Intestinal Vagal Research Articles

Neurotrophin-4 is essential for survival of the majority of vagal afferents to the mucosa of the small intestine, but not the stomach.

Vagal afferents form the primary gut-to-brain neural axis, communicating signals that regulate gastrointestinal (GI) function and promote satiation, appetition and reward. Neurotrophin-4 (NT-4) is essential for the survival of vagal smooth muscle afferents of the small intestine, but not the stomach. Here we took advantage of near-complete labeling of GI vagal mucosal afferents in Nav1.8cre-Rosa26tdTomato transgenic mice to determine whether these afferents depend on NT-4 for survival. We quantified the density and distribution of vagal afferent terminals in the stomach and small intestine mucosa and their central terminals in the solitary tract nucleus (NTS) and area postrema in NT-4 knockout (KO) and control mice. NT-4KO mice exhibited a 75% reduction in vagal afferent terminals in proximal duodenal villi and a 55% decrease in the distal ileum, whereas, those in the stomach glands remained intact. Vagal crypt afferents were also reduced in some regions of the small intestine, but to a lesser degree. Surprisingly, NT-4KO mice exhibited an increase in labeled terminals in the medial NTS. These findings, combined with previous results, suggest NT-4 is essential for survival of a large proportion of all classes of vagal afferents that innervate the small intestine, but not those that supply the stomach. Thus, NT-4KO mice could be valuable for distinguishing gastric and intestinal vagal afferent regulation of GI function and feeding. The apparent plasticity of central vagal afferent terminals - an increase in their density - could have compensated for loss of peripheral terminals by maintaining near-normal levels of satiety signaling.

TMEM16B determines cholecystokinin sensitivity of intestinal vagal afferents of nodose neurons.

The satiety effects and metabolic actions of cholecystokinin (CCK) have been recognized as potential therapeutic targets in obesity for decades. We identified a potentially novel Ca2+-activated chloride (Cl-) current (CaCC) that is induced by CCK in intestinal vagal afferents of nodose neurons. The CaCC subunit Anoctamin 2 (Ano2/TMEM16B) is the dominant contributor to this current. Its expression is reduced, as is CCK current activity in obese mice on a high-fat diet (HFD). Reduced expression of TMEM16B in the heterozygote KO of the channel in sensory neurons results in an obese phenotype with a loss of CCK sensitivity in intestinal nodose neurons, a loss of CCK-induced satiety, and metabolic changes, including decreased energy expenditure. The effect on energy expenditure is further supported by evidence in rats showing that CCK enhances sympathetic nerve activity and thermogenesis in brown adipose tissue, and these effects are abrogated by a HFD and vagotomy. Our findings reveal that Ano2/TMEM16B is a Ca2+-activated chloride channel in vagal afferents of nodose neurons and a major determinant of CCK-induced satiety, body weight control, and energy expenditure, making it a potential therapeutic target in obesity.

Sexually Dimorphic Ano2 Expression in Nodose Neurons Determines CCK‐mediated Satiation and Obesity in Heterozygote Male Mice

