GLP-1 influences food and drug reward

GLP-1 Analogues in the Neurobiology of Addiction: Translational Insights and Therapeutic Perspectives

Glucagon-like peptide-1 receptor agonists, originally developed for the treatment of metabolic disorders, have recently emerged as promising candidates for the management of substance use disorders. This review synthesizes preclinical, clinical, and translational evidence on the effects of glucagon-like peptide-1 receptor agonists across addiction models involving alcohol, nicotine, psychostimulants, and opioids. In animal studies, glucagon-like peptide-1 receptor agonists consistently reduce drug intake, attenuate dopamine release in reward circuits, and decrease relapse-like behavior. Clinical and observational studies provide preliminary support for these findings, particularly among individuals with comorbid obesity or insulin resistance. However, several translational barriers remain, including limited blood-brain barrier penetration, species differences in pharmacokinetics, and variability in treatment response due to genetic and metabolic factors. Ethical considerations and methodological heterogeneity further complicate clinical translation. Future directions include the development of central nervous system penetrant analogues, personalized medicine approaches incorporating pharmacogenomics, and rigorously designed trials in diverse populations. Glucagon-like peptide-1 receptor agonists may offer a novel therapeutic strategy that addresses both metabolic and neuropsychiatric dimensions of addiction, warranting further investigation to define their role in the evolving landscape of substance use disorder treatment.

Review Article: GLP-1 Receptor Agonists and Glucagon/GIP/GLP-1 Receptor Dual or Triple Agonists-Mechanism of Action and Emerging Therapeutic Landscape in MASLD

BACKGROUND

Metabolic dysfunction-associated steatotic liver disease (MASLD) is primarily managed through diet and lifestyle modifications. However, these behavioural interventions alone may not achieve disease regression or remission, and maintaining long-term adherence is challenging. Incretin mimetics and other gastrointestinal hormones targeting the pleiotropic pathophysiological pathways underlying MASLD have now emerged as promising disease-modifying therapies.

AIMS

This is a comprehensive review summarising the role of glucagon-like peptide-1 (GLP-1) receptor agonists and glucagon/glucose-dependent insulinotropic polypeptide (GIP)/GLP-1 receptor dual or triple agonists in the treatment of metabolic dysfunction-associated steatohepatitis (MASH).

METHODS

Only clinical trials with endpoints assessed by liver histology were included for a robust evaluation of therapeutic efficacy.

RESULTS

Recent evidence from phase 2 clinical trials for MASH demonstrated that pharmacological agents based on GLP-1 receptor agonism are effective in improving disease activity. Additionally, tirzepatide and survodutide showed potential clinical benefits in reducing fibrosis. Other cardiometabolic benefits observed include weight loss and improvements in glycaemic control and lipid profile. Adherence to treatment may be limited by gastrointestinal side effects, though they were found to be generally mild to moderate in severity. An interim analysis of the semaglutide phase 3 trial confirmed its efficacy in improving steatohepatitis and demonstrated its potential to improve fibrosis.

CONCLUSIONS

GLP-1 receptor agonists, alone or in combination with GIP and/or glucagon receptor agonists, represent promising, effective pharmacotherapies for the treatment of MASLD/MASH. Larger and longer-duration clinical trials are needed to further evaluate the efficacy and safety of GIP receptor and glucagon receptor agonism.

Glucagon-like peptide-1 receptor agonists and alcohol use disorders: An emerging unexpected beneficial effect

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are increasingly used for the management of people living with type 2 diabetes mellitus (T2DM) and/or obesity. Numerous concordant animal and human studies suggest that GLP-1RAs could reduce the risk of addiction, especially alcohol use disorders (AUD). This comprehensive review aims at summarising the known effects of GLP-1RAs on AUD. An extensive literature search detected clinical (either observational or controlled) studies that investigated the prevalence and severity of AUD in obese/T2DM patients treated with GLP-1RAs compared with a control group. In seven observational cohort studies (12 paired data for comparisons), the prevalence of AUD was reduced by 35% (hazard ratio 0.65; 95% confidence interval 0.56-0.74) with GLP-1RA therapy when compared to no-GLP-1 therapy. The protection by GLP-1RAs concerned both incidence and recurrence of AUD. These positive human findings confirm preclinical data in rodents and monkeys. Some genetic, experimental and functional neuroimaging human studies also supported a potential role of the GLP-1 system in the alcohol-related reward process. Only two randomised controlled trials are available yet with inconclusive results, but several are ongoing to confirm the protective effect of semaglutide on AUD. Different neuronal and psychological mechanisms involving the reward pathways are proposed to explain the favourable findings reported with GLP-1RAs. In conclusion, available data from observational cohort studies showed a concordant and significantly reduced risk of AUD and alcohol consumption habits with GLP-1RA therapy. However, further studies are required before considering any indication of GLP-1RAs for the prevention or management of AUD.

An inhibitory GLP-1 circuit in the lateral septum modulates reward processing and alcohol intake in rodents

BACKGROUND

Alcohol use disorder (AUD) is a complex psychiatric condition with limited effective treatment options. Glucagon-like peptide-1 receptor (GLP-1R) agonists have emerged as potential AUD treatment, as they have been shown to modulate reward-related behaviours, including those linked to alcohol consumption. However, the underlying mechanisms and neurocircuitry remain unclear. This study investigated the role of GLP-1R in the lateral septum (LS), a brain region highly expressing GLP-1R and implicated in reward-related behaviours, including alcohol-induced reward and consumption.

METHODS

Behavioural, neurochemical, molecular, and electrophysiological methods were used to investigate the effect of LS GLP-1R signalling in alcohol-mediated responses in rodents.

FINDINGS

LS GLP-1R activation attenuated alcohol's rewarding effects, reducing locomotor stimulation, place preference, and accumbal dopamine release. Intra-LS infusion of the GLP-1R agonist exendin-4 (Ex4) reduced alcohol intake dose-dependently without affecting food or water consumption, while GLP-1R inhibition increased alcohol intake. Furthermore, LS GLP-1R expression correlated with alcohol intake in male but not female rats, suggesting sex-specific effects of long-term alcohol exposure. Ex vivo electrophysiology indicated that GLP-1R activation depressed LS neurotransmission via a gamma-aminobutyric acid (GABA)A receptor-dependent mechanism.

INTERPRETATION

This study provides new insights into how GLP-1R agonists may reduce alcohol intake. Overall, the findings underscore the potentially inhibitory neuromodulatory role of LS GLP-1R in regulating alcohol consumption through the modulation of dopaminergic reward processes tentatively involving GABA transmission.

FUNDING

Swedish Research Council (2023-2600), Sahlgrenska University HospitalLUA/ALF (grant no. 723941), Adlerbertska Research Foundation and Professor Bror Gadelius Foundation.

How 'miracle' weight-loss semaglutide promises to change medicine but can we afford the expense?

Obesity is a complex and growing global concern, affecting one in eight individuals and compromising health, quality of life and life expectancy. It carries significant metabolic, cardiovascular, oncological, hepatorenal, skeletal and psychiatric risks, imposing substantial costs on health-care systems. Traditional treatments have often been ineffective or have led to relapse after lifestyle changes. Whereas bariatric surgery is effective, it also involves risks such as mortality and hospitalisation. Semaglutide, licensed in 2018, is a synthetic analogue of glucagon-like peptide 1 which regulates glucose metabolism and gastrointestinal (GI) motility. Studies show that semaglutide, administered either weekly and subcutaneously, or daily orally, induces an average weight loss of -11.62 kg compared to placebo and reduces waist circumference by up to -9.4 cm. It also improves blood pressure, fasting glucose levels, C-reactive protein levels and lipid profiles. The most common adverse events are mild-to-moderate GI complaints occurring more frequently with daily administration than weekly doses; hypoglycaemia is more common without lifestyle intervention. Weight regain often follows semaglutide withdrawal. Furthermore, semaglutide offers cardiovascular benefits for patients with established atherosclerotic cardiovascular disease (CVD), lowers the risk of kidney outcomes and cardiovascular-related death, resolves nonalcoholic steatohepatitis in many cases, and positively impacts mental health and quality of life. In conclusion, semaglutide therapy could significantly benefit many adults regarding CVD and mortality if made widely accessible. Ethical and financial considerations must be addressed for personalised obesity treatment approaches.

Weight loss therapy and addiction: Increased risk after bariatric surgery but reduced risk with GLP-1 receptor agonists

BACKGROUND

Obesity is an increasing public health problem because of its high prevalence and associated morbidity and mortality. Two weight-loss strategies are currently used, either bariatric surgery or pharmacological therapy with glucagon-like peptide-1 receptor agonists (GLP-1RAs). Preclinical studies in rodents suggested an increased risk of additive disorders after bariatric surgery contrasting with a reduced risk with GLP-1RAs.

METHODS

An extensive literature search to detect clinical studies that investigated the prevalence of addictive disorders (food addiction, alcohol abuse, smoking, cannabis, cocaine, opioid use) following bariatric surgery or GLP-1RA therapy in obese patients.

