Jejunal Afferents Research Articles

Dietary monosodium glutamate increases visceral hypersensitivity in a mouse model of visceral pain.

Monosodium glutamate (MSG) has been identified as a trigger of abdominal pain in irritable bowel syndrome (IBS), but the mechanism is unknown. This study examined whether MSG causes visceral hypersensitivity using a water-avoidance stress (WAS) mouse model of visceral pain. Mice were divided into four groups receiving treatment for 6 days: WAS + MSG gavage, WAS + saline gavage, sham-WAS + MSG gavage, and sham-WAS + saline gavage. The acute effects of intraluminal administration of 10 μM MSG on jejunal extrinsic afferent nerve sensitivity to distension (0-60 mmHg) were examined using ex vivo extracellular recordings. MSG was also applied directly to jejunal afferents from untreated mice. Glutamate concentration was measured in serum, and in the serosal compartment of Ussing chambers following apical administration. Acute intraluminal MSG application increased distension responses of jejunal afferent nerves from mice exposed to WAS + MSG. This effect was mediated by wide dynamic range and high-threshold units at both physiologic and noxious pressures (10-60 mmHg, p < 0.05). No effect of MSG was observed in the other groups, or when applied directly to the jejunal afferent nerves. Serum glutamate was increased in mice exposed to WAS + MSG compared to sham-WAS + saline, and serosal glutamate increased using WAS tissue (p = 0.0433). These findings demonstrate that repeated exposure to MSG in mice leads to sensitization of jejunal afferent nerves to acute ex vivo exposure to MSG. This may contribute to visceral hypersensitivity reported in response to MSG in patients with IBS.

Curcumin acts via transient receptor potential vanilloid‐1 receptors to inhibit gut nociception and reverses visceral hyperalgesia

An antinociceptive effect has been reported for curcumin in animal models and in humans, but the molecular mechanisms of curcumin's effect remain undefined. In this study, we explored the possibility that curcumin inhibit visceral nociception via antagonizing the transient receptor potential vanilloid-1 (TRPV1) receptor. The effects of curcumin were explored using two experimental models: viscero-motor response (VMR) to colorectal distension (CRD) in rats and jejunal afferent firing in the ex vivo mouse jejunum preparations [TRPV1 knockout (KO) and wild-type mice, naive and trinitrobenzene sulfonic acid (TNBS)-treated Kunming mice]. In addition, capsaicin-induced calcium transients and whole-cell currents were examined in acutely dissociated dorsal root ganglia (DRG) neurons. In the anesthetized rat, curcumin (4mgkg(-1) min(-1) for 3min) caused a marked and rapidly reversible inhibition of CRD-induced VMRs. In the mouse jejunum, the mesenteric afferent nerve response to ramp distension was attenuated by curcumin (3, 10μmolL(-1) ), an effect that was significantly reduced in TRPV1 KO mice compared with wild-type (WT) controls. Moreover, in WT mice, curcumin (1-30μmolL(-1) ) was found to inhibit the afferent responses to capsaicin in a concentration-dependent manner. Trinitrobenzene sulfonic acid-induced hypersensitivity of jejunal afferents was also attenuated by curcumin. Curcumin potently inhibited capsaicin-induced rise in intracellular calcium and inward currents in mouse or rat DRG neurons. Our results provide strong evidence that curcumin inhibit visceral nociception via antagonizing TRPV1 and may be a promising lead for the treatment of functional gastrointestinal diseases.

Impaired intestinal afferent nerve satiety signalling and vagal afferent excitability in diet induced obesity in the mouse

Gastrointestinal vagal afferents transmit satiety signals to the brain via both chemical and mechanical mechanisms. There is indirect evidence that these signals may be attenuated in obesity. We hypothesized that responses to satiety mediators and distension of the gut would be attenuated after induction of diet induced obesity. Obesity was induced by feeding a high fat diet (60% kcal from fat). Low fat fed mice (10% kcal from fat) served as a control. High fat fed mice were obese, with increased visceral fat, but were not hyperglycaemic. Recordings from jejunal afferents demonstrated attenuated responses to the satiety mediators cholecystokinin (CCK, 100 nm) and 5-hydroxytryptamine (5-HT, 10 μm), as was the response to low intensity jejunal distension, while responses to higher distension pressures were preserved. We performed whole cell patch clamp recordings on nodose ganglion neurons, both unlabelled, and those labelled by fast blue injection into the wall of the jejunum. The cell membrane of both labelled and unlabelled nodose ganglion neurons was less excitable in HFF mice, with an elevated rheobase and decreased number of action potentials at twice rheobase. Input resistance of HFF neurons was also significantly decreased. Calcium imaging experiments revealed reduced proportion of nodose ganglion neurons responding to CCK and 5-HT in obese mice. These results demonstrate a marked reduction in afferent sensitivity to satiety related stimuli after a chronic high fat diet. A major mechanism underlying this change is reduced excitability of the neuronal cell membrane. This may explain the development of hyperphagia when a high fat diet is consumed. Improving sensitivity of gastrointestinal afferent nerves may prove useful to limit food intake in obesity.