The gut peptide cholecystokinin (CCK) contributes to neurally mediated post prandial satiety. Our previous results indicate that high fat diet downregulates the CCK‐sensitive anoctamins (Ano1 and Ano2) that function as calcium‐activated chloride channels (CaCCs) in intestinal vagal afferents. Using Cre‐loxP system, we generated heterozygote (HET) Nav1.8CreAno2fl/WT mice. The endogenous Scn10a promoter drives Cre expression (Nav1.8Cre) selectively in sensory neurons of the nodose, dorsal root and trigeminal ganglia where loxP sites flanked Ano2 exon 12. The male HET mice exhibited an obese phenotype and decreased sensitivity to CCK. To assess the Ano2 expression in HET vs. control (Nav1.8Cre+/−) mice, we first did qRT‐PCR on whole nodose ganglia obtained under anesthesia at 50 weeks of age and found no significant difference in Ano2 mRNA expression (n=4, p>0.05). Ano2 gene may be expressed in non‐neuronal cells of nodose ganglia while Cre expression is selective to neurons. We measured Ano2 mRNAs in nodose neurons cultured for 16–18 hours using single cell qRT‐PCR. Cre positive neurons were 57% (12 of 21) in HET and 74% (29 of 39) in control, indicating a lower efficiency of Cre expression in HET. Correspondingly, Ano2 positive neurons were 48% (10 of 21) and 62% (24 of 39), respectively, indicating the Ano2 allelic deletion in HET. The combined Cre and Ano2 positivity in HET was 29% (6 of 21) vs. 54% (21 of 39) in control. Most importantly the Ano2 mRNA levels in HET neurons (n=10) were 20% of the levels measured in control neurons (n=24, p<0.05) (0.20±0.16 vs. 1.00±0.57). The Ano2 expression in individual nodose neurons of female mice did not show a reduction or even higher in HET (n=27) vs. control (n=28) (2.58±1.48 vs. 1.42±1.27, p>0.05). The female HET mice remained CCK sensitive indicating a sexual dimorphism. We conclude that differences in expression of Ano2 mRNA support our findings of CCK insensitivity and selective obesity in male but not female HET mice (HL14388).Support or Funding InformationNIH HL14388This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Abstract 020: Heterozygote Knockout of TMEM16B in Intestinal Vagal Afferents Causes Cholecystokinin Insensitivity and Obesity in Male but Not Female Mice

Cholecystokinin (CCK) is a well-known satiety peptide that inhibits food intake. The CCK induced satiety signal in intestinal vagal afferents is attenuated in mice on a High Fat Diet (HFD). We have shown that down regulation of a Ca 2+ -activated Cl - channel (CaCC) downstream of CCK receptors is responsible for the neuronal insensitivity to CCK. We also found that the CaCC subunit Ano2/TMEM16B is essential for the CCK-induced current in nodose neurons. In this study we tested the hypothesis that reduction of this subunit in vivo contributes to weight gain. One allele of the Ano2/TMEM16B was knocked out in sensory neurons by crossing the ano2 fl/ fl mice with Nav1.8Cre mice to generate the Nav1.8Cre;ano2 fl /wt mice. The Cre negative littermates were used as control. We found that CCK-induced suppression of food intake is eliminated in male Nav1.8Cre;ano2 fl /wt mice. Food intake measured over 4 hours was 1.21±0.11g (n=5) in male wild type (wt) mice injected with saline and was reduced to 0.77±0.18 g (n=7, p<0.05) in mice injected with CCK-8 (3μg/kg). Those values were 0.63±0.15 g (n=6) in saline injected and 0.91±0.13 g (n=7, p>0.05) in CCK injected male Nav1.8Cre;ano2 fl /wt mice. However, the CCK injection did not affect food intake in either female wt or Nav1.8Cre;ano2 fl /wt mice. The male Nav1.8/ano2 fl/wt mice were on the average 5.5g heavier than wt mice at 40 weeks of age (39.8±1.4 g, n=13 vs 34.3±1.4 g, n=14, p<0.01). Body weight of females was significantly lower than in males but was not different between wt and Nav1.8Cre;ano2 fl /wt mice (30.4±1.0 g, n=14 vs 28.5±1.0 g, n=11, p=0.20 respectively). Single cell mRNA level of Ano2 and CCK-induced TMEM16 currents in nodose neurons were reduced significantly in male Nav1.8Cre;ano2 fl/wt mice compared to Cre negative controls, but such changes were not seen in female mice. We conclude that heterozygote knockout of Ano2/TMEM16B specifically in sensory neurons causes neuronal insensitivity to CCK and excessive weight gain in male but not female mice. Reduction of this subunit may contribute to the HFD induced obesity. The reason for the phenotype and allele expression variability between sexes is unclear.

