Influence of ondansetron on gastric sensorimotor responses to short duodenal acid infusion in healthy volunteers

Psilocybin therapy and anorexia nervosa: a narrative review of safety considerations for researchers and clinicians

BACKGROUND

Clinical trials using psilocybin therapy to treat anorexia nervosa (AN) are currently underway. The safety and tolerability of psilocybin is of utmost importance in individuals with AN who may present unique medical vulnerabilities. The purpose of this review is to describe how the common physiologic adverse effects of psilocybin may impact medical complications experienced by individuals with AN in clinical trials of psilocybin therapy.

MAIN BODY

The physiologic underpinnings of common adverse effects following psilocybin administration are described, including tachycardia, hypertension, electrocardiogram changes, nausea, headache, and lightheadedness. These anticipated physiologic changes are described in relation to the common medical correlates seen in individuals with AN. Risk mitigation strategies for each adverse effect are proposed.

CONCLUSION

Early evidence suggests that psilocybin therapy is well-tolerated in individuals with AN. Understanding the unique medical complications of AN, and how they may be impacted by common physiologic adverse effects of psilocybin administration, leads to tailored risk mitigation strategies to enhance safety and tolerability of this novel intervention.

Potential Mechanisms of Acupuncture for Functional Dyspepsia Based on Pathophysiology

Functional dyspepsia (FD), a common disorder of gastrointestinal function, originated from the gastroduodenum. Although the therapeutic effect of acupuncture has been investigated by various high-quality randomized controlled trials, the potential mechanisms showed obvious heterogeneity. This review summarized the potential mechanisms of acupuncture on FD in order to guide for future laboratory and clinical studies. Here, we argued that the primary cause of FD was gastroduodenal low-grade inflammation and acid exposure, which impaired mucosal integrity, caused brain-gut axis dysfunction, and impaired brain network connectivity, all of which generated various symptom patterns. Overall the clinical studies indicated that acupuncture was a promising treatment to alleviate symptoms in FD patients, whose efficacy was influenced by acupoints and individual variance. Mechanistically, studies with animal models of FD and patients have shown that acupuncture, a non-invasive strategy for nerve stimulation, may have the potential to control intestinal inflammation and suppress acid-secretion via different somatic autonomic reflex pathways, regulate the brain-gut axis through intestinal microbiota, and has the potential to ameliorate FD-symptoms. The cumulative evidence demonstrated that acupuncture is a promising treatment to alleviate symptoms of FD patients.

Duodenal acidification induces gastric relaxation and alters epithelial barrier function by a mast cell independent mechanism

Duodenal hyperpermeability and low-grade inflammation in functional dyspepsia is potentially related to duodenal acid exposure. We aimed to evaluate in healthy volunteers the involvement of mast cell activation on the duodenogastric reflex and epithelial integrity during duodenal acidification. This study consisted of 2 parts: (1) Duodenal infusion of acid or saline during thirty minutes in a randomized, double-blind cross-over manner with measurement of intragastric pressure (IGP) using high resolution manometry and collection of duodenal biopsies to measure epithelial barrier function and the expression of cell-to-cell adhesion proteins. Mast cells and eosinophils were counted and activation and degranulation status were assessed. (2) Oral treatment with placebo or mast cell stabilizer disodiumcromoglycate (DSCG) prior to duodenal perfusion with acid, followed by the procedures described above. Compared with saline, acidification resulted in lower IGP (P < 0.01), increased duodenal permeability (P < 0.01) and lower protein expression of claudin-3 (P < 0.001). Protein expression of tryptase (P < 0.001) was increased after acid perfusion. Nevertheless, an ultrastructural examination did not reveal degranulation of mast cells. DSCG did not modify the drop in IGP and barrier dysfunction induced by acid. Duodenal acidification activates an inhibitory duodenogastric motor reflex and, impairs epithelial integrity in healthy volunteers. However, these acid mediated effects occur independently from mast cell activation.

Duodenal inflammation: an emerging target for functional dyspepsia?

Introduction: Functional dyspepsia (FD) is one of the most common functional gastrointestinal disorders and is classified into postprandial distress and epigastric pain syndrome. Despite the recognition of duodenal inflammation as a potential trigger of symptoms, only limited anti-inflammatory therapies exist.Areas covered: This narrative review summarizes the recent advances in the pathophysiology and treatment of FD; it identifies potential therapeutic targets and gaps in the field. An electronic literature search was conducted in Pubmed up to 31st of December 2019.Expert opinion: There is compelling evidence for the role of duodenal inflammation and the eosinophil-mast cell axis in the pathogenesis of dyspeptic symptoms. Traditional prokinetic drugs and neuromodulators target gastric dysmotility and visceral hypersensitivity but are hampered by limited efficacy and side effects. Independent of acid suppression, the anti-inflammatory action of proton pump inhibitors, which remain the first-line therapy in FD, may also explain their therapeutic effect. Other existing and newly established anti-inflammatory drugs should be investigated while trials including probiotics and selective antibiotics should examine the host microbiome and immune activation. Targeted treatments for potential causes of duodenal pathology, such as impaired permeability and dysbiosis, are likely to emerge in the future.

