Chronic Cognitive and Cerebrovascular Function Following Mild Traumatic Brain Injury in Rats

Severe traumatic brain injury results in cognitive dysfunction in part due to vascular perturbations. In contrast, the long-term vasculo-cognitive pathophysiology of mild TBI (mTBI) remains unknown. We evaluated mTBI effects on chronic cognitive and cerebrovascular function and assessed their interrelationships. Sprague-Dawley rats received midline fluid percussion injury (N=20) or sham (N=21). Cognitive function was assessed (3- and 6-month novel object recognition (NOR), novel object location (NOL) and temporal order object recognition (TOR)). 6-month cerebral blood flow (CBF) and blood volume (CBV) using contrast MRI and ex vivo pial artery endothelial and smooth muscle-dependent function were measured. mTBI rats showed impaired NOR, with similar (non-significant) trends in NOL/TOR. Regional CBF and CBV were similar in sham and mTBI. NOR correlated with CBF in lateral hippocampus, medial hippocampus and primary somatosensory barrel cortex while inversely correlating with arterial smooth muscle-dependent dilation. 6-month baseline endothelial and smooth muscle-dependent arterial function were similar among mTBI and sham, but post-angiotensin II stimulation, mTBI showed no change in smooth muscle-dependent dilation from baseline response, unlike the reduction in sham. mTBI led to chronic cognitive dysfunction and altered angiotensin II-stimulated smooth muscle-dependent vasoreactivity, a paradigm that could advance understanding of the long-term sequelae of human mild TBI.