-Alterations caused by a genotype III strain of Toxoplasma gondii were assessed with respect to the number and the morphometry of the myenteric neurons in the terminal ileum and the descending colon. Eighteen rats were divided 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). NaCl solution was administered through gavage to the animals in the ACG and CCG. Toxoplasma gondii tachyzoites (10 4 ) from a genotype III strain were orally administered to the AEG and CEG. Acute Groups were died after 24 hours, and the Chronic Groups after 30 days. Neuronal loss was not observed in both organs. The neurons atrophied in the terminal ileum as the opposite occurred with the neurons at the descending colon during the chronic phase of infection. In the terminal ileum, the neurons atrophied during the chronic phase of the infection as no alteration was found during the acute phase. For the descending colon, the neurons became hypertrophic during the chronic infection in opposition to the atrophy found during the acute phase.KEY WORDS: enteric nervous system, toxoplasmosis, morphology. Alterações do plexo mientérico do íleo e cólon descendente causadas por Toxoplasma gondii (genótipo III)Resumo -Objetivou-se avaliar as alterações causadas por uma cepa genótipo III de Toxoplasma gondii, sobre o número e a morfometria de neurônios mientéricos, do íleo terminal e do cólon descendente. Dividiuse dezoitos ratos em quatro grupos: controle agudo (GCA, n=4), experimental agudo (GEA, n=4), controle crônico (GCC, n=5) e experimental crônico (GEC, n=5). Os animais do GCA e GCC receberam solução de NaCl por gavagem, e os animais do GEA e GEC 10 4 taquizoítos de uma cepa genótipo III de T. gondii por via oral. Os grupos agudos após 24 horas foram mortos e os crônicos após 30 dias. Observou-se que não houve perda neuronal em ambos os órgãos. No íleo terminal, os neurônios atrofiaram-se na fase crônica da infecção, enquanto nenhuma alteração ocorreu na fase aguda. Já no cólon descendente, os neurônios tornaram-se hipertróficos na fase crônica da infecção, em oposição à atrofia observada na fase aguda. PALAVRAS-CHAVE: sistema nervoso entérico, toxoplasmose, morfologia.

The behavior of the gill epithelium of tilapias cultured in tanks at different altitudes and interconnected with PVC pipes was analyzed. Gill filaments of four specimens from four tanks (T 1 , T 2 , T 3 e T 4 ) sequentially interconnected were submitted to histological routine to obtain 5-mm-thick cuts that were stained with HE or submitted to histochemistry reactions PAS + diastase solution or Alcian Blue pH 2.5 or Alcian Blue pH 1.0. Considering the intermediary, apical and basal regions of the filaments, the lamellar area was measured and the amount of mucous cells was counted. It was verified that oxygen, pH, and temperature decreased progressively as the water flew from one tank to another. Thus, an increase was realized of the amount of mucous cells and the lamellar area in T 2, as well as a progressive decrease of these measures on the tanks which received water from T 2 . Moreover, detachment of the gill epithelium, cellular hyperplasia in the interlamellar space, and telangectasias were observed in the fishes from T 2 , T 3 e T 4. It was concluded that the aquatic environment in tanks sequentially interconnected with PVC pipes suffers alterations from one tank to another, as that physico-chemical fluctuations reflect on the behavior of the gill epithelium through variations of the lamellar area and the amount of mucous cells.