Alterations of the myenteric plexus of the ileum and the descending colon caused by Toxoplasma gondii (genotype III)

Toxoplasma gondii infection impairs the colonic motility of rats due to loss of myenteric neurons

BACKGROUND

Toxoplasma gondii infection causes intestinal inflammation and diarrhea indicating possible intestinal motor dysfunction. Anatomical studies have shown alterations in the colonic myenteric plexus, but it is unknown whether this impacts motility and therefore whether motility is a target for treatment. We determined whether colonic coordinated movements are compromised by toxoplasmic infection and how it is associated with anatomical changes.

METHODS

Male Wistar rats were evaluated at 6, 12, 24, 48, and 72 hours and 30 days postinfection (dpi) and controls. Infected rats received orally 5 × 10³ sporulated oocysts of strain ME-49 (genotype II) of T gondii. The colon was collected for anatomical analysis (including the myenteric plexus immunolabeled with HuC/D, nNOS, and ChAT) and motility analysis in vitro (conventional manometry). Fecal output was measured daily.

KEY RESULTS

At 12 hours postinfection, T gondii caused hypertrophy of the muscularis externa layer of the distal colon. There was loss of total, nitrergic, and cholinergic myenteric neurons in the proximal colon at 30 day postinfection (dpi); however, only loss of cholinergic neurons was found in the distal colon. Contractile complexes in the middle and distal colon were longer in duration in infected animals, which was associated with slower migration of the colonic motor complex. However, gastrointestinal transit time and fecal pellet output remained unchanged during the T gondii infection.

CONCLUSIONS AND INFERENCES

Toxoplasma gondii caused myenteric neuronal loss in the proximal and distal colon and altered the motility pattern in the middle and distal colon to a more propulsive phenotype.

Acute Toxoplasma gondii infection alters the number of neurons and the proportion of enteric glial cells in the duodenum in Wistar rats

BACKGROUND

Toxoplasma gondii infection can occur through the ingestion of raw meat that contains tissue cysts or food that contains oocysts. Through the ingestion of oocysts, the parasite crosses the intestinal barrier, where the enteric nervous system is located. The objective was to investigate the kinetics of neuronal and glial responses during acute T. gondii infection.

METHODS

We used 45 Wistar rats that were divided into a control group and infected groups that were evaluated at 6, 12, 24, 48, 72 hours, 7 days, 10 days, and 15 days after infection. The rats received 5000 sporulated oocysts of the parasite orally. To detect neurons and enteric glia cells, the myenteric and submucosal plexuses of the duodenum underwent double-labeling immunohistochemical techniques to evaluate HuC/HuD and S100, HuC/HuD and ChAT, and HuC/HuD and nNOS.

KEY RESULTS

We observed a reduction of the total neuron population in the submucosal plexus 72 hours after infection. Cholinergic neurons decreased in the submucosal plexus 15 days after infection, and nitrergic neurons decreased in the myenteric plexus 72 hours after infection. A decrease in the number of glial cells was observed 7 days after infection in the submucosal plexus, and an increase in the enteric glial cell (EGC)/neuron ratio was found in both plexuses 48 hours after infection.

CONCLUSIONS AND INFERENCES

We found decrease of neurons and increase in the EGC/neuron ratio in both plexuses caused by acute T. gondii infection, with major alterations 72 hours after oral infection. The number of cholinergic neurons decreased in the submucosal plexus, and the number of nitrergic neurons decreased in the myenteric plexus. A decrease in the number of enteric glial cells was observed in the submucosal plexus, and an increase in the enteric glial cell/neuron ratio was observed in both ganglionate plexuses of the duodenum.

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.

