Vagal Afferent Pathways Research Articles

Ghrelin Supresses Sympathetic Hyperexcitation in Acute Heart Failure in Male Rats: Assessing Centrally and Peripherally Mediated Pathways.

The hormone ghrelin prevents a dangerous increase in cardiac sympathetic nerve activity (SNA) after acute myocardial infarction (MI), although the underlying mechanisms remain unknown. This study aimed to determine whether ghrelin's sympathoinhibitory properties stem either from directly within the central nervous system, or via modulation of specific cardiac vagal inhibitory afferents. Cardiac SNA was recorded in urethane-anesthetized rats for 3 hours after the ligation of the left anterior descending coronary artery (ie, MI). Rats received ghrelin either sc (150 μg/kg) or intracerebroventricularly (5 μg/kg) immediately after the MI. In another two groups, the cervical vagi were denervated prior to the MI, followed by sc injection of either ghrelin or placebo. Acute MI induced a 188% increase in cardiac SNA, which was significantly attenuated in ghrelin-treated rats for both sc or intracerebroventricularly administration (36% and 76% increase, respectively). Consequently, mortality (47%) and the incidence of arrhythmic episodes (12 per 2 h) were improved with both routes of ghrelin administration (<13% and less than five per 2 h, respectively). Bilateral vagotomy significantly attenuated the cardiac SNA response to acute MI (99% increase). Ghrelin further attenuated the sympathetic response to MI in vagotomized rats so that the SNA response was comparable between vagotomized and vagal-intact MI rats treated with ghrelin. These results suggest that ghrelin may act primarily via a central pathway within the brain to suppress SNA after MI, although peripheral vagal afferent pathways may also contribute in part. The exact region(s) within the central nervous system whereby ghrelin inhibits SNA remains to be fully elucidated.

Estradiol alters the chemosensitive cardiac afferent reflex in female rats by augmenting sympathoinhibition and attenuating sympathoexcitation.

The chemosensitive cardiac vagal and sympathetic afferent reflexes are implicated in driving pathophysiological changes in sympathetic nerve activity (SNA) in cardiovascular disease states. This study investigated the impact of sex and ovarian hormones on the chemosensitive cardiac afferent reflex. Experiments were performed in anaesthetized, sinoaortic baroreceptor denervated male, female and ovariectomized female (OVX) Wistar rats with either intact cardiac innervation or bilateral vagotomy. To investigate the chemosensitive cardiac afferent reflexes renal SNA, heart rate (HR) and arterial pressure (AP) were recorded before and following application of capsaicin onto the epicardial surface of the left ventricle. Compared to males, ovary-intact females displayed similar cardiac afferent reflex mediated changes in renal SNA albeit with a reduced maximum sympathetic reflex driven increase in renal SNA. In females, ovariectomy significantly attenuated the cardiac vagal afferent reflex mediated inhibition of renal SNA (renal SNA decreased 2 ± 17% in OVX versus -50 ± 4% in ovary-intact females, P < 0.05) and augmented cardiac sympathetic afferent reflex mediated sympathoexcitation (renal SNA increased 91 ± 11% in OVX vs 62 ± 9% in ovary-intact females, P < 0.05) so that overall increases in reflex driven sympathoexcitation were significantly enhanced. Chronic estradiol replacement, but not progesterone replacement, begun at time of ovariectomy restored cardiac afferent reflex responses to be similar as ovary-intact females. Vagal denervation eliminated all group differences. The current findings show ovariectomy in female rats, mimicking menopause in women, results in greater chemosensitive cardiac afferent reflex driven sympathoexcitation and does so, at least partly, via the loss of estradiols actions on the cardiac vagal afferent reflex pathway.

Subdiaphragmatic vagotomy enhances stress-induced epinephrine release in rats.

