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

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

Characterization of the progression of pathology in the corpus callosum in a repetitive mild traumatic brain injury (r-mTBI) model. (A and B) Post-surgical data for r-mTBI. Apnea was not detected (nd) in r-sham mice (A), but was significantly increased after the first and the second impact in r-mTBI mice (A). The righting time is significantly delayed in r-mTBI versus r-sham mice (B). (C–E) Immunohistochemistry for β-APP is present mainly in neuronal cell bodies in r-sham mice (C). β-APP accumulations are readily detected in damaged axons (arrows) in r-mTBI mice acutely (D), but less marked by 7 days post-injury (E). (F–H) Immunohistochemistry for CD11b identifies microglia, which exhibit a resting phenotype in r-sham mice (F) with progressive activation evident at 24 h (G) and 7 days (H). (I–K) Immunohistochemistry for GFAP identifies astrocytes that have normal morphology in r-sham mice (I) and increasing cells with a reactive phenotype in r-mTBI mice between 24 h (J) and 7 days (K). (L–O) Quantification of immunohistochemistry in the corpus callosum. Axonal profiles with β-APP accumulations were increased very early after r-mTBI mice (L). Astrogliosis increases over the first week after r-mTBI (M). Microglial activation also increases significantly over the first week based on area of CD11b immunoreactivity (N) and an earlier reaction is detected by counting activated cells, which have intense CD11b and shorter, thicker processes (O). Dashed lines outline the corpus callosum. Values are mean ± standard error of the mean; n = 30 for post-surgical data; n = 5 per condition for histology data; scale bar (E), (H), and (K) = 50 μm; *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001. β-APP, beta amyloid precursor protein; GFAP, glial fibrillary acidic protein; r-sham, repetitive sham.
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f1: Characterization of the progression of pathology in the corpus callosum in a repetitive mild traumatic brain injury (r-mTBI) model. (A and B) Post-surgical data for r-mTBI. Apnea was not detected (nd) in r-sham mice (A), but was significantly increased after the first and the second impact in r-mTBI mice (A). The righting time is significantly delayed in r-mTBI versus r-sham mice (B). (C–E) Immunohistochemistry for β-APP is present mainly in neuronal cell bodies in r-sham mice (C). β-APP accumulations are readily detected in damaged axons (arrows) in r-mTBI mice acutely (D), but less marked by 7 days post-injury (E). (F–H) Immunohistochemistry for CD11b identifies microglia, which exhibit a resting phenotype in r-sham mice (F) with progressive activation evident at 24 h (G) and 7 days (H). (I–K) Immunohistochemistry for GFAP identifies astrocytes that have normal morphology in r-sham mice (I) and increasing cells with a reactive phenotype in r-mTBI mice between 24 h (J) and 7 days (K). (L–O) Quantification of immunohistochemistry in the corpus callosum. Axonal profiles with β-APP accumulations were increased very early after r-mTBI mice (L). Astrogliosis increases over the first week after r-mTBI (M). Microglial activation also increases significantly over the first week based on area of CD11b immunoreactivity (N) and an earlier reaction is detected by counting activated cells, which have intense CD11b and shorter, thicker processes (O). Dashed lines outline the corpus callosum. Values are mean ± standard error of the mean; n = 30 for post-surgical data; n = 5 per condition for histology data; scale bar (E), (H), and (K) = 50 μm; *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001. β-APP, beta amyloid precursor protein; GFAP, glial fibrillary acidic protein; r-sham, repetitive sham.

Mentions: The parameters of the r-mTBI model were based on pilot testing of multiple protocols (data not shown). An Impact One Stereotaxic Impactor (Leica, Wetzlar, Germany) was used to produce r-mTBI concussive impacts. A series of five impacts separated by 24-h intervals was chosen to target the period of decreased glucose uptake observed 24 h after a single mTBI in rats.30 Mice were anesthetized with 2.0% isoflurane in O2 and then the hair was shaved and depilated with Nair. Mice were positioned in a stereotaxic frame with rubber stoppers inserted between the external ear canal and ear bar. Impacts were made onto the skin approximately over bregma using a 3-mm-diameter tip (velocity set at 4.0 m/sec; depth of 1.0 mm; dwell time of 200 ms). Sham mice underwent identical procedures to the r-mTBI mice without receiving impacts. Body temperature was maintained with a warming pad. After each procedure, the duration of apnea and the righting reflex were recorded (Fig. 1). The repetitive injury study included 30 r-mTBI mice and 30 r-sham mice. A single impact (s-mTBI) model has been previously characterized31 and is included as supplementary data (Supplementary Fig. 1) (see online supplementary material at http://www.liebertpub.com) for direct comparison of assessment techniques with the novel r-mTBI model through 6 weeks post-injury.