RESULTS

In observational cohort studies, the prevalence of alcohol use disorder was twofold higher after > 2 years following surgery (eleven studies, mainly with gastric bypass) whereas it was reduced roughly by half with GLP-1RA therapy (five studies, mainly with semaglutide). Similar findings were reported with other addictive disorders. An addiction transfer from food addiction to other addictive disorders is hypothesized to explain the increased risk after bariatric surgery. Several mechanisms are proposed to explain the favorable findings reported with GLP-1RAs, i.e. effects on the dopamine reward pathway, central GABA (gamma-aminobutyric acid) release, negative emotional stress associated with food/drug restriction and/or neuronal inflammation.

CONCLUSION

Available data from observational cohort studies confirm an increased risk of addictive disorders following bariatric surgery, contrasting with a reduced risk with GLP-1RA therapy. Both physicians and patients should be informed of the higher risk post-surgery whereas available promising results with GLP-1RAs should be confirmed in ongoing dedicated randomized controlled trials before any official indication.

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.

The Effects of Metformin on Weight Loss, Cardiovascular Health, and Longevity

Metformin, a biguanide derived from Galega officinalis, was first synthesized by Werner and Bell in 1922. Metformin was approved for the treatment of diabetes by the US Food and Drug Administration in 1994. It has since become the most widely used oral antidiabetic agent. The exact mechanisms by which metformin exerts its clinical effects remain the subject of ongoing research. Metformin interacts with multiple molecular pathways, and the downstream effects of which affect weight, cardiovascular health, and longevity. Metformin reduces hunger by mitigating insulin resistance in the hypothalamic pro-opiomelanocortin neurons. It enhances satiety by stimulating the enteral release of glucagon-like peptide 1. It also induces favorable changes to enteric microbiota, enhancing metabolism. These effects cumulatively contribute to metformin-induced weight loss. Metformin use has shown associations with improved cardiovascular outcomes including reduced all-cause mortality, lower rates of myocardial infarctions, and improved heart failure outcomes. Many of these actions are mediated through the direct activation of adenosine monophosphate-activated kinase (AMPK), which, in turn, enhances cellular energy production and endothelial nitric oxide synthase-mediated vascular relaxation. It antagonizes proinflammatory cytokines, reducing cardiac fibrosis and remodeling. The metformin-AMPK pathway may also explain the potential utility of metformin in mitigating aging. Acting through AMPK, it inhibits the mammalian target of rapamycin, leading to increased autophagy and cell growth. The metformin-AMPK-sirtuin pathway may also contribute to longevity. In this review, we will discuss the use of metformin in weight loss, cardiovascular health, and longevity, highlighting the historic background, molecular mechanisms, and current evidence.

Semaglutide Ameliorates Diabetic Neuropathic Pain by Inhibiting Neuroinflammation in the Spinal Cord

Glucagon-like peptide 1 (GLP-1) receptor agonists are frequently used to treat type 2 diabetes and obesity. Despite the development of several drugs for neuropathic pain management, their poor efficacy, tolerance, addiction potential, and side effects limit their usage. Teneligliptin, a DPP-4 inhibitor, has been shown to reduce spinal astrocyte activation and neuropathic pain caused by partial sciatic nerve transection. Additionally, we showed its capacity to improve the analgesic effects of morphine and reduce analgesic tolerance. Recent studies indicate that GLP-1 synthesized in the brain activates GLP-1 receptor signaling pathways, essential for neuroprotection and anti-inflammatory effects. Multiple in vitro and in vivo studies using preclinical models of neurodegenerative disorders have shown the anti-inflammatory properties associated with glucagon-like peptide-1 receptor (GLP-1R) activation. This study aimed to investigate the mechanism of antinociception and the effects of the GLP-1 agonist semaglutide (SEMA) on diabetic neuropathic pain in diabetic rats.

METHODS

Male Wistar rats, each weighing between 300 and 350 g, were categorized into four groups: one non-diabetic sham group and three diabetic groups. The diabetic group received a single intraperitoneal injection of streptozotocin (STZ) at a dosage of 60 mg/kg to induce diabetic neuropathy. After 4 weeks of STZ injection, one diabetic group was given saline (vehicle), and the other two were treated with either 1× SEMA (1.44 mg/kg, orally) or 2× SEMA (2.88 mg/kg, orally). Following a 4-week course of oral drug treatment, behavioral, biochemical, and immunohistochemical analyses were carried out. The mechanical allodynia, thermal hyperalgesia, blood glucose, advanced glycation end products (AGEs), plasma HbA1C, and spinal inflammatory markers were evaluated.

RESULTS

SEMA treatment significantly reduced both allodynia and hyperalgesia in the diabetic group. SEMA therapy had a limited impact on body weight restoration and blood glucose reduction. In diabetic rats, SEMA lowered the amounts of pro-inflammatory cytokines in the spinal cord and dorsal horn. It also lowered the activation of microglia and astrocytes in the dorsal horn. SEMA significantly reduced HbA1c and AGE levels in diabetic rats compared to the sham control group.

CONCLUSIONS

These results indicate SEMA's neuroprotective benefits against diabetic neuropathic pain, most likely by reducing inflammation and oxidative stress by inhibiting astrocyte and microglial activity. Our findings suggest that we can repurpose GLP-1 agonists as potent anti-hyperalgesic and anti-inflammatory drugs to treat neuropathic pain without serious side effects.

Pharmacological Treatment of Binge Eating Disorder and Frequent Comorbid Diseases

Binge eating disorder (BED) is the most common specific eating disorder (ED). It is frequently associated with attention deficit hyperactivity disorder (ADHD), depression, bipolar disorder (BD), anxiety disorders, alcohol and nicotine use disorder, and obesity. The aim of this narrative review was to summarize the evidence for the pharmacological treatment of BED and its comorbid disorders. We recommend the ADHD medication lisdexamfetamine (LDX) and the antiepileptic and antimigraine drug topiramate for the pharmacological treatment of BED. However, only LDX is approved for the treatment of BED in some countries. Medications to treat diseases frequently comorbid with BED include atomoxetine and LDX for ADHD; citalopram, fluoxetine, sertraline, duloxetine, and venlafaxine for anxiety disorders and depression; aripiprazole for manic episodes of BD; lamotrigine, lirasidone and lumateperone for depressive episodes of BD; naltrexone for alcohol use disorder; bupropion for nicotine use disorder; and liraglutide, semaglutide, and the combination of bupropion and naltrexone for obesity. As obesity is a frequent health consequence of BED, weight gain-inducing medications, such as the atypical antipsychotics olanzapine or clozapine, the novel antidepressant mirtazapine and tricyclic antidepressants, and the mood stabilizer valproate should be avoided where possible. It is currently unclear whether the novel and promising glucagon, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide 1 (GLP-1) receptor agonists like tirzepatide and retatrutide help with BED and its comorbidities. However, these compounds have been reported to reduce binge eating in individuals with obesity or overweight.

Populations of Hindbrain Glucagon-Like Peptide 1 (GLP1) Neurons That Innervate the Hypothalamic PVH, Thalamic PVT, or Limbic Forebrain BST Have Axon Collaterals That Reach All Central Regions Innervated by GLP1 Neurons

Neurons in the caudal nucleus of the solitary tract (cNTS) and intermediate reticular nucleus (IRt) that express the glucagon gene (Gcg) give rise to glucagon-like peptide 1 (GLP1)-immunopositive axons in the spinal cord and many subcortical brain regions. Central GLP1 receptor signaling contributes to motivated behavior and stress responses in rats and mice, in which hindbrain GLP1 neurons are activated to express c-Fos in a metabolic state-dependent manner. The present study examined whether GLP1 inputs to distinct brain regions arise from distinct subsets of Gcg-expressing neurons, and mapped the distribution of axon collaterals arising from projection-defined GLP1 neural populations. Using our Gcg-Cre knock-in rat model, Cre-dependent adeno-associated virus (AAV) tracing was conducted in adult male and female rats to compare axonal projections of IRt versus cNTS GLP1 neurons. Overlapping projections were observed in all brain regions that receive GLP1 input, with the caveat that cNTS injections produced Cre-dependent labeling of some IRt neurons, and vice versa. In additional experiments, specific diencephalic or limbic forebrain nuclei were microinjected with Cre-dependent retrograde AAVs (AAVrg) that expressed reporters to fully label the axon collaterals of transduced GLP1 neurons. AAVrg injected into each forebrain site labeled Gcg-expressing neurons in both the cNTS and IRt. The collective axon collaterals of labeled neurons entered the spinal cord and every brain region previously reported to contain GLP1-positive axons. These results indicate that the axons of GLP1 neural populations that innervate the thalamic paraventricular nucleus, paraventricular nucleus of the hypothalamus, and/or bed nucleus of the stria terminalis collectively innervate all central regions that receive GLP1 axonal input.

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.

