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 m L of saline solution orally, and the infected group(IG)(n=15)inoculated with 1 m L of saline solution containing500 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. 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 m L of saline solution orally, and the infected group (IG) (n = 15) inoculated with 1 m L 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 th e. 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 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; 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; (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.