Repetitive Model of Mild Traumatic Brain Injury Produces Cortical Abnormalities Detectable by Magnetic Resonance Diffusion Imaging, Histopathology, and Behavior
Characterization of the progression of pathology in the corpus callosum in a repetitive mild traumatic brain injury (r-mTBI) model. (A and B) Post-surgical data for r-mTBI. Apnea was not detected (nd) in r-sham mice (A), but was significantly increased after the first and the second impact in r-mTBI mice (A). The righting time is significantly delayed in r-mTBI versus r-sham mice (B). (C–E) Immunohistochemistry for β-APP is present mainly in neuronal cell bodies in r-sham mice (C). β-APP accumulations are readily detected in damaged axons (arrows) in r-mTBI mice acutely (D), but less marked by 7 days post-injury (E). (F–H) Immunohistochemistry for CD11b identifies microglia, which exhibit a resting phenotype in r-sham mice (F) with progressive activation evident at 24 h (G) and 7 days (H). (I–K) Immunohistochemistry for GFAP identifies astrocytes that have normal morphology in r-sham mice (I) and increasing cells with a reactive phenotype in r-mTBI mice between 24 h (J) and 7 days (K). (L–O) Quantification of immunohistochemistry in the corpus callosum. Axonal profiles with β-APP accumulations were increased very early after r-mTBI mice (L). Astrogliosis increases over the first week after r-mTBI (M). Microglial activation also increases significantly over the first week based on area of CD11b immunoreactivity (N) and an earlier reaction is detected by counting activated cells, which have intense CD11b and shorter, thicker processes (O). Dashed lines outline the corpus callosum. Values are mean ± standard error of the mean; n = 30 for post-surgical data; n = 5 per condition for histology data; scale bar (E), (H), and (K) = 50 μm; *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001. β-APP, beta amyloid precursor protein; GFAP, glial fibrillary acidic protein; r-sham, repetitive sham.
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f1: Characterization of the progression of pathology in the corpus callosum in a repetitive mild traumatic brain injury (r-mTBI) model. (A and B) Post-surgical data for r-mTBI. Apnea was not detected (nd) in r-sham mice (A), but was significantly increased after the first and the second impact in r-mTBI mice (A). The righting time is significantly delayed in r-mTBI versus r-sham mice (B). (C–E) Immunohistochemistry for β-APP is present mainly in neuronal cell bodies in r-sham mice (C). β-APP accumulations are readily detected in damaged axons (arrows) in r-mTBI mice acutely (D), but less marked by 7 days post-injury (E). (F–H) Immunohistochemistry for CD11b identifies microglia, which exhibit a resting phenotype in r-sham mice (F) with progressive activation evident at 24 h (G) and 7 days (H). (I–K) Immunohistochemistry for GFAP identifies astrocytes that have normal morphology in r-sham mice (I) and increasing cells with a reactive phenotype in r-mTBI mice between 24 h (J) and 7 days (K). (L–O) Quantification of immunohistochemistry in the corpus callosum. Axonal profiles with β-APP accumulations were increased very early after r-mTBI mice (L). Astrogliosis increases over the first week after r-mTBI (M). Microglial activation also increases significantly over the first week based on area of CD11b immunoreactivity (N) and an earlier reaction is detected by counting activated cells, which have intense CD11b and shorter, thicker processes (O). Dashed lines outline the corpus callosum. Values are mean ± standard error of the mean; n = 30 for post-surgical data; n = 5 per condition for histology data; scale bar (E), (H), and (K) = 50 μm; *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001. β-APP, beta amyloid precursor protein; GFAP, glial fibrillary acidic protein; r-sham, repetitive sham.
Mentions: The parameters of the r-mTBI model were based on pilot testing of multiple protocols (data not shown). An Impact One Stereotaxic Impactor (Leica, Wetzlar, Germany) was used to produce r-mTBI concussive impacts. A series of five impacts separated by 24-h intervals was chosen to target the period of decreased glucose uptake observed 24 h after a single mTBI in rats.30 Mice were anesthetized with 2.0% isoflurane in O2 and then the hair was shaved and depilated with Nair. Mice were positioned in a stereotaxic frame with rubber stoppers inserted between the external ear canal and ear bar. Impacts were made onto the skin approximately over bregma using a 3-mm-diameter tip (velocity set at 4.0 m/sec; depth of 1.0 mm; dwell time of 200 ms). Sham mice underwent identical procedures to the r-mTBI mice without receiving impacts. Body temperature was maintained with a warming pad. After each procedure, the duration of apnea and the righting reflex were recorded (Fig. 1). The repetitive injury study included 30 r-mTBI mice and 30 r-sham mice. A single impact (s-mTBI) model has been previously characterized31 and is included as supplementary data (Supplementary Fig. 1) (see online supplementary material at http://www.liebertpub.com) for direct comparison of assessment techniques with the novel r-mTBI model through 6 weeks post-injury.

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&thinsp;&times;&thinsp;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&ndash;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&thinsp;=&thinsp;&minus;0.853; n&thinsp;=&thinsp;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