Increased substance P receptor expression by blood vessels and lymphoid aggregates in Clostridium difficile-induced pseudomembranous colitis

MiR-21 in Substance P-induced exosomes promotes cell proliferation and migration in human colonic epithelial cells

Exosomes are cellular vesicles involved in intercellular communication via their specialized molecular cargo, such as miRNAs. Substance P (SP), a neuropeptide/hormone, and its high-affinity receptor, NK-1R, are highly expressed during colonic inflammation. Our previous studies show that SP/NK-1R signaling stimulates differential miRNA expression and promotes colonic epithelial cell proliferation. In this study, we examined whether SP/NK-1R signaling regulates exosome biogenesis and exosome-miRNA cargo sorting. Moreover, we examined the role of SP/NK-1R signaling in exosome-regulated cell proliferation and migration. Exosomes produced by human colonic NCM460 epithelial cells overexpressing NK-1R (NCM460-NK1R) were isolated from culture media. Exosome abundance and uptake were assessed by Western blot analysis (abundance) and Exo-Green fluorescence microscopy (abundance and uptake). Cargo-miRNA levels were assessed by RT-PCR. Cell proliferation and migration were assessed using xCELLigence technology. Colonic epithelial exosomes were isolated from mice pretreated with SP for 3 days. Cell proliferation in vivo was assessed by Ki-67 staining. SP/NK-1R signaling in human colonic epithelial cells (in vitro) and mouse colons (in vivo) increased 1) exosome production, 2) the level of fluorescence in NCM460s treated with Exo-Green-labeled exosomes, and 3) the level of miR-21 in exosome cargo. Moreover, our results showed that SP/NK-1R-induced cell proliferation and migration are at least in part dependent on intercellular communication via exosomal miR-21 in vitro and in vivo. Our results demonstrate that SP/NK-1R signaling regulates exosome biogenesis and induces its miR-21 cargo sorting. Moreover, exosomal miR-21 promotes proliferation and migration of target cells.NEW & NOTEWORTHY Substance P signaling regulates exosome production in human colonic epithelial cells and colonic crypts in wild-type mice. MiR-21 is selectively sorted into exosomes induced by Substance P stimulation and promotes cell proliferation and migration in human colonocytes and mouse colonic crypts.

The role of toxins in Clostridium difficile infection

Clostridium difficile is a bacterial pathogen that is the leading cause of nosocomial antibiotic-associated diarrhea and pseudomembranous colitis worldwide. The incidence, severity, mortality and healthcare costs associated with C. difficile infection (CDI) are rising, making C. difficile a major threat to public health. Traditional treatments for CDI involve use of antibiotics such as metronidazole and vancomycin, but disease recurrence occurs in about 30% of patients, highlighting the need for new therapies. The pathogenesis of C. difficile is primarily mediated by the actions of two large clostridial glucosylating toxins, toxin A (TcdA) and toxin B (TcdB). Some strains produce a third toxin, the binary toxin C. difficile transferase, which can also contribute to C. difficile virulence and disease. These toxins act on the colonic epithelium and immune cells and induce a complex cascade of cellular events that result in fluid secretion, inflammation and tissue damage, which are the hallmark features of the disease. In this review, we summarize our current understanding of the structure and mechanism of action of the C. difficile toxins and their role in disease.

Induction of the neurokinin 1 receptor by TNFα in endometriotic tissue provides the potential for neurogenic control over endometriotic lesion growth

CONTEXT

Endometriosis is characterized by the growth of ectopic endometrial tissue. Nerve fibers are frequently associated with ectopic lesions, and neurogenic inflammation may play a role in endometriosis.

OBJECTIVE

The purpose of this study was to determine the presence of tachykinin receptors in endometriotic lesions and the role of TNFα on their expression.

DESIGN

This study was an assessment of matching eutopic and ectopic endometrial tissue and peritoneal fluid from patients with endometriosis and an in vitro analysis of primary endometrial cells.

SETTING

The setting was a university hospital.

PATIENTS

Participants were premenopausal women undergoing laparoscopy.

INTERVENTIONS

Endometriotic lesions were removed surgically.

MAIN OUTCOME MEASURES

Tachykinin mRNA (TACR1/2) and protein (neurokinin 1 receptor [NK1R]) expression in both eutopic and ectopic endometrial tissue from patients with endometriosis and the correlation to peritoneal fluid TNFα were measured. Primary endometrial epithelial and stromal cells were assessed in vitro to determine the induction of TACR1/2 and NK1R expression after TNFα treatment. Cell viability of endometrial stromal cells after substance P exposure was also assessed.

RESULTS

Expression of both TACR1 and TACR2 mRNA was significantly higher in the ectopic than in the eutopic tissue. Both TACR1 mRNA and NK1R protein expression was significantly correlated with peritoneal fluid TNFα, and in vitro studies confirmed that TNFα treatment induced both TACR1 mRNA and NK1R protein expression in endometrial stromal cells. In endometrial stromal cells, substance P treatment enhanced cell viability, which was inhibited by a specific NK1R antagonist.

CONCLUSIONS

NK1R expression is induced in ectopic endometrial tissue by peritoneal TNFα. Induction of NK1R expression may permit endometriotic lesion maintenance via exposure to substance P.

Viewpoints on Acid-induced inflammatory mediators in esophageal mucosa

We have focused on understanding the onset of gastroesophageal reflux disease by examining the mucosal response to the presence of acid in the esophageal lumen. Upon exposure to HCl, inflammation of the esophagus begins with activation of the transient receptor potential channel vanilloid subfamily member-1 (TRPV1) in the mucosa, and production of IL-8, substance P (SP), calcitonin gene related peptide (CGRP) and platelet activating factor (PAF). Production of SP and CGRP, but not PAF, is abolished by the neural blocker tetrodotoxin suggesting that SP and CGRP are neurally released and that PAF arises from non neural pathways. Epithelial cells contain TRPV1 receptor mRNA and protein and respond to HCl and to the TRPV1 agonist capsaicin with production of PAF. PAF, SP and IL-8 act as chemokines, inducing migration of peripheral blood leukocytes. PAF and SP activate peripheral blood leukocytes inducing the production of H₂O₂. In circular muscle, PAF causes production of IL-6, and IL-6 causes production of additional H₂O₂, through activation of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidases. Among these, NADPH oxidase 5 cDNA is significantly up-regulated by exposure to PAF; H₂O₂ content of esophageal and lower esophageal sphincter circular muscle is elevated in human esophagitis, causing dysfunction of esophageal circular muscle contraction and reduction in esophageal sphincter tone. Thus esophageal keratinocytes, that constitute the first barrier to the refluxate, may also serve as the initiating cell type in esophageal inflammation, secreting inflammatory mediators and pro-inflammatory cytokines and affecting leukocyte recruitment and activity.