Neuroendocrine stress response is regulated by several feedback loops. Since it has been suggested that afferent vagal pathways contribute to these feedback loops, we examined the effect of surgical subdiaphragmatic vagotomy on both baseline and stress-induced increases in plasma epinephrine, norepinephrine, and corticosterone levels in vagotomized and sham-operated Sprague Dawley rats. On either the 3rd or 14th day following vagotomy, the animals were exposed to acute immobilization stress and blood from the jugular vein was collected both before and during stress exposure. We found that vagotomy significantly enhanced immobilization-induced increases of plasma epinephrine, norepinephrine, and corticosterone levels on the 3rd day following surgery. However, on the 14th day following surgery, vagotomy enhanced only increase of plasma epinephrine levels in stressed rats. Our data indicate that afferent pathways of the vagus nerve are involved in negative feedback regulation of epinephrine secretion from the adrenal medulla during stressful conditions. We hypothesize that this feedback mechanism might be mediated by the binding of circulating epinephrine on β2-adrenergic receptors localized on sensory endings of the vagus nerve.

Ghrelin induces leptin resistance by activation of suppressor of cytokine signaling 3 expression in male rats: implications in satiety regulation.

The anorexigenic adipocyte-derived hormone leptin and the orexigenic hormone ghrelin act in opposition to regulate feeding behavior via the vagal afferent pathways. The mechanisms by which ghrelin exerts its inhibitory effects on leptin are unknown. We hypothesized that ghrelin activates the exchange protein activated by cAMP (Epac), inducing increased SOCS3 expression, which negatively affects leptin signal transduction and neuronal firing in nodose ganglia (NG) neurons. We showed that 91 ± 3% of leptin receptor (LRb) -bearing neurons contained ghrelin receptors (GHS-R1a) and that ghrelin significantly inhibited leptin-stimulated STAT3 phosphorylation in rat NG neurons. Studies of the signaling cascades used by ghrelin showed that ghrelin caused a significant increase in Epac and suppressor of cytokine signaling 3 (SOCS3) expression in cultured rat NG neurons. Transient transfection of cultured NG neurons to silence SOCS3 and Epac genes reversed the inhibitory effects of ghrelin on leptin-stimulated STAT3 phosphorylation. Patch-clamp studies and recordings of single neuronal discharges of vagal primary afferent neurons showed that ghrelin markedly inhibited leptin-stimulated neuronal firing, an action abolished by silencing SOCS3 expression in NG. Plasma ghrelin levels increased significantly during fasting. This was accompanied by enhanced SOCS3 expression in the NG and prevented by treatment with a ghrelin antagonist. Feeding studies showed that silencing SOCS3 expression in the NG reduced food intake evoked by endogenous leptin. We conclude that ghrelin exerts its inhibitory effects on leptin-stimulated neuronal firing by increasing SOCS3 expression. The SOCS3 signaling pathway plays a pivotal role in ghrelin's inhibitory effect on STAT3 phosphorylation, neuronal firing, and feeding behavior.

Heart rate variability biofeedback: how and why does it work?

In recent years there has been substantial support for heart rate variability biofeedback (HRVB) as a treatment for a variety of disorders and for performance enhancement (Gevirtz, 2013). Since conditions as widely varied as asthma and depression seem to respond to this form of cardiorespiratory feedback training, the issue of possible mechanisms becomes more salient. The most supported possible mechanism is the strengthening of homeostasis in the baroreceptor (Vaschillo et al., 2002; Lehrer et al., 2003). Recently, the effect on the vagal afferent pathway to the frontal cortical areas has been proposed. In this article, we review these and other possible mechanisms that might explain the positive effects of HRVB.

Deletion of leptin signaling in vagal afferent neurons results in hyperphagia and obesity.

The vagal afferent pathway senses hormones released from the gut in response to nutritional cues and relays these signals to the brain. We tested the hypothesis that leptin resistance in vagal afferent neurons (VAN) is responsible for the onset of hyperphagia by developing a novel conditional knockout mouse to delete leptin receptor selectively in sensory neurons (Nav1.8/LepRfl/fl mice). Chow fed Nav1.8/LepRfl/fl mice weighed significantly more and had increased adiposity compared with wildtype mice. Cumulative food intake, meal size, and meal duration in the dark phase were increased in Nav1.8/LepRfl/fl mice; energy expenditure was unaltered. Reduced satiation in Nav1.8/LepRfl/fl mice is in part due to reduced sensitivity of VAN to CCK and the subsequent loss of VAN plasticity. Crucially Nav1.8/LepRl/fl mice did not gain further weight in response to a high fat diet. We conclude that disruption of leptin signaling in VAN is sufficient and necessary to promote hyperphagia and obesity.

