Microbiota and host determinants of behavioural phenotype in maternally separated mice.

Early-life stress is a determinant of vulnerability to a variety of disorders that include dysfunction of the brain and gut. Here we exploit a model of early-life stress, maternal separation (MS) in mice, to investigate the role of the intestinal microbiota in the development of impaired gut function and altered behaviour later in life. Using germ-free and specific pathogen-free mice, we demonstrate that MS alters the hypothalamic-pituitary-adrenal axis and colonic cholinergic neural regulation in a microbiota-independent fashion. However, microbiota is required for the induction of anxiety-like behaviour and behavioural despair. Colonization of adult germ-free MS and control mice with the same microbiota produces distinct microbial profiles, which are associated with altered behaviour in MS, but not in control mice. These results indicate that MS-induced changes in host physiology lead to intestinal dysbiosis, which is a critical determinant of the abnormal behaviour that characterizes this model of early-life stress.

Altered colonic function and microbiota profile in a mouse model of chronic depression.

BACKGROUND: Depression often coexists with the irritable bowel syndrome (IBS) which is characterized by alterations in gut function. There is emerging evidence that the microbial composition (microbiota) of the gut is altered in IBS, but the basis for this is poorly understood. The aim of this study was to determine whether the induction of chronic depression results in changes in the colonic function and in its microbial community, and to explore underlying mechanisms. METHODS: Bilateral olfactory bulbectomy (OBx) was used to induce depression-like behavior in mice. Colonic function was assessed by measuring muscle contractility, pellet excretion, c-fos activity, and serotonin levels. Microbiota profiles were obtained using denaturing gradient gel electrophoresis (DGGE). The hypothalamic-pituitary axis (HPA) was assessed by the hypothalamic expression of corticotropin-releasing hormone (CRH). In separate studies, mice without OBx received CRH via intracerebroventricular (ICV) infusion for 4 weeks prior to assessing colonic function and microbiota profiles. KEY RESULTS: Olfactory bulbectomy mice demonstrated chronic depression- and anxiety-like behaviors associated with elevated central CRH expression and increases in c-Fos activity, serotonin levels, and motility in the colon. These changes were accompanied by an altered intestinal microbial profile. Central CRH administration produced similar changes in behavior and motility and altered the microbiota profile in the colon. CONCLUSIONS & INFERENCES: The induction of chronic depression alters motor activity and the microbial profile in the colon likely via activation of the HPA. These findings provide a basis for linking the behavioral and gastrointestinal manifestations of IBS.

The anxiolytic effect of Bifidobacterium longum NCC3001 involves vagal pathways for gut-brain communication.

BACKGROUND: The probiotic Bifidobacterium longum NCC3001 normalizes anxiety-like behavior and hippocampal brain derived neurotrophic factor (BDNF) in mice with infectious colitis. Using a model of chemical colitis we test whether the anxiolytic effect of B. longum involves vagal integrity, and changes in neural cell function. Methods Mice received dextran sodium sulfate (DSS, 3%) in drinking water during three 1-week cycles. Bifidobacterium longum or placebo were gavaged daily during the last cycle. Some mice underwent subdiaphragmatic vagotomy. Behavior was assessed by step-down test, inflammation by myeloperoxidase (MPO) activity and histology. BDNF mRNA was measured in neuroblastoma SH-SY5Y cells after incubation with sera from B. longum- or placebo-treated mice. The effect of B. longum on myenteric neuron excitability was measured using intracellular microelectrodes. KEY RESULTS: Chronic colitis was associated with anxiety-like behavior, which was absent in previously vagotomized mice. B. longum normalized behavior but had no effect on MPO activity or histological scores. Its anxiolytic effect was absent in mice with established anxiety that were vagotomized before the third DSS cycle. B. longum metabolites did not affect BDNF mRNA expression in SH-SY5Y cells but decreased excitability of enteric neurons. CONCLUSIONS & INFERENCES: In this colitis model, anxiety-like behavior is vagally mediated. The anxiolytic effect of B. longum requires vagal integrity but does not involve gut immuno-modulation or production of BDNF by neuronal cells. As B. longum decreases excitability of enteric neurons, it may signal to the central nervous system by activating vagal pathways at the level of the enteric nervous system.