Influence of Bariatric Surgery on Gut Microbiota Composition and Its Implication on Brain and Peripheral Targets

Obesity remains a significant global health challenge, with bariatric surgery remaining as one of the most effective treatments for severe obesity and its related comorbidities. This review highlights the multifaceted impact of bariatric surgery beyond mere physical restriction or nutrient malabsorption, underscoring the importance of the gut microbiome and neurohormonal signals in mediating the profound effects on weight loss and behavior modification. The various bariatric surgery procedures, such as Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG), act through distinct mechanisms to alter the gut microbiome, subsequently impacting metabolic health, energy balance, and food reward behaviors. Emerging evidence has shown that bariatric surgery induces profound changes in the composition of the gut microbiome, notably altering the Firmicutes/Bacteroidetes ratio and enhancing populations of beneficial bacteria such as Akkermansia. These microbiota shifts have far-reaching effects beyond gut health, influencing dopamine-mediated reward pathways in the brain and modulating the secretion and action of key gut hormones including ghrelin, leptin, GLP-1, PYY, and CCK. The resultant changes in dopamine signaling and hormone levels contribute to reduced hedonic eating, enhanced satiety, and improved metabolic outcomes. Further, post-bariatric surgical effects on satiation targets are in part mediated by metabolic byproducts of gut microbiota like short-chain fatty acids (SCFAs) and bile acids, which play a pivotal role in modulating metabolism and energy expenditure and reducing obesity-associated inflammation, as well as influencing food reward pathways, potentially contributing to the regulation of body weight and reduction in hedonic eating behaviors. Overall, a better understanding of these mechanisms opens the door to developing non-surgical interventions that replicate the beneficial effects of bariatric surgery on the gut microbiome, dopamine signaling, and gut hormone regulation, offering new avenues for obesity treatment.

GLP-1 Receptor Signaling Has Different Effects on the Perikarya and Axons of the Hypophysiotropic Thyrotropin-Releasing Hormone Synthesizing Neurons in Male Mice

Background: Glucagon-like peptide 1 (GLP-1) is involved in the regulation of energy and glucose homeostasis. As GLP-1 has similar effects on the energy homeostasis as the hypophysiotropic thyrotropin-releasing hormone (TRH) neurons that regulate the hypothalamic-pituitary-thyroid (HPT) axis, we raised the possibility that the TRH neurons are involved in the mediation of the effects of GLP-1. Therefore, the relationship and interaction of the GLP-1 system and the TRH neurons of the hypothalamic paraventricular nucleus (PVN) were studied. Methods: To examine the anatomical and functional relationship of TRH neurons and the GLP-1 system in the PVN, immunocytochemistry, in situ hybridization, in vitro patch-clamp electrophysiology, metabolic phenotyping, and explant experiments were performed. Results: Our data demonstrate that the TRH neurons of the PVN are innervated by GLP-1 producing neurons and express the GLP-1 receptor (GLP-1R). However, not only do the GLP-1-innervated TRH neurons express GLP-1R but the receptor is also present in the axons of the hypophysiotropic TRH neurons in the blood-brain barrier free median eminence (ME) suggesting that peripherally derived GLP-1 may also influence the TRH neurons. In vitro, GLP-1 increased the firing rate of TRH neurons and depolarized them. In addition, GLP-1 directly stimulated the GABAergic input of a population of TRH neurons. Furthermore, GLP-1 inhibited the release of TRH from the hypophysiotropic axons in the ME. In vivo, peripheral GLP-1R agonist administration markedly inhibited the food intake and the energy expenditure, but had no effect on the TRH expression in the PVN and resulted in lower circulating free T4 levels. Conclusions: Our results indicate that GLP-1R activation has a direct stimulatory effect on TRH neurons in the PVN, but the activation of GLP-1R may also inhibit TRH neurons by facilitating their inhibitory inputs or by inhibiting the axon terminals of these cells in the ME. The innervation of TRH neurons by GLP-1 neurons suggests that TRH neurons might be influenced by both circulating GLP-1 and by GLP-1 neurons of the nucleus tractus solitarii. The lack of GLP-1R agonist-induced regulation of TRH neurons in vivo suggests that the HPT axis does not mediate the GLP-1R agonist-induced weight loss.

Obesity and Depression: Common Link and Possible Targets

Depression is among the main causes of disability, and its protracted manifestations could make it even harder to treat metabolic diseases. Obesity is linked to episodes of depression, which is closely correlated to abdominal adiposity and impaired food quality. The present review is aimed at studying possible links between obesity and depression along with targets to disrupt it. Research output in Pubmed and Scopus were referred for writing this manuscript. Obesity and depression are related, with the greater propensity of depressed people to gain weight, resulting in poor dietary decisions and a sedentary lifestyle. Adipokines, which include adiponectin, resistin, and leptin are secretory products of the adipose tissue. These adipokines are now being studied to learn more about the connection underlying obesity and depression. Ghrelin, a gut hormone, controls both obesity and depression. Additionally, elevated ghrelin levels result in anxiolytic and antidepressant-like effects. The gut microbiota influences the metabolic functionalities of a person, like caloric processing from indigestible nutritional compounds and storage in fatty tissue, that exposes an individual to obesity, and gut microorganisms might connect to the CNS through interconnecting pathways, including neurological, endocrine, and immunological signalling systems. The alteration of brain activity caused by gut bacteria has been related to depressive episodes. Monoamines, including dopamine, serotonin, and norepinephrine, have been widely believed to have a function in emotions and appetite control. Emotional signals stimulate arcuate neurons in the hypothalamus that are directly implicated in mood regulation and eating. The peptide hormone GLP-1(glucagon-like peptide- 1) seems to have a beneficial role as a medical regulator of defective neuroinflammation, neurogenesis, synaptic dysfunction, and neurotransmitter secretion discrepancy in the depressive brain. The gut microbiota might have its action in mood and cognition regulation, in addition to its traditional involvement in GI function regulation. This review addressed the concept that obesity-related low-grade mild inflammation in the brain contributes to chronic depression and cognitive impairments.

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.

Glucagon-like peptide-1 analogues: a new way to quit smoking? (SKIP)-a structured summary of a study protocol for a randomized controlled study

BACKGROUND

Cigarette smoking is the leading preventable cause of premature death. Despite dedicated programmes, quit rates remain low due to barriers such as nicotine withdrawal syndrome or post-cessation weight gain. Glucagon-like peptide-1 (GLP-1) analogues reduce energy intake and body weight and seem to modulate addictive behaviour. These GLP-1 properties are of major interest in the context of smoking cessation. The aim of this study is to evaluate the GLP-1 analogue dulaglutide as a new therapy for smoking cessation.

METHODS

This is a placebo-controlled, double-blind, parallel group, superiority, single-centre randomized study including 255 patients. The intervention consists of a 12-week dulaglutide treatment phase with 1.5 mg once weekly or placebo subcutaneously, in addition to standard of care (behavioural counselling and pharmacotherapy with varenicline). A 40-week non-treatment phase follows. The primary outcome is the point prevalence abstinence rate at week 12. Smoking status is self-reported and biochemically confirmed by end-expiratory exhaled carbon monoxide measurement. Further endpoints include post-cessational weight gain, nicotine craving analysis, glucose homeostasis and long-term nicotine abstinence. Two separate substudies assess behavioural, functional and structural changes by functional magnetic resonance imaging and measures of energy metabolism (i.e. resting energy expenditure, body composition).

DISCUSSION

Combining behavioural counselling and medical therapy, e.g. with varenicline, improves abstinence rates and is considered the standard of care. We expect a further increase in quit rates by adding a second component of medical therapy and assume a dual effect of dulaglutide treatment (blunting nicotine withdrawal symptoms and reducing post-cessational weight gain). This project is of high relevance as it explores novel treatment options aimed at preventing the disastrous consequences of nicotine consumption and obesity.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03204396 . Registered on June 26, 2017.

The pleiotropic of GLP-1/GLP-1R axis in central nervous system diseases

Glucagon-like peptide-1(GLP-1) is a multifunctional polypeptide throughout the lifespan via activating Glucagon-like peptide-1 receptor (GLP-1R).GLP-1 can affect food ingestion, enhance the secretion of insulin from pancreatic islets induced by glucose and be utilized to treat type 2 diabetes mellitus(T2DM).But, accumulating evidences from the decades suggest that activation GLP-1R can not only regulate the blood glucose, but also sustain the homeostasis of intracellular environment and protect neuron from various damaged responses such as oxidative stress, inflammation, excitotoxicity, ischemia and so on. And more and more pre-clinical and clinical studies identified that GLP-1 and its analogues may play a significant role in improving multiple central nervous system (CNS) diseases including neurodegenerative diseases, epilepsy, mental disorders, ischemic stroke, hemorrhagic stroke, traumatic brain injury, spinal cord injury, chronic pain, addictive disorders, other diseases neurological complications and so on. In order to better reveal the relationship between GLP-1/GLP-1R axis and the growth, development and survival of neurons, herein, this review is aimed to summarize the multi-function of GLP-1/GLP-1R axis in CNS diseases.

