Student Johns Hopkins School of Medicine Baltimore, Maryland, United States
Introduction: The CNS vasculature tightly regulates trafficking of molecules across the endothelium, thereby limiting drug delivery and complicating treatment of CNS diseases. Concurrent application of focused ultrasound (FUS) and intravenous microbubbles (MBs) has been repeatedly shown to increase BBB permeability and improve delivery of therapeutics to the brain. Using a rat model, we demonstrate that pulsed FUS is a viable tool for targeted BSCB disruption and is unassociated with significant tissue damage or motor deficits.
Methods: T9-T11 laminectomies were performed on adult Sprague-Dawley rats. Tail vein catheters were placed, and diluted Evan’s Blue (EB) Dye and MB solutions were intravenously administered. A FUS transducer was placed directly above exposed cords, and the ultrasound (US) focal region was localized to T10. Rats were sonicated for 5 minutes at 250 kHz central frequency, 0.6 MPa peak pressure, and 1 Hz pulse repetition frequency. Two duty cycles were tested: 5% and 40%. After perfusion with phosphate-buffered saline and paraformaldehyde, spinal cords were excised, embedded in wax, and sliced into sections either stained with hematoxylin and eosin (H&E) for bright-field microscopy or counterstained with DAPI for fluorescence microscopy. Five additional rats underwent behavioral testing (BBB) pre- and post-FUS sonication.
Results: BSCB opening was confirmed with EB dye extravasation, which was visually observed at T10 immediately after FUS sonication for both 5% and 40% duty cycle conditions. Bright-field and fluorescence microscopy confirmed accumulation of EB dye at the targeted location in all samples. Histologic differences between the two duty cycles were characterized, with minimal cavity lesions present in both. There were no significant differences in BBB scores between pre- and post-FUS sonication timepoints in rats.
Conclusion : Application of MBs and FUS is a feasible and safe technique to achieve greater BSCB permeability. Future studies will explore the use of this tool in localized drug delivery to the spinal cord.
