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Microglia processes associate with diffusely injured axons following mild traumatic brain injury in the micro pig.

Lafrenaye AD, Todani M, Walker SA, Povlishock JT - J Neuroinflammation (2015)

Bottom Line: Mild traumatic brain injury (mTBI) is an all too common occurrence that exacts significant personal and societal costs.The physical relationship between microglia and DAI, assessed via confocal 3D analysis, revealed a dramatic increase in the number of Iba-1+ microglial processes that contacted APP+ proximal axonal swellings compared to uninjured myelinated thalamic axons in sham animals.These findings transform our understanding of acute neuroinflammation following mTBI and may suggest its potential as a diagnostic and/or a therapeutic target.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy and Neurobiology, Virginia Commonwealth University Medical Center, P.O. Box 980709, Richmond, VA, 23298, USA. forrestad@vcu.edu.

ABSTRACT

Background: Mild traumatic brain injury (mTBI) is an all too common occurrence that exacts significant personal and societal costs. The pathophysiology of mTBI is complex, with reports routinely correlating diffuse axonal injury (DAI) with prolonged morbidity. Progressive chronic neuroinflammation has also recently been correlated to morbidity, however, the potential association between neuroinflammatory microglia and DAI is not well understood. The majority of studies exploring neuroinflammatory responses to TBI have focused on more chronic phases of injury involving phagocytosis associated with Wallerian change. Little, however, is known regarding the neuroinflammatory response seen acutely following diffuse mTBI and its potential relationship to early DAI. Additionally, while inflammation is drastically different in rodents compared to humans, pigs and humans share very similar inflammatory profiles and responses.

Methods: In the current study, we employed a modified central fluid percussion model in micro pigs. Using this model of diffuse mTBI, paired with various immunohistological endpoints, we assessed the potential association between acute thalamic DAI and neuroinflammation 6 h following injury.

Results: Injured micro pigs displayed substantial axonal damage reflected in the presence of APP+ proximal axonal swellings, which were particularly prominent in the thalamus. In companion, the same thalamic sites displayed extensive neuroinflammation, which was observed using Iba-1 immunohistochemistry. The physical relationship between microglia and DAI, assessed via confocal 3D analysis, revealed a dramatic increase in the number of Iba-1+ microglial processes that contacted APP+ proximal axonal swellings compared to uninjured myelinated thalamic axons in sham animals.

Conclusions: In aggregate, these studies reveal acute microglial process convergence on proximal axonal swellings undergoing DAI, an interaction not previously recognized in the literature. These findings transform our understanding of acute neuroinflammation following mTBI and may suggest its potential as a diagnostic and/or a therapeutic target.

No MeSH data available.


Related in: MedlinePlus

Extensive microglial activation is observed in the micro pig thalamus 6 h following diffuse mTBI. Representative photomicrographs of the microglial marker Iba-1 in the thalamus of sham-injured (a–d) or central fluid percussion injured (e–h) micro pigs. b and f are magnified regions indicated in a and e, and c and d are magnified regions indicated in b and f, respectively. d and h are two-dimensional flattened images of three-dimensional stacks through microglia in the sham (d) or injured thalamus (h). Note that the microglia appear ramified in sham-injured animals, indicating a quiescent state. While ramified microglia are present in brain-injured pigs, a large proportion of microglia have retracted, amoeboid or stellate morphologies, indicating activation. Bar graphs illustrating the degree of microglial activation in the thalamus (i) as well as the average soma size (j), average process length (k), average process number (l), average number of primary processes (m), and average number of end points (n) per Iba-1+ cell. Scale bar a and e = 1 mm, b and f = 200 μm, c and g = 40 μm, d and h = 10 μm. Graph depicts the mean ± standard error of the mean. *p < 0.05
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Fig5: Extensive microglial activation is observed in the micro pig thalamus 6 h following diffuse mTBI. Representative photomicrographs of the microglial marker Iba-1 in the thalamus of sham-injured (a–d) or central fluid percussion injured (e–h) micro pigs. b and f are magnified regions indicated in a and e, and c and d are magnified regions indicated in b and f, respectively. d and h are two-dimensional flattened images of three-dimensional stacks through microglia in the sham (d) or injured thalamus (h). Note that the microglia appear ramified in sham-injured animals, indicating a quiescent state. While ramified microglia are present in brain-injured pigs, a large proportion of microglia have retracted, amoeboid or stellate morphologies, indicating activation. Bar graphs illustrating the degree of microglial activation in the thalamus (i) as well as the average soma size (j), average process length (k), average process number (l), average number of primary processes (m), and average number of end points (n) per Iba-1+ cell. Scale bar a and e = 1 mm, b and f = 200 μm, c and g = 40 μm, d and h = 10 μm. Graph depicts the mean ± standard error of the mean. *p < 0.05

Mentions: Neuroinflammation, as identified by Iba-1+ microglia with activated morphologies, within the micro pig thalamus was assessed using a graded scale from 0 to 5 (0 = no observed microglial activation and 5 = activated microglia observed in >50 % of the coronal thalamic section; sham n = 3, TBI n = 18). While the microglia within the sham thalami were evenly distributed and primarily non-reactive, with spindly ramified process networks that were lightly labeled with Iba-1, some isolated microglia demonstrated thicker, shorter processes with more substantial Iba-1 labeling (Fig. 5a–d). Following cFPI, however, microglia activation was pervasive, with pockets of morphologically active microglia, exhibiting heavy Iba-1 labeling, thicker processes, and less complex process networks, dispersed throughout the micro pig thalamus (Mann–Whitney U test, p = 0.006; Fig. 5e–h).Fig. 5


Microglia processes associate with diffusely injured axons following mild traumatic brain injury in the micro pig.

