title: Tissue vulnerability is increased following repetitive mild traumatic brain injury in the rat.
abstract: Repetitive mild traumatic brain injury (rmTBI) is an important medical concern for active sports and military personnel. Multiple mild injuries may exacerbate tissue damage resulting in cumulative brain injury and poor functional recovery. In the present study, we investigated the time course of brain vulnerability to rmTBI in a rat model of mild cortical controlled impact. An initial mild injury was followed by a second injury unilaterally at an interval of 1, 3, or 7 days. RmTBI animals were compared to single mTBI and sham treated animals. Neuropathology was assessed using multi-modal magnetic resonance imaging (MRI), followed by ex vivo tissue immunohistochemistry. Neurological and behavioral outcomes were evaluated in a subset of animals receiving rmTBI 3 days apart and shams. RmTBI 1 or 3 days apart but not 7 days apart revealed significantly exacerbated MRI-definable lesion volumes compared to single mTBI and shams. Increases in cortical tissue damage, extravascular iron and glial activation assessed by histology/immunohistochemistry correlated with in vivo MRI findings where shorter intervals (1 or 3 days apart) resulted in greater tissue pathology. There were no neurological deficits associated with rmTBI 3 day animals. At 1 mo post-injury, animals with rmTBI 3 days apart showed reduced exploratory behaviors and subtle spatial learning memory impairments were observed. Collectively, our findings suggest that the mildly-impacted brain is more vulnerable to repetitive injury when delivered within 3 days following initial mTBI.
authors.affiliation: Department of Anesthesiology, Loma Linda University, 11234 Anderson Street, Loma Linda, CA 92354, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Huang
authors.forename: Jacqueline S
authors.initials: JS
authors.lastname: Coats
authors.forename: Alena
authors.initials: A
authors.lastname: Mohd-Yusof
authors.forename: Yufang
authors.initials: Y
authors.lastname: Yin
authors.forename: Sarah
authors.initials: S
authors.lastname: Assaad
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Muellner
authors.forename: Joel E
authors.initials: JE
authors.lastname: Kamper
authors.forename: Richard E
authors.initials: RE
authors.lastname: Hartman
authors.forename: Melissa
authors.initials: M
authors.lastname: Dulcich
authors.forename: Virginia M
authors.initials: VM
authors.lastname: Donovan
authors.forename: Udo
authors.initials: U
authors.lastname: Oyoyo
authors.forename: André
authors.initials: A
authors.lastname: Obenaus
mesh_terms: D000818:Animals; D001921:Brain / Q000473:pathology*; D001924:Brain Concussion / Q000473:pathology*; D001930:Brain Injuries / Q000473:pathology; D004195:Disease Models, Animal; D008279:Magnetic Resonance Imaging; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D020127:Recovery of Function