Early Cerebral Blood Flow Changes, Cerebrovascular Reactivity and Cortical Spreading Depolarizations in Experimental Mild Traumatic Brain Injury Model.

To investigate the spatiotemporal dynamics of early cerebral blood flow (CBF) changes, cerebrovascular reactivity (CVR), and vascular responses to cortical spreading depolarization (CSD) in an experimental mild traumatic brain injury (mTBI) model with laser speckle contrast imaging (LSCI) technique. The weight-drop model was used to induce blunt head trauma. The mice were divided into two groups as mild TBI (n=12), and sham (n=6). The animals underwent continuous LSCI before and for 1 hour after trauma to evaluate the regional CBF changes, CVR in response to CO2, and CSD-associated vascular responses induced by pinprick. Our minor blunt head trauma protocol induced CSD in only 2 (16.7%) animals, which were excluded from further analyses. Of the remaining animals, 30% showed slight hyperemia following trauma, with mild ipsilateral hemisphere oligemia (15%?20% decrease in CBF) on average compared to baseline (p=0.027) and contralateral hemisphere (p=0.029). Maximal CBF decrease was measured in the peri-impact area (24.1% ± 5.1%). No significant difference was found between the sham and mTBI groups and two hemispheres of the mTBI group or pre/post-CSD periods of CO2 reactivity, as well as the characteristics of vascular CSD responses (net ischemia: 52.3% ± 2.6% vs. 56.3% ± 1.9% and prolonged oligemia duration 44.8 ± 1.8 min vs. 49.8 ± 2.3 min). The ipsilateral hemisphere, particularly in the peri-impact area, had mild hypoperfusion, within the first hour of minor blunt head trauma in mice. Nonetheless, mTBI does not alter CVR and vascular responses to an induced CSD, thus the overall CVR is largely preserved in mTBI without significant structural damage despite a mildly decreased CBF in the hyperacute phase.