Focused ultrasound opens the blood–brain barrier and reveals an age-dependent dissociation between resting cerebral blood flow and neurovascular coupling

Abstract

Focused ultrasound (FUS) in combination with nanobubbles enables transient, localized opening of the blood–brain barrier (BBB), facilitating targeted therapeutic delivery. However, the cerebrovascular consequences of BBB opening across the lifespan are not fully understood. Here, we compare the effects of FUS-mediated BBB opening on cerebral blood flow (CBF) and neurovascular coupling (NVC) in young and aged mice using functional ultrasound imaging (fUSI), tracer BBB permeability assays, and histology. FUS reliably opened the BBB in both age groups, confirmed by penetration of high-molecular-weight tracers. In aged animals, FUS induced a more pronounced and sustained reduction in resting CBF relative to young controls. Surprisingly, despite lower baseline perfusion, aged mice exhibited preserved or enhanced NVC responses, suggesting that vasodilatory reserve remains intact or sensitized in the aging brain. Immunohistochemistry revealed greater microglial activation after FUS in aged mice, consistent with heightened neuroinflammatory responses. These findings demonstrate an age-dependent dissociation between resting perfusion and activity-evoked vascular responses following BBB opening. Our results highlight both the vulnerabilities and compensatory adaptations of the aging cerebrovasculature, emphasizing the importance of age as a critical variable in the development of FUS-based therapeutic strategies.