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Chronic murine toxoplasmosis is defined by subtle changes in neuronal connectivity.

Parlog A, Harsan LA, Zagrebelsky M, Weller M, von Elverfeldt D, Mawrin C, Korte M, Dunay IR - Dis Model Mech (2014)

Bottom Line: Recent studies correlate chronic Toxoplasma gondii (T. gondii) infection with behavioral changes in rodents; additionally, seropositivity in humans is reported to be associated with behavioral and neuropsychiatric diseases.Altered fiber density was confirmed by morphological analysis of individual, pyramidal and granule neurons, showing a reduction in dendritic arbor and spine density within the SSC, as well as in the hippocampus.Our results demonstrate that persistent T. gondii infection in a murine model results in synaptic deficits within brain structures leading to disturbances in the morphology of noninfected neurons and modified brain connectivity, suggesting a potential explanation for the behavioral and neuropsychiatric alterations.

View Article: PubMed Central - PubMed

Affiliation: Institute of Medical Microbiology, Otto-von-Guericke University, 39120-Magdeburg, Germany.

ABSTRACT
Recent studies correlate chronic Toxoplasma gondii (T. gondii) infection with behavioral changes in rodents; additionally, seropositivity in humans is reported to be associated with behavioral and neuropsychiatric diseases. In this study we investigated whether the described behavioral changes in a murine model of chronic toxoplasmosis are associated with changes in synaptic plasticity and brain neuronal circuitry. In mice chronically infected with T. gondii, magnetic resonance imaging (MRI) data analysis displayed the presence of heterogeneous lesions scattered throughout all brain areas. However, a higher density of lesions was observed within specific regions such as the somatosensory cortex (SSC). Further histopathological examination of these brain areas indicated the presence of activated resident glia and recruited immune cells accompanied by limited alterations of neuronal viability. In vivo diffusion-tensor MRI analysis of neuronal fiber density within the infected regions revealed connectivity abnormalities in the SSC. Altered fiber density was confirmed by morphological analysis of individual, pyramidal and granule neurons, showing a reduction in dendritic arbor and spine density within the SSC, as well as in the hippocampus. Evaluation of synapse efficacy revealed diminished levels of two key synaptic proteins, PSD95 and synaptophysin, within the same brain areas, indicating deficits in functionality of the synaptic neurotransmission in infected mice. Our results demonstrate that persistent T. gondii infection in a murine model results in synaptic deficits within brain structures leading to disturbances in the morphology of noninfected neurons and modified brain connectivity, suggesting a potential explanation for the behavioral and neuropsychiatric alterations.

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Structural abnormalities in axons and dendrites were observed within the cortex of T. gondii-infected mice. Immunofluorescence stainings with the neuronal cytoskeleton marker anti-pan-neuronal neurofilament (SMI311) revealed structural abnormalities in the axons and dendritic trees within the SSC (boundaries shown by lines in A,E) of T. gondii-infected (E,F) versus control (A,B) mice. Detailed examination of the cortical layers (dashed squares) demonstrated defective morphology of noninfected pyramidal neurons of chronically infected mice (G, arrows), as indicated by reduced expression of SMI311, in contrast to normal expression in control animals (C, arrows). Parallel immunofluorescence staining against microtubule associated protein-2 (MAP2) confirmed the structural alterations of the dendrites within the SSC of T. gondii-infected mice (H, arrows) versus control mice (D, arrows). Five to six coronal slides per mouse were analyzed; n=3–4 mice per group. Scale bars: 1 mm in A and E, 200 μm in B and F, 50 μm in C and G, 100 μm in D and H. (I) Western blot analysis of MAP2 content in cortical extracts from control and infected mice, alongside GAPDH loading controls. Histograms indicate densitometric analysis of blots, expressed as mean±s.e.m. Analysis was performed in three independent experiments. The circles show individual values, from one representative experiment. *P<0.05.
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f3-0070459: Structural abnormalities in axons and dendrites were observed within the cortex of T. gondii-infected mice. Immunofluorescence stainings with the neuronal cytoskeleton marker anti-pan-neuronal neurofilament (SMI311) revealed structural abnormalities in the axons and dendritic trees within the SSC (boundaries shown by lines in A,E) of T. gondii-infected (E,F) versus control (A,B) mice. Detailed examination of the cortical layers (dashed squares) demonstrated defective morphology of noninfected pyramidal neurons of chronically infected mice (G, arrows), as indicated by reduced expression of SMI311, in contrast to normal expression in control animals (C, arrows). Parallel immunofluorescence staining against microtubule associated protein-2 (MAP2) confirmed the structural alterations of the dendrites within the SSC of T. gondii-infected mice (H, arrows) versus control mice (D, arrows). Five to six coronal slides per mouse were analyzed; n=3–4 mice per group. Scale bars: 1 mm in A and E, 200 μm in B and F, 50 μm in C and G, 100 μm in D and H. (I) Western blot analysis of MAP2 content in cortical extracts from control and infected mice, alongside GAPDH loading controls. Histograms indicate densitometric analysis of blots, expressed as mean±s.e.m. Analysis was performed in three independent experiments. The circles show individual values, from one representative experiment. *P<0.05.

