Roux en Y gastric bypass increases ethanol intake in the rat

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.

Long-Term Lifestyle Habits and Quality of Life after Roux-in-Y Gastric Bypass in Brazilian Public versus Private Healthcare Systems: Beyond Weight Loss

Lifestyle and health-related quality of life (HRQoL) are good markers of surgical obesity treatment. This study aimed to investigate the lifestyle and HRQoL of patients at least five years after Roux-en-Y gastric bypass in public (SUS) and private (PVT) Brazilian healthcare systems. In this cross-sectional study, weight loss (WL), % of excess WL (%EWL), diet quality, physical activity, alcohol consumption, and HRQoL were evaluated. Analysis of covariance, binary and multinomial logistic regression, adjusted for confounders, were performed. The SUS group had more vulnerable socioeconomic statuses than the PVT group. Total %WL and % EWL were 24.64 ± 0.99% and 60.46 ± 2.41%, respectively, without difference between groups. In the Pain/Discomfort and Anxiety/Depression domains of HRQoL, more than 50% reported moderate problems without differences between groups. Processed food ingestion was higher in the PVT (132.10 ± 60.15 g/1000 kcal) than in the SUS (103.43 ± 41.72 g/1000 kcal), however, without statistical significance (p = 0.093). The PVT group showed lower physical activity (OR: 0.23; 95%CI: 0.87-0.63; p = 0.004) and a higher risk of alcohol-related problems (OR: 3.23; 95%CI; 1.03-10.10; p = 0.044) compared to SUS group. Participants generally achieved satisfactory WL, regardless of healthcare systems. However, PVT participants had unfavorable lifestyle characteristics, highlighting the need for studies investigating environmental issues post-bariatric surgery.

Association of Previous Gastric Bypass Surgery and Patient Outcomes in Alcohol-Associated Cirrhosis Hospitalizations

BACKGROUND AND AIM

Roux-En-Y gastric bypass (RYGB) is associated with risk of alcohol use disorder. The impact of RYGB among patients with alcohol-associated liver disease (ALD) remains unknown.

METHODS

A retrospective cohort from National Inpatient Sample (01/2006-09/2015) database on 421,156 admissions with alcohol-associated cirrhosis (AC) was stratified for non-primary discharge diagnosis of previous RYGB. Admissions with RYGB (cases) were matched 1:3 to without RYGB (controls) based on propensity score on demographics, calendar year, socioeconomic status (insurance and zip code income quartile), obesity, diabetes, anxiety, and alcohol use disorder. Primary outcome was concomitant discharge diagnosis of alcoholic hepatitis (AH) or development of acute on chronic liver failure (ACLF).

RESULTS

Of 10,168 admissions (mean age 49 yrs., 75% females, 79% whites), cases (N = 2542) vs. controls had higher prevalence of concomitant AH (18.8 vs. 17%, P = 0.032), hepatic encephalopathy (31 vs. 25%), infection (28 vs. 24%), and grade 3 ACLF (13 vs. 5%), P < 0.001. Conditional logistic regression models showed higher odds for AH, hepatic encephalopathy, and infection among cases. In-hospital mortality of 6.3% (43% in ACLF) was lower in cases, but similar in the sub-cohorts of AH (N = 1768) or ACLF (N = 768). Results were similar in a sensitivity analysis of matched cohort of 2016 hospitalizations (504 cases) with primary discharge diagnosis of AC.

CONCLUSION

Among patients with AC, previous RYGB is associated with increased likelihood of concomitant AH, hepatic encephalopathy, and infection, but similar in-hospital mortality. Prospective studies are needed to validate, determine causality, and understand mechanisms of these findings among patients with alcohol-associated cirrhosis.

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.

The rewarding effects of alcohol after bariatric surgery: do they change and are they associated with pharmacokinetic changes?

BACKGROUND

Research shows that surgery patients who have undergone Roux-en-Y gastric bypass (RYGB) are at increased risk for an alcohol use disorder (AUD). However, the mechanisms through which this increased risk is incurred are poorly understood. A host of variables have been proposed as potentially causal in developing AUDs, but empirical examination of many of these variables in human samples is lacking.