Differential association between the GLP1R gene variants and brain functional connectivity according to the severity of alcohol use

Growing evidence suggests that the glucagon-like peptide-1 (GLP-1) system is involved in mechanisms underlying alcohol seeking and consumption. Accordingly, the GLP-1 receptor (GLP-1R) has begun to be studied as a potential pharmacotherapeutic target for alcohol use disorder (AUD). The aim of this study was to investigate the association between genetic variation at the GLP-1R and brain functional connectivity, according to the severity of alcohol use. Participants were 181 individuals categorized as high-risk (n = 96) and low-risk (n = 85) alcohol use, according to their AUD identification test (AUDIT) score. Two uncommon single nucleotide polymorphisms (SNPs), rs6923761 and rs1042044, were selected a priori for this study because they encode amino-acid substitutions with putative functional consequences on GLP-1R activity. Genotype groups were based on the presence of the variant allele for each of the two GLP-1R SNPs of interest [rs6923761: AA + AG (n = 65), GG (n = 116); rs1042044: AA + AC (n = 114), CC (n = 67)]. Resting-state functional MRI data were acquired for 10 min and independent component (IC) analysis was conducted. Multivariate analyses of covariance (MANCOVA) examined the interaction between GLP-1R genotype group and AUDIT group on within- and between-network connectivity. For rs6923761, three ICs showed significant genotype × AUDIT interaction effects on within-network connectivity: two were mapped onto the anterior salience network and one was mapped onto the visuospatial network. For rs1042044, four ICs showed significant interaction effects on within-network connectivity: three were mapped onto the dorsal default mode network and one was mapped onto the basal ganglia network. For both SNPs, post-hoc analyses showed that in the group carrying the variant allele, high versus low AUDIT was associated with stronger within-network connectivity. No significant effects on between-network connectivity were found. In conclusion, genetic variation at the GLP-1R was differentially associated with brain functional connectivity in individuals with low versus high severity of alcohol use. Significant findings in the salience and default mode networks are particularly relevant, given their role in the neurobiology of AUD and addictive behaviors.

Impaired Brain Satiety Responses After Weight Loss in Children With Obesity

CONTEXT

Obesity interventions often result in increased motivation to eat.

OBJECTIVE

We investigated relationships between obesity outcomes and changes in brain activation by visual food cues and hormone levels in response to obesity intervention by family-based behavioral treatment (FBT).

METHODS

Neuroimaging and hormone assessments were conducted before and after 24-week FBT intervention in children with obesity (OB, n = 28), or children of healthy weight without intervention (HW, n = 17), all 9- to 11-year-old boys and girls. We evaluated meal-induced changes in neural activation to high- vs low-calorie food cues across appetite-processing brain regions and gut hormones.

RESULTS

Among children with OB who underwent FBT, greater declines of BMI z-score were associated with lesser reductions after the FBT intervention in meal-induced changes in neural activation to high- vs low-calorie food cues across appetite-processing brain regions (P < 0.05), and the slope of relationship was significantly different compared with children of HW. In children with OB, less reduction in brain responses to a meal from before to after FBT was associated with greater meal-induced reduction in ghrelin and increased meal-induced stimulation in peptide YY and glucagon-like peptide-1 (all P < 0.05).

CONCLUSION

In response to FBT, adaptations of central satiety responses and peripheral satiety-regulating hormones were noted. After weight loss, changes of peripheral hormone secretion support weight loss, but there was a weaker central satiety response. The findings suggest that even when peripheral satiety responses by gut hormones are intact, the central regulation of satiety is disturbed in children with OB who significantly improve their weight status during FBT, which could favor future weight regain.

Glucagon-Like Peptide-1 Agonist Exendin-4 Facilitates the Extinction of Cocaine-Induced Condition Place Preference

Accumulating studies suggest that the glucagon-like peptide-1 receptor agonist exendin-4 (Ex4) and toll-like receptor 4 (TLR4) play a pivotal role in the maladaptive behavior of cocaine. However, few studies have assessed whether Ex4 can facilitate the extinction of drug-associated behavior and attenuate the reinstatement of cocaine-induced condition place preference (CPP) in mice. The main objective of the present study was to evaluate Ex4's ability to regulate the extinction and reinstatement of cocaine-induced CPP. C57BL/6 mice were conditioned to either cocaine (20 mg/kg) or an equivalent volume of saline to establish a cocaine-mediated CPP paradigm. To investigate the potential effects of Ex4 on extinction, animals received an intraperitoneal injection of Ex4 either immediately or 6 h after each extinction or only on the test day. The persistence of extinction was measured using the reinstatement paradigm evoked by 10 mg/kg of cocaine. To explore the possible impacts of Ex4 and neuroinflammation on cocaine, the expression levels of TLR4 within the hippocampus was detected using western blotting. As a result, we found that systemic administration of Ex4 immediately after each extinction training, instead of 6 h after each extinction and on the day of extinction test, was capable of facilitating extinction in the confined or non-confined CPP extinction paradigms and blocking the cocaine-primed reinstatement of cocaine-induced CPP. Additionally, we also observed that Ex4 was competent to alleviate TLR4 signaling that has been up-regulated by cocaine. Altogether, our findings indicated that the combination of Ex4 with daily extinction training was sufficient to facilitate extinction of the conditioned behavior, attenuate reinstatement of cocaine-induced CPP and inhibit TLR4 signaling. Thus, Ex4 deserves further investigation as a potential intervention for the treatment of cocaine use disorder.

Effects of Glucagon-Like Peptide-1 Receptor Agonist Exendin-4 on the Reinstatement of Cocaine-Mediated Conditioned Place Preference in Mice

A high percentage of relapse to compulsive cocaine-taking and cocaine-seeking behaviors following abstinence constitutes a major obstacle to the clinical treatment of cocaine addiction. Thus, there is a substantial need to develop effective pharmacotherapies for the prevention of cocaine relapse. The reinstatement paradigm is known as the most commonly used animal model to study relapse in abstinent human addicts. The primary aim of this study is to investigate the potential effects of systemic administration of glucagon-like peptide-1 receptor agonist (GLP-1RA) exendin-4 (Ex4) on the cocaine- and stress-triggered reinstatement of cocaine-induced conditioned place preference (CPP) in male C57BL/6J mice. The biased CPP paradigm was induced by alternating administration of saline and cocaine (20 mg/kg), followed by extinction training and then reinstatement by either a cocaine prime (10 mg/kg) or exposure to swimming on the reinstatement test day. To examine the effects of Ex4 on the reinstatement, Ex4 was systemically administered 1 h after the daily extinction session. Additionally, we also explored the associated molecular basis of the behavioral effects of Ex4. The expression of nuclear factor κβ (NF-κβ) in the nucleus accumbens (NAc) was detected using Western blotting. As a result, all animals that were treated with cocaine during the conditioning period successfully acquired CPP, and their CPP response was extinguished after 8 extinction sessions. Furthermore, the animals that were exposed to cocaine or swimming on the reinstatement day showed a significant reinstatement of CPP. Interestingly, systemic pretreatment with Ex4 was sufficient to attenuate cocaine- and stress-primed reinstatement of cocaine-induced CPP. Additionally, the expression of NF-κβ, which was upregulated by cocaine, was normalized by Ex4 in the cocaine-experienced mice. Altogether, our study reveals the novel effect of Ex4 on the reinstatement of cocaine-induced CPP and suggests that GLP-1R agonists appear to be highly promising drugs in the treatment of cocaine use disorder.

A novel approach to treating opioid use disorders: Dual agonists of glucagon-like peptide-1 receptors and neuropeptide Y2 receptors

The widespread misuse of opioids and opioid use disorder (OUD) together constitute a major public health crisis in the United States. The greatest challenge for successfully treating OUD is preventing relapse. Unfortunately, there are few FDA-approved medications to treat OUD and, while effective, these pharmacotherapies are limited by high relapse rates. Thus, there is a critical need for conceptually new approaches to developing novel medications to treat OUD. Here, we review an emerging preclinical literature that suggests that glucagon-like peptide-1 receptor (GLP-1R) agonists could be re-purposed for treating OUD. Potential limitations of this approach are also discussed along with an alternative strategy that involves simultaneously targeting and activating GLP-1Rs and neuropeptide Y2 receptors (Y2Rs) in the brain using a novel monomeric dual agonist peptide. Recent studies indicate that this combinatorial pharmacotherapy approach attenuates voluntary fentanyl taking and seeking in rats without producing adverse effects associated with GLP-1R agonist monotherapy alone. While future studies are required to comprehensively determine the behavioral effects of GLP-1R agonists and dual agonists of GLP-1Rs and Y2Rs in rodent models of OUD, these provocative preclinical findings highlight a potential new GLP-1R-based approach to preventing relapse in humans with OUD.

