Mechanisms involved in the muscle relaxing effects of STW 5 in guinea pig stomach

INTRODUCTION

The herbal preparation STW 5 ameliorates functional dyspepsia partly by relaxing smooth muscle of the proximal stomach, thus improving gastric accommodation. We explored the unknown pathways responsible for this effect by testing targets known to modulate gastric smooth muscle relaxation.

METHODS

STW 5-induced relaxation of smooth muscle strips from guinea pig gastric corpus before and after pharmacological interventions were recorded with force transducers in an organ bath. ORAI1 mRNA expression was tested in the proximal stomach.

KEY RESULTS

Blockade of Ca2+ -activated K+ and Cl- channels, voltage-gated L- or T-type Ca2+ channels, TRPA1-, TRPV1-, adenosine or 5-HT4 receptors, antagonizing ryanodine receptors, inhibiting cyclooxygenase or sarcoplasmic reticulum calcium ATPase did not affect STW 5-evoked relaxation. Likewise, protein-kinase A or G were not involved. However, the relaxation evoked by STW 5 was significantly reduced by phorbol-12-myristat-13-acetat, an activator of protein-kinase C, by 2- aminoethyldiphenylborinate, an inhibitor of the IP3 receptor-mediated Ca2+ release from the sarcoplasmic reticulum or by SKF-96365, a nonselective store-operated calcium entry (SOCE) blocker. Furthermore, the mixed TRPC3/SOCE inhibitor Pyr3, but not the selective TRPC3 blocker Pyr10, reduced the effect of STW 5. Finally, BTP2, a potent blocker of ORAI-coupled SOCE, almost abolished STW 5-evoked relaxation. Expression of ORAI1 could be demonstrated in the corpus/fundus.

CONCLUSIONS & INFERENCES

STW 5 inhibited SOCE, most likely ORAI channels, which are modulated by IP3- and PKC-dependent mechanisms. Our findings impact on the design of drugs to induce muscle relaxation and help identify phytochemicals with similar modes of actions to treat gastrointestinal disturbances.

Allergen-free extracts from birch, ragweed, and hazel pollen activate human and guinea-pig submucous and spinal sensory neurons

BACKGROUND

Non-allergenic, low molecular weight components of pollen grains are suspected to trigger changes in gut functions, sometimes leading to inflammatory conditions. Based on extensive neuroimmune communication in the gut wall, we investigated the effects of aqueous pollen extracts (APE) on enteric and spinal sensory neurons.

METHODS

Using Ca²⁺ and fast potentiometric imaging, we recorded the responses of guinea-pig and human submucous and guinea-pig dorsal root ganglion (DRG) neurons to microejection of low (<3 kDa) and high (≥3 kDa) molecular weight APEs of birch, ragweed, and hazel. Histamine was determined pharmacologically and by mass spectrometry (LC-MS/MS).

KEY RESULTS

Birch APE_<3kDa evoked strong [Ca⁺² ]_i signals in the vast majority of guinea-pig DRG neurons, and in guinea-pig and human enteric neurons. The effect of birch APE_≥3kDa was much weaker. Fast neuroimaging in human enteric neurons revealed an instantaneous spike discharge after microejection of birch, ragweed, and hazel APE_<3kDa [median (interquartile range) at 7.0 Hz (6.2/9.8), 5.7 Hz (4.4/7.1), and 8.4 Hz (4.3/12.5), respectively]. The percentage of responding neurons per ganglion were similar [birch 40.0% (33.3/100.0), ragweed 50.8% (34.4/85.6), and hazel 83.3% (57.1/100.0)]. A mixture of histamine receptor (H1-H3) blockers significantly reduced nerve activation evoked by birch and ragweed APEs_<3kDa , but was ineffective on hazel. Histamine concentrations in ragweed, birch and hazel APE's < 3 kDa were 0.764, 0.047, and 0.013 μM, respectively.

CONCLUSIONS

Allergen-free APEs from birch, ragweed, and hazel evoked strong nerve activation. Altered nerve-immune signaling as a result of severe pollen exposure could be a pathophysiological feature of allergic and non-allergic gut inflammation.

Macrophages and glia are the dominant P2X7-expressing cell types in the gut nervous system-No evidence for the role of neuronal P2X7 receptors in colitis

The blockade or deletion of the pro-inflammatory P2X7 receptor channel has been shown to reduce tissue damage and symptoms in models of inflammatory bowel disease, and P2X7 receptors on enteric neurons were suggested to mediate neuronal death and associated motility changes. Here, we used P2X7-specific antibodies and nanobodies, as well as a bacterial artificial chromosome transgenic P2X7-EGFP reporter mouse model and P2rx7^-/- controls to perform a detailed analysis of cell type-specific P2X7 expression and possible overexpression effects in the enteric nervous system of the distal colon. In contrast to previous studies, we did not detect P2X7 in neurons but found dominant expression in glia and macrophages, which closely interact with the neurons. The overexpression of P2X7 per se did not induce significant pathological effects. Our data indicate that macrophages and/or glia account for P2X7-mediated neuronal damage in inflammatory bowel disease and provide a refined basis for the exploration of P2X7-based therapeutic strategies.

Distension evoked mucosal secretion in human and porcine colon in vitro

It was suggested that intestinal mucosal secretion is enhanced during muscle relaxation and contraction. Mechanisms of mechanically induced secretion have been studied in rodent species. We used voltage clamp Ussing technique to investigate, in human and porcine colonic tissue, secretion evoked by serosal (Pser) or mucosal (Pmuc) pressure application (2-60 mmHg) to induce distension into the mucosal or serosal compartment, respectively. In both species, Pser or Pmuc caused secretion due to Cl- and, in human colon, also HCO3- fluxes. In the human colon, responses were larger in proximal than distal regions. In porcine colon, Pmuc evoked larger responses than Pser whereas the opposite was the case in human colon. In both species, piroxicam revealed a strong prostaglandin (PG) dependent component. Pser and Pmuc induced secretion was tetrodotoxin (TTX) sensitive in porcine colon. In human colon, a TTX sensitive component was only revealed after piroxicam. However, synaptic blockade by ω-conotoxin GVIA reduced the response to mechanical stimuli. Secretion was induced by tensile rather than compressive forces as preventing distension by a filter inhibited the secretion. In conclusion, in both species, distension induced secretion was predominantly mediated by PGs and a rather small nerve dependent response involving mechanosensitive somata and synapses.

How big is the little brain in the gut? Neuronal numbers in the enteric nervous system of mice, Guinea pig, and human

BACKGROUND

Despite numerous studies on the enteric nervous system (ENS), we lack fundamental knowledge on neuronal densities or total neuron numbers in different species. There are more anecdotal than actual figures on nerve counts.

METHODS

We used standardized preparation techniques and immunohistochemistry with validated panneuronal markers (human or mouse anti-HuD/C) to determine neuronal densities in specimen from the entire gastrointestinal tract of mice, guinea pig, and humans. In parallel, we measured the dimensions of the gastrointestinal regions in mouse and guinea pig. For humans, we had to rely on literature data.

KEY RESULTS

The average neuronal densities along the gastrointestinal tract were 35,011 ± 25,017 1/cm² for the myenteric and 16,685 ± 9098 1/cm² for the submucous plexus in mice, 24,315 ± 16,627 and 11,850 ± 6122 1/cm² for guinea pig myenteric and submucous plexus, respectively, and 21,698 ± 9492 and 16,367 ± 5655 1/cm² for human myenteric and submucous plexus, respectively. The total number of neurons in the ENS was 2.6 million for mice, 14.6 million for guinea pig, and 168 million for human.

CONCLUSIONS & INFERENCES

This study reports the first comprehensive nerve cell count in mice, guinea pig, and human ENS. Neuronal densities were comparable between the three species and the differences in the total numbers of enteric neurons are likely due to body size and intestinal length. The number of enteric neurons is comparable to the number of neurons in the spinal cord for all three species.

Metabotropic 5-HT receptor-mediated effects in the human submucous plexus

BACKGROUND

Serotonin (5-HT) is an important mediator in the gastrointestinal tract, acting on different neuronal 5-HT receptors. The ionotropic 5-HT₃ receptor mediates immediate but transient spike discharge in human enteric neurons. We studied the role of the metabotropic 5-HT_1P , 5-HT₄ , and 5-HT₇ receptors to activate human submucous neurons.