OBJECTIVES

Our objective was to examine the extent to which alcohol pharmacokinetics (PK), the rewarding effects of alcohol, and the relationship between these variables change from before to after weight loss surgery.

SETTING

Large healthcare facility in the Midwest United States METHODS: Thirty-four participants completed assessments before and 1 year after RYGB. They completed laboratory sessions and provided data on the PK of alcohol and the extent to which alcohol was reinforcing to them at each timepoint.

RESULTS

Findings show that the PK effects of alcohol (P < .01) and how rewarding alcohol was reported to be (P < .01) changed from before to 1 year after weight loss surgery. Further, statistically significant increases in the association between these variables were witnessed from before to 1 year after surgery (P < .01).

CONCLUSION

These results implicate changes (from before surgery to one year after) in the reinforcing and PK effects of alcohol as possible mechanisms for increased risk of alcohol use disorder following Roux-en-Y gastric bypass surgery.

Review of Changes in the Reinforcing Effects of Alcohol in Weight Loss Surgery Patients

PURPOSE OF REVIEW

The reinforcing effects of alcohol are well documented, and they have been shown to play a role in the development of alcohol use disorders (AUDs). Also well established is the fact that post-weight loss surgery (WLS) patients are at an increased risk for AUDs. In the current manuscript, we review the notion that the reinforcing effects of alcohol may change from before to after WLS and discuss a number of determinants of alcohol reinforcement change in WLS patients.

RECENT FINDINGS

It has been increasingly well understood that WLS patients are at an increased risk for AUD, but empirical support for the mechanisms that may cause this phenomenon have been lacking. Recently, a model was proposed that offered a number of different potentially causal variables as mechanisms that result in increased risk for AUD in these surgical patients. Change in the extent to which alcohol is reinforcing to WLS patients may be key in determining the likelihood of AUDs in this group. We review a host of biological, psychological, and social variables that ultimately impact how reinforcing alcohol is to WLS patients.

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 risk of alcohol use disorder: a register-based cohort study

BACKGROUND

Bariatric surgery has been associated with altered alcohol metabolism. We examined whether patients undergoing bariatric surgery have a higher risk of developing alcohol use disorder (AUD) compared with individuals with obesity who have not received bariatric surgery.

METHODS

In this prospective cohort study, we followed 13 430 patients undergoing bariatric surgery (95% gastric bypass) between 2005 and 2013 and a reference group of 21 021 individuals with obesity for a median of 6.9 years (5th-95th percentile: 4.0-9.8). Four different approaches were used to account for baseline differences between the two groups: (i) adjustment; (ii) inverse probability of treatment weighting (IPTW); (iii) 1:1 matching based on propensity scores; and (iv) before-and-after analysis comparing the bariatric surgery group with itself 5 years before and after surgery. Cox proportional hazard modelling was used to estimate hazard ratios of AUD defined from national registers.

RESULTS

When applying the IPTW approach, the hazard ratio (HR) of AUD for bariatric surgery patients was 7.29 [95% confidence interval (CI): 5.06-9.48] compared with individuals without surgery. When employing different approaches (adjustment for baseline variables, matching on propensity scores, before-and-after analyses), results were of similar magnitude. Analysis stratified by time after surgery revealed a higher risk of AUD already within the first year following surgery [HR: 2.77 (95% CI: 1.39-5.53)].

CONCLUSIONS

Patients undergoing bariatric surgery have a higher risk of developing AUD compared with individuals without bariatric surgery. The higher risk observed in this group of patients cannot be explained by differences in baseline characteristics such as socioeconomic factors. Despite the higher risk of AUD, only few individuals developed AUD. Individuals with disabling obesity should therefore not rule out surgery based on these results but rather be aware of negative implications.