HCl-activated neural and epithelial vanilloid receptors (TRPV1) in cat esophageal mucosa

To test whether transient receptor potential channel vanilloid subfamily member-1 (TRPV1) mediates acid-induced inflammation in the esophagus, a tubular segment of esophageal mucosa was tied at both ends, forming a sac. The sac was filled with 0.01 N HCl (or Krebs buffer for control) and kept in oxygenated Krebs buffer at 37 degrees C. The medium around the sac (supernatant) was collected after 3 h. Supernatant of the HCl-filled sac abolished contraction of esophageal circular muscle strips in response to electric field stimulation. Contraction was similarly abolished by supernatant of mucosal sac filled with the TRPV1 agonist capsaicin (10(-6) M). These effects were reversed by the selective TRPV1 antagonist 5'-iodoresiniferatoxin (IRTX) and by the platelet-activating factor (PAF) receptor antagonist CV9388. Substance P and CGRP levels in mucosa and in supernatant increased in response to HCl, and these increases were abolished by IRTX and by tetrodotoxin (TTX) but not affected by CV9388, indicating that substance P and CGRP are neurally released and PAF independent. In contrast, the increase in PAF was blocked by IRTX but not by TTX. Presence of TRPV1 receptor was confirmed by RT-PCR and by Western blot analysis in whole mucosa and in esophageal epithelial cells enzymatically isolated and sorted by flow cytometry or immunoprecipitated with cytokeratin antibodies. In epithelial cells PAF increased in response to HCl, and the increase was abolished by IRTX. We conclude that HCl-induced activation of TRPV1 receptors in esophageal mucosa causes release of substance P and CGRP from neurons and release of PAF from epithelial cells.

Role of neuropeptides in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic, relapsing condition involving complex interactions between genes and the environment. The mechanisms triggering the initial attack and relapses, however, are not well understood. In the past several years the enteric nervous system (ENS) has been implicated in the pathophysiology of IBD. Both the ENS and the central nervous system (CNS) can amplify or modulate aspects of intestinal inflammation through secretion of neuropeptides that serve as a link between the ENS and CNS. Neuropeptides are defined as any peptide released from the nervous system that serves as an intercellular signaling molecule. Neuropeptides thought to play a potentially key role in IBD include substance P, corticotropin-releasing hormone, neurotensin, vasoactive intestinal peptide, mu-opioid receptor agonists, and galanin. This review focuses on the role of these neuropeptides in the pathophysiology of IBD and discusses the cell types and mechanisms involved in this process. The available evidence that neuropeptide blockade may be considered a therapeutic approach in both Crohn's disease and ulcerative colitis will also be discussed.

A neurokinin 1 receptor antagonist decreases adhesion reformation after laparoscopic lysis of adhesions in a rat model of adhesion formation

BACKGROUND

Up to 94% of patients experience fibrous adhesions after abdominal surgery, and a significant number of these patients require a second operation for open or laparoscopic lysis of adhesions (LOA). The authors have previously shown that inhibition of the binding of tachykinin ligands to the neurokinin 1 receptor (NK-1R) using the neurokinin 1 receptor antagonist (NK-1RA) CJ-12,255 decreases primary adhesion formation and upregulates the peritoneal fibrinolytic system in a rat model. Whereas most studies have focused on the prevention of primary adhesions, few have addressed adhesion reformation after LOA. This study aimed to determine the effects of NK-1RA administration on adhesion reformation and peritoneal fibrinolytic activity after laparoscopic LOA.

METHODS

Adhesions were induced in 31 rats using our previously described ischemic button model. The rats underwent laparoscopy 7 days later, during which adhesions were scored and lysed followed by administration of the NK-1RA or saline. Then 7 days after LOA, 23 rats were killed and adhesions were scored. Eight rats also were killed 24 h after the LOA to obtain peritoneal tissue and fluid, which were analyzed for tissue plasminogen activator (tPA) mRNA expression and peritoneal fibrinolytic activity by reverse transcriptase-polymerase chain reaction (RT-PCR) and bioassay, respectively.

RESULTS

At laparoscopy, 79% +/- 3% of the buttons formed adhesions. In the saline-administered control animals, 42% +/- 3.2% of the buttons reformed adhesions after LOA (p < 0.05), whereas in the animals that received the NK-1RA, 18.2% +/- 3.5% of the buttons reformed adhesions (p < 0.05). As compared with control animals, NK-1RA administration increased tPA mRNA levels by 38% and fibrinolytic activity sixfold (p < 0.05; 7.0 +/- 2.1 U/ml vs 1.2 +/- 0.54 U/ml).

CONCLUSIONS

When administered during laparoscopic LOA, an NK-1RA significantly upregulates peritoneal fibrinolytic activity and decreases adhesion reformation.

Immunomodulatory properties of substance P: the gastrointestinal system as a model

Communication between nerves and immune and inflammatory cells of the small and large intestine plays a major role in the modulation of several intestinal functions, including intestinal motility, ion transport, and mucosal permeability. Neuroimmune interactions at intestinal sites have been associated with the pathophysiology of infectious and enterotoxin-mediated diarrhea and intestinal inflammation, including inflammatory bowel disease (IBD). During the past 20 years the neuropeptide substance P (SP) has been identified as an important mediator in the development and progress of intestinal inflammation by binding to its high-affinity neurokinin-1 receptor (NK-1R). This peptide, released from enteric nerves, sensory neurons, and inflammatory cells of the lamina propria during intestinal inflammation, participates in gut inflammation by interacting, directly or indirectly, with NK-1R expressed on nerves, epithelial cells, and immune and inflammatory cells, such as mast cells, macrophages, and T cells. SP-dependent activation of these cells leads to the release of cytokines and chemokines as well as other neuropeptides that modulate diarrhea, inflammation, and motility associated with the pathophysiology of several intestinal disease states. The recent development of specific nonpeptide NK-1R antagonists and NK-1R-deficient mice helped us understand the functional importance of the SP-NK-1R system in mediating intestinal neuroimmune interactions and to identify the particular cells and signaling pathways involved in this response. This review summarizes our understanding on the immunomodulatory properties of SP and its receptor in the intestinal tract with particular focus on their involvement in intestinal physiology as well as in the pathophysiology of several intestinal disease states at the in vivo and cell signaling level.

