Intestinal Motility Dysfunction in Goto-Kakizaki Rats: Role of the Myenteric Plexus.

Diabetes mellitus is associated with changes in intestinal morphology and the enteric nervous system. We previously reported constipation in Goto-Kakizaki (GK) rats, a non-obese model for type 2 diabetes mellitus. AIM: The morpho-quantitative analysis of myenteric plexus neurons in the small and large intestines of 120-day-old male GK rats was investigated. METHODS: The diabetes was confirmed by high fasting blood glucose levels. The myenteric plexus was evaluated through wholemount immunofluorescence. The morpho-quantitative analyses included evaluating neuronal density (neurons per ganglion) of the total neuronal population, the cholinergic and nitrergic subpopulations, and enteric glial cells per ganglion. The cell body area of 100 neurons per segment per animal was measured. RESULTS: The total neurons and nitrergic subpopulation were unaltered in the GK rats' small and large intestines. The cholinergic subpopulation exhibited decreased density in the three segments of the small intestine and an increased number in the proximal colon of the GK rats. The number of enteric glial cells increased in the ileum of the GK rats, which could indicate enteric gliosis caused by the intestinal inflammatory state. The area of the cell body was increased in the total neuronal population of the jejunum and ileum of the GK rats. Frequency histograms of the cell body area distribution revealed the contribution of cholinergic neurons to larger areas in the jejunum and nitrergic neurons in the ileum. CONCLUSION: The constipation previously reported in GK rats might be explained by the decrease in the density of cholinergic neurons in the small intestine of this animal model.

Acute infection with an avirulent strain of Toxoplasma gondii causes decreasing and atrophy of nitrergic myenteric neurons of rats.

In the enteric nervous system (ENS), nitrergic neurons produce and use nitric oxide (NO) as an inhibitory motor neurotransmitter in response to parasitic infections, including those caused by Toxoplasma gondii. However, damage to the host caused by NO has been reported by various authors, and the role of NO in protection or cytotoxicity continues to be extensively studied. In this study, nitrergic neurons were investigated in the myenteric plexus of the jejunum and the distal colon of rats infected with 500 oocysts of the M7741 strain of T. gondii. Ten rats were randomly assigned into a control group (CG) and infected group (IG; received 500 sporulated oocysts of T. gondii orally). After 24h, the rats were euthanized, and samples of the jejunum and distal colon were obtained and processed for NADPH-diaphorase histochemical analysis. Quantitative and morphometric analysis of the nitrergic neurons in whole mounts containing the myenteric plexus was performed. There was a numeric reduction of nitrergic neurons per mm2 in both jejunum and distal colon. The remaining nitrergic neurons suffered atrophy in the areas of the cell body and nucleus, which resulted in a decrease in cytoplasm. Thus, we conclude that an avirulent strain of T. gondii in a short time causes neuroplastic changes in the small and large intestine of rats.

Aspirin prevents atrophy of esophageal nitrergic myenteric neurons in a mouse model of chronic Chagas disease.

The consequences of using aspirin (ASA) for the pathogenesis of Chagas disease are unclear. This study evaluated the effects of treatment of Chagas disease with ASA on the esophageal nitrergic myenteric neuron population and esophageal wall in mice. We observed that treatment of chagasic infection with ASA protects the esophageal myenteric neurons from the atrophy caused by the Trypanosoma cruzi infection. The mice were infected with 1300 trypomastigotes of Y strain T. cruzi intraperitoneally. Part of infected mice was treated with ASA from fifth to twelfth day after inoculation. Our data support the hypothesis that eicosanoids given during the acute phase of the chagasic infection may act as immunomodulators aiding the transition to and maintenance of the chronic phase of the disease. Besides, ASA treatment did not provoke alterations in the esophageal wall and the myenteric neurons in infected mice.

Resveratrol Reduces Morphologic Changes in the Myenteric Plexus and Oxidative Stress in the Ileum in Rats with Ischemia/Reperfusion Injury.

BACKGROUND: Intestinal ischemia/reperfusion injury can be caused by surgical procedures and inflammatory bowel disease. It is normally associated with the increased production of free radicals and changes in the enteric nervous system. AIMS: Given the antioxidant and neuroprotective properties of resveratrol, the present study assessed its influence on oxidative stress in the intestinal wall and the morphology of myenteric neurons in the ileum of rats subjected to ischemia/reperfusion. METHODS: Resveratrol was orally administered daily at a dose of 10 mg/kg for 5 days. Changes in the ileum response to ischemia after 45 min were investigated followed by 3 h reperfusion. Lipoperoxide and carbonylated protein levels, and the activity of the antioxidant enzymes glutathione reductase, glutathione peroxidase, and glucose-6-phosphate dehydrogenase were measured following ischemia/reperfusion injury. RESULTS: The density and morphometry of the general neuronal population, nitrergic neurons and glial cells, and morphometry of VIP varicosities in the ileum were also studied. Lipoperoxide and carbonylated protein levels were 171 and 40% higher during the ischemia/reperfusion, respectively, compared to control cohorts, and resveratrol attenuated these values. The glutathione ratio was 64% lower during ischemia/reperfusion, compared to control cohorts. Resveratrol increased the reduced/oxidized glutathione ratio, attenuated the changes in the activity of the antioxidant enzymes and the detrimental morphologic changes caused by ischemia/reperfusion in the general neuronal population and nitrergic neurons. CONCLUSIONS: Oral treatment with resveratrol reduced the oxidative stress in the ileum and attenuated the morphologic changes that occurred in the myenteric plexus of the ileum in rats subjected to ischemia/reperfusion.