A randomized controlled trial of the GLP-1 receptor agonist dulaglutide in primary polydipsia

BackgroundPrimary polydipsia, characterized by excessive fluid intake, carries the risk of water intoxication and hyponatremia, but treatment options are scarce. Glucagon-like peptide 1 (GLP-1) reduces appetite and food intake. In experimental models, GLP-1 has also been shown to play a role in thirst and drinking behavior. The aim of this trial was to investigate whether GLP-1 receptor agonists reduce fluid intake in patients with primary polydipsia.MethodsIn this randomized, double-blind, placebo-controlled, 3-week crossover trial, 34 patients with primary polydipsia received weekly dulaglutide (1.5 mg, Trulicity) in one treatment segment and placebo (0.9% sodium chloride) in the other. During the last treatment week, patients attended an 8-hour evaluation visit with free access to water. The primary endpoint was total fluid intake during the evaluation visits. Treatment effects were estimated using linear mixed-effects models. In a subset of 15 patients and an additional 15 matched controls, thirst perception and neuronal activity in response to beverage pictures were assessed by functional MRI.RESULTsPatients on dulaglutide reduced their fluid intake by 490 mL (95% CI: -780, -199; P = 0.002), from 2950 mL (95% CI: 2435, 3465) on placebo to 2460 mL (95% CI: 1946, 2475) on dulaglutide (model estimates), corresponding to a relative reduction of 17%. Twenty-four-hour urinary output was reduced by -943 mL (95% CI: -1473, -413; P = 0.001). Thirst perception in response to beverage pictures was higher for patients with primary polydipsia than for controls, and lower for patients on dulaglutide versus placebo, but functional activity was similar among groups and treatments.CONCLUSIONSGLP-1 receptor agonists reduce fluid intake and thirst perception in patients with primary polydipsia and could therefore be a treatment option for these patients.Trial registrationClinicaltrials.gov NCT02770885.FundingSwiss National Science Foundation (grant 32473B_162608); University Hospital and University of Basel; Young Talents in Clinical Research grant from the Swiss Academy of Medical Sciences and the Gottfried & Julia Bangerter-Rhyner Foundation; Top-up Grant from the PhD Programme in Health Sciences, University of Basel.

Gastrointestinal peptides in eating-related disorders

Food intake is tightly controlled by homeostatic signals sensitive to metabolic need for the regulation of body weight. This review focuses on the peripherally-secreted gastrointestinal peptides (i.e., ghrelin, cholecystokinin, glucagon-like peptide 1, and peptide tyrosine tyrosine) that contribute to the control of appetite and discusses how these peptides or the signals arising from their release are disrupted in eating-related disorders across the weight spectrum, namely anorexia nervosa, bulimia nervosa, and obesity, and whether they are normalized following weight restoration or weight loss treatment. Further, the role of gut peptides in the pathogenesis and treatment response in human weight conditions as identified by rodent models are discussed. Lastly, we review the incretin- and hormone-based pharmacotherapies available for the treatment of obesity and eating-related disorders.

Glucagon-Like Peptide-1 Analog Exendin-4 Ameliorates Cocaine-Mediated Behavior by Inhibiting Toll-Like Receptor 4 Signaling in Mice

Exendin-4 (Ex4), a long-lasting glucagon-like peptide-1 analog, was reported to exert favourable actions on inhibiting cocaine-associated rewarding and reinforcing effects of drug in animal models of addiction. However, the therapeutic potential of different dose of GLP-1 receptor agonist Ex4 in different behavioral paradigms and the underlying pharmacological mechanisms of action are incompletely understood. Herein, we firstly investigated the effects of Ex4 on cocaine-induced condition place preference (CPP) as well as extinction and reinstatement in male C57BL/6J mice. Additionally, we sought to elucidate the underlying pharmacological mechanism of these actions of Ex4. The paradigm of cocaine-induced CPP was established using 20 mg/kg cocaine or saline alternately during conditioning, while the reinstatement paradigm was modeled using 10 mg/kg cocaine on the reinstatement day. Different dose of Ex4 was administrated intraperitoneally either during conditioning or during extinction state or only on the test day. To elucidate the molecular mechanism underlying the potential effects of Ex4 on maladaptive behaviors of cocaine, the TLR4-related inflammation within the hippocampus was observed by immunofluorescence staining, and the expression levels of toll-like receptor 4 (TLR4), tumor necrosis factor (TNF)-α, and interleukin (IL)-1β were detected by Western blotting. As a consequence, systemic administration of different dose of Ex4 was sufficient to inhibit the acquisition and expression of cocaine-induced CPP, facilitate the extinction of cocaine-associated reward and attenuate reinstatement of cocaine-induced behavior. Furthermore, Ex4 treatment diminished expression levels of TLR4, TNF-α, and IL-1β, which were up-regulated by cocaine exposure. Altogether, our results indicated that Ex4 effectively ameliorated cocaine-induced behaviors likely through neurobiological mechanisms partly attributable to the inhibition of TLR4, TNF-α and IL-1β in mice. Consequently, our findings improved our understanding of the efficacy of Ex4 for the amelioration of cocaine-induced behavior and suggested that Ex4 may be applied as a drug candidate for cocaine addiction.

A novel dual agonist of glucagon-like peptide-1 receptors and neuropeptide Y2 receptors attenuates fentanyl taking and seeking in male rats

There has been a dramatic increase in illicit fentanyl use in the United States over the last decade. In 2018, more than 31,000 overdose deaths involved fentanyl or fentanyl analogs, highlighting an urgent need to identify effective treatments for fentanyl use disorder. An emerging literature shows that glucagon-like peptide-1 receptor (GLP-1R) agonists attenuate the reinforcing efficacy of drugs of abuse. However, the effects of GLP-1R agonists on fentanyl-mediated behaviors are unknown. The first goal of this study was to determine if the GLP-1R agonist exendin-4 reduced fentanyl self-administration and the reinstatement of fentanyl-seeking behavior, an animal model of relapse, in rats. We found that systemic exendin-4 attenuated fentanyl taking and seeking at doses that also produced malaise-like effects in rats. To overcome these adverse effects and enhance the clinical potential of GLP-1R agonists, we recently developed a novel dual agonist of GLP-1Rs and neuropeptide Y2 receptors (Y2Rs), GEP44, that does not produce nausea-like behavior in drug-naïve rats or emesis in drug-naïve shrews. The second goal of this study was to determine if GEP44 reduced fentanyl self-administration and reinstatement with fewer adverse effects compared to exendin-4 alone. In contrast to exendin-4, GEP44 attenuated opioid taking and seeking at a dose that did not suppress food intake or produce adverse malaise-like effects in fentanyl-experienced rats. Taken together, these findings indicate a novel role for GLP-1Rs and Y2Rs in fentanyl reinforcement and highlight a potential new therapeutic approach to treating opioid use disorders.

Corrination of a GLP-1 Receptor Agonist for Glycemic Control without Emesis

Glucagon-like peptide-1 receptor (GLP-1R) agonists used to treat type 2 diabetes mellitus often produce nausea, vomiting, and in some patients, undesired anorexia. Notably, these behavioral effects are caused by direct central GLP-1R activation. Herein, we describe the creation of a GLP-1R agonist conjugate with modified brain penetrance that enhances GLP-1R-mediated glycemic control without inducing vomiting. Covalent attachment of the GLP-1R agonist exendin-4 (Ex4) to dicyanocobinamide (Cbi), a corrin ring containing precursor of vitamin B12, produces a "corrinated" Ex4 construct (Cbi-Ex4). Data collected in the musk shrew (Suncus murinus), an emetic mammal, reveal beneficial effects of Cbi-Ex4 relative to Ex4, as evidenced by improvements in glycemic responses in glucose tolerance tests and a profound reduction of emetic events. Our findings highlight the potential for clinical use of Cbi-Ex4 for millions of patients seeking improved glycemic control without common side effects (e.g., emesis) characteristic of current GLP-1 therapeutics.

Similarities in alcohol and opioid withdrawal syndromes suggest common negative reinforcement mechanisms involving the interoceptive antireward pathway

Alcohol and opioids are two major contributors to so-called deaths of despair. Though the effects of these substances on mammalian systems are distinct, commonalities in their withdrawal syndromes suggest a shared pathophysiology. For example, both are characterized by marked autonomic dysregulation and are treated with alpha-2 agonists. Moreover, alcohol and opioids rapidly induce dependence motivated by withdrawal avoidance. Resemblances observed in withdrawal syndromes and abuse behavior may indicate common addiction mechanisms. We argue that neurovisceral feedback influences autonomic and emotional circuits generating antireward similarly for both substances. Amygdala is central to this hypothesis as it is principally responsible for negative emotion, prominent in addiction and motivated behavior, and processes autonomic inputs while generating autonomic outputs. The solitary nucleus (NTS) has strong bidirectional connections to the amygdala and receives interoceptive inputs communicating visceral states via vagal afferents. These visceral-emotional hubs are strongly influenced by the periphery including gut microbiota. We propose that gut dysbiosis contributes to alcohol and opioid withdrawal syndromes by contributing to peripheral and neuroinflammation that stimulates these antireward pathways and motivates substance dependence.

Insights into a possible role of glucagon-like peptide-1 receptor agonists in the treatment of depression

Depression is a highly prevalent mood disorder and one of the major health concerns in modern society. Moreover, it is characterized by a high prevalence of coexistence with many other diseases including metabolic disorders such as type 2 diabetes mellitus (T2DM) and obesity. Currently used antidepressant drugs, which mostly target brain monoaminergic neurotransmission, have limited clinical efficacy. Although the etiology of depression has not been fully elucidated, current scientific data emphasize the role of neurotrophic factors deficiencies, disturbed homeostasis between the nervous system and the immune and endocrine systems, as well as disturbances in brain energy metabolism and dysfunctions in the gut-brain axis as important factors in the pathogenesis of this neuropsychiatric disorder. Therefore, therapeutic options that could work in a way other than classic antidepressants are being sought to increase the effectiveness of the treatment. Interestingly, glucagon-like peptide-1 receptor agonists (GLP-1RAs), used in the treatment of T2DM and obesity, are known to show pro-cognitive and neuroprotective properties, and exert modulatory effects on immune, endocrine and metabolic processes in the central nervous system. This review article discusses the potential antidepressant effects of GLP-1RAs, especially in the context of their action on the processes related to neuroprotection, inflammation, stress response, energy metabolism, gut-brain crosstalk and the stability of the gut microbiota.