On the linear stability of Stokes layers.

Oscillatory flows occur naturally, with applications ranging across many disciplines from engineering to physiology. Transition to turbulence in such flows is a topic of practical interest and this article discusses some recent work that has furthered our understanding of the stability of a class of time-periodic fluid motions. Our study starts with an examination of the linear stability of a classical flat Stokes layer. Although experiments conducted over many years have demonstrated conclusively that this layer is unstable at a sufficiently large Reynolds number, it has only been relatively recently that rigorous theoretical confirmation of this behaviour has been obtained. The analysis and numerical calculations for the planar Stokes layer were subsequently extended to flows in channels and pipes and for the flow within a torsionally oscillating circular cylinder. We discuss why our predictions for the onset of instability in these geometries are in disappointingly poor agreement with experimental results. Finally, some suggestions for future experimental work are given and some areas for future theoretical analysis outlined.

Gliadin-dependent neuromuscular and epithelial secretory responses in gluten-sensitive HLA-DQ8 transgenic mice.

Celiac disease is a gluten intolerance caused by a T-cell response against human leukocyte antigen (HLA)-DQ2 and DQ8-bound gluten peptides. Some subjects experience gastrointestinal symptoms in the absence of villous atrophy. Here we investigate the potential mechanisms of gut dysfunction in gluten-sensitive HLA-DQ8 transgenic mice. HLA-DQ8 mice were sensitized and gavaged with gliadin 3x/wk for 3 wk (G/G). Controls included 1) nonsensitized mice gavaged with rice (C); 2) gliadin-sensitized mice gavaged with rice (G/R); and 3) BSA-sensitized mice gavaged with BSA (BSA/BSA). CD3(+) intraepithelial lymphocyte, macrophage, and FOX-P3-positive cell counts were determined. Acetylcholine release, small intestinal contractility, and epithelial ion transport were measured. Gut function was investigated after gluten withdrawal and in HLA-DQ6 mice. Intestinal atrophy was not observed in G/G mice. Recruitment of intraepithelial lymphocyte, macrophages, and FOX-P3+ cells were observed in G/G, but not in C, G/R, or BSA/BSA mice. This was paralleled by increased acetylcholine release from the myenteric plexus, muscle hypercontractility, and increased active ion transport in G/G mice. Changes in muscle contractility normalized in DQ8 mice after a gluten withdrawal. HLA-DQ6 controls did not exhibit the abnormalities in gut function observed in DQ8 mice. Gluten sensitivity in HLA-DQ8 mice induces immune activation in the absence of intestinal atrophy. This is associated with cholinergic dysfunction and a prosecretory state that may lead to altered water movements and dysmotility. The results provide a mechanism by which gluten could induce gut dysfunction in patients with a genetic predisposition but without fully evolved celiac disease.

Specific probiotic therapy attenuates antibiotic induced visceral hypersensitivity in mice.

BACKGROUND AND AIMS: Abdominal pain and discomfort are common symptoms in functional disorders and are attributed to visceral hypersensitivity. These symptoms fluctuate over time but the basis for this is unknown. Here we examine the impact of changes in gut flora and gut inflammatory cell activity on visceral sensitivity. METHODS: Visceral sensitivity to colorectal distension (CRD) was assessed at intervals in healthy mice for up to 12 weeks, and in mice before and after administration of dexamethasone or non-absorbable antibiotics with or without supplementation with Lactobacillus paracasei (NCC2461). Tissue was obtained for measurement of myeloperoxidase activity (MPO), histology, microbiota analysis, and substance P (SP) immunolabelling. RESULTS: Visceral hypersensitivity developed over time in healthy mice maintained without sterile precautions. This was accompanied by a small increase in MPO activity. Dexamethasone treatment normalised MPO and CRD responses. Antibiotic treatment perturbed gut flora, increased MPO and SP immunoreactivity in the colon, and produced visceral hypersensitivity. Administration of Lactobacillus paracasei in spent culture medium normalised visceral sensitivity and SP immunolabelling, but not intestinal microbiota counts. CONCLUSION: Perturbations in gut flora and in inflammatory cell activity alter sensory neurotransmitter content in the colon, and result in altered visceral perception. Changes in gut flora may be a basis for the variability of abdominal symptoms observed in functional gastrointestinal disorders and may be prevented by specific probiotic administration.