The Medical Implications of Gastrointestinal Vagal Afferent Pathways in Nausea and Vomiting

Nausea and vomiting are biological systems for defense against food poisoning that are also provoked by numerous drugs (e.g., chemotherapy, anesthesia) and chronic diseases (e.g., cancer, diabetic gastroparesis). The sensory pathways that stimulate nausea and vomiting include vestibular, area postrema, and forebrain inputs, but gastrointestinal vagal afferent fibers arguably play the most prominent role as a first-line defense. Vagal sensory neurons detect toxins that enter the gastrointestinal lumen and transmit information to the hindbrain, leading to nausea (an unconditioned stimulus that serves to facilitate the avoidance of offending foods) and vomiting (a mechanism to clear contents from the stomach). Despite the major importance of these systems to human physiology, progress on the biological basis of nausea and vomiting has been slow - partly because laboratory rats and mice, which represent the largest thrust of preclinical biomedical research, lack a vomiting reflex (although they appear to have indices of nausea, e.g., conditioned food aversion). Several established models are a mainstay of preclinical nausea and vomiting research in academia and pharmaceutical companies, including the dog, cat, ferret, and musk shrew. An argument is made for broader testing across species since each model possesses often unique experimental advantages and sensitivity to emetic and antiemetic agents. This review focuses on the state of knowledge on the neural pathways for nausea and vomiting, behavioral indices of nausea used in preclinical models, role of vagal afferent fibers, current antiemetic and antinausea treatments, and potential future directions.

Reprint of: Role of enteric neurotransmission in host defense and protection of the gastrointestinal tract

Host defense is a vital role played by the gastrointestinal tract. As host to an enormous and diverse microbiome, the gut has evolved an elaborate array of chemical and physicals barriers that allow the digestion and absorption of nutrients without compromising the mammalian host. The control of such barrier functions requires the integration of neural, humoral, paracrine and immune signaling, involving redundant and overlapping mechanisms to ensure, under most circumstances, the integrity of the gastrointestinal epithelial barrier. Here we focus on selected recent developments in the autonomic neural control of host defense functions used in the protection of the gut from luminal agents, and discuss how the microbiota may potentially play a role in enteric neurotransmission. Key recent findings include: the important role played by subepithelial enteric glia in modulating intestinal barrier function, identification of stress-induced mechanisms evoking barrier breakdown, neural regulation of epithelial cell proliferation, the role of afferent and efferent vagal pathways in regulating barrier function, direct evidence for bacterial communication to the enteric nervous system, and microbial sources of enteric neurotransmitters. We discuss these new and interesting developments in our understanding of the role of the autonomic nervous system in gastrointestinal host defense.

Effect of activated peripheral κ-opioid receptors on the action of nicotine and its withdrawal in nicotine-dependent rats.

We studied the possibilities of modulating the effects of nicotine and its withdrawal in nicotine-dependent rats by peripheral injection of κ-opioid receptor agonist ICI 204,448. Injection of nicotine to rats previously treated with nicotine for 14 days reduced motor activity, suppressed metabolism, and increased food intake. In rats receiving ICI 204,448 after chronic administration of nicotine, food intake did not differ from that in control animals receiving isotonic NaCl solution. ICI 204,448 had virtually no effect on suppression of motor activity and metabolism. The rats receiving the last injection of nicotine 24 h prior to the experiment demonstrated an increase in metabolism, locomotor activity, and food intake. In these animals, ICI 204,448 completely abolished the effects of nicotine withdrawal. It was found that peripheral administration of compound ICI 204,448 did not significantly inhibit the effect of nicotine in nicotine-dependent rats, but abolished symptoms of nicotine withdrawal. It can be hypothesized that nicotine withdrawal syndrome is related to inhibition of dopamine release in the nucleus accumbens probably caused by enhanced κ-opioid activity in presynaptic terminals. Activation of peripheral κ-opioid receptors apparently suppressed (via vagal afferent pathways) central κ-opioid activity and reduced nicotine withdrawal symptoms in nicotine-dependent subjects.

