Gastric distension-induced pyloric relaxation: central nervous system regulation and effects of acute hyperglycaemia in the rat

Interoceptive processing in the nucleus of the solitary tract

The interoceptive nervous system continuously monitors the status of visceral organs to synthesize internal perceptions and regulate behavioral and physiological responses. The nucleus of the solitary tract (NTS) in the brainstem serves as a central interoceptive hub and the initial site where sensory information from internal organs is processed in the brain. Here we review the neurobiological underpinnings of interoceptive processing in the NTS, focusing on recent progress enabled by modern genetic and optical tools for neural circuit dissection and neuronal recordings. Sensory information from internal organs is organized into a topographic map within the NTS, computed locally, modulated by descending inputs from higher brain regions, and distributed to downstream targets via projection neurons to control behavior and physiology. We present a sensory processing perspective on interoceptive coding within this brain structure.

Current Concepts in Gastroparesis and Gastric Neuromuscular Disorders-Pathophysiology, Diagnosis, and Management

Upper gastrointestinal concerns including gastroparesis-like symptoms affect a large portion of the population, and determining the culprit condition can be difficult due to largely shared symptoms, clinical course, pathophysiology, and treatment pathways. The understanding of gastric neuromuscular disorders (GNDs) is emerging as a heterogeneous group encompassing conditions from gastroparesis to functional dyspepsia with chronic nausea, early satiety, bloating, or abdominal pain, irrespective of gastric emptying. This article aims to review the current concepts in gastroparesis and GNDs including pathophysiology, diagnosis, and management. While some established standards in their diagnosis and management exist, a number of novel diagnostics are becoming available. Durable therapeutic options are notably limited for such common conditions with chronic and debilitating symptoms, and neuromodulators may play a key role in symptom control, which has been previously under-recognized and underutilized. Advances in both pharmacologic treatment targets as well as noninvasive and invasive interventions and devices show promise in improving the experience of patients with gastroparesis-like symptoms. At this time, treatment of GNDs requires comprehensive multidisciplinary care from providers to achieve successful treatment outcomes.

CNS sites controlling the gastric pyloric sphincter: Neuroanatomical and functional study in the rat

The pyloric sphincter receives parasympathetic vagal innervation from the dorsal motor nucleus of the vagus (DMV). However, little is known about its higher-order neurons and the nuclei that engage the DMV neurons controlling the pylorus. The purpose of the present study was twofold. First, to identify neuroanatomical connections between higher-order neurons and the DMV. This was carried out by using the transneuronal pseudorabies virus PRV-152 injected into rat pylorus torus and examining the brains of these animals for PRV labeling. Second, to identify the specific sites within the DMV that functionally control the motility and tone of the pyloric sphincter. For these studies, experiments were performed to assess the effect of DMV stimulation on pylorus activity in urethane-anesthetized male rats. A strain gauge force transducer was sutured onto the pyloric tonus to monitor tone and motility. L-glutamate (500 pmol/30 nL) was microinjected unilaterally into the rostral and caudal areas of the DMV. Data from the first study indicated that neurons labeled with PRV occurred in the DMV, hindbrain raphe nuclei, midbrain Edinger-Westphal nucleus, ventral tegmental area, lateral habenula, and arcuate nucleus. Data from the second study indicated that microinjected L-glutamate into the rostral DMV results in contraction of the pylorus blocked by intravenously administered atropine and ipsilateral vagotomy. L-glutamate injected into the caudal DMV relaxed the pylorus. This response was abolished by ipsilateral vagotomy but not by intravenously administered atropine or L-NG-nitroarginine methyl ester (L-NAME). These findings identify the anatomical and functional brain neurocircuitry involved in controlling the pyloric sphincter. Our results also show that site-specific stimulation of the DMV can differentially influence the activity of the pyloric sphincter by separate vagal nerve pathways.

Altered Vagal Signaling and Its Pathophysiological Roles in Functional Dyspepsia

The vagus nerve is crucial in the bidirectional communication between the gut and the brain. It is involved in the modulation of a variety of gut and brain functions. Human studies indicate that the descending vagal signaling from the brain is impaired in functional dyspepsia. Growing evidence indicate that the vagal signaling from gut to brain may also be altered, due to the alteration of a variety of gut signals identified in this disorder. The pathophysiological roles of vagal signaling in functional dyspepsia is still largely unknown, although some studies suggested it may contribute to reduced food intake and gastric motility, increased psychological disorders and pain sensation, nausea and vomiting. Understanding the alteration in vagal signaling and its pathophysiological roles in functional dyspepsia may provide information for new potential therapeutic treatments of this disorder. In this review, we summarize and speculate possible alterations in vagal gut-to-brain and brain-to-gut signaling and the potential pathophysiological roles in functional dyspepsia.

