The role of perivascular innervation and neurally mediated vasoreactivity in the pathophysiology of Alzheimer's disease

Neuronal death is a hallmark of Alzheimer's disease (AD) and considerable work has been done to understand how the loss of interconnectivity between neurons contributes to the associated dementia. Often overlooked however, is how the loss of neuronal innervation of blood vessels, termed perivascular innervation, may also contribute to the pathogenesis of AD. There is now considerable evidence supporting a crucial role for the neurovascular unit (NVU) in mediating the clearance of the beta-amyloid (A beta) peptide, one of the main pathological constituents of AD, from the brain. Moreover, efficient removal appears to be dependent on the communication of cells within the NVU to maintain adequate vascular tone and pulsatility. This review summarizes the composition of the NVU, including the sources of perivascular innervation and how the NVU mediates A beta clearance from the brain. It also explores evidence supporting the hypothesis that loss of neurally mediated vasoreactivity contributes to A beta pathology in the AD brain.