Vagal Afferent Input Research Articles

Parallel gut-to-brain pathways orchestrate feeding behaviors.

The caudal nucleus of the solitary tract (cNTS) in the brainstem serves as a hub for integrating interoceptive cues from diverse sensory pathways. However, the mechanisms by which cNTS neurons transform these signals into behaviors remain debated. We analyzed 18 cNTS-Cre mouse lines and cataloged the dynamics of nine cNTS cell types during feeding. We show that Th+ cNTS neurons encode esophageal mechanical distension and transient gulp size via vagal afferent inputs, providing quick feedback regulation of ingestion speed. By contrast, Gcg+ cNTS neurons monitor intestinal nutrients and cumulative ingested calories and have long-term effects on food satiation and preference. These nutritive signals are conveyed through a portal vein-spinal ascending pathway rather than vagal sensory neurons. Our findings underscore distinctions among cNTS subtypes marked by differences in temporal dynamics, sensory modalities, associated visceral organs and ascending sensory pathways, all of which contribute to specific functions in coordinated feeding regulation.

Viscerosensory signalling to the nucleus accumbens via the solitary tract nucleus.

The nucleus of the solitary tract (NTS) receives direct viscerosensory vagal afferent input that drives autonomic reflexes, neuroendocrine function and modulates behaviour. A subpopulation of NTS neurons project to the nucleus accumbens (NAc); however, the function of this NTS-NAc pathway remains unknown. A combination of neuroanatomical tracing, slice electrophysiology and fibre photometry was used in mice and/or rats to determine how NTS-NAc neurons fit within the viscerosensory network. NTS-NAc projection neurons are predominantly located in the medial and caudal portions of the NTS with 54 ± 7% (mice) and 65 ± 3% (rat) being TH-positive, representing the A2 NTS cell group. In horizontal brainstem slices, solitary tract (ST) stimulation evoked excitatory post-synaptic currents (EPSCs) in NTS-NAc projection neurons. The majority (75%) received low-jitter, zero-failure EPSCs characteristic of monosynaptic ST afferent input that identifies them as second order to primary sensory neurons. We then examined whether NTS-NAc neurons respond to cholecystokinin (CCK, 20 μg/kg ip) invivo in both mice and rats. Surprisingly, there was no difference in the number of activated NTS-NAc cells between CCK and saline-treated mice. In rats, just 6% of NTS-NAc cells were recruited by CCK. As NTS TH neurons are the primary source for NAc noradrenaline, we measured noradrenaline release in the NAc and showed that NAc noradrenaline levels declined in response to cue-induced reward retrieval but not foot shock. Combined, these findings suggest that high-fidelity afferent information from viscerosensory afferents reaches the NAc. These signals are likely unrelated to CCK-sensitive vagal afferents but could interact with other sensory and higher order inputs to modulate learned appetitive behaviours.

Analysis of the distribution of vagal afferent projections from different peripheral organs to the nucleus of the solitary tract in rats.

Anatomical tracing studies examining the vagal system can conflate details of sensory afferent and motor efferent neurons. Here, we used a serotype of adeno-associated virus that transports retrogradely and exhibits selective tropism for vagal afferents, to map their soma location and central termination sites within the nucleus of the solitary tract (NTS). We examined the vagal sensory afferents innervating the trachea, duodenum, stomach, or heart, and in some animals, from two organs concurrently. We observed no obvious somatotopy in the somata distribution within the nodose ganglion. The central termination patterns of afferents from different organs within the NTS overlap substantially. Convergence of vagal afferent inputs from different organs onto single NTS neurons is observed. Abdominal and thoracic afferents terminate throughout the NTS, including in the rostral NTS, where the 7th cranial nerve inputs are known to synapse. To address whether the axonal labeling produced by viral transduction is so widespread because it fills axons traveling to their targets, and not just terminal fields, we labeled pre and postsynaptic elements of vagal afferents in the NTS . Vagal afferents form multiple putative synapses as they course through the NTS, with each vagal afferent neuron distributing sensory signals to multiple second-order NTS neurons. We observe little selectivity between vagal afferents from different visceral targets and NTS neurons with common neurochemical phenotypes, with afferents from different organs making close appositions with the same NTS neuron. We conclude that specific viscerosensory information is distributed widely within the NTS and that the coding of this input is probably determined by the intrinsic properties and projections of the second-order neuron.