The gene transfer of soluble VEGF type I receptor (Flt-1) attenuates peritoneal fibrosis formation in mice but not soluble TGF-beta type II receptor gene transfer.

Peritoneal fibrosis formation is a consequence of inflammation/injury and a significant medical problem to be solved. The effects of soluble VEGF receptor type I (sFlt-1) gene transfer on experimental peritoneal fibrosis were examined and compared with soluble transforming growth factor-beta (TGF-beta) receptor type II (sTGF beta RII) gene transfer. Male C57BL/6 mice were injected with 1.5 x 10(8) plaque-forming unit of adenovirus encoding active TGF-beta (AdTGF beta) intraperitoneally. Some mice had been treated with sTGF betaRII or sFlt-1 plasmid injection into skeletal muscle with electroporation 4 days before virus administration. Mice were euthanized at day 14 after virus administration. AdTGF beta induced significant elevation of serum active TGF-beta, caused significant inflammatory response [weight loss, elevation of serum amyloid-P (SAP) and IL-12, increased expression of monocyte chemoattractant protein-1 (MCP-1) mRNA], and induced marked thickening of the peritoneum and collagen deposition. Gene transfer of sFlt-1 reduced the collagen deposition approximately 81% in mesenteric tissue. Treatment with sFlt-1 decreased ICAM-1 and MCP-1 mRNA expression significantly. Significant negative correlation between serum sFlt-1 and placental growth factor level was observed, whereas there was no significant negative correlation between sFlt-1 and VEGF. On the other hand, sTGF beta RII treatment enhanced the AdTGF beta-induced inflammation (significant elevation of SAP, TNF-alpha, and IL-12 levels and upregulation of ICAM-1 and MCP-1 mRNA expressions) and failed to prevent collagen deposition. These observations indicate that sFlt-1 gene transfer might be of therapeutic benefit in peritoneal fibrosis.

Disruption of CD40-CD40 ligand pathway inhibits the development of intestinal muscle hypercontractility and protective immunity in nematode infection.

In our previous studies, we demonstrated that during Trichinella spiralis infection, T helper (Th) 2 cells contribute to the development of intestinal muscle hypercontractility and worm expulsion from the gut via STAT6. In addition, we have linked the altered muscle contractility to the eviction of the parasite and thereby to the host defense. However, the initial events linking infection to the development of muscle hypercontractility are poorly understood. In this study, we examined the contribution of CD40-CD40 ligand (CD40L) interaction in the development of intestinal muscle hypercontractility, in monocyte chemoattractant protein-1 (MCP-1) production, and in the Th2 response in CD40 ligand-deficient (CD40L -/-) mice infected with T. spiralis. Expulsion of intestinal worms was substantially delayed in CD40L -/- mice compared with the wild-type mice after T. spiralis infection. Consistent with delayed worm expulsion, there was a significant attenuation of intestinal muscle contractility in CD40L -/- mice. Infected CD40L -/- mice also exhibited marked impairment in the production of MCP-1, IL-4, IL-13, IgG1, IgE, and mouse mucosal MCP 1 (MMCP-1), and in goblet cell response. These results demonstrate that CD40-CD40 ligand interaction plays an important role in MCP-1 production, Th2 response, intestinal muscle hypercontractility, and worm expulsion in nematode infection. The present data suggest that the early events leading to the generation of Th2 response include CD40-CD40 ligand interaction, which subsequently influences the production of Th2 cytokines, most likely via upregulation of MCP-1.

Establishment of T-Helper-2 immune response based gerbil model of enteric infection.

