title: The Involvement of Pial Microvessels in Leukocyte Invasion after Mild Traumatic Brain Injury.
abstract: The pathophysiological mechanisms underlying mild traumatic brain injury (mTBI) are not well understood, but likely involve neuroinflammation. Here the controlled cortical impact model of mTBI in rats was used to test this hypothesis. Mild TBI caused a rapid (within 6 h post-mTBI) upregulation of synthesis of TNF-α and IL-1β in the cerebral cortex and hippocampus, followed by an increase in production of neutrophil (CXCL1-3) and monocyte (CCL2) chemoattractants. While astrocytes were not a significant source of CXC chemokines, they highly expressed CCL2. An increase in production of CXC chemokines coincided with the influx of neutrophils into the injured brain. At 6 h post-mTBI, we observed a robust influx of CCL2-expressing neutrophils across pial microvessels into the subarachnoid space (SAS) near the injury site. Mild TBI was not accompanied by any significant influx of neutrophils into the brain parenchyma until 24 h after injury. This was associated with an early induction of expression of intercellular adhesion molecule 1 on the endothelium of the ipsilateral pial, but not intraparenchymal, microvessels. At 6 h post-mTBI, we also observed a robust influx of neutrophils into the ipsilateral cistern of velum interpositum (CVI), a slit-shaped cerebrospinal fluid space located above the 3rd ventricle with highly vascularized pia mater. From SAS and CVI, neutrophils appeared to move along the perivascular spaces to enter the brain parenchyma. The monocyte influx was not observed until 24 h post-mTBI, and these inflammatory cells predominantly entered the ipsilateral SAS and CVI, with a limited invasion of brain parenchyma. These observations indicate that the endothelium of pial microvessels responds to injury differently than that of intraparenchymal microvessels, which may be associated with the lack of astrocytic ensheathment of cerebrovascular endothelium in pial microvessels. These findings also suggest that neuroinflammation represents the potential therapeutic target in mTBI.
authors.affiliation: Neurotrauma and Brain Barriers Research Laboratory, Department of Emergency Medicine, Alpert Medical School of Brown University, Providence, Rhode Island, United States of America.
authors.forename: Joanna
authors.identifier: http://orcid.org/0000-0001-7670-0706
authors.initials: J
authors.lastname: Szmydynger-Chodobska
authors.affiliation: Neurotrauma and Brain Barriers Research Laboratory, Department of Emergency Medicine, Alpert Medical School of Brown University, Providence, Rhode Island, United States of America.
authors.forename: Rongzi
authors.initials: R
authors.lastname: Shan
authors.affiliation: Neurotrauma and Brain Barriers Research Laboratory, Department of Emergency Medicine, Alpert Medical School of Brown University, Providence, Rhode Island, United States of America.
authors.forename: Nicole
authors.initials: N
authors.lastname: Thomasian
authors.affiliation: Neurotrauma and Brain Barriers Research Laboratory, Department of Emergency Medicine, Alpert Medical School of Brown University, Providence, Rhode Island, United States of America.
authors.forename: Adam
authors.initials: A
authors.lastname: Chodobski
mesh_terms: D000818:Animals; D000070642:Brain Injuries, Traumatic / Q000276:immunology* / Q000378:metabolism / Q000503:physiopathology*; D018836:Inflammation Mediators / Q000378:metabolism; D007962:Leukocytes / Q000276:immunology* / Q000378:metabolism; D008297:Male; D055806:Microvessels / Q000276:immunology* / Q000378:metabolism; D020556:Neutrophil Infiltration; D010841:Pia Mater / Q000098:blood supply* / Q000276:immunology; D051381:Rats
chemical_list: D018836:Inflammation Mediators