Effect of vertical sleeve gastrectomy on alcohol consumption and preferences in dietary obese rats and mice: A plausible role for altered ghrelin signaling

Ghrelin system and GLP-1 as potential treatment targets for alcohol use disorder

Peptides of the gut-brain axis have gained recent attention as potential treatment targets for addiction. While the number of gut-brain peptides is vast, ghrelin and glucagon-like peptide-1 (GLP-1) have been suggested as important players. Ghrelin is traditionally considered an orexigenic peptide, but recent studies found that it increases alcohol intake in rodents and craving for alcohol in humans. Additionally, suppression of the ghrelin receptor attenuates alcohol-related responses in animal models reflecting alcohol use disorder (AUD). For instance, a lower alcohol intake, suppressed motivation to consume alcohol, and attenuated reward from alcohol is observed after ghrelin receptor antagonism treatment. On a similar note, a partial ghrelin receptor agonist prevents hangover symptoms in humans. When it comes to the anorexigenic peptide GLP-1, agonists of its receptor are approved to treat diabetes type 2 and obesity. Extensive preclinical studies have revealed that these GLP-1 receptor agonists reduce alcohol intake, suppress the motivation to consume alcohol, and prevent relapse drink, with effects tentatively associated with a reduced alcohol-induced reward. These preclinical findings have to some extent been varied in humans, as GLP-1 receptor agonists decrease alcohol intake in overweight patients with AUD. Furthermore, genetic variations in either the genes encoding for pre-pro-ghrelin, GHSR, GLP-1, or its receptor, are associated with AUD and heavy alcohol drinking. While central mechanisms appear to modulate the ability of either ghrelin or GLP-1 to regulate alcohol-related responses the exact mechanisms have not been defined. Taken together these preclinical and clinical data imply that gut-brain peptides participate in the addiction process and should be considered as potential targets for AUD treatment.

Alcohol associated liver disease and bariatric surgery: Current perspectives and future directions

Bariatric surgery is a routinely performed procedure and is associated with a reduction in all-cause mortality in patients with obesity. However, bariatric surgery has also been linked to increased alcohol use with up to 30% of these patients developing alcohol use disorder (AUD). The mechanism of AUD after bariatric surgery is multifactorial and includes anatomic, metabolic, and neurohumoral changes associated with post-surgical anatomy. These patients are at increased risk of alcohol associated liver disease and, in some cases, require liver transplantation. In this article, we provide a scoping review of epidemiology, pathophysiology, and clinical outcomes of alcohol-related health conditions after bariatric surgery.

Vagus nerve damage increases alcohol intake and preference in a nonpreferring rat line: Relationship to vagal regulation of the hypothalamic-pituitary-adrenal axis

BACKGROUND

Clinical and preclinical research indicates that gastric weight loss surgeries, such as Roux-en-Y gastric bypass surgery, can induce alcohol use disorder (AUD). While numerous mechanisms have been proposed for these effects, one relatively unexplored potential mechanism is physical damage to the gastric branch of the vagus nerve, which can occur during bypass surgery. Therefore, we hypothesized that direct damage to the gastric branch of the vagus nerve, without altering other aspects of gastric anatomy, could result in increased alcohol intake.

METHODS

To test this hypothesis, we compared alcohol intake and preference in multiple models in male Sprague-Dawley rats that received selective gastric branch vagotomy (VX) with rats who underwent sham surgery. Because the vagus nerve regulates hypothalamic-pituitary-adrenal (HPA) axis function, and alterations to HPA function are critical to the escalation of non-dependent alcohol intake, we also tested the hypothesis that gastric VX increases HPA function.

RESULTS

We found that VX increases alcohol intake and preference in the every-other-day, two-bottle choice test and increases preference for 1 g/kg alcohol in the conditioned place preference test. The effects were selective for alcohol, as sucrose intake and preference were not altered by VX. We also found that VX increases corticotropin releasing factor (CRF) mRNA in the paraventricular nucleus of the hypothalamus (PVN), increases putative PVN CRF neuronal action potential firing, and increases corticosterone levels.

CONCLUSIONS

Overall, these findings suggest that the vagus nerve may play a critical role in regulating HPA axis function via modulation of PVN CRF mRNA expression and putative PVN CRF neuronal activity. Furthermore, disruptions to vagal regulation of HPA axis function may increase alcohol intake and preference.