Avian Neuropeptide Y: Beyond Feed Intake Regulation

Neuropeptide Y (NPY) is one of the most abundant and ubiquitously expressed neuropeptides in both the central and peripheral nervous systems, and its regulatory effects on feed intake and appetite- have been extensively studied in a wide variety of animals, including mammalian and non-mammalian species. Indeed, NPY has been shown to be involved in the regulation of feed intake and energy homeostasis by exerting stimulatory effects on appetite and feeding behavior in several species including chickens, rabbits, rats and mouse. More recent studies have shown that this neuropeptide and its receptors are expressed in various peripheral tissues, including the thyroid, heart, spleen, adrenal glands, white adipose tissue, muscle and bone. Although well researched centrally, studies investigating the distribution and function of peripherally expressed NPY in avian (non-mammalian vertebrates) species are very limited. Thus, peripherally expressed NPY merits more consideration and further in-depth exploration to fully elucidate its functions, especially in non-mammalian species. The aim of the current review is to provide an integrated synopsis of both centrally and peripherally expressed NPY, with a special focus on the distribution and function of the latter.

Mechanism of Soy Isoflavone Daidzein-Induced Female-Specific Anorectic Effect

Epidemiological studies suggest that regular intake of soy isoflavone exerts a preventive effect on postmenopausal obesity and other forms of dysmetabolism. Estrogens inhibit eating behavior. Soy isoflavones may act as estrogen agonist in estrogen-depleted conditions, whereas they may either act as an estrogen antagonist or be ineffective in estrogen-repleted conditions. We investigated the effects of dietary soy isoflavone on food intake under various estrogen conditions using male, ovariectomized (OVX), and non-OVX female rats, and compared the effects with those of estradiol. We found that soy isoflavones reduced food intake in females specifically, regardless of whether ovariectomy had been performed, whereas subcutaneous implantation of estradiol pellet did not reduce food intake in intact female rats, but did so in OVX female and male rats. Contrary to this hypothesis, the reduction in food intake may not be caused by the estrogenic properties of soy isoflavones. It is of great interest to understand the mechanisms underlying the anorectic effects of soy isoflavones. In this non-systematic review, we summarize our recent studies that have investigated the bioactive substances of anorectic action, pharmacokinetic properties of soy isoflavones, and the modification of central and peripheral signals regulating appetite by soy isoflavones, and selected studies that were identified via database mining.

Neural signalling of gut mechanosensation in ingestive and digestive processes

Eating and drinking generate sequential mechanosensory signals along the digestive tract. These signals are communicated to the brain for the timely initiation and regulation of diverse ingestive and digestive processes - ranging from appetite control and tactile perception to gut motility, digestive fluid secretion and defecation - that are vital for the proper intake, breakdown and absorption of nutrients and water. Gut mechanosensation has been investigated for over a century as a common pillar of energy, fluid and gastrointestinal homeostasis, and recent discoveries of specific mechanoreceptors, contributing ion channels and the well-defined circuits underlying gut mechanosensation signalling and function have further expanded our understanding of ingestive and digestive processes at the molecular and cellular levels. In this Review, we discuss our current understanding of the generation of mechanosensory signals from the digestive periphery, the neural afferent pathways that relay these signals to the brain and the neural circuit mechanisms that control ingestive and digestive processes, focusing on the four major digestive tract parts: the oral and pharyngeal cavities, oesophagus, stomach and intestines. We also discuss the clinical implications of gut mechanosensation in ingestive and digestive disorders.

Acute effects of vagus nerve stimulation parameters on gastric motility assessed with magnetic resonance imaging

BACKGROUND

Vagus nerve stimulation (VNS) is an emerging bioelectronic therapy for regulating food intake and controlling gastric motility. However, the effects of different VNS parameters and polarity on postprandial gastric motility remain incompletely characterized.

METHODS

In anesthetized rats (N = 3), we applied monophasic electrical stimuli to the left cervical vagus and recorded compound nerve action potential (CNAP) as a measure of nerve response. We evaluated to what extent afferent or efferent pathway could be selectively activated by monophasic VNS. In a different group of rats (N = 13), we fed each rat a gadolinium-labeled meal and scanned the rat stomach with oral contrast-enhanced magnetic resonance imaging (MRI) while the rat was anesthetized. We evaluated the antral and pyloric motility as a function of pulse amplitude (0.13, 0.25, 0.5, 1 mA), width (0.13, 0.25, 0.5 ms), frequency (5, 10 Hz), and polarity of VNS.

KEY RESULTS

Monophasic VNS activated efferent and afferent pathways with about 67% and 82% selectivity, respectively. Primarily afferent VNS increased antral motility across a wide range of parameters. Primarily efferent VNS induced a significant decrease in antral motility as the stimulus intensity increased (R = -.93, P < .05 for 5 Hz, R = -.85, P < .05 for 10 Hz). The VNS with either polarity tended to promote pyloric motility to a greater extent given increasing stimulus intensity.

CONCLUSIONS AND INFERENCES

Monophasic VNS biased toward the afferent pathway is potentially more effective for facilitating occlusive contractions than that biased toward the efferent pathway.

Postpyloric Balloon Occlusion to Increase Technical Success during Pediatric Percutaneous Gastrostomy/Gastrojejunostomy Tube Placement

Gastric distension through insufflation is a key step in creating a safe percutaneous window during gastrostomy/gastrojejunostomy (G/GJ) placement; however, poor or incomplete gastric distention can occur, despite the use of glucagon, and lead to rapid egress of air from the stomach into the duodenum. This report describes the adjunctive technique using postpyloric balloon occlusion in 29 patients to maximize gastric insufflation during G/GJ tube placement after failure of conventional methods. Balloon occlusion was successful in salvaging 23 of 29 (79.3%) of G/GJ tube placements without any complications.