Mentions: To investigate the impact of T. gondii infection on the mouse brain neuronal wiring, we performed a detailed qualitative and quantitative analysis of brain connectional microstructure using in vivo DT-MRI and high-resolution fiber mapping (hrFM). We adopted a novel fiber tracking and mapping methodology (Harsan et al., 2013), which provided fine-grained maps of the living mouse brain structural connectivity (Fig. 2A,B, hrFM). At first, we focused our investigation on the somatosensory cortical areas, showing the highest density of hypointense lesions on T2*-weighted images of the infected mice (Fig. 2). hrFM revealed an altered connectivity pattern with a loss in fiber coherence and density at the lesion sites (Fig. 2B, arrows). Using a special reconstruction algorithm (Reisert et al., 2011; Calamante et al., 2012), the resolution of the final fiber maps was increased by eight times (final resolution of 19.2×19.2×62 μm3) versus the scale of the original DT-MRI data. This allows a close comparison with the cortical pattern of axonal cytoskeletal proteins evaluated ex vivo with immunofluorescence (Fig. 3). The impaired cortical connectivity blueprints depicted in vivo in T. gondii-infected brains (Fig. 2B, hrFM) were paralleled by the observation of an abnormal expression pattern of the axonal and dendritic cytoskeleton markers pan-neuronal neurofilament (SMI311; Fig. 3A,F,G) and microtubule associated protein-2 (MAP2; Fig. 3H) in the same cortical areas. Clear reductions of the SMI311 and MAP2 immunofluorescence signals were detected, unraveling structural abnormalities along the cortical (Fig. 3) and hippocampal (supplementary material Fig. S2) dendritic trees in infected mice. Further analysis by western blot revealed a significant reduction in MAP2 content in the cortical extracts in T. gondii-infected mice (Fig. 3I; relative intensities normalized to GAPDH: control animals, 0.74±0.12; T. gondii-infected mice, 0.32±0.08; P=0.02; unpaired Student’s t-test). However, such modifications would not only involve the local cortical connectivity, but would influence the overall brain fiber microstructure and wiring.


Chronic murine toxoplasmosis is defined by subtle changes in neuronal connectivity.

Parlog A, Harsan LA, Zagrebelsky M, Weller M, von Elverfeldt D, Mawrin C, Korte M, Dunay IR - Dis Model Mech (2014)

Structural abnormalities in axons and dendrites were observed within the cortex of T. gondii-infected mice. Immunofluorescence stainings with the neuronal cytoskeleton marker anti-pan-neuronal neurofilament (SMI311) revealed structural abnormalities in the axons and dendritic trees within the SSC (boundaries shown by lines in A,E) of T. gondii-infected (E,F) versus control (A,B) mice. Detailed examination of the cortical layers (dashed squares) demonstrated defective morphology of noninfected pyramidal neurons of chronically infected mice (G, arrows), as indicated by reduced expression of SMI311, in contrast to normal expression in control animals (C, arrows). Parallel immunofluorescence staining against microtubule associated protein-2 (MAP2) confirmed the structural alterations of the dendrites within the SSC of T. gondii-infected mice (H, arrows) versus control mice (D, arrows). Five to six coronal slides per mouse were analyzed; n=3–4 mice per group. Scale bars: 1 mm in A and E, 200 μm in B and F, 50 μm in C and G, 100 μm in D and H. (I) Western blot analysis of MAP2 content in cortical extracts from control and infected mice, alongside GAPDH loading controls. Histograms indicate densitometric analysis of blots, expressed as mean±s.e.m. Analysis was performed in three independent experiments. The circles show individual values, from one representative experiment. *P<0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