The effectiveness of a single intraperitoneal infusion of a neurokinin-1 receptor antagonist in reducing postoperative adhesion formation is time dependent

BACKGROUND

Current methods to prevent intraabdominal adhesions are not uniformly effective. We recently showed in rats that a neurokinin-1 receptor (NK-1R) antagonist is capable of reducing adhesion formation. To determine the clinical feasibility of using an NK-1R antagonist to reduce adhesions, this study examined the time dependence for the effectiveness of NK-1R antagonist administration and its effects on wound healing.

METHODS

Adhesions were surgically induced in rats receiving a single intraperitoneal infusion of the NK-1R antagonist, CJ-12,255, during or 1, 5, 12, or 24 hours after surgery. Adhesion formation was assessed 7 days later. In a subset of animals, tissue plasminogen activator (tPA) activity, which is a measure of peritoneal fibrinolytic activity, was determined in peritoneal fluid 24 hours after surgery (48 hours for animals infused at 24 hours). The tPA activity was also determined in nonoperated animals 24 hours after peritoneal injection of the NK-1R antagonist. Colonic burst pressures were measured 7 days after creation of anastomoses in rats that were administered the antagonist at surgery.

RESULTS

The NK-1R antagonist significantly reduced (P=.003) intraabdominal adhesions when administered during or 1 hour after surgery, only moderately reduced (P=.08) adhesions when administered at 5 hours, and had no effect at 12 or 24 hours. Peritoneal tPA activity was significantly increased (P<.05) in peritoneal fluid 24 hours after administration of the NK-1R antagonist regardless of the surgical procedure. The NK-1R antagonist did not alter colonic anastomotic healing.

CONCLUSIONS

These data show that some of the events critical to adhesion formation occur within the first 5 hours following an abdominal operation in this model. The fact that the NK-1R antagonist does not impair colonic anastomotic healing enhances its usefulness as a therapeutic agent to inhibit adhesion formation.

The role of neurokinin 1 receptors in the maintenance of visceral hyperalgesia induced by repeated stress in rats

BACKGROUND & AIMS

The neurokinin 1 receptors (NK(1)Rs) and substance P (SP) have been implicated in the stress and/or pain pathways involved in chronic pain conditions. Here we examined the participation of NK(1)Rs in sustained visceral hyperalgesia observed in rats exposed to chronic psychological stress.

METHODS

Male Wistar rats were exposed to daily 1-hour water avoidance stress (WA) or sham WA for 10 consecutive days. We tested intraperitoneal or intrathecal injection of the NK(1)R antagonist SR140333 on the visceromotor reflex to colorectal distention in both groups at day 11. Real-time reverse-transcription polymerase chain reaction, Western blot, and immunohistochemistry were used to assess the expression of NK(1)Rs and/or SP in samples of colon, spinal cord, and dorsal root ganglia.

RESULTS

Both intraperitoneal and intrathecal SR140333 injection diminished the enhanced visceromotor reflex to colorectal distention at day 11 in stressed rats but did not affect the response in control animals. Real-time polymerase chain reaction and Western blotting demonstrated stress-induced up-regulation of spinal NK(1)Rs. Immunohistochemistry showed an increased number of NK(1)R-expressing neurons in the laminae I of the dorsal horn in stressed rats. The expression of NK(1)Rs was decreased in colon from stressed rats compared with control. The expression of SP gene precursor in dorsal root ganglia was unchanged in stressed rats compared with controls.

CONCLUSIONS

Stress-induced increased NK(1)R expression on spinal neurons and the inhibitory effect of intrathecal NK(1)R antagonist on visceral hyperalgesia support the key contribution of spinal NK(1)Rs in the molecular pathways involved in the maintenance of visceral hyperalgesia observed after chronic WA.

Clostridium difficile toxins: mechanism of action and role in disease

As the leading cause of hospital-acquired diarrhea, Clostridium difficile colonizes the large bowel of patients undergoing antibiotic therapy and produces two toxins, which cause notable disease pathologies. These two toxins, TcdA and TcdB, are encoded on a pathogenicity locus along with negative and positive regulators of their expression. Following expression and release from the bacterium, TcdA and TcdB translocate to the cytosol of target cells and inactivate small GTP-binding proteins, which include Rho, Rac, and Cdc42. Inactivation of these substrates occurs through monoglucosylation of a single reactive threonine, which lies within the effector-binding loop and coordinates a divalent cation critical to binding GTP. By glucosylating small GTPases, TcdA and TcdB cause actin condensation and cell rounding, which is followed by death of the cell. TcdA elicits effects primarily within the intestinal epithelium, while TcdB has a broader cell tropism. Important advances in the study of these toxins have been made in the past 15 years, and these are detailed in this review. The domains, subdomains, and residues of these toxins important for receptor binding and enzymatic activity have been elegantly studied and are highlighted herein. Furthermore, there have been major advances in defining the role of these toxins in modulating the inflammatory events involving the disruption of cell junctions, neuronal activation, cytokine production, and infiltration by polymorphonuclear cells. Collectively, the present review provides a comprehensive update on TcdA and TcdB's mechanism of action as well as the role of these toxins in disease.

Substance P and the neurokinin-1 receptor in relation to eosinophilia in ulcerative colitis

Substance P (SP) has been implicated in the pathophysiology of ulcerative colitis (UC) and it has been suggested that blocking of its effect would be advantageous in this disease. Eosinophils have also been implicated in the pathophysiology of UC. In the present study, specimens from the sigmoid colon of UC patients were investigated by the use of antisera against SP and the neurokinin-1 receptor (NK-1R) and staining for demonstration of eosinophils. The degrees of SP innervation and NK-1R immunoreaction, as well as the levels of eosinophil infiltration, varied between different patients. Interestingly, NK-1R immunoreaction in the epithelium was often seen to be the most marked where there were numerous eosinophils in the underlying mucosa and where the mucosa showed a marked morphologic derangement. The observations suggest that there are marked fluctuations in effects of SP and eosinophils during the disease. The infiltrating eosinophils may be involved in the destruction of the mucosal tissue. Furthermore, for the majority of cases where there is marked derangement of the mucosa, it is apparent that there is an upregulation of the NK-1 receptor in the epithelium in parallel with the infiltration of the eosinophils.

