Endogenous vagal activation dampens intestinal inflammation independently of splenic innervation in postoperative ileus.

Postoperative ileus is encountered by patients undergoing open abdominal surgery and is characterized by intestinal inflammation associated with impaired gastrointestinal motility. We recently showed that inflammation of the gut muscularis triggered activation of the vagal efferent pathway mainly targeting the inflamed zone. In the present study we investigate further the modulatory role of endogenous activation of the vagal motor pathway on the innate immune response. Intestinal or splenic denervation was performed two weeks prior to intestinal manipulation (IM) or laparotomy (L). Twenty-four hour post-surgery, the gastrointestinal transit, immune cell influx, and pro-inflammatory cytokine levels were measured in the gut muscularis. Manipulation of the small intestine led to a delay in intestinal transit, an influx of leukocytes and increased pro-inflammatory cytokine expression. Surgical lesion of the vagal branch that selectively innervates the small intestine did not further delay the intestinal transit but significantly enhanced the expression levels of the pro-inflammatory cytokines IL-1ß and IL-6 in the gut muscularis. Splenic denervation did not affect intestinal inflammation or gastrointestinal transit after intestinal manipulation. Our study demonstrates that selective vagotomy, leaving the splenic innervation intact, increases surgery-induced intestinal inflammation. These data suggest that endogenous activation of the vagal efferent pathway by intestinal inflammation directly dampens the local immune response triggered by intestinal manipulation independently of the spleen.

Susceptibility to stress induced visceral hypersensitivity in maternally separated rats is transferred across generations.

BACKGROUND: In irritable bowel syndrome (IBS), familial clustering and transfer across generations may largely depend on environmental factors but this is difficult to establish in the human setting. Therefore, we aimed to set up a relevant animal model. We investigated whether susceptibility to stress induced visceral hypersensitivity in maternally separated (MS) Long Evans rats can be transferred across generations without further separation protocols and, if so, whether this depends on maternal care. METHODS: At adult age, we evaluated pre- vs post water avoidance (WA) changes in visceromotor response to distension in non-handled second filial generation offspring (NH-F2) of previously separated MS-F1 dams. Furthermore, the role of maternal care was evaluated by cross-fostering F2 offspring of NH-F1 and MS-F1 dams and subsequent sensitivity measurements at adult age. Involvement of mast cells in post stress hypersensitivity of NH-F2 rats was evaluated by mast cell stabilization. KEY RESULTS: In adult NH-F2 offspring of MS-F1 dams, post-WA hypersensitivity to colorectal distension was observed in 80% of rats compared with 19% in offspring of NH-F1 dams. Cross-fostered pups adapted to the phenotype of the foster mother: pups of NH-F1 dams nursed by MS-F1 dams showed post-WA hypersensitivity to distension at adult age and vice versa (100% and 20% respectively). In NH-F2 rats, post-WA hypersensitivity was reversed by mast cell stabilizer doxantrazole. CONCLUSIONS & INFERENCES: Maternal separated-induced susceptibility to stress-triggered visceral hypersensitivity is transferred across generations and this transfer depends on maternal care. Thus, MS is a suitable model to evaluate environmental triggers relevant to IBS clustering in families.

Systemic inflammation with enhanced brain activation contributes to more severe delay in postoperative ileus.

BACKGROUND: The severity of postoperative ileus (POI) has been reported to result from decreased contractility of the muscularis inversely related to the number of infiltrating leukocytes. However, we previously observed that the severity of POI is independent of the number of infiltrating leukocytes, indicating that different mechanisms must be involved. Here, we hypothesize that the degree of tissue damage in response to intestinal handling determines the upregulation of local cytokine production and correlates with the severity of POI. METHODS: Intestinal transit, the inflammatory response, I-FABP (marker for tissue damage) levels and brain activation were determined after different intensities of intestinal handling. KEY RESULTS: Intense handling induced a more pronounced ileus compared with gentle intestinal manipulation (IM). No difference in leukocytic infiltrates in the handled and non-handled parts of the gut was observed between the two intensities of intestinal handling. However, intense handling resulted in significantly more tissue damage and was accompanied by a systemic inflammation with increased plasma levels of pro-inflammatory cytokines. In addition, intense but not gentle handling triggered enhanced c-Fos expression in the nucleus of the solitary tract (NTS) and area postrema (AP). In patients, plasma levels of I-FABP and inflammatory cytokines were significantly higher after open compared with laparoscopic surgery, and were associated with more severe POI. CONCLUSIONS & INFERENCES: Not the influx of leukocytes, rather the manipulation-induced damage and subsequent inflammatory response determine the severity of POI. The release of tissue damage mediators and pro-inflammatory cytokines into the systemic circulation most likely contribute to the impaired motility of non-manipulated intestine.

Neuroanatomical evidence demonstrating the existence of the vagal anti-inflammatory reflex in the intestine.