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f3-0070459: Structural abnormalities in axons and dendrites were observed within the cortex of T. gondii-infected mice. Immunofluorescence stainings with the neuronal cytoskeleton marker anti-pan-neuronal neurofilament (SMI311) revealed structural abnormalities in the axons and dendritic trees within the SSC (boundaries shown by lines in A,E) of T. gondii-infected (E,F) versus control (A,B) mice. Detailed examination of the cortical layers (dashed squares) demonstrated defective morphology of noninfected pyramidal neurons of chronically infected mice (G, arrows), as indicated by reduced expression of SMI311, in contrast to normal expression in control animals (C, arrows). Parallel immunofluorescence staining against microtubule associated protein-2 (MAP2) confirmed the structural alterations of the dendrites within the SSC of T. gondii-infected mice (H, arrows) versus control mice (D, arrows). Five to six coronal slides per mouse were analyzed; n=3–4 mice per group. Scale bars: 1 mm in A and E, 200 μm in B and F, 50 μm in C and G, 100 μm in D and H. (I) Western blot analysis of MAP2 content in cortical extracts from control and infected mice, alongside GAPDH loading controls. Histograms indicate densitometric analysis of blots, expressed as mean±s.e.m. Analysis was performed in three independent experiments. The circles show individual values, from one representative experiment. *P<0.05.
Mentions: To investigate the impact of T. gondii infection on the mouse brain neuronal wiring, we performed a detailed qualitative and quantitative analysis of brain connectional microstructure using in vivo DT-MRI and high-resolution fiber mapping (hrFM). We adopted a novel fiber tracking and mapping methodology (Harsan et al., 2013), which provided fine-grained maps of the living mouse brain structural connectivity (Fig. 2A,B, hrFM). At first, we focused our investigation on the somatosensory cortical areas, showing the highest density of hypointense lesions on T2*-weighted images of the infected mice (Fig. 2). hrFM revealed an altered connectivity pattern with a loss in fiber coherence and density at the lesion sites (Fig. 2B, arrows). Using a special reconstruction algorithm (Reisert et al., 2011; Calamante et al., 2012), the resolution of the final fiber maps was increased by eight times (final resolution of 19.2×19.2×62 μm3) versus the scale of the original DT-MRI data. This allows a close comparison with the cortical pattern of axonal cytoskeletal proteins evaluated ex vivo with immunofluorescence (Fig. 3). The impaired cortical connectivity blueprints depicted in vivo in T. gondii-infected brains (Fig. 2B, hrFM) were paralleled by the observation of an abnormal expression pattern of the axonal and dendritic cytoskeleton markers pan-neuronal neurofilament (SMI311; Fig. 3A,F,G) and microtubule associated protein-2 (MAP2; Fig. 3H) in the same cortical areas. Clear reductions of the SMI311 and MAP2 immunofluorescence signals were detected, unraveling structural abnormalities along the cortical (Fig. 3) and hippocampal (supplementary material Fig. S2) dendritic trees in infected mice. Further analysis by western blot revealed a significant reduction in MAP2 content in the cortical extracts in T. gondii-infected mice (Fig. 3I; relative intensities normalized to GAPDH: control animals, 0.74±0.12; T. gondii-infected mice, 0.32±0.08; P=0.02; unpaired Student’s t-test). However, such modifications would not only involve the local cortical connectivity, but would influence the overall brain fiber microstructure and wiring.

Bottom Line: Recent studies correlate chronic Toxoplasma gondii (T. gondii) infection with behavioral changes in rodents; additionally, seropositivity in humans is reported to be associated with behavioral and neuropsychiatric diseases.Altered fiber density was confirmed by morphological analysis of individual, pyramidal and granule neurons, showing a reduction in dendritic arbor and spine density within the SSC, as well as in the hippocampus.Our results demonstrate that persistent T. gondii infection in a murine model results in synaptic deficits within brain structures leading to disturbances in the morphology of noninfected neurons and modified brain connectivity, suggesting a potential explanation for the behavioral and neuropsychiatric alterations.

View Article: PubMed Central - PubMed

Affiliation: Institute of Medical Microbiology, Otto-von-Guericke University, 39120-Magdeburg, Germany.

ABSTRACT
Recent studies correlate chronic Toxoplasma gondii (T. gondii) infection with behavioral changes in rodents; additionally, seropositivity in humans is reported to be associated with behavioral and neuropsychiatric diseases. In this study we investigated whether the described behavioral changes in a murine model of chronic toxoplasmosis are associated with changes in synaptic plasticity and brain neuronal circuitry. In mice chronically infected with T. gondii, magnetic resonance imaging (MRI) data analysis displayed the presence of heterogeneous lesions scattered throughout all brain areas. However, a higher density of lesions was observed within specific regions such as the somatosensory cortex (SSC). Further histopathological examination of these brain areas indicated the presence of activated resident glia and recruited immune cells accompanied by limited alterations of neuronal viability. In vivo diffusion-tensor MRI analysis of neuronal fiber density within the infected regions revealed connectivity abnormalities in the SSC. Altered fiber density was confirmed by morphological analysis of individual, pyramidal and granule neurons, showing a reduction in dendritic arbor and spine density within the SSC, as well as in the hippocampus. Evaluation of synapse efficacy revealed diminished levels of two key synaptic proteins, PSD95 and synaptophysin, within the same brain areas, indicating deficits in functionality of the synaptic neurotransmission in infected mice. Our results demonstrate that persistent T. gondii infection in a murine model results in synaptic deficits within brain structures leading to disturbances in the morphology of noninfected neurons and modified brain connectivity, suggesting a potential explanation for the behavioral and neuropsychiatric alterations.

Show MeSH
Related in: MedlinePlus