Vagal Afferent Activity Research Articles

Vasopressin-Induced Constriction of the Isolated Rat Occipital Artery is Segment Dependent

Background: Circulating factors delivered to the nodose ganglion (NG) by the occipital artery (OA) have been shown to affect vagal afferent activity, and thus the contractile state of the OA may influence blood flow to the NG. Methods: OA were isolated and bisected into proximal and distal segments relative to the external carotid artery. Results: Bisection highlighted stark differences between maximal contractile responses and OA sensitivity. Specifically, maximum responses to vasopressin and the V₁ receptor agonist were significantly higher in distal than proximal segments. Distal segments were significantly more sensitive to 5-hydroxytryptamine (5-HT) and the 5-HT₂ receptor agonist than proximal segments. Angiotensin II (AT)₂, V₂ and 5-HT_1B/1D receptor agonists did not elicit vascular responses. Additionally, AT₁ receptor agonists elicited mild, yet not significantly different maximal responses between segments. Conclusion: The results of this study are consistent with contractile properties of rat OA being mediated via AT₁, V₁ and 5-HT₂ receptors and dependent upon the OA segment. Furthermore, vasopressin-induced constriction of the OA, regardless of a bolus dose or a first and second concentration-response curve, retained this unique segmental difference. We hypothesize that these segmental differences may be important in the regulation of blood flow through the OA in health and disease.

Modulation of murine gastric vagal afferent mechanosensitivity by neuropeptide W

Neuropeptide W (NPW) is an endogenous ligand for the receptors GPR7 and GPR8 and is involved in central regulation of energy homeostasis. NPW in the periphery is found in gastric gastrin (G) cells. In the stomach, energy intake is influenced by vagal afferent signals, so we aimed to determine the effect of NPW on mechanosensitive gastric vagal afferents under different feeding conditions. Female C57BL/6 mice (N > 10 per group) were fed a standard laboratory diet (SLD), high-fat diet (HFD) or were food restricted. The relationship between NPW immunopositive cells and gastric vagal afferent endings was determined by anterograde tracing and NPW immunohistochemistry. An in vitro gastro-oesophageal preparation was used to determine the functional effects of NPW on gastric vagal afferents. Expression of NPW in the gastric mucosa and GPR7 in whole nodose ganglia was determined by quantitative RT-PCR (QRT-PCR). The expression of GPR7 in gastric vagal afferent neurones was determined by retrograde tracing and QRT-PCR. Neuropeptide W immunoreactive cells were found in close proximity to traced vagal afferents. NPW selectively inhibited responses of gastric vagal tension receptors to stretch in SLD but not HFD or fasted mice. In the nodose ganglia, GPR7 mRNA was specifically expressed in gastric vagal afferent neurones. In fasted mice gastric mucosal NPW and nodose GPR7, mRNA was reduced compared with SLD. A HFD had no effect on gastric NPW mRNA, but down-regulated nodose GPR7 expression. Neuropeptide W modulates gastric vagal afferent activity, but the effect is dynamic and related to feeding status.

A chronic high fat diet alters the homologous and heterologous control of appetite regulating peptide receptor expression

Leptin, ghrelin and neuropeptide W (NPW) modulate vagal afferent activity, which may underlie their appetite regulatory actions. High fat diet (HFD)-induced obesity induces changes in the plasma levels of these peptides and alters the expression of receptors on vagal afferents. We investigated homologous and heterologous receptor regulation by leptin, ghrelin and NPW. Mice were fed (12 weeks) a standard laboratory diet (SLD) or HFD. Nodose ganglia were cultured overnight in the presence or absence of each peptide. Leptin (LepR), ghrelin (GHS-R), NPW (GPR7) and cholecystokinin type-1 (CCK1R) receptor mRNA, and the plasma leptin, ghrelin and NPW levels were measured. SLD: leptin reduced LepR, GPR7, increased GHS-R and CCK1R mRNA; ghrelin increased LepR, GPR7, CCK1R, and decreased GHS-R. HFD: leptin decreased GHS-R and GPR7, ghrelin increased GHS-R and GPR7. NPW decreased all receptors except GPR7 which increased with HFD. Plasma leptin was higher and NPW lower in HFD. Thus, HFD-induced obesity disrupts inter-regulation of appetite regulatory receptors in vagal afferents.