Vanilloid receptor 1 antagonists attenuate disease severity in dextran sulphate sodium-induced colitis in mice

Neurogenic mechanisms have been implicated in the induction of inflammatory bowel disease (IBD). Vanilloid receptor type 1 (TRPV1) has been visualized on nerve terminals of intrinsic and extrinsic afferent neurones innervating the gastrointestinal tract and local administration of a TRPV1 antagonist, capsazepine, reduces the severity of dextran sulphate sodium (DSS)-induced colitis in rats (Gut 2003; 52: 713-9(1)). Our aim was to test whether systemically or orally administered TRPV1 antagonists attenuate experimental colitis induced by 5% DSS in Balb/c mice. Intraperitoneal capsazepine (2.5 mg kg(-1), bid), significantly reduced the overall macroscopic damage severity compared with vehicle-treated animals (80% inhibition, P < 0.05); however, there was no effect on myeloperoxidase (MPO) levels. An experimental TRPV1 antagonist given orally was tested against DSS-induced colitis, and shown to reverse the macroscopic damage score at doses of 0.5 and 5.0 mg kg(-1). Epithelial damage assessed microscopically was significantly reduced. MPO levels were attenuated by approximately 50%, and diarrhoea scores were reduced by as much as 70%. These results suggest that pharmacological modulation of TRPV1 attenuates indices of experimental colitis in mice, and that development of orally active TRPV1 antagonists might have therapeutic potential for the treatment of IBD.

The role of substance P in inflammatory disease

The diffuse neuroendocrine system consists of specialised endocrine cells and peptidergic nerves and is present in all organs of the body. Substance P (SP) is secreted by nerves and inflammatory cells such as macrophages, eosinophils, lymphocytes, and dendritic cells and acts by binding to the neurokinin-1 receptor (NK-1R). SP has proinflammatory effects in immune and epithelial cells and participates in inflammatory diseases of the respiratory, gastrointestinal, and musculoskeletal systems. Many substances induce neuropeptide release from sensory nerves in the lung, including allergen, histamine, prostaglandins, and leukotrienes. Patients with asthma are hyperresponsive to SP and NK-1R expression is increased in their bronchi. Neurogenic inflammation also participates in virus-associated respiratory infection, non-productive cough, allergic rhinitis, and sarcoidosis. SP regulates smooth muscle contractility, epithelial ion transport, vascular permeability, and immune function in the gastrointestinal tract. Elevated levels of SP and upregulated NK-1R expression have been reported in the rectum and colon of patients with inflammatory bowel disease (IBD), and correlate with disease activity. Increased levels of SP are found in the synovial fluid and serum of patients with rheumatoid arthritis (RA) and NK-1R mRNA is upregulated in RA synoviocytes. Glucocorticoids may attenuate neurogenic inflammation by decreasing NK-1R expression in epithelial and inflammatory cells and increasing production of neutral endopeptidase (NEP), an enzyme that degrades SP. Preventing the proinflammatory effects of SP using tachykinin receptor antagonists may have therapeutic potential in inflammatory diseases such as asthma, sarcoidosis, chronic bronchitis, IBD, and RA. In this paper, we review the role that SP plays in inflammatory disease.

Stress-induced modulation of skin immune function: two types of antigen-presenting cells in the epidermis are differentially regulated by chronic stress

BACKGROUND

Inflammatory skin diseases are exacerbated by psychiatric stress. Previous studies have shown that the activity of epidermal antigen-presenting cells (APCs), Langerhans cells (LCs) and keratinocytes (KCs), is affected by stress. Hapten application causes migration of LCs to draining lymph nodes (DLNs). Recently, we found that hapten application also activates epidermal cells (ECs) to mature potent APCs, and that the main APCs in these populations are KCs. Thus, DLN cells and ECs following hapten application are available for estimating the APC function of LCs and KCs in stress studies.

OBJECTIVES

To investigate the mechanism of exacerbation of skin inflammation by chronic stress by observing the effect of isolation stress transversally on the skin immune and neurohormonal systems.

METHODS

Contact sensitivity (CS) was elicited in BALB/c mice. The APC function of LCs and ECs following hapten application was assessed by the CS-inducing activity in the recipient mice. Levels of neurohormonal transmitters and proinflammatory cytokines were measured by enzyme-linked immunosorbent assay. Cell surface molecules were detected using flow cytometry. Expression of mRNA for cytokines, neurohormonal receptors and a differentiation marker by ECs was determined by reverse transcription-polymerase chain reaction.

RESULTS

Acute stress (2-day isolation) suppressed induction of CS, while chronic stress (30-day isolation) markedly enhanced induction of CS. DLN cells from chronically stressed mice contained increased numbers of LCs and exhibited enhanced APC function for inducing CS. In contrast, the APC function of KCs from these mice was markedly suppressed. Serum corticosterone levels were enhanced in acute stress, while substance P (SP) levels were enhanced in chronic stress. Corticotrophin-releasing hormone receptor-1 mRNA expression in ECs was enhanced in acute stress, while SP receptor (i.e. neurokinin-1 receptor) mRNA expression in ECs was enhanced in chronic stress. Production and mRNA expression of the proinflammatory cytokines interleukin-1 alpha and tumour necrosis factor-alpha by ECs following hapten application was markedly suppressed in chronic stress. Expression by ECs of E-cadherin, which adheres LCs and KCs homophilically, was suppressed in chronic stress. In addition, these cells exhibited impaired differentiation, i.e. suppressed spontaneous proliferation and enhanced mRNA expression for transglutaminase-3.

CONCLUSIONS

Chronic isolation stress may enhance CS responses by upregulation of the APC activity of LCs and the SP system. However, dysregulation of KC function and differentiation by chronic stress suggests that KCs may not contribute to the enhancement of the CS response positively. These complex changes suggest that chronic isolation stress in mice may provide a possible model system for studying the mechanism of exacerbation of skin inflammation by stress.