Gastroparesis: a turning point in understanding and treatment

Gastroparesis is defined by delayed gastric emptying (GE) and symptoms of nausea, vomiting, bloating, postprandial fullness, early satiety and abdominal pain. Most common aetiologies include diabetes, postsurgical and postinfectious, but in many cases it is idiopathic. Clinical presentation and natural history vary by the aetiology. There is significant morbidity and healthcare utilisation associated with gastroparesis. Mechanistic studies from diabetic animal models of delayed GE as well as human full-thickness biopsies have significantly advanced our understanding of this disorder. An innate immune dysregulation and injury to the interstitial cells of Cajal and other components of the enteric nervous system through paracrine and oxidative stress mediators is likely central to the pathogenesis of gastroparesis. Scintigraphy and 13C breath testing provide the most validated assessment of GE. The stagnant gastroparesis therapeutic landscape is likely to soon see significant changes. Relatively newer treatment strategies include antiemetics (aprepitant), prokinetics (prucalopride, relamorelin) and fundic relaxants (acotiamide, buspirone). Endoscopic pyloromyotomy appears promising over the short term, especially for symptoms of nausea and vomiting. Further controlled trials and identification of the appropriate subgroup with pyloric dysfunction and assessment of long-term outcomes are essential. This review highlights the clinical presentation, diagnosis, mechanisms and treatment advancements for gastroparesis.

Alcohol Drinking and Blood Alcohol Concentration Revisited

BACKGROUND

It is widely assumed that the amount of alcohol in the blood reflects the amount of alcohol consumed. However, several factors in addition to amount of alcohol consumed can influence blood alcohol concentration (BAC). This study examines the effect of alcohol dose, concentration, and volume on BAC in rats with a high-alcohol-drinking (HAD) phenotype.

METHODS

Study 1 examined the relationship between the amount of alcohol consumed and BAC. Alcohol-naïve, male, HAD rats (N = 7) were given access to alcohol for 2 h/d for 9 consecutive days with food and water ad libitum. Alcohol intake and BAC were measured at 30, 60, and 90 minutes after onset of access. Study 2 examined the effects of altering alcohol dose, concentration, and volume on BAC (as measured by area under the curve). Alcohol-naïve, male, HAD rats (N = 39) were infused, via an intragastric cannulus, with 1.16, 2.44, or 3.38 g alcohol/kg body weight (BW), produced by varying alcohol volume while holding concentration constant or by holding volume constant while varying concentration. Other rats were infused with 10, 15, or 20% v/v alcohol solutions while holding dose constant.

RESULTS

BAC was more strongly correlated with the ratio of alcohol intake (g/kg BW) to total fluid intake (mls) (R = 0.85 to 0.97, p < 0.05 to p < 0.001) than it was with the amount of alcohol consumed (g/kg BW) (R = 0.70 to 0.81, p < 0.05). No effect of alcohol dose was seen during the first hour following the onset of an alcohol infusion regardless of whether dose was achieved by altering alcohol volume or concentration. After 1 hour, higher alcohol doses were predictive of greater BACs.

CONCLUSIONS

The fact that a 3-fold difference in alcohol dose did not result in significant differences in BACs during the first 30 minutes after ingestion of alcohol has potentially important implications for interpretation of studies that measure alcohol-sensitive end points during this time.

What the Gut Can Teach Us About Migraine

During gestation, cells of the brain and gut develop almost simultaneously into the central nervous system (CNS) and enteric nervous system (ENS), respectively. They remain connected via the vagal nerve lifelong. While it is well known that the brain sends signal to the gut, communication is in fact bidirectional. Just as the brain can modulate gut functioning, the gut, and likely what we ingest, can in fact influence our brain functioning. We will first review both gastrointestinal (GI) function and migraine pathophysiology and then discuss evidence linking the migraine brain to various GI disorders. Lastly, we discuss the effects of gut microbiota on brain functioning and speculate how the gut and particularly diet may affect migraine.

Pyloroplasty for Refractory Gastroparesis

Gastroparesis is a chronic gastric motility disorder in which the pathophysiology mimics a post-vagotomy state. Pyloroplasty is beginning to emerge as a successful drainage procedure for refractory gastroparesis. Here we report our experience using pyloroplasty in the surgical management of diabetic and nondiabetic gastroparesis. A retrospective study was performed of 46 patients undergoing pyloroplasty for refractory gastroparesis from January 2010 through December 2013. Gastric emptying scintigraphy and the Gastroparesis Cardinal Symptom Index were assessed pre-and postoperatively. Laparoscopic pyloroplasty was performed in 42 patients, open pyloroplasty in three, and one patient was converted from laparoscopic to open pyloroplasty. Studies were repeated during the six to 12 month postoperative interval. The postoperative gastric emptying scintigraphy improved in 90 per cent of patients and normalized in 60 per cent. Postoperative T½ was significantly reduced ( P = 0.001) as was four-hour retention ( P < 0.001). The Gastroparesis Cardinal Symptom Index showed statistically significant reduction in symptom severity for all nine categories ( P < 0.0005) as well as total symptom score ( P < 0.005). No patients developed dumping syndrome. Pyloroplasty is a highly effective therapy for refractory gastroparesis, offering significant reduction in symptom severity, improvement in quality of life, and acceleration of gastric emptying.

