Impaired colonic motility and reduction in tachykinin signalling in the aged mouse

Nonlinear DNA methylation trajectories in aging male mice

Although DNA methylation data yields highly accurate age predictors, little is known about the dynamics of this quintessential epigenomic biomarker during lifespan. To narrow the gap, we investigate the methylation trajectories of male mouse colon at five different time points of aging. Our study indicates the existence of sudden hypermethylation events at specific stages of life. Precisely, we identify two epigenomic switches during early-to-midlife (3-9 months) and mid-to-late-life (15-24 months) transitions, separating the rodents' life into three stages. These nonlinear methylation dynamics predominantly affect genes associated with the nervous system and enrich in bivalently marked chromatin regions. Based on groups of nonlinearly modified loci, we construct a clock-like classifier STageR (STage of aging estimatoR) that accurately predicts murine epigenetic stage. We demonstrate the universality of our clock in an independent mouse cohort and with publicly available datasets.

The Involvement of the Endogenous Opioid System in the Gastrointestinal Aging in Mice and Humans

Nearly 20% of elderly patients suffer from constipation, but the age-related changes in the gastrointestinal (GI) tract remain insufficiently elucidated. In this study, the alterations within the endogenous opioid system (EOS) as a potential cause of constipation in the elderly were evaluated. The GI functions were assessed in vitro and in vivo and compared between 6-, 12- and 18-month old mice. Moreover, the effect of opioid receptor (MOP, DOP, KOP) agonists on the mouse GI tract functions and the EOS components expression in mouse tissues and colonic biopsies from patients with functional constipation were determined. In the oldest mice, the GI peristalsis was significantly impaired as compared to the younger groups. The tissue response to MOP and DOP, but not KOP, agonists weakened with age in vitro; for DOP, it was confirmed in vivo. In the mouse upper GI tract, Oprm1, Oprd1, Oprk1 expression decreased with age; in the colon, Oprm1 expression increased. There were no differences in the expression of these genes in the colonic biopsies from patients >50 years old as compared to the younger group. In conclusion, the age-related impairment of the GI peristalsis may result from reduced MOP and DOP response to the activation with opioid agonists or the alterations in the EOS expression.

Epithelial 5-HT4 Receptors as a Target for Treating Constipation and Intestinal Inflammation

Because of their importance in the regulation of gut functions, several therapeutic targets involving serotonin-related proteins have been developed or repurposed to treat motility disorders, including serotonin transporter inhibitors, tryptophan hydroxylase blockers, 5-HT3 antagonists, and 5-HT4 agonists. This chapter focuses on our discovery of 5-HT4 receptors in the epithelial cells of the colon and our efforts to evaluate the effects of stimulating these receptors. 5-HT4 receptors appear to be expressed by all epithelial cells in the mouse colon, based on expression of a reporter gene driven by the 5-HT4 receptor promoter. Application of 5-HT4 agonists to the mucosal surface causes serotonin release from enterochromaffin cells, mucus secretion from goblet cells, and chloride secretion from enterocytes. Luminal administration of 5-HT4 agonists speeds up colonic motility and suppresses distention-induced nociceptive responses. Luminal administration of 5-HT4 agonists also decreases the development of, and improves recovery from, experimental colitis. Recent studies determined that the prokinetic actions of minimally absorbable 5-HT4 agonists are just as effective as absorbable compounds. Collectively, these findings indicate that targeting epithelial receptors with non-absorbable 5-HT4 agonists could offer a safe and effective strategy for treating constipation and colitis.

