Modulation of gastric motor activity by a centrally acting stimulus, circular vection, in humans

An assessment of the effects of neurokinin1 receptor antagonism against nausea and vomiting: Relative efficacy, sites of action and lessons for future drug development

A broad-spectrum anti-vomiting effect of neurokinin1 receptor antagonists (NK1 RA), shown in pre-clinical animal studies, has been supported by a more limited range of clinical studies in different indications. However, this review suggests that compared with vomiting, the self-reported sensation of nausea is less affected or possibly unaffected (depending on the stimulus) by NK1 receptor antagonism, a common finding for anti-emetics. The stimulus-independent effects of NK1 RAs against vomiting are explicable by actions within the central pattern generator (ventral brainstem) and the nucleus tractus solitarius (NTS; dorsal brainstem), with additional effects on vagal afferent activity for certain stimuli (e.g., highly emetogenic chemotherapy). The central pattern generator and NTS neurones are multifunctional so the notable lack of obvious effects of NK1 RAs on other reflexes mediated by the same neurones suggests that their anti-vomiting action is dependent on the activation state of the pathway leading to vomiting. Nausea requires activation of cerebral pathways by projection of information from the NTS. Although NK1 receptors are present in cerebral nuclei implicated in nausea, and imaging studies show very high receptor occupancy at clinically used doses, the variable or limited ability of NK1 RAs to inhibit nausea emphasizes: (i) our inadequate understanding of the mechanisms of nausea; and (ii) that classification of a drug as an anti-emetic may give a false impression of efficacy against nausea vs. vomiting. We discuss the potential mechanisms for the differential efficacy of NK1 RA and the implications for future development of drugs that can effectively treat nausea, an area of unmet clinical need.

Synergistic augmentation of rhythmic myogenic contractions of human stomach by arginine vasopressin and adrenaline: Implications for the induction of nausea

BACKGROUND AND PURPOSE

Nausea is associated with the hormonal secretion of vasopressin and adrenaline, although their actions in inducing nausea is poorly understood. Here, we have investigated their actions on human stomach muscle.

EXPERIMENTAL APPROACH

Muscle strips were suspended in tissue baths and neuronal-/non-neuronally-mediated contractions were measured. Custom software analysed eight motility parameters defining spontaneous phasic non-neuronally mediated contractions. Receptor distributions were assessed by qPCR and immunofluorescence.

KEY RESULTS

V_1A receptors and α₁ -adrenoceptors were located on muscle as well as interstitial cells of Cajal (ICCs). Myogenic contractions of human proximal and distal stomach (respectively, 2.6 ± 0.1 and 2.7 ± 0.0 per minute; n = 44) were larger in the distal area (1.1 ± 0.1 and 5.0 ± 0.1 mN), developing relatively slowly (proximal) or rapidly (distal). Vasopressin caused tonic (proximal) or short-lived (distal) increases in muscle tone and increased myogenic contraction amplitude, frequency and rate (acting at V_1A receptors; thresholds 10^-11 -10^-10  M); by contrast, cholinergically mediated contractions were unaffected. Oxytocin acted similarly to vasopressin but less potently, at OT receptors). Adrenaline increased (10^-10 -10^-5  M; α₁ -adrenoceptors) and decreased (≥10^-6  M; β-adrenoceptors) muscle tone and enhanced/reduced myogenic contractions. Cholinergically mediated contractions were reduced (α₂ -adrenoceptors). Combined, vasopressin (10^-9  M) and adrenaline (10^-8  M) increased muscle tone and phasic myogenic activity in a synergistic manner.

CONCLUSIONS AND IMPLICATIONS

Vasopressin and adrenaline increased human gastric tone and myogenic contraction amplitude, rate of contraction and frequency. In combination, their actions were further increased in a synergistic manner. Such activity may promote nausea.

The gastric conduction system in health and disease: a translational review

Gastric peristalsis is critically dependent on an underlying electrical conduction system. Recent years have witnessed substantial progress in clarifying the operations of this system, including its pacemaking units, its cellular architecture, and slow-wave propagation patterns. Advanced techniques have been developed for assessing its functions at high spatiotemporal resolutions. This review synthesizes and evaluates this progress, with a focus on human and translational physiology. A current conception of the initiation and conduction of slow-wave activity in the human stomach is provided first, followed by a detailed discussion of its organization at the cellular and tissue level. Particular emphasis is then given to how gastric electrical disorders may contribute to disease states. Gastric dysfunction continues to grow in their prevalence and impact, and while gastric dysrhythmia is established as a clear and pervasive feature in several major gastric disorders, its role in explaining pathophysiology and informing therapy is still emerging. New insights from high-resolution gastric mapping are evaluated, together with historical data from electrogastrography, and the physiological relevance of emerging biomarkers from body surface mapping such as retrograde propagating slow waves. Knowledge gaps requiring further physiological research are highlighted.