W1361 Colon Electrical Stimulation: A Potential Treatment for Obesity

In Vitro extracellular recordings were performed from jejunal afferents. Nodose ganglion neurons (NGNs) were dissociated and plated onto coverslips. Whole cell patch clamp recordings or Fura-2AM calcium imaging experiments on NGNs were performed 18-24 h post-dissociation. Results: In recordings from jejunal afferents, responses to 100nM CCK (11.5 ± 3.2 vs. 3.35 ± 1.0 spikes/s n=10, p<0.05) and 10μM 5-HT (4.85 ± 1.4 vs. 1.75 ± 0.25, n=10, p<0.05) were decreased in HFF mice compared to LFF controls. However responses to non satiety related compounds such as nicotine, and baseline firing rate were also decreased, suggesting a global decrease in excitability. Current clamp experiments were performed on NGNs to assess the membrane properties in LFF and HFF neurons. Resting membrane potentials were similar -46.6 ± 3.5 mV (LFF, n=5) and -43.1 ± 2.5mV (HFF, n=5). Rheobase was significantly increased (34.0 ± 9.3 vs. 128.0 ± 24.6 pA, n=5, P < 0.05) and the number of action potentials at 2X rheobase was decreased (3.0 ± 0.8 vs. 1 ± 0, n= 5 p<0.05) in HFF compared to LFF, and there was a large, but non statistically significant reduction in input resistance (LFF, 725.6 ± 266.9 MΩ vs. HFF, 141 ± 15.6 MΩ). In Calcium imaging studies on HFF neurons, 0.5% (1/21) and 9.5% (2/21) of the neurons responded to 100nM CCK-8s and 1μM 5-HT respectively. The number of responsive neurons was higher in LFF mice CCK; 18.9 % (7/37), 5-HT; 21.6% (8/37). Conclusions: Responses to the satiety mediators CCK and 5-HT are significantly attenuated in gut vagal afferents. This reduction in response appears to be due at least in part to a global reduction in excitability of vagal afferents in diet induced obese mice, raising the possibility that high fat diet can cause vagal hyposensitivity, impairing normal satiety signals from the GI tract.

W1360 Effects of Rimonabant on Gastrointestinal Transit in Dogs

In Vitro extracellular recordings were performed from jejunal afferents. Nodose ganglion neurons (NGNs) were dissociated and plated onto coverslips. Whole cell patch clamp recordings or Fura-2AM calcium imaging experiments on NGNs were performed 18-24 h post-dissociation. Results: In recordings from jejunal afferents, responses to 100nM CCK (11.5 ± 3.2 vs. 3.35 ± 1.0 spikes/s n=10, p<0.05) and 10μM 5-HT (4.85 ± 1.4 vs. 1.75 ± 0.25, n=10, p<0.05) were decreased in HFF mice compared to LFF controls. However responses to non satiety related compounds such as nicotine, and baseline firing rate were also decreased, suggesting a global decrease in excitability. Current clamp experiments were performed on NGNs to assess the membrane properties in LFF and HFF neurons. Resting membrane potentials were similar -46.6 ± 3.5 mV (LFF, n=5) and -43.1 ± 2.5mV (HFF, n=5). Rheobase was significantly increased (34.0 ± 9.3 vs. 128.0 ± 24.6 pA, n=5, P < 0.05) and the number of action potentials at 2X rheobase was decreased (3.0 ± 0.8 vs. 1 ± 0, n= 5 p<0.05) in HFF compared to LFF, and there was a large, but non statistically significant reduction in input resistance (LFF, 725.6 ± 266.9 MΩ vs. HFF, 141 ± 15.6 MΩ). In Calcium imaging studies on HFF neurons, 0.5% (1/21) and 9.5% (2/21) of the neurons responded to 100nM CCK-8s and 1μM 5-HT respectively. The number of responsive neurons was higher in LFF mice CCK; 18.9 % (7/37), 5-HT; 21.6% (8/37). Conclusions: Responses to the satiety mediators CCK and 5-HT are significantly attenuated in gut vagal afferents. This reduction in response appears to be due at least in part to a global reduction in excitability of vagal afferents in diet induced obese mice, raising the possibility that high fat diet can cause vagal hyposensitivity, impairing normal satiety signals from the GI tract.