METHODS

Neuroimaging using the voltage sensitive dye Di-8-ANEPPS was performed in submucous plexus preparations from human surgical specimens of the small and large intestine. We synthesized a new, stable 5-HT_1P agonist, 5-benzyloxyhydrazonoindalpine (5-BOHIP).

KEY RESULTS

5-HT evoked a fast and late-onset spike discharge in enteric neurons. The fast component was blocked by the 5-HT₃ receptor antagonist cilansetron, while the remaining sustained response was significantly reduced by the 5-HT_1P receptor antagonist 5-hydroxytryptophanyl-5-hydroxytryptophan amide (5-HTP-DP). The newly synthesized 5-HT_1P agonist 5-BOHIP induced a slowly developing, long-lasting activation of submucous neurons, which was blocked by 5-HTP-DP. We could not demonstrate any 5-HT₇ receptor-induced spike discharge based on the lack of response to 5-carboxamidotryptamine. Similarly, the 5-HT₄ agonists 5-methoxytryptamine and prucalopride evoked no immediate or late-onset spike discharge.

CONCLUSIONS & INFERENCES

Our work demonstrated for the first time the presence of functional 5-HT_1P receptors on human submucous neurons. Furthermore, we found no evidence for a role of 5-HT₄ or 5-HT₇ receptors in the postsynaptic activation of human submucous neurons by 5-HT.

Contribution of the Enteric Nervous System to Autoimmune Diseases and Irritable Bowel Syndrome

Anti-neuronal autoantibodies can lead to subacute gastrointestinal dysmotility, presenting with various symptoms typical of intestinal pseudoobstruction, achalasia, gastroparesis, or slow intestinal transit, among others. Such autoantibodies may be produced in response to a remote tumor and accelerate the diagnosis of malignancy, but in other cases they appear without an identifiable underlying cause. One example is the type I anti-neuronal nuclear antibody (ANNA-1 otherwise known as anti-Hu), which is usually linked to small cell-lung carcinoma. Anti-Hu can directly activate enteric neurons and visceral sensory nerve fibers and has a cytotoxic effect. Various other anti-neuronal antibodies have been described, targeting different ion channels or receptors on nerve cells of the central or the enteric nervous system. Autoimmune processes targeting enteric neurons may also play a role in more common disorders such as esophageal achalasia, celiac disease, or multiple sclerosis. Furthermore, anti-enteric neuronal antibodies have been found more abundant in the common functional gastrointestinal disorder, irritable bowel syndrome (IBS), than in controls. The pathogenesis of IBS is very complex, involving the release of various mediators from immune cells in the gut wall. Products of mast cells, such as histamine and tryptase, excite visceral afferents and enteric neurons, which may contribute to symptoms like abdominal pain and disturbed motility. Elevated serine- and cysteine-protease activity in stool of IBS-D and IBS-C patients, respectively, can be a factor leading to leaky gut and visceral hypersensitivity. More knowledge on these mediators in IBS may facilitate the development of novel diagnostic methods or therapies.

Immunofluorescence Staining of P2X7 Receptors in Whole-Mount Myenteric Plexus Preparations

P2X7 receptors play an important role in cytokine release and immune cell regulation. Their upregulation has been described in inflammatory and degenerative processes and P2X7 blockade or deletion has been shown to reduce tissue damage and severity of symptoms in animal models of inflammatory bowel disease (IBD). Several studies have found that P2X7 receptors are present on enteric neurons and glia and it was proposed that they mediate neuronal death during IBD. However, the cell type-specific localization of P2X7 receptors has been a matter of debate, since some antibodies have been found to be unspecific. Here we describe the preparation of whole-mount myenteric plexus from the colon of BAC transgenic P2X7-EGFP reporter mice and subsequent immunofluorescence staining of P2X7 receptors together with cell type-specific marker proteins.

Fast synaptic excitatory neurotransmission in the human submucosal plexus

BACKGROUND

Acetylcholine is the main excitatory neurotransmitter in the enteric nervous system (ENS) in all animal models examined so far. However, data for the human ENS is scarce.

METHODS

We used neuroimaging using voltage and calcium dyes, Ussing chamber, and immunohistochemistry to study fast synaptic neurotransmission in submucosal plexus neurons of the human gut.

KEY RESULTS

Electrical stimulation of intraganglionic fiber tracts led to fast excitatory postsynaptic potentials (fEPSPs) in 29 submucosal neurons which were all blocked by the nicotinic antagonist hexamethonium. The nicotinic agonist DMPP mimicked the effects of electrical stimulation and had excitatory effects on 56 of 73 neurons. The unselective NMDA antagonist MK-801 blocked fEPSPs in 14 out of 22 neurons as well as nicotine evoked spike discharge. In contrast, the application of NMDA showed only weak effects on excitability or calcium transients. This agreed with the finding that the specific NMDA antagonist D-APV reduced fEPSPs in only 1 out of 40 neurons. Application of AMPA or kainite had no effect in 41 neurons or evoked spike discharge in only one out of 41 neurons, respectively. Immunohistochemistry showed that 98.7 ± 2.4% of all submucosal neurons (n = 6 preparations, 1003 neurons) stained positive for the nicotinic receptor (α₁ , α₂ or α₃ -subunit). Hexamethonium (200 µM) reduced nerve-evoked chloride secretion by 34.3 ± 18.6% (n = 14 patients), whereas D-APV had no effect.

CONCLUSION & INFERENCE

Acetylcholine is the most important mediator of fast excitatory postsynaptic transmission in human submucous plexus neurons whereas glutamatergic fEPSPs were rarely encountered.

Translating the seminal findings of Carl Lüderitz: A description in English of his extraordinary studies of gastrointestinal motility accompanied by a historical view of peristalsis

BACKGROUND

Carl Lüderitz provided the first comprehensive description of peristalsis in vivo in his publication from 1889 before Bayliss and Starling described the peristaltic reflex in isolated intestinal segments ex vivo 10 years later. At that time, the peristaltic reflex, responsible for progression of intestinal content, was referred to as the Lüderitz-Bayliss-Starling reflex. This shows that his peers around 1900 were very well aware of the significant impact of Lüderitz´s papers.

PURPOSE

A major intention in this review is to bring the significant contributions by Dr. Carl Lüderitz (1854-1930) to the attention of our colleagues working in the field of Gastroenterology, in particular those interested in Neurogastroenterology and Gastrointestinal Motility. Until 1891, Carl Lüderitz published five more papers on the sensory and motor components of peristalsis including one seminal paper on stimulus-evoked muscle responses in the stomach in vivo. For most of his life, Carl Lüderitz was a practicing physician and doctor for the poor in Berlin. He spent a rather short time in academia, mostly during his studies in Jena under supervision of his cousin, the famous internist Hermann Nothnagel, and later in Berlin, where he volunteered for short periods at various university institutes but without any formal appointment. This paper is to honor Carl Lüderitz. We divided it into four chapters: a short biography, a summary and evaluation of his contributions, a translation of his seminal paper on peristalsis, and finally a historical view on peristalsis.

Region-specific effects of the cysteine protease papain on gastric motility

BACKGROUND

Papaya is a traditional remedy for gastrointestinal complaints in the folk medicine. On this basis, papain, a cysteine protease of the fruit, is sold as a nutritional supplement, although scientific data on its effects in the gastrointestinal tract are lacking. We aimed to explore the effect of papain on gastric motility in vitro.

METHODS

Guinea pig antrum and corpus strips were mounted in organ bath.

KEY RESULTS

Papain reversibly increased the amplitude of ongoing phasic contractions in both circular and longitudinal antrum strips without having an effect on the frequency or on the muscle tone. All three tested doses of papain (end cc.: 12.5 mg L^-1 , 50 mg L^-1 , 100 mg L^-1 ) were similarly effective. Contrarily, in the corpus circular and longitudinal muscle strips, papain caused a dose-dependent relaxation, which was preceded by a transient contraction in most tissues. The effect was resistant to tetrodotoxin (1 µM), but diminished by the cysteine protease inhibitor E64 (4.5 µM) in both regions. In the corpus, L-NAME (100 µM) and the protease-activated receptor (PAR)-1 antagonist SCH79797 (5 µM) or the PAR-2 antagonist GB 83 (3 µM) did not change the effect of papain significantly. This demonstrates that the effects of papain are not neurally mediated and nitrergic pathways are not involved in the mechanism. The effects are linked to the enzymatic activity, but not executed via PAR-1 or 2.

