Toxoplasma gondii infection causes morphological changes in caecal myenteric neurons Larissa Marchi Zaniolo a , Aristeu Vieira da Silva b , Débora de Mello Gonçales Sant’Ana c , Eduardo José de Almeida Araújo d,⇑ a Mestrado em Ciência Animal, Universidade Paranaense (UNIPAR), Umuarama, Paraná, Brazil b Departamento de Ciências Biológicas, Universidade Estadual de Feira de Santana, Feira de Santana, Bahia, Brazil c Departamento de Ciências Morfológicas, Universidade Estadual de Maringá, Maringá, Paraná, Brazil d Departamento de Histologia, Universidade Estadual de Londrina, Londrina, Paraná, Brazil article info Article history: Received 29 September 2011 Received in revised form 13 December 2011 Accepted 14 December 2011 Available online 22 December 2011 Keywords: Enteric nervous system Enteric neural plasticity Gut Infection Large intestine Toxoplasmosis abstract 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 ani- mals 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 ana- lysed 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. Ó 2011 Elsevier Inc. All rights reserved. 1. Introduction Toxoplasmosis is a zoonosis, widely distributed geographically and which affects more than a third of the human population; therefore, it is a disease that requires the attention of public health regulators (Weiss and Kim, 2007). Moreover, it constitutes one of the primary causes of damage to livestock causing abortion in sev- eral animal species (Dubey and Beattie, 1988). Toxoplasma gondii, the causative organism, which has a heteroxenic life cycle. Cats are primary hosts although most homoeothermic animals can act as intermediate hosts (Neves et al., 2005). This parasite has three clone lineages: genotypes I, II and III (Howe and Sibley, 1995). The strains isolated in Brazil have been classified as genotypes I and III and are highly virulent in mice (Da Silva et al., 2005). Most individuals infected with T. gondii are asymptomatic; however, immunocompromised humans and some species of animals (mice, dogs, pigs, sheep and goats) may suffer blindness, severe neurolog- ical disorders, hepatitis, pneumonia and diarrhoea (Weiss and Kim, 2007). Each species has a different reaction to parasite exposure (Dubey and Beattie, 1988), as the pathogenesis is related to the genotype of the strain, the number of parasites entering the body, the immune resistance of the individual and the type of infection (route of entry of T. gondii)(Neves et al., 2005). T. gondii is an obligate intracellular parasite that can invade and multiply in any nucleated cell in mammals or birds. However, the parasite has greater tropism for muscle and nerve cells, especially in the central nervous system (CNS) (Neves et al., 2005). Numerous studies have reported CNS damage, such as seizures, confusion, coma, hydrocephalus and encephalitis due to T. gondii infection (Weiss and Kim, 2007). Since the natural route of entry for T. gondii is through the digestive tract, causing inflammation in the intestinal wall (Schreiner and Liesenfeld, 2009; Shiraishi et al., 2009; Bonapaz et al., 2010; Da Silva et al., 2010), investigations evaluating the impact of T. gondii infections on the enteric nervous system are important and some studies have been performed (Sugauara et al., 2008; Barbosa et al., 2009; Soares et al., 2009; Sugauara 0014-4894/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.exppara.2011.12.008 ⇑ Corresponding author. Fax: +55 43 3371 5828. E-mail address: ejaaraujo@gmail.com (E.J.A. Araújo). Experimental Parasitology 130 (2012) 103–109 Contents lists available at SciVerse ScienceDirect Experimental Parasitology journal homepage: www.elsevier.com/locate/yexpr