Glucagon-like peptide-1 inhibits voltage-gated potassium currents in mouse nodose ganglion neurons

Glucagon-like peptide-1 (GLP-1) is a major hormone known to regulate glucose homeostasis and gut function, and is an important satiety mediator. These actions are at least in part mediated via an action on vagal afferent neurons. However, the mechanism by which GLP-1 activates vagal afferents remains unknown. We hypothesized that GLP-1 acts on nodose ganglion neuron voltage-gated potassium (KV) channels, increasing membrane excitability. Employing perforated patch clamp recordings we examined the effects of GLP-1 on membrane properties as well as voltage-gated potassium currents. Extracellular recordings of jejunal afferents were performed to demonstrate the functional relevance of these effects at the nerve terminal. Glucagon-like peptide-1 depolarized a subpopulation of nodose neurons. This membrane depolarization was used to identify neurons containing functional GLP-1 receptors. In these neurons, GLP-1 decreased rheobase and broadened the action potential, and increased the number of action potentials elicited at twice rheobase. We identified a GLP-1 sensitive current whose reversal potential shifted in a depolarizing direction when extracellular potassium was increased. We identified two macroscopic K currents, IA, an inactivating current and IK a sustained current. GLP-1 caused inhibition of these currents, IK by 45%, P < 0.05 and IA currents by 52%P < 0.01, associated with a hyperpolarizing shift of steady-state inactivation curves for both currents. In extracellular recordings of jejunal afferents, GLP-1 increased firing rate, the effect blocked by the K(+) channel antagonist 4-AP. These experiments indicate that GLP-1 receptor activation results in vagal afferent excitation, due at least in part to inhibition of sustained and inactivating potassium currents. This mechanism may be important in satiety and glucose homeostatic signals arising from the gastrointestinal tract.

Differential afferent sensitivity to mucosal lipopolysaccharide from Salmonella typhimurium and Escherichia coli in the rat jejunum

Postinfectious irritable bowel syndrome may develop subsequent to acute bacterial enteritis. We therefore hypothesized that intestinal afferents may develop hypersensitivity upon exposure to luminal lipopolysaccharide (LPS) from pathogens but not from commensal bacteria and that this may be prostaglandin mediated. Extracellular recordings of jejunal afferents were obtained in vivo from male Wistar rats (n = 5 per group; 300-400 g). Lipopolysaccharide from Escherichia coli (E-LPS), Salmonella typhimurium (S-LPS) or vehicle were infused into the intestinal lumen at 5 mg mL(-1). The selective 5-HT(3)-receptor agonist 2-methyl-5-HT (2m5-HT, 15 microgkg(-1), i.v.) was administered at 15-min intervals before and up to 2 h after S-LPS administration. Intraluminal E-LPS had no effect on mesenteric afferent nerve discharge at baseline. By contrast, afferent discharge increased from 21.7 +/- 0.3 impsec(-1) to 28.8 +/- 3.4 impsec(-1) 40 min after S-LPS administration (mean +/- SEM; P < 0.05) and reached 38.8 +/- 4.1 impsec(-1) after 2 h (P < 0.05). The afferent response to 2m5-HT was enhanced 30 min following S-LPS by 30.9 +/- 3.9% (P < 0.05) and remained elevated thereafter. The increase in baseline discharge and sensitivity to 2m5-HT following S-LPS was prevented by pretreatment with naproxen (COX inhibitor, 10 mgkg(-1) i.v.) or AH-6809 (EP1/EP2 receptor antagonist, 1 mg kg(-1)). Intestinal afferents do not alter their discharge rate to LPS from E. coli but to LPS from the pathogenic bacterium S. typhimurium. The latter response entails afferent sensitisation to 2m5-HT that depends on prostanoid release. This acute sensitisation may prime the intestinal afferent innervation for a later development of persistent hypersensitivity.

Distinct chemical classes of medium-sized transient receptor potential channel vanilloid 1-immunoreactive dorsal root ganglion neurons innervate the adult mouse jejunum and colon

Physiological studies suggest visceral spinal afferents are generally small diameter, unmyelinated C-fibers or myelinated Aδ-fibers, but little is known about the size and chemical phenotypes of visceral sensory neurons supplying the small intestine. This study examines the size and expression patterns of transient receptor potential vanilloid 1 (TRPV1), calcitonin gene-related peptide (CGRP), substance P (SP), neuronal nitric oxide synthase (NOS) and isolectin B 4-binding (IB 4) in dorsal root ganglion (DRG) neurons projecting to the gastrointestinal tract. The spinal afferent innervation of mouse jejunum and distal colon was investigated with retrograde neuronal tracing and multi-label immunohistochemistry. Expression of histochemical markers and soma sizes of retrogradely labeled DRG profiles were determined with confocal microscopy. Most (>75%) jejunal and colonic afferent neurons were medium- and large-sized cells. The majority (82%) of jejunal afferents expressed TRPV1, but few bound IB 4. All retrogradely labeled jejunal afferents expressing NOS-immunoreactivity (64%) also expressed TRPV1 and CGRP and most expressed SP. Most labeled colonic afferents expressed TRPV1 (62%) and half expressed NOS. Taken together these data demonstrate that the spinal afferent supply of the jejunum and colon is largely from medium and large sensory neurons, suggesting most intestinal afferent axons are A fibers. The various chemically-defined subpopulations of afferents may play multiple roles in sensory innervation of the jejunum apart from nociceptive transduction. Additionally, we have identified a unique chemical code, TRPV1/NOS/CGRP/SP, that distinguishes many spinal afferent terminals from those of enteric neurons.