Intraportal GLP-1 stimulates insulin secretion predominantly through the hepatoportal-pancreatic vagal reflex pathways

We previously reported that glucagon-like peptide-1 (GLP-1) appearance in the portal vein facilitates hepatic vagal afferent activity, and this further augments reflexively the pancreatic vagal efferents in anesthetized rats, suggesting a neuroincretin effect of GLP-1. To determine whether the GLP-1-induced vagal pathways lead to a neuronal-mediated component (NMC) of insulin secretion, we infused GLP-1 at a physiological or pharmacological dose (1 or 3 pmol·kg(-1)·min(-1), respectively) into the portal vein in conscious rats with selective hepatic vagotomy (Vagox) or sham operation (Sham). The experiments consisted of two sequential 10-min intraportal infusions (P1 and P2): glucose at a physiological rate (56 μmol·kg(-1)·min(-1)) in P1 and the glucose plus GLP-1 or vehicle in P2. Under arterial isoglycemia across the groups, the physiological GLP-1 infusion in Sham augmented promptly and markedly arterial insulin levels, approximately twofold the levels in glucose alone infusion (P < 0.005), and insulin levels in Vagox diminished apparently (P < 0.05). Almost 60% of the GLP-1-induced insulin secretion (AUC) in Sham met the NMC, i.e., difference between insulin secretion in Sham and Vagox, (AUC 976 ± 65 vs. 393 ± 94 pmol·min/l, respectively, P < 0.005). Intraportal pharmacological GLP-1 infusion further augmented insulin secretion in both groups, but the NMC remained in 46% (NS; Sham vs. Vagox). In contrast, "isoglycemic" intravenous GLP-1 infusion (3 pmol·kg(-1)·min(-1)) evoked an equal insulin secretion in both groups. Thus, the present results indicate that GLP-1 appearing in the portal vein evokes a powerful neuronal-mediated insulinotropic effect, suggesting the neuroincretin effect.

Evidence for swallowing reflexes evoked by acid and mechanical stimulation of the vagal afferent nerves innervating the larynx in anesthetized guinea pigs

PurposeSwallowing protects the lungs from aspiration and is evoked from the upper airways (UA) by activation of pharyngeal afferent nerves. We have tested the hypothesis that laryngeal (LX) afferent nerve activation may also evoke swallowing.MethodsSternohyoid muscle EMGs and UA airflow were used to detect swallows in anesthetized guinea pigs (GPs). Citric acid (CA; 0.01M, 50μL), applied topically to the LX mucosa, and UA pressure distensions, both applied 5× repetitively in 5 min intervals and delivered rostrally via the trachea, were used to evoke swallows.ResultsRepetitive LX CA challenge evoked swallowing (13±5 swallows; n=7). Severing both the recurrent (RLN) and superior (SLN) laryngeal nerves nearly abolished LX CA evoked swallows (0.3±0.3; n=4). Severing just the RLNs also nearly abolished the LX acid‐evoked swallows (1.3±0.9; n=4). By contrast, swallows evoked by 30sec pressure distensions of the UA were not prevented by RLN transection, with all intact (50±5; n=4) and RLN transected (26±3; n=4) GPs swallowing in response to each of 5 distensions. RLN transection did, however, delay the onset of UA distension evoked swallows (4.0±1.3s and 13.6±1.4s in intact and RLN transected GPs; n=4 each). A single, subsequent LX CA challenge evoked swallows in all 4 of these control GPs (4±1) but in none of the GPs with RLNs cut (0±0).ConclusionsLaryngeal vagal afferent nerve activation initiates swallowing.

Effects of airway pressure, hypercapnia, and hypoxia on pulmonary vagal afferent activity in the alligator

The American alligator (Alligator mississippiensis) is an aquatic vertebrate that dives and has a periodic breathing pattern. The effects of airway pressure, hypercapnia, and hypoxia on dynamic and static responses of pulmonary stretch receptors (PSR) were studied in juvenile alligators (mean mass = 246 g) at room temperature (24°C). Alligators were initially anesthetized with isoflurane, pithed, tracheotomized and attached to a small animal ventilator. The vagus nerve (cranial nerve X) was exposed, sectioned and submerged in mineral oil. Nerve filaments were teased from the nerve trunk and placed over platinum electrodes for differential nerve recording. Afferent tonic and phasic activity was recorded. The majority of receptors appeared to be slowly‐adapting PSRs (SAR) with varying thresholds and degrees of adaptation and no CO2 sensitivity. Dives were simulated in order to characterize receptor activity during and after prolonged periods of inflation and deflation. Some stretch receptors showed a change in dynamic response, exhibiting inhibition after lung inflation and potentiation after lung deflation. These airway stretch receptors may be involved in buoyancy control and/or recovery of breathing patterns and lung volume during pre– and post‐diving behavior and apneic periods. Supported by NSF CAREER IOS 0845741 (DAC).