Roux-en-Y gastric bypass increases GABA-A receptor levels in regions of the rat brain involved in object recognition memory and perceptual acuity

Roux-en-Y gastric bypass surgery (RYGB), one of the most common and successful procedures for combatting obesity, is associated with post-surgery substance use disorder (SUD) and other addictive behaviors in a subset of patients. We investigated the effects of RYGB on GABA-A receptor levels in the rat brain to identify potential mechanisms of this behavior. The GABAergic system is affected in addiction and has been implicated in the pathology of obesity. We assigned male Sprague-Dawley rats to four groups: standard, low fat diet with sham surgery (control), ad libitum HFD with sham surgery (Sham), calorie restricted HFD with sham surgery (Sham-FR), or HFD with RYGB surgery. Surgery was performed after 8 weeks on the control or HFD diet. Rats maintained their respective diets for 9 weeks post-surgery, then were sacrificed for GABA-A receptor autoradiography using the [³H] Flunitrazepam ligand. We identified increased GABA-A binding in the perirhinal cortex of ad-libitum HFD fed rats compared to normal diet controls. RYGB surgery increased GABA-A in the ectorhinal cortex compared to normal diet controls, and increased binding in the jaw region of the primary somatosensory cortex compared to food-restricted rats that received sham surgery. Hypothalamus GABA-A was also negatively correlated with body weight in the RYGB group, where GABA signaling may play a role in obesity regulation. These results suggest that HFD and RYGB modulate GABA signaling in regions important for object recognition memory, and that increased GABA-A levels in the jaw's perceptual field cortex arise from the surgery itself, independent of caloric restriction.

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.

Changes in Alcohol Use after Metabolic and Bariatric Surgery: Predictors and Mechanisms

PURPOSE OF REVIEW

This review synthesized the literature on predictors and mechanisms of post-bariatric alcohol problems, in order to guide future research on prevention and treatment targets.

RECENT FINDINGS

Consistent evidence suggests an elevated risk of developing problems with alcohol following bariatric surgery. While there is a paucity of empirical data on predictors of problematic alcohol use after bariatric surgery, being male, a younger age, smoking, regular alcohol consumption, pre-surgical alcohol use disorder, and a lower sense of belonging have predicted alcohol misuse post-operatively. This review synthesizes potential mechanisms including specific bariatric surgical procedures, peptides and reinforcement/reward pathways, pharmacokinetics, and genetic influences. Finally, potential misperceptions regarding mechanisms are explored. Certain bariatric procedures elevate the risk of alcohol misuse post-operatively. Future research should serve to elucidate the complexities of reward signaling, genetically mediated mechanisms, and pharmacokinetics in relation to alcohol use across gender and developmental period by surgery type.

Roux-en-Y gastric bypass in rat reduces mu-opioid receptor levels in brain regions associated with stress and energy regulation

Roux-en-Y gastric bypass surgery (RYGB) is the most common and effective weight loss procedure for severe obesity. However, a significant increase in addictive behaviors and new-onset substance use disorder (SUD) are sometimes observed post-surgery. The endogenous opioid system is known to play a major role in motivated behavior and reward, as well as the abuse of substances, including alcohol, tobacco, opioids and highly palatable foods. Here, we examined the effects of RYGB on mu-opioid receptor levels in the brain. Male Sprague-Dawley rats were assigned to one of four groups: standard diet with sham surgery (control), ad libitum high-energy high-fat (HF) diet with sham surgery, calorie restricted HF diet with sham surgery (Sham-FR), or HF diet with RYGB surgery. Control and HF groups were fed their respective diets for 8 weeks, with surgery performed on the eighth week. After 9 weeks on their respective diets post-surgery, animals were sacrificed for mu-opioid receptor autoradiography using the [³H] [D-Ala2,N-Me-Phe4-Gly5-ol]- enkephalin (DAMGO) ligand. Rats with RYGB showed reduced DAMGO binding in the central amygdala compared to sham-operated HF diet controls, and in the hypothalamus compared to high-fat fed Sham-FR. Diet alone did not change [³H] DAMGO binding in any region. These findings show that RYGB surgery, independent of diet or caloric restriction, decreases mu opioid signaling in specific regions important for stress and energy regulation. Thus, RYGB surgery may lead to greater stress sensitivity via downregulated mu opioid signaling in the central amygdala, which may contribute to the observed increased risk in some subjects for addictive behavior.

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.