Diminished androgen levels are linked to irritable bowel syndrome and cause bowel dysfunction in mice

Functional gastrointestinal disorders (FGIDs) have prominent sex differences in incidence, symptoms, and treatment response that are not well understood. Androgens are steroid hormones present at much higher levels in males than females and could be involved in these differences. In adults with irritable bowel syndrome (IBS), a FGID that affects 5-10% of the population worldwide, we found that free testosterone levels were lower than those in healthy controls and inversely correlated with symptom severity. To determine how this diminished androgen signaling could contribute to bowel dysfunction, we depleted gonadal androgens in adult mice and found that this caused a profound deficit in gastrointestinal transit. Restoring a single androgen hormone was sufficient to rescue this deficit, suggesting that circulating androgens are essential for normal bowel motility in vivo. To determine the site of action, we probed androgen receptor expression in the intestine and discovered, unexpectedly, that a large subset of enteric neurons became androgen-responsive upon puberty. Androgen signaling to these neurons was required for normal colonic motility in adult mice. Taken together, these observations establish a role for gonadal androgens in the neural regulation of bowel function and link altered androgen levels with a common digestive disorder.

Effect of paraquat on cytotoxicity involved in oxidative stress and inflammatory reaction: A review of mechanisms and ecological implications

Paraquat (PQ) is a cheap and an effective herbicide, which is widely being used worldwide to remove weeds in cultivated crop fields. However, it can cause soil and water pollution, and pose serious harm to the environment and organisms. Several countries have started to limit or prohibit the use of PQ because of the increasing number of human deaths. Its toxicity can damage the organisms with a multi-target mechanism, which has not been fully understood yet. That is why it is hard to treat as well. The current research on PQ focuses on its targeted organ, the lungs, in which PQ mostly trigger pulmonary fibrosis. While there is a lack of systematic research, there are few studies published discussing its toxic effects at systematic level. This review summarizes the major damages caused by PQ in different organisms and partial mechanisms by which it causes these damages. For this purpose, we consulted several research articles that studied the toxicity of PQ in various tissues. We also listed some drugs that can be used to alleviate the toxicity of PQ. However, at present, the effectiveness of these drugs is still being explored in animal experiments and the study of their mechanism will also help in understanding the poisoning mechanism of PQ, which will ultimately lead to effective treatment in future.

The enteric nervous system in gastrointestinal disease etiology

A highly conserved but convoluted network of neurons and glial cells, the enteric nervous system (ENS), is positioned along the wall of the gut to coordinate digestive processes and gastrointestinal homeostasis. Because ENS components are in charge of the autonomous regulation of gut function, it is inevitable that their dysfunction is central to the pathophysiology and symptom generation of gastrointestinal disease. While for neurodevelopmental disorders such as Hirschsprung, ENS pathogenesis appears to be clear-cut, the role for impaired ENS activity in the etiology of other gastrointestinal disorders is less established and is often deemed secondary to other insults like intestinal inflammation. However, mounting experimental evidence in recent years indicates that gastrointestinal homeostasis hinges on multifaceted connections between the ENS, and other cellular networks such as the intestinal epithelium, the immune system, and the intestinal microbiome. Derangement of these interactions could underlie gastrointestinal disease onset and elicit variable degrees of abnormal gut function, pinpointing, perhaps unexpectedly, the ENS as a diligent participant in idiopathic but also in inflammatory and cancerous diseases of the gut. In this review, we discuss the latest evidence on the role of the ENS in the pathogenesis of enteric neuropathies, disorders of gut-brain interaction, inflammatory bowel diseases, and colorectal cancer.

Prokinetic actions of luminally acting 5-HT4 receptor agonists

BACKGROUND

5-HT₄ receptor (5-HT₄ R) agonists exert prokinetic actions in the GI tract, but non-selective actions and potential for stimulation of non-target 5-HT₄ Rs have limited their use. Since 5-HT₄ Rs are expressed in the colonic epithelium and their stimulation accelerates colonic propulsion in vitro, we tested whether luminally acting 5-HT₄ R agonists promote intestinal motility.

METHODS

Non-absorbed 5-HT₄ R agonists, based on prucalopride and naronapride, were assessed for potency at the 5-HT₄ R in vitro, and for tissue and serum distribution in vivo in mice. In vivo assessment of prokinetic potential included whole gut transit, colonic motility, fecal output, and fecal water content. Colonic motility was also studied ex vivo in mice treated in vivo. Immunofluorescence was used to evaluate receptor distribution in human intestinal mucosa.

