Fat deposition in the tunica muscularis and decrease of interstitial cells of Cajal and nNOS-positive neuronal cells in the aged rat colon

Impact of Activity-Based Training on Bowel Function in a Rat Model of Spinal Cord Injury

Significant bowel-related issues after spinal cord injury (SCI) that affect morbidity and quality of life (QOL) include diminished bowel motility, loss of sphincter control, gastric ulcers, autonomic dysreflexia, pain, diarrhea, constipation, and fecal incontinence. Clinical diagnoses and research in humans have largely relied on anorectal manometry (ARM) procedures to increase understanding of the functional effects of SCI on colorectal motility and defecation physiology. Recent pre-clinical rodent studies have also used ARM to further our understanding of bowel-related dysfunctions post-SCI. In the present study, the benefits of different activity-based training (ABT) durations on bowel function were examined. Six groups of male rats including two non-training (NT; uninjured and SCI) and four ABT (quadrupedal [Quad or Q] stepping on a treadmill) groups. All ABT animals received 4 weeks of 1-h daily stepping beginning 2 weeks post-SCI followed by variable amounts for 4 additional weeks (none; daily; once a week; daily for final 4th week only). Outcome measures included fecal output (home cage; metabolic cage) throughout the study and terminal measurements (post 8-week ABT) of external anal sphincter (EAS) electromyography, resting anorectal pressure, and giant contraction (GC) activation under urethane anesthesia. The results indicate that treadmill training normalized defecation amount based on feces weight and food intake, as well as GC frequency, EAS latency and amplitude during fecal expulsion, and resting pressure in specific areas within the colorectum. The two intermittent training groups consistently showed recorded metrics comparable to the non-injured group. The results demonstrate bowel dysfunction in the rodent SCI contusion model with improvements in functional outcomes following ABT. Importantly, the benefits to bowel-related functions with versus without intermittent ABT illustrate the need for periodic therapy to maintain the functional gains of ABT.

The Effect of Clostridium butyricum on Gut Microbial Changes and Functional Profiles of Metabolism in High-fat Diet-fed Rats Depending on Age and Sex

Background/Aims

A high-fat diet (HFD) causes dysbiosis and promotes inflammatory responses in the colon. This study aims to evaluate the effects of Clostridium butyricum on HFD-induced gut microbial changes in rats.

Methods

Six-week-old Fischer-344 rats with both sexes were given a control or HFD during 8 weeks, and 1-to-100-fold diluted Clostridium butyricum were administered by gavage. Fecal microbiota analyses were conducted using 16S ribosomal RNA metagenomic sequencing and predictive functional profiling of microbial communities in metabolism.

Results

A significant increase in Ruminococcaceae and Lachnospiraceae, which are butyric acid-producing bacterial families, was observed in the probiotics groups depending on sex. In contrast, Akkermansia muciniphila, which increased through a HFD regardless of sex, and decreased in the probiotics groups. A. muciniphila positively correlated with Claudin-1 expression in males (P < 0.001) and negatively correlated with the expression of Claudin-2 (P = 0.042), IL-1β (P = 0.037), and IL-6 (P = 0.044) in females. In terms of functional analyses, a HFD decreased the relative abundances of M00131 (carbohydrate metabolism module), M00579, and M00608 (energy metabolism), and increased those of M00307 (carbohydrate metabolism), regardless of sex. However, these changes recovered especially in male C. butyricum groups. Furthermore, M00131, M00579, and M00608 showed a positive correlation and M00307 showed a negative correlation with the relative abundance of A. muciniphila (P < 0.001).

Conclusion

The beneficial effects of C. butyricum on HFD-induced gut dysbiosis in young male rats originate from the functional profiles of carbohydrate and energy metabolism.

Effect of Clostridium butyricum on High-Fat Diet-Induced Intestinal Inflammation and Production of Short-Chain Fatty Acids

BACKGROUND/AIMS

A high-fat diet (HFD) can cause intestinal inflammation and alter the gut microbiota; probiotics, however, are known to have anti-inflammatory effects. This study aimed to investigate the response of rat colon to HFD and the effect of Clostridium butyricum on HFD-induced intestinal inflammation and production of short-chain fatty acids (SCFAs) according to sex.