The gut in the brain: the effects of bariatric surgery on alcohol consumption

Obesity represents a major medical and public health problem worldwide. Efforts have been made to develop novel treatments, and among them bariatric surgery is used as an effective treatment to achieve significant, long-term weight loss and alleviate medical problems related to obesity. Alcohol use disorder (AUD) is also a leading cause of morbidity and mortality worldwide. Recent clinical studies have revealed a concern for bariatric surgery patients developing an increased risk for alcohol consumption, and for AUD. A better understanding of the relationship between bariatric surgery and potential later development of AUD is important, given the critical need of identifying patients at high risk for AUD. This paper reviews current clinical and basic science research and discusses potential underlying mechanisms. Special emphasis in this review is given to recent work suggesting that, alterations in alcohol metabolism/pharmacokinetics resulting from bariatric surgery are unlikely to be the primary or at least the only explanation for increased alcohol use and development of AUD, as changes in brain reward processing are also likely to play an important role. Additional studies are needed to clarify the potential role and mechanisms of how bariatric surgery may increase alcohol use and lead to AUD development.

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

Vertical sleeve gastrectomy (VSG) and Roux-en-Y gastric bypass (RYGB) are the most common surgical options for the treatment of obesity and metabolic disorder. Whereas RYGB may result in greater and more durable weight loss, recent clinical and pre-clinical studies in rats have raised concerns that RYGB surgery may increase risk for alcohol use disorder (AUD). In contrast, recent clinical reports suggest a lesser risk for AUD following VSG, although no preclinical studies have been done to confirm that. Therefore, the present study sought to determine the effects of VSG on ethanol intake and preferences in rodent models using protocols similar to those previously used in animal studies for RYGB. Male Sprague Dawley rats and male C57B6 mice were made obese on a high fat diet (60%kcal from fat) and received VSG or no surgery (controls). All animals then were given access to increasing concentrations of ethanol (2%, 4%, 6%, and 8%), presented for few days each. Compared to controls, VSG rats consumed significantly less of 2, 6 and 8% ethanol and showed significantly reduced preferences to 6 and 8% ethanol over water. VSG mice also displayed reduced intake and preference for 6 and 8% ethanol solutions. After a two-week period of forced abstinence, 8% ethanol was reintroduced and the VSG rats and mice continued to exhibit reduced consumption and less preference for ethanol. Regarding the underlying mechanism, we hypothesized that the removal of the ghrelin producing part of the stomach in the VSG surgery is a possible contributor to the observed reduced ethanol preference. To test for functional changes at the ghrelin receptors, the VSG and control rats were given IP injections of acyl-ghrelin (2.5nmol and 5nmol) prior to ethanol access. Neither concentration of ghrelin resulted in a significant increase in 8% ethanol consumption of VSG or control subjects. Next, the rats were given IP injections of the ghrelin receptor antagonist, JMV (2.5mg/kg body weight). This dose induced a significant reduction in 8% ethanol consumption in the VSG group, but no effect on ethanol intake in the controls. While ghrelin injection was uninformative, increased sensitivity to subthreshold doses of the ghrelin receptor antagonist may indicate reduced ghrelin signaling following VSG. Overall, these findings suggest that bariatric patients with increased susceptibility to AUD may benefit from receiving VSG instead of RYGB surgery, and that changes in ghrelin signaling, at least in part, may play a role in the differential AUD risks between the two most commonly performed bariatric surgical procedures.

Obesity and addiction: can a complication of surgery help us understand the connection?

Obesity is a multifactorial, chronic disease that has proven difficult to treat. An increased understanding of aetiological mechanisms is critical to the development of more effective obesity prevention and treatment strategies. A growing body of empirical evidence has demonstrated parallels between obesity, overeating and substance abuse, including shared behavioural, psychological and neurophysiological factors implicated in the excessive intake of both food and substances of abuse. Several different lines of research have recently emerged that hold the potential to shed light on the connection between obesity, food reward and addiction, with studies examining changes in alcohol use/misuse after weight loss surgery providing a particularly interesting perspective on these interrelationships. However, these lines of investigation have proceeded in relative isolation, and relevant research findings have yet to be integrated in a synthesized, comprehensive manner. To provide an opportunity to achieve such a synthesis, a scientific symposium was convened at the Radcliffe Institute in Cambridge, Massachusetts. Invited participants were researchers working in diverse domains related to the intersection between obesity and addiction. Extensive discussion was generated suggesting novel research directions. In this article, we summarize and synthesize the symposium participants' ongoing research in this area, incorporating additional relevant research holding potential clues regarding the connections between obesity, weight loss surgery and addiction.