Synthesis, Optimization, and Biological Evaluation of Corrinated Conjugates of the GLP-1R Agonist Exendin-4

Corrination is the conjugation of a corrin ring containing molecule, such as vitamin B₁₂ (B12) or B12 biosynthetic precursor dicyanocobinamide (Cbi), to small molecules, peptides, or proteins with the goal of modifying pharmacology. Recently, a corrinated GLP-1R agonist (GLP-1RA) exendin-4 (Ex4) has been shown in vivo to have reduced penetration into the central nervous system relative to Ex4 alone, producing a glucoregulatory GLP-1RA devoid of anorexia and emesis. The study herein was designed to optimize the lead conjugate for GLP-1R agonism and binding. Two specific conjugation sites were introduced in Ex4, while also utilizing various linkers, so that it was possible to identify Cbi conjugates of Ex4 that exhibit improved binding and agonist activity at the GLP-1R. An optimized conjugate (22), comparable with Ex4, was successfully screened and subsequently assayed for insulin secretion in rat islets and in vivo in shrews for glucoregulatory and emetic behavior, relative to Ex4.

Activation of PPG neurons following acute stressors differentially involves hindbrain serotonin in male rats

Within the hindbrain, serotonin (5-HT) functions as a modulator of the central glucagon-like peptide-1 (GLP-1) system. This interaction between 5-HT and GLP-1 is achieved via 5-HT2C and 5-HT3 receptors and is relevant for GLP-1-mediated feeding behavior. The central GLP-1 system is activated by various stressors, activates the hypothalamic pituitary adrenocortical (HPA) axis, and contributes to stress-related behaviors. Whether 5-HT modulates GLP-1's role in the stress response in unknown. We hypothesized that the serotonergic modulation of GLP-1-producing neurons (i.e., PPG neurons) is stimuli-specific and that stressed-induced PPG activity is one of the modalities in which 5-HT plays a role. In this study, we investigated the roles of 5-HT2C and 5-HT3 receptors in mediating the activation of PPG neurons in the nucleus tractus solitarius (NTS) following exposure to three different acute stressors: lithium chloride (LiCl), noncontingent cocaine (Coc), and novel restraint stress (RES). Results showed that increased c-Fos expression in PPG neurons following LiCl and RES-but not Coc-is dependent on hindbrain 5-HT2C and 5-HT3 receptor signaling. Additionally, stressors that depend on 5-HT signaling to activate PPG neurons (i.e., LiCl and RES) increased c-Fos expression in 5-HT-expressing neurons within the caudal raphe (CR), specifically in the raphe magnus (RMg). Finally, we showed that RMg neurons innervate NTS PPG neurons and that some of these PPG neurons lie in close proximity to 5-HT axons, suggesting RMg 5-HT-expressing neurons are the source of 5-HT input responsible for engaging NTS PPG neurons. Together, these findings identify a direct RMg to NTS pathway responsible for the modulatory effect of 5-HT on the central GLP-1 system-specifically via activation of 5-HT2C and 5-HT3 receptors-in the facilitation of acute stress responses.

Central and peripheral GLP-1 systems independently suppress eating

The anorexigenic peptide glucagon-like peptide-1 (GLP-1) is secreted from gut enteroendocrine cells and brain preproglucagon (PPG) neurons, which, respectively, define the peripheral and central GLP-1 systems. PPG neurons in the nucleus tractus solitarii (NTS) are widely assumed to link the peripheral and central GLP-1 systems in a unified gut-brain satiation circuit. However, direct evidence for this hypothesis is lacking, and the necessary circuitry remains to be demonstrated. Here we show that PPGNTS neurons encode satiation in mice, consistent with vagal signalling of gastrointestinal distension. However, PPGNTS neurons predominantly receive vagal input from oxytocin-receptor-expressing vagal neurons, rather than those expressing GLP-1 receptors. PPGNTS neurons are not necessary for eating suppression by GLP-1 receptor agonists, and concurrent PPGNTS neuron activation suppresses eating more potently than semaglutide alone. We conclude that central and peripheral GLP-1 systems suppress eating via independent gut-brain circuits, providing a rationale for pharmacological activation of PPGNTS neurons in combination with GLP-1 receptor agonists as an obesity treatment strategy.

Obesity and Dietary Added Sugar Interact to Affect Postprandial GLP-1 and Its Relationship to Striatal Responses to Food Cues and Feeding Behavior

It has been hypothesized that the incretin hormone, glucagon-like peptide-1 (GLP-1), decreases overeating by influencing mesolimbic brain regions that process food-cues, including the dorsal striatum. We previously showed that habitual added sugar intake was associated with lower glucose-induced circulating GLP-1 and a greater striatal response to high calorie food cues in lean individuals. Less is known about how dietary added sugar and obesity may interact to affect postprandial GLP-1 and its relationship to striatal responses to food cues and feeding behavior. The current study aimed to expand upon previous research by assessing how circulating GLP-1 and striatal food cue reactivity are affected by acute glucose consumption in participants with varied BMIs and amounts of habitual consumption of added sugar. This analysis included 72 participants from the Brain Response to Sugar Study who completed two study visits where they consumed either plain water or 75g glucose dissolved in water (order randomized; both drinks were flavored with non-caloric cherry flavoring) and underwent repeated blood sampling, a functional magnetic resonance imaging (fMRI) based food-cue task, and an ad-libitum buffet meal. Correlations between circulating GLP-1 levels, striatal food-cue reactivity, and food intake were assessed, and interactions between obesity and added sugar on GLP-1 and striatal responses were examined. An interaction between BMI and dietary added sugar was associated with reduced post-glucose GLP-1 secretion. Participants who were obese and consumed high levels of added sugar had the smallest increase in plasma GLP-1 levels. Glucose-induced GLP-1 secretion was correlated with lower dorsal striatal reactivity to high-calorie versus low-calorie food-cues, driven by an increase in reactivity to low calorie food-cues. The increase in dorsal striatal reactivity to low calorie food-cues was negatively correlated with sugar consumed at the buffet. These findings suggest that an interaction between obesity and dietary added sugar intake is associated with additive reductions in postprandial GLP-1 secretion. Additionally, the results suggest that changes to dorsal striatal food cue reactivity through a combination of dietary added sugar and obesity may affect food consumption.

Distribution and ultrastructural localization of the glucagon-like peptide-1 receptor (GLP-1R) in the rat brain

Glucagon-like peptide-1 (GLP-1) inhibits food intake and regulates glucose homeostasis. These actions are at least partly mediated by central GLP-1 receptor (GLP-1R). Little information is available, however, about the subcellular localization and the distribution of the GLP-1R protein in the rat brain. To determine the localization of GLP-1R protein in the rat brain, immunocytochemistry was performed at light and electron microscopic levels. The highest density of GLP-1R-immunoreactivity was observed in the circumventricular organs and regions in the vicinity of these areas like in the arcuate nucleus (ARC) and in the nucleus tractus solitarii (NTS). In addition, GLP-1R-immunreactive (IR) neuronal profiles were also observed in a number of telencephalic, diencephalic and brainstem areas and also in the cerebellum. Ultrastructural examination of GLP-1R-immunoreactivity in energy homeostasis related regions showed that GLP-1R immunoreactivity is associated with the membrane of perikarya and dendrites but GLP-1R can also be observed inside and on the surface of axon varicosities and axon terminals. In conclusion, in this study we provide a detailed map of the GLP-1R-IR structures in the CNS. Furthermore, we demonstrate that in addition to the perikaryonal and dendritic distribution, GLP-1R is also present in axonal profiles suggesting a presynaptic action of GLP-1. The very high concentration of GLP-1R-profiles in the circumventricular organs and in the ARC and NTS suggests that peripheral GLP-1 may influence brain functions via these brain areas.

Understanding the Mechanism of Activation/Deactivation of GLP-1R via Accelerated Molecular Dynamics Simulation

Glucagon-like peptide-1 receptor (GLP-1R), as a member of the class B G protein-coupled receptors (GPCRs), plays a crucial role in regulating blood glucose level signal recognition through its activation. The conformation changes during the activation pathway are of particular importance for its function. To investigate the activation mechanism of GLP-1R, the crystal structures of active and inactive forms are chosen to perform a total of 2 μs of accelerated molecular dynamics (aMD) simulations and 400ns of conventional molecular dynamics (cMD) simulations. With the aid of structural analysis and potential of mean force (PMF) calculations, we reveal the role of different helices in the activation and deactivation process and obtain the intermediate states during activation and deactivation that are difficult to capture in experiments. Protein structure network (PSN) was utilised to clarify the allosteric communication pathways of activation and deactivation and reveal the mechanisms of its activation and deactivation. The results could advance our understanding of the activation mechanism of GLP-1R and the related drug design.