KEY RESULTS

Pharmacological screening demonstrated selectivity and potency of test agonists for 5-HT₄ R. Bioavailability studies showed negligible serum detection. Gavage of agonists caused faster whole gut transit and colonic motility, increased fecal output, and elevated fecal water content. Prokinetic actions were blocked by a 5-HT₄ R antagonist and were not detected in 5-HT₄ R knockout mice. Agonist administration promoted motility in models of constipation. Evaluation of motility patterns ex vivo revealed enhanced contractility in the middle and distal colon. Immunoreactivity for 5-HT₄ R is present in the epithelial layer of the human small and large intestines.

CONCLUSIONS AND INFERENCES

These findings demonstrated that stimulation of epithelial 5-HT₄ Rs can potentiate propulsive motility and support the concept that mucosal 5-HT₄ Rs could represent a safe and effective therapeutic target for the treatment of constipation.

Colonic 5-HT4 receptors are targets for novel prokinetic drugs

5-HT₄ receptors are G protein-coupled receptors that link to the stimulatory protein Gs which activates adenylate cyclase to increase intracellular cyclic AMP which then activates protein kinase A (PKA). 5-HT₄ receptors are expressed by neurons in the central and peripheral nervous systems especially the enteric nervous system (ENS). In general, 5-HT₄ receptors are stimulatory and their activation in the ENS enhances neurotransmitter release and propulsive motility patterns. 5-HT₄ receptors are expressed by enterochromaffin (EC) cells, Goblet cells, and most enteric neurons. The study by Konen and colleagues in this issue of Neurogastroenterology and Motility features two novel 5-HT₄ receptor agonists (5-HT₄ -LA1 and 5-HT₄ -LA-2) that are not absorbed from the gastrointestinal tract of mice and act locally in the colonic mucosa to stimulate propulsive motility. The authors show that 5-HT₄ -LA1 and 5-HT₄ -LA2 were not absorbed from the colon and that both drugs stimulated colonic transit when administered by gavage. Both agonists stimulated colonic glass bead expulsion, and 5-HT₄ LA1 activation stimulated fecal output and increased fecal water content. These effects were detected in young and aged mice. 5-HT₄ receptors were also localized to the epithelium of the human duodenum, ileum, and colon. These studies highlight novel 5-HT₄ receptor agonists that have prokinetic actions on the GI tract. These drugs are not absorbed and act locally in the gut mucosa to stimulate propulsive motility while minimizing access to systemic 5-HT₄ receptors and avoiding potential unwanted side effects.

Developmental and age-dependent plasticity of GABAA receptors in the mouse colon: Implications in colonic motility and inflammation

Lifelong functional plasticity of the gastrointestinal (GI) tract is essential for health, yet the underlying molecular mechanisms are poorly understood. The enteric nervous system (ENS) regulates all aspects of the gut function, via a range of neurotransmitter pathways, one of which is the GABA-GABA_A receptor (GABA_AR) system. We have previously shown that GABA_A receptor subunits are differentially expressed within the ENS and are involved in regulating various GI functions. We have also shown that these receptors are involved in mediating stress-induced colonic inflammation. However, the expression and function of intestinal GABA_ARs, at different ages, is largely unexplored and was the focus of this study. Here we show that the impact of GABA_AR activation on colonic contractility changes from early postnatal period through to late adulthood, in an age-dependant manner. We also show that the highest levels of expression for all GABA_AR subunits is evident at postnatal day (P) 10 apart from the α3 subunit which increased with age. This increase in the α3 subunit expression in late adulthood (18 months old) is accompanied by an increase in the expression of inflammatory markers within the mouse colon. Finally, we demonstrate that the deletion of the α3 subunit prevents the increase in the expression of colonic inflammatory markers associated with healthy ageing. Collectively, the data provide the first demonstration of the molecular and functional plasticity of the GI GABA_AR system over the course of a lifetime, and its possible role in mediating the age-induced colonic inflammation associated with healthy ageing.