Metalloproteinases and transforming growth factor-alpha mediate substance P-induced mitogen-activated protein kinase activation and proliferation in human colonocytes

Substance P (SP) participates in acute intestinal inflammation via binding to the G-protein-coupled neurokinin-1 receptor (NK-1R) and release of proinflammatory cytokines from colonic epithelial cells. SP also stimulates cell proliferation, a critical event in tissue healing during chronic colitis, via transactivation of the epidermal growth factor (EGF) receptor (EGFR) and activation of mitogen-activated protein kinase (MAPK). Here we examined the mechanism by which SP induces EGFR and MAPK activation. We used non-transformed human NCM460 colonocytes stably transfected with the human NK-1R (NCM460-NK-1R cells) as well as untransfected U373 MG cells expressing high levels of endogenous NK-1R. Exposure of both cell lines to SP (10(-7) m) stimulated EGFR activation (1 min) followed by extracellular signal-regulated protein kinase (ERK1/2) activation (2-5 min). SP-induced ERK1/2 activation was blocked by pretreatment with the metalloproteinase inhibitor Batimastat/GM6001, the EGFR phosphorylation inhibitor AG1478, and the tumor necrosis factor-alpha-converting enzyme (TACE) inhibitor TAPI-1. Pretreatment with antibodies against potential EGFR ligands suggested that transforming growth factor-alpha (TGFalpha), but not the other EGFR ligands EGF, heparin-binding EGF, or amphiregulin, mediates SP-induced EGFR transactivation. SP stimulated TGFalpha release into the extracellular space that was measurable within 2 min, and this release was inhibited by metalloproteinase inhibitors and the TACE inhibitor TAPI-1. SP also induced MAPK-mediated cell proliferation that was inhibited by TACE, matrix metalloproteinase (MMP), EGFR, and MEK1 inhibitors. Thus, in human colonocytes, NK-1R-induced EGFR and MAPK activation and cell proliferation involve matrix metalloproteinases (most likely TACE) and the release of TGFalpha. These signaling mechanisms may be involved in the protective effects of NK-1R in chronic colitis.

A neurokinin 1 receptor antagonist decreases postoperative peritoneal adhesion formation and increases peritoneal fibrinolytic activity

Fibrous adhesions remain a major sequela of abdominal surgery. The proinflammatory peptide substance P (SP), known to participate in inflammatory events, may play a key role in adhesion formation. This hypothesis was tested by using an antagonist, CJ-12,255 (Pfizer), that blocks the binding of SP to the neurokinin 1 receptor (NK-1R). Adhesion formation was surgically induced in the peritoneum of rats receiving daily doses of the NK-1R antagonist (NK-1RA; 5.0 or 10.0 mg/kg per day) or saline. On postoperative day 7, both the low and high doses of NK-1RA significantly (P < 0.05) reduced adhesion formation by 45% and 53%, respectively, compared with controls. Subsequently, the effect of NK-1RA administration on peritoneal fibrinolytic activity was investigated to determine a potential mechanism for SP action in the peritoneum. Samples were collected from nonoperated controls and from animals 24 h postsurgery that were administered either NK-1RA or saline. Fibrinolytic activity in peritoneal fluid was assayed by zymography, and expression of tissue plasminogen activator (tPA) and plasminogen activator inhibitor 1, both regulators of fibrinolytic activity, was assessed in peritoneal tissue and fluid by RT-PCR and bioassay, respectively. NK-1RA administration led to a marked (P < 0.05) increase in tPA mRNA levels in peritoneal tissue compared with nonoperated and saline-administered animals. Likewise, NK-1RA administration significantly (P < 0.05) increased tPA in the peritoneal fluid. These data suggest that activation of the NK-1R promotes peritoneal adhesion formation by limiting fibrinolytic activity in the postoperative peritoneum, thus enabling fibrinous adhesions to persist.

Expression of functional neurokinin-1 receptors in regenerative glands during gastric wound healing in rodents

BACKGROUND & AIMS

Although functions of the neurokinin-1 receptor have been well explored in neurogenic inflammation and immunoinflammatory responses, little is known about neurokinin-1 receptors during gastric wound healing. The aim of this study was to assess whether neurokinin-1 receptors play a role in gastric wound healing.

METHODS

In vitro neurokinin-1 receptor autoradiography and immunohistochemistry were performed to identify, locate, and quantify neurokinin-1 receptors during wound healing in rodents with cryoulcers in the gastric corpus and antrum. Moreover, to assess the functionality of these receptors, the effect of the neurokinin-1 receptor antagonist NKP608 on gastric wound healing was quantified in vivo in wild-type and cyclooxygenase-2(-/-) mice.

RESULTS

Regenerative glands of the mucosal ulcer margin of rat cryoulcers of the gastric corpus showed strong expression of neurokinin-1 receptors in binding studies between days 3 and 22, with little expression on days 29-84. In addition, strong immunoreactivity for neurokinin-1 receptors was detected on the cell membrane of these regenerative glands. Expression of neurokinin-1 receptors in regenerative glands was confirmed in the rat antrum and the mouse gastric corpus. Moreover, in vivo functional tests during gastric ulcer healing showed that cell proliferation in the regenerative epithelia of the ulcer margin was significantly decreased by NKP608 compared with placebo; furthermore, gastric ulcer healing was significantly delayed by NKP608 both in wild-type and cyclooxygenase-2(-/-) mice.

CONCLUSIONS

This report shows the time-limited overexpression of neurokinin-1 receptors in the mucosal repair tissue of the corpus and antrum. Our in vitro and in vivo data suggest that neurokinin-1 receptors are involved in gastric wound healing.

Neurokinin-1 receptor (NK-1R) expression is induced in human colonic epithelial cells by proinflammatory cytokines and mediates proliferation in response to substance P

We have previously shown that the receptor for substance P (SP), neurokinin-1 receptor (NK-1R), is a marker of human mucosal but not peripheral mononuclear cells. In the present study, we investigate NK-1R expression in the human colonic mucosa in vivo, particularly in the epithelial cells. We investigate the influence of proinflammatory Th1 cytokines and SP on expression and function of NK-1R in colonic epithelial cells in vitro. Using in situ hybridization to detect NK-1R mRNA, and immunohistochemistry to detect NK-1R protein, colonic epithelial cells were found to express NK-1R in vivo. In contrast, colon epithelial cell lines (Caco-2, HT29, SW620, T84) were negative for NK-1R mRNA and protein. However, stimulation with a proinflammatory cytokine cocktail containing IFN-gamma, TNF-alpha, and IL-1beta, caused induction of NK-1R expression. Expression of NK-1R in human colonic epithelial cells in vivo may therefore reflect cytokine conditioning by the mucosal microenvironment. SP did not alter ion transport in monolayers of cytokine-treated T84 cells. While SP stimulated epithelial ion transport in colonic mucosae ex vivo, this was not a direct effect of SP on the epithelial cells, and appeared to be neurally mediated. However, SP (10(-10)-10(-8) M) elicited a dose-dependent proliferative effect on cytokine-stimulated, but not unstimulated, SW620 cells. Proliferation of the epithelial cells in response to SP was mediated specifically via cytokine-induced NK-1R, since an NK-1R-specific antagonist (Spantide 1) completely blocked SP-mediated proliferation in the cytokine-treated cells. Our results therefore demonstrate that proinflammatory cytokines induce expression of NK-1R in human colonic epithelial cell lines, and that SP induces proliferation of the epithelial cells via cytokine-induced NK-1R.

