Memantine Mitigates Oligodendrocyte Damage after Repetitive Mild Traumatic Brain Injury

Repetitive mild traumatic brain injury (rmTBI; e.g., sports concussions) is common and results in significant cognitive impairment, white matter injury and increased risk of neurodegeneration. Targeted therapies for rmTBI are lacking, though evidence from other injury models indicates that targeting N-methyl-d-aspartate (NMDA) receptor (NMDAR)-mediated glutamatergic toxicity might mitigate rmTBI-induced injury. We have previously shown that the NMDAR antagonist memantine lessens axonal injury and restores long term potentiation after rmTBI. Here, we evaluated whether the protective effects of memantine include oligodendrocyte specific mechanisms, as prior studies suggest that oligodendrocytes are particularly vulnerable to glutamatergic toxicity. Mice were subjected to rmTBI injury (5 injuries in 5 days) and randomized to treatment with memantine or with vehicle (n = 32/group). At the molecular level, oligodendrocyte counts and function (myelin basic protein, MBP) were assessed by immunohistochemistry and western blot at days 3, 7 and 28 days after the last injury. Axon integrity was assessed by neurofilament light chain (NF-l) expression and axonal ultrastructure was evaluated by electron microscopy. Compared to vehicle-treated mice, memantine-treated mice were protected against oligodendrocyte loss and decreased MBP expression at subacute time points after injury. Memantine treatment also protected against axon damage assessed by NF-l expression. These data suggest that the therapeutic effects of post-concussive NMDAR antagonism may in part work through oligodendrocyte specific mechanisms, which may have implications for long term neurodegenerative sequelae after multiple concussions.