Oligodendrocyte vulnerability following traumatic brain injury in rats

Abstract

Experimental and clinical findings demonstrate that traumatic brain injury (TBI) results in injury to both gray and white matter structures. The purpose of this study was to document patterns of oligodendrocyte vulnerability to TBI. Sprague Dawley rats underwent sham operated procedures or moderate fluid percussion brain injury. Quantitative immunohistochemical analysis was performed on animals perfusion-fixed at 3 (n=9) or 7 (n=9) days post-surgery. Within the ipsilateral external capsule and corpus callosum, numbers of APC-CC1 immunoreactive oligodendrocytes were significantly decreased at 3 or 7 days post-TBI compared to sham rats (p<0.03). At both posttraumatic survival periods, double-labeling studies indicated that oligodendrocytes showed increased Caspase 3 activation compared to sham. These data demonstrate regional patterns of oligodendrocyte vulnerability after TBI and that oligodendrocyte cell loss may be due to Caspase 3-mediated cell death mechanisms. Further studies are needed to test therapeutic interventions that prevent trauma-induced oligodendrocyte cell death, subsequent demyelination and circuit dysfunction.

Figure 1

Micrographs of CC1 immunoreactive oligodendrocytes. Sham (A) animal exhibiting robust staining of CC1 positive cells in the external capsule (B) and corpus callosum (C). In contrast, at 3 days post-TBI animal (D) shows reduced numbers of CC1 positive cells in the external capsule (E) and corpus callosum (F). Magnification 1X (A,D), 10X (B, C, E, F), inset of B, C, E, F (20X).

Figure 2

Confocal micrographs of representative double-labeled CC1 and GFAP immunoreactive cells. CC1 (red) and GFAP (green) positive cells in the external capsule (Row 1) and corpus callosum (Row 2) were investigated in traumatized rats 7 days post injury. CC1 and GFAP colocalization was not observed in these regions of the rat brain (Merged). Bar = 10 microns.

Figure 3

Confocal micrographs of representative double-labeled CC1 (red)/Caspase 3 (green) positive cells in the external capsule. Sham animals showed CC1 positive cells with no Caspase 3 positive cells (Row 1). In contrast, a 3 day TBI animal demonstrates robust double-labeling (merged) of Caspase 3 and CC1 indicating apoptotic cell death of these oligodendrocyte (Row 2, arrows). Bar = 10 microns.

Figure 4

Quantitative assessment of CC1 positive cells within vulnerable white matter regions. A. Representative micrograph indicating where the stereological cell counts were conducted, corpus callosum (a) and external capsule (b). B. T-test was significant (p<0.001) for both time points compared to sham in the corpus callosum. Both 3 and 7 day TBI animals showed significant (*p<0.001) reductions in CC1 positive cells compared to sham. C. T-test was significant (*p<0.02) for the 3 day TBI group compared to sham in the external capsule. These data demonstrate a reduction in the number of CC1 positive cells in the 3 day TBI group compared to sham.