Mitsuhisa Kawai

A selective, high affinity 5-HT 2B receptor antagonist inhibits visceral hypersensitivity in rats

Background  RS‐127445 is a selective, high affinity 5‐HT2Breceptor antagonist. We investigated whether 5‐HT2Breceptor antagonists can reduce colonic visceral hypersensitivity caused by restraint stress or by proximal colonic inflammation.

Abolishment of TNBS-induced visceral hypersensitivity in mast cell deficient rats

Mucosal mast cells are implicated in visceral hypersensitivity associated with irritable bowel syndrome (IBS). In this study, we investigated the role of mast cells in the development of visceral hypersensitivity by using mast cell deficient (Ws/Ws) rats and their control (W+/W+). In W+/W+ rats, an injection of 2,4,6-trinitrobenzene sulfonic acid (TNBS) into the proximal colon produced a significant decrease in pain threshold of the distal colon. Severe mucosal necrosis and inflammatory cell infiltration with concomitant increase in tissue myeloperoxidase activity were observed in the proximal colon that was directly insulted by TNBS, whereas neither necrosis nor increased myeloperoxidase activity occurred in the distal colon, indicating that TNBS-induced hypersensitivity is not caused by the local tissue damage or inflammation in the region of the gut where distention stimuli were applied. On the other hand, TNBS failed to elicit visceral hypersensitivity in Ws/Ws rats. This finding indicates that mast cells are essential for development of TNBS-induced visceral hypersensitivity in rats. Since the severity of TNBS-induced proximal colon injury and MPO activity was not affected by mast cell deficiency, it is unlikely that abolishment of visceral hypersensitivity in mast cell deficient rats was a result of altered development of the primary injury in the proximal colon. There was no difference between sham-operated Ws/Ws and W+/W+ rats in colonic pain threshold to distention stimuli, indicating that mast cells play no modulatory roles in normal colonic nociception. The present results support the view that mucosal mast cells play key roles in the pathogenesis of IBS.

Effect of a New α2δ Ligand PD-217014 on Visceral Hypersensitivity Induced by 2,4,6-Trinitrobenzene Sulfonic Acid in Rats

PD-217014, a new GABA analog (1α,3α,5α-3-aminomethyl-bicyclo[3.2.0]heptane-3-acetic acid), inhibited [3H]-gabapentin binding to α2δ subunit of voltage-gated calcium channels in a concentration-dependent manner (Ki = 18 nmol/l). Oral treatment with PD-217014 significantly inhibited the visceral hypersensitivity induced by an intra-colonic injection of trinitrobenzene sulfonic acid in rats. The anti-hyperalgesic effect of PD-217014 increased in a dose-dependent manner, and reached a plateau level at 60 mg/kg p.o. The visceral analgesia produced by PD-217014 at 30 and 60 mg/kg p.o. correlated with blood concentrations within 4 h after dosing, and maximal efficacy was obtained 2 h after dosing when the maximal blood concentration was achieved at either dose. These results indicate that PD-217014 is a potent α2δ ligand and possesses visceral analgesic activity.

Chronic Psychological Stress Disrupted the Composition of the Murine Colonic Microbiota and Accelerated a Murine Model of Inflammatory Bowel Disease

The effect of psychological stress on the gastrointestinal microbiota is widely recognized. Chronic psychological stress may be associated with increased disease activity in inflammatory bowel disease, but the relationships among psychological stress, the gastrointestinal microbiota, and the severity of colitis is not yet fully understood. Here, we examined the impact of 12-week repeated water-avoidance stress on the microbiota of two inbred strains of T cell receptor alpha chain gene knockout mouse (background, BALB/c and C57BL/6) by means of next-generation sequencing of bacterial 16S rRNA genes. In both mouse strains, knockout of the T cell receptor alpha chain gene caused a loss of gastrointestinal microbial diversity and stability. Chronic exposure to repeated water-avoidance stress markedly altered the composition of the colonic microbiota of C57BL/6 mice, but not of BALB/c mice. In C57BL/6 mice, the relative abundance of genus Clostridium, some members of which produce the toxin phospholipase C, was increased, which was weakly positively associated with colitis severity, suggesting that expansion of specific populations of indigenous pathogens may be involved in the exacerbation of colitis. However, we also found that colitis was not exacerbated in mice with a relatively diverse microbiota even if their colonic microbiota contained an expanded phospholipase C-producing Clostridium population. Exposure to chronic stress also altered the concentration of free immunoglobulin A in colonic contents, which may be related to both the loss of bacterial diversity in the colonic microbiota and the severity of the colitis exacerbation. Together, these results suggest that long-term exposure to psychological stress induces dysbiosis in the immunodeficient mouse in a strain-specific manner and also that alteration of microbial diversity, which may be related to an altered pattern of immunoglobulin secretion in the gastrointestinal tract, might play a crucial role in the development of chronic stress-induced colitis.