Intragastric gavage with denatonium benzoate acutely induces neuronal activation in the solitary tract nucleus via the vagal afferent pathway.

Natural toxic substances have a bitter taste and their ingestion sends signals to the brain leading to aversive oral sensations. In the present study, we investigated chronological changes in c-Fos immunoreactivity in the nucleus tractus solitarius (NTS) to study the bitter taste reaction time of neurons in the NTS. Equal volumes (0.5 mL) of denatonium benzoate (DB), a bitter tastant, or its vehicle (distilled water) were administered to rats intragastrically. The rats were sacrificed at 0, 0.5, 1, 2, 4, 8, or 16 h after treatment. In the vehicle-treated group, the number of c-Fos-positive nuclei started to increase 0.5 h after treatment and peaked 2 h after gavage. In contrast, the number of c-Fos-positive nuclei in the DB-treated group significantly increased 1 h after gavage. Thereafter, the number of c-Fos immunoreactive nuclei decreased over time. The number of c-Fos immunoreactive nuclei in the NTS was also increased in a dose-dependent manner 1 h after gavage. Subdiaphragmatic vagotomy significantly decreased DB-induced neuronal activation in the NTS. These results suggest that intragastric DB increases neuronal c-Fos expression in the NTS 1 h after gavage and this effect is mediated by vagal afferent fibers.

Role of enteric neurotransmission in host defense and protection of the gastrointestinal tract

Host defense is a vital role played by the gastrointestinal tract. As host to an enormous and diverse microbiome, the gut has evolved an elaborate array of chemical and physicals barriers that allow the digestion and absorption of nutrients without compromising the mammalian host. The control of such barrier functions requires the integration of neural, humoral, paracrine and immune signaling, involving redundant and overlapping mechanisms to ensure, under most circumstances, the integrity of the gastrointestinal epithelial barrier. Here we focus on selected recent developments in the autonomic neural control of host defense functions used in the protection of the gut from luminal agents, and discuss how the microbiota may potentially play a role in enteric neurotransmission. Key recent findings include: the important role played by subepithelial enteric glia in modulating intestinal barrier function, identification of stress-induced mechanisms evoking barrier breakdown, neural regulation of epithelial cell proliferation, the role of afferent and efferent vagal pathways in regulating barrier function, direct evidence for bacterial communication to the enteric nervous system, and microbial sources of enteric neurotransmitters. We discuss these new and interesting developments in our understanding of the role of the autonomic nervous system in gastrointestinal host defense.

Injection of Lactobacillus casei strain Shirota affects autonomic nerve activities in a tissue-specific manner, and regulates glucose and lipid metabolism in rats.

Previously, it was observed that long-term ingestion of a probiotic strain Lactobacillus casei Shirota (LcS) ameliorates insulin resistance and glucose intolerance in rats fed a high-fat diet. In the present study, we examined its possible role in the autonomic nervous system during LcS-induced modulations in glucose and lipid metabolism or cardiovascular functions. The present study examined the effects of intragastric (IG) LcS injection on autonomic nerve tones in anesthetized rats by electrophysiological method. We found that an IG injection of LcS suppressed neural activity of sympathetic nerves supplying the white adipose tissue of urethane-anesthetized rats in a dose-dependent manner, whereas sympathetic nerve outflow to brown adipose tissue was not affected by the IG LcS injection. Furthermore, the IG LcS injection reduced efferent sympathetic nerve outflow to the adrenal gland and liver, but did not alter gastric vagal nerve activity, renal sympathetic nerve activity, as well as mean arterial pressure. To test the involvement of afferent vagal nerves and the abdominal organs, we examined the adrenal sympathetic response to an LcS injection in rats with ablated afferent vagal nerves, and found that the adrenal sympathetic nerve response to LcS was inhibited in vagotomized rats. In addition, we found that oral ingestion of LcS attenuated the hyperglycemic response to glucose loading and blood glycerol levels in conscious rats. Our data suggest that LcS might affect tissue-specific autonomic nerves through the afferent vagal nerve pathway to modulate glucose and lipid metabolism.