BACKGROUND: The reciprocal antagonism of T-helper-1 (Th-1) and Th-2 type immune responses suggests that helminth parasitic infection may ameliorate disease where a Th-1 type response dominates. The Mongolian gerbil has been useful in the investigation of the pathogenesis of gastric cancer, since long-term infection of gerbils with Helicobacter pylori induces adenocarcinoma. In this study the kinetics of worm expulsion and associated immune responses in gerbils infected with Trichinella spiralis were investigated in an attempt to establish an animal model of parasitic infection that could be helpful when investigating the effect of a Th-2 type response on Th-1-based intestinal disorders. METHODS: Gerbils were infected with various doses of infective T. spiralis larvae and were euthanized on different days after infection to investigate the intestinal worm recovery, goblet cell population, eosinophil response and serum IgG1 responses. RESULTS: The number of worms recovered from the intestine was dependent on the number of larvae used for the infection. Almost all worms were expelled spontaneously by day 26 post-infection, when the gerbils had been infected with 375 or 750 larvae. The number of intestinal goblet cells, eosinophils and the serum IgG1 level significantly increased following infection compared with the control. CONCLUSION: This is the first comprehensive report on the time-course of T. spiralis infection in gerbils. The data indicate that the T. spiralis-infected gerbil could be used as a model of the Th-2-based response to investigate the effect of a parasite-induced Th-2 response on various Th-1-mediated intestinal disorders such as H. pylori-induced gastritis and gastric carcinoma.

Neutral endopeptidase (EC 3.4.24.11) downregulates the onset of intestinal inflammation in the nematode infected mouse.

BACKGROUND AND AIMS: Substance P (SP) release from sensory nerves induces neurogenic inflammation. Neutral endopeptidase (NEP) degrades SP, thereby limiting its proinflammatory effects. Intestinal inflammation following Trichinella spiralis infection markedly downregulates NEP, resulting in diminished SP degradation, with unknown functional consequences. We hypothesised that diminished expression of NEP would exacerbate T spiralis induced enteritis. METHODS: NEP knockout (NEP-/-) and wild-type (NEP+/+) mice were infected with T spiralis and studied at 6, 12, 24, and 48 hours post infection (PI). Tissue inflammation was quantified by computerised cell counting and myeloperoxidase activity (MPO). The leucocyte adhesion molecule, intercellular adhesion molecule 1 (ICAM-1), and SP were assessed by immunohistochemistry. RESULTS: Before infection, the lack of NEP was not associated with changes in mucosal cellularity or MPO activity. Twelve hours PI, NEP-/- mice showed a 2.5-fold increase in MPO activity at a time when values in NEP+/+ mice were still within normal limits. MPO activity and cellularity peaked at 24 hours PI. This was accompanied by increased staining for both ICAM-1 and SP in NEP-/- mice. Infusion of rhNEP to NEP-/- mice significantly reduced MPO activity 24 hours PI. CONCLUSIONS: These findings demonstrate that NEP downregulates the early onset of nematode intestinal inflammation and that increased bioavailability of SP and overexpression of ICAM-1 in NEP-/- mice likely play a role in the earlier onset of intestinal inflammation.

Intestinal inflammation and activation of sensory nerve pathways: a functional and morphological study in the nematode infected rat.