The long chain fatty acid oleate activates mouse intestinal afferent nerves in vitro

Vagal afferents innervating the gastrointestinal tract serve an important nutrient-sensing function, and these signals contribute to satiety. Detection of nutrients occurs largely through the release of mediators from specialized enteroendocrine cells within the mucosa of the gastrointestinal tract. The signaling pathways leading to vagal afferent activation are not clear; however, previous in-vivo studies have implicated a role for cholecystokinin (CCK). We used an in vitro intestinal afferent extracellular recording preparation to study the effect of luminal perfusion of the long chain fatty acid oleate on mouse intestinal afferent activity. Oleate activated intestinal afferents in a concentration-dependent fashion, with an EC50 value of approximately 25 mmol/L. The L-type calcium channel blocker nicardipine attenuated the effect of oleate. Vagotomy resulted in a significant (>60%) reduction of the responses to both oleate and CCK. The CCK-1 receptor antagonist lorglumide nearly abolished responses to CCK and oleate. Our experiments therefore suggest that oleate activates intestinal afferents, with vagal afferents primarily involved; however, nonvagal fibres also contribute. The activation is dependent on CCK release, likely via activation of L-type channels on mucosal enteroendocrine cells, finally resulting in activation of CCK-1 receptors on the afferent terminals.

Anti-emetic Effect of Mosapride Citrate Hydrate, a 5-HT4 Receptor Agonist, on Selective Serotonin Reuptake Inhibitors (SSRIs)-Induced Emesis in Experimental Animals

Although selective serotonin reuptake inhibitors (SSRIs) are widely used to treat depression, they frequently cause gastrointestinal adverse effects, such as nausea and emesis. In the present study, we investigated the anti-emetic effect of mosapride, a 5-HT4 receptor agonist, on SSRIs-induced emesis in Suncus murinus and dogs. We also examined the effect of mosapride on SSRIs-induced delay in gastric emptying and increase in gastric vagal afferent activity in rats. Oral administration of paroxetine, but not its subcutaneous administration, dose-dependently caused emesis in both animals. Mosapride inhibited paroxetine-induced emesis in Suncus murinus and dogs with ID50 values of 7.9 and 1.1 mg/kg, respectively. The anti-emetic effect of mosapride was partially inhibited by SB207266, a selective 5-HT4 antagonist. Intragastric administration of paroxetine increased gastric vagal afferent discharge in anesthetized rats. Mosapride failed to suppress this increase. On the other hands, mosapride improved the delay in gastric emptying caused by paroxetine in rats. We have shown in this study that oral administration of SSRIs causes emesis and activates gastric vagal afferent activity in experimental animals and that mosapride inhibits SSRIs-induced emesis, probably via improvement of SSRIs-induced delay in gastric emptying. These findings highlight the promising potential of mosapride as an anti-emetic agent.

Anti-emetic and emetic effects of erythromycin in Suncus murinus: Role of vagal nerve activation, gastric motility stimulation and motilin receptors

Paradoxically, erythromycin is associated with nausea when used as an antibiotic but at lower doses erythromycin activates motilin receptors and is used to treat delayed gastric emptying and nausea. The aim of this study was to characterise pro- and anti-emetic activity of erythromycin and investigate mechanisms of action. Japanese House musk shrews (Suncus murinus) were used. Erythromycin was administered alone or prior to induction of emesis with abnormal motion or subcutaneous nicotine (10mg/kg). The effects of erythromycin and motilin on vagal nerve activity and on cholinergically mediated contractions of the stomach (evoked by electrical field stimulation) were studied in vitro. The results showed that erythromycin (1 and 5mg/kg) reduced vomiting caused by abnormal motion (e.g., from 10.3±1.8 to 4.0±1.1 emetic episodes at 5mg/kg) or by nicotine (from 9.5±2.0 to 3.1±2.0 at 5mg/kg), increasing latency of onset to emesis; lower or higher doses had no effects. When administered alone, erythromycin 100mg/kg induced vomiting in two of four animals, whereas lower doses did not. In vitro, motilin (1, 100nM) increased gastric vagal afferent activity without affecting jejunal afferent mesenteric nerve activity. Cholinergically mediated contractions of the stomach (prevented by tetrodotoxin 1μM or atropine 1μM, facilitated by l-NAME 300μM) were facilitated by motilin (1–100nM) and erythromycin (10–30μM). In conclusion, low doses of erythromycin have anti-emetic activity. Potential mechanisms of action include increased gastric motility (overcoming gastric stasis) and/ or modulation of vagal nerve pathways involved in emesis, demonstrated by first-time direct recording of vagal activation by motilin.