Different inoculum loads of Toxoplasma gondii induce reduction of myenteric neurons of the rat colon

Abstract Toxoplasmosis, a disease caused by Toxoplasma gondii, is an important health problem, especially in immunocompromised hosts. T. gondii uses the gut wall as an infection gateway, with tropism for muscular and nervous tissues causing intestinal alterations, including some in the enteric nervous system. This study aims at investigating the colon of rats infected by T. gondii in order to understand how the amount of oocysts influences in myenteric neuronal changes. Sixty Wistar rats (Rattus norvegicus) were divided into six groups. One group remained as a control and the others received inocula of 10, 50, 100, 500 or 5,000 oocysts of T. gondii. The animals were euthanized after 30 days of infection. The total neuronal population and the nitrergic subpopulation in the colon myenteric plexus of each animal was counted. The data were statistically analyzed showing less weight gain in rats with 10, 500 and 5,000 oocysts. A decrease in the number of total neurons with 50, 100 or 5,000 oocysts and an increase in the nitrergic population with 10, 100, 500 or 5,000 oocysts were verified. These results show that neuronal alterations are more significant when the infection is induced by larger inocula and reinforces the suspicion that neuronal loss is directed at cholinergic neurons.

Gastrointestinal Parasites and the Neural Control of Gut Functions

Gastrointestinal motility and transport of water and electrolytes play key roles in the pathophysiology of diarrhea upon exposure to enteric parasites. These processes are actively modulated by the enteric nervous system (ENS), which includes efferent, and afferent neurons, as well as interneurons. ENS integrity is essential to the maintenance of homeostatic gut responses. A number of gastrointestinal parasites are known to cause disease by altering the ENS. The mechanisms remain incompletely understood. Cryptosporidium parvum, Giardia duodenalis (syn. Giardia intestinalis, Giardia lamblia), Trypanosoma cruzi, Schistosoma species and others alter gastrointestinal motility, absorption, or secretion at least in part via effects on the ENS. Recent findings also implicate enteric parasites such as C. parvum and G. duodenalis in the development of post-infectious complications such as irritable bowel syndrome, which further underscores their effects on the gut-brain axis. This article critically reviews recent advances and the current state of knowledge on the impact of enteric parasitism on the neural control of gut functions, and provides insights into mechanisms underlying these abnormalities.

Oral dependent-dose toxoplasmic infection model induced by oocysts in rats: Myenteric plexus and jejunal wall changes

Toxoplasmosis is a widely distributed disease caused by the protozoan Toxoplasma gondii that is mainly transmitted orally. Once ingested, the parasite crosses the intestinal barrier to reach the blood and lymph systems to migrate to other regions of the host. The objective of this study was to evaluate the changes in the myenteric plexus and the jejunal wall of Wistar rats caused by oral infection with T. gondii oocysts (ME-49 strain). Inocula of 10, 100, 500 and 5000 oocysts were used. The total population of myenteric neurons and the most metabolically active subpopulation (NADH-diaphorase positive - NADH-dp) exhibited a decrease proportional to the dose of T. gondii. There was also a quantitative increase in the subpopulation of NADPH-diaphorase-positive (NADPH-dp) myenteric neurons, indicating greater expression of the NOS enzyme. Neuronal atrophy was observed, and morphological and morphometric alterations such as jejunal atrophy were found in the infected groups. Hypertrophy of the external muscle with the presence of inflammatory foci was observed in the group infected with 5000 oocysts. The changes observed in the infected groups were proportional to the number of oocysts inoculated.

Toxoplasma gondii causes death and plastic alteration in the jejunal myenteric plexus

AIM: To assess the effects of ME-49 Toxoplasma gondii (T. gondii) strain infection on the myenteric plexus and external muscle of the jejunum in rats.

METHODS: Thirty rats were distributed into two groups: the control group (CG) (n = 15) received 1 mL of saline solution orally, and the infected group (IG) (n = 15) inoculated with 1 mL of saline solution containing 500 oocysts of M-49 T. gondii strain orally. After 36 d of infection, the rats were euthanized. Infection with T. gondii was confirmed by blood samples collected from all rats at the beginning and end of the experiment. The jejunum of five animals was removed and submitted to routine histological processing (paraffin) for analysis of external muscle thickness. The remaining jejunum from the others animals was used to analyze the general population and the NADH-diaphorase, VIPergic and nitrergic subpopulations of myenteric neurons; and the enteric glial cells (S100-IR).