Lipopolysaccharide Induced Activation of VRAC (LRRC8) in Nodose Neurons Is Dependent on TLR4 Receptor Mediated ROS Generation

The Volume‐Regulated Anion Channel and its essential subunit Leucine Rich Repeats Containing protein 8a (VRAC/LRRC8) is a widely expressed Cl− channel critical for cell volume regulation. This channel is activated by osmotic gradient and ionic strength (Voss et al., 2014, Qiu et al., 2014, Syeda et al., 2016). Using patch‐clamp techniques, we reported that channel activation is also induced in the majority of vagal afferent neurons isolated from mouse (C57BL/6) nodose ganglia by hypoosmolarity and by extracellular low pH (Wang et al., 2017). We have also observed that this current is activated by lipopolysaccharide (LPS) at 10μg/ml. Here we tested the hypothesis that the response to LPS is dependent on toll‐like receptor 4 (TLR4) and is mediated by intracellular reactive oxygen species (ROS). The current was reduced from 26.7±5.4 pA/pF (n=5) in control peptide‐treated neurons to 6.4±2.1 pA/pF (n=6, p<0.05) in neurons treated with the TLR4 inhibitor peptide VIPER. Application of LPS at a lower dose (100ng/ml) increased intracellular neuronal ROS measured by dihydroethidium within several minutes. The cell permeable hydrogen peroxide scavenger PEG‐catalase decreased the LPS‐induced current from 10.2±2.5 pA/pF (n=7) to 2.3±1.2 pA/pF (n=5, p<0.05). We conclude that LPS induces activation of the VRAC/LRRC8 channel in nodose neurons via TLR4 receptor‐mediated ROS generation. The results indicate a diverse functional role of this channel beyond volume homeostasis with potential implications in high fat diet‐ or LPS‐induced decrease in satiety signaling in intestinal vagal afferents.Support or Funding InformationHL14388

The insulinotropic effect of exogenous glucagon-like peptide-1 is not affected by acute vagotomy in anaesthetized pigs.

What is the central question of this study? We investigated whether intestinal vagal afferents are necessary for the insulinotropic effect of glucagon-like peptide-1 (GLP-1) infused into a mesenteric artery or a peripheral vein before and after acute truncal vagotomy. What is the main finding and its importance? We found no effect of truncal vagotomy on the insulinotropic effect of exogenous GLP-1 and speculate that high circulating concentrations of GLP-1 after i.v. and i.a. infusion might have overshadowed any neural signalling component. We propose that further investigations into the possible vagal afferent signalling of GLP-1 would best be pursued using enteral stimuli to provide high subepithelial levels of endogenous GLP-1. Glucagon-like peptide 1 (GLP-1) is secreted from the gut in response to luminal stimuli and stimulates insulin secretion in a glucose-dependent manner. As a result of rapid enzymatic degradation of GLP-1 by dipeptidyl peptidase-4, a signalling pathway involving activation of intestinal vagal afferents has been proposed. We conducted two series of experiments in α-chloralose-anaesthetized pigs. In protocolI, pigs (n=14) were allocated for either i.v. or i.a. (mesenteric) GLP-1 infusions (1 and 2pmolkg(-1) min(-1) , 30min) while maintaining permissive glucose concentrations at 6mmoll(-1) by i.v. glucose infusion. The GLP-1 infusions were repeated after acute truncal vagotomy. In protocolII, pigs (n=27) were allocated into six groups. Glucagon-like peptide 1 was infused i.v. or i.a. (mesenteric) for 1h at 3 or 30pmolkg(-1) min(-1) . During the steady state (21min into the GLP-1 infusion), glucose (0.2gkg(-1) , i.v.) was administered over 9min to stimulate β-cell secretion. Thirty minutes after the glucose infusion, GLP-1 infusions were discontinued. Following a washout period, the vagal trunks were severed in four of six groups (vagal trunks were left intact in two of six groups), whereupon all infusions were repeated. We found no effect of vagotomy on insulin or glucagon secretion during administration of exogenous GLP-1 in any experiment. We speculate that the effect of exogenous GLP-1 overshadowed any effect occurring via the vagus. Within dosage groups, total GLP-1 concentrations were similar, but intact GLP-1 concentrations were much lower when infused via the mesenteric artery because of extensive degradation of GLP-1 in the splanchnic bed. This demonstrates the effectiveness with which intestinal capillary dipeptidyl peptidase-4 protects the systemic circulation from intact GLP-1, consistent with a local role for GLP-1 involving activation of vagal pathways.