Modeling and simulation of vagal afferent input of the cough reflex

We employed computational modeling to investigate previously conducted experiments of the effect of vagal afferent modulation on the cough reflex in an anesthetized cat animal model. Specifically, we simulated unilateral cooling of the vagus nerve and analyzed characteristics of coughs produced by a computational model of brainstem cough/respiratory neuronal network. Unilateral vagal cooling was simulated by a reduction of cough afferent input (corresponding to unilateral vagal cooling) to the cough network. All these attempts resulted in only mild decreases in investigated cough characteristics such as cough number, amplitudes of inspiratory and expiratory cough efforts in comparison with experimental data. Multifactorial alterations of model characteristics during cough simulations were required to approximate cough motor patterns that were observed during unilateral vagal cooling in vivo. The results support the plausibility of a more complex NTS processing system for cough afferent information than has been proposed.

Effects of methyl methacrylate on the excitability of the area postrema neurons in rats

ObjectivesThe aim of the present study is to demonstrate the effects of inhaled methyl methacrylate (MMA) on the excitability of neurons in the area postrema (AP). We also investigated the relation between vagal afferent inputs and responding cells in the AP. MethodsWe set up two groups of experimental animals, such as rats inhaling MMA and rats inhaling room air. To visualize the changes of AP neuron excitability after inhalation of MMA for 90 min, c-Fos protein expression was identified and quantified by immunohistochemical analysis. Some rats receiving ventral gastric branch vagotomy were also subjected to the abovementioned experiment. ResultsThe number of c-Fos-immunoreactive (Fos-ir) cells in the MMA group was more than six times greater than that of the control group (statistically significant, p < 0.01). In vagotomized rats inhaling MMA, markedly smaller number of Fos-ir cells was identified in the AP compared to that of rats inhaling MMA without vagotomy. ConclusionsThese results indicate that inhalation of MMA increases neuronal excitability in the AP, suggesting that vagal afferent inputs are involved in the induction mechanism of Fos-ir cells by MMA.

Stimulation of the vagus nerve reduces learning in a go/no-go reinforcement learning task

When facing decisions to approach rewards or to avoid punishments, we often figuratively go with our gut, and the impact of metabolic states such as hunger on motivation are well documented. However, whether and how vagal feedback signals from the gut influence instrumental actions is unknown. Here, we investigated the effect of non-invasive transcutaneous auricular vagus nerve stimulation (taVNS) vs. sham (randomized cross-over design) on approach and avoidance behavior using an established go/no-go reinforcement learning paradigm in 39 healthy human participants (23 female) after an overnight fast. First, mixed-effects logistic regression analysis of choice accuracy showed that taVNS acutely impaired decision-making, p = .041. Computational reinforcement learning models identified the cause of this as a reduction in the learning rate through taVNS (∆α = −0.092, pboot = .002), particularly after punishment (∆αPun = −0.081, pboot = .012 vs. ∆αRew =−0.031, pboot = .22). However, taVNS had no effect on go biases, Pavlovian response biases or response time. Hence, taVNS appeared to influence learning rather than action execution. These results highlight a novel role of vagal afferent input in modulating reinforcement learning by tuning the learning rate according to homeostatic needs.