CONCLUSIONS AND INFERENCES

Papain alters gastric motility in a region-specific manner, which could at least partly explain its claimed beneficial effects in functional gastrointestinal disorders.

Woran starben Dr. Carl Lüderitz (1854–1930) und seine Vor- und Nachfahren?

Diagnostik allein auf der Basis von Symptomen und Symptombeschreibungen ist heute selten, war aber im 18. und 19. Jahrhundert eher die Regel.

Methoden In diesem medizinhistorischen Projekt wurden die Todesursachen von 25 Vor- und Nachfahren des Berliner Arztes und Wissenschaftlers Dr. Carl Lüderitz (1854–1930) aus historischen Quellen zusammengetragen und mit Daten zur Todesursachenstatistik des 18. und 19. Jahrhunderts verglichen. Zehn aktiven Gastroenterologen/-innen wurde ein Tagebuchausschnitt des laienhaft beschriebenen Todes eines Berliner Kaufmanns (des Großvaters von Carl Lüderitz) im Jahr 1846 durch seinen Sohn vorgelegt mit der Bitte um eine Verdachtsdiagnose.

Ergebnisse Vier bzw. 5 Fälle von vermutlicher Leberzirrhose unter den 26 Angehörigen der Familie Lüderitz sind überproportional im Vergleich zu Sterbestatistiken in Berlin und auf dem Lande, während die Schwindsucht (Tuberkulose) mit nur einem Fall unterrepräsentiert ist. Durchschnittlich wurden Frauen in dieser Familie 10 Jahre älter, unabhängig vom Jahr des Todes (1787 bis 2006). Acht der befragten Gastroenterologen/-innen waren der Meinung, dass der Tod aufgrund einer dekompensierten Leberzirrhose mit Blutungen aus Ösophagusvarizen eintrat, mit Ödemen auf der Basis einer daraus folgenden Herzinsuffizienz.

Schlussfolgerung Auch historische Dokumente können zur Aus- und Fortbildung oder zur Qualitätskontrolle in der Gastroenterologie beitragen.

Effects of the herbal preparation STW 5-II on in vitro muscle activity in the guinea pig stomach

BACKGROUND

STW 5 is a combination of nine medicinal herbal extracts and used to treat functional gastrointestinal disorders including functional dyspepsia. It has a region-specific effect by relaxing the proximal and contracting the distal stomach. The research combination STW 5-II (Iberogast^® Advance) lacks three herbal extracts but seems clinically as effective as STW 5. However, the action of STW 5-II on gastric motility is unknown.

METHODS

In vitro circular and longitudinal muscle tone and contractility were recorded from guinea pig gastric fundus and antrum with isometric force transducers.

KEY RESULTS

STW 5-II decreased concentration-dependently (64-512 µg/ml) the tone of circular and longitudinal muscle strips from the fundus. In contrast, STW 5-II increased concentration-dependently contraction amplitude in antral circular and longitudinal muscle. The effects were region-dependent but comparable in the two muscle layers. Application of 512 µg STW 5 or STW 5-II revealed comparable effects in the fundus and antrum circular and longitudinal muscle strips.

CONCLUSIONS AND INTERFERENCES

STW 5-II had a region-specific effect and relaxed the proximal stomach but increased the contractility in the antrum. It was as effective as STW 5 which may explain its comparable clinical effects in treating functional dyspepsia. Impaired accommodation may be normalized through relaxation of the fundus, while the motility-promoting effects leading to an increase in antral motility may activate the gastric pump.

Autoimmune encephalitis and gastrointestinal dysmotility: achalasia, gastroparesis, and slow transit constipation

BACKGROUND

 Neurological autoimmune disorders (NAD) are caused by autoimmune inflammation triggered by specific antibody subtypes. NAD may disturb the gut-brain axis at several levels including brain, spinal cord, peripheral, or enteric nervous system.

CASE REPORT

 We present a case with antinuclear neuronal Hu (ANNA-1)- and antiglial nuclear (SOX-1) autoimmune antibody-positive limbic encephalitis and significant gastrointestinal dysmotility consisting of achalasia type II, gastroparesis, altered small intestinal interdigestive motility, and severe slow transit constipation. The autoantibodies of the patient's serum labeled enteric neurons and interstitial cells of Cajal but no other cells in the gut wall. Achalasia was treated successfully by pneumatic cardia dilation and gastrointestinal dysmotility successfully with prucalopride.

CONCLUSION

 NAD may disturb gastrointestinal motility by altering various levels of the gut-brain axis.

Submucosal enteric neurons of the cavine distal colon are sensitive to hypoosmolar stimuli

KEY POINTS

Neurons of the enteric submucous plexus are challenged by osmolar fluctuations during digestion and absorption of nutrients. Central neurons are very sensitive to changes in osmolality but knowledge on that issue related to enteric neurons is sparse. The present study focuses on investigation of osmosensitivity of submucosal neurons including potential molecular mediating mechanisms. Results show that submucosal neurons respond to hypoosmolar stimuli with increased activity which is partially mediated by the transient receptor potential vanilloid 4 channel. We provided important information on osmosensitive properties of enteric neurons. These data are fundamental to better explain the nerve-mediated control of the gastrointestinal functions during physiological and pathophysiological (diarrhoea) conditions.

ABSTRACT

Enteric neurons are located inside the gut wall, where they are confronted with changes in osmolality during (inter-) digestive periods. In particular, neurons of the submucous plexus (SMP), located between epithelial cells and blood vessels may sense and respond to osmotic shifts. The present study was conducted to investigate osmosensitivity of enteric submucosal neurons and the potential role of the transient receptor potential vanilloid 4 channel (TRPV4) as a mediator of enteric neuronal osmosensitivity. Therefore, freshly dissected submucosal preparations from guinea pig colon were investigated for osmosensitivity using voltage-sensitive dye and Ca²⁺ imaging. Acute hypoosmolar stimuli (final osmolality reached at ganglia of 94, 144 and 194 mOsm kg^-1 ) were applied to single ganglia using a local perfusion system. Expression of TRPV4 in the SMP was quantified using qRT-PCR, and GSK1016790A and HC-067047 were used to activate or block the receptor, respectively, revealing its relevance in enteric osmosensitivity. On average, 11.0 [7.0/17.0] % of submucosal neurons per ganglion responded to the hypoosmolar stimulus. The Ca²⁺ imaging experiments showed that glia responded to the hypoosmolar stimulus, but with a delay in comparison with neurons. mRNA expression of TRPV4 could be shown in the SMP and blockade of the receptor by HC-067047 significantly decreased the number of responding neurons (0.0 [0.0/6.3] %) while the TRPV4 agonist GSK1016790A caused action potential discharge in a subpopulation of osmosensitive enteric neurons. The results of the present study provide insight into the osmosensitivity of submucosal enteric neurons and strongly indicate the involvement of TRPV4 as an osmotransducer.

The enteric nervous system: “A little brain in the gut”

The gut’s own autonomous nervous system, the enteric nervous system (ENS), has fascinated scientists for more than 100 years. It functions, in the true sense of the word, autonomously, by performing complex tasks and controlling vital functions independently of extrinsic inputs. At the same time, the ENS is bombarded with signals from other cells in the gut wall and lumen and has to integrate all of these inputs. We describe the main functions of the ENS under physiological conditions and give a few examples of its role in gut diseases. The ENS has received increasing attention recently as scientists outside the field of Neurogastroenterology realize its important role in the pathogenesis of Parkinson’s, autism and multiple sclerosis.

Peppermint and caraway oils have muscle inhibitory and pro-secretory activity in the human intestine in vitro

BACKGROUND

Herbal medicinal products with a broad activity spectrum may be promising alternatives to treat functional gastrointestinal disorders (FGD). Menthacarin^® is a drug with a fixed combination of peppermint and caraway oils, which is clinically used to treat FGD-associated symptoms.

