Repeated mild traumatic brain injury causes focal response in lateral septum and hippocampus.

AIM To advance our understanding of regional and temporal cellular responses to repeated mild traumatic brain injury (rmTBI), we used a mouse model of rmTBI that incorporated acceleration, deceleration and rotational forces. MATERIALS & METHODS A modified weight-drop method was used to compare two inter-injury intervals, rmTBI-short (five hits delivered over 3 days) and rmTBI-long (five hits delivered over 15 days). Regional investigations of forebrain and midbrain histological alterations were performed at three post-injury time points (immediate, 2 weeks and 6 weeks). RESULTS The rmTBI-short protocol generated an immediate, localized microglial and astroglial response in the dorsolateral septum and hippocampus, with the astroglial response persisting in the dorsolateral septum. The rmTBI-long protocol showed only a transitory astroglial response in the dorsolateral septum. CONCLUSION Our results indicate that the lateral septum and hippocampus are particularly vulnerable regions in rmTBI, possibly contributing to memory and emotional impairments associated with repeated concussions.