Smooth muscle-derived neurotrophins regulate development and function of vagal gastrointestinal (GI) afferents

Brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) regulate development of overlapping populations of vagal sensory neurons. During development, they are expressed in GI smooth muscle, a tissue innervated by vagal mechanoreceptors. To investigate the contributions of this BDNF and NT-3 to vagal development, they were ablated from smooth muscle (smBDNF-KO, smNT-3-KO). As GI vagal afferents signal meal termination (satiation), adult meal patterns were utilized as a functional assay of altered GI vagal development. smNT-3-KO mice exhibited a decrease in meal-induced c-Fos activation in the solitary tract nucleus and area postrema compared to controls, suggesting vagal afferent innervation of the gut was decreased. Consistent with this, smNT-3-KO mice showed increased meal duration, and increased size of their first daily meal, suggesting vagal satiation signaling was reduced. In contrast, smBDNF-KO mice had increased intestinal vagal mechanoreceptor innervation. Increased numbers of vagal sensory neurons and intestinal fiber bundles in the knockout mice suggested this was due to increased survival of intestinal vagal mechanoreceptors. Thus, BDNF may normally suppress survival of these mechanoreceptors, counter to expectations for a growth factor. smBDNF-KO mice ate meals of shorter duration and smaller size than controls, suggesting the increased intestinal innervation provided increased satiation signaling. The opposite effects of smBDNF-KO and smNT-3-KO on GI vagal sensory development/function may result from interactions of smooth muscle-derived BDNF, but not NT-3, with the low affinity nerve growth factor receptor, p75. This receptor is expressed by vagal afferent neurons during development and its activation by BDNF typically results in cell death.

Abstract 20340: Defect of Ca 2+ -activated Cl - Channel in Intestinal Nodose Neurons Contributes to Impaired Satiety Signal in High-Fat Diet Induced Obesity

High fat diet inhibits the cholecystokinin (CCK) induced satiety signal in vagal afferents, which may contribute to the associated increased food intake. We hypothesized that a defect of Ca 2+ -activated chloride channel (CaCC) in high fat (HFD) fed mice leads to the reduction of CCK responses in intestinal vagal afferent nodose neurons. By using the whole cell patch-clamp in cultured nodose ganglia neurons isolated from C57BL/6 mice, we found that CCK (10nM) induced large inward chloride (Cl - ) currents (36.0±11pA/pF) that were eliminated with the fast Ca 2+ chelator BAPTA (1.0±0.5pA/pF, n=7), and reduced significantly by the CaCC channel inhibitor niflumic acid (100 μM, 13.6±2.0pA/pF, p<0.05, n=8). The response to CCK in DiI-labeled proximal intestinal nodose neurons from obese mice fed a 60% HFD for 10 weeks was reduced significantly (6.1±2.9pA/pF, n=7, p<0.01) relative to control lean mice (24.8±4.9pA/pF, n=7). The underlying molecular mechanism of the reduced CCK response in mice fed a HFD did not involve altered expression of CCK receptors in nodose neurons. We found that the relative mRNA (qPCR) of CCK receptor B was not significantly changed (1.01±0.13 in control vs. 1.18±0.31 in HFD nodose ganglia, n=4, p>0.05) and the mRNA of CCK receptor A was even increased from 1.06±0.37 in control to 1.54±0.41 in HFD ganglia (n=4, p<0.05). In contrast, the CaCC channel mRNA (Ano I) was decreased to 0.61±0.09 relative to 1.01±0.20 (n=4, p<0.001), and Ano II mRNA was decreased to 0.31±0.07 relative to 1.02±0.22 (n=4, p<0.001) in nodose ganglia from HFD fed vs. control lean mice. Since the maximum current induced by a saturation level of ligand reflects the level of protein expressed on the cytoplasmic membrane, we tested the CaCC current induced by a high level of intracellular Ca 2+ (20μM). We found that the maximum current was smaller in DiI labeled intestinal nodose neurons from HFD fed mice (13.7±2.9 pA/pF vs. 26.9±3.6 pA/pF in control mice, n=10, p<0.05). Our results indicate that CCK-activated currents recorded from intestinal vagal afferent nodose neurons are reduced in mice fed a HFD, and are associated with reduced expression of a CCK-activated Ca 2+ -dependent Cl - channel. This mechanism may contribute significantly to HFD-induced suppression of the satiety reflex.