Bariatric Surgery Is Associated with Alcohol-Related Liver Disease and Psychiatric Disorders Associated with AUD

BACKGROUND/AIMS

Bariatric surgery can increase the risk of addictive disorders and nutritional deficiencies. The aim of this study was to evaluate the association between bariatric surgery and alcohol use disorder (AUD), alcohol-related liver disease (ALD), and psychiatric disorders associated with AUD. The impact of vitamin D deficiency in these associations was also investigated.

METHODS

A cross-sectional study was performed using the National Inpatient Sample database and its ICD-9 codes information. Diagnostic and comorbidity data from hospital discharges were obtained from patients with bariatric surgery and other abdominal surgeries between 2005 and 2015. The two groups were then compared for alcohol-related outcomes after propensity-score matching.

RESULTS

The final study cohort included 537,757 patients with bariatric surgery and 537,757 with other abdominal surgeries. The bariatric surgery group had an increased risk of AUD [odds ratio (OR): 1.90; 95% CI: 1.85-1.95], ALD [OR: 1.29; 95% CI: 1.22-1.37], cirrhosis [OR, 1.39; 95% CI: 1.37-1.42], and psychiatric disorders associated with AUD [OR, 3.59; 95% CI: 3.37-3.84]. Vitamin D deficiency did not impact in the association between bariatric surgery and AUD, ALD, or psychiatric disorders associated with AUD.

CONCLUSIONS

Bariatric surgery is associated with an increased prevalence of AUD, ALD, and psychiatric disorders associated with AUD. These associations appear to be independent from vitamin D deficiency.

Changes in Plasma Ghrelin Levels Following Surgical and Non-Surgical Weight-Loss in Female Rats Predict Alcohol Use

The weight-loss surgery Roux-en Y gastric bypass (RYGB) is a relatively effective, long-term treatment option for patients with morbid obesity. However, accumulating clinical evidence suggests that patients receiving RYGB may be at increased risk of developing alcohol use disorder. This observation has been repeatedly supported by preclinical studies showing rodents increase intake of ethanol (EtOH) after RYGB, and has been further confirmed by human studies. A promising alternative to RYGB is sleeve gastrectomy (SG), which has resulted in decreased EtOH consumption in some rodent studies. The exact mechanism underlying the differential alcohol outcomes after RYGB versus SG has yet to be elucidated. However, the gut hormone ghrelin has emerged as a potential candidate from previous preclinical studies specific to RYGB surgeries and due to its action to stimulate food and alcohol intake and cravings. To directly assess changes in plasma ghrelin levels following weigh loss surgeries in the context of alcohol intake, 24 female rats were separated into three surgical groups receiving RYGB, SG, or Sham surgery followed by caloric restriction to produce adiposity matched controls (Sham-AM). Blood was drawn for fasted and fed plasma ghrelin (acyl and des-acyl) assays at multiple time points: while on a normal diet (ND), after 5-week exposure to a high fat diet (HFD), following surgery, and after a series of two-bottle alcohol choice test with increasing concentrations (2%, 4%, 6%, 8%) of EtOH. Consistent with previous observations, RYGB rats drank more EtOH than SG rats across all concentrations. As expected, fasted ghrelin levels were blunted after HFD feeding, compared to normal diet baseline. After RYGB, fasted ghrelin levels returned to higher levels while remained blunted after SG and Sham-AM. Fed acyl ghrelin levels were significantly increased to above "normal" levels after RYGB, but remain low after SG and Sham-AM. Given that post-RYGB acyl ghrelin levels are raised to a fasted state regardless of actual prandial status, we conclude that RYGB may results in a hormonal state reminiscence of a fasted state with the inability of feeding to inhibit ghrelin production, an effect which could potentially contribute to increased EtOH intake following the surgery. In contrast, following SG, ghrelin levels in rats remain consistent with the fed state regardless of prandial status, potentially explaining lower alcohol intake and lower risk of developing AUD.