Impact of Roux-en-Y gastric bypass surgery on appetite, alcohol intake behaviors, and midbrain ghrelin signaling in the rat

OBJECTIVE

Roux-en-Y gastric bypass (RYGB) surgery reduces appetite and stimulates new onset alcohol misuse; however, the genesis of these behavioral changes is unclear. This study is hypothesized that new onset alcohol intake is a behavioral adaptation that occurs secondary to reduced appetite and correlates with altered central ghrelin signaling.

METHODS

Hedonic high-fat diet (HFD) intake was evaluated prior to the assessment of alcohol intake behaviors in RYGB and control rats. Measurements were also taken of circulating ghrelin and ghrelin receptor (GHSR) regulation of neuronal firing in ventral tegmental area (VTA) dopamine (DA) neurons.

RESULTS

RYGB rats displayed reduced HFD intake relative to controls. Sham and RYGB rats consumed more alcohol and preferred lower concentrations of alcohol, whereas only RYGB rats escalated alcohol intake during acute withdrawal. Remarkably, GHSR activity, independent of peripheral ghrelin release, set the tonic firing of VTA DA neurons, a response selectively diminished in RYGB rats.

CONCLUSIONS

This study indicates that gut manipulations lead to increased alcohol intake, whereas RYGB promotes behaviors that may maintain alcohol misuse. Reductions in hedonic feeding and diminished GHSR control of VTA firing further distinguish gut manipulation from complete bypass and present a potential mechanism linking reduced appetite with alcohol misuse after RYGB surgery.

Increased intravenous morphine self-administration following Roux-en-Y gastric bypass in dietary obese rats

Roux-en-Y gastric bypass (RYGB) surgery is a commonly performed and very effective method to achieve significant, long-term weight loss. Opioid analgesics are primarily used to manage postoperative pain as fewer alternative medication options are available for bariatric surgery patients than for the general population. Recent clinical studies support a greater risk for substance use following bariatric surgery, including an increased use of opioid medications. The present study is the first to study morphine self-administration in a rat model of RYGB. High fat diet-induced obese (HFD-DIO) rats underwent RYGB (n=14) or sham-surgery with ad libitum HFD (SHAM, n=14) or a restricted amount that resulted in weight matched to the RYGB cohort (SHAM-WM, n=8). An additional normal-diet (ND, n=7), intact (no surgery) group of rats was included. Two months after the surgeries, rats were fitted with jugular catheters and trained on a fixed ratio-2 lick task to obtain morphine intravenously. Both morphine-seeking (number of licks on an empty spout to obtain morphine infusion) and consumption (number of infusion) were significantly greater in RYGB than any control group beginning on day 3 and reached a two-fold increase over a period of two weeks. These findings demonstrate that RYGB increases motivation for taking morphine and that this effect is independent of weight loss. Further research is warranted to reveal the underlying mechanisms and to determine whether increased morphine use represents a risk for opioid addiction following RYGB. Identifying risk factors preoperatively could help with personalized postoperative care to prevent opioid abuse and addiction.

Roux-en-Y Gastric Bypass Alters Brain Activity in Regions that Underlie Reward and Taste Perception

BACKGROUND

Roux-en-Y gastric bypass (RYGB) surgery is a very effective bariatric procedure to achieve significant and sustained weight loss, yet little is known about the procedure's impact on the brain. This study examined the effects of RYGB on the brain's response to the anticipation of highly palatable versus regular food.

METHODS

High fat diet-induced obese rats underwent RYGB or sham operation and were then tested for conditioned place preference (CPP) for the bacon-paired chamber, relative to the chow-paired chamber. After CPP, animals were placed in either chamber without the food stimulus, and brain-glucose metabolism (BGluM) was measured using positron emission tomography (μPET).

RESULTS

Bacon CPP was only observed in RYGB rats that had stable weight loss following surgery. BGluM assessment revealed that RYGB selectively activated regions of the right and midline cerebellum (Lob 8) involved in subjective processes related to reward or expectation. Also, bacon anticipation led to significant activation in the medial parabrachial nuclei (important in gustatory processing) and dorsomedial tegmental area (key to reward, motivation, cognition and addiction) in RYGB rats; and activation in the retrosplenial cortex (default mode network), and the primary visual cortex in control rats.