Bisphenol A attenuates phenylbiguanide-induced cardio-respiratory reflexes in anaesthetized rats

Bisphenol A (BPA), a toxic chemical released from plastics, produces respiratory arrest and hypotension after a latency. The latency was similar to the reflex apnoea induced by the vagal C fibre stimulation. Therefore, the present study was undertaken to examine the effects of chronic and acute exposure to BPA on cardio-respiratory reflexes elicited by phenylbiguanide (PBG). Acute and chronic experiments were performed on adult female rats. In chronic experiments, the animals were ingested with pellets containing BPA (2μg/kg body weight) or without BPA (time-matched control) for 30 days. Subsequently, the animals were anaesthetized and prepared for recording blood pressure, ECG and respiratory excursions. PBG was injected through jugular vein to evoke reflexes in these animals. In acute experiments, the PBG reflexes were obtained before and after injecting BPA/ethanol. Also vagal afferent activity was recorded in some rats. In time-matched control rats, PBG produced bradycardia, hypotension and tachypnoea over a period of time. The maximal changes were around 50–65%. In BPA treated group, the PBG-induced heart rate and respiratory frequency changes were attenuated significantly. Acute exposure of animals to BPA (35mg/kg body weight) for 30min also attenuated the PBG-induced responses significantly. The attenuation of the PBG reflex responses by BPA in acute experiments was associated with decreased vagal afferent activity. The present results indicate that BPA attenuates the protective cardio-respiratory reflexes due to decreased vagal afferent activity.

The wonders of the Wanderer

Vagus is Latin for wandering, and the vagus nerve fully deserves this name due to its extensive distribution through the body. Indeed, one of the lines of the song that accompanied the 2012 G. L. Brown Prize Lecture exaggerates this diversity, 'My function's almost anythin', and vagus is my name'. Alteration of vagal activity was first investigated in the 1880s as a treatment for epilepsy, and vagus nerve stimulation is now an approved treatment for refractory epilepsy and depression in the USA, despite an incomplete understanding of the mechanisms involved. Vagus nerve stimulation could be beneficial in many other conditions, including heart failure, tinnitus, chronic hiccups, Alzheimer's disease and inflammatory diseases. Inhibition of vagal activity could also be beneficial in some conditions, e.g. reducing activation of vagal respiratory afferents to treat chronic cough. This review discusses evidence underlying some current and potential therapeutic applications of vagal modulation, illustrating the wonders of the Wanderer.

Comparative pharmacology of cholecystokinin induced activation of cultured vagal afferent neurons from rats and mice.

Cholecystokinin (CCK) facilitates the process of satiation via activation of vagal afferent neurons innervating the upper gastrointestinal tract. Recent findings indicate CCK acts on these neurons via a ruthenium red (RuR) sensitive pathway that involves members of the vanilloid (V) subfamily of transient receptor potential (TRP) channels. To further test this mechanism, the mouse provides an ideal model in which genetic tools could be applied. However, whether CCK acts by similar mechanism(s) in mice has not been determined. In the present study we explored the actions of CCK on nodose neurons isolated from Sprague Dawley (SD) rat and two strains of mice; C57BL/6 and BalbC using fluorescence-based calcium imaging. With minor exceptions nodose neurons isolated from all species/strains behaved similarly. They all respond to brief depolarization with a large calcium transient. A significant subset of neurons responded to capsaicin (CAP), a TRPV1 agonist, although neurons from C57BL/6 were 10-fold more sensitive to CAP than SD rats or BalbC mice, and a significantly smaller fraction of neurons from BalbC mice responded to CAP. CCK-8 dose-dependently activated a subpopulation of neurons with similar dose dependency, percent responders, and overlap between CCK and CAP responsiveness. In all species/strains CCK-8 induced activation was significantly attenuated (but not completely blocked) by pretreatment with the TRPV channel blocker RuR. Surprisingly, the CCK analogue JMV-180, which is reported to have pure antagonistic properties in rat but mixed agonist/antagonist properties in mice, behaved as a pure antagonist to CCK in both rat and mouse neurons. The pure antagonistic action of JMV-180 in this in vitro preparation suggests that prior reported differential effects of JMV-180 on satiation in rats versus mouse must be mediated by a site other than vagal afferent activation.