METHODS

Male and female 6-week-old Fischer-344 rats were fed a chow diet or HFD for 8 weeks, and Biovita or three different concentrations of C. butyricum were orally gavaged. The levels of tight junction proteins (TJPs), inflammatory markers in the ascending colonic mucosa, and bile acids (BAs) and SCFAs in stool were measured.

RESULTS

HFD significantly increased the histological inflammation scores and fat proportions. Fecal BA levels were higher in the HFD group than in the control group, with a more prominent increase in deoxycholic acid/cholic acid after probiotics administration in females; however, no statistically significant differences were observed. TJPs showed an opposite response to HFD depending on sex, and tended to increase and decrease after HFD in males and females, respectively. The HFD-reduced TJPs were recovered by probiotics, with some statistical significance in females. HFD-decreased butyric acid in stools appeared to be recovered by probiotics in males, but not in females. The expression of inflammatory markers (TNF-α) was increased by HFD in males and decreased with medium-concentration probiotic supplementation. The opposite was observed in females. MPO was increased by HFD in both sexes and decreased by probiotic supplementation.

CONCLUSIONS

The probiotic C. butyricum improved indicators of HFD-induced colonic inflammation such as levels of inflammatory markers and increased the production of SCFAs and the expression of TJPs. These effects tended to be more pronounced in male rats, showing sex difference.

Cannabinoid 1 and mu-Opioid Receptor Agonists Synergistically Inhibit Abdominal Pain and Lack Side Effects in Mice

While effective in treating abdominal pain, opioids have significant side effects. Recent legalization of cannabis will likely promote use of cannabinoids as an adjunct or alternative to opioids, despite a lack of evidence. We aimed to investigate whether cannabinoids inhibit mouse colonic nociception, alone or in combination with opioids at low doses. Experiments were performed on C57BL/6 male and female mice. Visceral nociception was evaluated by measuring visceromotor responses (VMR), afferent nerve mechanosensitivity in flat-sheet colon preparations, and excitability of isolated DRG neurons. Blood oxygen saturation, locomotion, and defecation were measured to evaluate side effects. An agonist of cannabinoid 1 receptor (CB1R), arachidonyl-2'-chloroethylamide (ACEA), dose-dependently decreased VMR. ACEA and HU-210 (another CB1R agonist) also attenuated colonic afferent nerve mechanosensitivity. Additionally, HU-210 concentration-dependently decreased DRG neuron excitability, which was reversed by the CB1R antagonist AM-251. Conversely, cannabinoid 2 receptor (CB2R) agonists did not attenuate VMR, afferent nerve mechanosensitivity, or DRG neuron excitability. Combination of subanalgesic doses of CB1R and µ-opioid receptor agonists decreased VMR; importantly, this analgesic effect was preserved after 6 d of twice daily treatment. This combination also attenuated afferent nerve mechanosensitivity and DRG neuron excitability, which was inhibited by neuronal nitric oxide synthase and guanylate cyclase inhibitors. This combination avoided side effects (decreased oxygen saturation and colonic transit) caused by analgesic dose of morphine. Activation of CB1R, but not CB2R, decreased colonic nociception both alone and in synergy with µ-opioid receptor. Thus, CB1R agonists may enable opioid dose reduction and avoid opioid-related side effects.SIGNIFICANCE STATEMENT One of the most cited needs for patients with abdominal pain are safe and effective treatment options. The effectiveness of opioids in the management of abdominal pain is undermined by severe adverse side effects. Therefore, strategies to replace opioids or reduce the doses of opioids to suppress abdominal pain is needed. This study in mice demonstrates that cannabinoid 1 receptor (CB1R) agonists inhibit visceral sensation. Furthermore, a combination of subanalgesic doses of µ-opioid receptor agonist and CB1R agonist markedly reduce abdominal pain without causing the side effects of high-dose opioids. Thus, CB1R agonists, alone or in combination with low-dose opioids, may be a novel and safe treatment strategy for abdominal pain.