BACKGROUND: In the rat, gastric distension elicits an intensity dependent pseudoaffective bradycardia mediated via capsaicin sensitive afferent and cholinergic efferent vagal pathways. Inflammation alters visceral perception although the mediators responsible have not been identified. In the nematode infected rat, there is a substantial increase in neuronal substance P (SP) content of the gut. AIMS: To examine the effects of inflammation on perception of a noxious visceral stimulus and on SP and neurokinin 1 (NK-1) receptor immunoreactivity (IR) in visceral afferent pathways. METHODS: Immunohistochemistry was performed on sections from the jejunum, dorsal root ganglia (DRG), and spinal cord (T1-L1) using SP and NK-1 rabbit polyclonal antibodies. In the DRG, the number of SP-IR or NK-1-IR neurones per section was visually quantified. The pseudoaffective cardiac reflex response to gastric stimulation was compared in control and Trichinella spiralis infected rats. RESULTS: Intestinal inflammation induced a rightward shift in the intensity dependent bradycardic response to gastric distension. This was associated with a marked increase in SP-IR not only in the gut wall but also in the DRG and dorsal horn of the spine. In contrast, NK-1-IR was not increased in the gut wall. Moreover, inflammation evoked a decrease in NK-1-IR in the dorsal horn. No NK-1-IR was identified in the DRG of either control or infected animals. CONCLUSIONS: Intestinal inflammation modulates the capsaicin sensitive pseudoaffective autonomic response to gastric distension, increases SP-IR in afferent pathways, and downregulates dorsal horn NK-1-IR. As the pseudoaffective response is capsaicin sensitive, the rightward shift of the response is likely the consequence of the decrease in NK-1 receptors in the sensory pathways.

IL-12 gene transfer alters gut physiology and host immunity in nematode-infected mice.

Immune responses elicited by nematode parasite infections are characterized by T helper 2 (Th2) cell induction. The immunologic basis for changes in intestinal physiology accompanying nematode infection is poorly understood. This study examined whether worm expulsion and associated goblet cell hyperplasia and muscle contractility share a similar immune basis by shifting the response from Th2 to Th1 using interleukin-12 (IL-12) overexpression. We used a single administration of recombinant adenovirus vector expressing IL-12 (Ad5IL-12) in Trichinella spiralis-infected mice. Ad5IL-12 administered 1 day after infection prolonged worm survival and inhibited infection-induced muscle hypercontractility and goblet cell hyperplasia. This was correlated with upregulated interferon-gamma (IFN-gamma) expression and downregulated IL-13 expression in the muscularis externa layer. We also observed increased IFN-gamma production and decreased IL-4 and IL-13 production from in vitro stimulated spleen and mesenteric lymph node cells of infected Ad5IL-12-treated mice. These results indicate that transfer and overexpression of the IL-12 gene during Th2-based nematode infection shifts the immune response toward Th1 and delays worm expulsion. Moreover, the immune response shift abrogated the physiological responses to infection, attenuating both muscle hypercontractility and goblet cell hyperplasia. These findings strongly indicate that worm expulsion, muscle hypercontractility, and goblet cell hyperplasia share a common immunologic basis and may be causally linked.

Neural change in Trichinella-infected mice is MHC II independent and involves M-CSF-derived macrophages.

Intestinal inflammation due to nematode infection impairs enteric cholinergic nerve function and induces hypercontractility of intestinal muscle. Macrophages have been implicated in the neural changes, but the subpopulation and mechanism involved are unknown. We examined whether macrophages alter nerves by virtue of their ability to activate lymphocytes via major histocompatibility complex (MHC) II-restricted antigen presentation. We also attempted to evaluate the role of macrophage subsets using op/op mice deficient in macrophage colony-stimulating factor (M-CSF). ACh release from the myenteric plexus was measured in MHC II- and M-CSF-deficient (op/op) mice infected with Trichinella spiralis. F4/80-positive macrophages and interleukin-1 beta were constitutively present in op/op and op/? mice but increased only in op/? mice postinfection. After infection, a marked suppression of ACh release occurred only in infected MHC II-deficient and op/? mice. Muscle hypercontractility remained evident in infected op/? mice. Treatment with M-CSF restored macrophage number, and this was accompanied by suppression of cholinergic nerve function during infection. Thus M-CSF plays a critical role in this model by recruiting a subset of macrophages that selectively suppresses enteric neural function.

Role of immunologic factors and cyclooxygenase 2 in persistent postinfective enteric muscle dysfunction in mice.

