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Repetitive Model of Mild Traumatic Brain Injury Produces Cortical Abnormalities Detectable by Magnetic Resonance Diffusion Imaging, Histopathology, and Behavior

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ABSTRACT

Noninvasive detection of mild traumatic brain injury (mTBI) is important for evaluating acute through chronic effects of head injuries, particularly after repetitive impacts. To better detect abnormalities from mTBI, we performed longitudinal studies (baseline, 3, 6, and 42 days) using magnetic resonance diffusion tensor imaging (DTI) and diffusion kurtosis imaging (DKI) in adult mice after repetitive mTBI (r-mTBI; daily × 5) or sham procedure. This r-mTBI produced righting reflex delay and was first characterized in the corpus callosum to demonstrate low levels of axon damage, astrogliosis, and microglial activation, without microhemorrhages. High-resolution DTI-DKI was then combined with post-imaging pathological validation along with behavioral assessments targeted for the impact regions. In the corpus callosum, only DTI fractional anisotropy at 42 days showed significant change post-injury. Conversely, cortical regions under the impact site (M1–M2, anterior cingulate) had reduced axial diffusivity (AD) at all time points with a corresponding increase in axial kurtosis (Ka) at 6 days. Post-imaging neuropathology showed microglial activation in both the corpus callosum and cortex at 42 days after r-mTBI. Increased cortical microglial activation correlated with decreased cortical AD after r-mTBI (r = −0.853; n = 5). Using Thy1-YFP-16 mice to fluorescently label neuronal cell bodies and processes revealed low levels of axon damage in the cortex after r-mTBI. Finally, r-mTBI produced social deficits consistent with the function of this anterior cingulate region of cortex. Overall, vulnerability of cortical regions is demonstrated after mild repetitive injury, with underlying differences of DTI and DKI, microglial activation, and behavioral deficits.

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r-mTBI does not alter myelination at 6 weeks post-injury. (A and B) Immunohistochemistry for myelin oligodendrocyte glycoprotein (MOG) to study myelination status post-imaging. No change of myelination was visible in either corpus callosum or cortex after r-mTBI (B) compared to r-sham (A), which was confirmed by quantification of MOG (E and G). (C and D) Oligodendrocyte progenitors, detected by immunolabeling for NG2 (C and D), also were not changed in either corpus callosum (F) or cortex (H) after r-mTBI compared to r-sham. Dashed lines outline the corpus callosum. n = 6 for MOG; n = 3 for NG2; values are mean ± standard error of the mean; scale bars = 50 μm. NG2, neural antigen 2; r-mTBI, repetitive mild traumatic brain injury; r-sham, repetitive sham.
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f6: r-mTBI does not alter myelination at 6 weeks post-injury. (A and B) Immunohistochemistry for myelin oligodendrocyte glycoprotein (MOG) to study myelination status post-imaging. No change of myelination was visible in either corpus callosum or cortex after r-mTBI (B) compared to r-sham (A), which was confirmed by quantification of MOG (E and G). (C and D) Oligodendrocyte progenitors, detected by immunolabeling for NG2 (C and D), also were not changed in either corpus callosum (F) or cortex (H) after r-mTBI compared to r-sham. Dashed lines outline the corpus callosum. n = 6 for MOG; n = 3 for NG2; values are mean ± standard error of the mean; scale bars = 50 μm. NG2, neural antigen 2; r-mTBI, repetitive mild traumatic brain injury; r-sham, repetitive sham.

Mentions: We next examined changes related to myelination (Fig. 6). Immunohistochemistry for MOG myelin protein correlates well with electron microscopy and Luxol fast blue myelin stain to estimate demyelination within the corpus callosum.44,45 After r-mTBI, MOG immunolabeling was examined both in the corpus callosum as well as in the cortex to explore the basis for the changes observed in cortical DTI/DKI (Fig. 6A,B). MOG in r-mTBI mice was not changed from r-sham levels for the corpus callosum (Fig. 6E), and the reduction in the cortex did not reach significance (Fig. 6G; p = 0.083; power = 99%). Post-imaging analysis of the s-mTBI model cohort for MOG immunostaining detected subtle diffuse demyelination (Supplementary Fig. 4) (see online supplementary material at http://www.liebertpub.com), consistent with demyelination observed by electron microscopy in this model at 6 weeks post-TBI.31


