Acute and delayed neuroinflammatory response following experimental penetrating ballistic brain injury in the rat.
BACKGROUND
Neuroinflammation following acute brain trauma is considered to play a prominent role in both the pathological and reconstructive response of the brain to injury. Here we characterize and contrast both an acute and delayed phase of inflammation following experimental penetrating ballistic brain injury (PBBI) in rats out to 7 days post-injury.


METHODS
Quantitative real time PCR (QRT-PCR) was used to evaluate changes in inflammatory gene expression from the brain tissue of rats exposed to a unilateral frontal PBBI. Brain histopathology was assessed using hematoxylin and eosin (H&E), silver staining, and immunoreactivity for astrocytes (GFAP), microglia (OX-18) and the inflammatory proteins IL-1beta and ICAM-1.


RESULTS
Time course analysis of gene expression levels using QRT-PCR indicated a peak increase during the acute phase of the injury between 3-6 h for the cytokines TNF-alpha (8-11 fold), IL-1beta (11-13 fold), and IL-6 (40-74 fold) as well as the cellular adhesion molecules VCAM (2-3 fold), ICAM-1 (7-15 fold), and E-selectin (11-13 fold). Consistent with the upregulation of pro-inflammatory genes, peripheral blood cell infiltration was a prominent post-injury event with peak levels of infiltrating neutrophils (24 h) and macrophages (72 h) observed throughout the core lesion. In regions of the forebrain immediately surrounding the lesion, strong immunoreactivity for activated astrocytes (GFAP) was observed as early as 6 h post-injury followed by prominent microglial reactivity (OX-18) at 72 h and resolution of both cell types in cortical brain regions by day 7. Delayed thalamic inflammation (remote from the primary lesion) was also observed as indicated by both microglial and astrocyte reactivity (72 h to 7 days) concomitant with the presence of fiber degeneration (silver staining).


CONCLUSIONS
In summary, PBBI induces both an acute and delayed neuroinflammatory response occurring in distinct brain regions, which may provide useful diagnostic information for the treatment of this type of brain injury.
Williams
Anthony J
AJ
Walter Reed Army Institute of Research, Dept. of Applied Neurobiology, Silver Spring, MD, USA. anthony.williams@na.amedd.army.mil <anthony.williams@na.amedd.army.mil>
Wei
Hans H
HH
Dave
Jitendra R
JR
Tortella
Frank C
FC
D000818:Animals; D001253:Astrocytes / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D001921:Brain / Q000276:immunology / Q000378:metabolism / Q000473:pathology*; D005904:Glial Fibrillary Acidic Protein / Q000096:biosynthesis; D020197:Head Injuries, Penetrating / Q000276:immunology / Q000378:metabolism / Q000473:pathology*; D018836:Inflammation Mediators / Q000502:physiology*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D014948:Wounds, Gunshot / Q000276:immunology / Q000378:metabolism / Q000473:pathology*
D005904:Glial Fibrillary Acidic Protein; D018836:Inflammation Mediators