Neurotrophin-3, but not nerve growth factor, promotes survival of human intestinal mast cells

Neurotrophins are potent regulators of neuronal cell survival and function. Nerve growth factor (NGF) was shown to reduce apoptosis in cord blood-derived mast cells. Here, we examined the effect of the neurotrophins NGF and neurotrophin (NT)-3 on survival and mediator release of human intestinal mast cells. Mast cells isolated from normal intestinal tissue were cultured in the presence of NGF, NT-3, or stem cell factor (SCF) alone or in the presence of SCF together with each neurotrophin. NGF or NT-3 alone did not promote mast cell survival. In contrast, mast cell recovery was increased twofold when mast cells were cultured with NT-3 in addition to SCF for 14 days compared with control. Mast cell recovery was further increased following a combined addition of NT-3, SCF and IL-4. NT-3 mediated mast cell growth was dependent on the primary receptor for NT-3 TrkC. NGF in combination with SCF or with SCF and IL-4 showed no effect on mast cell survival. Histamine release and histamine content per mast cell remained unchanged, whereas leukotriene C4 release decreased if mast cells were cultured with NGF or NT-3 in addition to SCF. In summary, NT-3 affects mature human mast cells by promoting mast cell survival, whereas NGF does not.     

The d-alanine content of lipoteichoic acid is crucial for Lactobacillus plantarum-mediated protection from visceral pain perception in a rat colorectal distension model

Abstract  The mechanisms leading to positive effects of probiotics in irritable bowel syndrome and inflammatory bowel disease have not been clarified, but the possible involvement of cell wall components is widely discussed. Reduction of the d -alanine content of lipoteichoic acid (LTA) in Lactobacillus plantarum (Dlt ⁻ mutant) enhanced its anti-inflammatory properties in a mouse colitis model. Another lactobacillus species inhibited visceral pain perception in response to colorectal distension (CRD) in rats. Therefore, we investigated if LTA modification influences the constitutive intestinal pain perception in addition to modulation of cytokine release. Male Sprague-Dawley rats were gavaged with L. plantarum , L. plantarum Dlt ⁻ mutant or buffer control, respectively and the responses to CRD were tested in this non-inflammatory model. Tumour necrosis factor (TNF), interferon (IFN)-gamma and interleukin (IL)-10 release were measured in colon tissue homogenates and upon anti-CD3/CD28 activation of isolated splenocytes and mesenteric lymphocytes. Control animals showed significant bradycardia following noxious CRD, whereas only the L. plantarum Dlt ⁻ mutant inhibited the response. The mutant also decreased the activation-induced release of TNF and IFN-gamma from mesenteric T cells and the IL-10 concentration in colonic tissue, while increasing the activation-induced secretion of IL-10 in splenocytes and mesenteric lymphocytes and the baseline IL-10 release of splenocytes. In conclusion, d -alanine depletion of LTA in L. plantarum inhibited visceral pain perception in healthy, non-inflamed rats. Regardless of the non-inflammatory nature of the model decreased visceral pain perception was seen in parallel with anti-inflammatory properties.     

Lactobacillus reuteri ingestion and IKCa channel blockade have similar effects on rat colon motility and myenteric neurones

Abstract Background We have previously shown that ingestion of Lactobacillus reuteri may modulate colonic enteric neuron activity but with unknown effects on colon motility. The aim of the present report was to elucidate the neuronal mechanisms of action of the probiotic by comparing the effects on motility of L. reuteri ingestion with blockade of a specific ionic current in enteric neurons. Methods We have used intraluminal pressure recordings from ex vivo rat colon segments and whole cell patch clamp recordings from neurons of rat longitudinal muscle myenteric plexus preparations to investigate the effects of L. reuteri and TRAM‐34 on colon motility and neurophysiology. The effects of daily feeding of 10⁹L. reuteri bacteria or acute application of TRAM‐34 on threshold fluid filling pressure or pulse pressure was measured. Key Results Lactobacillus reuteri increased intraluminal fluid filling pressure thresholds for evoking pressure pulses by 51% from 0.47 ± 0.17 hPa; the probiotic also decreased the pulse pressure amplitudes, but not frequency, by 18% from 3.91 ± 0.52 hPa. The intermediate conductance calcium‐dependent potassium (IK_Ca) channel blocker TRAM‐34 (3 μmol L^?1) increased filling threshold pressure by 43% from 0.52 ± 0.22 hPa and reduced pulse pressure amplitude by 40% from 2.63 ± 1.11 hPa; contraction frequency was unaltered. TRAM‐34 (3 μmol L^?1) reduced membrane polarization, leak conductance and the slow afterhyperpolarization current in 16/16 myenteric rat colon AH cells but 19/19 S cells were unaffected. Conclusions & Inferences The present results are consistent with L. reuteri enhancing tonic inhibition of colon contractile activity by acting via the IK_Ca channel current in AH cells.     

Vagal dysfunction in irritable bowel syndrome assessed by rectal distension and baroreceptor sensitivity

Abstract Autonomic nervous system dysfunction has been implicated in the pathophysiology of irritable bowel syndrome (IBS). This study characterized the autonomic response to rectal distension in IBS using baroreceptor sensitivity (BRS), a measure of autonomic function. Rectal bag pressure, discomfort, pain, ECG, blood pressure and BRS were continuously measured before, during and after rectal distension in 98 healthy volunteers (34 ± 12 years old, 52 females) and 39 IBS patients (39 ± 11 years old, 35 females). In comparison with the healthy volunteers, IBS patients experienced significantly more discomfort (69 ± 2.2% vs 56 ± 3.6%; P < 0.05), but not pain (9 ± 1.4% vs 6 ± 2.4%; ns) with rectal distension despite similar distension pressures (51 ± 1.4 vs 54 ± 2.4 mmHg; ns) and volumes (394 ± 10.9 vs 398 ± 21.5 mL; ns). With rectal distension, heart rate increased in both healthy volunteers (66 ± 1 to 71 ± 1 bpm; P < 0.05) and IBS patients (66 ± 2 to 74 ± 3 bpm; P < 0.05). Systolic blood pressure also increased in both healthy volunteers (121 ± 2 to 143 ± 2 mmHg; P < 0.05) and patients (126 ± 3 to 153 ± 4 mmHg (P < 0.05) as did diastolic blood pressure, 66 ± 2 to 80 ± 2 mmHg (P < 0.05), compared with 68 ± 3 to 84 ± 3 mmHg (P < 0.05) in IBS patients. The systolic blood pressure increase observed in IBS patients was greater than that seen in healthy volunteers and remained elevated in the post distension period (139 ± 3 mmHg vs 129 ± 2 mmHg; P < 0.05). IBS patients had lower BRS (7.85 ± 0.4 ms mmHg^?1) compared with healthy volunteers (9.4 ± 0.3; P < 0.05) at rest and throughout rectal distension. Greater systolic blood pressure response to rectal distension and associated diminished BRS suggests a compromise of the autonomic nervous system in IBS patients.