Initial Effects of Electroacupuncture for Chronic Severe Functional Constipation and the Potential Underlying Factors: Secondary Analysis of a Randomized Controlled Trial

Background

Electroacupuncture (EA) has been found to be effective for treating chronic severe functional constipation (CSFC). However, the initial effects of treatment usually affect the acceptability and compliance of patients with chronic disease in particular. Which class of CSFC patients will have a better initial response to EA remains uncertain and requires investigation.

Methods

This was a secondary analysis of an original multicenter randomized controlled trial in which patients with CSFC were randomly assigned to receive 28 sessions of EA or sham electroacupuncture (SA) over 8 weeks with 12 weeks of follow-up. The primary outcome, namely, response with complete spontaneous bowel movements (CSBMs), required participants to have ≥ 3 CSBMs and an increase of ≥ 1 CSBM from the baseline over the first week of treatment. Logistic regression analysis with bootstrapping techniques was performed to determine independent factors related to the response.

Results

A total of 1051 eligible patients were included in this study of whom 161 patients were classified as responders at week 1. The CSBM response rate was higher in the EA group (17.5%) than in the SA group (13.2%). And the proportion of these 1-week early responders remained to have higher clinical response at the end of 8-week treatment and 12 weeks after treatment. Age and higher baseline CSBMs were related to CSBM response within the first week: with every 1-year increase in age, the likelihood of clinical response was reduced by 1.7% (odds ratio [OR] 0.983, 95% confidence interval [CI] 0.972 to 0.993; P=0.001). The odds of a CSBM response in patients with 1< CSBMs ≤ 2 at baseline were 4.64 times higher than that in patients with CSBMs ≤ 1 (OR 4.64, 95%CI 4.01 to 5.27).

Conclusions

EA produced its initial effects within the first week of treatment. And the effects could last until week 8 and week 20. A younger age and higher number of CSBMs at baseline may increase likelihood of a response.

Changes in murine anorectum signaling across the life course

BACKGROUND

Increasing age is associated with an increase in the incidence of chronic constipation and fecal impaction. The contribution of the natural aging process to these conditions is not fully understood. This study examined the effects of increasing age on the function of the murine anorectum.

METHODS

The effects of increasing age on cholinergic, nitrergic, and purinergic signaling pathways in the murine anorectum were examined using classical organ bath assays to examine tissue function and electrochemical sensing to determine age-related changes in nitric oxide and acetylcholine release.

KEY RESULTS

Nitrergic relaxation increased between 3 and 6 months, peaked at 12 months and declined in the 18 and 24 months groups. These changes were in part explained by an age-related decrease in nitric oxide (NO) release. Cholinergic signaling was maintained with age by an increase in acetylcholine (ACh) release and a compensatory decrease in cholinesterase activity. Age-related changes in purinergic relaxation were qualitatively similar to nitrergic relaxation although the relaxations were much smaller. Increasing age did not alter the response of the anorectum smooth muscle to exogenously applied ACh, ATP, sodium nitroprusside or KCl. Similarly, there was no change in basal tension developed by the anorectum.

CONCLUSIONS AND INFERENCES

The decrease in nitrergic signaling with increasing age may contribute to the age-related fecal impaction and constipation previously described in this model by partially obstructing defecation.