Evidence that activation of both vagal and glossopharyngeal afferents cause the release of 5‐HT in the NTS

Pharmacological studies indicate that 5‐HT is released in the nucleus tractus solitarii (NTS) in response to cardiovascular afferent activation. Experiments using a modified form of fast differential voltammetry were carried out to determine if this release of 5‐HT could be detected in the NTS. Rats were anaesthetized with [alpha]‐chloralose (120 mg kg−1; i.v), neuromuscular blocked and artificially ventilated. Activation of cardiopulmonary afferents by phenylbiguanide (PBG; i.a.) caused a transient rise in 5‐HT of 17.8 ± 2.5nM. Citalopram (1 mg kg−1; i.v.) had no effect, while the OCT3/PMAT inhibitor decynium‐22 (600 [micro]g kg−1, i.v.) potentiated this increase in 5‐HT from 18 ± 4 to 70 ± 11 nM. Increasing baroreceptor afferent input with i.v. noradrenaline increased 5‐HT release, while decreasing this input with i.v. sodium nitroprusside had no effect. Citalopram (1 mg kg−1) had no effect on these responses. Activation of the chemoreflex with i.a. sodium cyanide caused a maintained rise in 5‐HT of 27 ± 6 nM. The data supports the view that cardiovascular afferents cause the release of 5‐HT in the NTS.

Diet and gastric neurons

Diet and gastric neurons

Duodenal lipid‐induced symptom generation in gastroesophageal reflux disease: role of apolipoprotein A‐IV and cholecystokinin

Duodenal lipid intensifies the perception of esophageal acid perfusion. Recently, we showed that genes implicated in lipid absorption were upregulated in the duodenum of fasting gastro-esophageal reflux disease (GERD) patients. This suggests that chylomicron production and secretion may be enhanced and, consequently, the release of apolipoprotein A-IV (apoA-IV), a chylomicron-derived signaling protein. ApoA-IV may stimulate release of cholecystokinin (CCK), an activator of vagal afferents. This study evaluated putative involvement of abnormal apoA-IV and CCK responses to lipid in GERD. Ten GERD patients and 10 healthy volunteers (HV) underwent duodenal perfusion with Intralipid 20%, 2 kcal min(-1) , for 60 min. Symptoms were scored, blood samples collected every 15 min during lipid perfusion and 15 min after discontinuation when duodenal biopsies were taken. Plasma and mucosal concentrations of apoA-IV and CCK and transcript levels of 21 genes implicated in lipid absorption, differentially expressed under fasting conditions, were quantified. Heartburn (P = 0.003), abdominal discomfort (P = 0.037) and nausea (P = 0.008) only increased significantly during lipid infusion in GERD patients. Following lipid infusion mean mucosal apoA-IV concentration was lower in GERD patients compared with HV (P = 0.023), whereas plasma concentration tended to be elevated (P = 0.068). Mean mucosal CCK concentration was also lower in GERD patients (P = 0.009). Two genes, HIBADH and JTB, were upregulated in GERD patients (P = 0.008 and P = 0.038, respectively). Our results suggest excessive duodenal lipid-induced release of apoA-IV and CCK in GERD. We postulate that the resulting heightened activation of duodenal vagal afferents may underlie central sensitization, thereby increasing the perception of reflux events.