Adeno Associated Virus Mediated Neural Tracing of TRPV1‐Expressing Airway Afferent Nerves

The various sensory nerve subtypes deliver different types of information to brainstem in which the integration of the information takes place to regulate respiratory reflexes. The bronchopulmonary C‐fibers, the main sensory afferent regulating respiratory reflexes, arise from vagal ganglia and those are known to innervate the nucleus of the solitary tract in the medulla. However, the innervation patterns may vary depending on the subsets of vagal afferents. Vagal afferent nerve subtypes express particular ion channels/receptors which are stimulated by various stimuli resulting in different information being conveyed to the brainstem. The variation makes it difficult to understand how distinct peripheral vagal afferent inputs are processed in the central nervous system.In the current study, we determined the central projections of Transient receptor potential vanilloid 1 (TRPV1)‐expressing vagal sensory afferent innervating the airways using AAV mediated retrograde neural tracing. TRPV1 is expressed on nociceptive afferents involved in defensive/protective reflexes (e.g. cough, apnea). TRPV1‐Cre mice were used, along with a rAAV2 vector with a flex‐tdTomato reporter. In the presence of cre the AAV will be recombined to express tdTomato. Without cre the AAV does not express the reporter. Mice (6 to 8‐week‐old) received intratracheal instillation of AAV virus and housed for three weeks. Vagal ganglia and brainstem were collected and cryosectioned sequentially. Immunohistochemistry was performed and images were taken using Olympus FV1200 confocal microscope.As a result, we observed tdTomato labeled cells and nerves in vagal ganglia. With immunohistochemistry using anti‐DsRed and anti‐TRPV1 antibodies, we confirmed that the red fluorescent cells and nerves are TRPV1 positive. In medulla, we were able to see tdTomato labeled projections starting from caudal (approximately −780 μm to obex) to rostral (approximately +210 μm to obex) ends of medulla. The tdTomato labeled projections are mainly located in the nucleus of solitary tract (NTS) as well as along the solitary tract. The tdTomato labeled projections were seen mainly in gelatinous NTS and dorsolateral NTS, as well as in area postrema. These data suggest that airway nociceptor central terminals are located within a specific region of the NTS.Support or Funding InformationThis study is funded by National Institutes of Health Common Fund SPARC OT2 (2016–2019): “Functional mapping of peripheral and central circuits for airway protection and breathing”This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Vagal afferents contribute to sympathoexcitation-driven metabolic dysfunctions.

Multiple crosstalk between peripheral organs and the nervous system are required to maintain physiological and metabolic homeostasis. Using Vav3-deficient mice as a model for chronic sympathoexcitation-associated disorders, we report here that afferent fibers of the hepatic branch of the vagus nerve are needed for the development of the peripheral sympathoexcitation, tachycardia, tachypnea, insulin resistance, liver steatosis and adipose tissue thermogenesis present in those mice. This neuronal pathway contributes to proper activity of the rostral ventrolateral medulla, a sympathoregulatory brainstem center hyperactive in Vav3-/- mice. Vagal afferent inputs are also required for the development of additional pathophysiological conditions associated with deregulated rostral ventrolateral medulla activity. By contrast, they are dispensable for other peripheral sympathoexcitation-associated disorders sparing metabolic alterations in liver.

Central Respiration and Mechanical Ventilation in the Gating of Swallow With Breathing.

Swallow-breathing coordination safeguards the lower airways from tracheal aspiration of bolus material as it moves through the pharynx into the esophagus. Impaired movements of the shared muscles or structures of the aerodigestive tract, or disruptions in the interaction of brainstem swallow and respiratory central pattern generators (CPGs) result in dysphagia. To maximize lower airway protection these CPGs integrate respiratory rhythm generation signals and vagal afferent feedback to synchronize swallow with breathing. Despite extensive study, the roles of central respiratory activity and vagal feedback from the lungs as key elements for effective swallow-breathing coordination remain unclear. The effect of altered timing of bronchopulmonary vagal afferent input on swallows triggered during electrical stimulation of the superior laryngeal nerves or by injection of water into the pharyngeal cavity was studied in decerebrate, paralyzed, and artificially ventilated cats. We observed two types of single swallows that produced distinct effects on central respiratory-rhythm across all conditions: post-inspiratory type swallows disrupted central-inspiratory activity without affecting expiration, whereas expiratory type swallows prolonged expiration without affecting central-inspiratory activity. Repetitive swallows observed during apnea reset the E2 phase of central respiration and produced facilitation of swallow motor output nerve burst durations. Moreover, swallow initiation was negatively modulated by vagal feedback and was reset by lung inflation. Collectively, these findings support a novel model of reciprocal inhibition between the swallow CPG and inspiratory or expiratory cells of the respiratory CPG where lung distension and phases of central respiratory activity represent a dual peripheral and central gating mechanism of swallow-breathing coordination.

