulating alcohol and drug consumption patterns, unveiling a novel aspect of addiction medicine.

The gut-to-brain axis for toxin-induced defensive responses

After ingestion of toxin-contaminated food, the brain initiates a series of defensive responses (e.g., nausea, retching, and vomiting). How the brain detects ingested toxin and coordinates diverse defensive responses remains poorly understood. Here, we developed a mouse-based paradigm to study defensive responses induced by bacterial toxins. Using this paradigm, we identified a set of molecularly defined gut-to-brain and brain circuits that jointly mediate toxin-induced defensive responses. The gut-to-brain circuit consists of a subset of Htr3a+ vagal sensory neurons that transmit toxin-related signals from intestinal enterochromaffin cells to Tac1+ neurons in the dorsal vagal complex (DVC). Tac1+ DVC neurons drive retching-like behavior and conditioned flavor avoidance via divergent projections to the rostral ventral respiratory group and lateral parabrachial nucleus, respectively. Manipulating these circuits also interferes with defensive responses induced by the chemotherapeutic drug doxorubicin. These results suggest that food poisoning and chemotherapy recruit similar circuit modules to initiate defensive responses.

Activation of arcuate nucleus glucagon-like peptide-1 receptor-expressing neurons suppresses food intake

BACKGROUND

Central nervous system (CNS) control of metabolism plays a pivotal role in maintaining energy balance. In the brain, Glucagon-like peptide 1 (GLP-1), encoded by the proglucagon 'Gcg' gene, produced in a distinct population of neurons in the nucleus tractus solitarius (NTS), has been shown to regulate feeding behavior leading to the suppression of appetite. However, neuronal networks that mediate endogenous GLP-1 action in the CNS on feeding and energy balance are not well understood.

RESULTS

We analyzed the distribution of GLP-1R-expressing neurons and axonal projections of NTS GLP-1-producing neurons in the mouse brain. GLP-1R neurons were found to be broadly distributed in the brain and specific forebrain regions, particularly the hypothalamus, including the arcuate nucleus of the hypothalamus (ARC), a brain region known to regulate energy homeostasis and feeding behavior, that receives dense NTS^Gcg neuronal projections. The impact of GLP-1 signaling in the ARC GLP-1R-expressing neurons and the impact of activation of ARC GLP-1R on food intake was examined. Application of GLP-1R specific agonist Exendin-4 (Exn-4) enhanced a proportion of the ARC GLP-1R-expressing neurons and pro-opiomelanocortin (POMC) neuronal action potential firing rates. Chemogenetic activation of the ARC GLP-1R neurons by using Cre-dependent hM3Dq AAV in the GLP-1R-ires-Cre mice, established that acute activation of the ARC GLP-1R neurons significantly suppressed food intake but did not have a strong impact on glucose homeostasis.

CONCLUSIONS

These results highlight the importance of central GLP-1 signaling in the ARC that express GLP-1R that upon activation, regulate feeding behavior.

Interactions between central nervous system and peripheral metabolic organs

According to Descartes, minds and bodies are distinct kinds of "substance", and they cannot have causal interactions. However, in neuroscience, the two-way interaction between the brain and peripheral organs is an emerging field of research. Several lines of evidence highlight the importance of such interactions. For example, the peripheral metabolic systems are overwhelmingly regulated by the mind (brain), and anxiety and depression greatly affect the functioning of these systems. Also, psychological stress can cause a variety of physical symptoms, such as bone loss. Moreover, the gut microbiota appears to play a key role in neuropsychiatric and neurodegenerative diseases. Mechanistically, as the command center of the body, the brain can regulate our internal organs and glands through the autonomic nervous system and neuroendocrine system, although it is generally considered to be outside the realm of voluntary control. The autonomic nervous system itself can be further subdivided into the sympathetic and parasympathetic systems. The sympathetic division functions a bit like the accelerator pedal on a car, and the parasympathetic division functions as the brake. The high center of the autonomic nervous system and the neuroendocrine system is the hypothalamus, which contains several subnuclei that control several basic physiological functions, such as the digestion of food and regulation of body temperature. Also, numerous peripheral signals contribute to the regulation of brain functions. Gastrointestinal (GI) hormones, insulin, and leptin are transported into the brain, where they regulate innate behaviors such as feeding, and they are also involved in emotional and cognitive functions. The brain can recognize peripheral inflammatory cytokines and induce a transient syndrome called sick behavior (SB), characterized by fatigue, reduced physical and social activity, and cognitive impairment. In summary, knowledge of the biological basis of the interactions between the central nervous system and peripheral organs will promote the full understanding of how our body works and the rational treatment of disorders. Thus, we summarize current development in our understanding of five types of central-peripheral interactions, including neural control of adipose tissues, energy expenditure, bone metabolism, feeding involving the brain-gut axis and gut microbiota. These interactions are essential for maintaining vital bodily functions, which result in homeostasis, i.e., a natural balance in the body's systems.