Selective inhibition of vagal afferent nerve pathways regulating cough using Nav 1.7 shRNA silencing in guinea pig nodose ganglia

Adeno-associated virus delivery systems and short hairpin RNA (shRNA) were used to selectively silence the voltage-gated sodium channel NaV 1.7 in the nodose ganglia of guinea pigs. The cough reflex in these animals was subsequently assessed. NaV 1.7 shRNA was delivered to the majority of nodose ganglia neurons [50-60% transfection rate determined by green fluorescent protein (GFP) gene cotransfection] and action potential conduction in the nodose vagal nerve fibers, as evaluated using an extracellular recording technique, was markedly and significantly reduced. By contrast, <5% of neurons in the jugular vagal ganglia neurons were transfected, and action potential conduction in the jugular vagal nerve fibers was unchanged. The control virus (with GFP expression) was without effect on action potential discharge and conduction in either ganglia. In vivo, NaV 1.7 silencing in the nodose ganglia nearly abolished cough evoked by mechanically probing the tracheal mucosa in anesthetized guinea pigs. Stimuli such as capsaicin and bradykinin that are known to stimulate both nodose and jugular C-fibers evoked coughing in conscious animals was unaffected by NaV 1.7 silencing in the nodose ganglia. Nodose C-fiber selective stimuli including adenosine, 2-methyl-5-HT, and ATP all failed to evoke coughing upon aerosol challenge. These results indicate that cough is independently regulated by two vagal afferent nerve subtypes in guinea pigs, with nodose Aδ fibers regulating cough evoked mechanically from the trachea and bradykinin- and capsaicin-evoked cough regulated by C-fibers arising from the jugular ganglia.

The heat is on: does direct application of capsaicin to autonomic nerves produce a specific deafferentation?