Interstitial cell network volume is reduced in the terminal bowel of ageing mice

Ageing is associated with impaired neuromuscular function of the terminal gastrointestinal (GI) tract, which can result in chronic constipation, faecal impaction and incontinence. Interstitial cells of cajal (ICC) play an important role in regulation of intestinal smooth muscle contraction. However, changes in ICC volume with age in the terminal GI tract (the anal canal including the anal sphincter region and rectum) have not been studied. Here, the distribution, morphology and network volume of ICC in the terminal GI tract of 3‐ to 4‐month‐old and 26‐ to 28‐month‐old C57BL/6 mice were investigated. ICC were identified by immunofluorescence labelling of wholemount preparations with an antibody against c‐Kit. ICC network volume was measured by software‐based 3D volume rendering of confocal Z stacks. A significant reduction in ICC network volume per unit volume of muscle was measured in aged animals. No age‐associated change in ICC morphology was detected. The thickness of the circular muscle layer of the anal sphincter region and rectum increased with age, while that in the distal colon decreased. These results suggest that ageing is associated with a reduction in the network volume of ICC in the terminal GI tract, which may influence the normal function of these regions.

Communication Between Enteric Neurons, Glia, and Nociceptors Underlies the Effects of Tachykinins on Neuroinflammation

Background & Aims

Tachykinins are involved in physiological and pathophysiological mechanisms in the gastrointestinal tract. The major sources of tachykinins in the gut are intrinsic enteric neurons in the enteric nervous system and extrinsic nerve fibers from the dorsal root and vagal ganglia. Although tachykinins are important mediators in the enteric nervous system, how they contribute to neuroinflammation through effects on neurons and glia is not fully understood. Here, we tested the hypothesis that tachykinins contribute to enteric neuroinflammation through mechanisms that involve intercellular neuron-glia signaling.

Methods

We used immunohistochemistry and quantitative real-time polymerase chain reaction, and studied cellular activity using transient-receptor potential vanilloid-1 (TRPV1)tm1(cre)Bbm/J::Polr2atm1(CAG-GCaMP5g,-tdTomato)Tvrd and Sox10CreERT2::Polr2atm1(CAG-GCaMP5g,-tdTomato)Tvrd mice or Fluo-4. We used the 2,4-di-nitrobenzene sulfonic acid (DNBS) model of colitis to study neuroinflammation, glial reactivity, and neurogenic contractility. We used Sox10::CreERT2+/-/Rpl22tm1.1Psam/J mice to selectively study glial transcriptional changes.

Results

Tachykinins are expressed predominantly by intrinsic neuronal varicosities whereas neurokinin-2 receptors (NK2Rs) are expressed predominantly by enteric neurons and TRPV1-positive neuronal varicosities. Stimulation of NK2Rs drives responses in neuronal varicosities that are propagated to enteric glia and neurons. Antagonizing NK2R signaling enhanced recovery from colitis and prevented the development of reactive gliosis, neuroinflammation, and enhanced neuronal contractions. Inflammation drove changes in enteric glial gene expression and function, and antagonizing NK2R signaling mitigated these changes. Neurokinin A-induced neurodegeneration requires glial connexin-43 hemichannel activity.

Conclusions

Our results show that tachykinins drive enteric neuroinflammation through a multicellular cascade involving enteric neurons, TRPV1-positive neuronal varicosities, and enteric glia. Therapies targeting components of this pathway could broadly benefit the treatment of dysmotility and pain after acute inflammation in the intestine.

Factors related to acupuncture response in patients with chronic severe functional constipation: Secondary analysis of a randomized controlled trial

Background

Acupuncture has been demonstrated to be effective and safe for chronic severe functional constipation (CSFC). However, which patients with CSFC will have a better response to acupuncture remains unclear.

Objective

To explore factors related to acupuncture response in patients with CSFC.

Methods

We performed a secondary analysis of a previous multicenter randomized controlled trial consisting of a 2-week run-in period, 8-week treatment, and 12-week follow-up without treatment in which patients with CSFC were randomly allocated to an electroacupuncture group or a sham electroacupuncture group. Responders were defined as participants with an increase of at least one complete spontaneous bowel movement (CSBM) in week 20 compared with the baseline period. The CSBM responder rate in both groups was described, and the baseline characteristics of participants potentially related to acupuncture response were mainly analyzed using logistic regression analysis with bootstrapping techniques.