Activation of mesocorticolimbic dopamine projections initiates cue-induced reinstatement of reward seeking in mice

Drug addiction is characterized by relapse when addicts are re-exposed to drug-associated environmental cues, but the neural mechanisms underlying cue-induced relapse are unclear. In the present study we investigated the role of a specific dopaminergic (DA) pathway from ventral tegmental area (VTA) to nucleus accumbens core (NAcore) in mouse cue-induced relapse. Optical intracranial self-stimulation (oICSS) was established in DAT-Cre transgenic mice. We showed that optogenetic excitation of DA neurons in the VTA or their projection terminals in NAcore, NAshell or infralimbic prefrontal cortex (PFC-IL) was rewarding. Furthermore, activation of the VTA-NAcore pathway alone was sufficient and necessary to induce reinstatement of oICSS. In cocaine self-administration model, cocaine-associated cues activated VTA DA neurons as assessed by intracellular GCaMP signals. Cue-induced reinstatement of cocaine-seeking was triggered by optogenetic stimulation of the VTA-NAcore pathway, and inhibited by chemogenetic inhibition of this pathway. Together, these results demonstrate that cue-induced reinstatement of reward seeking is in part mediated by activation of the VTA-NAcore DA pathway.

Gut microbes and food reward: From the gut to the brain

Inappropriate food intake behavior is one of the main drivers for fat mass development leading to obesity. Importantly the gut microbiota-mediated signals have emerged as key actors regulating food intake acting mainly on the hypothalamus, and thereby controlling hunger or satiety/satiation feelings. However, food intake is also controlled by the hedonic and reward systems leading to food intake based on pleasure (i.e., non-homeostatic control of food intake). This review focus on both the homeostatic and the non-homeostatic controls of food intake and the implication of the gut microbiota on the control of these systems. The gut-brain axis is involved in the communications between the gut microbes and the brain to modulate host food intake behaviors through systemic and nervous pathways. Therefore, here we describe several mediators of the gut-brain axis including gastrointestinal hormones, neurotransmitters, bioactive lipids as well as bacterial metabolites and compounds. The modulation of gut-brain axis by gut microbes is deeply addressed in the context of host food intake with a specific focus on hedonic feeding. Finally, we also discuss possible gut microbiota-based therapeutic approaches that could lead to potential clinical applications to restore food reward alterations. Therapeutic applications to tackle these dysregulations is of utmost importance since most of the available solutions to treat obesity present low success rate.

The ins and outs of the caudal nucleus of the solitary tract: An overview of cellular populations and anatomical connections

The body and brain are in constant two-way communication. Driving this communication is a region in the lower brainstem: the dorsal vagal complex. Within the dorsal vagal complex, the caudal nucleus of the solitary tract (cNTS) is a major first stop for incoming information from the body to the brain carried by the vagus nerve. The anatomy of this region makes it ideally positioned to respond to signals of change in both emotional and bodily states. In turn, the cNTS controls the activity of regions throughout the brain that are involved in the control of both behaviour and physiology. This review is intended to help anyone with an interest in the cNTS. First, I provide an overview of the architecture of the cNTS and outline the wide range of neurotransmitters expressed in subsets of neurons in the cNTS. Next, in detail, I discuss the known inputs and outputs of the cNTS and briefly highlight what is known regarding the neurochemical makeup and function of those connections. Then, I discuss one group of cNTS neurons: glucagon-like peptide-1 (GLP-1)-expressing neurons. GLP-1 neurons serve as a good example of a group of cNTS neurons, which receive input from varied sources and have the ability to modulate both behaviour and physiology. Finally, I consider what we might learn about other cNTS neurons from our study of GLP-1 neurons and why it is important to remember that the manipulation of molecularly defined subsets of cNTS neurons is likely to affect physiology and behaviours beyond those monitored in individual experiments.