The discovery that capsaicin could excite and block transmission in small-diameter afferent nerve fibres provided an important tool for many researchers to investigate the role of this class of neuron in the regulation of physiological and pathophysiological processes. Systemic administration of capsaicin to neonatal animals produces a life-long deafferentation of all capsaicin-sensitive neurons and, in adults, produces a temporary ‘defunctionalization’ (Holzer, 1991). However, for those interested in reflex regulation of gastrointestinal (GI) function, these useful techniques were limited because the gut receives a dual afferent innervation from both the craniosacral and the thoracolumbar outflow from the central nervous system. The use of perineural application of capsaicin to nerve bundles provided an extremely important tool to determine the specific role of an afferent pathway in homeostatic reflexes. For example, total cervical or subdiaphragmatic vagal transection had been used experimentally to demonstrate a vago-vagal reflex pathway in the regulation of gastric motility and secretion, but delineation of the vagal afferent pathway was confounded by concomitant removal of the vagal efferent pathway. Application of capsaicin to the cervical vagal trunks clearly showed a role for the vagal afferent pathway in mediating inhibition of gastric emptying in response to gut peptides and intestinal nutrients (Raybould & Tache, 1988; Raybould & Holzer, 1992). Taken together with morphological studies (in particular those of Powley and his group; see Powley & Philips, 2002) and electrophysiological recordings (for example, Blackshaw & Grundy, 1990), the importance of vagal afferent neurons in the regulation of postprandial gastrointestinal function became evident. Observations using perineural application of capsaicin were also key in uncovering the ability of the gut peptide cholecystokinin to act via the vagal afferent pathway to inhibit food intake (South & Ritter, 1988). Fast forwarding to today, these initial observations led to profound changes in the way we think about the role of the gut and the gut–brain axis in control of body weight and glucose homeostasis. Decades later, however, it is not necessarily surprising to find that direct application of capsaicin to nerve bundles does not produce a specific ‘defunctionalization’ of afferent neurons, as previously supposed (or hoped). In this issue of The Journal of Physiology, Browning et al. (2013) convincingly show that perivagal application of capsaicin induces a degeneration of vagal efferent neurons and a decrease in vagal efferent responses. Researchers using perineural application of capsaicin attempted to control for the specificity of the treatment, but Browning et al. (2013) perform a number of well-designed morphological and electrophysiological experiments that clearly show the lesion produced by perivagal application of capsaicin is not restricted to vagal afferent fibres. One can quibble with the technique of capsaicin application – the use of DMSO and ethanol as the vehicle rather than oil as used by most previous investigators – oil allows for a much more controlled, local application with reduced risk of systemic absorption. The important message from the data in this study is to call into question some previous conclusions that the vagal afferent pathway is the sole mediator of changes in GI function in response to peripheral stimuli. The receptor for capsaicin has been identified and mapped, and capsaicin (particularly at high concentrations) has been shown to have non-TRPV1 receptor-mediated effects. Earlier publications showing altered functional response to vagal ‘efferent’ stimulation by perineural application of capsaicin ascribed these unexpected effects to retrograde activation of vagal afferent neurons or the lack of input to second-order neurons in the nucleus tractus solitarii as being important in the function of the overall reflex pathway (Raybould et al. 1990; Thiefin et al. 1990). The data of Browning et al. (2013) suggest a different interpretation to explain these findings, and the authors urge caution in the use of this technique. Happily, since the heyday of the use of this technique in the 1980s and 1990s, the advent of different technologies, including transgenic mice with specific receptor deletions, have, to a large extent, reinforced initial observations from the early work using perineural application of capsaicin. While past studies may have been overinterpreted, the central tenet that the vagal afferent pathway plays a crucial role in the control of GI function and food intake remains vindicated.

Valsartan, a specific angiotensin II receptor blocker, inhibits pancreatic fluid secretion via vagal afferent pathway in conscious rats

Background/aimThe renin–angiotensin system (RAS) exists in the pancreas, but the role of RAS in the regulation of pancreatic exocrine secretion under physiological conditions has been little known. The present study addressed the RAS's effect on the pancreatic secretion by using valsartan, a specific angiotensin II receptor blocker, in conscious rats. MethodMale Wistar rats prepared with pancreatic, biliary, duodenal and jugular vein cannulas were used. To examine the role of RAS in the pancreatic secretion, valsartan at 1, 5, or 25mg/kg was administered into the duodenum via cannula, and volume of pancreatic juice and protein concentration were determined. In addition, to examine the role of RAS in hormone-stimulated pancreatic hypersecretion, pancreatic secretion was examined in response to stimulation of secretin or cholecystokinin after intraduodenal infusion of valsartan at 25mg/kg. Furthermore, to examine the mechanism of action of RAS on pancreatic secretion, intravenous infusion of atropine or perivagal application of capsaicin was conducted and then the pancreatic secretion was examined following intraduodenal infusion of valsartan at 25mg/kg. ResultsVolume of pancreatic juice, but not protein output, significantly decreased after administration of valsartan. However, administration of valsartan did not exert significant effects on secretin- or cholesystokinin-stimulated pancreatic secretion. Treatment with atropine and perivagal application of capsaicin completely abolished the suppressive effect of valsartan on pancreatic juice secretion. ConclusionPresent results suggest that RAS plays a stimulatory role in pancreatic juice secretion via cholinergic afferent pathway without affecting protein secretion and hormonally stimulated pancreatic secretion under physiological conditions.

Peripheral neural targets in obesity.