BACKGROUND & AIMS: Chronic abdominal symptoms develop in some patients after acute enteric infection. This study examined mechanisms underlying smooth muscle hypercontractility that persists after acute infection in mice. METHODS: Euthymic and athymic National Institutes of Health (NIH) Swiss mice were infected with Trichinella spiralis and studied 4 weeks postinfection (PI). Isometric tension was assessed in longitudinal muscle. Cytokine and cyclooxygenase (COX)-2 messenger RNA was determined in the muscularis externa by reverse-transcription polymerase chain reaction. COX-2 protein was identified by immunohistochemistry and prostaglandin E(2) was measured by enzymatic immunoassay. Studies were performed in euthymic and athymic NIH Swiss mice 28 days PI and in the presence or absence of treatment with corticosteroid or COX inhibitors. RESULTS: Muscle hypercontractility was evident in euthymic mice but was attenuated in athymic mice or in steroid-treated euthymic mice 28 days PI. Expression of Th2 cytokines interleukins 4, 5, and 13 was increased during the acute infection but not thereafter. COX-2 was localized to muscle and its enzymatic activity remained significantly increased in the muscle on day 28 PI. Selective COX-2 inhibition in vitro reduced the sustained increase in tension generation. CONCLUSIONS: These findings show that COX-2 activation in resident cells of the muscularis externa contributes to the muscle hypercontractility that persists after infection.

Mast cell-independent impairment of host defense and muscle contraction in T. spiralis-infected W/W(V) mice.

In response to nematode infection, the host presumably attempts to create an unfavorable environment to prevent larval penetration of the host and to expedite parasite expulsion from the gut. In this study, we have used W/W(V) mice with or without mast cells after bone marrow reconstitution (BMR-W/W(V)) to examine the role of mast cells in the host response. W/W(V), BMR-W/W(V), and wild-type (+/+) mice were infected with Trichinella spiralis. Infected W/W(V) mice exhibited less tissue damage and experienced a delay in worm expulsion and a greater degree of larval penetration of the gut leading to encystment in skeletal muscle. Tissue injury was greater and worm expulsion was normalized in BMR-W/W(V) mice, but larval penetration remained unchanged. Spontaneous contractile activity of jejunal muscle was disrupted in W/W(V) mice, as was the contractile response to carbachol. These abnormalities were also present in BMR-W/W(V) mice. These results indicate that mast cells mediate tissue damage and contribute to the timely expulsion of nematodes from the gut during primary infection.

Critical role for signal transducer and activator of transcription factor 6 in mediating intestinal muscle hypercontractility and worm expulsion in Trichinella spiralis-infected mice.

Intestinal nematode infections in rats or mice are accompanied by intestinal muscle hyper contractility that may contribute to parasite expulsion from the gut. Previous studies demonstrated that both the expulsion of nematode parasites and the associated muscle hyper contractility are dependent on CD4(+) T helper cells. Nevertheless, the precise immunological mechanism underlying changes in intestinal muscle function remains to be determined. In this study, we investigated the role of interleukin 4 (IL-4) and signal transducer and activator of transcription factor 6 (STAT6) in the development of intestinal muscle hypercontractility and worm expulsion by infecting IL-4 and STAT6-deficient mice with Trichinella spiralis. Worm expulsion was almost normal in IL-4-deficient mice but substantially delayed in STAT6-deficient mice. Consistent with delayed worm expulsion, we also observed a marked attenuation of carbachol-induced muscle contraction in STAT6-deficient mice but only a moderate decrease in muscle hypercontractility in IL-4-deficient mice. In addition, we also observed severe impairment of T helper type 2 cytokine responses and intestinal mucosal mastocytosis in STAT6-deficient mice, although some degree of intestinal tissue eosinophilia was evident in these animals. These results are consistent with the hypothesis that STAT6-dependent changes in intestinal muscle function contribute to host protection in nematode infection.

The role of CD4+ lymphocytes in the susceptibility of mice to stress-induced reactivation of experimental colitis.