Auricular vagal nerve stimulation enhances gastrointestinal motility and improves interstitial cells of Cajal in rats treated with loperamide

BACKGROUND

Gastrointestinal (GI) motility disorders affect a large proportion of the population with limited treatment options. The aims of this study were to investigate the potential of a non-invasive method of auricular vagal nerve stimulation (aVNS) for treating GI dysmotility and to explore possible mechanisms involving slow waves and interstitial cells of Cajal (ICC).

METHODS

Normal rats were treated daily with loperamide for 1 week and then treated, while still on daily loperamide, with aVNS/Sham-aVNS for another 1 week. Gastric emptying (GE), small intestine transit (SIT), and GI slow waves were measured. The plasma level of pancreatic polypeptide (PP) and noradrenaline (NE) was assessed by ELISA. ICC in the gastric antrum were detected by immunohistochemistry.

KEY RESULTS

(a) aVNS significantly increased the percentage of normal GI slow waves (p < 0.05 for both fasting and postprandial states, vs. Sham-aVNS) and accelerated GE (p < 0.05, vs. Sham-aVNS) and SIT (p < 0.05, vs. Sham-aVNS) impaired by loperamide. (b) aVNS increased plasma PP (p < 0.01) and decreased plasma NE (p < 0.01), compared with Sham-aVNS. (c) Gastric ICC was decreased by loperamide (p < 0.01) but increased after aVNS (p < 0.01, vs. Sham aVNS).

CONCLUSIONS & INFERENCES

Loperamide induces upper GI dysmotility. aVNS accelerates upper GI transit and improving pace-making activity mediated via the ICC. Non-invasive aVNS may have a therapeutic potential for upper GI dysmotility.

Auricular Vagal Nerve Stimulation Improves Constipation by Enhancing Colon Motility via the Central-Vagal Efferent Pathway in Opioid-Induced Constipated Rats

OBJECTIVES

Constipation and opioid-induced constipation (OIC) are common with limited treatment options. We investigated whether a noninvasive method of auricular vagal nerve stimulation (aVNS) could be used for treating OIC and explored its potential mechanisms and neural pathways in a rodent model of OIC.

MATERIALS AND METHODS

Sprague-Dawley were chronically implanted with one pair of auricular electrodes for aVNS. Sixteen rats were treated with loperamide for a week while another 16 rats received bilateral vagotomy, then randomly treated with aVNS or sham-aVNS for a week. In addition, eight normal rats were implanted with a polyethylene catheter in the proximal colon for assessing whole colon transit.

RESULTS

1) The number of fecal pellets and water content in feces increased after aVNS, compared with sham-aVNS. 2) aVNS accelerated colon transit and whole gut transit, compared with sham-aVNS. 3) In colon tissues, aVNS increased the protein expression of choline acetyltransferase, glial cell line-derived neurotrophic factor and the c-kit expression in myenteric interstitial cells of Cajal but decreased the protein expression of neural nitric oxide synthase (p < 0.05 for all, vs. sham-VNS). 4) The prokinetic effects of aVNS were abolished by both subdiaphragmatic vagotomy and atropine. 5) aVNS increased the c-fos expression in both nucleus tractus solitarius and dorsal motor nucleus of vagus, and increased vagal efferent activity (p < 0.05, vs. sham-VNS).

CONCLUSIONS

aVNS improves OIC by enhancing colon motility and restoring enteric neural functions mediated via the central and vagal efferent pathway.

