Abstract:

Objective To explore the glial response and the relationship with secondary axonal degeneration in rats after diffuse axonal injury (DAI). Methods Adult male Sprague-Dawley rats were randomly assigned to control or DAI groups sacrificed at 1, 2, 3, 5 and 7 days with 10 rats in each group. DAI model was made referring to modified Marmarou method and glial fibrillary acidic protein(GFAP), ionized calcium binding adaptor molecule-1 (Iba1), recombinant oligodendrocyte lineage transcription factor 2 (Olig2), CC-1, NG2 immunohistochemistry, TUNEL staining and transmission electron microscopy were performed in brain stem.
Results The number of Iba1 labeled positive cells was significantly increased at day 3 and day 7 after injury. Moreover, different hypertrophic morphology was identified after injury. There was no effect of DAI on GFAP expression in brain stem. Numbers of mature oligodendrocyte marker CC-1 immunoreactivity cells within brain stem were significantly decreased at each of the time points after injury. The number of TUNEL positive cells in brain stem was significantly increased with injured time. Olig2 expression was significantly increased throughout the first week and reached peak at day 3 after injury in brain stem. The number of NG2 labeled positive cells was significantly increased at day 3 and day 7 after DAI. Ultrastructural evidence showed myelin release then further developed as widespread delamination and collapse, and leading to degeneration of axonal partner. Conclusion Mature oligodendrocytes are vulnerable in DAI and myelin loss may contribute to axonal degeneration. OPCs proliferate with activation of microglia. This insight of glial response will further explain the pathophysiological mechanism of secondary axonal damage in DAI.

Key words: Diffuse axonal injury, Glial cells, Demyelination, Secondary axonal degeneration, Immunohistochemistry, Rat