MATERIALS

We studied the effects of peppermint and caraway oils on contractile and secretory activity in 255 human small and large intestinal preparations derived from surgical resections (73 patients). Motility was recorded in circular smooth muscle strips and secretion with the Ussing chamber-voltage clamp technique. Electrical field stimulation evoked nerve induced contractile responses. KEY RESULTS: Peppermint and caraway oil concentrations dependently inhibited muscle contractility as indicated by sustained muscle relaxation and decrease in phasic contractility. These effects occurred in small and large intestinal preparations with IC₅₀ values ranging between 17 and 90 µg/mL for peppermint oil and between 7 and 127 µg/mL for caraway oil. Neither peppermint nor caraway oil influenced the nerve evoked contractile response. The inhibition of contractile activity, but not the muscle relaxation, was prevented by the L-type calcium channel activator Bay K8644 but not by the neurotoxin tetrodotoxin. Both peppermint oil and caraway oil increased epithelial secretion, which remained in tetrodotoxin.

CONCLUSION & INTERFERENCE

The findings revealed a strong muscle inhibitory and pro-secretory action of peppermint and caraway oils at clinically relevant concentrations. Both actions were nerve-independent. The inhibition of contractility was mediated by inhibition of L-type calcium channels. The effects on muscle and epithelial activity may contribute to the beneficial effects observed in patients with FGD.

To learn, to remember, to forget-How smart is the gut?

The enteric nervous system (ENS) resides within the gut wall and autonomously controls gut functions through coordinated activation of sensory, inter and motor neurons. Its activity is modulated by the enteric immune and endocrine system as well as by afferent and efferent nerves of the parasympathetic and sympathetic nervous system. The ENS is often referred to as the second brain and hence is able to perform sophisticated tasks. We review the evidence that the "smartness" of the ENS may even extend to its ability to learn and to memorize. Examples for habituation, sensitization, conditioned behaviour and long-term facilitation are evidence for various forms of implicit learning. Moreover, we discuss how this may change not only basic Neurogastroenterology but also our understanding of development of gut diseases and chronic disorders in gut functions. At the same time, we identify open questions and future challenges to confirm learning, memory and memory deficits in the gut. Despite some remaining experimental challenges, we are convinced that the gut is able to learn and are tempted to answer the question with: Yes, the gut is smart.

The Diagnosis and Treatment of Functional Dyspepsia

BACKGROUND

Functional dyspepsia (FD) is one of the more common functional disorders, with a prevalence of 10-20%. It affectsthe gastrointestinal tract.

METHODS

This article is based on publications retrieved by a selective search of PubMed, with special attention to controlled trials, guidelines, and reviews.

RESULTS

Typical dyspeptic symptoms in functional dyspepsia include epigastric pain, sensations of pressure and fullness, nausea, and early subjective satiety. The etiology of the disorder is heterogeneous and multifactorial. Contributory causes include motility disturbances, visceral hypersensitivity, elevated mucosal permeability, and disturbances of the autonomic and enteric nervous system. There is as yet no causally directed treatment for functional dyspepsia. Its treatment should begin with intensive patient education regarding the benign nature of the disorder and with the establishment of a therapeutic pact for long-term care. Given the absence of a causally directed treatment, drugs to treat functional dyspepsia should be given for no more than 8-12 weeks. Proton-pump inhibitors, phytotherapeutic drugs, and Helicobacter pylori eradication are evidence-based interventions. For intractable cases, tricyclic antidepressants and psychotherapy are further effective treatment options.

CONCLUSION

The impaired quality of life of patients with functional dyspepsia implies the need for definitive establishment of the diagnosis, followed by symptom-oriented treatment for the duration of the symptomatic interval.

Targeting nNOS ameliorates the severe neuropathic pain due to chronic pancreatitis

BACKGROUND

Pain due to pancreatic cancer/PCa or chronic pancreatitis/CP, is notoriously resistant to the strongest pain medications. Here, we aimed at deciphering the specific molecular mediators of pain at surgical-stage pancreatic disease and to discover novel translational targets.

METHODS

We performed a systematic, quantitative analysis of the neurotransmitter/neuroenzmye profile within intrapancreatic nerves of CP and PCa patients. Ex vivo neuronal cultures treated with human pancreatic extracts, conditional genetically engineered knockout mouse models of PCa and CP, and the cerulein-induced CP model were employed to explore the therapeutic potential of the identified targets.

FINDINGS

We identified a unique enrichment of neuronal nitric-oxide-synthase (nNOS) in the pancreatic nerves of CP patients with increasing pain severity. Employment of ex vivo neuronal cultures treated with pancreatic tissue extracts of CP patients, and brain-derived-neurotrophic-factor-deficient (BDNF^+/-) mice revealed neuronal enrichment of nNOS to be a consequence of BDNF loss in the progressively destroyed pancreatic tissue. Mechanistically, nNOS upregulation in sensory neurons was induced by tryptase secreted from perineural mast cells. In a head-to-head comparison of several genetically induced, painless mouse models of PCa (KPC, KC mice) or CP (Ptf1a-Cre;Atg5^fl/fl) against the hypersecretion/cerulein-induced, painful CP mouse model, we show that a similar nNOS enrichment is present in the painful cerulein-CP model, but absent in painless genetic models. Consequently, mice afflicted with painful cerulein-induced CP could be significantly relieved upon treatment with the specific nNOS inhibitor NPLA.

INTERPRETATION

We propose nNOS inhibition as a novel strategy to treat the unbearable pain in CP. FUND: Deutsche Forschungsgemeinschaft/DFG (DE2428/3-1 and 3-2).

Imaging of mast cells

Mast cells are a part of the innate immune system implicated in allergic reactions and the regulation of host-pathogen interactions. The distribution, morphology and biochemical composition of mast cells has been studied in detail in vitro and on tissue sections both at the light microscopic and ultrastructural level. More recently, the development of fluorescent reporter strains and intravital imaging modalities has enabled first glimpses of the real-time behavior of mast cells in situ. In this review, we describe commonly used imaging approaches to study mast cells in cell culture as well as within normal and diseased tissues. We further describe the interrogation of mast cell function via imaging by providing a detailed description of mast cell-nerve plexus interactions in the intestinal tract. Together, visualizing mast cells has expanded our view of these cells in health and disease.

bis-(p-hydroxyphenyl)-pyridyl-2-methane (BHPM)-the active metabolite of the laxatives bisacodyl and sodium picosulfate-enhances contractility and secretion in human intestine in vitro

BACKGROUND

Stimulant laxatives are widely used to treat constipation. We investigated in human small and large intestinal preparations the effects of bis-(p-hydroxyphenyl)-pyridyl-2-methane (BHPM), the active metabolite of the laxatives bisacodyl and sodium picosulfate on smooth muscle tone and epithelial secretion.

METHODS

Circular and longitudinal muscle tone of small or large intestinal preparations were recorded with isometric force transducers. Epithelial ion flux (I_SC ) and tissue resistance was measured with Ussing chamber technique after apical and basolateral BHPM application to large intestinal mucosa/submucosa preparations. Studies were performed in macroscopically normal specimens from 79 patients.

KEY RESULTS

BHPM concentration-dependently (0.5-5 μM) increased the tone of circular and longitudinal muscle from small to large intestine. The effect was strongest in large intestinal longitudinal muscle and smallest in small intestinal circular muscle. Increase in muscle tone was prevented by the L-type Ca⁺⁺ channel blocker nifedipine but insensitive to the nerve blocker tetrodotoxin. Apical or basolateral BHPM concentration-dependently decreased or increased I_SC, respectively. The K_Ca 1.1 (BK) channel blocker iberiotoxin reversed apical I_SC decrease whereas tetrodotoxin reversed basolateral I_SC increase. BHPM had no effect on tissue resistance or nerve-mediated secretory or muscle response with one exception: at the highest concentration basolateral BHPM reduced nerve-mediated secretion.

CONCLUSIONS AND INTERFERENCES

BHPM enhanced mucosal secretion and muscle contractility. Results suggested that the laxative effect of BHPM was a consequence of the increase in muscle tone as well as an increased K⁺ secretion when acting luminally and a nerve-driven Cl^- and HCO₃^- secretion once acting basolaterally after absorption.

High prevalence and functional effects of serum antineuronal antibodies in patients with gastrointestinal disorders

BACKGROUND

Antineuronal antibodies can be associated with both gastrointestinal (GI) and brain disorders. For example, antibodies against the potassium channel subunit dipeptidyl-peptidase-like protein-6 (DPPX) bind to neurons in the central nervous system (CNS) and myenteric plexus and cause encephalitis, commonly preceded by severe unspecific GI symptoms. We therefore investigated the prevalence of antineuronal antibodies indicative of treatable autoimmune CNS etiologies in GI patients.