BACKGROUND: The cholinergic anti-inflammatory pathway is proposed to be part of the so-called vago-vagal 'inflammatory reflex'. The aim of this study is to provide neuro-anatomical evidence to support the existence of a functional neuronal circuit and its activation in response to intestinal inflammation. METHODS: The expression of c-fos was evaluated at different levels of the neurocircuitry in the course of postoperative ileus (POI) in a mouse model. Specific activation of the motor neurons innervating the inflamed intestine and the spleen was monitored by retrograde tracing using cholera toxin-b. The role of the vagal afferent pathway nerve was evaluated by selective vagal denervation of the intestine. KEY RESULTS: Abdominal surgery resulted in subtle inflammation of the manipulated intestine at 24 h (late phase), but not after 2 and 6 h (early) after surgery. This local inflammation was associated with activation of neurons in the nucleus of the solitary tract and in the dorsal nucleus of the vagus. The vagal output mainly targeted the inflamed zone: 42% of motor neurons innervating the intestine expressed c-fos IR in contrast to 7% of those innervating the spleen. Vagal denervation of the intestine abolished c-fos expression in the brain nuclei involved in the neuronal network activated by intestinal inflammation. CONCLUSIONS & INFERENCES: Our data demonstrate that intestinal inflammation triggers a vagally mediated circuit leading mainly to activation of vagal motor neurons connected to the inflamed intestine. These findings for the first time provide neuro-anatomical evidence for the existence of the endogenous 'inflammatory reflex' and its activation during inflammation.

Mast cells trigger epithelial barrier dysfunction, bacterial translocation and postoperative ileus in a mouse model.

BACKGROUND: Abdominal surgery involving bowel manipulation commonly results in inflammation of the bowel wall, which leads to impaired intestinal motility and postoperative ileus (POI). Mast cells have shown to play a key role in the pathogenesis of POI in mouse models and human studies. We studied whether mast cells contribute to the pathogenesis of POI by eliciting intestinal barrier dysfunction. METHODS: C57BL/6 mice, and two mast cell-deficient mutant mice Kit(W/W-v) , and Kit(W-sh/W-sh) underwent laparotomy (L) or manipulation of the small bowel (IM). Postoperative inflammatory infiltrates and cytokine production were assessed. Epithelial barrier function was determined in Ussing chambers, by measuring transport of luminal particles to the vena mesenterica, and by assessing bacterial translocation. KEY RESULTS: In WT mice, IM resulted in pro-inflammatory cytokine and chemokine production, and neutrophil extravasation to the manipulated bowel wall. This response to IM was reduced in mast cell-deficient mice. IM caused epithelial barrier dysfunction in WT mice, but not in the two mast cell-deficient strains. IM resulted in a decrease in mean arterial pressure in both WT and mast cell-deficient mice, indicating that impaired barrier function was not explained by tissue hypoperfusion, but involved mast cell mediators. CONCLUSIONS & INFERENCES: Mast cell activation during abdominal surgery causes epithelial barrier dysfunction and inflammation of the muscularis externa of the bowel. The impairment of the epithelial barrier likely contributes to the pathogenesis of POI. Our data further underscore that mast cells are bona fide cellular targets to ameliorate POI.

Central activation of the cholinergic anti-inflammatory pathway reduces surgical inflammation in experimental post-operative ileus.

BACKGROUND AND PURPOSE: Electrical stimulation of the vagus nerve reduces intestinal inflammation following mechanical handling, thereby shortening post-operative ileus in mice. Previous studies in a sepsis model showed that this cholinergic anti-inflammatory pathway can be activated pharmacologically by central administration of semapimod, an inhibitor of p38 mitogen-activated protein kinase. We therefore evaluated the effect of intracerebroventricular (i.c.v.) semapimod on intestinal inflammation and post-operative ileus in mice. EXPERIMENTAL APPROACH: Mice underwent a laparotomy or intestinal manipulation 1 h after i.c.v. pre-treatment with semapimod (1 µg·kg(-1) ) or saline. Drugs were administered through a cannula placed in the left lateral ventricle 1 week prior to experimentation. Twenty-four hours after surgery, gastric emptying was measured using scintigraphy, and the degree of intestinal inflammation was assessed. Finally, activation of brain regions was assessed using quantitative immunohistochemistry for c-fos. KEY RESULTS: Intestinal manipulation induced inflammation of the manipulated intestine and significantly delayed gastric emptying, 24 h after surgery in saline-treated animals. Semapimod significantly reduced this inflammation and improved gastric emptying. Vagotomy enhanced the inflammatory response induced by intestinal manipulation and abolished the anti-inflammatory effect of semapimod. Semapimod but not saline induced a significant increase in c-fos expression in the paraventricular nucleus, the nucleus of the solitary tract and the dorsal motor nucleus of the vagus nerve. CONCLUSIONS AND IMPLICATIONS: Our findings show that i.c.v. semapimod reduces manipulation-induced intestinal inflammation and prevented post-operative ileus. This anti-inflammatory effect depends on central activation of the vagus nerve.

SCN outputs and the hypothalamic balance of life.

The circadian clock in the suprachiasmatic nucleus (SCN) is composed of thousands of oscillator neurons, each dependent on the cell-autonomous action of a defined set of circadian clock genes. Still, the major question remains how these individual oscillators are organized into a biological clock producing a coherent output able to time all the different daily changes in behavior and physiology. In the present review, the authors discuss the anatomical connections and neurotransmitters used by the SCN to control the daily rhythms in hormone release. The efferent SCN projections mainly target neurons in the medial hypothalamus surrounding the SCN. The activity of these preautonomic and neuroendocrine target neurons is controlled by differentially timed waves of, among others, vasopressin, GABA, and glutamate release from SCN terminals. Together, the data on the SCN control of neuroendocrine rhythms provide clear evidence not only that the SCN consists of phenotypically (i.e., according to neurotransmitter content) different subpopulations of neurons but also that subpopulations should be distinguished (within phenotypically similar groups of neurons) based on the acrophase of their (electrical) activity. Moreover, the specialization of the SCN may go as far as a single body structure, that is, the SCN seems to contain neurons that specifically target the liver, pineal, and adrenal.