Cholecystokinin activates a Ca2+‐dependent Cl‐ conductance in intestinal nodose neurons that is inhibited in diet‐induced obesity and may suppress satiety (1107.8)

The cholecystokinin (CCK) induced satiety signaling of vagal afferents is suppressed in diet‐induced obese mice, which contributes to the increased food intake. In this study we tested the hypothesis that a Ca2+‐activated chloride channel (CaCC) mediates the response of normal intestinal vagal afferent nodose neurons to CCK and that excessively high fat diet (HFD) suppresses the channel activation and leads to obesity. We first used Ca2+ imaging techniques and the whole cell patch‐clamp on cultured nodose ganglia neurons isolated from anesthetized C57/BL6 mice. Application of CCK increased [Ca2+]i in a dose‐dependent manner reaching near maximal level at 10 μM. This dose of CCK also induced a large inward current (36.0±11.0 pA/pF, n=7) that was eliminated with the fast Ca2+ chelator BAPTA (1.0±0.5 pA/pF, n=7). The reversal potential of the current was ~0mV with equal concentration of Cl‐ on both sides of the cell membrane and shifted to a more positive direction after lowering the extracellular [Cl‐]o confirming that it is an outward Cl‐ conductance. Moreover, the CCK‐induced response was reduced significantly from 35.2±3.2 pA/pF in untreated control neurons (n=9) to 13.6±2.0 pA/pF in the presence of niflumic acid (100μM, n=8), a blocker of the CaCC channel (p<0.05). DiI labeled proximal intestinal nodose neurons obtained from control mice responded to CCK with an average current of 24.8±4.9 pA/pF (n=7), whereas the response of labeled neurons from obese mice fed a 60% HFD for 10 weeks was significantly lower at 6.1±2.9 pA/pF (n=7) (p<0.01). Our results demonstrate that a CCK‐sensitive CaCC in proximal intestinal nodose neurons is desensitized in mice fed a high fat diet. This CaCC ionic conductance may be responsible for satiety signaling of vagal afferents and its impairment may contribute to excessive food intake and obesity.Grant Funding Source: Supported by NIH HL 14388

Effects of tumor necrosis factor α on leptin-sensitive intestinal vagal mechanoreceptors in the cat

The involvement of tumour necrosis factor α (TNF-α) in inflammatory bowel disease (IBD) has been established, and anti-TNF-α has been suggested as a therapeutic approach for the treatment of these pathologies. We studied the effects of TNF-α on leptin-sensitive intestinal vagal units to determine whether TNF-α exerts its effects through the intestinal vagal mechanoreceptors and to investigate its interactions with substances regulating food intake. The activity of intestinal vagal mechanoreceptors was recorded via microelectrodes implanted into the nodose ganglion in anesthetized cats. TNF-α (1 μg, i.a.) increased the discharge frequency of leptin-activated units (type 1 units; P < 0.05) and had no effect on the discharge frequency of leptin-inhibited units (type 2 units). When TNF-α was administered 20 min after sulfated cholecystokinin-8 (CCK), its excitatory effects on type 1 units were significantly enhanced (P < 0.0001) and type 2 units were significantly (P < 0.05) activated. Pre-treatment with Il-1ra (250 μg, i.a.) blocked the excitatory effects of TNF-α on type 1 units whereas the excitatory effects of TNF-α administration after CCK treatment on type 2 units were not modified. The activation of leptin-sensitive units by TNF-α may explain, at least in part, the weight loss observed in IBD.

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.