Novel concepts in the pathophysiology and treatment of functional dyspepsia

Emerging data increasingly point towards the duodenum as a key region underlying the pathophysiology of functional dyspepsia (FD), one of the most prevalent functional GI disorders. The duodenum plays a major role in the control and coordination of gastroduodenal function. Impaired duodenal mucosal integrity and low-grade inflammation have been associated with altered neuronal signalling and systemic immune activation, and these alterations may ultimately lead to dyspeptic symptoms. Likely luminal candidates inducing the duodenal barrier defect include acid, bile, the microbiota and food antigens although no causal association with symptoms has been convincingly demonstrated. Recognition of duodenal pathology in FD will hopefully lead to the discovery of new biomarkers and therapeutic targets, allowing biologically targeted rather than symptom-based therapy. In this review, we summarise the recent advances in the diagnosis and treatment of FD with a focus on the duodenum.

Role of central vagal 5-HT3 receptors in gastrointestinal physiology and pathophysiology

Vagal neurocircuits are vitally important in the co-ordination and modulation of GI reflexes and homeostatic functions. 5-hydroxytryptamine (5-HT; serotonin) is critically important in the regulation of several of these autonomic gastrointestinal (GI) functions including motility, secretion and visceral sensitivity. While several 5-HT receptors are involved in these physiological responses, the ligand-gated 5-HT3 receptor appears intimately involved in gut-brain signaling, particularly via the afferent (sensory) vagus nerve. 5-HT is released from enterochromaffin cells in response to mechanical or chemical stimulation of the GI tract which leads to activation of 5-HT3 receptors on the terminals of vagal afferents. 5-HT3 receptors are also present on the soma of vagal afferent neurons, including GI vagal afferent neurons, where they can be activated by circulating 5-HT. The central terminals of vagal afferents also exhibit 5-HT3 receptors that function to increase glutamatergic synaptic transmission to second order neurons of the nucleus tractus solitarius within the brainstem. While activation of central brainstem 5-HT3 receptors modulates visceral functions, it is still unclear whether central vagal neurons, i.e., nucleus of the tractus solitarius (NTS) and dorsal motor nucleus of the vagus (DMV) neurons themselves also display functional 5-HT3 receptors. Thus, activation of 5-HT3 receptors may modulate the excitability and activity of gastrointestinal vagal afferents at multiple sites and may be involved in several physiological and pathophysiological conditions, including distention- and chemical-evoked vagal reflexes, nausea, and vomiting, as well as visceral hypersensitivity.

Inhibitory effect of the selective serotonin 5-HT₃ receptor antagonist ramosetron on duodenal acidification-induced gastric hypersensitivity in rats

Irritable bowel syndrome (IBS) and functional dyspepsia (FD) are both functional gastrointestinal disorders and frequently co-occur in patients. While one cause of FD appears to be gastric hypersensitivity, whether the hypersensitivity is affected by IBS treatments remains unclear, given the lack of appropriate animal models for testing. Here, we established an experimental model of duodenal acidification-induced gastric hypersensitivity in conscious rats. The model involved duodenal acidification induced by the infusion of hydrochloric acid into the proximal duodenum, with the nociceptive response being determined as the change in mean arterial pressure (MAP) during gastric distension via an indwelling latex balloon. Using our model we evaluated the effects of duodenal acidification, increased distension pressure, and orally administered therapeutic agents for IBS with diarrhea (IBS-D). Duodenal acidification enhanced the pressor response during gastric distension, and pretreatment with the opioid κ-receptor agonist fedotozine (10mg/kg, intra-arterial) inhibited the pressor response. Pressure levels of 15-60 mm Hg increased MAP in response to gastric distension. The serotonin 5-HT3 receptor antagonist ramosetron (30 μg/kg) inhibited MAP increase induced by duodenal acidification, with no other IBS-D therapeutic agents showing any effect. In contrast, the serotonin 5-HT3 receptor agonist m-chlorophenylbiguanide (1mg/kg) significantly enhanced the pressor response during gastric distension. These findings indicate that the serotonin 5-HT3 receptor plays a key role in duodenal acidification-induced gastric hypersensitivity in rats, suggesting that ramosetron may reduce FD symptoms by ameliorating sensitized gastric perception.

Safety and efficacy of cyproheptadine for treating dyspeptic symptoms in children

OBJECTIVE

To present our experience using cyproheptadine, a potent serotonin antagonist used to stimulate appetite, to treat dyspeptic symptoms in children.

