Dynamics of focused ultrasound-enhanced glymphatic transportation in the mouse brain

The glymphatic system, a perivascular network in the brain, regulates the exchange of cerebrospinal fluid and interstitial fluid in the perivascular space. Focused ultrasound combined with microbubbles (FUSMB) has been recently shown feasible to manipulate the glymphatic transportation by enhancing the intranasal delivery of agents in the perivascular space. The objective of this study was to reveal the dynamics of FUSMB-enhanced agent transport in the glymphatic system. A ring-shaped FUS transducer was confocally aligned with an objective of a two-photon microscope (2PM). Fluorescently labeled albumin was administered to the mouse nose, where it transported along olfactory nerve and trigeminal nerve from nose to brain and then spread in perivascular space in the brain. FUS sonication was performed after intravenous injection of microbubbles. In vivo 2PM recorded the dynamics of agent transportation before, during, and after FUS sonication. Time-lapse recording showed that FUSMB enhanced the agent accumulation at the perivascular space. FUS significantly increased the accumulation of the agent in the perivascular space by 1.2-folds immediately after the sonication (p = 0.0325), and 1.6-folds at 5 min after the sonication (p < 0.0001). In conclusion, this study showed, for the first time, direct evidence of FUSMB-enhanced glymphatic transportation in the mouse brain.