Functional expression of neurokinin 1 receptors on mast cells induced by IL-4 and stem cell factor

It is widely accepted that neurokinin 1 (NK(1)) receptors are not generally expressed on mast cells but little is known about their expression in inflammation. The present study shows expression of NK(1) receptors on bone marrow-derived mast cells (BMMC) under the influence of IL-4 or stem cell factor (SCF). Highest expression was found when both cytokines are present. Six days of coculture with the cytokines IL-4 and SCF showed significant expression of NK(1) receptors (NK(1) receptor(+)/c-kit(+) BMMC; control: 7%, IL-4/SCF: 16%), while 12 days of cytokine coculture increased this expression to 37% positive cells. A longer coculture with IL-4 and SCF did not give an additional effect. Increased expression in IL-4/SCF-treated BMMC was further confirmed using Western blot analysis. Next, we demonstrated the functional relevance of NK(1) receptor expression for mast cell activation, resulting in an enhanced degranulation upon stimulation by substance P. BMMC activation was significantly diminished by the NK(1) receptor antagonist RP67580 (10 micro M) when stimulated with low concentrations of substance P. The inactive enantiomer RP65681 had no effect. In addition, BMMC cultured from bone marrow of NK(1) receptor knockout mice showed significantly decreased exocytosis to low concentrations of substance P. The present study clearly shows that NK(1) receptor-induced activation contributes significantly at low physiological substance P concentrations (<100 micro M). In conclusion, BMMC were shown to express NK(1) receptors upon IL-4/SCF coculture. This expression of NK(1) receptors has been demonstrated to be of functional relevance and leads to an increase in the sensitivity of BMMC to substance P.

Regulation of the NK-1 receptor gene expression in human macrophage cells via an NF-kappa B site on its promoter

We report here that human monocytic/macrophage THP-1 cells express the neurokinin 1 receptor (NK-1R), and that exposure of these cells to the proinflammatory cytokine IL-1 beta increased the expression of the NK-1R gene at the mRNA and protein levels. Because IL-1 beta function involves nuclear factor kappa B (NF-kappa B) activation, these data suggest that this increase in the expression of the NK-1R gene is mediated by the NF-kappa B transcription factor. An earlier report noted that the promoter region of the human NK-1R gene contains a putative binding site for NF-kappa B [Takahashi, K., Tanaka, A., Hara, M. & Nakanishi, S. (1992) Eur. J. Biochem. 204, 1025-1033]. Here we demonstrate that this is indeed a functional NF-kappa B-binding site, and that NF-kappa B is responsible for regulating the expression of the NK-1R gene by binding to the promoter region of the NK-1R gene. To further substantiate that the observed NF-kappa B-dependent IL-1 beta induction of the human NK-1R gene is regulated via a transcriptional event through this NF-kappa B site on the NK-1R gene promoter, we transfected THP-1 cells with a luciferase promoter-reporter construct containing the 5' promoter region of the human NK-1R gene. Exposure of these cells to IL-1 beta or overexpression of NF-kappa B cDNAs resulted in a significant increase in the amount of luciferase activity that was diminished greatly in cells transfected with I kappa B alpha, the NF-kappa B inhibitor. These results directly implicate NF-kappa B in the regulation of the NK-1R gene and provide a molecular mechanism for the increase in expression of the NK-1R gene in responsive cells.

Expression of authentic substance P receptors in murine and human dendritic cells

Recent studies from our laboratory have shown that substance P can elicit transcription factor activation in dendritic cells. In the present study, we extend these findings by demonstrating the presence of authentic substance P (NK-1) receptors on both normal murine and human dendritic cells. Specifically, we demonstrate the presence of mRNA encoding NK-1 tachykinin receptors and have utilized specific antibodies to detect the expression of NK-1 receptor protein in dendritic cells by Western blot analysis and flow cytometry. These data provide a crucial first step in determining the potential of substance P to modulate dendritic cell function.

Effects of Clostridium difficile toxins on epithelial cell barrier

Clostridium difficile is the primary agent responsible for many patients with antibiotic-associated diarrhea and almost all patients with pseudomembranous colitis following antibiotic therapy. C. difficile infection is the most frequent form of colitis in hospitals and nursing homes and affects millions of patients in the United States and abroad. The first event in the pathogenesis of C. difficile infection involves alterations of the indigenous colonic microflora by antibiotics, followed by colonization with C. difficile. C. difficile causes diarrhea and colitis by releasing two high molecular weight protein exotoxins, toxin A and toxin B, with potent cytotoxic and enterotoxic properties. Evidence presented here indicates that C. difficile toxins compromise the epithelial cell barrier by at least two pathophysiologic pathways, one involving disaggregation of actin microfilaments in colonocytes via glucosylation of the Rho family of proteins leading to epithelial cell destruction and opening of the tight junctions, whereas the other appears to involve early release of proinflammatory cytokines from intestinal epithelial cells probably via activation of MAP kinases. We speculate that cytokines released from intestinal epithelial cells in response to toxin A exposure will diffuse into the lamina propria and activate macrophages, enteric nerves, and sensory neurons to release SP, CGRP, and NT, which, in turn, interact with immune and inflammatory cells and amplify the inflammatory response. Dissection of this inflammatory cascade may help us understand the pathophysiology of inflammatory diarrhea caused by this important pathogen.

IL-4 and IFN-gamma up-regulate substance P receptor expression in murine peritoneal macrophages

While the ability of macrophages to express authentic substance P receptors (i.e., NK-1 receptors) has been inferred from radioreceptor binding assays and functional assays and, most recently, by identification of NK-1 receptor mRNA expression, we know little about NK-1 expression at the protein level or what host factors might up-regulate expression of this receptor. In the present study we demonstrate that the cytokines IL-4 and IFN-gamma can increase the expression of NK-1 receptors on murine peritoneal macrophages. Specifically, we show that IL-4 and IFN-gamma can elicit increases in the level of mRNA encoding the NK-1 receptor by up to 12- and 13-fold, respectively. Furthermore, these cytokines can significantly increase the expression of the NK-1 receptor protein as measured by Western blot and FACS analysis using specific Abs developed in our laboratory. In addition, we have demonstrated the ability of both IL-4 and IFN-gamma to enhance the ability of macrophages to bind substance P as measured by radiolabeled binding assay. The observation that the level of expression of this receptor protein can be enhanced by cytokines that promote either cell-mediated (Th1) or humoral (Th2) immune responses supports the idea that this receptor can be induced during either type of immune response. As such, these results may point to a more ubiquitous role for substance P in the generation of optimal immune responses than previously appreciated.