Involvement of the Dorsal Vagal Complex in Alcohol-Related Behaviors

The neurobiological mechanisms that regulate the development and maintenance of alcohol use disorder (AUD) are complex and involve a wide variety of within and between systems neuroadaptations. While classic reward, preoccupation, and withdrawal neurocircuits have been heavily studied in terms of AUD, viable treatment targets from this established literature have not proven clinically effective as of yet. Therefore, examination of additional neurocircuitries not classically studied in the context of AUD may provide novel therapeutic targets. Recent studies demonstrate that various neuropeptides systems are important modulators of alcohol reward, seeking, and intake behaviors. This includes neurocircuitry within the dorsal vagal complex (DVC), which is involved in the control of the autonomic nervous system, control of intake of natural rewards like food, and acts as a relay of interoceptive sensory information via interactions of numerous gut-brain peptides and neurotransmitter systems with DVC projections to central and peripheral targets. DVC neuron subtypes produce a variety of neuropeptides and transmitters and project to target brain regions critical for reward such as the mesolimbic dopamine system as well as other limbic areas important for the negative reinforcing and aversive properties of alcohol withdrawal such as the extended amygdala. This suggests the DVC may play a role in the modulation of various aspects of AUD. This review summarizes the current literature on neurotransmitters and neuropeptides systems in the DVC (e.g., norepinephrine, glucagon-like peptide 1, neurotensin, cholecystokinin, thyrotropin-releasing hormone), and their potential relevance to alcohol-related behaviors in humans and rodent models for AUD research. A better understanding of the role of the DVC in modulating alcohol related behaviors may lead to the elucidation of novel therapeutic targets for drug development in AUD.

Therapeutic potential of GHSR-1A antagonism in alcohol dependence, a review

Growth hormone secretagogue receptor type 1A (GHSR-1A) is a functional receptor of orexigenic peptide ghrelin and is highly expressed in mesolimbic dopaminergic systems that regulate incentive value of artificial reward in substance abuse. Interestingly, GHSR-1A has also shown ligand-independent constitutive activity. Alcohol use disorder (AUD) is one of the growing concerns worldwide as it involves complex neuro-psycho-endocrinological interactions. Positive correlation of acylated ghrelin and alcohol-induced human brain response in the right and left ventral striatum are evident. In the last decade, the beneficial effects of ghrelin receptor (GHSR-1A) antagonism to suppress artificial reward circuitries and induce self-control for alcohol consumption have drawn significant attention from researchers. In this updated review, we summarize the available recent preclinical, clinical, and experimental data to discuss functional, molecular actions of central ghrelin-GHSR-1A signaling in different craving levels for alcohol as well as to promote "GHSR-1A antagonism" as one of the potential therapies in early abstinence.

An Overview of Appetite-Regulatory Peptides in Addiction Processes; From Bench to Bed Side

There is a substantial need for new pharmacological treatments of addiction, and appetite-regulatory peptides are implied as possible candidates. Appetite regulation is complex and involves anorexigenic hormones such as glucagon-like peptide-1 (GLP-1) and amylin, and orexigenic peptides like ghrelin and all are well-known for their effects on feeding behaviors. This overview will summarize more recent physiological aspects of these peptides, demonstrating that they modulate various aspects of addiction processes. Findings from preclinical, genetic, and experimental clinical studies exploring the association between appetite-regulatory peptides and the acute or chronic effects of addictive drugs will be introduced. Short or long-acting GLP-1 receptor agonists independently attenuate the acute rewarding properties of addictive drugs or reduce the chronic aspects of drugs. Genetic variation of the GLP-1 system is associated with alcohol use disorder. Also, the amylin pathway modulates the acute and chronic behavioral responses to addictive drugs. Ghrelin has been shown to activate reward-related behaviors. Moreover, ghrelin enhances, whereas pharmacological or genetic suppression of the ghrelin receptor attenuates the responses to various addictive drugs. Genetic studies and experimental clinical studies further support the associations between ghrelin and addiction processes. Further studies should explore the mechanisms modulating the ability of appetite-regulatory peptides to reduce addiction, and the effects of combination therapies or different diets on substance use are warranted. In summary, these studies provide evidence that appetite-regulatory peptides modulate reward and addiction processes, and deserve to be investigated as potential treatment target for addiction.