Protective effects of curcumin against rat intestinal inflammation‑related motility disorders

Intestinal inflammation frequently occurs alongside dysmotility, which is characterized by altered myosin light chain phosphorylation levels. Curcumin, an active component from the ginger family, is reported to confer anti‑inflammatory effects. However, the effects of curcumin on both diarrhea and constipation associated inflammation remains to be elucidated. The present study was designed to investigate the effects of curcumin on diarrhea and constipation and to determine the related mechanisms. Sprague‑Dawley rats were used to establish diarrhea and constipation models via intracolonic acetic acid (4%) instillation or cold water gavage for 2 weeks, respectively. Blood samples were collected to measure the serum levels of the cytokines TNF‑α and IL‑1β using ELISA kits. Western blotting was performed to measure NF‑κB, RhoA, Rho‑related kinase 2, phosphorylated MLC₂₀, phosphorylated myosin phosphorylated target subunit 1, 130k Da‑MLC kinase (MLCK), c‑kit tyrosine kinase protein expression, and reverse transcription‑quantitative PCR was conducted to measure MLCK expression levels. The results indicated that curcumin reversed the elevations in the pro‑inflammatory cytokines IL‑1β and TNF‑α by inhibiting the NF‑κB pathway in rats with diarrhea and constipation. The results also indicated that myosin light chain (MLC) phosphorylation in intestinal smooth muscle was positively and negatively associated with the motility of inflammation‑related diarrhea and constipation in rats, respectively. Curcumin significantly reversed the increased MLC phosphorylation in the jejunum of the rats with diarrhea, significantly enhanced the reductions in inflammatory mediators, including TNF‑α and IL‑1β, of rats with constipation and significantly ameliorated the related hyper‑motility and hypo‑motility in rats with both diarrhea and constipation. In conclusion, the potential roles of the MLC kinase, c‑kit tyrosine and Rho A/Rho‑associated kinase 2 pathways, which are involved in curcumin‑induced amelioration of inflammation‑related diarrhea and constipation, were explored in the present study. Results from the present study suggested that curcumin has potential therapeutic value for treating intestinal inflammation and inflammation‑related motility disorders.

Investigation of Bowel Function with Anorectal Manometry in a Rat Spinal Cord Contusion Model

Bowel dysfunction after chronic spinal cord injury (SCI) is a common source of morbidity and rehospitalization. Typical complications include constipation, fecal impaction, incontinence, abdominal distention, autonomic dysreflexia, and the necessity of interventions (i.e., suppositories, digital stimulation) to defecate. Numerous surveys have confirmed that the remediation of bowel complications is more highly valued for quality of life than improvements in walking. Much of what is known about bowel function after SCI for diagnosis and research in humans has been gained using anorectal manometry (ARM) procedures. However, ARM has been underutilized in pre-clinical animal work. Therefore, a novel combination of outcome measures was examined in the current study that incorporates functional output of the bowel (weekly fecal measurements), weight gain (pre-injury to terminal weight), and terminal ARM measurement with external anal sphincter electromyography under urethane anesthesia. The results indicate higher fecal output after contusion during the sub-acute period (4-7 days) post-injury, changes in the composition of the feces, and functionally obstructive responses in a specific section of the rectum (increased baseline pressure, increased frequency of contraction, and reduced ability to trigger a giant contraction to a distension stimulus). These results demonstrate significant bowel dysfunction in the rodent SCI contusion model that is consistent with data from human research. Thus, the combined measurement protocol enables the detection of changes and can be used, with minimal cost, to assess effectiveness of therapeutic interventions on bowel complications.

Diminished enteric neuromuscular transmission in the distal colon following experimental spinal cord injury