STUDY DESIGN

This was a retrospective open-label study conducted to evaluate the safety and efficacy of cyproheptadine in children with refractory upper gastrointestinal symptoms (eg, nausea, early satiety, vomiting, retching after fundoplication, abdominal pain). Response was graded as resolution if symptoms resolved and medication was discontinued, as significant improvement if symptoms resolved with no further interventions, and as failure with any other outcome.

RESULTS

A total of 80 children (65% females) aged <12 years (mean age, 10 years) were included. Response to therapy was reported in 55% of patients. Multivariate analysis revealed better response in children and females (P = .04 and .03, respectively). No associations were found between response to therapy response and gastric emptying, antroduodenal manometry, functional dyspepsia, vomiting, and use of cyproheptadine as first therapy. Early vomiting (occurring within 1 hour after starting a meal) responded better than late vomiting (P = .03), and patients with retching after undergoing Nissen fundoplication had an 86% response rate. Twenty-four patients (30%) complained of side effects, all mild, including somnolence (16%), irritability and behavioral changes (6%), increased appetite and weight gain (5%), and abdominal pain (2.5%), but only 2 of these patients discontinued therapy. Multivariate analysis demonstrated an association between side effects and lack of response to therapy (P = .04), but no associations with age and sex.

CONCLUSION

Cyproheptadine is safe and effective for treating dyspeptic symptoms in children, particularly in young children and those with early vomiting and retching after fundoplication.

Food and symptom generation in functional gastrointestinal disorders: physiological aspects

The response of the gastrointestinal tract (GIT) to ingestion of food is a complex and closely controlled process, which allows optimization of propulsion, digestion, absorption of nutrients, and removal of indigestible remnants. This review summarizes current knowledge on the mechanisms that control the response of the GIT to food intake. During the cephalic phase, triggered by cortical food-related influences, the GIT prepares for receiving nutrients. The gastric phase is dominated by the mechanical effect of the meal volume. Accumulation of food in the stomach activates tension-sensitive mechanoreceptors, which in turn stimulate gastric accommodation and gastric acid secretion through the intrinsic and vago-vagal reflex pathways. After meal ingestion, the tightly controlled process of gastric emptying starts, with arrival of nutrients in the duodenum triggering negative feedback on emptying and stimulating secretion of digestive enzymes through the neural (mainly vago-vagal reflex, but also intrinsic) and endocrine (release of peptides from entero-endocrine cells) pathways. Several types of specialized receptors detect the presence of all main categories of nutrients. In addition, the gastrointestinal mucosa expresses receptors of the T1R and T2R families (taste receptors) and several members of the transient receptor potential channel family, all of which are putatively involved in the detection of specific tastants in the lumen. Activation of nutrient and taste sensors also activates the extrinsic and intrinsic neural, as well as entero-endocrine, pathways. During passage through the small bowel, nutrients are progressively extracted, and electrolyte-rich liquid intestinal content with non-digestible residue is delivered to the colon. The colon provides absorption of the water and electrolytes, storage of non-digestible remnants of food, aboral propulsion of contents, and finally evacuation through defecation.

Role of duodenal mucosal nerve endings in the acid-induced duodenogastric sensorimotor reflex: effect of benzocaine in healthy humans

BACKGROUND

Duodenal acid exposure induces a duodenogastric reflex resulting in gastric relaxation, inhibition of antral motility, and sensitization of the proximal stomach to distension. Duodenal hypersensitivity to acid has been identified as a potential pathogenic mechanism in functional dyspepsia. The nature and localization of the duodenal acid-sensitive receptors are still elusive. We hypothesize that acid directly activates superficial afferent nerve endings in the duodenal mucosa, triggering the duodenogastric reflex.

METHODS

In a double-blind, randomized, crossover study in 13 healthy volunteers, benzocaine, a local anesthetic, vs saline was perfused in the duodenum 15 min before duodenal acid perfusion. Gastric responses were monitored by a barostat. Stepwise isobaric gastric distensions were performed before and during acid perfusion. Symptoms were evaluated by visual analogue scales for six dyspeptic symptoms and an overall perception score.

KEY RESULTS

Benzocaine perfusion caused a relaxation of the stomach prior to duodenal acidification, indicating the existence of an excitatory duodenogastric tone. Pretreatment of the duodenum with benzocaine reduced the acid-induced gastric relaxation by 50% and abolished the inhibition of phasic motility of the proximal stomach. Finally, sensitization to distension was more pronounced in the benzocaine condition because of higher proximal gastric volumes.

CONCLUSIONS & INFERENCES

These findings support a model in which different neuronal subpopulations are responsible for the motor and sensory limb of the acid-sensitive duodenogastric reflex, making benzocaine an unsuitable drug to treat duodenal hypersensitivity to acid. These data provide more insight in the contribution of duodenal neuronal input to gastric physiology in the fasting state.