Risks and Rewards of Bariatric Surgery in Advanced Chronic Liver Diseases

The burden of obesity and metabolic syndrome has determined a sharp increase in bariatric surgery (BS) procedures, which lead to marked weight loss, improved metabolic syndrome, reduced cardiovascular risk, and even improvement in nonalcoholic steatohepatitis (NASH). Despite these promising results, BS in patients with chronic liver disease can rarely lead to worsening of liver function, progression to cirrhosis and its complications, and even liver transplantation. On the other hand, since obesity in patients with cirrhosis is a major cofactor for progression to a decompensated stage of the disease and a risk factor for hepatocellular carcinoma, BS has been used to achieve weight loss in this population. In this review, we critically analyze the existing data on outcomes of BS in patients with cirrhosis and the possible mechanisms leading to fibrosis progression and worsening liver function in patients undergoing BS. Finally, we propose a set of measures that could be taken to improve the multidisciplinary management of liver disease in patients undergoing BS, including early recognition of malnutrition and alcohol misuse.

Potential gut-brain mechanisms behind adverse mental health outcomes of bariatric surgery

Bariatric surgery induces sustained weight loss and metabolic benefits via notable effects on the gut-brain axis that lead to alterations in the neuroendocrine regulation of appetite and glycaemia. However, in a subset of patients, bariatric surgery is associated with adverse effects on mental health, including increased risk of suicide or self-harm as well as the emergence of depression and substance use disorders. The contributing factors behind these adverse effects are not well understood. Accumulating evidence indicates that there are important links between gut-derived hormones, microbial and bile acid profiles, and disorders of mood and substance use, which warrant further exploration in the context of changes in gut-brain signalling after bariatric surgery. Understanding the basis of these adverse effects is essential in order to optimize the health and well-being of people undergoing treatment for obesity.

Bariatric surgery and the liver-Mechanisms, benefits, and risks

The prevalence of obesity and metabolic diseases such as type 2 diabetes and nonalcoholic fatty liver disease (NAFLD) has risen dramatically over the past decades. At present, bariatric surgery is the most effective treatment for this global health problem, through effects on food intake, gut hormone secretion, metabolic signaling pathways, and adipose tissue dysfunction. The liver occupies a central role in carbohydrate, protein, and lipid metabolism. Notably, a reduction in hepatic fat content and an improvement in hepatic insulin resistance are among the earliest beneficial effects of bariatric surgery, which has therefore emerged as an attractive treatment option for NAFLD. However, as the scope and popularity of weight loss surgery have expanded, new questions have arisen regarding its safety in patients with liver cirrhosis, the outcome of liver transplantation in patients with a history of bariatric surgery, and over incidental reports of liver failure following surgery. Studies in humans and rodents have also linked bariatric surgery to an increased risk of developing alcohol use disorder, a major risk factor for liver disease. This review integrates data from clinical and translational research to delineate both the beneficial impact of bariatric surgery on the liver and the potential risks involved.

Differential Response in Ethanol Behaviors of Female Rats Given Various Weight Loss Surgeries

AIMS

Currently, the only effective treatment for morbid obesity and its comorbidities is weight loss surgery (WLS). Growing evidence suggests that different types of WLS, such as Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG), have differential effects on alcohol consumption in humans and rats. Thus, we aimed to directly compare the effects of these two surgical procedures, for the first time in female rats, and to determine whether presence or absence of the ghrelin-producing stomach tissue has critical influence on postoperative alcohol intake.

METHODS

We performed two experiments using an identical behavioral protocol, a continuous-access two-bottle choice protocol for various concentrations of ethanol (EtOH). In Experiment 1, 23 high fat diet (HFD) obese, female rats were randomized to three groups: RYGB, SG or sham-operated food-restricted (Sham) controls. In Experiment 2, HFD obese female rats received either sham (n = 11) or a modified RYGB surgery where the remnant stomach was removed (RYGB-X; n = 12).

RESULTS

SG rats drank significantly less than RYGB for 4, 6 and 8% and significantly less than Sham for 6, 8 and 8% reinstatement. RYGB-X consumed significantly less EtOH than Sham across all concentrations, reaching significance for 6 and 8% reinstatement.