METHODS

Serum samples of 107 patients (Crohn's disease n = 42, ulcerative colitis n = 16, irritable bowel syndrome n = 13, others n = 36) and 44 healthy controls were screened for anti-DPPX and further antineuronal antibodies using immunofluorescence on rat brain and intestine and cell-based assays. Functional effects of high-titer reactive sera were assessed in organ bath and Ussing chamber experiments and compared to non-reactive patient sera.

KEY RESULTS

Twenty-one of 107 patients (19.6%) had antibodies against the enteric nervous system, and 22 (20.6%) had anti-CNS antibodies, thus significantly exceeding frequencies in healthy controls (4.5% each). Screening on cell-based assays excluded established antienteric antibodies. Antibody-positive sera were not associated with motility effects in organ bath experiments. However, they induced significant, tetrodotoxin (TTX)-insensitive secretion in Ussing chambers compared to antibody-negative sera.

CONCLUSIONS & INFERENCES

Antineuronal antibodies were significantly more frequent in GI patients and associated with functional effects on bowel secretion. Future studies will determine whether such antibodies indicate patients who might benefit from additional antibody-directed therapies. However, well-characterized encephalitis-related autoantibodies such as against DPPX were not detected, underlining their rarity in routine cohorts.

Protease signaling through protease activated receptor 1 mediate nerve activation by mucosal supernatants from irritable bowel syndrome but not from ulcerative colitis patients

Background & aims

The causes of gastrointestinal complaints in irritable bowel syndrome (IBS) remain poorly understood. Altered nerve function has emerged as an important pathogenic factor as IBS mucosal biopsy supernatants consistently activate enteric and sensory neurons. We investigated the neurally active molecular components of such supernatants from patients with IBS and quiescent ulcerative colitis (UC).

Method

Effects of supernatants from 7 healthy controls (HC), 20 IBS and 12 UC patients on human and guinea pig submucous neurons were studied with neuroimaging techniques. We identify differentially expressed proteins with proteome analysis.

Results

Nerve activation by IBS supernatants was prevented by the protease activated receptor 1 (PAR1) antagonist SCHE79797. UC supernatants also activated enteric neurons through protease dependent mechanisms but without PAR1 involvement. Proteome analysis of the supernatants identified 204 proteins, among them 17 proteases as differentially expressed between IBS, UC and HC. Of those the four proteases elastase 3a, chymotrypsin C, proteasome subunit type beta-2 and an unspecified isoform of complement C3 were significantly more abundant in IBS compared to HC and UC supernatants. Of eight proteases, which were upregulated in IBS, the combination of elastase 3a, cathepsin L and proteasome alpha subunit-4 showed the highest prediction accuracy of 98% to discriminate between IBS and HC groups. Elastase synergistically potentiated the effects of histamine and serotonin–the two other main neuroactive substances in the IBS supernatants. A serine protease inhibitor isolated from the probiotic Bifidobacterium longum NCC2705 (SERPIN_BL), known to inhibit elastase-like proteases, prevented nerve activation by IBS supernatants.

Conclusion

Proteases in IBS and UC supernatants were responsible for nerve activation. Our data demonstrate that proteases, particularly those signalling through neuronal PAR1, are biomarker candidates for IBS, and protease profiling may be used to characterise IBS.

Sensitivity to Strain and Shear Stress of Isolated Mechanosensitive Enteric Neurons

Within the enteric nervous system, the neurons in charge to control motility of the gastrointestinal tract reside in a particular location nestled between two perpendicular muscle layers which contract and relax. We used primary cultured myenteric neurons of male guinea pigs to study mechanosensitivity of enteric neurons in isolation. Ultrafast Neuroimaging with a voltage-sensitive dye technique was used to record neuronal activity in response to shear stress and strain. Strain was induced by locally deforming the elastic cell culture substrate next to a neuron. Measurements showed that substrate strain was mostly elongating cells. Shear stress was exerted by hydrodynamic forces in a microchannel. Both stimuli induced excitatory responses. Strain activated 14% of the stimulated myenteric neurons that responded with a spike frequency of 1.9 (0.7/3.2) Hz, whereas shear stress excited only a few neurons (5.6%) with a very low spike frequency of 0 (0/0.6) Hz. Thus, shear stress does not seem to be an adequate stimulus for mechanosensitive enteric neurons (MEN) while strain activates enteric neurons in a relevant manner. Analyzing the adaptation behavior of MEN showed that shear stress activated rapidly/slowly/ultraslowly adapting MEN (2/62/36%) whereas strain only slowly (46%) and ultraslowly (54%) MEN. Paired experiments with strain and normal stress revealed three mechanosensitive enteric neuronal populations: one strain-sensitive (37%), one normal stress-sensitive (17%) and one strain- and stress-sensitive (46%). These results indicate that shear stress does not play a role in the neuronal control of motility but normal stress and strain.

Calcium Imaging of Nerve-Mast Cell Signaling in the Human Intestine

Introduction: It is suggested that an altered microenvironment in the gut wall alters communication along a mast cell nerve axis. We aimed to record for the first time signaling between mast cells and neurons in intact human submucous preparations. Methods: We used the Ca2+ sensitive dye Fluo-4 AM to simultaneously image changes in intracellular calcium [Ca+2]i (%ΔF/F) in neurons and mast cells. Data are presented as median with interquartile ranges (25/75%). Results: We recorded nerve responses in 29 samples upon selective activation of 223 mast cells by IgE receptor cross linking with the antibody mAb22E7. Mast cells responded to mAb22E7 with a median [Ca+2]i increase of 20% (11/39) peaking 90 s (64/144) after the application. Only very few neurons responded and the median percentage of responding neuronal area was 0% (0/5.9). Mast cell activation remained in the presence of the fast sodium channel blocker tetrodotoxin. Specific neuronal activation by transmural electrical field stimulation (EFS) in 34 samples evoked instantaneously [Ca+2]i signals in submucous neurons. This was followed by a [Ca+2]i peak response of 8%ΔF/F (4/15) in 33% of 168 mast cells in the field of view. The mast cell response was abolished by the nerve blocker tetrododoxin, reduced by the Calcitonin Gene-Related Peptide receptor 1 antagonist BIBN-4096 and the Vasoactive Intestinal Peptide receptor antagonist PG97-269, but not by blockade of the neurokinin receptors 1-3. Conclusion: The findings revealed bidirectional signaling between mast cells and submucous neurons in human gut. In our macroscopically normal preparations a nerve to mast cell signaling was very prominent whereas a mast cell to nerve signaling was rather rare.

Tryptase potentiates enteric nerve activation by histamine and serotonin: Relevance for the effects of mucosal biopsy supernatants from irritable bowel syndrome patients

BACKGROUND

We previously showed that mucosal biopsy supernatants from irritable bowel syndrome patients activated neurons despite low concentrations of tryptase, histamine, and serotonin which individually would not cause spike discharge. We studied the potentiating responses between these mediators on excitability of enteric neurons.

METHODS

Calcium-imaging was performed using the calcium-sensitive dye Fluo-4 AM in human submucous plexus preparations from 45 individuals. Histamine, serotonin, and tryptase were applied alone and in combinations to evaluate nerve activation which was assessed by analyzing increase in intracellular Ca²⁺ ([Ca²⁺ ]_i ), the proportion of responding neurons and the product of both defined as Ca-neuroindex (NI). Protease activated receptor (PAR) 2 activating peptide, PAR2 antagonist and the serine protease-inhibitor FUT-175 were used to particularly investigate the role of proteases.

KEY RESULTS

Histamine or serotonin (1 μmol/L each) evoked only few small responses (median NI [25%/75%]: 0 [0/148]; 85 [0/705] respectively). Their combined application evoked statistically similar responses (216 [21/651]). Addition of the PAR2 activator tryptase induced a significantly higher Ca-NI (1401 [867/4075]) compared to individual application of tryptase or to coapplied histamine and serotonin. This synergistic potentiation was neither mimicked by PAR2 activating peptide nor reversed by the PAR2 antagonist GB83, but abolished by FUT-175.

CONCLUSIONS & INFERENCES

We observed synergistic potentiation between histamine, serotonin, and tryptase in enteric neurons, which is mediated by proteolytic activity rather than PAR2 activation. This explained neuronal activation by a cocktail of these mediators despite their low concentrations and despite a relatively small PAR2-mediated response in human submucous neurons.