Improvements In AF Ablation Outcome Will Be Based More On Technological Advancement Versus Mechanistic Understanding

Atrial fibrillation (AF) is one of the most common cardiac arrhythmias. Catheter ablation has proven more effective than antiarrhythmic drugs in preventing clinical recurrence of AF, however long-term outcome remains unsatisfactory. Ablation strategies have evolved based on progress in mechanistic understanding, and technologies have advanced continuously. This article reviews current mechanistic concepts and technological advancements in AF treatment, and summarizes their impact on improvement of AF ablation outcome.

Recent advances in the pathophysiology and treatment of gastroparesis

Gastroparesis is a clinical disorder characterized by upper gastrointestinal symptoms related with delayed gastric emptying of solids and liquids in the absence of mechanical obstruction. Diabetes mellitus has been the most common cause of gastroparesis and idiopathic gastroparesis also accounts for a third of all chronic cases. The most important mechanisms of gastroparesis, as understood to date, are loss of expression of neuronal nitric oxide synthase and loss of the interstitial cells of Cajal. However, the pathogenesis of gastroparesis is poorly understood. There have been several studies on specific molecules related to the pathogenesis of gastroparesis. Additionally, the Gastroparesis Clinical Research Consortium of the National Institutes of Health has achieved several promising results regarding the pathophysiology of gastroparesis. As the progress in the pathophysiology of gastroparesis has been made, a promising new drug therapy has been found. The pathophysiology and drug therapy of gastroparesis are focused in this review. Until now, the real-world medication options for treatment of gastroparesis are limited. However, it is expected to be substantially improved as the pathophysiology of gastroparesis is elucidated.

Diabetic gastroparesis

BACKGROUND

Diabetic gastroparesis (DGP) is a gastric complication of diabetes mellitus that causes nausea, vomiting, early satiety, bloating and abdominal pain, in addition to significant morbidity.

SOURCES OF DATA

Original and review articles were reviewed through PubMed, including relevant guidelines from the European and American Neurogastroenterology Societies.

AREAS OF AGREEMENT

Diagnosis of DGP requires endoscopy and measurement of gastric emptying. Management requires prokinetic therapy, usually in addition to antinausea or other medications.

AREAS OF CONTROVERSY

The pathogenesis of DGP is poorly understood. Management strategies are highly variable. Growing points Prokinetic and neuromodulatory medications are in human clinical trials specifically for gastroparesis.

AREAS TIMELY FOR DEVELOPING RESEARCH

Further understanding of the molecular pathology leading to DGP is required to potentially arrest the development of this serious diabetic complication. Evaluation of novel agents for use in DGP is sorely needed.

Inhibition of gastric motility by hyperglycemia is mediated by nodose ganglia KATP channels

The inhibitory action of hyperglycemia is mediated by vagal afferent fibers innervating the stomach and duodenum. Our in vitro studies showed that a subset of nodose ganglia neurons is excited by rising ambient glucose, involving inactivation of ATP-sensitive K(+) (K(ATP)) channels and leading to membrane depolarization and neuronal firing. To investigate whether nodose ganglia K(ATP) channels mediate gastric relaxation induced by hyperglycemia, we performed in vivo gastric motility studies to examine the effects of K(ATP) channel activators and inactivators. Intravenous infusion of 20% dextrose induced gastric relaxation in a dose-dependent manner. This inhibitory effect of hyperglycemia was blocked by diazoxide, a K(ATP) channel activator. Conversely, tolbutamide, a K(ATP) channel inactivator, induced dose-dependent gastric relaxation, an effect similar to hyperglycemia. Vagotomy, perivagal capsaicin treatment, and hexamethonium each prevented the inhibitory action of tolbutamide. Similarly, N(G)-nitro-l-arginine methyl ester, an inhibitor of nitric oxide synthase, also blocked tolbutamide's inhibitory effect. To show that K(ATP) channel inactivation at the level of the nodose ganglia induces gastric relaxation, we performed electroporation of the nodose ganglia with small interfering RNA of Kir6.2 (a subunit of K(ATP)) and plasmid pEGFP-N1 carrying the green fluorescent protein gene. The gastric responses to hyperglycemia and tolbutamide were not observed in rats with Kir6.2 small interfering RNA-treated nodose ganglia. However, these rats responded to secretin, which acts via the vagal afferent pathway, independently of K(ATP) channels. These studies provide in vivo evidence that hyperglycemia induces gastric relaxation via the vagal afferent pathway. This action is mediated through inactivation of nodose ganglia K(ATP) channels.