CONCLUSION

These findings confirm reduced EtOH consumption by female SG rats as opposed to increased intake following RYGB, and provide the first experimental evidence that the remnant stomach in the RYGB procedure is contributory. Future studies in rats and humans are warranted to confirm that ghrelin plays a critical role in susceptibility to AUD development following WLS.

Malnutrition and Alcohol in Patients Presenting with Severe Complications of Cirrhosis After Laparoscopic Bariatric Surgery

Factors and outcomes associated with decompensation of liver disease and liver failure in obese patients who underwent modern bariatric surgery are unclear. We present here a cohort of seventeen consecutive patients referred because of decompensation of liver disease following laparoscopic bariatric surgery. All patients showed signs of malnutrition (sarcopenia in 76.5%). In ten (58.8%), decompensation was associated with alcohol ingestion, which started after bariatric surgery in six patients. One patient died and three patients required liver transplantation, in one case preceded by transjugular intrahepatic portosystemic shunt (TIPS). However, thirteen patients achieved stabilization or full re-compensation with medical therapy and nutritional support. Our cases underline the risk of alcohol intake and malnutrition after laparoscopic bariatric surgery as causes of severe liver decompensation and underline the need for careful interdisciplinary care of these patients after surgery to early identify and treat alcohol misuse, malnutrition, and liver disease.

Vagotomy increases alcohol intake in female rats in diet dependent manner: Implications for increased alcohol use disorder after roux-en-y gastric bypass surgery

A variety of weight loss surgeries have been developed to fight the obesity epidemic, with Roux-en-Y gastric bypass (RYGB) being one of the most effective and popular procedures. However, the underlying mechanisms behind its efficacy are still not well understood. Furthermore, growing clinical evidence suggests that RYGB may result in increased risk for development of alcohol use disorder (AUD). The vagus nerve is a potentially critical contributor to increased risk of AUD following RYGB due to the potential for significant damage to the vagus during surgery, which has been confirmed in rodent studies. Studies aiming at the mechanisms underlying development of alcohol or substance use disorders following the surgery have exclusively used male rats, despite the majority of RYGB patients being female. Thus, the current study had two objectives: 1) to investigate the effect of RYGB on ethanol (EtOH) intake in female rats using a protocol previously established in male rats, and 2) to test the effect of vagal damage and high fat diet (HFD) on EtOH intake in female rats. In the first study, 22 female rats were maintained on HFD for four weeks and then split into two surgical groups, RYGB (n = 10) and Sham (n = 12). All rats then underwent a two-bottle choice test of increasing EtOH concentrations: 2%, 4%, 6%, 8%. Rats were then forced to abstain from EtOH for two weeks, after which access to 8% EtOH was reinstated. The RYGB female rats significantly increased their intake for low concentrations of EtOH (2% and 4%) and during the reinstatement period for 8%. These results mirror those seen in male rats, and thus, confirms RYGB in female rats as an equally viable model to males. In the second study, 40 female rats were separated into four groups: HFD/Sham, HFD/Vagotomy, normal diet (ND)/Sham, and ND/Vagotomy. All rats then were subjected to the same two-bottle choice test protocol as in the previous study. Rats in the vagotomy condition had significantly greater preference for 2% and 4% EtOH compared with Sham-operated controls. EtOH intake, either in ml or adjusted for body weight, was greater in rats maintained on ND compared with rats maintained on HFD. These data suggest that vagal damage may, at least in part, contribute to increased preference for EtOH. Furthermore, this increase in EtOH preference is counter to the blunting effect of HFD. In conclusion, the data presented here suggest a role for vagal damage in risk of AUD after weight loss surgery.

Revisiting the Ghrelin Changes Following Bariatric and Metabolic Surgery

Since the description of ghrelin in 1999, several studies have dug into the effects of this hormone and its relationship with bariatric surgery. While some aspects are still unresolved, a clear connection between ghrelin and the changes after metabolic surgery have been established. Besides weight loss, a significant amelioration in obesity-related comorbidities following surgery has also been reported. These changes in patients occur in the early postoperative period, before the weight loss appears, so that amelioration may be mainly due to hormonal changes. The purpose of this review is to go through the current body of knowledge of ghrelin's physiology, as well as to update and clarify the changes that take place in ghrelin concentrations following bariatric/metabolic surgery together with their potential consolidation to outcomes.