Involvement of parasympathetic pelvic efferent pathway in psychological stress-induced defecation

AIM To investigate the role of the pelvic nerve pathway in stress-induced acceleration of colorectal transit and defecation in rats. METHODS Surgical transection of rectal nerves (rectal branches of the pelvic nerve), vagotomy (Vag) or adrenalectomy (Adx) were performed bilaterally in rats. Number of fecal pellet output of these rats was measured during 1-h water avoidance stress (WAS). To evaluate the colonic transit, rats were given phenol red through the catheter indwelled in the proximal colon and subjected to WAS. After WAS session, entire colon and rectum were isolated and distribution of phenol red was measured. Distal colonic and rectal transit was evaluated using glass bead. Rats were inserted the glass bead into the distal colon and evacuation rate of the bead was measured. Neural activation was assessed by immunohistochemical staining of c-Fos and PGP9.5 in colonic whole-mount preparations of longitudinal muscle myenteric plexus (LMMP). RESULTS In the sham-operated rats (sham op), WAS significantly increased defecation and accelerated colorectal transit with marked elevation of plasma corticosterone level. Compared with sham-operated rats, increase in the excretion of fecal pellets during WAS was significantly reduced by rectal nerve transection (RNT) (sham op: 6.9 ± 0.8 vs RNT: 4.3 ± 0.6, P < 0.05) or Vag (sham op: 6.4 ± 0.8 vs Vag: 3.7 ± 1.1, P < 0.05), although corticosterone level remained elevated. Adx-rats significantly increased the defecation despite the lower corticosterone level. Distribution pattern of phenol red showed RNT inhibited distal colonic and rectal transit accelerated by WAS, while Vag inhibited proximal colonic transit. Suppression of distal colonic and rectal transit by RNT was further confirmed by the bead evacuation rate (sham op: 80.0% vs RNT: 53.8%). WAS significantly increased the number of c-Fos-immunoreactive neural cells in the LMMP of the proximal and distal colon, whereas c-Fos expression was decreased by RNT in the distal colon (sham op: 9.0 ± 2.0 vs RNT: 4.4 ± 1.0, P < 0.05) and decreased by Vag in the proximal colon. CONCLUSION Pelvic nerve conveys WAS stimuli from the brain to the distal colon, and directly activate the myenteric neurons, followed by the increase of its motility.

Disturbance in the Mucosa-Associated Commensal Bacteria Is Associated with the Exacerbation of Chronic Colitis by Repeated Psychological Stress; Is That the New Target of Probiotics?

Psychological stress can exacerbate inflammatory bowel disease. However, the mechanisms underlying how psychological stress affects gut inflammation remain unclear. Here, we focused on the relationship between changes in the microbial community of mucosa-associated commensal bacteria (MACB) and mucosal immune responses induced by chronic psychological stress in a murine model of ulcerative colitis. Furthermore, we examined the effect of probiotic treatment on exacerbated colitis and MACB composition changes induced by chronic psychological stress. Repeated water avoidance stress (rWAS) in B6-Tcra-/- mice severely exacerbated colitis, which was evaluated by both colorectal tissue weight and histological score of colitis. rWAS treatment increased mRNA expression of UCN2 and IFN-γ in large intestinal lamina propria mononuclear cells (LI-LPMC). Interestingly, exacerbated colitis was associated with changes in the microbial community of MACB, specifically loss of bacterial species diversity and an increase in the component ratio of Clostridium, revealed by 16S rRNA gene amplicon analysis. Finally, the oral administration of a probiotic Lactobacillus strain was protective against the exacerbation of colitis and was associated with a change in the bacterial community of MACB in rWAS-exposed Tcra-/- mice. Taken together, these results suggested that loss of species diversity in MACB might play a key role in exacerbated colitis induced by chronic psychological stress. In addition, probiotic treatment may be used as a tool to preserve the diversity of bacterial species in MACB and alleviate gut inflammation induced by psychological stress.

Tu1979 Involvement of Parasympathetic Pelvic Efferent Pathway in Acceleration of Distal Colonic Transit and Defecation in Response to Psychological Stress in Rats

Background: Stress is a major contributing factor to the pathophysiology of IBS and accelerates colonic transit and increases in defecation. The parasympathetic vagal and pelvic nerves regulate colonic motility and defecation in physiological state. It was shown that physical stress altered colonic functions via vagal efferent in rats. However, it remains still unclear whether the pelvic efferent pathway is involved in accelerating colonic and rectal functions induced by stress. The aim of this study was to investigate whether distal colonic transit and defecation are accelerated via pelvic efferent nerve in psychological stress-loaded rats. We also evaluated the effect of HPA-axis activation on stress -induced defecation. Method: The rats were subjected to water avoidance stress (WAS) or sham stress for 1-hr or 2-hr. The number of fecal pellets was counted for 1-hr in WASor sham stress-rats. Adrenalectomy (Adx), subdiaphragmatic vagotomy (Vag), pelvic nerve rectal branches (Rectal nerves) transection (RNT), or each sham operation was performed at 1 week before WAS. Colonic transit was assessed by the distribution of phenol red injected from catheter located in proximal colon. The distal part of colonic and rectal transit was measured over a 2-hr WAS period from the evacuation rate of a bead inserted into distal colon. c-Fos immunoreactivity (IR), used as a marker of neuronal activation, was monitored in longitudinal muscle/myenteric plexus (LMMP) whole mount preparations of proximal and distal colon after WAS and sham stress. Results: WAS significantly accelerated colorectal transit and defecation with a marked elevation of plasma corticosterone (CORT) levels. Increased defecation induced by WAS was significantly reduced by Vag and RNT, even though CORT levels were elevated. WASinduced acceleration of transit in distal colon and rectum was significantly reduced by RNT, compared with sham-operation. The number of c-Fos-IR cells were significantly increased by WAS in LMMP of proximal and distal colon. In RNTrats, an increase in c-Fos IR cells after WAS was decreased in distal colon, but not in proximal colon, whereas Vag did not affect an increase of c-Fos IR cells in distal colon. In contrast, in Adx-rats WAS increased the number of defecation without an elevation of plasma CORT. Conclusion: It is concluded that psychological stress accelerated distal colonic transit and rectal transit via a parasympathetic efferent pelvic pathway. It seems that the stimulation of pelvic nerve in response to stress activates myenteric neurons in distal colon, followed by an increase of colonic motility. On the other hand, a vagal efferent pathway affects proximal colonic transit. However, an increase in defecation induced by acute psychological stress might not involve the activation of the HPA axis.