CONCLUSIONS

RYGB alters brain activity in areas involved in reward expectation and sensory (taste) processing when anticipating a palatable fatty food. Thus, RYGB may lead to changes in brain activity in regions that process reward and taste-related behaviors. Specific cerebellar regions with altered metabolism following RYGB may help identify novel therapeutic targets for treatment of obesity.

Appetite and body weight regulation after bariatric surgery

Bariatric surgery continues to be remarkably efficient in treating obesity and type 2 diabetes mellitus and a debate has started whether it should remain the last resort only or also be used for the prevention of metabolic diseases. Intense research efforts in humans and rodent models are underway to identify the critical mechanisms underlying the beneficial effects with a view towards non-surgical treatment options. This non-systematic review summarizes and interprets some of this literature, with an emphasis on changes in the controls of appetite. Contrary to earlier views, surgery-induced reduction of energy intake and subsequent weight loss appear to be the main drivers for rapid improvements of glycaemic control. The mechanisms responsible for suppression of appetite, particularly in the face of the large weight loss, are not well understood. Although a number of changes in food choice, taste functions, hedonic evaluation, motivation and self-control have been documented in both humans and rodents after surgery, their importance and relative contribution to diminished appetite has not yet been demonstrated. Furthermore, none of the major candidate mechanisms postulated in mediating surgery-induced changes from the gut and other organs to the brain, such as gut hormones and sensory neuronal pathways, have been confirmed yet. Future research efforts should focus on interventional rather than descriptive approaches in both humans and rodent models.

Roux-en-Y gastric bypass does not affect daily water intake or the drinking response to dipsogenic stimuli in rats

Bariatric surgery is currently the most effective treatment for severe obesity, and Roux-en-Y gastric bypass (RYGB) is the most common approach in the United States and worldwide. Many studies have documented the changes in body weight, food intake, and glycemic control associated with the procedure. Although dehydration is commonly listed as a postoperative complication, little focus has been directed to testing the response to dipsogenic treatments after RYGB. Accordingly, we used a rat model of RYGB to test for procedure-induced changes in daily water intake and in the response to three dipsogenic treatments: central administration of ANG II, peripheral injection of hypertonic saline, and overnight water deprivation. We did not find any systematic differences in daily water intake of sham-operated and RYGB rats, nor did we find any differences in the response to the dipsogenic treatments. The results of these experiments suggest that RYGB does not impair thirst responses and does not enhance any satiating effect of water intake. Furthermore, these data support the current view that feedback from the stomach is unnecessary for the termination of drinking behavior and are consistent with a role of orosensory or postgastric feedback.

Altered ghrelin secretion in mice in response to diet-induced obesity and Roux-en-Y gastric bypass

The current study examined potential mechanisms for altered circulating ghrelin levels observed in diet-induced obesity (DIO) and following weight loss resulting from Roux-en-Y gastric bypass (RYGB). We hypothesized that circulating ghrelin levels were altered in obesity and after weight loss through changes in ghrelin cell responsiveness to physiological cues. We confirmed lower ghrelin levels in DIO mice and demonstrated elevated ghrelin levels in mice 6 weeks post-RYGB. In both DIO and RYGB settings, these changes in ghrelin levels were associated with altered ghrelin cell responsiveness to two key physiological modulators of ghrelin secretion - glucose and norepinephrine. In DIO mice, increases in ghrelin cell density within both the stomach and duodenum and in somatostatin-immunoreactive D cell density in the duodenum were observed. Our findings provide new insights into the regulation of ghrelin secretion and its relation to circulating ghrelin within the contexts of obesity and weight loss.