The stomach-brain axis

The stomach has distinct functions in relation to the ingestion and handling of solids and liquids. These functions include storage of the food before it is gradually emptied into the duodenum, mechanical crushing of larger food particles to increase the surface area, secretion of an acidic enzyme rich gastric juice and mixing the ingested food with the gastric juice. In addition, the stomach 'senses' the composition of the gastric content and this information is passed via the vagal nerve to the lateral hypothalamus and the limbic system, most likely as palatability signals that influence eating behaviour. Other sensory qualities related to the stimulation of gastric tension receptors are satiety and fullness. Receptors that respond to macronutrient content or gastric wall tension influence appetite and meal related hormone responses. The ingestion of food - in contrast to an infusion of nutrients into the stomach - has distinct effects on the activation of specific brain regions. Brain areas such as thalamus, amygdala, putamen and praecuneus are activated by the ingestion of food. Gastric nutrient infusion evokes greater activation in the hippocampus and anterior cingulate. The brain integrates these interrelated neural and hormonal signals arising from the stomach as well as visual, olfactory and anticipatory stimuli that ultimately influence eating and other behavioural patterns. Furthermore, there is now good evidence from experimental studies that gastric afferents influence mood, and animal studies point towards the possibility that gastric dysfunction may be a risk factor for mood disorders such as anxiety and depression. The stomach is also not only colonised by Helicobacter pylori but a large array of bacteria. While there is sufficient evidence to suggest that H. pylori may alter caloric intake and mood, the role of other gastric microbiome for the brain function is unknown. To address this appropriate targeted gastric microbiome studies would be required instead of widely utilised opportunistic stool microbiome studies. In summary, it is now well established that there are important links between the brain and the stomach that have significant effects on gastric function. However, the stomach also influences the brain. Disturbances in the crosstalk between the stomach and the brain may manifest as functional GI disorders while disturbances in the stomach-brain communication may also result in an altered regulation of satiety and as a consequence may affect eating behaviour and mood. These observations may enable the identification of novel therapies targeted at the gastroduodenum that positively alter brain function and treat or prevent conditions such as obesity or functional gastrointestinal disorders.

Hunger Enhances Vertical Vection

Hunger was found to facilitate visually induced illusory upward and downward self-motions (vertical vection), but not illusory self-motion in depth (vection in depth). We propose that the origin of this hunger effect lies in the possibility that vertical self-motions (both real and illusory) are more likely to induce changes in visceral state.

Treatment approaches of gastrointestinal dysfunction in Parkinson's disease, therapeutical options and future perspectives

Gastrointestinal (GI) dysfunction is a common but underestimated feature in Parkinson's disease (PD). Out of the multimodal spectrum of treatment options, there currently are only a few pharmacological treatments available to improve gastrointestinal motility and symptoms. Because enteric nervous function is mainly regulated by transmitters different from those involved in the brain, dopamine replacement is not a treatment option in PD patients. This article focuses on the known regulative mechanism of GI function and presents known and upcoming treatment options for GI dysfunction in PD.

Acute tryptophan depletion increases experimental nausea but also induces hunger in healthy female subjects

BACKGROUND

Acute tryptophan depletion (ATD) is an experimental model to reduce central serotonin levels.

METHODS

Thirty-eight healthy female subjects were randomly assigned to two groups (ATD and control) in a randomized, double-blinded parallel-group design. Following a standardized and balanced amino acid diet (including 1.21 g tryptophan) on the first day, they received either a protein drink without tryptophan (but substituted by other amino acids) (ATD condition) or the balanced protein drink with tryptophan (control condition) 24 h later. Four hours after its consumption, they were exposed to a standard rotation procedure. Symptom ratings (SR), ratings of hunger and mood scores were taken prior to rotation, at each break, and 15 and 30 min thereafter, together with saliva cortisol samples.