Intestinal and neuronal myenteric adaptations in the small intestine induced by a high-fat diet in mice.

BACKGROUND: The prevalence of obesity has increased at alarming rates, particularly because of the increased consumption of high-fat diets (HFDs). The influence of HFDs on intrinsic innervation and the intestinal wall has not been fully characterized. The aim of this study was to investigate the morpho-quantitative aspects of myenteric neurons and the wall of the small intestine in mice fed a HFD. METHODS: Swiss mice were fed a HFD (59% kcal from fat) or standard chow (9% Kcal from fat) for 8 weeks. Segments of the duodenum, jejunum, and ileum were subjected to histological processing for morpho-quantitative examination of the intestinal wall and mucosal cells, and immunohistochemistry was performed to evaluate myenteric neurons. The data for each segment were compared between the groups using an unpaired Student's t-test or an equivalent nonparametric test. RESULTS: The HFD increased body weight and visceral fat and decreased the length of the small intestine and the circumference of the ileum. In the duodenum, the HFD increased the density of the nitrergic subpopulation and decreased the area of nitrergic neurons and vasoactive intestinal peptide (VIP) varicosities. In the jejunum, the density of the nitrergic subpopulation was increased and the neuronal areas of the general population, nitrergic subpopulation and (VIP) varicosities were reduced. In the ileum, the density of the general population and nitrergic subpopulation were increased and the neuronal areas of the general population, nitrergic subpopulation and (VIP) varicosities were reduced. The morphometric parameters of the villi, crypts, muscular layer and total wall generally increased in the duodenum and jejunum and decreased in the ileum. In the duodenum and jejunum, the HFD promoted a decreased in the proportion of intraepithelial lymphocytes. In the ileum, the proportion of intraepithelial lymphocytes and goblet cells reduced, and the enteroendocrine cells increased. CONCLUSIONS: The high-fat diet induces changes in the myenteric innervation of the small intestine, intestinal wall and mucosal cells responsible for the secretion of hormones and maintenance of the protective intestinal barrier. The morpho-quantitative data provide a basis for further studies to clarify the influence of HFD in the motility, digestive and absorptive capacity, and intestinal barrier.

Decreased nitric oxide markers and morphological changes in the brain of arsenic-exposed rats.

Epidemiological studies demonstrate an association between chronic consumption of arsenic contaminated water and cognitive deficits, especially when the exposure takes place during childhood. This study documents structural changes and nitrergic deficits in the striatum of adult female Wistar rats exposed to arsenic in drinking water (3 ppm, approximately 0.4 mg/kg per day) from gestation, throughout lactation and development until the age of 4 months. Kainic acid injected animals (10mg/kg, i.p.) were also analyzed as positive controls of neural cell damage. Morphological characteristics of cells, fiber tracts and axons were analyzed by means of light microscopy as well as immunoreactivity to neuronal nitric oxide synthase (nNOS). As nitrergic markers, nitrite/nitrate concentrations, nNOS levels and expression of nNOS-mRNA were quantified in striatal tissue. Reactive oxygen species (ROS) and lipid peroxidation (LPx) were determined as oxidative stress markers. Arsenic exposure resulted in moderate to severe alterations of thickness, organization, surrounding space and shape of fiber tracts and axons, while cell bodies remained healthy. These anomalies were not accompanied by ROS and/or LPx increases. By contrast, except the expression of nNOS-mRNA, all nitrergic markers including striatal nNOS immunoreactivity presented a significant decrease. These results indicate that arsenic targets the central nitrergic system and disturbs brain structural organization at low exposure levels.

Modulation of stress consequences by hippocampal monoaminergic, glutamatergic and nitrergic neurotransmitter systems.

Several findings relate the hippocampal formation to the behavioural consequences of stress. It contains a high concentration of corticoid receptors and undergoes plastic modifications, including decreased neurogenesis and cellular remodelling, following stress exposure. Various major neurotransmitter systems in the hippocampus are involved in these effects. Serotonin (5-HT) seems to exert a protective role in the hippocampus and attenuates the behavioural consequences of stress by activating 5-HT1A receptors in this structure. These effects may mediate the therapeutic actions of several antidepressants. The role of noradrenaline is less clear and possibly depends on the specific hippocampal region (dorsal vs. ventral). The deleterious modifications induced in the hippocampus by stress might involve a decrease in neurotrophic factors such as brain derived neurotrophic factor (BDNF) following glutamate N-methyl-D-aspartate (NMDA) receptor activation. In addition to glutamate, nitric oxide (NO) could also be related to these effects. Systemic and intra-hippocampal administration of nitric oxide synthase (NOS) inhibitors attenuates stress-induced behavioural consequences. The challenge for the future will be to integrate results related to these different neurotransmitter systems in a unifying theory about the role of the hippocampus in mood regulation, depressive disorder and antidepressant effects.