Diabetic gastroparesis: what we have learned and had to unlearn in the past 5 years

Diabetic gastroparesis is a disorder that occurs in both type 1 and type 2 diabetes. It is associated with considerable morbidity among these patients and with the resultant economic burden on the health system. It is primarily a disease seen in middle-aged women, although the increased predisposition in women still remains unexplained. Patients often present with nausea, vomiting, bloating, early satiety and abdominal pain. The pathogenesis of this complex disorder is still not well understood but involves abnormalities in multiple interacting cell types including the extrinsic nervous system, enteric nervous system, interstitial cells of Cajal (ICCs), smooth muscles and immune cells. The primary diagnostic test remains gastric scintigraphy, although other modalities such as breath test, capsule, ultrasound, MRI and single photon emission CT imaging show promise as alternative diagnostic modalities. The mainstay of treatment for diabetic gastroparesis has been antiemetics, prokinetics, nutritional support and pain control. In recent years, gastric stimulation has been used in refractory cases with nausea and vomiting. As we better understand the pathophysiology, newer treatment modalities are emerging with the aim of correcting the underlying defect. In this review, what has been learned about diabetic gastroparesis in the past 5 years is highlighted. The epidemiology, pathogenesis, diagnosis and treatment of diabetic gastroparesis are reviewed, focusing on the areas that are still controversial and those that require more studies. There is also a focus on advances in our understanding of the cellular changes that underlie development of diabetic gastroparesis, highlighting new opportunities for targeted treatment.

Juvenile polyposis of the stomach--a novel cause of hypergastrinemia

BACKGROUND

A 38-year-old female presented with a 3-year history of postprandial abdominal pain, refractory nausea, vomiting and hematemesis. She appeared malnourished and her symptoms were refractory to previous treatment with acid-suppressive drugs, prokinetics and antiemetics. Her medical history was significant for a diagnosis of juvenile polyposis syndrome at the age of 14 resulting in a transverse colectomy, and a diagnosis of Crohn's disease in her residual colon at the age of 35 resulting in a total colectomy.

INVESTIGATIONS

Physical examination, blood analysis, esophagogastroduodenoscopy with biopsy, abdominal endoscopic ultrasound, abdominal CT scan, MRI, 24 h urine analysis, MIBG scintigraphy, ocreotide scintigraphy, fluorodeoxyglucose-PET scan and genetic testing for defined polyposis syndromes (SMAD4, BMPR1A).

DIAGNOSIS

Juvenile polyposis syndrome with outlet obstruction of the stomach and excessive hypergastrinemia.

MANAGEMENT

Continuous acid-suppressive therapy, prokinetic therapy and total parenteral nutrition. Repetitive endoscopic polypectomy (also known as debulking) was performed twice and was followed by gastrectomy with duodenoesophageal anastomosis.

Effect of anesthetics on gastric damage using two models of portal hypertension

AIM: To investigate the effect of sodium pentobarbitone (SP) or ketamine/xylazine (KX) anesthetics on acute gastric injury.

METHODS: Portal hypertension was induced by bile duct ligation (BDL) or portal vein stenosis (PVS). Ethanol (EtOH)-induced gastric damage was assessed using ex vivo gastric chamber experiments. Gastric blood flow (GBF) was also measured by laser doppler flowmetry.

RESULTS: EtOH-induced gastric damage was reduced in BDL rats under KX anesthesia in comparison to those under SP anesthesia. GBF dysfunction in fasted BDL rats was partially restored under KX anesthesia. In contrast, in fasted PVS rats, EtOH-induced gastric damage was increased under KX anesthesia while GBF was reduced.

CONCLUSION: The use of KX anesthesia in experimental procedures involving cirrhotic rats (but not those with pure portal hypertension) is preferable to SP anesthesia.

Central oxytocin is involved in restoring impaired gastric motility following chronic repeated stress in mice

Accumulation of continuous life stress (chronic stress) often causes gastric symptoms. The development of gastric symptoms may depend on how humans adapt to the stressful events in their daily lives. Although acute stress delays gastric emptying and alters upper gastrointestinal motility in rodents, the effects of chronic stress on gastric motility and its adaptation mechanism remains unclear. Central oxytocin has been shown to have antistress effects. We studied whether central oxytocin is involved in mediating the adaptation mechanism following chronic repeated stress. Mice were loaded with acute and chronic stress (repeated stress for five consecutive days), and solid gastric emptying and postprandial gastric motility were compared between acute and chronic repeated stress. Expression of oxytocin and CRF mRNA in the hypothalamus was studied following acute and chronic repeated stress. Delayed gastric emptying during acute stress (43.1 +/- 7.8%; n = 6, P < 0.05) was completely restored to normal levels (72.1 +/- 2.4%; n = 6) following chronic repeated stress. Impaired gastric motility induced by acute stress was also restored following chronic repeated stress. Intracerebroventricular injection of oxytocin (0.1 and 0.5 microg) restored the impaired gastric emptying and motility induced by acute stress. The restored gastric emptying and motility following chronic repeated stress were antagonized by intracerebroventricular injection of oxytocin antagonists. Oxytocin mRNA expression in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus was significantly increased following chronic repeated stress. In contrast, increased CRF mRNA expression in the SON and PVN in response to acute stress was significantly reduced following chronic repeated stress. Our study suggests the novel finding that the upregulation of central oxytocin expression is involved in mediating the adaptation mechanism following chronic repeated stress in mice.