Fluorescent Based Tracing of Sensory Nerve Subtypes in Brainstem

Processing vagal and trigeminal afferent inputs in the brainstem is essential for regulating reflexes including those from the respiratory tract. Afferent nerves can be categorized into several subtypes depending on the ganglionic origin of cell bodies (placodal vs. neural crest), conduction velocity and response patterns to stimuli. These various nerve subtypes convey different types of information which is integrated at the brainstem to control respiratory reflexes. Vagal afferent nerve subtypes express particular ion channels/receptors which are stimulated by various stimuli resulting in different information being relayed to the brainstem. For example, stimulation of vagal jugular C‐fiber nociceptors evokes cough, whereas stimulation of vagal nodose C‐fiber nociceptors inhibits cough. Vagal afferents are known to innervate the nucleus of the solitary tract in the dorsal medulla. However, the innervation patterns may vary depending on the subsets of vagal afferents. The variation makes it difficult to understand how distinct peripheral vagal afferent inputs are processed in the central nervous system.In the current study, we focused on developing a neuroanatomical map of various sensory afferent nerve subtypes using a transgenic mouse model system. Cre‐LoxP reporter system allows us to target the specific ion channel/receptor positive sensory nerve subtypes enabling tracking of afferent nerve subtypes throughout medulla. Transient receptor potential vanilloid 1 (Trpv1), tachykinin 1 (Tac1) and 5‐hydroxytriptamine receptor 3 (5HT3) Cre strains were bred with Floxed Ai9 ROSA tdTomato; thus, expressing red fluorescent specific to Trpv1, Tac1 and 5HT3 positive cells. Mice (6 to 8‐week‐old) were euthanized and tissue was collected. Brainstem were cryosectioned at 30 μm thickness and slide mounted sequentially. Additionally, we used a passive tissue clearing technique (CLARITY‐PACT) to visualize the sensory nerve projections in dissected whole medulla. Images were taken using Nikon Eclipse microscope and Olympus FV1200 confocal microscope. The 3D images were processed with Imaris software.As a result, we were able to identify each sensory nerve subtype in the medulla and define their projections to different regions of medulla ‐ these include the nucleus of solitary tract (NTS), paratrigeminal nucleus (Pa5) and spinal trigeminal tract (sp5). While brainstem projection of the Trpv1, Tac1 and 5ht3 Cre/Rosa strains showed similarities in gross regional expression, the patterns of these projections were distinct depending on the strains. For example, Trpv1‐tdTomato projections were found in the commissural NTS but not the medial NTS, whereas Tac1‐tdTomato projections were largely absent from the commissural NTS but were abundantly present in the medial NTS. The only overlap of Trpv1 and Tac1 projections was not in the NTS, but rather in Pa5 and sp5, suggesting that vagal jugular C‐fiber nociceptors may terminate in Pa5 as opposed to the NTS. The cleared whole medulla from each strain were consistent with the medulla sections and were used to yield 3D maps of the sensory afferent nerve projections. Based on these observations, a genetic tool using Cre‐LoxP reporter system allowed us to define the neuronal circuitry of major vagal sensory afferent nerve subtypes. This information may be useful to study functionalities of each sensory nerve subtypes to better understand the mechanism of respiratory reflexes.Support or Funding InformationNIH Common Fund SPARC OT2This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