Irritable bowel syndrome – dissection of a disease. A 13-steps polemic

The last 35 years (since about 1985) have produced a vast amount of scientific publications with respect to the irritable bowel syndrome (IBS), but no real progress: The etiology and pathogenesis of IBS is still incompletely understood, and diagnosis and therapy is left to the individual understanding of the treating physicians in general medicine, gastroenterology and psychosomatic/psychiatry. In this gloss, three prominent representatives of neurogastroenterology in Germany assess their own contributions and those of their colleagues and lament the huge gap between ambitions and reality in clinical and basic science in IBS.

Anti-Hu antibodies activate enteric and sensory neurons

IgG of type 1 anti-neuronal nuclear antibody (ANNA-1, anti-Hu) specificity is a serological marker of paraneoplastic neurological autoimmunity (including enteric/autonomic) usually related to small-cell lung carcinoma. We show here that IgG isolated from such sera and also affinity-purified anti-HuD label enteric neurons and cause an immediate spike discharge in enteric and visceral sensory neurons. Both labelling and activation of enteric neurons was prevented by preincubation with the HuD antigen. Activation of enteric neurons was inhibited by the nicotinic receptor antagonists hexamethonium and dihydro-β-erythroidine and reduced by the P2X antagonist pyridoxal phosphate-6-azo (benzene-2,4-disulfonic acid (PPADS) but not by the 5-HT₃ antagonist tropisetron or the N-type Ca-channel blocker ω-Conotoxin GVIA. Ca⁺⁺ imaging experiments confirmed activation of enteric neurons but not enteric glia. These findings demonstrate a direct excitatory action of ANNA-1, in particular anti-HuD, on visceral sensory and enteric neurons, which involves nicotinic and P2X receptors. The results provide evidence for a novel link between nerve activation and symptom generation in patients with antibody-mediated gut dysfunction.

Human native kappa opioid receptor functions not predicted by recombinant receptors: Implications for drug design

If activation of recombinant G protein-coupled receptors in host cells (by drugs or other ligands) has predictive value, similar data must be obtained with native receptors naturally expressed in tissues. Using mouse and human recombinant κ opioid receptors transfected into a host cell, two selectively-acting compounds (ICI204448, asimadoline) equi-effectively activated both receptors, assessed by measuring two different cell signalling pathways which were equally affected without evidence of bias. In mouse intestine, naturally expressing κ receptors within its nervous system, both compounds also equi-effectively activated the receptor, inhibiting nerve-mediated muscle contraction. However, whereas ICI204448 acted similarly in human intestine, where κ receptors are again expressed within its nervous system, asimadoline was inhibitory only at very high concentrations; instead, low concentrations of asimadoline reduced the activity of ICI204448. This demonstration of species-dependence in activation of native, not recombinant κ receptors may be explained by different mouse/human receptor structures affecting receptor expression and/or interactions with intracellular signalling pathways in native environments, to reveal differences in intrinsic efficacy between receptor agonists. These results have profound implications in drug design for κ and perhaps other receptors, in terms of recombinant-to-native receptor translation, species-dependency and possibly, a need to use human, therapeutically-relevant, not surrogate tissues.

Irritable bowel syndrome

Irritable bowel syndrome (IBS) is a functional gastrointestinal disease with a high population prevalence. The disorder can be debilitating in some patients, whereas others may have mild or moderate symptoms. The most important single risk factors are female sex, younger age and preceding gastrointestinal infections. Clinical symptoms of IBS include abdominal pain or discomfort, stool irregularities and bloating, as well as other somatic, visceral and psychiatric comorbidities. Currently, the diagnosis of IBS is based on symptoms and the exclusion of other organic diseases, and therapy includes drug treatment of the predominant symptoms, nutrition and psychotherapy. Although the underlying pathogenesis is far from understood, aetiological factors include increased epithelial hyperpermeability, dysbiosis, inflammation, visceral hypersensitivity, epigenetics and genetics, and altered brain-gut interactions. IBS considerably affects quality of life and imposes a profound burden on patients, physicians and the health-care system. The past decade has seen remarkable progress in our understanding of functional bowel disorders such as IBS that will be summarized in this Primer.

Neural influences on human intestinal epithelium in vitro

KEY POINTS

We present the first systematic and, up to now, most comprehensive evaluation of the basic features of epithelial functions, such as basal and nerve-evoked secretion, as well as tissue resistance, in over 2200 surgical specimens of human small and large intestine. We found no evidence for impaired nerve-evoked epithelial secretion or tissue resistance with age or disease pathologies (stomach, pancreas or colon cancer, polyps, diverticulitis, stoma reversal). This indicates the validity of future studies on epithelial secretion or resistance that are based on data from a variety of surgical specimens. ACh mainly mediated nerve-evoked and basal secretion in the small intestine, whereas vasoactive intestinal peptide and nitric oxide were the primary pro-secretory transmitters in the large intestine. The results of the present study revealed novel insights into regional differences in nerve-mediated secretion in the human intestine and comprise the basis by which to more specifically target impaired epithelial functions in the diseased gut.

ABSTRACT

Knowledge on basic features of epithelial functions in the human intestine is scarce. We used Ussing chamber techniques to record basal tissue resistance (R-basal) and short circuit currents (ISC; secretion) under basal conditions (ISC-basal) and after electrical field stimulation (ISC-EFS) of nerves in 2221 resectates from 435 patients. ISC-EFS was TTX-sensitive and of comparable magnitude in the small and large intestine. ISC-EFS or R-basal were not influenced by the patients' age, sex or disease pathologies (cancer, polyps, diverticulitis). Ion substitution, bumetanide or adenylate cyclase inhibition studies suggested that ISC-EFS depended on epithelial cAMP-driven chloride and bicarbonate secretion but not on amiloride-sensitive sodium absorption. Although atropine-sensitive cholinergic components prevailed for ISC-EFS of the duodenum, jejunum and ileum, PG97-269-sensitive [vasoactive intestinal peptide (VIP) receptor 1 antagonist] VIPergic together with L-NAME-sensitive nitrergic components dominated the ISC-EFS in colonic preparations. Differences in numbers of cholinergic or VIPergic neurons, sensitivity of epithelial muscarinic or VIP receptors, or stimulus frequency-dependent transmitter release were not responsible for the region-specific transmitter contribution to ISC-EFS. Instead, the low atropine-sensitivity of ISC-EFS in the colon was the result of high cholinesterase activity because neostigmine revealed cholinergic components. Colonic ISC-EFS remained unchanged after tachykinin, P2X, P2Y or A1 and A2 receptor blockade. R-basal was smaller and ISC-basal was higher in the small intestine. TTX and bumetanide decreased ISC-basal in all regions, suggesting nerve-dependent secretory tone. ISC-basal was atropine-sensitive in the small intestine and PG97-269-sensitive in the large intestine. This comprehensive study reveals novel insights into region-specific nerve-mediated secretion in the human small and large intestine.

Extracts from peppermint leaves, lemon balm leaves and in particular angelica roots mimic the pro-secretory action of the herbal preparation STW 5 in the human intestine

AIM

The herbal preparation STW 5 contains fresh plant extracts from bitter candytuft whole plant, extracts from greater celandine herb, angelica root, lemon balm leaves, peppermint leaves, caraway fruit, liquorice root, chamomile flower and milk thistle fruit. We recently reported that STW 5 increased intestinal chloride secretion and proposed that this action may be involved in its clinical efficacy in the treatment of irritable bowel syndrome. The aim of this study was to identify the extracts responsible for the secretory action in order to provide the basis to develop novel target oriented herbal combinations.

METHODS

We used the Ussing chamber voltage clamp technique to study the effects of individual extracts of STW 5 on short circuit current (Isc, reflecting electrogenic ion transport across epithelial cells) in mucosal/submucosal preparations of human small or large intestinal specimens and the human epithelial cell line T84.