An Overview of Similarities and Differences in Metabolic Actions and Effects of Central Nervous System Between Glucagon-Like Peptide-1 Receptor Agonists (GLP-1RAs) and Sodium Glucose Co-Transporter-2 Inhibitors (SGLT-2is)

GLP-1 receptor agonists (GLP-1RAs) and SGLT-2 inhibitors (SGLT-2is) are novel antidiabetic medications associated with considerable cardiovascular benefits therapying treatment of diabetic patients. GLP-1 exhibits atherosclerosis resistance, whereas SGLT-2i acts to ameliorate the neuroendocrine state in the patients with chronic heart failure. Despite their distinct modes of action, both factors share pathways by regulating the central nervous system (CNS). While numerous preclinical and clinical studies have demonstrated that GLP-1 can access various nuclei associated with energy homeostasis and hedonic eating in the CNS via blood-brain barrier (BBB), research on the activity of SGLT-2is remains limited. In our previous studies, we demonstrated that both GLP-1 receptor agonists (GLP-1RAs) liraglutide and exenatide, as well as an SGLT-2i, dapagliflozin, could activate various nuclei and pathways in the CNS of Sprague Dawley (SD) rats and C57BL/6 mice, respectively. Moreover, our results revealed similarities and differences in neural pathways, which possibly regulated different metabolic effects of GLP-1RA and SGLT-2i via sympathetic and parasympathetic systems in the CNS, such as feeding, blood glucose regulation and cardiovascular activities (arterial blood pressure and heart rate control). In the present article, we extensively discuss recent preclinical studies on the effects of GLP-1RAs and SGLT-2is on the CNS actions, with the aim of providing a theoretical explanation on their mechanism of action in improvement of the macro-cardiovascular risk and reducing incidence of diabetic complications. Overall, these findings are expected to guide future drug design approaches.

Alleviation of Depression by Glucagon-Like Peptide 1 Through the Regulation of Neuroinflammation, Neurotransmitters, Neurogenesis, and Synaptic Function

Depression has emerged as a major cause of mortality globally. Many studies have reported risk factors and mechanisms associated with depression, but it is as yet unclear how these findings can be applied to the treatment and prevention of this disorder. The onset and recurrence of depression have been linked to diverse metabolic factors, including hyperglycemia, dyslipidemia, and insulin resistance. Recent studies have suggested that depression is accompanied by memory loss as well as depressive mood. Thus, many researchers have highlighted the relationship between depressive behavior and metabolic alterations from various perspectives. Glucagon-like peptide-1 (GLP-1), which is secreted from gut cells and hindbrain areas, has been studied in metabolic diseases such as obesity and diabetes, and was shown to control glucose metabolism and insulin resistance. Recently, GLP-1 was highlighted as a regulator of diverse pathways, but its potential as the therapeutic target of depressive disorder was not described comprehensively. Therefore, in this review, we focused on the potential of GLP-1 modulation in depression.

Impact of dose-escalation schemes and drug discontinuation on weight loss outcomes with liraglutide 3.0 mg: A model-based approach

AIMS

To investigate the impact on weight loss of the treatment changes in overweight or obese people that may be needed in case of gastrointestinal (GI) tolerability issues during escalation of the glucagon-like peptide-1 analogue liraglutide.

MATERIALS AND METHODS

The individual longitudinal body weight data from the main trial periods of three phase II/III trials in overweight or obese patients (56-week treatment with once-daily liraglutide 1.2, 1.8, 2.4 or 3.0 mg or placebo, n = 4952) were analysed using a non-linear mixed-effect modelling approach. Individual pharmacokinetic profiles were derived based on published pharmacokinetic models. Baseline body weight, baseline glycated haemoglobin (HbA1c), age, gender, diabetes status (no diabetes, prediabetes or type 2 diabetes), race and trial region were investigated as covariates. As a form of external validation, the model was used to predict the weight regain after treatment cessation at week 56 (data not included in model development).

RESULTS

A pharmacokinetic/pharmacodynamic model provided an adequate description of the weight loss trajectories for all studied doses. Gender and diabetes status were identified as the most influential covariates, and an underlying seasonal weight fluctuation was identified. Slower than that recommended, one-week dose-escalation algorithms led up to 2 weeks slower initial weight loss but similar long-term weight loss trajectories.

CONCLUSIONS

The relationship between liraglutide systemic exposure and weight loss was successfully established in overweight or obese people. The model could predict the time course of weight regain after treatment cessation and suggests that GI tolerability can be mitigated by slower escalation with only minor impact on the weight loss trajectory.

Binge-like palatable food intake in rats reduces preproglucagon in the nucleus tractus solitarius

Binge eating involves eating larger than normal quantities of food within a discrete period of time. The neurohormonal controls governing binge-like palatable food intake are not well understood. Glucagon-like peptide-1 (GLP-1), a hormone produced peripherally in the intestine and centrally in the nucleus tractus solitarius (NTS), reduces food intake. Given that the NTS plays a critical role in integrating peripheral and central signals relevant for food intake, as well as the role of GLP-1 in motivated feeding, we tested the hypothesis that expression of the GLP-1 precursor preproglucagon (PPG) would be reduced in the NTS of rats with a history of binge-like palatable food intake. Adult male rats received access to fat for 1 h shortly before lights off, either every day (Daily, D) or only 3d/week (Intermittent, INT). INT rats ate significantly more fat than did D rats in sessions where all rats had fat access. After ~8.5 weeks of diet maintenance, we measured plasma GLP-1 as well as NTS PPG and GLP-1 receptor expression. INT rats had significantly lower NTS PPG mRNA expression compared to D rats. However, plasma GLP-1 was significantly increased in the INT group versus D rats. No significant differences were observed in NTS GLP-1 receptor expression. We also measured plasma insulin levels, fasted blood glucose, and plasma corticosterone but no differences were detected between groups. These results support the hypothesis that binge-like eating reduces NTS GLP-1 expression, and furthermore, demonstrate divergent impacts of binge-like eating on peripheral (plasma) versus central GLP-1.

Reframing appetitive reinforcement learning and reward valuation as effects mediated by hippocampal-dependent behavioral inhibition

Traditional theories of neuroeconomics focus on reinforcement learning and reward value. We propose here a novel reframing of reinforcement learning and motivation that includes a hippocampal-dependent regulatory mechanism which balances cue-induced behavioral excitation with behavioral inhibition. This mechanism enables interoceptive cues produced by respective food or drug satiety to antagonize the ability of excitatory food- and drug-related environmental cues to retrieve the memories of food and drug reinforcers, thereby suppressing the power of those cues to evoke appetitive behavior. When the operation of this mechanism is impaired, ability of satiety signals to inhibit appetitive behavior is weakened because the relative balance between inhibition and simple excitation is shifted toward increased retrieval of food and drug memories by environmental cues. In the present paper, we (1) describe the associative processes that constitute this mechanism of hippocampal-dependent behavior inhibition; (2) describe how a prevailing obesity-promoting diet and drugs of abuse produce hippocampal pathophysiologies that can selectively impair this inhibitory function; and (3) propose how glucagon-like peptide 1 (GLP-1), an incretin hormone that is recognized as an important satiety signal, may work to protect the hippocampal-dependent inhibition. Our perspective may add to neuroscientific and neuroeconomic analyses of both overeating and drug abuse by outlining the role of hippocampal-dependent memory processes in the control of both food and drug seeking behaviors. In addition, this view suggests that consideration should be given to diet- and drug induced hippocampal pathophysiologies, as potential novel targets for the treatment of dysregulated energy and drug intake.

The role of appetite-related hormones, adaptive thermogenesis, perceived hunger and stress in long-term weight-loss maintenance: a mixed-methods study

BACKGROUND/OBJECTIVES

Weight-loss maintenance is challenging, and few succeed in the long term. This study aimed to explain how appetite-related hormones, adaptive thermogenesis, perceived hunger and stress influence weight-loss maintenance.

SUBJECTS/METHODS

Fifteen adult women (age, 46.3 ± 9.5 years; BMI, 39.4 ± 4.3 kg/m²) participated in a 24-month intervention, which included 3-5 months total diet replacement (825-853 kcal/d). Body weight and composition (Magnetic Resonance Imaging), resting metabolic rate (indirect calorimetry), and fasting plasma concentration of leptin, ghrelin, glucagon-like peptide-1 (GLP-1), peptide YY (PYY), and growth differentiation factor 15 (GDF-15) were measured at baseline and after weight loss, around 6 months. Perceptions relating to weight-loss maintenance were explored using qualitative interviews.

RESULTS

Mean (SD) changes in body weight (-13.8 ± 6.3 kg) and total adipose tissue (-11.5 ± 4.9 kg) were significant (P < 0.001). Weight loss was associated with a significant reduction in resting metabolic rate (-291 ± 226 kcal/day, P < 0.001) and adaptive thermogenesis (-150 ± 162 kcal/day, P = 0.003), reduction in leptin (P < 0.001) and GLP-1 (P = 0.015), an increase in ghrelin (P < 0.001), and no changes in PYY and GDF-15. Weight regain between 6 and 24 months (6.1 ± 6.3 kg, P < 0.05) was negatively correlated with GLP-1 at baseline (r = −0.7, P = 0.003) and after weight loss (r = -0.7, P = 0.005). Participants did not report increased hunger after weight loss, and stress-related/emotional eating was perceived as the main reason for regain.