Idiopathic inflammatory bowel disease is a chronic relapsing condition. The role of stress in causing relapses of inflammatory bowel disease remains controversial. We now show that colitis induced in mice by dinitrobenzenesulfonic acid (DNBS) resolves by 6 weeks, but can subsequently be reactivated by stress plus a sub-threshold dose of DNBS, but not by DNBS alone. Stress reduced colonic mucin and increased colon permeability. Susceptibility to reactivation by stress required CD4+ lymphocytes and could be adoptively transferred. We conclude that stress reactivates experimental colitis by facilitating entry of luminal contents that activate previously sensitized CD4 cells in the colon.

Cigarette smoke aggravates experimental colitis in rats.

BACKGROUND & AIMS: Tobacco smoking has a complex effect on intestinal inflammation, being protective in ulcerative colitis, whereas it aggravates Crohn's disease. The beneficial effect of smoking has been attributed to nicotine, but the mechanisms underlying the adverse effect are still under investigation. The aim of this study was to examine the effect of cigarette smoking on experimental colitis in rats and to investigate the underlying mechanism. METHODS: Rats were exposed daily to cigarette smoke by means of a specialized smoking chamber. Control rats were placed in the same chamber without introducing smoke. In parallel experiments, rats received the ganglionic blocker hexamethonium before smoke exposure. After 2 weeks, colitis was induced by dinitrobenzenesulfonic acid (DNBS), and inflammation was assessed 3 days later. RESULTS: Exposure to cigarette smoke significantly increased macroscopic and histological damages as well as myeloperoxidase activity compared with sham-treated controls. Treatment with hexamethonium before smoking reversed the effect of the smoke on the colitis, improving all parameters. CONCLUSIONS: Exposure to cigarette smoke aggravates DNBS-induced colitis in the rat. This effect is reversed by hexamethonium, suggesting that a neural pathway is involved.

IL-5 contributes to worm expulsion and muscle hypercontractility in a primary T. spiralis infection.

Enteric nematode infections lead to increased interleukin (IL)-5 expression, eosinophilic inflammation, and intestinal smooth muscle hypercontractility. Although eosinophils release inflammatory mediators that cause smooth muscle contraction, the role of IL-5 and eosinophils in enteric smooth muscle hypercontractility is unclear. IL-5-deficient mice and their wild-type controls were infected with the nematode Trichinella spiralis. Intestinal parasites and eosinophils were counted, and jejunal longitudinal muscle contractility was assessed. During infection, IL-5 gene expression increased significantly in wild-type mice and was accompanied by significant intestinal eosinophilia in wild-type but not IL-5-deficient mice. Although both strains developed increased muscle contractility during infection, contraction was significantly less in the IL-5-deficient mice at days 16 and 21 postinfection. In addition, parasite expulsion was transiently delayed at day 16 in IL-5-deficient mice. Thus, in the nematode-infected mouse, IL-5 appears essential for intestinal eosinophilia and contributes to, but is not essential for, the development of muscle hypercontractility. IL-5 also appears to play a minor role in expelling a primary T. spiralis infection from the gut.

Increased intestinal muscle contractility and worm expulsion in nematode-infected mice.

Intestinal nematode infections are accompanied by mucosal inflammation and an increase in propulsive motor activity that may contribute to parasite eviction from the gut. To examine whether differences in worm expulsion correspond to the increased intestinal muscle contractility that accompanies nematode infection, we studied mice with genetically determined differences in their ability to expel the nematode parasite Trichinella spiralis. Specifically, we examined isometric contraction of longitudinal muscle, worm counts, and inflammation, as measured by myeloperoxidase activity, in two strains of mice infected with T. spiralis. The strong responder strain, NIH Swiss, expelled the parasites by day 16 postinfection, whereas the poorer responding B10.BR strain was still heavily infected by day 21 postinfection. However, both strains developed similar increases in jejunal myeloperoxidase activity. Both strains demonstrated increased isometric tension development after infection, but peak tension occurred earlier in NIH Swiss mice (day 8 vs. day 12 postinfection) and was of significantly greater magnitude than in B10.BR mice. We conclude that the ability to expel T. spiralis from the small bowel is not related to the degree of granulocyte-dependent mucosal inflammation but is reflected in the magnitude of the accompanying increase in force generation by intestinal smooth muscle.