Repetitive Model of Mild Traumatic Brain Injury Produces Cortical Abnormalities Detectable by Magnetic Resonance Diffusion Imaging, Histopathology, and Behavior
r-mTBI does not alter myelination at 6 weeks post-injury. (A and B) Immunohistochemistry for myelin oligodendrocyte glycoprotein (MOG) to study myelination status post-imaging. No change of myelination was visible in either corpus callosum or cortex after r-mTBI (B) compared to r-sham (A), which was confirmed by quantification of MOG (E and G). (C and D) Oligodendrocyte progenitors, detected by immunolabeling for NG2 (C and D), also were not changed in either corpus callosum (F) or cortex (H) after r-mTBI compared to r-sham. Dashed lines outline the corpus callosum. n = 6 for MOG; n = 3 for NG2; values are mean ± standard error of the mean; scale bars = 50 μm. NG2, neural antigen 2; r-mTBI, repetitive mild traumatic brain injury; r-sham, repetitive sham.
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f6: r-mTBI does not alter myelination at 6 weeks post-injury. (A and B) Immunohistochemistry for myelin oligodendrocyte glycoprotein (MOG) to study myelination status post-imaging. No change of myelination was visible in either corpus callosum or cortex after r-mTBI (B) compared to r-sham (A), which was confirmed by quantification of MOG (E and G). (C and D) Oligodendrocyte progenitors, detected by immunolabeling for NG2 (C and D), also were not changed in either corpus callosum (F) or cortex (H) after r-mTBI compared to r-sham. Dashed lines outline the corpus callosum. n = 6 for MOG; n = 3 for NG2; values are mean ± standard error of the mean; scale bars = 50 μm. NG2, neural antigen 2; r-mTBI, repetitive mild traumatic brain injury; r-sham, repetitive sham.
Mentions: We next examined changes related to myelination (Fig. 6). Immunohistochemistry for MOG myelin protein correlates well with electron microscopy and Luxol fast blue myelin stain to estimate demyelination within the corpus callosum.44,45 After r-mTBI, MOG immunolabeling was examined both in the corpus callosum as well as in the cortex to explore the basis for the changes observed in cortical DTI/DKI (Fig. 6A,B). MOG in r-mTBI mice was not changed from r-sham levels for the corpus callosum (Fig. 6E), and the reduction in the cortex did not reach significance (Fig. 6G; p = 0.083; power = 99%). Post-imaging analysis of the s-mTBI model cohort for MOG immunostaining detected subtle diffuse demyelination (Supplementary Fig. 4) (see online supplementary material at http://www.liebertpub.com), consistent with demyelination observed by electron microscopy in this model at 6 weeks post-TBI.31

View Article: PubMed Central - PubMed

ABSTRACT

Noninvasive detection of mild traumatic brain injury (mTBI) is important for evaluating acute through chronic effects of head injuries, particularly after repetitive impacts. To better detect abnormalities from mTBI, we performed longitudinal studies (baseline, 3, 6, and 42 days) using magnetic resonance diffusion tensor imaging (DTI) and diffusion kurtosis imaging (DKI) in adult mice after repetitive mTBI (r-mTBI; daily × 5) or sham procedure. This r-mTBI produced righting reflex delay and was first characterized in the corpus callosum to demonstrate low levels of axon damage, astrogliosis, and microglial activation, without microhemorrhages. High-resolution DTI-DKI was then combined with post-imaging pathological validation along with behavioral assessments targeted for the impact regions. In the corpus callosum, only DTI fractional anisotropy at 42 days showed significant change post-injury. Conversely, cortical regions under the impact site (M1–M2, anterior cingulate) had reduced axial diffusivity (AD) at all time points with a corresponding increase in axial kurtosis (Ka) at 6 days. Post-imaging neuropathology showed microglial activation in both the corpus callosum and cortex at 42 days after r-mTBI. Increased cortical microglial activation correlated with decreased cortical AD after r-mTBI (r = −0.853; n = 5). Using Thy1-YFP-16 mice to fluorescently label neuronal cell bodies and processes revealed low levels of axon damage in the cortex after r-mTBI. Finally, r-mTBI produced social deficits consistent with the function of this anterior cingulate region of cortex. Overall, vulnerability of cortical regions is demonstrated after mild repetitive injury, with underlying differences of DTI and DKI, microglial activation, and behavioral deficits.

No MeSH data available.


Related in: MedlinePlus