Problematic intake of high-sugar/low-fat and high glycemic index foods by bariatric patients is associated with development of post-surgical new onset substance use disorders

Bariatric or weight loss surgery (WLS) patients are overrepresented in substance abuse treatment, constituting about 3% of admissions; about 2/3 of such patients deny problematic substance use prior to WLS. It is important to advance our understanding of the emergence of substance use disorders (SUDs) - particularly the New Onset variant - after WLS. Burgeoning research with both animal models and humans suggests that "food addiction" may play a role in certain forms of obesity, with particular risk conferred by foods high in sugar but low in fat. Therefore, we hypothesized that WLS patients who reported pre-WLS problems with High-Sugar/Low-Fat foods and those high on the glycemic index (GI) would be those most likely to evidence New Onset SUDs after surgery. Secondary data analyses were conducted using a de-identified database from 154 bariatric surgery patients (88% female, Mage=48.7 yrs, SD=10.8, Mtime since surgery=2.7 yrs, SD=2.2 yrs). Participants who endorsed pre-surgical problems with High-Sugar/Low-Fat foods and High GI foods were at greater risk for New Onset SUD in the post-surgical period. These findings remained significant after controlling for other predictors of post-surgical SUD. Our findings provide evidence for the possibility of addiction transfer among certain bariatric patients.

Substance misuse following Roux-en-Y gastric bypass surgery

Post-bariatric surgery patients are overrepresented in substance abuse treatment, particularly those who have had the Roux-en-Y gastric bypass (RYGB) procedure. The severity of the substance use disorder (SUD; i.e., warranting inpatient treatment) and related consequences necessitate a better understanding of the variables associated with post-RYGB SUDs. This investigation assessed factors associated with post-RYGB substance misuse. Post-RYGB patients (N = 141; at least 24 months postsurgery) completed an online survey assessing variables hypothesized to contribute to post-RYGB SUDs. Fourteen percent of participants met criteria for postoperative substance misuse. Those with a lower percent total weight loss (%TWL) were more likely to endorse substance misuse. Family history of substance misuse was strongly associated with postoperative substance misuse. Eating-related variables including presurgical food addiction and postsurgical nocturnal eating, subjective hunger, and environmental responsiveness to food cues were also associated with a probable postoperative SUD. These findings have clinical utility in that family history of substance misuse can be easily assessed, and at-risk patients can be advised accordingly. In addition, those who endorse post-RYGB substance misuse appear to have stronger cognitive and behavioral responses to food, providing some support for the theory of behavioral substitution (or "addiction transfer").

Roux-en-Y gastric bypass increases intravenous ethanol self-administration in dietary obese rats

Roux-en-Y gastric bypass surgery (RYGB) is an effective treatment for severe obesity. Clinical studies however have reported susceptibility to increased alcohol use after RYGB, and preclinical studies have shown increased alcohol intake in obese rats after RYGB. This could reflect a direct enhancement of alcohol’s rewarding effects in the brain or an indirect effect due to increased alcohol absorption after RGYB. To rule out the contribution that changes in alcohol absorption have on its rewarding effects, here we assessed the effects of RYGB on intravenously (IV) administered ethanol (1%). For this purpose, high fat (60% kcal from fat) diet-induced obese male Sprague Dawley rats were tested ∼2 months after RYGB or sham surgery (SHAM) using both fixed and progressive ratio schedules of reinforcement to evaluate if RGYB modified the reinforcing effects of IV ethanol. Compared to SHAM, RYGB rats made significantly more active spout responses to earn IV ethanol during the fixed ratio schedule, and achieved higher breakpoints during the progressive ratio schedule. Although additional studies are needed, our results provide preliminary evidence that RYGB increases the rewarding effects of alcohol independent of its effects on alcohol absorption.

Moving beyond energy homeostasis: new roles for glucagon-like peptide-1 in food and drug reward

Glucagon-like peptide-1 (GLP-1), a hormone and neuropeptide, is known to regulate energy homeostasis in part through an established central role in controlling food intake. Historically this central role has largely been attributed to GLP-1 receptor signaling in the brainstem and hypothalamus. However, emerging data indicate that GLP-1 also contributes to non-homeostatic regulation of food reward and motivated behaviors in brain reward centers, including the ventral tegmental area and nucleus accumbens. The hypothesis that GLP-1 signaling modulates reward circuitry has provided the impetus for studies demonstrating that GLP-1 attenuates reward for psychostimulants and alcohol. Here, we examine current evidence for GLP-1-mediated regulation of food and drug reward and use these findings to hypothesize mechanisms of action within brain reward centers.