Small intestinal pathology

During the past year, important studies on various mechanisms of small bowel disease have been reported. The section on enterocyte function evaluates studies on hypoxia and apoptosis. Many of the studies of small intestinal epithelia use as models T84 cells. When these cells are referred to as intestinal cells, it may be in a general sense. This may be of relevance in permeability studies because the transepithelial resistance of T84 cells is on the order of 1000 to 2000 ohm.cm, much higher than the resistance of the small intestine. These studies produce added insights into cellular function. Hypoxia causes changes in epithelial permeability through autocrine pathways. Additional studies methodically detail apoptosis in the small intestinal cell caused by ischemia-reperfusion and the potential mechanisms. Apoptosis is also important in graft-versus-host disease. A number of studies of the mechanism of action of Clostridium difficile toxins are reviewed; these may have therapeutic implications in the future. Finally, the role of mast cells in immunity and in postischemic inflammation is reviewed.

Functional characterisation of tachykinin receptors mediating ion transport in porcine jejunum

In the present study, tachykinin receptors (designated NK 1, NK2 and NK3) involved in regulation of ion transport in porcine jejunum were characterised. Stripped tissue preparations were mounted in Ussing chambers and short-circuited. Substance P produced a concentration dependent increase in short-circuit current, the relationship showing a double sigmoidal form. The non-peptide NK1 receptor antagonist, CP 99,994 ((2S,3S)-3-(2-methoxybenzyl)amino-2-phenylpiperidine), caused a dextral shift of the first sigmoidal response, indicating the involvement of an NK1 receptor. This was further supported by a concentration-dependent response of the NK1 receptor agonist [Sar9Met(O2)11]substance P with an EC50 value of 235.0+/-53.9 nM. Increasing concentrations of CP 99,994 (0.1, 0.3 and 1 microM) produced a parallel dextral shift of the [Sar9Met(O2)11]substance P curve with a slope of the Schild regression significantly different from unity (1.59). The neurokinin A concentration-response curve, with an EC50 value of 68.87+/-16.23 nM, was not significantly changed by the non-peptide NK2 receptor antagonist SR 48,968 ((S)-N-methyl-N-(4-(4-acetylamino-4-phenylpiperidino)-2-(3,4-dichlorophe nyl)butyl)bezamide). In additional studies, the peptide NK2 receptor antagonists, GR 94,800 (PhCO-Ala-Ala-DTrp-Phe-DPro-Pro-NleNH2) and PD 147,714 ((2,3-diOMeZ)-(S)Trp(S)alphaMePheGlyNH2), did not change the response to neurokinin A. However, CP 99,994 totally inhibited neurokinin A responses at 0.5 microM and above. The NK2 receptor agonist, [beta-Ala8]neurokinin A-(4-10), caused only an increase in short-circuit current in microM concentrations, whereas the NK3 receptor agonist, senktide, did not elicit a response. These results indicate, that substance P and neurokinin A mediate ion transport in porcine jejunum through NK1 receptors. However, tachykinins seem to activate another receptor. Two active conformers of the NK1 receptor might be present.

Tachykinins mediate changes in ion transport in porcine jejunum through release of prostaglandins and neurotransmitters

In the present study, we investigated the mediators involved in substance P (SP) and neurokinin A (NKA) induced ion transport. Stripped preparations of porcine jejunal tissue were mounted in Ussing-chambers and short-circuited. The cyclo-oxygenase inhibitor, piroxicam (10 microM) and the neuronal conduction blocker, tetrodotoxin (TTX) (0.1 microM) both significantly decreased the SP (0.1 microM) (66% and 36%, respectively) and NKA (1 microM) (64% and 31%, respectively) induced increase in short-circuit current (SCC). Pretreatment with both piroxicam and TTX totally abolished the SP and NKA response. SP (0.1 microM) caused a significant release of prostaglandin E2 (PGE2), whereas the release of PGE2 induced by NKA was not significant. Experiments were performed to clarify if vasoactive intestinal polypeptide (VIP) was mediating SP or NKA responses. VIP caused a TTX-insensitive and a concentration-dependent increase in SCC. Two VIP antagonists did not change the response to VIP (10 nM and 0.1 microM). Thus, these antagonists could not be used to further elucidate the role of VIP. We were unable to measure a significant release of VIP after SP or NKA treatment. These results indicate, that SP and NKA regulate ion transport in porcine jejunum, entirely through the release of prostaglandins and enteric neurotransmitters.

Substance P receptor expression in intestinal epithelium in clostridium difficile toxin A enteritis in rats

We previously reported that the inflammatory effects of Clostridium difficile toxin A on rat intestine can be significantly inhibited with a specific neurokinin-1 receptor (NK-1R) antagonist. In this study we investigated the localization and expression of NK-1R mRNA and protein in rat intestine by in situ hybridization, Northern blot analysis, and immunohistochemistry, respectively, after exposure to toxin A. Northern blot analysis showed increased mucosal levels of NK-1R mRNA starting 30 min after toxin A administration. In situ hybridization showed that toxin A increased NK-1R mRNA expression in intestinal epithelial cells after 30, 120, and 180 min. In rats pretreated with the NK-1R antagonist CP-96345 the increase in NK-1R mRNA levels after exposure to toxin A was inhibited, indicating that NK-1R upregulation is substance P (SP) dependent. One hour after exposure to toxin A many of the intestinal epithelial cells showed staining for NK-1R compared with controls. Specific 125I-SP binding to purified epithelial cell membranes obtained from ileum exposed to toxin A for 15 min was increased twofold over control and persisted for 4 h. This report provides evidence that NK-1R expression is increased in the intestinal epithelium shortly after exposure to toxin A and may be important in toxin A-induced inflammation.