Actions of feeding-related peptides on the mesolimbic dopamine system in regulation of natural and drug rewards

The mesolimbic dopamine system is the primary neural circuit mediating motivation, reinforcement, and reward-related behavior. The activity of this system and multiple behaviors controlled by it are affected by changes in feeding and body weight, such as fasting, food restriction, or the development of obesity. Multiple different peptides and hormones that have been implicated in the control of feeding and body weight interact with the mesolimbic dopamine system to regulate many different dopamine-dependent, reward-related behaviors. In this review, we summarize the effects of a selected set of feeding-related peptides and hormones acting within the ventral tegmental area and nucleus accumbens to alter feeding, as well as food, drug, and social reward.

Identification of an endocannabinoid gut-brain vagal mechanism controlling food reward and energy homeostasis

The regulation of food intake, a sine qua non requirement for survival, thoroughly shapes feeding and energy balance by integrating both homeostatic and hedonic values of food. Unfortunately, the widespread access to palatable food has led to the development of feeding habits that are independent from metabolic needs. Among these, binge eating (BE) is characterized by uncontrolled voracious eating. While reward deficit seems to be a major contributor of BE, the physiological and molecular underpinnings of BE establishment remain elusive. Here, we combined a physiologically relevant BE mouse model with multiscale in vivo approaches to explore the functional connection between the gut-brain axis and the reward and homeostatic brain structures. Our results show that BE elicits compensatory adaptations requiring the gut-to-brain axis which, through the vagus nerve, relies on the permissive actions of peripheral endocannabinoids (eCBs) signaling. Selective inhibition of peripheral CB1 receptors resulted in a vagus-dependent increased hypothalamic activity, modified metabolic efficiency, and dampened activity of mesolimbic dopamine circuit, altogether leading to the suppression of palatable eating. We provide compelling evidence for a yet unappreciated physiological integrative mechanism by which variations of peripheral eCBs control the activity of the vagus nerve, thereby in turn gating the additive responses of both homeostatic and hedonic brain circuits which govern homeostatic and reward-driven feeding. In conclusion, we reveal that vagus-mediated eCBs/CB1R functions represent an interesting and innovative target to modulate energy balance and counteract food-reward disorders.

Possible Mechanisms Underlying the Effects of Glucagon-Like Peptide-1 Receptor Agonist on Cocaine Use Disorder

Cocaine use disorder (CUD) is a major public health challenge with a high relapse rate and lack of effective pharmacotherapies; therefore, there is a substantial need to identify novel medications to treat this epidemic. Since the advent of glucagon-like peptide-1 (GLP-1) receptors (GLP-1Rs) agonists (GLP-1RAs), their potential has been extensively explored and expanded. In this review, we first summarized the biological effects of GLP-1, GLP-1Rs, and GLP-1RAs. Subsequently, the recent literature examining the behavioral effects and the possible pharmacological mechanisms of GLP-1RAs on CUD was reviewed. Increasing preclinical evidence suggests that GLP-1RAs are promising in regulating dopamine release, dopamine transporter (DAT) surface expression and function, mesolimbic reward system and GABAergic neurons, and maladaptive behaviors in animal models of self-administration and conditioned place preference. In addition, the emerging role of GLP-1RAs in inhibiting inflammatory cytokines was reported. These findings indicate that GLP-1RAs perform essential functions in the modulation of cocaine-seeking and cocaine-taking behaviors likely through multifaceted mechanisms. Although the current preclinical evidence provides convincing evidence to support GLP-1RA as a promising pharmacotherapy for CUD, other questions concerning clinical availability, impact and specific mechanisms remain to be addressed in further studies.