RESULTS

STW 5 at concentrations of 512 µg/ml and 5120 µg/ml evoked an increase in Isc. The increase at the lower concentration was due to pro-secretory effects of angelica which were nerve mediated. The increase at the higher concentration was additionally mimicked by peppermint and lemon balm. The remaining extracts did not influence ISC in the large intestine. The results were similar in T84 cells except that angelica had no effect while chamomile induced secretion. These pro-secretory effects were reduced by adenylate cyclase inhibitor MDL-12330A, cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor CFTRinh-172 and calcium activated chloride channels blocker 4-acetamido-4-isothiocyanatostilbene-2,2-disulphonic acid (SITS). Liquorice decreased ISC only in small intestine which was reversed by the epithelial sodium channel blocker amiloride.

CONCLUSIONS

Results suggested that the pro-secretory action of STW 5 is mainly due to angelica with lesser contribution of peppermint and lemon balm. Their effects involve activation of cAMP- and Ca(++)-activated Cl(-) channels. We suggest that peppermint, lemon balm and in particular angelica may be the basis to develop novel herbal preparations to specifically treat secretory disorder based on impaired epithelial secretion, such as constipation.

Mechanosensitive enteric neurons in the guinea pig gastric corpus

For long it was believed that a particular population of enteric neurons, referred to as intrinsic primary afferent neuron (IPAN)s, encodes mechanical stimulation. We recently proposed a new concept suggesting that there are in addition mechanosensitive enteric neurons (MEN) that are multifunctional. Based on firing pattern MEN behaved as rapidly, slowly, or ultra-slowly adapting RAMEN, SAMEN, or USAMEN, respectively. We aimed to validate this concept in the myenteric plexus of the gastric corpus, a region where IPANs were not identified and existence of enteric sensory neurons was even questioned. The gastric corpus is characterized by a particularly dense extrinsic sensory innervation. Neuronal activity was recorded with voltage sensitive dye imaging after deformation of ganglia by compression (intraganglionic volume injection or von Fry hair) or tension (ganglionic stretch). We demonstrated that 27% of the gastric neurons were MEN and responded to intraganglionic volume injection. Of these 73% were RAMEN, 25% SAMEN, and 2% USAMEN with a firing frequency of 1.7 (1.1/2.2), 5.1 (2.2/7.7), and of 5.4 (5.0/15.5) Hz, respectively. The responses were reproducible and stronger with increased stimulus strength. Even after adaptation another deformation evoked spike discharge again suggesting a resetting mode of the mechanoreceptors. All MEN received fast synaptic input. Fifty five percent of all MEN were cholinergic and 45% nitrergic. Responses in some MEN significantly decreased after perfusion of TTX, low Ca(++)/high Mg(++) Krebs solution, capsaicin induced nerve defunctionalization and capsazepine indicating the involvement of TRPV1 expressing extrinsic mechanosensitive nerves. Half of gastric MEN responded to intraganglionic volume injection as well as to ganglionic stretch and 23% responded to stretch only. Tension-sensitive MEN were to a large proportion USAMEN (44%). In summary, we demonstrated for the first time compression and tension-sensitive MEN in the stomach; many of them responded to one stimulus modality only. Their proportions and the basic properties were similar to MEN previously identified by us in other intestinal region and species. Unlike in the intestine, the responsiveness of some gastric MEN is enhanced by extrinsic TRPV1 expressing visceral afferents.

Mechanosensitivity in the enteric nervous system

The enteric nervous system (ENS) autonomously controls gut muscle activity. Mechanosensitive enteric neurons (MEN) initiate reflex activity by responding to mechanical deformation of the gastrointestinal wall. MEN throughout the gut primarily respond to compression or stretch rather than to shear force. Some MEN are multimodal as they respond to compression and stretch. Depending on the region up to 60% of the entire ENS population responds to mechanical stress. MEN fire action potentials after mechanical stimulation of processes or soma although they are more sensitive to process deformation. There are at least two populations of MEN based on their sensitivity to different modalities of mechanical stress and on their firing pattern. (1) Rapidly, slowly and ultra-slowly adapting neurons which encode compressive forces. (2) Ultra-slowly adapting stretch-sensitive neurons encoding tensile forces. Rapid adaptation of firing is typically observed after compressive force while slow adaptation or ongoing spike discharge occurs often during tensile stress (stretch). All MEN have some common properties: they receive synaptic input, are low fidelity mechanoreceptors and are multifunctional in that some serve interneuronal others even motor functions. Consequently, MEN possess processes with mechanosensitive as well as efferent functions. This raises the intriguing hypothesis that MEN sense and control muscle activity at the same time as servo-feedback loop. The mechanosensitive channel(s) or receptor(s) expressed by the different MEN populations are unknown. Future concepts have to incorporate compressive and tensile-sensitive MEN into neural circuits that controls muscle activity. They may interact to control various forms of a particular motor pattern or regulate different motor patterns independently from each other.

Mechanical stress activates neurites and somata of myenteric neurons

The particular location of myenteric neurons, sandwiched between the 2 muscle layers of the gut, implies that their somata and neurites undergo mechanical stress during gastrointestinal motility. Existence of mechanosensitive enteric neurons (MEN) is undoubted but many of their basic features remain to be studied. In this study, we used ultra-fast neuroimaging to record activity of primary cultured myenteric neurons of guinea pig and human intestine after von Frey hair evoked deformation of neurites and somata. Independent component analysis was applied to reconstruct neuronal morphology and follow neuronal signals. Of the cultured neurons 45% (114 out of 256, 30 guinea pigs) responded to neurite probing with a burst spike frequency of 13.4 Hz. Action potentials generated at the stimulation site invaded the soma and other neurites. Mechanosensitive sites were expressed across large areas of neurites. Many mechanosensitive neurites appeared to have afferent and efferent functions as those that responded to deformation also conducted spikes coming from the soma. Mechanosensitive neurites were also activated by nicotine application. This supported the concept of multifunctional MEN. 14% of the neurons (13 out of 96, 18 guinea pigs) responded to soma deformation with burst spike discharge of 17.9 Hz. Firing of MEN adapted rapidly (RAMEN), slowly (SAMEN), or ultra-slowly (USAMEN). The majority of MEN showed SAMEN behavior although significantly more RAMEN occurred after neurite probing. Cultured myenteric neurons from human intestine had similar properties. Compared to MEN, dorsal root ganglion neurons were activated by neurite but not by soma deformation with slow adaptation of firing. We demonstrated that MEN exhibit specific features very likely reflecting adaptation to their specialized functions in the gut.

Anti-DPPX encephalitis: pathogenic effects of antibodies on gut and brain neurons

OBJECTIVE

To characterize pathogenic effects of antibodies to dipeptidyl-peptidase-like protein 6 (DPPX), a subunit of Kv4.2 potassium channels, on gut and brain neurons.

METHODS

We identified a new patient with anti-DPPX encephalitis and analyzed the effects of the patient's serum and purified immunoglobulin G (IgG), and of serum of a previous patient with anti-DPPX encephalitis, on the activity of enteric neurons by voltage-sensitive dye imaging in guinea pig myenteric and human submucous plexus preparations. We studied the subcellular localization of DPPX by immunocytochemistry in cultured murine hippocampal neurons using sera of 4 patients with anti-DPPX encephalitis. We investigated the influence of anti-DPPX-containing serum and purified IgG on neuronal surface expression of DPPX and Kv4.2 by immunoblots of purified murine hippocampal neuron membranes.

RESULTS

The new patient with anti-DPPX encephalitis presented with a 2-month episode of diarrhea, which was followed by tremor, disorientation, and mild memory impairment. Anti-DPPX-IgG-containing sera and purified IgG increased the excitability and action potential frequency of guinea pig and human enteric nervous system neurons. Patient sera revealed a somatodendritic and perisynaptic neuronal surface staining that colocalized with the signal of commercial anti-DPPX and Kv4.2 antibodies. Incubation of hippocampal neurons with patient serum and purified IgG resulted in a decreased expression of DPPX and Kv4.2 in neuronal membranes.

CONCLUSIONS

Hyperexcitability of enteric nervous system neurons and downregulation of DPPX and Kv4.2 from hippocampal neuron membranes mirror the clinical phenotype of patients with anti-DPPX encephalitis and support a pathogenic role of anti-DPPX antibodies in anti-DPPX encephalitis.

Neuropharmacology of purinergic receptors in human submucous plexus: Involvement of P2X₁, P2X₂, P2X₃ channels, P2Y and A₃ metabotropic receptors in neurotransmission

RATIONALE

The role of purinergic signaling in human ENS is not well understood. We sought to further characterize the neuropharmacology of purinergic receptors in human ENS and test the hypothesis that endogenous purines are critical regulators of neurotransmission.