Effects of toxin A from Clostridium difficile on mast cell activation and survival

Toxins A and B from Clostridium difficile are the main cause of antibiotic-associated diarrhea and pseudomembranous colitis. They cause fluid accumulation, necrosis, and a strong inflammatory response when inoculated in intestinal loops. Since mast cells are a rich source of inflammatory mediators, abundant in the gut, and known to be involved in C. difficile-induced enteritis, we studied the in vitro effect of toxin A on isolated mast cells. Normal rats sensitized by infection with Nippostrongilus brasiliensis were used to isolate peritoneal mast cells (PMC). PMC from naive rats were stimulated with calcium ionophore A23187 as a model of antigen-independent activation, and PMC from sensitized rats were stimulated with N. brasiliensis antigens to study immunoglobulin E-dependent mast cell activation. After 4 h, toxin A did not induce release of nitric oxide or histamine in naive PMC. However, 10 ng of toxin per ml caused a significant release of tumor necrosis factor alpha (TNF-alpha). In contrast, 1 microg of toxin per ml inhibited antigen or A23187-induced histamine release by PMC. Toxin A at 1 microg/ml for 4 h caused disruption of actin which aggregated in the cytoplasm and around the nucleus. After 24 h, chromatin condensation, cytoplasmic blebbing, and apoptotic-like vesicles were observed; DNA fragmentation was documented also. These results suggest that mast cells may participate in the initial inflammatory response to C. difficile infection by releasing TNF-alpha upon interaction with toxin A. However, longer exposure to toxin A affects the release of inflammatory mediators, perhaps because of the alteration of the cytoskeleton and induction of apoptosis. The impaired functions and survival of mast cells by C. difficile toxin A could hamper the capacity of these cells to counteract the infection, thus prolonging the pathogenic effects of C. difficile toxins.

Neurokinin-1 (NK-1) receptor is required in Clostridium difficile- induced enteritis

Toxin A, a 308,000-Mr enterotoxin from Clostridium difficile, mediates antibiotic-associated diarrhea and colitis in humans. Injection of toxin A into animal intestine triggers an acute inflammatory response characterized by activation of sensory neurons and immune cells of the intestinal lamina propria, including mast cells and macrophages, and migration of circulating neutrophils in the involved intestinal segment. In this study we show that mice genetically deficient in the neurokinin-1 receptor are protected from the secretory and inflammatory changes as well as from epithelial cell damage induced by toxin A. The protective effect of neurokinin-1R deletion correlates with diminished intestinal levels of the cytokine TNF-alpha and its mRNA and the leukocyte enzyme myeloperoxidase. These results demonstrate a major requirement for substance P receptors in the pathogenesis of acute inflammatory diarrhea.

The tachykinin NK1 receptor. Part II: Distribution and pathophysiological roles

The tachykinin NK1 receptor is widely distributed in both the central and peripheral nervous system. In the CNS, NK1 receptors have been implicated in various behavioural responses and in regulating neuronal survival and degeneration. Moreover, central NK1 receptors regulate cardiovascular and respiratory function and are involved in activating the emetic reflex. At the spinal cord level, NK1 receptors are activated during the synaptic transmission, especially in response to noxious stimuli applied at the receptive field of primary afferent neurons. Both neurophysiological and behavioural evidences support a role of spinal NK1 receptors in pain transmission. Spinal NK1 receptors also modulate autonomic reflexes, including the micturition reflex. In the peripheral nervous system, tachykinin NK1 receptors are widely expressed in the respiratory, genitourinary and gastrointestinal tracts and are also expressed by several types of inflammatory and immune cells. In the cardiovascular system, NK1 receptors mediate endothelium-dependent vasodilation and plasma protein extravasation. At respiratory level, NK1 receptors mediate neurogenic inflammation which is especially evident upon exposure of the airways to irritants. In the carotid body, NK1 receptors mediate the ventilatory response to hypoxia. In the gastrointestinal system, NK1 receptors mediate smooth muscle contraction, regulate water and ion secretion and mediate neuro-neuronal communication. In the genitourinary tract, NK1 receptors are widely distributed in the renal pelvis, ureter, urinary bladder and urethra and mediate smooth muscle contraction and inflammation in response to noxious stimuli. Based on the knowledge of distribution and pathophysiological roles of NK1 receptors, it has been anticipated that NK1 receptor antagonists may have several therapeutic applications at central and peripheral level. At central level, it is speculated that NK1 receptor antagonists could be used to produce analgesia, as antiemetics and for treatment of certain forms of urinary incontinence due to detrusor hyperreflexia. In the peripheral nervous system, tachykinin NK1 receptor antagonists could be used in several inflammatory diseases including arthritis, inflammatory bowel diseases and cystitis. Several potent tachykinin NK1 receptor antagonists are now under evaluation in the clinical setting, and more information on their usefulness in treatment of human diseases will be available in the next few years.

Substance P diminishes lipopolysaccharide and interferon-gamma-induced TGF-beta 1 production by cultured murine macrophages

Recent evidence has demonstrated the importance of substance P and its receptor in macrophage-mediated inflammatory responses. While previous studies have shown that substance P can augment proinflammatory monokine production, little is known about the effects of this neuropeptide on the production of monokines that might limit inflammation. In the present study we have investigated the effect of substance P treatment on the production of transforming growth factor-beta 1 (TGF-beta 1) in cultured murine macrophages. We report that, while substance P agonist alone elicited increases in TGF-beta 1 mRNA expression and modest increases in TGF-beta 1 secretion, substance P dramatically diminished LPS- or IFN-gamma-induced TGF-beta 1 production. These results suggest a previously unrecognized mechanism where substance P may act as a proinflammatory mediator by limiting the production of excessive levels of TGF-beta 1 by LPS- or IFN-gamma-activated macrophages.

Tachykinins in the gut. Part II. Roles in neural excitation, secretion and inflammation

The preprotachykinin-A gene-derived peptides substance (substance P; SP) and neurokinin (NK) A are expressed in intrinsic enteric neurons, which supply all layers of the gut, and extrinsic primary afferent nerve fibers, which innervate primarily the arterial vascular system. The actions of tachykinins on the digestive effector systems are mediated by three different types of tachykinin receptor, termed NK1, NK2 and NK3 receptors. Within the enteric nervous system, SP and NKA are likely to mediate, or comediate, slow synaptic transmission and to modulate neuronal excitability via stimulation of NK3 and NK1 receptors. In the intestinal mucosa, tachykinins cause net secretion of fluid and electrolytes, and it appears as if SP and NKA play a messenger role in intramural secretory reflex pathways. Secretory processes in the salivary glands and pancreas are likewise influenced by tachykinins. The gastrointestinal arterial system may be dilated or constricted by tachykinins, whereas constriction and an increase in the vascular permeability are the only effects seen in the venous system. Various gastrointestinal disorders are associated with distinct changes in the tachykinin system, and there is increasing evidence that tachykinins participate in the hypersecretory, vascular and immunological disturbances associated with infection and inflammatory bowel disease. In a therapeutic perspective, it would seem conceivable that tachykinin antagonists could be exploited as antidiarrheal, antiinflammatory and antinociceptive drugs.