Gastric relaxation induced by hyperglycemia is mediated by vagal afferent pathways in the rat

Hyperglycemia has a profound effect on gastric motility. However, little is known about the site and mechanism that sense alteration in blood glucose level. The identification of glucose-sensing neurons in the nodose ganglia led us to hypothesize that hyperglycemia acts through vagal afferent pathways to inhibit gastric motility. With the use of a glucose-clamp rat model, we showed that glucose decreased intragastric pressure in a dose-dependent manner. In contrast to intravenous infusion of glucose, intracisternal injection of glucose at 250 and 500 mg/dl had little effect on intragastric pressure. Pretreatment with hexamethonium, as well as truncal vagotomy, abolished the gastric motor responses to hyperglycemia (250 mg/dl), and perivagal and gastroduodenal applications of capsaicin significantly reduced the gastric responses to hyperglycemia. In contrast, hyperglycemia had no effect on the gastric contraction induced by electrical field stimulation or carbachol (10(-5) M). To rule out involvement of serotonergic pathways, we showed that neither granisetron (5-HT(3) antagonist, 0.5 g/kg) nor pharmacological depletion of 5-HT using p-chlorophenylalanine (5-HT synthesis inhibitor) affected gastric relaxation induced by hyperglycemia. Lastly, N(G)-nitro-L-arginine methyl ester (L-NAME) and a VIP antagonist each partially reduced gastric relaxation induced by hyperglycemia and, in combination, completely abolished gastric responses. In conclusion, hyperglycemia inhibits gastric motility through a capsaicin-sensitive vagal afferent pathway originating from the gastroduodenal mucosa. Hyperglycemia stimulates vagal afferents, which, in turn, activate vagal efferent cholinergic pathways synapsing with intragastric nitric oxide- and VIP-containing neurons to mediate gastric relaxation.

Mechanisms of disease: the pathological basis of gastroparesis--a review of experimental and clinical studies

The pathogenesis of gastroparesis is complicated and poorly understood. This lack of understanding remains a major impediment to the development of effective therapies for this condition. Most of the scientific information available on the pathogenesis of gastroparesis has been derived from experimental studies of diabetes in animals. These studies suggest that the disease process can affect nerves (particularly those producing nitric oxide, but also the vagus nerve), interstitial cells of Cajal and smooth muscle. By contrast, human data are sparse, outdated and generally inadequate for the validation of data obtained from experimental models. The available data do, however, suggest that multiple cellular targets are involved. In practice, though, symptoms seldom correlate with objective measures of gastric function and there is still a lot to learn about the pathophysiology of gastroparesis. Future studies should focus on understanding the molecular pathways that lead to gastric dysfunction, in animal models and in humans, and pave the way for the development of rational therapies.

Central neuropeptide Y induces proximal stomach relaxation via Y1 receptors in the dorsal vagal complex of the rat

Effects of neuropeptide Y (NPY) on motility of the proximal stomach was examined in anesthetized rats. Intragastric pressure was measured using a balloon situated in the proximal part of the stomach. Administration of NPY into the fourth ventricle induced relaxation of the proximal stomach in a dose-dependent manner. Administration of an Y1 receptor (Y1R) agonist [Leu31, Pro34]NPY induced a larger relaxation than NPY. The administration of an Y2 receptor agonist (NPY 13-36) did not induce significant changes in motility. Microinjections of [Leu31, Pro34]NPY into the caudal part of the dorsal vagal complex (DVC) induced relaxation of the proximal stomach. In contrast, similar injections into the intermediate part of the DVC increased IGP of the proximal stomach. Administration of NPY into the fourth ventricle did not induce relaxation after bilateral injections of the Y1R antagonist (1229U91) into the caudal DVC. These results indicate that NPY induces relaxation in the proximal stomach via Y1Rs situated in the DVC. Because bilateral vagotomy below the diaphragm abolished the relaxation induced by the administration of NPY into the fourth ventricle, relaxation induced by NPY is probably mediated by vagal preganglionic neurons. Intravenous injection of atropine methyl nitrate reduced relaxation induced by administration of NPY. Therefore, relaxation induced by NPY is likely mediated by peripheral cholinergic neurons.

Gastrointestinal function regulation by nitrergic efferent nerves

Gastrointestinal (GI) smooth muscle responses to stimulation of the nonadrenergic noncholinergic inhibitory nerves have been suggested to be mediated by polypeptides, ATP, or another unidentified neurotransmitter. The discovery of nitric-oxide (NO) synthase inhibitors greatly contributed to our understanding of mechanisms involved in these responses, leading to the novel hypothesis that NO, an inorganic, gaseous molecule, acts as an inhibitory neurotransmitter. The nerves whose transmitter function depends on the NO release are called "nitrergic", and such nerves are recognized to play major roles in the control of smooth muscle tone and motility and of fluid secretion in the GI tract. Endothelium-derived relaxing factor, discovered by Furchgott and Zawadzki, has been identified to be NO that is biosynthesized from l-arginine by the constitutive NO synthase in endothelial cells and neurons. NO as a mediator or transmitter activates soluble guanylyl cyclase and produces cyclic GMP in smooth muscle cells, resulting in relaxation of the vasculature. On the other hand, NO-induced GI smooth muscle relaxation is mediated, not only by cyclic GMP directly or indirectly via hyperpolarization, but also by cyclic GMP-independent mechanisms. Numerous cotransmitters and cross talk of autonomic efferent nerves make the neural control of GI functions complicated. However, the findingsrelated to the nitrergic innervation may provide us a new way of understanding GI tract physiology and pathophysiology and might result in the development of new therapies of GI diseases. This review article covers the discovery of nitrergic nerves, their functional roles, and pathological implications in the GI tract.