Dietary fat sensing via fatty acid oxidation in enterocytes: possible role in the control of eating

Various mechanisms detect the presence of dietary triacylglycerols (TAG) in the digestive tract and link TAG ingestion to the regulation of energy homeostasis. We here propose a novel sensing mechanism with the potential to encode dietary TAG-derived energy by translating enterocyte fatty acid oxidation (FAO) into vagal afferent signals controlling eating. Peripheral FAO has long been implicated in the control of eating (141). The prevailing view was that mercaptoacetate (MA) and other FAO inhibitors stimulate eating by modulating vagal afferent signaling from the liver. This concept has been challenged because hepatic parenchymal vagal afferent innervation is scarce and because experimentally induced changes in hepatic FAO often fail to affect eating. Nevertheless, intraperitoneally administered MA acts in the abdomen to stimulate eating because this effect was blocked by subdiaphragmatic vagal deafferentation (21), a surgical technique that eliminates all vagal afferents from the upper gut. These and other data support a role of the small intestine rather than the liver as a FAO sensor that can influence eating. After intrajejunal infusions, MA also stimulated eating in rats through vagal afferent signaling, and after infusion into the superior mesenteric artery, MA increased the activity of celiac vagal afferent fibers originating in the proximal small intestine. Also, pharmacological interference with TAG synthesis targeting the small intestine induced a metabolic profile indicative of increased FAO and inhibited eating in rats on a high-fat diet but not on chow. Finally, cell culture studies indicate that enterocytes oxidize fatty acids, which can be modified pharmacologically. Thus enterocytes may sense dietary TAG-derived fatty acids via FAO and influence eating through changes in intestinal vagal afferent activity. Further studies are necessary to identify the link between enterocyte FAO and vagal afferents and to examine the specificity and potential physiological relevance of such a mechanism.

Enterocyte fatty acid oxidation may influence eating through vagal afferent signals

Mercaptoacetate (MA) and other fatty acid oxidation (FAO) inhibitors supposedly stimulate eating by inhibiting hepatic FAO, thus activating a hepatic vagal afferent signal to eat. This concept has been challenged because hepatic parenchymal vagal afferent innervation is scarce and because experimentally induced changes in hepatic FAO often fail to affect eating. Nevertheless, IP MA must act in the abdomen to stimulate eating because its effect was blocked by subdiaphragmatic vagal deafferentation (SDA) (Brandt et al, Neurosci Letters 411:104, 2007). This suggests a role of the small intestine in the effects of IP MA on eating. To examine this idea, we equipped adult male rats with jejunal catheters and tested the effects on eating of intrajejunal infusions (30 sec, 1 ml/kg, start at 3 h into the light phase) of MA (100, 200, and 400 μmol/kg BW). MA (200 and 400 μmol/kg) increased (P &lt; 0.05) 30 and 60 min food intake vs. control, this effect was absent in rats after SDA, and MA infused into the superior mesenteric artery (SMA) increased (within 10 min) the activity of 34 (out of 37) serotonin‐sensitive single units isolated from celiac vagal fascicles originating in the proximal small intestine. Because the SMA supplies most of the small intestine, these data support the hypothesis that small intestinal enterocytes may serve as FAO sensors and influence eating through changes in intestinal vagal afferent activity.

Mercaptoacetate (MA) increases intestinal vagal afferent activity

Mercaptoacetate (MA) increases intestinal vagal afferent activity

Alterations in the Brain–Gut Axis Underlying Visceral Chemosensitivity in Nippostrongylus brasiliensis-Infected Mice

Visceral hypersensitivity, a hallmark of irritable bowel syndrome, is generally considered to be mechanosensitive in nature and mediated via spinal afferents. Both stress and inflammation are implicated in visceral hypersensitivity, but the underlying molecular mechanisms of visceral hypersensitivity are unknown. Mice were infected with Nippostrongylus brasiliensis (Nb) larvae, exposed to environmental stress and the following separate studies performed 3-4 weeks later. Mesenteric afferent nerve activity was recorded in response to either ramp balloon distention (60 mm Hg), or to an intraluminal perfusion of hydrochloric acid (50 mmol/L), or to octreotide administration (2 micromol/L). Intraperitoneal injection of cholera toxin B-488 identified neurons projecting to the abdominal viscera. Fluorescent neurons in dorsal root and nodose ganglia were isolated using laser-capture microdissection. RNA was hybridized to Affymetrix Mouse whole genome arrays for analysis to evaluate the effects of stress and infection. In mice previously infected with Nb, there was no change in intestinal afferent mechanosensitivity, but there was an increase in chemosensitive responses to intraluminal hydrochloric acid when compared with control animals. Gene expression profiles in vagal but not spinal visceral sensory neurons were significantly altered in stressed Nb-infected mice. Decreased afferent responses to somatostatin receptor 2 stimulation correlated with lower expression of vagal somatostatin receptor 2 in stressed Nb-infected mice, confirming a link between molecular data and functional sequelae. Alterations in the intestinal brain-gut axis, in chemosensitivity but not mechanosensitivity, and through vagal rather than spinal pathways, are implicated in stress-induced postinflammatory visceral hypersensitivity.