CONCLUSIONS

Weight regain is more likely with lower fasting GLP-1 at baseline and following weight loss, but psychological aspects of eating behaviour appear as important in attenuating weight-loss maintenance.

Activation of GLP-1 receptors attenuates oxycodone taking and seeking without compromising the antinociceptive effects of oxycodone in rats

Despite the effectiveness of current medications to treat opioid use disorder, there is still a high rate of relapse following detoxification. Thus, there is critical need for innovative studies aimed at identifying novel neurobiological mechanisms that could be targeted to treat opioid use disorder. A growing body of preclinical evidence indicates that glucagon-like peptide-1 (GLP-1) receptor agonists reduce drug reinforcement. However, the efficacy of GLP-1 receptor agonists in attenuating opioid-mediated behaviors has not been thoroughly investigated. Using recently established models of opioid-taking and -seeking behaviors, we showed that systemic administration of the GLP-1 receptor agonist exendin-4 reduced oxycodone self-administration and the reinstatement of oxycodone-seeking behavior in rats. We also identified behaviorally selective doses of exendin-4 that reduced opioid-taking and -seeking behaviors and did not produce adverse feeding effects in oxycodone-experienced rats. To identify a central site of action, we showed that systemic exendin-4 penetrated the brain and bound putative GLP-1 receptors on dopamine D1 receptor- and dopamine D2 receptor-expressing medium spiny neurons in the nucleus accumbens shell. Consistent with our systemic studies, infusions of exendin-4 directly into the accumbens shell attenuated oxycodone self-administration and the reinstatement of oxycodone-seeking behavior without affecting ad libitum food intake. Finally, exendin-4 did not alter the analgesic effects of oxycodone, suggesting that activation of GLP-1 receptors attenuated opioid reinforcement without reducing the thermal antinociceptive effects of oxycodone. Taken together, these findings suggest that GLP-1 receptors could serve as potential molecular targets for pharmacotherapies aimed at reducing opioid use disorder.

Behavioral and Neurobiological Consequences of Hedonic Feeding on Alcohol Drinking

A complex interplay of peripheral and central signaling mechanisms within the body of an organism maintains energy homeostasis. In addition, energy/food intake is modified by various external factors (e.g., palatability, food availability, social and environmental triggers). Highly palatable foods can provoke maladaptive feeding behavior, which in turn disrupts normal homeostatic regulation resulting in numerous health consequences. Furthermore, neuroendocrine peptides, traditionally considered to regulate appetite and energy homeostasis, also control the intake and reinforcing properties of alcohol and drugs of abuse. Therefore, dysregulated eating as a result of a hedonic/binge-like intake of hyper-palatable food may impact alcohol drinking behavior. Relevant in this case is the fact that eating disorders are highly comorbid with several neuropsychiatric conditions, including alcohol use disorder. The present review is intended to summarize the neurobiological and functional consequences of hedonic feeding on alcohol intake.

Ovarian Hormones Mediate Changes in Adaptive Choice and Motivation in Female Rats

In female rodents, sexual receptivity is coordinated with cyclic changes in the release of gonadal hormones. Increases in estradiol (E) and progesterone (P) during proestrus and estrus not only induce ovulation but also modulate behaviors that increase the likelihood that the female will find a mate and reproduce. This includes changes in receptive behaviors, such as lordosis, as well as changes in appetitive or proceptive behaviors, including motivation. Interestingly, the direction of these changes in motivation is dependent on the type of reward that is being pursued. While induction of sexual receptivity by E and P increases motivation for access to a male, motivation for a palatable food reward is decreased. These concurrent changes may facilitate adaptive choice across the estrous cycle; females bias their choice for sex when fertilization is most likely to occur, but for food when copulation is unlikely to result in impregnation. In order to test this hypothesis, we developed a novel paradigm to measure the motivated choice between a palatable food reward and access to a male conspecific. Ovariectomized, hormone primed females were trained to operantly respond for both food and sex on a fixed interval (FI) schedule. After training, unprimed and primed females were tested in a chamber that allows them to choose between food and sex while still requiring responding on the FI schedule for reach reward. From this we can not only determine the impact of hormone priming on female choice for food or sex, but also how this is reflected by changes in motivation for each specific reward, as measured by the average number of responses made during each fixed interval. Induction of sexual receptivity by hormone priming biases choice toward sex over food and this change is accompanied by an increase in motivation for sex but a decrease in motivation for food. This work provides evidence in support of a novel framework for understanding how the release of ovarian hormones over the course of the estrous cycle modulates adaptive behavioral choice in females by directly assessing motivation via operant responding when multiple rewards are available.

Recent Advances in the Neurobiology of Altered Motivation Following Bariatric Surgery

PURPOSE OF REVIEW

There is compelling evidence in the clinical population that long-term weight loss secondary to bariatric surgery is mitigated by the reemergence of maladaptive feeding behaviors and in some cases new onset substance abuse.

RECENT FINDINGS

A review of the current literature suggests that physical restructuring of the GI tract during WLS alters secretion of feeding peptides and nutrient-sensing mechanisms that directly target the brain's endogenous reward system, the mesolimbic dopamine system. Post-surgical changes in GI physiology augment activation of the mesolimbic system. In some patients, this process may contribute to a reduced appetite for palatable food whereas in others it may support maladaptive motivated behavior for food and chemical drugs. It is concluded that future studies are required to detail the timing and duration of surgical-induced changes in GI-mesolimbic communication to more fully understand this phenomenon.

Synaptic Inputs to the Mouse Dorsal Vagal Complex and Its Resident Preproglucagon Neurons

Stress responses are coordinated by widespread neural circuits. Homeostatic and psychogenic stressors activate preproglucagon (PPG) neurons in the caudal nucleus of the solitary tract (cNTS) that produce glucagon-like peptide-1; published work in rodents indicates that these neurons play a crucial role in stress responses. While the axonal targets of PPG neurons are well established, their afferent inputs are unknown.

Stress responses are coordinated by widespread neural circuits. Homeostatic and psychogenic stressors activate preproglucagon (PPG) neurons in the caudal nucleus of the solitary tract (cNTS) that produce glucagon-like peptide-1; published work in rodents indicates that these neurons play a crucial role in stress responses. While the axonal targets of PPG neurons are well established, their afferent inputs are unknown. Here we use retrograde tracing with cholera toxin subunit b to show that the cNTS in male and female mice receives axonal inputs similar to those reported in rats. Monosynaptic and polysynaptic inputs specific to cNTS PPG neurons were revealed using Cre-conditional pseudorabies and rabies viruses. The most prominent sources of PPG monosynaptic input include the lateral (LH) and paraventricular (PVN) nuclei of the hypothalamus, parasubthalamic nucleus, lateral division of the central amygdala, and Barrington's nucleus (Bar). Additionally, PPG neurons receive monosynaptic vagal sensory input from the nodose ganglia and spinal sensory input from the dorsal horn. Sources of polysynaptic input to cNTS PPG neurons include the hippocampal formation, paraventricular thalamus, and prefrontal cortex. Finally, cNTS-projecting neurons within PVN, LH, and Bar express the activation marker cFOS in mice after restraint stress, identifying them as potential sources of neurogenic stress-induced recruitment of PPG neurons. In summary, cNTS PPG neurons in mice receive widespread monosynaptic and polysynaptic input from brain regions implicated in coordinating behavioral and physiological stress responses, as well as from vagal and spinal sensory neurons. Thus, PPG neurons are optimally positioned to integrate signals of homeostatic and psychogenic stress.

SIGNIFICANCE STATEMENT Recent research has indicated a crucial role for glucagon-like peptide-1-producing preproglucagon (PPG) neurons in regulating both appetite and behavioral and autonomic responses to acute stress. Intriguingly, the central glucagon-like peptide-1 system defined in rodents is conserved in humans, highlighting the translational importance of understanding its anatomical organization. Findings reported here indicate that PPG neurons receive significant monosynaptic and polysynaptic input from brain regions implicated in autonomic and behavioral responses to stress, as well as direct input from vagal and spinal sensory neurons. Improved understanding of the neural pathways underlying the recruitment of PPG neurons may facilitate the development of novel therapies for the treatment of stress-related disorders.

The perceptions of natural compounds against dipeptidyl peptidase 4 in diabetes: from in silico to in vivo

Dipeptidyl peptidase IV (DPP-4), an incretin glucagon-like peptide-1 (GLP-1) degrading enzyme, contains two forms and it can exert various physiological functions particular in controlling blood glucose through the action of GLP-1. In diabetic use, the DPP-4 inhibitor can block the DDP-4 to attenuate GLP-1 degradation and prolong GLP-1 its action and sensitize insulin activity for the purpose of lowering blood glucose. Nonetheless the adverse effects of DPP-4 inhibitors severely hinder their clinical applications, and notably there is a clinical demand for novel DPP-4 inhibitors from various sources including chemical synthesis, herbs, and plants with fewer side effects. In this review, we highlight various strategies, namely computational biology (in silico), in vitro enzymatic and cell assays, and in vivo animal tests, for seeking natural DPP-4 inhibitors from botanic sources including herbs and plants. The pros and cons of all approaches for new inhibitor candidates or hits will be under discussion.