KEY RESULTS

Five subjects could not tolerate the entire rotation procedure and were excluded from analysis. For the remaining n = 33, SR and hunger ratings were higher during ATD than during control conditions, but mood was unaffected. Cortisol levels rose significantly with rotation but were unaffected by ATD. High baseline cortisol levels were associated with lower SR during rotation. The protective effects of morning cortisol were pronounced during the menstrual and follicular phase of the cycle and not present during ovulation and the luteal phase.

CONCLUSIONS & INFERENCES

Acute tryptophan depletion is associated with increased symptoms of nausea in healthy female subjects when exposed to body rotation. Acute tryptophan depletion also increases hunger rating. These opposite effects may indicate independent actions of the serotonin on central and peripheral functions.

Opportunities for the replacement of animals in the study of nausea and vomiting

Nausea and vomiting are among the most common symptoms encountered in medicine as either symptoms of disease or side effects of treatments. Developing novel anti-emetics and identifying emetic liability in novel chemical entities rely on models that can recreate the complexity of these multi-system reflexes. Animal models (especially the ferret and dog) are the current gold standard; however, the selection of appropriate models is still a matter of debate, especially when studying the subjective human sensation of nausea. Furthermore, these studies are associated with animal suffering. Here, following a recent workshop held to review the utility of animal models in nausea and vomiting research, we discuss the limitations of some of the current models in the context of basic research, anti-emetic development and emetic liability detection. We provide suggestions for how these limitations may be overcome using non-animal alternatives, including greater use of human volunteers, in silico and in vitro techniques and lower organisms.

Gastroparesis secondary to a demyelinating disease: a case series

Background

Gastroparesis has a number of etiologies. The main ones are secondary to a complication from diabetes mellitus, related to post vagotomy or post gastric surgical resections, or idiopathic when the etiology is unclear. Gastroparesis secondary to a demyelinating disease of the brain is unusual.

Case presentation

A 22-year-old woman was referred for acute onset of intractable nausea and vomiting. She also had cerebellar deficits, dysphagia and paresthesias. Magnetic resonance imaging (MRI) of the brain revealed an isolated area of demyelination in the medullary region. Another 24-year-old woman had a similar presentation with right hemiplegia and MRI of the brain revealed a distal medullary region. Both these patients had an abnormal gastric emptying test. Gastroparesis and neurological deficits improved with intravenous corticosteroids. While the former patient has had no further recurrences, the latter patient developed multiple sclerosis within three months of presentation.

Conclusion

A demyelinating disease is a rare cause gastropareis, but should be suspected when symptoms of gastroparesis are associated with neurological deficits. MRI might help in the diagnosis and intravenous coriticosteroids can address the underlying disease process and improve gastric emptying, especially when used early during the course of the disease.

Functional cortical imaging of nausea and vomiting: a possible approach

From a naive point of view, a study on functional cortical imaging of nausea and vomiting should deliver insight into the basic cortical mechanisms, connections, and time courses, of nausea and vomiting as perceived and processed in the human brain of affected subjects. Until now the brain's response to nausea and vomiting are only inadequately characterized, because studies have been focused mostly on understanding the different mechanisms leading to nausea rather than to cortical activations during nausea or vomiting, respectively. Consequently, the imaging of the "personal experience" of nausea and vomiting can currently be regarded as terra incognita. Nonetheless, the wide variety of the results published on diverse aspects of the topic can be helpful in providing guidelines for a paradigm to further investigations. This paper presents a brief outline for a study on the functional imaging of nauseated humans by means of functional magnetic resonance imaging (fMRI).

Relationships between intragastric food maldistribution, disturbances of antral contractility, and symptoms in functional dyspepsia

We investigated the relationships between intragastric food maldistribution and antral dysmotility in functional dyspepsia, and whether these abnormalities relate to meal-induced symptoms. Intragastric distribution of food throughout gastric emptying was determined in patients (n = 24) and controls (n = 38) after a liquid nutrient meal labeled with (99m)technetium phytate. Antral contractility was also periodically assessed by dynamic scintigraphy and postprandial symptoms were monitored with visual analog scales. Residence of food in the proximal stomach was decreased in 8 (33%) and antral contractility was increased in 9 (37.5%) and decreased in 2 (8%) patients. Proximal and distal stomach motor abnormalities were neither significantly correlated nor associated. Increased antral contractility was significantly correlated (Rs = 0.54; P < .01) with postprandial nausea. We conclude that diminished residence of food in the proximal stomach and disturbed antral contractility occur independently in different subsets of functional dyspepsia patients. Increased antral contractility seems to play a role in postprandial nausea in functional dyspepsia.