Results

A total of 1021 participants were analyzed in this study, of whom 516 (50.5%) were classified as responders. The CSBM responder rate in week 20 was significantly greater in the electroacupuncture group than in the sham electroacupuncture group (62.9% vs. 37.9%, respectively; P<0.001). Both age and comorbidity were negatively associated with clinical response: with every one-year increase in age, the likelihood of clinical response was reduced by 1.2% (OR 0.988, 95%CI 0.980 to 0.996; P = 0.005), and patients with comorbidities were approximately 42% less likely to respond to treatment (OR 0.581, 95%CI 0.248 to 0.914; P = 0.001).

Conclusion

CSFC patients with increasing age and comorbidity may be less likely to respond to acupuncture. These findings contribute to guiding clinical practice in terms of pretreatment patient selection. Further research is needed to confirm the association.

Ablation of Tacr2 in mice leads to gastric emptying disturbance

BACKGROUND

Tacr2 is one of the G protein-coupled receptors(GPCRs) that mediate the biological actions of tachykinins. It is abundantly expressed in the gastrointestinal (GI) system and is thought to play an important role in GI motility, secretion, and visceral sensitivity. Previously, the physiological and pathophysiological functions of Tacr2 were mainly studied using Tacr2 selective agonists or antagonists. Here, we seek to investigate the effect of Tacr2 disruption in mice to provide further insights.

METHODS

The Tacr2 knockout mice were generated by homologous recombination and the phenotypic changes of the Tacr2-null mice were analyzed and compared with their wild type (wt) littermates.

KEY RESULTS

Increased food retention was detected in Tacr2^-/- mice. The stomach of Tacr2^-/- mice had thinner muscularis externa and less neurons in the myenteric plexus. The stomach and small intestine exhibited longer duration of electrical field stimulation (EFS)-induced inhibition in the gastric fundus and decreased frequency of migrating motor complex (MMC), respectively. Neuronal nitric oxide synthase (nNOS) and vasoactive intestinal polypeptide (VIP) were significantly up-regulated due to Tarc2 deficiency, contributing to enhanced nitric oxide (NO) signaling in the stomach of Tacr2^-/- mice. Intraperitoneal application of 7-nitroindazole (7-NI) to Tacr2^-/- mice effectively relieved the gastric emptying disturbance. Moreover, Creb and NF-κB signalings were involved in the regulation of these physiological changes initiated by Tacr2 deficiency.

CONCLUSIONS & INFERENCES

Tacr2 negatively regulated the expression of nNOS and VIP both in vivo and in vitro. Its ablation in mice elevated the expression of nNOS and VIP, enhanced NO signaling and changed the Creb and NF-κB signalings, finally leading to the gastric emptying disturbance of Tacr2^-/- mice.

Nicotinamide adenine dinucleotide replenishment rescues colon degeneration in aged mice

Susceptibility of gastrointestinal dysmotility increases with age-associated colonic degeneration. A paucity of remedies reversing colonic degeneration per se hinders the fundamental relief of symptoms. Here we discovered the correlation between colon degeneration and altered nicotinamide adenine dinucleotide (NAD) level in aged mice. Compared to 3-month-old young controls, 2-year-old mice showed a spectrum of degenerative colonic phenotypes and exhibited a significant elongated transit time and slowed stool frequency in the context of Lomotil-induced slow-transit constipation. Despite upregulated colonic tryptophan hydroxylases expression, serotonin release and expression of colon-predominant type IV serotonin receptor, reduced viability of interstitial cells of Cajal while enhanced aquaporins (Aqp1, 3 and 11) led to a less colonic motility and increased luminal dehydration in aged mice. Notably, this colonic degeneration was accompanied with reduced key NAD⁺-generating enzyme expression and lowered NAD⁺/NADH ratio in aged colon. Three-month continuous administration of beta nicotinamide mononucleotide, a NAD⁺ precursor, elevated colonic NAD⁺ level and improved defecation in aged mice. In contrast, pharmacological inhibition of nicotinamide phosphoribosyltransferase, the rate-limiting enzyme for NAD⁺ biosynthesis, induced a reduction in colonic NAD content and impaired gastrointestinal function in young mice. Taken together, these findings suggest the beneficial effect of NAD⁺ in maintaining colonic homoeostasis and reactivating NAD⁺ biosynthesis may represent a promising strategy to counteract age-related gastrointestinal degeneration.