Targeted disruption of the murine CCK1 receptor gene reduces intestinal lipid-induced feedback inhibition of gastric function

Cholecystokinin (CCK), acting at CCK1 receptors (CCK1Rs) on intestinal vagal afferent terminals, has been implicated in the control of gastrointestinal function and food intake. Using CCK1R(-/-) mice, we tested the hypothesis that lipid-induced activation of the vagal afferent pathway and intestinal feedback of gastric function is CCK1R dependent. In anesthetized CCK1R(+/+) ("wild type") mice, meal-stimulated gastric acid secretion was inhibited by intestinal lipid infusion; this was abolished in CCK1R(-/-) mice. Gastric emptying of whole egg, measured by nuclear scintigraphy in awake mice, was significantly faster in CCK1R(-/-) than CCK1R(+/+) mice. Gastric emptying of chow was significantly slowed in response to administration of CCK-8 (22 pmol) in CCK1R(+/+) but not CCK1R(-/-) mice. Activation of the vagal afferent pathway was measured by immunohistochemical localization of Fos protein in the nucleus of the solitary tract (NTS; a region where vagal afferents terminate). CCK-8 (22 pmol ip) increased neuronal Fos expression in the NTS of fasted CCK1R(+/+) mice; CCK-induced Fos expression was reduced by 97% in CCK1R(-/-) compared with CCK1R(+/+) mice. Intralipid (0.2 ml of 20% Intralipid and 0.04 g lipid), but not saline, gavage increased Fos expression in the NTS of fasted CCK1R(+/+) mice; lipid-induced Fos expression was decreased by 47% in CCK1R(-/-) compared with CCK1R(+/+)mice. We conclude that intestinal lipid activates the vagal afferent pathway, decreases gastric acid secretion, and delays gastric emptying via a CCK1R-dependent mechanism. Thus, despite a relatively normal phenotype, intestinal feedback in response to lipid is severely impaired in these mice.

High-fat hyperphagia in neurotrophin-4 deficient mice reveals potential role of vagal intestinal sensory innervation in long-term controls of food intake

Neurotrophin-4 (NT-4) deficient mice exhibit substantial loss of intestinal vagal afferent innervation and short-term deficits in feeding behavior, suggesting reduced satiation. However, they do not show long-term changes in feeding or body weight because of compensatory behaviors. The present study examined whether high-fat hyperphagia induction would overcome compensation and reveal long-term effects associated with the reduced vagal sensory innervation of NT-4 mutants. First, modifications of a feeding schedule previously developed in rats were examined in wild-type mice to identify the regimen most effective at producing hyperphagia. The most successful schedule, which was run for 26 days, included access to a 43%-fat diet and pelleted chow every other day and access to only powdered chow on the alternate days. On high-fat access days mice consumed 25% more calories than mice with continuous daily access to the same high-fat diet and pelleted chow. This feeding regimen also induced hyperphagia in NT-4 deficient mice and their wild-type controls: on high-fat exposure days mutants consumed 35% more calories relative to continuous-access mutants, and wild types ate 25% more than continuous-access wild types. Moreover, on high-fat access days the alternating NT-4 mutants significantly increased caloric intake by 9% compared to alternating wild types. Thus, high-fat hyperphagia appeared to override compensation, permitting short-term changes in meal consumption by mutants that accrued into long-term changes in total daily food intake. This raises the possibility that intestinal vagal sensory innervation contributes to long-term, as well as to short-term regulation of food intake.

