Focus Ultrasound Based Microbubble Mediated Blood-Brain Barrier Opening: A Technique to Create Localized Transient Openings in Blood-Brain Barrier of Mouse by Sonoporation

The blood-brain barrier or BBB consists of closely arranged endothelial cells connected through tight junctions. This forms a compact seal that restricts the movement of molecules to the brain.  To permeate BBB, prep an anesthetized mouse by securing it in the prone position onto a stereotactic unit.

Next, insert a catheter into the tail vein and flush it with an anticoagulant solution to avoid blood clotting. Take a suspension of microbubbles – microspheres of gas enclosed within a lipid layer. Inject the microbubbles into the lateral tail vein. These microbubbles enter the bloodstream, eventually reaching the brain.

Subsequently, identify the location of the brain and apply ultrasound gel to the corresponding spot on the head for better conduction of waves. Implant an ultrasound transducer over the designated area on the mouse's head. Use the transducer to apply strong and targeted ultrasound waves.

Due to the acoustic pressure from ultrasound waves, microbubbles rapidly expand and contract several times. These oscillations cause sonopermeation – disruption of the endothelial tight junctions – generating localized openings in BBB. These openings facilitate the delivery of microbubbles to the brain.

Finally, inject the dye-containing solution intravascularly. The dye molecules extravasate from vessels through the transient openings in BBB. The presence of dye in the mouse brain indicates successful sonoporation.