Hindbrain chemical mediators of reflex-induced inhibition of gastric tone produced by esophageal distension and intravenous nicotine

The purpose of this study was to activate a vagovagal reflex by using esophageal distension and nicotine and test whether hindbrain nitric oxide and norepinephrine are involved in this reflex function. We used double-labeling immunocytochemical methods to determine whether esophageal distension (and nicotine) activates c-Fos expression in nitrergic and noradrenergic neurons in the nucleus tractus solitarii (NTS). We also studied c-Fos expression in the dorsal motor nucleus of the vagus (DMV) neurons projecting to the periphery. Esophageal distension caused 19.7 +/- 2.3% of the noradrenergic NTS neurons located 0.60 mm rostral to the calamus scriptorius (CS) to be activated but had little effect on c-Fos in DMV neurons. Intravenous administration of nicotine caused 19.7 +/- 4.2% of the noradrenergic NTS neurons 0.90 mm rostral to CS to be activated and, as reported previously, had no effect on c-Fos expression in DMV neurons. To determine whether norepinephrine and nitric oxide were central mediators of esophageal distension-induced decrease in intragastric pressure (balloon recording), N(G)-nitro-L-arginine methyl ester microinjected into the NTS (n = 5), but not into the DMV, blocked the vagovagal reflex. Conversely, alpha2-adrenergic blockers microinjected into the DMV (n = 7), but not into the NTS, blocked the vagovagal reflex. These data, in combination with our earlier pharmacological microinjection data with nicotine, indicate that both esophageal distension and nicotine produce nitric oxide in the NTS, which then activates noradrenergic neurons that terminate on and inhibit DMV neurons.

Role of vagus nerve in postprandial antropyloric coordination in conscious dogs

It is generally believed that gastric emptying of solids is regulated by a coordinated motor pattern between the antrum and pylorus. We studied the role of the vagus nerve in mediating postprandial coordination between the antrum and pylorus. Force transducers were implanted on the serosal surface of the body, antrum, pylorus, and duodenum in seven dogs. Dogs were given either a solid or a liquid meal, and gastroduodenal motility was recorded over 10 h. Gastric emptying was evaluated with radiopaque markers mixed with a solid meal. Dogs were treated with hexamethonium, N(G)-nitro-l-arginine methyl ester (l-NAME), or transient vagal nerve blockade by cooling. A postprandial motility pattern showed three distinct phases: early, intermediate, and late. In the late phase, profound pyloric relaxations predominantly synchronized with giant antral contractions that were defined as postprandial antropyloric coordination. A gastric emptying study revealed that the time at which gastric contents entered into the duodenum occurred concomitantly with antropyloric coordination. Treatment by vagal blockade or hexamethonium significantly reduced postprandial antral contractions and pyloric relaxations of the late phase. l-NAME changed pyloric motor patterns from relaxation dominant to contraction dominant. Solid gastric emptying was significantly attenuated by treatment with hexamethonium, l-NAME, and vagal blockade. Postprandial antropyloric coordination was not seen after feeding a liquid meal. It is concluded that postprandial antropyloric coordination plays an important role to regulate gastric emptying of a solid food. Postprandial antropyloric coordination is regulated by the vagus nerve and nitrergic neurons in conscious dogs.

Glucose does not activate nonadrenergic, noncholinergic inhibitory neurons in the rat stomach

We reported previously that intravenously administered d-glucose acts in the central nervous system to inhibit gastric motility induced by hypoglycemia in anesthetized rats. The purpose of this study was to determine whether this effect is due to inhibition of dorsal motor nucleus of the vagus (DMV) cholinergic motoneurons, which synapse with postganglionic cholinergic neurons, or to excitation of DMV cholinergic neurons, which synapse with postganglionic nonadrenergic, noncholinergic (NANC) neurons, particularly nitrergic neurons. Three approaches were employed: 1) assessment of the efficacy of d-glucose-induced inhibition of gastric motility in hypoglycemic rats with and without inhibition of nitric oxide synthase [10 mg/kg iv nitro-l-arginine methyl ester (l-NAME)], 2) assessment of the efficacy of intravenous bethanechol (30 mug.kg(-1).min(-1)) to stimulate gastric motility in hypoglycemic rats during the time of d-glucose-induced inhibition of gastric motility, and 3) determination of c-Fos expression in DMV neurons after intravenous d-glucose was administered to normoglycemic rats. Results obtained demonstrated that l-NAME treatment had no effect on d-glucose-induced inhibition of gastric motility; there was no reduction in the efficacy of intravenous bethanechol to increase gastric motility, and c-Fos expression was not induced by d-glucose in DMV neurons that project to the stomach. These findings indicate that excitation of DMV cholinergic motoneurons that synapse with postganglionic NANC neurons is not a significant contributing component of d-glucose-induced inhibition of gastric motility.