New insights into a decerebrate feline model of swallow‐breathing coordination

In the medulla, the swallow and respiratory central pattern generators (CPGs) interact to coordinate swallow initiation and permit swallow execution during the expiratory phase of breathing. Disruption of swallow‐breathing coordination can result in dysphagia, which is a major cause of morbidity and mortality in many neuro‐muscular diseases, especially stroke. Despite extensive study, the precise mechanisms of swallow‐breathing coordination are not known. We tested the hypothesis that both central inspiratory activity and vagal feedback from the lungs are key elements for effective swallow‐breathing coordination. Swallows were triggered by electrical stimulation of the superior laryngeal nerves (SLN) or by injection of water into the pharyngeal cavity in decerebrate, paralyzed and artificially ventilated cats while motor activities were recorded from phrenic, hypoglossal, lumbar and vagal nerves. Mechanical ventilation was either triggered by central inspiratory activity or set independently from the phrenic activity to alter the timing of bronchopulmonary vagal afferent input and allow analysis of its influence on swallow‐breathing coordination. We observed two types of swallows that produced opposite effects on central respiratory‐rhythm resetting across all conditions: post‐Inspiratory type swallows disrupted central I activity without affecting expiration, whereas expiratory type swallows prolonged expiration without affecting central inspiratory activity. Repetitive swallows observed during apnea reset the E2 phase of central respiration and produced facilitation of swallow motor output. Moreover, swallow initiation was negatively modulated by vagal feedback and was reset by lung inflation. Collectively, these findings support a reciprocal inhibition between central inspiration and the swallow CPG and they are consistent with a role for pulmonary stretch receptors in the coordination between brainstem CPGs for breathing and swallowing. They may also prove relevant for healthcare management of dysphagia.Support or Funding InformationOT2OD023854‐01, HL109025This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Chronic kidney disease impairs renal nerve and haemodynamic reflex responses to vagal afferent input through a central mechanism

We investigated age- and sex-related changes in reflex renal sympathetic nerve activity (RSNA) and haemodynamic responses to vagal afferent stimulation in a rodent model of chronic kidney disease (CKD). Using anaesthetised juvenile (7-8weeks) and adult (12-13weeks) Lewis Polycystic Kidney (LPK) and Lewis control rats of either sex (n=63 total), reflex changes in RSNA, heart rate (HR) and mean arterial pressure (MAP) to vagal afferent stimulation (5-s train, 4.0V, 2.0-ms pulses, 1-16Hz) were measured. In all groups, stimulation of the vagal afferents below 16Hz produced frequency-dependent reductions in RSNA, HR and MAP, while a 16Hz stimulus produced an initial sympathoinhibition followed by sympathoexcitation. In juvenile LPK versus age-matched Lewis, sympathoinhibition was reduced when responses were expressed as % baseline (P<0.05), but not as microvolts, while bradycardic responses were greater. Reflex depressor responses were greater (P=0.015) only in juvenile female LPK. In adult LPK, reflex sympathoinhibition (%) was blunted (P<0.05), and an age-related decline apparent (when expressed as microvolts). Reflex reductions in HR and MAP were only diminished (P<0.05) in adult female LPK versus age-matched Lewis. Peak reflex sympathoexcitation at 16Hz did not differ between groups; however, area under the curve values were greater in the LPK versus Lewis (overall, 9±1 versus 19±3μVs, P<0.05) irrespective of age, suggestive of enhanced sympathoexcitatory drive in the LPK. Our data demonstrates a progressive deficit in the central processing of vagal afferent input and a differential sex influence on reflex regulation of autonomic function and blood pressure homeostasis in CKD.

A high-fat diet impairs cooling-evoked brown adipose tissue activation via a vagal afferent mechanism.

In dramatic contrast to rats on a control diet, rats maintained on a high-fat diet (HFD) failed to activate brown adipose tissue (BAT) during cooling despite robust increases in their BAT activity following direct activation of their BAT sympathetic premotor neurons in the raphe pallidus. Cervical vagotomy or blockade of glutamate receptors in the nucleus of the tractus solitarii (NTS) reversed the HFD-induced inhibition of cold-evoked BAT activity. Thus, a HFD does not prevent rats from mounting a robust, centrally driven BAT thermogenesis; however, a HFD does alter a vagal afferent input to NTS neurons, thereby preventing the normal activation of BAT thermogenesis to cooling. These results, paralleling the absence of cooling-evoked glucose uptake in the BAT of obese humans, reveal a neural mechanism through which consumption of a HFD contributes to reduced energy expenditure and thus to weight gain.