Neurogenic bowel following spinal cord injury (SCI) leads to decreased colonic motility, remodeling of the neuromuscular compartment and results in chronic evacuation difficulties. The distal colon of the rat serves a dual role for fluid absorption and storage that is homologous to the descending colon of humans. Dysmotility of the descending colon is one component of neurogenic bowel. We investigated the integrity of the enteric neuromuscular transmission responsible for the generation of excitatory and inhibitory junction potentials (EJPs and IJPs, respectively) in the distal colon of rats. We previously demonstrated a chronic reduction in colonic enteric neurons from rats with acute and chronic high-thoracic (T3) SCI and hypothesized that neurogenic bowel following T3-SCI results from diminished enteric neuromuscular transmission. Immunohistochemical labeling for myenteric neuronal nitric oxide synthase (nNOS) and choline acetyltransferase (ChAT) neurons demonstrated a significant loss of presumptive nitric oxide (NO) and acetylcholine (ACh) immunoreactive neurons in both 3-day and 3-week injured animals. Colonic neuromuscular transmission in response to transmural electrical stimulation of the colon was significantly reduced 3-days and 3-weeks following SCI in male rats. Specifically, cholinergic-mediated excitatory junction potentials (EJPs) and nitrergic-mediated slow inhibitory junction potentials (IJPs) were significantly reduced while ATP-mediated fast IJPs remained unaffected. We conclude that a reduction in excitatory and inhibitory enteric neuromuscular transmission contributes to neurogenic bowel observed following SCI, and that these loss-of-function changes involve enteric-mediated cholinergic and nitrergic pathways.

Aging-dependent decrease in the numbers of enteric neurons, interstitial cells of Cajal and expression of connexin43 in various regions of gastrointestinal tract

Aging is a significant risk factor for gastrointestinal dysmotility, but aging-associated differences between different organs and the exact time to start degenerating have remained obscure. Here we evaluated alterations of interstitial cells of Cajal, enteric neurons and connexin43 expression in the stomach, jejunum and colon in 2-, 12-, 16-, 20- and 24-month-old mice, as well as in aged human colon. Interstitial cells of Cajal, cholinergic and nitrergic neurons within the whole digestive tract were reduced over time, but their loss first appeared in stomach, then in intestine, helping to understand that gastric function was first impaired during aging. The decrease of connexin43 expression occurred before interstitial cells of Cajal and neurons loss, suggesting that connexin43 might be the major target influenced during senescence. Furthermore, changes in expressions of pro-inflammatory cytokines (tumour necrosis factor-α, interleukin-1β, interleukin-6) and apoptosis-related proteins (B-cell lymphoma-2, caspase-3) which indicated “inflammaging”, might contribute to the loss of enteric neurons and interstitial cells of Cajal in aged gastrointestinal tract. Our results provide possible therapeutic time window for beneficial intervention for geriatric patients with gastrointestinal motility disorders.

Gut microbiota and butyrate level changes associated with the long-term administration of proton pump inhibitors to old rats

The association between adverse effects of PPI and gut microbiota in old age has yet to be elucidated. We assessed changes in the gut microbiota and butyrate levels following the long-term administration of PPIs to old rats and investigated their associations. F344 aged male rats were fed a PPI-supplemented diet for 50 weeks. The ileal microbiota was analysed by metagenomic sequencing of the 16S rRNA, while the butyrate concentration was measured by high-performance liquid chromatography. We observed a significant decrease in microbial diversity following PPI administration in the 2-year-old rats but not in the 74-week-old rats. PPI treatment reduced both commensal bacteria and opportunistic pathogens, particularly in the 2-year-old rats. Enterotypes comprising the majority of the control samples were enriched in Lactobacillus, while other enterotypes in the PPI group were dominated by Turicibacter or Romboutsia. The PPI treatment reduced the butyrate concentrations in the intestines and colons of 74-week-old rats compared to the control group. The abundance of Lactobacillus significantly correlated with butyrate concentrations in 74-week-old rats. In conclusion, long-term administration of PPIs alters the gut microbiota and butyrate concentrations in rats, particularly in old age, which may be an underlying mechanism of PPI-induced adverse effects such as pseudomembranous colitis.

