In vivo two-photon microscopy imaging of focused ultrasound-mediated glymphatic transport in the mouse brain.

The glymphatic system regulates cerebrospinal fluid (CSF) transport and brain waste clearance. Focused ultrasound combined with microbubbles (FUSMB) has shown feasibility for manipulating glymphatic transport, yet its mechanisms remain poorly understood. In this work, we used in vivo two-photon microscopy to reveal how FUSMB manipulates the CSF tracer transport in the mouse brain. A FUS transducer was confocally aligned with the objective of a two-photon microscope. Fluorescently labeled albumin was infused into the CSF via cisterna magna. FUS sonication was applied following an intravenous injection of microbubbles. Dynamic imaging was performed through a cranial window to record local changes in vessel and tracer dynamics. The fluorescence intensity of the CSF tracer within the treated region decreased rapidly upon FUSMB treatment. Concurrently, vessel deformation was observed, and the fastest diameter changes were observed during FUSMB treatment. A linear correlation was identified between the rate of vessel diameter change and the rate of tracer intensity change. Moreover, given the same rate of vessel diameter change, the tracer intensity changed faster around larger vessels than smaller vessels. These findings offer insight into the potential biophysical mechanism of FUSMB-mediated glymphatic transport.

Introduction

Purpose Transport without BBB opening

Study Objective To determine how focused ultrasound combined with microbubbles (FUSMB) alters cerebrospinal fluid tracer transport and vessel dynamics in the mouse brain using in vivo two-photon microscopy.

Animal model / Human subject Mouse (Mus musculus); strain: None; age: None; sex: None

Disease model Healthy

MRI or image guidance method Confocal alignment with the two-photon microscope objective (two-photon image guidance)

Cargo name and characteristics Fluorescently labeled albumin (protein; CSF tracer infused into the cisterna magna to visualize glymphatic/CSF transport)

Route of administration Cisterna magna infusion (intracisternal)

Outcomes and Safety

Summary of Outcomes Focused ultrasound with microbubbles (FUSMB) rapidly reduced CSF tracer (fluorescent albumin) fluorescence in the treated cortical region and induced vessel deformation, with a linear correlation between the rate of vessel diameter change and the rate of tracer intensity change; for the same diameter-change rate, tracer clearance was faster around larger vessels than smaller ones. The study applied FUS sonication following intravenous microbubble injection but did not report testing multiple FUS parameter sets or identify specific parameter variations as more successful.

Safety-related matter No adverse effects or safety concerns were reported; the paper notes vessel deformation during FUSMB but does not describe any tissue damage or other safety outcomes.

Brain Region

Visualization unavailable

Ultrasound Parameters

Focal Characteristics Focal depth: None; Focal length: None; Aperture size: None

Treatment frequency single session

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