Surgical Mouse Models of Vertical Sleeve Gastrectomy and Roux-en Y Gastric Bypass: a Review

Reviewed here are multiple mouse models of vertical sleeve gastrectomy (VSG) and Roux-en Y gastric bypass (RYGB) that have emerged over the past decade. These models use diverse approaches to both operative and perioperative procedures. Scrutinizing the benefits and pitfalls of each surgical model and what to expect in terms of post-operative outcomes will enhance our assessment of studies using mouse models, as well as advance our understanding of their translational potential. Two mouse models of bariatric surgery, VSG-lembert and RYGB-small pouch, demonstrate low mortality and most closely recapitulate the human forms of surgery. The use of liquid diets can be minimized, and in mice, RYGB demonstrates more reliable and longer lasting effects on weight loss compared to that of VSG.

Alcohol consumption after laparoscopic sleeve gastrectomy: 1-year results

INTRODUCTION

Laparoscopic sleeve gastrectomy (SG) represents, at present, the most performed bariatric procedure worldwide with excellent long-term results on weight loss and comorbidities control. After the gastrectomy procedure, together with hormonal modification, several changes in taste and habits occur, including the potential modification in alcohol consumption. The aim of this prospective study was to determine the frequency and the amount of alcohol use before and after SG using a modified version of the Alcohol Use Disorder Identification Test (AUDIT) at 1-year follow-up and eventually to evaluate relationships between different ages and sexes.

MATERIALS AND METHODS

A total of 142 patients were prospectively enrolled and evaluated before and 1 year after SG with a modified AUDIT. The exclusion criteria were as follows: history of alcohol abuse, presence of psychopathology or cognitive impairments, diabetes mellitus type II decompensated, or previous gastrointestinal, liver, and pancreatic resective surgery. Subgroup analyses were performed between male and female and between under and over 40 years old.

RESULTS

The median AUDIT score decreased from 2.70 (range 1-18) before surgery to 1.38 (range 1-7) after 1 year of SG, indicating a marked reduction in alcohol use. The most consumed alcoholic drink was beer (36.6%/n = 52) while after surgery the consumption of beer decreased considerably (21.1%/n = 30). The frequency of alcohol consumption also decreased: at baseline 45% of patients consumed alcoholic drinks "from 2 to 4 times per month", whereas 26 and 39.4% consumed alcohol "never" and "less than once a month," respectively. After surgery, nobody consumed more then six alcoholic drinks. No differences were found between the subgroups in terms of alcohol consumption and social behavior.

CONCLUSIONS

The alcohol preference is modified and decreased 1 year after SG and this could be related to the strict nutritional follow-up and to the hormonal changes. Studies with large samples and long-term follow-up are needed to confirm our data.

LEVEL OF EVIDENCE

IV.

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.

Vertical Sleeve Gastrectomy Attenuates Hedonic Feeding Without Impacting Alcohol Drinking in Rats

OBJECTIVE

Roux-en-Y gastric bypass surgery and vertical sleeve gastrectomy (VSG) are the most commonly performed bariatric procedures. Whereas studies report new-onset alcohol misuse following Roux-en-Y gastric bypass, the impact of VSG on alcohol intake is less clear. Hedonic feeding, alcohol drinking, and hypothalamic obesity-related gene expression following VSG were evaluated.

METHODS

Male Long-Evans rats underwent VSG or sham surgery. To evaluate hedonic feeding, rats received a high-fat diet following behavioral satiation on chow. Alcohol (5%-10% v/v) drinking was assessed in a two-bottle choice paradigm. Finally, polymerase chain reaction array evaluated gene expression.

RESULTS

VSG induced moderate but significant weight loss. Sham rats significantly escalated high-fat diet intake following behavioral satiation, an effect significantly reduced in VSG rats. A moderate decrease in alcohol intake was observed in VSG rats at low (5%) alcohol concentration. However, overall, no significant between-group differences were evident. Key hypothalamic orexigenic transcripts linked to stimulation of food and alcohol intake were significantly decreased in VSG rats.

CONCLUSIONS

VSG attenuated hedonic feeding without impacting alcohol drinking, an effect potentially mediated by alterations in genetic information flow within the hypothalamus. Importantly, these data highlight VSG as an effective bariatric procedure with a potentially reduced risk of developing alcohol use disorder.

