Aversion learning can reduce meal size without taste avoidance in rats

Novel Insights into the Physiology of Nutrient Sensing and Gut-Brain Communication in Surgical and Experimental Obesity Therapy

Despite standardized surgical technique and peri-operative care, metabolic outcomes of bariatric surgery are not uniform. Adaptive changes in brain function may play a crucial role in achieving optimal postbariatric weight loss. This review follows the anatomic-physiologic structure of the postbariatric nutrient-gut-brain communication chain through its key stations and provides a concise summary of recent findings in bariatric physiology, with a special focus on the composition of the intestinal milieu, intestinal nutrient sensing, vagal nerve-mediated gastrointestinal satiation signals, circulating hormones and nutrients, as well as descending neural signals from the forebrain. The results of interventional studies using brain or vagal nerve stimulation to induce weight loss are also summarized. Ultimately, suggestions are made for future diagnostic and therapeutic research for the treatment of obesity.

Possible origins of consciousness in simple control over "involuntary" neuroimmunological action

The origin(s) and purpose(s) of consciousness continue to be fervently debated by neuroscientists. A recent unconventional hypothesis put forth by Morsella et al. suggests the primary function of consciousness is the integration, selection, and execution of advantageous lower-level voluntary skeletal muscle behavior on surrounding external environments. However, at main issue is whether more precise, adaptable voluntary skeletal motor action, and therefore the corresponding workings of consciousness, first emerged and evolved in animals to exert control over external environments or internal ones regulated by less flexible autonomic function. Using the example of voluntary immunomodulation, one can identify the strengths and weaknesses of either rationale. For instance, highly trained meditative techniques for immunomodulation more-or-less conform to Morsella et al.'s assumptions on higher-level indirect conscious control of autonomic function. Whereas, untrained skeletal motor resolution of infection-related approach-avoidance conflicts support conclusions contrary to those of Morsella et al. In such cases, primitive voluntary changes in host respiration rate and volume may selectively facilitate/inhibit acute autonomic psychophysiological stress responses to pathogen insult. This and other types of scenarios predictably give evolutionary and ecological rise to self-awareness of (visceral) internal states as well as to voluntary regulation of internal state action conflicts.

Potential mechanisms underlying the effect of bariatric surgery on eating behaviour

PURPOSE OF REVIEW

Reduced energy intake, resulting from favourable changes in eating behaviour, is the predominant driver of weight loss following bariatric surgery. Here we review the most recent studies examining the impact of Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy, the two most common bariatric procedures, upon eating behaviour and the suggested underlying biological mechanisms.

RECENT FINDINGS

Following RYGB or sleeve gastrectomy, most people report subjective changes in appetite, taste and food preference, with decreased high-fat preference most commonly reported. Objective postsurgery changes in taste and olfactory acuity occur. A new phenomenon, 'meal-size aversion', may contribute to reduced postoperative energy intake. Recent studies provide evidence for peptide YY3-36, glucagon-like peptide-1, ghrelin, neurotensin and oleoylethanolamide as mediators of postoperative eating behaviour changes. Factors modulating these changes include sex, type 2 diabetes status, genetics and bariatric procedure. New studies implicate central dopaminergic and opioid receptor signalling as key neural mediators driving altered eating behaviour. Brain neuroimaging studies show that obesity-associated changes in food-cue responses, brain connectivity and structural abnormalities are normalized following bariatric surgery.

SUMMARY

Understanding the biological mechanisms mediating the eating behaviour changes engendered by bariatric surgery may lead to the development of novel therapeutic strategies for people with obesity.

Regulation of Energy Homeostasis After Gastric Bypass Surgery

The obesity epidemic continues to escalate each year in the United States more than anywhere else in the world. The existing pharmaceutical and other nonsurgical treatments for morbid obesity produce suboptimal physiologic outcomes compared with those of Roux-en-Y gastric bypass (RYGB) surgery. RYGB has been the gold standard of bariatric surgery because the beneficial long-term outcomes, which include sustainable weight loss and type 2 diabetes mellitus (T2DM) resolution, are far superior to those obtained with other bariatric surgeries. However, the current understanding of RYGB's mechanisms of actions remains limited and incomplete. There is an urgent need to understand these mechanisms as gaining this knowledge may lead to the development of innovative and less invasive procedures and/or medical devices, which can mirror the favorable outcomes of RYGB surgery. In this review, we highlight current observations of the metabolic and physiologic events following RYGB, with a particular focus on the role of the anatomical reconfiguration of the gastrointestinal tract after RYGB.

Ginsenoside-Rb1 ameliorates lithium-induced nephrotoxicity and neurotoxicity: Differential regulation of COX-2/PGE2 pathway

To investigate the effect of Ginsenoside-Rb1 (GRb1) on lithium (Li⁺)-induced toxicity, GRb1 was given to rats orally (100mg/kg) for 14days. In independent groups, lithium chloride (4meq/kg/day i.p.) was administered at day 4 of the experiment for 10days, with or without GRb1. Li⁺ caused significant deterioration of behavioral responses including righting reflex, spontaneous motor activity and catalepsy. Li⁺ also caused distortion in normal renal, cerebral and cerebellum architecture and significantly worsened all kidney functional parameters tested compared to control. In addition, Li caused oxidative stress in both kidney and brain, evident by significant increase in malondialdehyde and nitric oxide levels, with decrease in reduced glutathione and catalase activity. Administration of GRb1 prior to Li⁺ significantly improved behavioral responses, renal and brain histopathological picture, kidney function tests and oxidative stress markers compared to sole Li⁺-treated group. Concomitant administration of GRb1 decreased Li⁺ levels by about 50% in serum, urine and brain and by 35% in the kidney. Interestingly, Li⁺ had a differential effect on cyclooxygenase (COX)-2/prostaglandin E₂ (PGE₂) pathway, as it significantly increased COX-2 expression and PGE₂ level in the kidney, while decreasing them in the brain compared to control. On the other hand, administering GRb1 with Li⁺ suppressed COX-2/PGE₂ pathway in both kidney and brain compared to Li⁺ alone. In conclusion, GRb1 can alter Li⁺ pharmacokinetics resulting in extensively decreasing its serum and tissue concentrations. Furthermore, COX-2/PGE₂ pathway has a mechanistic role in the nephro- and neuro-protective effects of GRb1 against Li⁺-induced toxicity.

Recent advances in the modification of taste and food preferences following bariatric surgery

There is a large body of evidence indicating that bariatric surgery provides durable weight loss and health benefits to patients who are obese and have comorbidities such as type 2 diabetes (T2D). However, there are still many questions related to mechanisms of metabolic improvement, predictors of success/failure, and long term consequences, which need to be answered. More recently, there has been a particular interest in the modulation of taste and food preferences that occurs after bariatric surgery and how this affects weight loss in different individuals. Animal models as well as human studies have shed some light on the role of taste in changing food preferences and how these changes may affect weight loss after surgery. The goal of this review is to discuss the physiological and behavioral consequences of bariatric surgery as a treatment for obesity and T2D, with particular emphasis on recent studies describing bariatric surgery-induced modifications in taste perception and food preferences.