Microbial Changes and Host Response in F344 Rat Colon Depending on Sex and Age Following a High-Fat Diet

Gut microbiota, an important component that affects host health, change rapidly and directly in response to altered diet composition. Recently, the role of diet–microbiome interaction on the development of colon cancer has been the focus of interest. Colon cancer occurs more frequently in an aged population, and in males. However, the effect of dietary changes on the gut microbiome has been studied mainly in young males, even though it may vary with age and sex. The aim of this study was to investigate microbial changes and host response in the colons of male and female 6-week-old (young) and 2-year-old (old) Fisher-344 rats exposed to a high-fat diet (HFD). Our results showed that exposure to HFD for 8 weeks decreased the species richness of microbiota (Chao1) and increased Firmicutes/Bacteroidetes ratio only in aged rats, and not in young rats. Sex differences underlying the alteration by HFD in the gut microbiome were observed in the microbiome of aged rats. For instance, the abundance ratio of Akkermansia muciniphila and Desulfovibrio spp. increased in response to HFD in young rats and female aged rats, but not in male aged rats. Histological inflammation and cell proliferation of colon mucosa (indexed by Ki67) were significantly increased by HFD even in young rats; aged rats showed significantly higher cell proliferation in the HFD group than in the control. The HFD-induced decrease of species richness and the increase in specific species (Desulfovibrio spp. and Clostridium lavalense), which produce carcinogenic compounds such as H₂S and N-nitroso compounds, were significantly correlated with Ki67 index. In colon mucosa, the concentration of myeloperoxidase was increased by HFD only in males, and not in females. In conclusion, the results suggest a link between HFD-induced gut dysbiosis (particularly the low species richness and high abundance ratios of Desulfovibrio spp. and C. lavalense) and cell proliferation of colon mucosa (indicated by Ki67 IHC). In addition, sex differences influence the response of gut microbiome to HFD particularly in old age. Such sex differences in the gut microbiota might be related to sex differences in inflammation in the colon mucosa.

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.

Comparative Analysis of Ileal and Cecal Microbiota in Aged Rats

Background

Gut microbiota contributes to intestinal and immune homeostasis through host-microbiota interactions. Distribution of the gut microbiota differs according to the location in the gastrointestinal tract. Although the microbiota properties change with age, evidence for the regional difference of gut microbiota has been restricted to the young. The aim of this study is to compare the gut microbiota between terminal ileum and cecum of old rats.

Methods

We analyzed gut microbiome of luminal contents from ileum and cecum of 74-week-old and 2-year-old rats (corresponding to 60-year and 80-year-old of human age) by metagenome sequencing of 16S rRNA.

Results

Inter-individual variation (beta diversity) of microbiota was higher in ileum than in cecum. Conversely, alpha diversity of microbiota composition was higher in cecum than in ileum. Lactobacillaceae were more abundant in ileum compared to cecum while Ruminococcaceae and Lachnospiraceae were more enriched in cecum. The proportions of Deltaproteobacteria were increased in cecal microbiota of 2-year-old rats compared to 74-week-old rats.

Conclusions

Major regional distinctions of microbiota between ileum and cecum of old rats appear consistent with those of young rats. Age-related alterations of gut microbiota in old rats seem to occur in minor compositions.

Gut Microbes and Health: A Focus on the Mechanisms Linking Microbes, Obesity, and Related Disorders

The past decade has been characterized by tremendous progress in the field of the gut microbiota and its impact on host metabolism. Although numerous studies show a strong relationship between the composition of gut microbiota and specific metabolic disorders associated with obesity, the key mechanisms are still being studied. The present review focuses on specific complex pathways as well as key interactions. For instance, the nervous routes are explored by examining the enteric nervous system, the vagus nerve, and the brain, as well as the endocrine routes (i.e., glucagon-like peptide-1, peptide YY, endocannabinoids) by which gut microbes communicate with the host. Moreover, the key metabolites involved in such specific interactions (e.g., short chain fatty acids, bile acids, neurotransmitters) as well as their targets (i.e., receptors, cell types, and organs) are briefly discussed. Finally, the review highlights the role of metabolic endotoxemia in the onset of metabolic disorders and the implications for alterations in gut microbiota-host interactions and ultimately the onset of diseases.