Gastric distension-induced release of 5-HT stimulates c-fos expression in specific brain nuclei via 5-HT3 receptors in conscious rats

We examined c-fos expression in specific brain nuclei in response to gastric distension and investigated whether 5-HT released from enterochromaffin (EC) cells was involved in this response. The role of 5-HT3 receptors in this mechanism was also addressed. Release of 5-HT was examined in an ex vivo-perfused stomach model, whereas c-fos expression in brain nuclei induced by gastric distension was examined in a freely moving conscious rat model. Physiological levels of gastric distension stimulated the vascular release of 5-HT more than luminal release of 5-HT, and induced c-fos expression in the nucleus of the solitary tract (NTS), area postrema (AP), paraventricular nucleus (PVN), and supraoptic nucleus (SON). The c-fos expression in all these brain nuclei was blocked by truncal vagotomy as well as by perivagal capsaicin treatment, suggesting that vagal afferent pathways may mediate this response. Intravenous injection of 5-HT3 receptor antagonist granisetron blocked c-fos expression in all brain nuclei examined, although intracerebroventricular injection of granisetron had no effect, suggesting that 5-HT released from the stomach may activate 5-HT3 receptors located in the peripheral vagal afferent nerve terminals and then induce brain c-fos expression. c-fos Positive cells in the NTS were labeled with retrograde tracer fluorogold injected in the PVN, suggesting that neurons in the NTS activated by gastric distension project axons to the PVN. The present results suggest that gastric distension stimulates 5-HT release from the EC cells and the released 5-HT may activate 5-HT3 receptors located on the vagal afferent nerve terminals in the gastric wall leading to neuron activation in the NTS and AP and subsequent activation of neurons in the PVN and SON.

Ghrelin, appetite, and gastric motility: the emerging role of the stomach as an endocrine organ

Recent progress in the field of energy homeostasis was triggered by the discovery of adipocyte hormone leptin and revealed a complex regulatory neuroendocrine network. A late addition is the novel stomach hormone ghrelin, which is an endogenous agonist at the growth hormone secretagogne receptor and is the motilin-related family of regulatory peptides. In addition to its ability to stimulate GH secretion and gastric motility, ghrelin stimulates appetite and induces a positive energy balance leading to body weight gain. Leptin and ghrelin are complementary, yet antagonistic, signals reflecting acute and chronic changes in energy balance, the effects of which are mediated by hypothalamic neuropeptides such as neuropeptide Y and agouti-related peptide. Endocrine and vagal afferent pathways are involved in these actions of ghrelin and leptin. Ghrelin is a novel neuroendocrine signal possessing a wide spectrum of biological activities that illustrates the importance of the stomach in providing input into the brain. Defective ghrelin signaling from the stomach could contribute to abnormalities in energy balance, growth, and associated gastrointestinal and neuroendocrine functions.

Glucose acts in the CNS to regulate gastric motility during hypoglycemia

Our purposes were to 1) develop an animal model where intravenously (iv) administered d-glucose consistently inhibited antral motility, and 2) use this model to assess whether iv glucose acts to inhibit motility from a peripheral or a central nervous system site and to elucidate the factor(s) that determine(s) whether stomach motor function is sensitive to changes in blood glucose. Rats were anesthetized with alpha-chloralose-urethane, and antral motility was measured by a strain-gauge force transducer sutured to the antrum. In some cases, antral motility and gastric tone were measured by monitoring intragastric balloon pressure. Increases in blood glucose were produced by continuous iv infusion of 25% d-glucose at 2 ml/h. Inhibition of antral motility and gastric tone was observed when gastric contractions were induced by hypoglycemia (subcutaneously administered insulin, 2.5 IU/animal). In contrast, no inhibition of gastric motor function was observed when glucose infusion was tested on gastric contractions that were 1) spontaneously occurring, 2) evoked by iv administered bethanechol in vagotomized animals, and 3) evoked by the TRH analog RX77368, microinjected into the dorsal motor nucleus of the vagus. Using the model of insulin-induced hypoglycemia to increase gastric motor activity, we found that neither sectioning the hepatic branch of the vagus (n = 5), nor treating animals with capsaicin to destroy sensory vagal afferent nerves (n = 5) affected the ability of iv d-glucose to inhibit gastric motor function. Our results indicate that an important factor determining whether stomach motor function will be sensitive to changes in blood glucose is the method used to stimulate gastric contractions, and that the primary site of the inhibitory action of iv glucose on gastric motility is the central nervous system rather than the periphery.

Intravenous glucose infusion decreases intracisternal thyrotropin-releasing hormone induced vagal stimulation of gastric acid secretion in anesthetized rats

Gastroparesis is a common complication of diabetes attributed to autonomic neuropathy. This study investigated whether acute hyperglycemia influences central thyrotropin-releasing hormone (TRH), a well-established brain medullary vagal stimulus, induced gastric acid secretion in overnight fasted, urethane-anesthetized rats. Intravenous infusion of D-glucose (20%, 30% and 40%) dose dependently reduced intracisternal TRH-induced gastric acid secretion (71+/-28 micromol/90 min) by 39%, 90% and 100% respectively. Pretreatment with cholecystokinin(A) (CCK(A)) receptor antagonist devazepide (1 mg/kg) did not influence the inhibitory effect of intravenous glucose (30%). These results indicate that hyperglycemia may have a central effect to antagonize medullary TRH stimulation of vagal outflow to the stomach.