Mechanistic relationship between the vagal afferent pathway, central nervous system and peripheral organs in appetite regulation

The hypothalamus is a center of food intake and energy metabolism regulation. Information signals from peripheral organs are mediated through the circulation or the vagal afferent pathway and input into the hypothalamus, where signals are integrated to determine various behaviors, such as eating. Numerous appetite‐regulating peptides are expressed in the central nervous system and the peripheral organs, and interact in a complex manner. Of such peptides, gut peptides are known to bind to receptors at the vagal afferent pathway terminal that extend into the mucosal layer of the digestive tract, modulate the electrical activity of the vagus nerve, and subsequently send signals to the solitary nucleus and furthermore to the hypothalamus. All peripheral peptides other than ghrelin suppress appetite, and they synergistically suppress appetite through the vagus nerve. In contrast, the appetite‐enhancing peptide, ghrelin, antagonizes the actions of appetite‐suppressing peptides through the vagus nerve, and appetite‐suppressing peptides have attenuated effects in obesity as a result of inflammation in the vagus nerve. With greater understanding of the mechanism for food intake and energy metabolism regulation, medications that apply the effects of appetite‐regulating peptides or implantable devices that electrically stimulate the vagus nerve are being investigated as novel treatments for obesity in basic and clinical studies.

Localization of TRPV1 and P2X3 in unmyelinated and myelinated vagal afferents in the rat

The vagus nerve is dominated by afferent fibers that convey sensory information from the viscera to the brain. Most vagal afferents are unmyelinated, slow-conducting C-fibers, while a smaller portion are myelinated, fast-conducting A-fibers. Vagal afferents terminate in the nucleus tractus solitarius (NTS) in the dorsal brainstem and regulate autonomic and respiratory reflexes, as well as ascending pathways throughout the brain. Vagal afferents form glutamatergic excitatory synapses with postsynaptic NTS neurons that are modulated by a variety of channels. The organization of vagal afferents with regard to fiber type and channels is not well understood. In the present study, we used tract tracing methods to identify distinct populations of vagal afferents to determine if key channels are selectively localized to specific groups of afferent fibers. Vagal afferents were labeled with isolectin B4 (IB4) or cholera toxin B (CTb) to detect unmyelinated and myelinated afferents, respectively. We find that TRPV1 channels are preferentially found in unmyelinated vagal afferents identified with IB4, with almost half of all IB4 fibers showing co-localization with TRPV1. These results agree with prior electrophysiological findings. In contrast, we found that the ATP-sensitive channel P2X3 is found in a subset of both myelinated and unmyelinated vagal afferent fibers. Specifically, 18% of IB4 and 23% of CTb afferents contained P2X3. The majority of CTb-ir vagal afferents contained neither channel. Since neither channel was found in all vagal afferents, there are likely further degrees of heterogeneity in the modulation of vagal afferent sensory input to the NTS beyond fiber type.

Sa2028 Activation of Vagal Afferent Input Correlates With Reduced Meal Consumption in Rats With Gastric Sensory-Motor Dysfunctions and With Mood Disorders