Anatomical and Functional Changes to the Colonic Neuromuscular Compartment after Experimental Spinal Cord Injury

A profound reduction in colorectal transit time accompanies spinal cord injury (SCI), yet the colonic alterations after SCI have yet to be understood fully. The loss of descending supraspinal input to lumbosacral neural circuits innervating the colon is recognized as one causal mechanism. Remodeling of the colonic enteric nervous system/smooth muscle junction in response to inflammation, however, is recognized as one factor leading to colonic dysmotility in other pathophysiological models. We investigated the alterations to the neuromuscular junction in rats with experimental high-thoracic (T3) SCI. One day to three weeks post-injury, both injured and age-matched controls underwent in vivo experimentation followed by tissue harvest for histological evaluation. Spontaneous colonic contractions were reduced significantly in the proximal and distal colon of T3-SCI rats. Histological evaluation of proximal and distal colon demonstrated significant reductions of colonic mucosal crypt depth and width. Markers of intestinal inflammation were assayed by qRT-PCR. Specifically, Icam1, Ccl2 (MCP-1), and Ccl3 (MIP-1α) mRNA was acutely elevated after T3-SCI. Smooth muscle thickness and collagen content of the colon were increased significantly in T3-SCI rats. Colonic cross sections immunohistochemically processed for the pan-neuronal marker HuC/D displayed a significant decrease in colonic enteric neuron density that became more pronounced at three weeks after injury. Our data suggest that post-SCI inflammation and remodeling of the enteric neuromuscular compartment accompanies SCI. These morphological changes may provoke the diminished colonic motility that occurs during this same period, possibly through the disruption of intrinsic neuromuscular control of the colon.

Changes in the interstitial cells of Cajal and neuronal nitric oxide synthase positive neuronal cells with aging in the esophagus of F344 rats

The aging-associated cellular and molecular changes in esophagus have not been established, yet. Thus we evaluated histological structure, interstitial cells of Cajal (ICCs), neuronal nitric oxide synthase (nNOS)-positive cells, and contractility in the esophagus of Fischer 344 rat at different ages (6-, 31-, 74-weeks, and 2-years). The lamina propria thickness and endomysial area were calculated. The immunoreactivity of c-Kit, nNOS and protein gene product (PGP) 9.5 was counted after immunohistochemistry. Expression of c-Kit, stem cell factor (SCF), nNOS and PGP 9.5 mRNA was measured by real-time PCR, and expression of c-Kit and nNOS protein was detected by Western blot. Isovolumetric contractile force measurement and electrical field stimulation (EFS) were conducted. The lamina propria thickness increased (6 week vs 2 year, P = 0.005) and the endomysial area of longitudinal muscle decreased with aging (6 week vs 2 year, P<0.001), while endomysial area of circular muscle did not significantly decrease. The proportions of NOS-immunoreactive cells and c-Kit-immunoreactive areas declined with aging (6 week vs 2 year; P<0.001 and P = 0.004, respectively), but there was no significant change of PGP 9.5-immunopositiviy. The expressions of nNOS, c-Kit and SCF mRNA also reduced with aging (6 week vs 2 year; P = 0.006, P = 0.001 and P = 0.006, respectively), while the change of PGP 9.5 mRNA expression was not significant. Western blot showed the significant decreases of nNOS and c-Kit protein expression with aging (6 week vs 2 year; P = 0.008 and P = 0.012, respectively). The EFS-induced esophageal contractions significantly decreased in 2-yr-old rat compared with 6-wk-old rats, however, L-NG-Nitroarginine methylester did not significantly increase the spontaneous and EFS-induced contractions in the 6-wk- and 2-yr-old rat esophagus. In conclusion, an increase of lamina propria thickness, a decrease of endomysial area, c-Kit, SCF and NOS expression with preserved total enteric neurons, and contractility in aged rat esophagus may explain the aging-associated esophageal dysmotility.

Comparison of Changes in the Interstitial Cells of Cajal and Neuronal Nitric Oxide Synthase-positive Neuronal Cells With Aging Between the Ascending and Descending Colon of F344 Rats

Background/Aims

Neuronal degeneration and changes in interstitial cells of Cajal (ICCs) are important mechanisms of age-related constipation. This study aims to compare the distribution of ICCs and neuronal nitric oxide synthase (nNOS) with regard to age-related changes between the ascending colon (AC) and descending colon (DC) in 6-, 31-, and 74-week old and 2-year old male Fischer-344 rats.