Interest in pharmacological treatments for obesity that act in the brain to reduce appetite has increased exponentially over recent years, but failures of clinical trials and withdrawals due to adverse effects have so far precluded any success. Treatments that do not act within the brain are, in contrast, a neglected area of research and development. This is despite the fact that a vast wealth of molecular mechanisms exists within the gut epithelium and vagal afferent system that could be manipulated to increase satiety. Here we discuss mechano- and chemosensory pathways from the gut involved in appetite suppression, and distinguish between gastric and intestinal vagal afferent pathways in terms of their basic physiology and activation by enteroendocrine factors. Gastric bypass surgery makes use of this system by exposing areas of the intestine to greater nutrient loads resulting in greater satiety hormone release and reduced food intake. A non-surgical approach to this system is preferable for many reasons. This review details where the opportunities may lie for such approaches by describing nutrient-sensing mechanisms throughout the gastrointestinal tract.

896 Protease-Activated Receptor 2 Activates Transient Receptor Potential Vanilloid 4 by SRC Kinase-Mediated Tyrosine Phosphorylation

Introduction: PGD2 is an important mediator released after mast cell activation. Our previous studies demonstrated PGD2 sensitizes esophageal nodose C-fibers to increase their response to esophageal distension. This study aims to determine the underlying mechanism of the sensitization process. Methods: PGD2 DP1 receptor expressions in nodose neurons were determined by immunofluorescent-staining, Western blot, and RT-PCR. Extracellular single fiber recordings were performed from vagal nodose neurons using ex vivo esophageal-vagal preparations with intact nerve endings in the esophagus. We recorded action potentials evoked by esophageal distensions before and after perfusion of PGD2 with/without pretreatment of DP1 receptor antagonist BWA 868C. Whole-cell patch-clamp recording was performed to investigate the action of PGD2 on isolated nodose neurons. Viscermotor responses (VMR) to esophageal distension were recorded by electromyography from acromiotrapezius muscles in animals receiving PGD2 injection (20 μl, 100 nM) into the wall of the esophagus before and after truncal vagatomy. Results: DP1 receptor expressions were identified in nodose neurons by immunofluorescent-labeling, Western blot, and RT-PCR. 98% of DP1positive neurons were of smalland medium-diameters (φ 0.05, n=4). Whole-cell patch-clamp recording from isolated nodose neurons demonstrated PGD2 (1 μM) depolarized recorded neurons (13±2 mV, n=5) accompanied by an increase in the neuronal input resistance from 360±20 to 420±25 MΩ. IV relationship studies showed current reversed at 105 mV suggesting the effect was mediated by the closure of K+ channel(s). Compared to controls, PGD2 injection into the esophagus significantly enhanced esophageal distension evoked-VMRs at distension pressures 20, 40, 60, and 80 mmHg respectively (p <0.05, n=3). Left truncal vagatomy attenuated PGD2induced enhancements of VMR in response to esophageal distension (p <0.05, n=3) indicating the participation of vagal afferent pathway in this sensitization process. Conclusion: These data demonstrate mast cell mediator PGD2 plays a crucial role in sensitization of esophageal nodose C-fiber neurons to induce esophageal mechanical hypersensitivity. This sensitization effect is mediated via DP1 receptor and involves downstream K+ channel.

898 Chronic Stress-Induced Visceral Hyperalgesia: Evidence That the Formation of CB1 and TRPV1 Receptor Complexes Modulates Pain in Dorsal Root Ganglion (DRG) Neurons