RESULTS: Serological analysis showed that animals from the IG were infected with the parasite. Hypertrophy affecting jejunal muscle thickness was observed in the IG rats (77.02 ± 42.71) in relation to the CG (51.40 ± 12.34), P < 0.05. In addition, 31.2% of the total number of myenteric neurons died (CG: 39839.3 ± 5362.3; IG: 26766.6 ± 2177.6; P < 0.05); hyperplasia of nitrergic myenteric neurons was observed (CG: 7959.0 ± 1290.4; IG: 10893.0 ± 1156.3; P < 0.05); general hypertrophy of the cell body in the remaining myenteric neurons was noted [CG: 232.5 (187.2-286.0); IG: 248.2 (204.4-293.0); P < 0.05]; hypertrophy of the smallest varicosities containing VIP neurotransmitter was seen (CG: 0.46 ± 0.10; IG: 0.80 ± 0.16; P < 0.05) and a reduction of 25.3% in enteric glia cells (CG: 12.64 ± 1.27; IG: 10.09 ± 2.10; P < 0.05) was observed in the infected rats.

CONCLUSION: It was concluded that infection with oocysts of ME-49 T. gondii strain caused quantitative and plastic alterations in the myenteric plexus of the jejunum in rats.

Myenteric neuronal plasticity induced by Toxoplasma gondii (genotype III) on the duodenum of rats

The effects of acute and chronic infection caused by Toxoplasma gondii on duodenal myenteric neurons were analyzed. Eighteen rats were assigned into four groups: Acute Control Group (ACG, n=4); Acute Experimental Group (AEG, n=4); Chronic Control Group (CCG, n=5); and Chronic Experimental Group (CEG, n=5). Rats from the AEG and CEG were inoculated orally with 105 genotype III (BTU-II strain) tachyzoites of T. gondii isolated from a dog with neurological signs. Acute groups were killed after 24 hours after the inoculation and the chronic groups after 30 days. Whole-mount from the duodenum were stained with Giemsa. The population density of myenteric neurons, as well the body cell, nuclear and cytoplasmic area were analyzed. Both acute and chronic toxoplasmic infection did not provoke neuronal loss. On the other hand, plastic alterations were observed: decreasing of the nuclear and cytoplasmic area during the acute phase and neuronal hypertrophy during the chronic phase.

Toxoplasma gondii infection causes morphological changes in caecal myenteric neurons

The aim of this study was to evaluate the effects of chronic infection of Toxoplasma gondii (with genotype I and genotype III strains) on the population density and morphometry of caecal myenteric neurons in rats. Fifteen, 60-day-old, male Wistar rats (Rattus norvegicus) were used. The animals were assigned into three groups: Control Group (CG), Experimental Group 1 (EG1) and Experimental Group 2 (EG2). EG1 animals received 10(5) tachyzoites of the genotype I (BTU IV) T. gondii strain orally, and the EG2 animals received 10(5) tachyzoites of the genotype III (BTU II) strain orally. Thirty days after inoculation, caecal whole-mount preparations were stained by Giemsa technique. The caecal preparations were then analysed by assessing the population density and morphometry of myenteric neurons in specific regions of the caecum: mesenteric apical (MA), antimesenteric apical (AA), antimesenteric basal (AB) and next to caecal ampulla (NA). Myenteric neurons from the AA region were more clustered in EG1 animals (P<0.05). The EG1 animals presented a 16.8% reduction in the area of the nucleus, whereas the EG2 animals showed 18.4% increase (P<0.05). There was a more marked reduction in the cytoplasm of the animals in EG1 (↓23.2%) compared to EG2 (↓6.2%). There was 35.8% neuronal atrophy in the AB region and 16.8% in the region NA of the EG1 animals (P<0.05). In conclusion, different strains of T. gondii cause morphometric changes in caecal myenteric neurons of rats. Only the genotype I strain was able to cause neuronal density changes.

Toxoplasma gondii: myenteric neurons of intraperitoneally inoculated rats show quantitative and morphometric alterations

Several studies have demonstrated that the myenteric plexus experiences quantitative and morphometric changes in rats inoculated orally with Toxoplasma gondii. This paper aims to verify if these alterations are also seen when the same animals are inoculated intraperitoneally with the parasite. In order to do that, six Wistar rats (Rattus norvegicus) 60 days of age were infected intraperitoneally with 10(6) tachyzoites of a genotype I T. gondii strain (BTU IV). After 60 days, the animals were anaesthetised and underwent laparotomy. All organs from the small and large intestines were removed, measured, dissected and underwent whole-mount Giemsa technique to stain the neurons in the myenteric plexus. A quantitative and morphometric analysis of these cells was made, and it showed that the parasite causes the death of myenteric neurons in the jejunum and morphometric alterations in these cells throughout the intestine. However, the cellular response of myenteric neurons to T. gondii is heterogeneous compared the different organs from the gut.