The TNF-α antagonist etanercept reverses age-related decreases in colonic SERT expression and faecal output in mice

Treatment for chronic constipation in older people is challenging and the condition has a major impact on quality of life. A lack of understanding about the causes of this condition has hampered the development of effective treatments. 5-HT is an important pro-kinetic agent in the colon. We examined whether alterations in colonic 5-HT signalling underlie age-related changes in faecal output in mice and whether these changes were due to an increase in TNF-α. Components of the 5-HT signalling system (5-HT, 5-HIAA, SERT) and TNF-α expression were examined in the distal colon of 3, 12, 18 and 24-month old mice and faecal output and water content monitored under control conditions and following the administration of etanercept (TNF-α inhibitor; 1 mg Kg^-1). Faecal output and water content were reduced in aged animals. Age increased mucosal 5-HT availability and TNF-α expression and decreased mucosal SERT expression and 5-HIAA. Etanercept treatment of old mice reversed these changes, suggesting that age-related changes in TNFα expression are an important regulator of mucosal 5-HT signalling and pellet output and water content in old mice. These data point to "anti-TNFα" drugs as potential treatments for age-related chronic constipation.

Acute paraquat exposure impairs colonic motility by selectively attenuating nitrergic signalling in the mouse

Paraquat, a common herbicide, is responsible for large numbers of deaths worldwide through both deliberate and accidental ingestion. Previous studies have eluded that the bioavailability of paraquat increases substantially with increasing dose and that these changes may in part be due to the effects that these high concentrations have on the gastrointestinal tract (GI tract). To date, the actions of acute, high concentrations (20mM for 60 min) of paraquat on the GI tract, particularly the colon which is a major site of paraquat absorption, are unknown. This study examined the effects of acute paraquat administration on colonic motility in the C57BL/6 mouse. Acute paraquat exposure decreased colonic motility and the amplitude of colonic migrating motor complexes (CMMCs), which are major motor patterns involved in faecal pellet propulsion. In isolated segments of distal colon, paraquat increased resting tension and markedly attenuated electrical field stimulation-evoked relaxations. Pharmacological dissection of paraquat's mechanism of action on both the CMMCs and field stimulated tissue using the nitric oxide synthase inhibitor NG-nitro-L-arginine and direct measurement of NO release from the myenteric plexus, demonstrated that paraquat selectively attenuates nitrergic signalling pathways. These changes did not appear to be due to alterations in colonic oxidative stress, inflammation or complex 1 activity, but were most likely caused by paraquat's ability to act as a redox couple. In summary, these data demonstrate that acute paraquat exposure attenuates colonic transit. These changes may facilitate the absorption of paraquat into the circulation and so facilitate its toxicity.

The ageing gastrointestinal tract

PURPOSE OF REVIEW

This article reviews the impact of ageing on the gastrointestinal tract, including effects on the absorption of nutrients and drugs and the gastrointestinal tract defence system against ingested pathogens.

RECENT FINDINGS

Recent publications support earlier observations of an age-related selective decline in gut function including changes in taste, oesophageal sphincter motility, gastric emptying, and neurons of the myenteric plexus related to gut transit which may impact the nutritional status. Ageing is also associated with structural and functional mucosal defence defects, diminished abilities to generate protective immunity, and increased incidence of inflammation and oxidative stress. A number of gastrointestinal disorders occur more frequently in the elderly population.