Systematic review of olfactory shifts related to obesity

OBJECTIVE

The modern food environment is a key driver of rising levels of obesity. While olfaction is known to play a major role in food choice; however, its relationship to obesity is yet to be understood. This review assesses current knowledge of the interaction between obesity and olfaction.

METHODS

This review is based on observational studies comparing olfactory abilities across weight groups (N = 10) and clinical studies evaluating olfactory changes following bariatric surgery (N = 9). Meta-analyses were performed on data collected by a standard olfactory assessment tool (Sniffin΄ Sticks), to test whether olfaction has any association with body weight or bariatric surgery.

RESULTS

This review synthesizes findings derived from 38 datasets, with a total of 1432 individual olfactory assessments. The meta-analyses suggest that olfactory function is negatively correlated with body weight. In addition, Roux-en-Y gastric bypass patients frequently report olfactory changes, yet more pronounced and immediate shifts have been observed among sleeve gastrectomy recipients.

CONCLUSIONS

Our review finds strong evidence for the link between olfaction and obesity and indicates that bariatric surgery (particularly the sleeve gastrectomy) is effective in reversing olfactory decline associated with obesity. In conclusion, we present mechanistic models to underpin the observed relationship between olfaction and obesity.

Gut-brain axis and addictive disorders: A review with focus on alcohol and drugs of abuse

Due to the limited efficacy of existing medications for addictive disorders including alcohol use disorder (AUD), the need for additional medications is substantial. Potential new medications for addiction can be identified through investigation of the neurochemical substrates mediating the ability of drugs of abuse such as alcohol to activate the mesolimbic dopamine system. Interestingly, recent studies implicate neuropeptides of the gut-brain axis as modulators of reward and addiction processes. The present review therefore summarizes the current studies investigating the ability of the gut-brain peptides ghrelin, glucagon-like peptide-1 (GLP-1), amylin and neuromedin U (NMU) to modulate alcohol- and drug-related behaviors in rodents and humans. Extensive literature demonstrates that ghrelin, the only known orexigenic neuropeptide to date, enhances reward as well as the intake of alcohol, and other drugs of abuse, while ghrelin receptor antagonism has the opposite effects. On the other hand, the anorexigenic peptides GLP-1, amylin and NMU independently inhibits reward from alcohol and drugs of abuse in rodents. Collectively, these rodent and human studies imply that central ghrelin, GLP-1, amylin and NMU signaling may contribute to addiction processes. Therefore, the need for randomized clinical trials investigating the effects of agents targeting these aforementioned systems on drug/alcohol use is substantial.

Roux-en-Y gastric bypass surgery normalizes dopamine D1, D2, and DAT levels

Roux-en-Y gastric bypass surgery (RYGB) is one of the most effective treatments for morbid obesity. However, increased substance abuse following RYGB has been observed clinically. This study examined the effects of RYGB on the dopamine system to elucidate these observed changes in reward-related behavior. Rats were assigned to four groups: normal diet with sham surgery, ad libitum high fat (HF) diet with sham surgery, restricted HF diet with sham surgery, and HF diet with RYGB surgery. Following surgeries, rats were kept on their respective diets for 9 weeks before they were sacrificed. [3 H]SCH 23390, [3 H]Spiperone, and [3 H]WIN35 428 autoradiography was performed to quantify the effects of diet and RYGB surgery on dopamine type 1-like receptor (D1R)-like, dopamine type 2-like receptor (D2R)-like, and dopamine transporter (DAT) binding. Rats on a chronic HF diet became obese with reduced D1R-like binding within the ventrolateral striatum and the nucleus accumbens core, reduced D2R-like binding in all areas of the striatum and nucleus accumbens core and shell, and reduced DAT binding in the dorsomedial striatum. Restricted HF diet rats showed similar reductions in D1R-like and D2-R-like binding as the obese rats, and reduced DAT binding within all areas of the striatum. Both RYGB and restricted HF diet rats showed similar weight reductions, with RYGB rats showing no difference in binding compared to controls. The observed changes in binding between non-treated obese rats and RYGB rats demonstrates that HF dietary effects on the dopamine system were reversed by RYGB.