Chronic infection with Toxoplasma gondii causes myenteric neuroplasticity of the jejunum in rats

Toxoplasma gondii is an aetiological agent of toxoplasmosis, which commonly causes diarrhoea in a number of species. This observation and the parasite's affinity for the nervous tissue support the theory that T. gondii infection may affect the myenteric neurons. The aim of this study was to evaluate the changes caused by T. gondii (genotype III) in the myenteric neurons of the jejunum in rats. Fifteen rats were distributed into three groups: control (CG), inoculated for 30 days (G30) and inoculated for 90 days (G90). Rats from the G30 and G90 groups received an oral inoculum with 500 oocysts from a genotype III (M7741) T. gondii strain. At 180 days of age, all animals were anaesthetised and euthanised. Whole mounts were stained by using Giemsa (total population) and NADPH-diaphorase (nitrergic subpopulation) histochemistry. Maintenance of the width, length, area and neuronal density was observed; there was neuronal atrophy in the G30 group and a tendency to hypertrophy in the G90 group. Rats inoculated orally with sporulated oocysts did not show clinical illness or macroscopic or microscopic lesions, as do the majority of animal species. Therefore, infection was confirmed by a serum agglutination test; 30 days of infection caused increased weight gain and atrophy of myenteric neurons. At 90 days post-infection, weight gain became normal, and myenteric neurons hypertrophied.

Effects of infection with Toxoplasma gondii oocysts on the intestinal wall and the myenteric plexus of chicken (Gallus gallus)

This paper aims to analyze the effects of the Toxoplasma gondii infection in the intestinal wall and myenteric plexus of chicken (Gallus gallus). Ten 36-day-old chickens were separated into two groups: control and experimental, orally inoculated with oocysts of the T. gondii strain M7741 genotype III. After 60 days the birds were submitted to euthanasia and had their duodenum removed. Part of the intestinal segments was submitted to histological routine, HE staining, PAS histochemical technique, and Alcian Blue. Qualitative analysis of the intestinal wall and comparative measurements among the groups with respect to total wall thickness, muscle tunic, mucosa, and tunica mucosa were carried out. Caliciform cells were quantified. The other part of the intestinal segments was fixed in formol acetic acid and dissected having the tunica mucosa and the tela submucosa removed. Neurons were stained with Giemsa, counted, and measured. Chickens from the experimental group presented diarrhea and inflammatory infiltrates in the tunica mucosa, thickness reduction of all the parameters assessed in the intestinal wall, and an increase of the number of caliciform cells. There was a ~70% reduction regarding the intensity of myenteric neurons; and the remaining cells presented a reduction of ~2.4% of the perikarion and ~40.5% of the nucleus (p<0.05). Chronic infection induced by T. gondii oocysts resulted in intestinal wall atrophy, mucin secretion increase, death and atrophy of chicken myenteric plexus neurons. Death and atrophy of myenteric plexus neurons may be related with the causes of diarrhea observed in chickens with toxoplasmosis.

Quantitative and morphometric changes of subpopulations of myenteric neurons in swines with toxoplasmosis

The consequences of the infection caused by Toxoplasma gondii in myenteric neurons of the jejunum of swines reactive to NADH-diaphorase and NADPH-diaphorase were evaluated in this study. Ten 88-day-old mixed-breed swines (Pietrain and Wessex) were assigned into two groups: Control (n=5) and Experimental (n=5), which orally received 5000 sporulated oocysts from a genotype III T. gondii strain. After 30days, the animals were anesthetized, having part of their jejunum removed and stained with NADPH-diaphorase and NADH-diaphorase. NADPHd-p neurons (nitrergic) presented increase of the number of cells per ganglion and hypertrophy. The number of NADHd-p neurons (metabolic more active) and their nuclear area decreased.