SUMMARY

Alterations in gut function with ageing have particular implications for oesophageal, gastric, and colonic motility. Older individuals are particularly susceptible to malnutrition, postprandial hypotension, dysphagia, constipation, and faecal incontinence. Decrease in the number of nerve cells of the myenteric plexus that impact digestive absorption and the surface area of the small intestine because of degeneration of villi may lead to blunted absorption of nutrients. Impairment of the intestinal immune system as a result of ageing, including the mucosal layer of the gastrointestinal tract, appears to be a significant contributor to the age-related increase in the incidence and severity of infections.

Escherichia coli Nissle 1917 enhances bioavailability of serotonin in gut tissues through modulation of synthesis and clearance

Accumulating evidence shows indigenous gut microbes can interact with the human host through modulation of serotonin (5-HT) signaling. Here we investigate the impact of the probiotic Escherichia coli Nissle 1917 (EcN) on 5-HT signalling in gut tissues. Ex-vivo mouse ileal tissue sections were treated with either EcN or the human gut commensal MG1655, and effects on levels of 5-HT, precursors, and metabolites, were evaluated using amperometry and high performance liquid chromatography with electrochemical detection (HPLC-EC). Exposure of tissue to EcN cells, but not MG1655 cells, was found to increase levels of extra-cellular 5-HT. These effects were not observed when tissues were treated with cell-free supernatant from bacterial cultures. In contrast, when supernatant recovered from untreated ileal tissue was pre-incubated with EcN, the derivative cell-free supernatant was able to elevate 5-HT overflow when used to treat fresh ileal tissue. Measurement of 5-HT precursors and metabolites indicated EcN also increases intracellular 5-HTP and reduces 5-HIAA. The former pointed to modulation of tryptophan hydroxylase-1 to enhance 5-HT synthesis, while the latter indicates an impact on clearance into enterocytes through SERT. Taken together, these findings show EcN is able to enhance 5-HT bioavailability in ileal tissues through interaction with compounds secreted from host tissues.

A non-invasive method to evaluate gastrointestinal transit behavior in rat

INTRODUCTION

Many factors alter gastrointestinal transit. Animal models are useful for preclinical studies of gastrointestinal transit, but terminal methods do not allow later study, and stressful assessment methods will likely alter the transit of the animal. To overcome these factors, we developed a new method to assay rat total gastrointestinal transit.

METHODS

Standard plastic cages with their bottoms cut off were placed on wire mesh floors. Custom apparatuses were built to contain fecal pellets as they fell through the floors. Webcams connected to a computer running a security program were placed to image the pellets at regular intervals. Custom food was obtained with and without blue pigment. After habituating to the cages and the non-pigmented food, the pigmented food was administered. The duration to the appearance of the first pigmented pellet was determined by reviewing the photographs. This duration represents the complete gastrointestinal behavior, including feeding. We compared 24-hour fecal pellet counts using images to counts by visual inspection, and also made hourly counts. After establishing baseline transit times and hourly fecal pellet discharge, rats were given buprenorphine, known to alter gastrointestinal transit. Transit times and hourly discharge were obtained again and compared to the baselines.

RESULTS

The methods were successful in determining transit times. Baseline measures were consistent between three groups of 8 rats. Visual and image-based counts were highly correlated. Transit times and hourly pellet discharge were reduced by buprenorphine.

DISCUSSION

The described method offers a relatively simple, inexpensive, and non-invasive means to measure rat gastrointestinal behavior. The method has potential for any study where altered total gastrointestinal transit is an experimental concern.

Neurogenic mechanisms in bladder and bowel ageing

The prevalence of both urinary and faecal incontinence, and also chronic constipation, increases with ageing and these conditions have a major impact on the quality of life of the elderly. Management of bladder and bowel dysfunction in the elderly is currently far from ideal and also carries a significant financial burden. Understanding how these changes occur is thus a major priority in biogerontology. The functions of the bladder and terminal bowel are regulated by complex neuronal networks. In particular neurons of the spinal cord and peripheral ganglia play a key role in regulating micturition and defaecation reflexes as well as promoting continence. In this review we discuss the evidence for ageing-induced neuronal dysfunction that might predispose to neurogenic forms of incontinence in the elderly.