The neuronal cytoskeleton is at risk after mild and moderate brain injury

Recent studies have described alterations in cytoskeletal proteins such as microtubule-associated protein 2 (MAP-2) and neurofilament (NF) resulting from moderate and severe experimental brain injury; however, few have investigated the consequences of mild injury, which is associated clinically and experimentally with cognitive dysfunction and neuronal damage. To contrast cytoskeletal changes within 7 days following mild injury with those following moderate injury, we subjected anesthetized, adult rats to mild (1.1-1.3 atm) or moderate (2.3-2.5 atm) lateral fluid percussion brain injury or sham injury. Rats were sacrificed at 6 h (n=4 mild; n=4 moderate; n=2 sham), 24 h (n=4 mild; n=4 moderate; n=1 sham), or 7 days (n=5 mild; n=4 moderate; n=1 sham) following injury, and immunohistochemistry was performed for MAP-2 and NF. Both mild and moderate injury produced notable cytoskeletal changes in multiple brain regions; however, mild injury generally resulted in a lesser degree of MAP-2 and NF loss over a smaller spatial extent. When compared to moderately injured animals, animals subjected to mild injury showed substantially delayed MAP-2 and NF alterations within the cortex and hippocampal dentate gyrus and no evidence of MAP-2 loss in the hippocampal CA3 region. While mild and moderate injury resulted for the most part in similar patterns of axonal injury, tissue tears in the fimbria and loss of NF immunoreactivity in regions containing injured axons were only observed following moderate injury. Elucidating the effects of modulating injury severity may yield insight into the mechanisms involved in traumatic damage to the cytoskeleton and guide future treatment strategies.