Hippocampal cognitive impairment in juvenile rats after repeated mild traumatic brain injury.

There is growing awareness that repeated mild traumatic brain injury (r-mTBI) can cause deficits in learning and memory performance, however there is still a paucity of preclinical data identifying the extent of these deficits. Epidemiological data shows that juveniles are at high risk to sustain r-mTBI, and these injuries may cause significant changes in cognitive abilities, as they occur during a period where the brain is still maturing. This is particularly true for the hippocampus, a brain region important for learning and memory processes. R-mTBI during the juvenile period may disrupt functional capacity of the hippocampus, and thus the normal development of cognitive processes associated with this structure. To examine this issue we used a model of awake closed head injury (ACHI) and administered 8 impacts over a 4 day period to juvenile male and female rats (P25-28). A neurological assessment was preformed after each impact, and anxiety and learning related behaviours were examined 1 and 7 days after the last impact. Our results indicate that r-mTBI was associated with sensorimotor deficits in the acute phase immediately after each procedure. R-mTBI also reduced the capacity for hippocampal-dependent learning for at least 7 days post-injury, but did not result in any long-lasting changes in anxiety-related behaviours.