Lafrenaye AD, Todani M, Walker SA, Povlishock JT - J Neuroinflammation (2015)

Extensive microglial activation is observed in the micro pig thalamus 6 h following diffuse mTBI. Representative photomicrographs of the microglial marker Iba-1 in the thalamus of sham-injured (a–d) or central fluid percussion injured (e–h) micro pigs. b and f are magnified regions indicated in a and e, and c and d are magnified regions indicated in b and f, respectively. d and h are two-dimensional flattened images of three-dimensional stacks through microglia in the sham (d) or injured thalamus (h). Note that the microglia appear ramified in sham-injured animals, indicating a quiescent state. While ramified microglia are present in brain-injured pigs, a large proportion of microglia have retracted, amoeboid or stellate morphologies, indicating activation. Bar graphs illustrating the degree of microglial activation in the thalamus (i) as well as the average soma size (j), average process length (k), average process number (l), average number of primary processes (m), and average number of end points (n) per Iba-1+ cell. Scale bar a and e = 1 mm, b and f = 200 μm, c and g = 40 μm, d and h = 10 μm. Graph depicts the mean ± standard error of the mean. *p < 0.05
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Fig5: Extensive microglial activation is observed in the micro pig thalamus 6 h following diffuse mTBI. Representative photomicrographs of the microglial marker Iba-1 in the thalamus of sham-injured (a–d) or central fluid percussion injured (e–h) micro pigs. b and f are magnified regions indicated in a and e, and c and d are magnified regions indicated in b and f, respectively. d and h are two-dimensional flattened images of three-dimensional stacks through microglia in the sham (d) or injured thalamus (h). Note that the microglia appear ramified in sham-injured animals, indicating a quiescent state. While ramified microglia are present in brain-injured pigs, a large proportion of microglia have retracted, amoeboid or stellate morphologies, indicating activation. Bar graphs illustrating the degree of microglial activation in the thalamus (i) as well as the average soma size (j), average process length (k), average process number (l), average number of primary processes (m), and average number of end points (n) per Iba-1+ cell. Scale bar a and e = 1 mm, b and f = 200 μm, c and g = 40 μm, d and h = 10 μm. Graph depicts the mean ± standard error of the mean. *p < 0.05
Mentions: Neuroinflammation, as identified by Iba-1+ microglia with activated morphologies, within the micro pig thalamus was assessed using a graded scale from 0 to 5 (0 = no observed microglial activation and 5 = activated microglia observed in >50 % of the coronal thalamic section; sham n = 3, TBI n = 18). While the microglia within the sham thalami were evenly distributed and primarily non-reactive, with spindly ramified process networks that were lightly labeled with Iba-1, some isolated microglia demonstrated thicker, shorter processes with more substantial Iba-1 labeling (Fig. 5a–d). Following cFPI, however, microglia activation was pervasive, with pockets of morphologically active microglia, exhibiting heavy Iba-1 labeling, thicker processes, and less complex process networks, dispersed throughout the micro pig thalamus (Mann–Whitney U test, p = 0.006; Fig. 5e–h).Fig. 5

Bottom Line: Mild traumatic brain injury (mTBI) is an all too common occurrence that exacts significant personal and societal costs.The physical relationship between microglia and DAI, assessed via confocal 3D analysis, revealed a dramatic increase in the number of Iba-1+ microglial processes that contacted APP+ proximal axonal swellings compared to uninjured myelinated thalamic axons in sham animals.These findings transform our understanding of acute neuroinflammation following mTBI and may suggest its potential as a diagnostic and/or a therapeutic target.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy and Neurobiology, Virginia Commonwealth University Medical Center, P.O. Box 980709, Richmond, VA, 23298, USA. forrestad@vcu.edu.

ABSTRACT

Background: Mild traumatic brain injury (mTBI) is an all too common occurrence that exacts significant personal and societal costs. The pathophysiology of mTBI is complex, with reports routinely correlating diffuse axonal injury (DAI) with prolonged morbidity. Progressive chronic neuroinflammation has also recently been correlated to morbidity, however, the potential association between neuroinflammatory microglia and DAI is not well understood. The majority of studies exploring neuroinflammatory responses to TBI have focused on more chronic phases of injury involving phagocytosis associated with Wallerian change. Little, however, is known regarding the neuroinflammatory response seen acutely following diffuse mTBI and its potential relationship to early DAI. Additionally, while inflammation is drastically different in rodents compared to humans, pigs and humans share very similar inflammatory profiles and responses.

Methods: In the current study, we employed a modified central fluid percussion model in micro pigs. Using this model of diffuse mTBI, paired with various immunohistological endpoints, we assessed the potential association between acute thalamic DAI and neuroinflammation 6 h following injury.

Results: Injured micro pigs displayed substantial axonal damage reflected in the presence of APP+ proximal axonal swellings, which were particularly prominent in the thalamus. In companion, the same thalamic sites displayed extensive neuroinflammation, which was observed using Iba-1 immunohistochemistry. The physical relationship between microglia and DAI, assessed via confocal 3D analysis, revealed a dramatic increase in the number of Iba-1+ microglial processes that contacted APP+ proximal axonal swellings compared to uninjured myelinated thalamic axons in sham animals.

Conclusions: In aggregate, these studies reveal acute microglial process convergence on proximal axonal swellings undergoing DAI, an interaction not previously recognized in the literature. These findings transform our understanding of acute neuroinflammation following mTBI and may suggest its potential as a diagnostic and/or a therapeutic target.

No MeSH data available.


Related in: MedlinePlus