Methods

The amount of fecal pellet and the bead expulsion times were measured. Fat proportion in the muscle layer of the colon was analyzed by hematoxylin and eosin staining. Proto-oncogene receptor tyrosine kinase (KIT) and neuronal nitric oxide synthase (nNOS) expression were analyzed with Western blotting and immunohistochemistry. Isovolumetric contractile measurements and electrical field stimulation were used to assess smooth muscle contractility.

Results

Colon transit and bead expulsion slowed with senescence. Fat in the muscle layer accumulated with age in the AC, but not in the DC. The proportion of KIT-immunoreactive ICCs in the submucosal and myenteric plexus was higher in the DC than in the AC, and it declined with age, especially in the AC. In contrast, the proportion of NOS-immunoreactive neurons in the myenteric plexus was higher in the AC than in the DC, and both decreased in older rats. Nitric oxide levels declined with age in the DC. Muscle strip experiments showed that the inhibitory response mediated by nitric oxide in the circular direction of the DC was reduced in 2-year old rats.

Conclusion

The AC and DC differ in their distribution of ICCs and nNOS, and age-related loss of nitrergic neurons more severely affects the DC than the AC.

Change in the Interstitial Cells of Cajal and nNOS Positive Neuronal Cells with Aging in the Stomach of F344 Rats

The gastric accommodation reflex is an important mechanism in gastric physiology. However, the aging-associated structural and functional changes in gastric relaxation have not yet been established. Thus, we evaluated the molecular changes of interstitial cell of Cajal (ICC) and neuronal nitric oxide synthase (nNOS) and the function changes in the corpus of F344 rats at different ages (6-, 31-, 74-wk and 2-yr). The proportion of the c-Kit-positive area in the submucosal border (SMB) and myenteric plexus (MP) layer was significantly lower in the older rats, as indicated by immunohistochemistry. The density of the nNOS-positive immunoreactive area also decreased with age in the SMB, circular muscle (CM), and MP. Similarly, the percent of nNOS-positive neuronal cells per total neuronal cells and the proportion of nNOS immunoreactive area of MP also decreased in aged rats. In addition, the mRNA and protein expression of c-Kit and nNOS significantly decreased with age. Expression of stem cell factor (SCF) and the pan-neuronal marker PGP 9.5 mRNA was significantly lower in the older rats than in the younger rats. Barostat studies showed no difference depending on age. Instead, the change of volume was significantly decreased by L-NG63-nitroarginine methyl ester in the 2-yr-old rats compared with the 6-wk-old rats (P = 0.003). Taken together, the quantitative and molecular nNOS changes in the stomach might play a role in the decrease of gastric accommodation with age.

Understanding the gastrointestinal tract of the elderly to develop dietary solutions that prevent malnutrition

Although the prevalence of malnutrition in the old age is increasing worldwide a synthetic understanding of the impact of aging on the intake, digestion, and absorption of nutrients is still lacking. This review article aims at filling the gap in knowledge between the functional decline of the aging gastrointestinal tract (GIT) and the consequences of malnutrition on the health status of elderly. Changes in the aging GIT include the mechanical disintegration of food, gastrointestinal motor function, food transit, chemical food digestion, and functionality of the intestinal wall. These alterations progressively decrease the ability of the GIT to provide the aging organism with adequate levels of nutrients, what contributes to the development of malnutrition. Malnutrition, in turn, increases the risks for the development of a range of pathologies associated with most organ systems, in particular the nervous-, muscoskeletal-, cardiovascular-, immune-, and skin systems. In addition to psychological, economics, and societal factors, dietary solutions preventing malnutrition should thus propose dietary guidelines and food products that integrate knowledge on the functionality of the aging GIT and the nutritional status of the elderly. Achieving this goal will request the identification, validation, and correlative analysis of biomarkers of food intake, nutrient bioavailability, and malnutrition.

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.