EXPERIMENTAL APPROACH

LSCM-Fluo-4/(Ca(2+))-imaging of postsynaptic Ca(2+) transients (PSCaTs) was used as a reporter of synaptic transmission evoked by fiber tract electrical stimulation in human SMP surgical preparations. Pharmacological analysis of purinergic signaling was done in 1,556 neurons (identified by HuC/D-immunoreactivity) in 235 ganglia from 107 patients; P2XR-immunoreactivity was evaluated in 19 patients. Real-time MSORT (Di-8-ANEPPS) imaging tested effects of adenosine on fast excitatory synaptic potentials (fEPSPs).

RESULTS

Synaptic transmission is sensitive to pharmacological manipulations that alter accumulation of extracellular purines: Apyrase blocks PSCaTs in a majority of neurons. An ecto-NTPDase-inhibitor 6-N,N-diethyl-D-β,γ-dibromomethyleneATP or adenosine deaminase augments PSCaTs. Blockade of reuptake/deamination of eADO inhibits PSCaTs. Adenosine inhibits fEPSPs and PSCaTs (IC50 = 25 µM), sensitive to MRS1220-antagonism (A3AR). A P2Y agonist ADPβS inhibits PSCaTs (IC50 = 111 nM) in neurons without stimulatory ADPbS responses (EC50 = 960 nM). ATP or a P2X1,2,2/3 (α,β-MeATP) agonist evokes fast, slow, biphasic Ca(2+) transients or Ca(2+) oscillations (ATP,EC50 = 400 mM). PSCaTs are sensitive to P2X1 antagonist NF279. Low (20 nM) or high (5 µM) concentrations of P2X antagonist TNP-ATP block PSCaTs in different neurons; proportions of neurons with P2XR-immunoreactivity follow the order P2X2 > P2X1 >> P2X3; P2X1 + P2X2 and P2X3 + P2X2 are co-localized. RT-PCR identified mRNA-transcripts for P2X1-7, P2Y1,2,12-14R.

CONCLUSIONS

Purines are critical regulators of neurotransmission in human ENS. Purinergic signaling involves P2X1, P2X2, P2X3 channels, P2X1 + P2X2 co-localization and inhibitory P2Y or A3 receptors. These are potential novel therapeutic targets for neurogastroenterology.

Reduced Responses of Submucous Neurons from Irritable Bowel Syndrome Patients to a Cocktail Containing Histamine, Serotonin, TNFα, and Tryptase (IBS-Cocktail)

BACKGROUND AND AIMS

Malfunctions of enteric neurons are believed to play an important role in the pathophysiology of irritable bowel syndrome (IBS). Our aim was to investigate whether neuronal activity in biopsies from IBS patients is altered in comparison to healthy controls (HC).

METHODS

Activity of human submucous neurons in response to electrical nerve stimulation and local application of nicotine or a mixture of histamine, serotonin, tryptase, and TNF-α (IBS-cocktail) was recorded in biopsies from 17 HC and 35 IBS patients with the calcium-sensitive-dye Fluo-4 AM. The concentrations of the mediators resembeled those found in biopsy supernatants or blood. Neuronal activity in guinea-pig submucous neurons was studied with the voltage-sensitive-dye di-8-ANEPPS.

RESULTS

Activity in submucous ganglia in response to nicotine or electrical nerve stimulation was not different between HC and IBS patients (P = 0.097 or P = 0.448). However, the neuronal response after application of the IBS-cocktail was significantly decreased (P = 0.039) independent of whether diarrhea (n = 12), constipation (n = 5) or bloating (n = 5) was the predominant symptom. In agreement with this we found that responses of submucous ganglia conditioned by overnight incubation with IBS mucosal biopsy supernatant to spritz application of this supernatant was significantly reduced (P = 0.019) when compared to incubation with HC supernatant.

CONCLUSION

We demonstrated for the first time reduced neuronal responses in mucosal IBS biopsies to an IBS mediator cocktail. While excitability to classical stimuli of enteric neurons was comparable to HC, the activation by the IBS-cocktail was decreased. This was very likely due to desensitization to mediators constantly released by mucosal and immune cells in the gut wall of IBS patients.

Nutrient-induced changes in the phenotype and function of the enteric nervous system

The enteric nervous system (ENS) integrates numerous sensory signals in order to control and maintain normal gut functions. Nutrients are one of the prominent factors which determine the chemical milieu in the lumen and, after absorption, also within the gut wall. This review summarizes current knowledge on the impact of key nutrients on ENS functions and phenotype, covering their acute and long-term effects. Enteric neurones contain the molecular machinery to respond specifically to nutrients. These transporters and receptors are not expressed exclusively in the ENS but are also present in other cells such as enteroendocrine cells (EECs) and extrinsic sensory nerves, signalling satiety or hunger. Glucose, amino acids and fatty acids all activate enteric neurones, as suggested by enhanced c-Fos expression or spike discharge. These excitatory effects are the result of a direct neuronal activation but also involve the activation of EECs which, upon activation by luminal nutrients, release mediators such as ghrelin, cholecystokinin or serotonin. The presence or absence of nutrients in the intestinal lumen induces long-term changes in neurotransmitter expression, excitability, neuronal survival and ultimately impact upon gut motility, secretion or intestinal permeability. Together with EECs and vagal nerves, the ENS must be recognized as an important player initiating concerted responses to nutrients. It remains to be studied how, for instance, nutrient-induced changes in the ENS may influence additional gut functions such as intestinal barrier repair, intestinal epithelial stem cell proliferation/differentiation and also the signalling of extrinsic nerves to brain regions which control food intake.

A distinct vagal anti-inflammatory pathway modulates intestinal muscularis resident macrophages independent of the spleen

The cholinergic anti-inflammatory pathway (CAIP) has been proposed as a key mechanism by which the brain, through the vagus nerve, modulates the immune system in the spleen. Vagus nerve stimulation (VNS) reduces intestinal inflammation and improves postoperative ileus. We investigated the neural pathway involved and the cells mediating the anti-inflammatory effect of VNS in the gut. The effect of VNS on intestinal inflammation and transit was investigated in wild-type, splenic denervated and Rag-1 knockout mice. To define the possible role of α7 nicotinic acetylcholine receptor (α7nAChR), we used knockout and bone marrow chimaera mice. Anterograde tracing of vagal efferents, cell sorting and Ca(2+) imaging were used to reveal the intestinal cells targeted by the vagus nerve. VNS attenuates surgery-induced intestinal inflammation and improves postoperative intestinal transit in wild-type, splenic denervated and T-cell-deficient mice. In contrast, VNS is ineffective in α7nAChR knockout mice and α7nAChR-deficient bone marrow chimaera mice. Anterograde labelling fails to detect vagal efferents contacting resident macrophages, but shows close contacts between cholinergic myenteric neurons and resident macrophages expressing α7nAChR. Finally, α7nAChR activation modulates ATP-induced Ca(2+) response in small intestine resident macrophages. We show that the anti-inflammatory effect of the VNS in the intestine is independent of the spleen and T cells. Instead, the vagus nerve interacts with cholinergic myenteric neurons in close contact with the muscularis macrophages. Our data suggest that intestinal muscularis resident macrophages expressing α7nAChR are most likely the ultimate target of the gastrointestinal CAIP.

Using human intestinal biopsies to study the pathogenesis of irritable bowel syndrome

BACKGROUND

Although animal models of the irritable bowel syndrome (IBS) have provided important insights, there are no models that fully express the features of this complex condition. One alternative approach is the use of human intestinal biopsies obtained during endoscopic procedures to examine peripheral mechanisms in this disorder. These studies have served to confirm the existence of peripheral pathways in humans with IBS and have provided many new mechanistic insights. Two general approaches have been employed; one approach has been to examine the biological activity of mediators within the mucosal tissue of IBS patients and the other has been to examine changes in the structural properties of key signaling pathways contained within the biopsies. Using these approaches, important changes have been discovered involving the enteric nervous system and the extrinsic sensory pathway (dorsal root ganglia neurons), the immune system, and epithelial signaling in IBS patients compared to healthy subjects.

PURPOSE

This review will systematically explore these mechanistic pathways, highlight the implications of these novel findings and discuss some of the important limitations of this approach.