Toward Optimal Health: Scott Grundy, M.D., Ph.D. Discusses Metabolic Syndrome

Journal of Women's HealthVol. 14, No. 10 Conversation with the ExpertsToward Optimal Health: Scott Grundy, M.D., Ph.D. Discusses Metabolic SyndromeJodi R. GodfreyJodi R. GodfreySearch for more papers by this authorPublished Online:22 Dec 2005https://doi.org/10.1089/jwh.2005.14.883AboutSectionsPDF/EPUB ToolsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail FiguresReferencesRelatedDetailsCited ByTMEM16B determines cholecystokinin sensitivity of intestinal vagal afferents of nodose neurons7 March 2019 | JCI Insight, Vol. 4, No. 5The Metabolic Syndrome and Type 2 Diabetes Mellitus19 November 2009 Volume 14Issue 10Dec 2005 InformationCopyright 2005, Mary Ann Liebert, Inc.To cite this article:Jodi R. Godfrey.Toward Optimal Health: Scott Grundy, M.D., Ph.D. Discusses Metabolic Syndrome.Journal of Women's Health.Dec 2005.883-888.http://doi.org/10.1089/jwh.2005.14.883Published in Volume: 14 Issue 10: December 22, 2005PDF download

Effects of leptin on cat intestinal motility.

In a previous study, we established that leptin controls food intake and immune responses by acting on intestinal vagal chemosensitive mechanoreceptors via a functional link with interleukin-1 beta (Il-1 beta). Since the control of intestinal motility is one of the main roles of the vagal afferent fibres, we investigated the effects of leptin on intestinal electromyographic (EMG) activity which reflects intestinal motility. For this purpose, the effects of locally injected leptin on small intestine spontaneous EMG activity were studied in 23 anaesthetised cats. The EMG activity was recorded using bipolar electrodes implanted in the proximal small intestine. Leptin and Il-1 beta (0.1, 1 and 10 microg), administered through the artery irrigating the upper part of the intestine 20 min after cholecystokinin (CCK, 10 microg, I.A.), had significant (P < 0.001) excitatory effects on intestinal EMG activity. The effects of both substances were blocked by the endogenous interleukin-1 beta receptor antagonist (Il-1ra, 250 microg, I.A.), by atropine (250 microg, I.A.) and by vagotomy. In the absence of CCK, leptin and Il-1 beta had no effect on intestinal electrical activity. It can therefore be concluded that: (1) leptin is effective only after the previous intervention of CCK, (2) the enhancement of the electrical activity induced by leptin involves Il-1 beta receptors and the cholinergic excitatory pathway, (3) the modes whereby the leptin-induced enhancement of EMG activity occurs strongly suggest that these effects are due to a long-loop reflex involving intestinal vagal afferent fibres and the parasympathetic nervous system.

Effects of leptin on cat intestinal vagal mechanoreceptors.

Vagal afferent nerve fibres are involved in the transmission to the central nervous system of information relating to food intake and immune reactions. Leptin is involved in the control of food intake and has specific receptors in afferent vagal neurones. To investigate the role of these receptors, we studied the effects of leptin on single vagal afferent activities from intestinal mechanoreceptors in anaesthetized cats. The activity of 35 intestinal vagal mechanoreceptors was recorded by means of glass microelectrodes implanted in the nodose ganglion. Leptin (10 microg), administered into the artery irrigating the upper part of the intestine, induced activation in 17 units (P < 0.001), inhibition in 8 units (P < 0.05), and had no effect on 10 units. The excitatory effects of leptin were blocked by the endogenous interleukine-1beta receptor antagonist, (Il-1ra, 250 microg, I.A.). Cholecystokinin (CCK, 10 microg, I.A.) induced an activatory response only in the two types of units which were responsive to leptin alone. When leptin was administered after CCK, its excitatory effects were enhanced and its inhibitory effects were blocked, whereas it had no effect on the units which were not affected by leptin alone. The interactions between leptin and CCK are specific ones, since other substances (phenylbiguanide, a serotoninergic agonist; substance P) known to activate the mechanoreceptors did not modify the effects of leptin. These results indicate that leptin appears to play a role in the control of immune responses and food intake via intestinal vagal afferent nerve fibres and that there is a functional link between leptin and Il-1beta.