Cholecystokinin enhances visceral pain-related affective memory via vagal afferent pathway in rats

BackgroundPain contains both sensory and affective dimensions. Using a rodent visceral pain assay that combines the colorectal distension (CRD) model with the conditioned place avoidance (CPA) paradigms, we measured a learned behavior that directly reflects the affective component of visceral pain, and showed that perigenual anterior cingulate cortex (pACC) activation is critical for memory processing involved in long-term visceral affective state and prediction of aversive stimuli by contextual cue. Progress has been made and suggested that activation of vagal afferents plays a role in the behavioral control nociception and memory storage processes.In human patients, electrical vagus nerve stimulation enhanced retention of verbal learning performance. Cholecystokinin-octapeptide (CCK), which is a gastrointestinal hormone released during feeding, has been shown to enhance memory retention. Mice access to food immediately after training session enhanced memory retention. It has been well demonstrated that CCK acting on vagal afferent fibers mediates various physiological functions. We hypothesize that CCK activation of vagal afferent enhances visceral pain-related affective memory.ResultsIn the presented study, infusion of CCK-8 at physiological concentration combining with conditional training significantly increased the CRD-induced CPA scores, and enhanced the pain affective memory retention. In contrast, CCK had no effect on CPA induced by non-nociceptive aversive stimulus (U69,593). The physiological implications were further strengthened by the similar effects observed in the rats with duodenal infusion of 5% peptone, which has been shown to induce increases in plasma CCK levels. CCK-8 receptor antagonist CR-1409 or perivagal application of capsaicin abolished the effect of CCK on aversive visceral pain memory, which was consistent with the notion that vagal afferent modulates affective aspects of visceral pain. CCK does not change the nociceptive response (visceral pain sensitivity) and anterior cingulate cortex neuronal responses to CRD.ConclusionCCK activating vagal afferent C fibers enhances memory consolidation and retention involved in long-term visceral negative affective state. Thus, in a number of gastrointestinal disorders, such as irritable bowel syndrome, nutrient content may contribute to painful visceral perception by enhancing visceral aversive memory via acts on vagal afferent pathway.

Inhibition of Cardiac Sympathetic Afferent Reflex and Sympathetic Activity by Baroreceptor and Vagal Afferent Inputs in Chronic Heart Failure

BackgroundCardiac sympathetic afferent reflex (CSAR) contributes to sympathetic activation and angiotensin II (Ang II) in paraventricular nucleus (PVN) augments the CSAR in vagotomized (VT) and baroreceptor denervated (BD) rats with chronic heart failure (CHF). This study was designed to determine whether it is true in intact (INT) rats with CHF and to determine the effects of cardiac and baroreceptor afferents on the CSAR and sympathetic activity in CHF.Methodology/Principal FindingsSham-operated (Sham) or coronary ligation-induced CHF rats were respectively subjected to BD+VT, VT, cardiac sympathetic denervation (CSD) or INT. Under anesthesia, renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded, and the CSAR was evaluated by the RSNA and MAP responses to epicardial application of capsaicin. Either CSAR or the responses of RSNA, MAP and CSAR to Ang II in PVN were enhanced in CHF rats treated with BD+VT, VT or INT. Treatment with VT or BD+VT potentiated the CSAR and the CSAR responses to Ang II in both Sham and CHF rats. Treatment with CSD reversed the capsaicin-induced RSNA and MAP changes and the CSAR responses to Ang II in both Sham and CHF rats, and reduced the RSNA and MAP responses to Ang II only in CHF rats.ConclusionsThe CSAR and the CSAR responses to Ang II in PVN are enhanced in intact CHF rats. Baroreceptor and vagal afferent activities inhibit CSAR and the CSAR responses to Ang II in intact Sham and CHF rats.

Effects of gastric distension and infusion of umami and bitter taste stimuli on vagal afferent activity

Until recently, sensory nerve pathways from the stomach to the brain were thought to detect distension and play little role in nutritional signaling. Newer data have challenged this view, including reports on the presence of taste receptors in the gastrointestinal lumen and the stimulation of multi-unit vagal afferent activity by glutamate infusions into the stomach. However, assessing these chemosensory effects is difficult because gastric infusions typically evoke a distension-related vagal afferent response. In the current study, we recorded gastric vagal afferent activity in the rat to investigate the possibility that umami (glutamate, 150mM) and bitter (denatonium, 10mM) responses could be dissociated from distension responses by adjusting the infusion rate and opening or closing the drainage port in the stomach. Slow infusions of saline (5ml over 2min, open port) produced no significant effects on vagal activity. Using the same infusion rate, glutamate or denatonium solutions produced little or no effects on vagal afferent activity. In an attempt to reproduce a prior report that showed distention and glutamate responses, we produced a distension response by closing the exit port. Under this condition, response to the infusion of glutamate or denatonium was similar to saline. In summary, we found little or no effect of gastric infusion of glutamate or denatonium on gastric vagal afferent activity that could be distinguished from distension responses. The current results suggest that sensitivity to umami or bitter stimuli is not a common property of gastric vagal afferent fibers.

