Concussions or mild traumatic brain injuries (mTBIs) are often described and diagnosed by the acute signs and symptoms of neurological dysfunction including weakness, dizziness, disorientation, headaches, and altered mental state. The cellular and physiological mechanisms of neurological dysfunction and acute symptoms are unclear. Spreading depolarizations (SDs) occur after severe TBIs and have recently been identified in closed-skull mouse models of mTBIs. SDs are massive waves of complete depolarization that result in suppression of cortical activity for multiple minutes. Despite the clear disruption of brain physiology after SDs, the role of SDs in the acute neurological dysfunction and acute behavioral deficits following mTBIs remains unclear. We used a closed-skull mouse model of mTBI and a series of behavioral tasks collectively scored as the neurological severity score (NSS) to assess acute behavior. Our results indicate that mTBIs are associated with significant behavioral deficits in the open field and NSS tasks relative to sham-condition animals. The behavioral deficits associated with the mTBI recovered within 3 h. We show here that the presence of mTBI-induced bilateral SDs were significantly associated with the acute behavioral deficits. To identify the role of SDs in the acute behavioral deficits, we used exogenous potassium and optogenetic approaches to induce SDs in the absence of the mTBI. Bilateral SDs alone were associated with similar behavioral deficits in the open field and NSS tasks. Collectively, these studies demonstrate that bilateral SDs are linked to the acute behavioral deficits associated with mTBIs.
Keywords: balance beam; cortical spreading depression; motor deficits; optogenetics; startle response.