G A A b st ra ct s medicine with ghrelin enhancing properties, is used to treat gastroparesis (Takahashi T et al. World J Surg 2009). Aim: To assess the brain sites activated by abdominal surgery in mice and whether rikkunshito modified this pattern and the inhibited food intake.Methods: RKT (0.5 g/kg/day) or vehicle (distilled water, 4 ml/kg) was given daily by gavage for 7 days and on day 8 at 6 h and 1 h before the surgery. Male mice (C57BL/6, 23-26 g) fasted for 6 h received laparotomy and cecal palpation under isoflurane anesthesia 2 h before the dark phase. Controls remained in home cages. For Fos immunohistochemistry in brain sections, mice were euthanized 2 h post-surgery. For food intake monitoring, mice were maintained in an automated feeding monitoring system (BioDAQ, Research Diet). Results: In vehicle-treated mice, there was moderate Fos immunoreactivity (ir) in the paraventricular nucleus (PVN), arcuate nucleus (Arc), and preoptic, lateral and dorsomedial areas of the hypothalamus, medial bed nucleus of stria terminalis and Edinger-westphal nucleus (E-W), which could be resulted from gavage and 6-h fasting. Abdominal surgery induced robust Fos-ir in the lateral septum, supraoptic nuclei (SON), PVN, Arc, lateral parabrachial nucleus, locus ceruleus, ventrolateral medulla and nucleus tractus solitarius (NTS); and moderate increase in Fos-ir in the prelimbic, insular and cingulate cortex, nucleus of accumbens, subfornical organ, E-W, periaqueductal area (PAG), Barrington's nucleus, A5 and area postrema. Compared to vehicle, RKT treatment in control mice induced significant more numbers of Fos-ir neurons of the SON (1.9±0.8 vs 6.2±1.0 cells/section) and E-W (22.7±1.1 vs 31.3±2.6). In mice received surgery, RKT induced a significant increase in Fos-ir in the lateral PAG (68.3±4.8 vs 49.5±5.4) and decrease in the NTS (82.4±4.1 vs 96.1±8.0). Abdominal surgery reduced food intake significantly at 6, 12 and 24 h by 83%, 94% and 94%, respectively compared to control. RKT resulted in a small, but significant increase in food intake at 6 and 12 h after surgery compared to vehicle plus surgery (0.31±0.04 vs 0.11±0.04, and 0.62±0.11 vs 0.37±0.01 g). Conclusion: Brain circuits of mice responsive to abdominal surgery include visceral regulatory centers, forebrain and midbrain areas involved in pain, and integrative nuclei related to stress. The partially restored food intake by RKT after abdominal surgery may reply on reducing the inhibitory inputs from the NTS related to visceral afferents and enhancing the descending pain inhibitory pathway via the PAG. Supported by Tsumura &Co., and NIH DDK-41303

Delineation of vagal emetic pathways: intragastric copper sulfate-induced emesis and viral tract tracing in musk shrews

Signals from the vestibular system, area postrema, and forebrain elicit nausea and vomiting, but gastrointestinal (GI) vagal afferent input arguably plays the most prominent role in defense against food poisoning. It is difficult to determine the contribution of GI vagal afferent input on emesis because various agents (e.g., chemotherapy) often act on multiple sensory pathways. Intragastric copper sulfate (CuSO4) potentially provides a specific vagal emetic stimulus, but its actions are not well defined in musk shrews (Suncus murinus), a primary small animal model used to study emesis. The aims of the current study were 1) to investigate the effects of subdiaphragmatic vagotomy on CuSO4-induced emesis and 2) to conduct preliminary transneuronal tracing of the GI-brain pathways in musk shrews. Vagotomy failed to inhibit the number of emetic episodes produced by optimal emetic doses of CuSO4 (60 and 120 mg/kg ig), but the effects of lower doses were dependent on an intact vagus (20 and 40 mg/kg). Vagotomy also failed to affect emesis produced by motion (1 Hz, 10 min) or nicotine administration (5 mg/kg sc). Anterograde transport of the H129 strain of herpes simplex virus-1 from the ventral stomach wall identified the following brain regions as receiving inputs from vagal afferents: the nucleus of the solitary tract, area postrema, and lateral parabrachial nucleus. These data indicate that the contribution of vagal pathways to intragastric CuSO4-induced emesis is dose dependent in musk shrews. Furthermore, the current neural tracing data suggest brain stem anatomical circuits that are activated by GI signaling in the musk shrew.

