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.Keywords: Enteric nervous system, myenteric plexus, ascending colon, toxoplasmosis. ResumoA toxoplasmose, doença causada pelo Toxoplasma gondii, é um importante problema de saúde, principalmente em imunocomprometidos. T. gondii utiliza a parede do intestino como porta de entrada no hospedeiro e tem tropismo pelos tecidos muscular e nervoso provocando alterações intestinais, inclusive no sistema nervoso entérico. Este estudo buscou analisar o cólon de ratos infectados por T. gondii para entender como a quantidade de oocistos influencia nas alterações neuronais mientéricas. Foram utilizados 60 ratos Wistar (Rattus norvegicus) em seis grupos. Um dos grupos permaneceu como controle e os demais receberam inóculos de 10, 50, 100, 500 ou 5.000 oocistos de T. gondii. Os animais foram submetidos a eutanásia após 30 dias de infecção. No plexo mientérico do cólon dos animais foram quantificadas a população neuronal total e a subpopulação nitrérgica. Os dados foram analisados estatisticamente demonstrando inferior ganho de peso nos ratos com 10, 500 e 5.000 oocistos. Verificamos diminuição no número de neurônios totais com inóculos de 50, 100 ou 5.000 oocistos e aumento da população nitrérgica com 10, 100, 500 ou 5000 oocistos. Estes resultados mostram que alterações neuronais são mais significativas quando a infecção é induzida por inóculos maiores e reforça a suspeita de perda neuronal direcionada a neurônios colinérgicos.Palavras-chave: Sistema nervoso entérico, plexo mientérico, cólon ascendente, toxoplasmose.

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

“…We previously showed that different loads of the ME‐49 strain of T gondii are able to cause progressive anatomical changes in the colon of rats at 30 days postinoculation, concluding that the load to cause death of myenteric neurons is 5 × 10 3 oocysts 30 . Now, we evaluated how the of colonic wall changes during the course of infection, from 6 hours up to 30 days, in rats infected with this load.…”

“…We previously showed that different loads of the ME-49 strain of T gondii are able to cause progressive anatomical changes in the colon of rats at 30 days postinoculation, concluding that the load to cause death of myenteric neurons is 5 × 10 3 oocysts. 30 Loss of myenteric neurons upon T gondii is not a common finding in rats, unless when they are infected with high loads of oocysts. 30 Other species can lose myenteric neurons more easily, as we demonstrated before in chicken 13 and pigs.…”

“…30 Loss of myenteric neurons upon T gondii is not a common finding in rats, unless when they are infected with high loads of oocysts. 30 Other species can lose myenteric neurons more easily, as we demonstrated before in chicken 13 and pigs. 35 The use of rats in experimental infection with T gondii is relevant because they present similar response to immunocompetent humans.…”

“…In order to obtain the anatomical data, the animals were randomly assigned into control (CG) and T gondii-infected groups, which were chosen considering previous studies. 30 The oocysts were supplied by the Laboratory of Veterinary Parasitology of the State University of Londrina, Brazil.…”

Quantification of the neurons of myenteric plexus of the bat molossus rufus

“…Compared to the results of this study, the neuronal population Giemsa + among the different species are similar (Table 1). Ferezin et al (2017) reported the count of approximately 45 neurons Giemsa + in 0.249mm 2 , corresponding to 180.72 neurons/mm 2 , and 12 neurons NADPH-d + in 0.249mm 2 , equivalent to 48.19 neurons/mm 2 for the colon of rats.…”