Introduction: PGD2 is an important mediator released after mast cell activation. Our previous studies demonstrated PGD2 sensitizes esophageal nodose C-fibers to increase their response to esophageal distension. This study aims to determine the underlying mechanism of the sensitization process. Methods: PGD2 DP1 receptor expressions in nodose neurons were determined by immunofluorescent-staining, Western blot, and RT-PCR. Extracellular single fiber recordings were performed from vagal nodose neurons using ex vivo esophageal-vagal preparations with intact nerve endings in the esophagus. We recorded action potentials evoked by esophageal distensions before and after perfusion of PGD2 with/without pretreatment of DP1 receptor antagonist BWA 868C. Whole-cell patch-clamp recording was performed to investigate the action of PGD2 on isolated nodose neurons. Viscermotor responses (VMR) to esophageal distension were recorded by electromyography from acromiotrapezius muscles in animals receiving PGD2 injection (20 μl, 100 nM) into the wall of the esophagus before and after truncal vagatomy. Results: DP1 receptor expressions were identified in nodose neurons by immunofluorescent-labeling, Western blot, and RT-PCR. 98% of DP1positive neurons were of smalland medium-diameters (φ 0.05, n=4). Whole-cell patch-clamp recording from isolated nodose neurons demonstrated PGD2 (1 μM) depolarized recorded neurons (13±2 mV, n=5) accompanied by an increase in the neuronal input resistance from 360±20 to 420±25 MΩ. IV relationship studies showed current reversed at 105 mV suggesting the effect was mediated by the closure of K+ channel(s). Compared to controls, PGD2 injection into the esophagus significantly enhanced esophageal distension evoked-VMRs at distension pressures 20, 40, 60, and 80 mmHg respectively (p <0.05, n=3). Left truncal vagatomy attenuated PGD2induced enhancements of VMR in response to esophageal distension (p <0.05, n=3) indicating the participation of vagal afferent pathway in this sensitization process. Conclusion: These data demonstrate mast cell mediator PGD2 plays a crucial role in sensitization of esophageal nodose C-fiber neurons to induce esophageal mechanical hypersensitivity. This sensitization effect is mediated via DP1 receptor and involves downstream K+ channel.

Reappraisal of the role of dolasetron in prevention and treatment of nausea and vomiting associated with surgery or chemotherapy

Chemotherapy-induced nausea and vomiting and postoperative nausea and vomiting are one of the most frequent but also very concerning consequences for patients undergoing chemotherapy or surgical procedures under general anesthesia. There are a variety of mechanisms involved in the activation of nausea and vomiting. Serotonin, a ubiquitous central and peripheral neurotransmitter, is thought to be the predominant mediator of the perception of nausea and triggering of the vomiting response in both the brain and the periphery via the 5-hydroxytryptamine type 3 (5-HT(3)) receptor pathways. 5-HT(3) receptor antagonists disrupt this pathway, largely at the level of the vagal afferent pathways, to decrease nausea and vomiting. This review will focus on dolasetron, an older but sill commonly used 5-HT(3) receptor antagonist and its multimodal mechanism of action, safety and tolerability, patient considerations, and a review of the current literature on its use to combat both chemotherapy-induced and postoperative nausea and vomiting in these two important patient populations.

Abdominal vagal afferent pathways and their distributions of intraganglionic laminar endings in the rat duodenum

We examined abdominal vagal afferents (n = 33) and the distributions of their intraganglionic laminar endings (IGLEs) in the duodenum. Rats (male, Sprague-Dawley) received a partial subdiaphragmatic vagotomy that spared a single branch. Wheat germ agglutinin-horseradish peroxidase (0.5-1.0 μl) was injected into the nodose ganglion ipsilateral to the vagotomized side. We observed that the hepatic branch does not project to the stomach, that the accessory celiac and celiac branches course along the celiac artery and innervate the intestines, and that the left nodose afferents innervate predominantly the duodenum. The hepatic branch innervates the duodenum via the "hepatoduodenal" subbranch and has the densest IGLE distribution in both the dorsoventral and the rostrocaudal extensions of the first 4-cm segment. Both gastric branches have two subbranches that innervate the duodenum; the "lesser curvature" subbranches follow the lesser curvature artery and may join the "hepatoduodenal" subbranch, whereas the "pyloric" subbranches run through the antrum and pylorus to reach the proximal duodenum. Moreover, the subbranches of ventral and dorsal gastric branches innervate more in the ventral and dorsal parts of the duodenum, respectively, and have more IGLEs in the rostral region than in the caudal. A posteriori comparisons indicate that, in the first-centimeter segment, the ventral gastric branch has significantly more IGLEs, whereas, in the third- and fourth-centimeter segments, the hepatic branch has more IGLEs. The finding that three different vagal branches innervate the duodenum with different densities of afferent endings might indicate a viscerotopic receptive field that coordinates digestive functions in feeding.