Characterization of the hypotensive effects of glucagon-like peptide-2 in anesthetized rats

Glucagon-like peptide-2 (GLP-2) is a proglucagon-derived peptide released from enteroendocrine cells and neurons. We recently reported that GLP-2 induced hypotension. In the present study, we characterized the mechanisms of GLP-2-induced hypotension. GLP-2 was administered peripherally or centrally to male Wistar rats anesthetized with urethane and α-chloralose. The rats were vagotomized or systemically pretreated with atropine, prazosin, or propranolol before the GLP-2 administration. The central and peripheral administration of GLP-2 reduced mean arterial blood pressure (MAP). The maximum change of MAP (maximum ΔMAP) was reduced by vagotomy or prazosin, but not propranolol. The effects of the central but not peripheral administration of GLP-2 were reduced by atropine. These results suggest that GLP-2 modulates vagal afferent inputs and inhibits the sympathetic nervous system in the brain to induce hypotension.

Vagal afferent fibres determine the oxytocin‐induced modulation of gastric tone

Oxytocin (OXT) inputs to the dorsal vagal complex (DVC; nucleus of the tractus solitarius (NTS) dorsal motor nucleus of the vagus (DMV) and area postrema) decrease gastric tone and motility. Our first aim was to investigate the mechanism(s) of OXT-induced gastric relaxation. We demonstrated recently that vagal afferent inputs modulate NTS-DMV synapses involved in gastric and pancreatic reflexes via group II metabotropic glutamate receptors (mGluRs). Our second aim was to investigate whether group II mGluRs similarly influence the response of vagal motoneurons to OXT. Microinjection of OXT in the DVC decreased gastric tone in a dose-dependent manner. The OXT-induced gastric relaxation was enhanced following bethanechol and reduced by l-NAME administration, suggesting a nitrergic mechanism of gastroinhibition. DVC application of the group II mGluR antagonist EGLU induced a gastroinhibition that was not dose dependent and shifted the gastric effects of OXT to a cholinergic-mediated mechanism. Evoked and miniature GABAergic synaptic currents between NTS and identified gastric-projecting DMV neurones were not affected by OXT in any neurones tested, unless the brainstem slice was (a) pretreated with EGLU or (b) derived from rats that had earlier received a surgical vagal deafferentation. Conversely, OXT inhibited glutamatergic currents even in naive slices, but their responses were unaffected by EGLU pretreatment. These results suggest that the OXT-induced gastroinhibition is mediated by activation of the NANC pathway. Inhibition of brainstem group II mGluRs, however, uncovers the ability of OXT to modulate GABAergic transmission between the NTS and DMV, resulting in the engagement of an otherwise silent cholinergic vagal neurocircuit.

Acute Lung Injury Alters Synaptic Drive to Nucleus Tractus Solitarius Neurons

Acute lung injury (ALI) is a severe clinical problem where the progression of lung damage contributes to altered ventilatory patterns. Changes in central control of breathing may influence the pathophysiology of ALI. We have previously shown ALI induced upregulation of inflammatory cytokine production in the nucleus tractus solitarius (nTS). The effects of this immune‐modulation on central neural circuits are unclear. We hypothesized that ALI alters synaptic inputs to the nTS neurons. To test this hypothesis, we cut transverse slices (300 micrometers) of brainstem from juvenile (P15–P18) male Sprague‐Dawley rats 7d after intratracheal instillation of bleomycin (0.2 units) or saline. Whole‐cell perforated patch‐clamp recordings were done to characterize the spontaneous excitatory synaptic events in nTS neurons from bleomycin (n=4) and saline (n=2) animals. At least 200 synaptic events were analyzed from each cell and a student's t‐test was used for comparison. In bleomycin animals, the amplitude of spontaneous excitatory post‐synaptic currents (EPSCs) was significantly reduced (18.1 vs. 19.7 pA, p = 0.02) and the decay time of EPSCs was significantly longer (6.8 vs 5.7 ms, p &lt; 0.01). Our data suggest that bleomycin lung‐injured animals have altered central processing of vagal afferent input that may contribute to breathing dysregulation in ALI.