Gut perception in humans is modulated by interacting gut stimuli.

Digestive symptoms depend on multiple interacting gut stimuli, but integration of visceral afferent traffic is poorly understood. Our aim was to elucidate the contribution of simultaneous intestinal stimuli to conscious perception. In 17 healthy subjects, we performed stimulus-response trials of jejunal distensions (1-min duration at 5-min intervals in 8-ml increments) either alone or with a background electrical stimulus, and stimulus-response trials of electrical stimuli (1-min duration at 5-min intervals in 6-mA steps) either alone or with a background intestinal distension. The four stimulus-response trials were performed concomitantly applying the different types of stimuli in random order. Perception was measured on a scale of 0 to 6. Background stimulation markedly increased perception of test stimuli, reducing tolerance from 44 +/- 3 to 32 +/- 3 ml and from 67 +/- 6 to 33 +/- 4 mA (P < 0.05 for both). However, whereas jejunal distensions below the perception threshold did not modify perception of the background stimulus (4 +/- 1% change; not significant), unperceived electrical stimuli exerted a sensitizing effect and increased perception of the background distension up to uncomfortable levels (111 +/- 40% increment; P < 0.05). In conclusion, activation of different pools of jejunal afferents produces summative effects on perception, and this sensitizing effect can be exerted by unperceived stimulation of mechanoinsensitive jejunal afferents.

Somatostatin SST 2 receptor agonists inhibit bradykinin-sensitive jejunal afferents in the rat

Somatostatin SST 2 receptor agonists inhibit bradykinin-sensitive jejunal afferents in the rat

Modulation of gastrointestinal afferent sensitivity by a novel substituted benzamide (ecabapide)

The effects of ecabapide, a novel substituted benzamide compound (3-[2-(3,4-dimethoxyphenyl)ethylcarbamoylmethyl]amino- N-methylbenzamide) that has gastrointestinal prokinetic action, were examined on the discharge of extrinsic afferent nerves supplying the stomach and jejunum in anaesthetized rats. Ecabapide (60 and 180 μg kg −1, iv) had no effect on the baseline discharge of vagal gastric distension-sensitive afferents or the stimulus–response profile to gastric distension. Ecabapide also had no effect on either spontaneous jejunal mesenteric afferent nerve discharge or responses to intestinal distension. Ecabapide (180 μg kg −1) significantly inhibited the maximum discharge of jejunal afferents induced by cholecystokinin (CCK 8; 50 pmol, iv), whereas it failed to inhibit the excitatory action of 2-methyl-5-hydroxytryptamine (2Me-5-HT; 10 μg, iv), a selective 5-HT 3 receptor agonist. A model of acute focal intestinal ischaemia was used to evaluate the actions of ecabapide on the discharge of activated jejunal afferents. Ischaemia produced a substantial increase in afferent discharge which was reproducible when the duration of ischaemia was limited to less than 10 min and repeated every 15 min. Ecabapide at doses of 60 and 180 μg kg −1 significantly reduced ischaemia-induced increases in afferent discharge. In addition to its therapeutic efficacy as a gastrointestinal prokinetic agent, these findings show also that ecabapide may also have an inhibitory action on the discharge of intestinal afferents activated by ischaemia.

Serotonin and cholecystokinin activate different populations of rat mesenteric vagal afferents

This electrophysiological study was performed to elucidate the interactions of serotonin (5-hydroxytryptamine, 5-HT) and cholecystokinin (CCK) on mesenteric afferents supplying the rat jejunum. 5-HT and CCK produced characteristic responses in multi-unit recordings of mesenteric afferents. Waveform analysis to extract single units from the whole nerve recording identified populations of single afferents that were sensitive to either 5-HT or CCK, but not both. Furthermore, devazepide (0.5 mg/kg) completely abolished the response to CCK without altering the response to 5-HT while granisetron (0.5 mg/kg) abolished the response to 5-HT with no effect on the response to CCK. These results suggest that there are discrete, non-interactive populations of jejunal afferents that possess either 5-HT 3 or CCK-A receptors but not both.

Differential effects of naproxen on ischemia and reperfusion-induced excitation of jejunal afferents in the anaesthetised rat

Differential effects of naproxen on ischemia and reperfusion-induced excitation of jejunal afferents in the anaesthetised rat