Reflexes from pulmonary arterial baroreceptors in dogs: interaction with carotid sinus baroreceptors

In contrast to the reflex vasodilatation occurring in response to stimulation of baroreceptors in the aortic arch, carotid sinuses and coronary arteries, stimulation of receptors in the wall of pulmonary arteries results in reflex systemic vasoconstriction. It is rare for interventions to activate only one reflexogenic region, therefore we investigated how these two types of reflexes interact. In anaesthetized dogs connected to cardiopulmonary bypass, reflexogenic areas of the carotid sinuses, aortic arch and coronary arteries and the pulmonary artery were subjected to independently controlled pressures. Systemic perfusion pressure (SPP) measured in the descending aorta (constant flow) provided an index of systemic vascular resistance. In other experiments, sympathetic efferent neural activity was recorded in fibres dissected from the renal nerve (RSNA). Physiological increases in pulmonary arterial pressure (PAP) induced significant increases in SPP (+39.1 ± 10.4 mmHg) and RSNA (+17.6 ± 2.2 impulses s(−1)) whereas increases in carotid sinus pressure (CSP) induced significant decreases in SPP (−42.6 ± 10.8 mmHg) and RSNA (−42.8 ± 18.2 impulses s(−1)) (P < 0.05 for each comparison; paired t test). To examine possible interactions, PAP was changed at different levels of CSP in both studies. With CSP controlled at 124 ± 2 mmHg, the threshold, 'set point' and saturation pressures of the PAP–SPP relationship were higher than those with CSP at 60 ± 1 mmHg; this rightward shift was associated with a significant decrease in the reflex gain. Similarly, increasing CSP produced a rightward shift of the PAP–RSNA relationship, although the effect on reflex gain was inconsistent. Furthermore, the responses to changes in CSP were influenced by setting PAP at different levels; increasing the level of PAP from 5 ± 1 to 33 ± 3 mmHg significantly increased the set point and threshold pressures of the CSP–SPP relationship; the reflex gain was not affected. These results indicate the existence of interaction between pulmonary arterial and carotid sinus baroreceptor reflexes; physiological and pathological states that alter the stimulus to one may alter the reflex responses from the other.

Rotavirus Stimulates Release of Serotonin (5-HT) from Human Enterochromaffin Cells and Activates Brain Structures Involved in Nausea and Vomiting

Rotavirus (RV) is the major cause of severe gastroenteritis in young children. A virus-encoded enterotoxin, NSP4 is proposed to play a major role in causing RV diarrhoea but how RV can induce emesis, a hallmark of the illness, remains unresolved. In this study we have addressed the hypothesis that RV-induced secretion of serotonin (5-hydroxytryptamine, 5-HT) by enterochromaffin (EC) cells plays a key role in the emetic reflex during RV infection resulting in activation of vagal afferent nerves connected to nucleus of the solitary tract (NTS) and area postrema in the brain stem, structures associated with nausea and vomiting. Our experiments revealed that RV can infect and replicate in human EC tumor cells ex vivo and in vitro and are localized to both EC cells and infected enterocytes in the close vicinity of EC cells in the jejunum of infected mice. Purified NSP4, but not purified virus particles, evoked release of 5-HT within 60 minutes and increased the intracellular Ca2+ concentration in a human midgut carcinoid EC cell line (GOT1) and ex vivo in human primary carcinoid EC cells concomitant with the release of 5-HT. Furthermore, NSP4 stimulated a modest production of inositol 1,4,5-triphosphate (IP3), but not of cAMP. RV infection in mice induced Fos expression in the NTS, as seen in animals which vomit after administration of chemotherapeutic drugs. The demonstration that RV can stimulate EC cells leads us to propose that RV disease includes participation of 5-HT, EC cells, the enteric nervous system and activation of vagal afferent nerves to brain structures associated with nausea and vomiting. This hypothesis is supported by treating vomiting in children with acute gastroenteritis with 5-HT3 receptor antagonists.