Nitrous oxide enhances MR-guided focused ultrasound delivery of gene therapy to the murine hippocampus.

Transcranial Magnetic Resonance Guided Focused Ultrasound can oscillate intravenously delivered microbubbles and transiently open the blood brain barrier (BBB) in a targeted brain region. However, high microbubble doses or Focused ultrasound pressures (FUS) leads to injury. So, we administered nitrous oxide (N₂O), an anesthetic gas to determine reduced need of FUS pressure and microbubble dose for opening BBB. Swiss Webster mice were treated with N₂O or medical air (MA) at varying FUS pressures, while the microbubble dose was kept constant and the vice-versa. Consequently, BBB opening was quantified by acoustic emissions and enhancement rate on T1-weighted MR. To compare the effect of N₂O on gene delivery, following BBB opening with either MA or N₂O, a viral vector expressing GFP was subsequently delivered. Additionally, Immunohistochemical studies quantified viral transfection efficacy and assessed acute cell injury. We observed that N₂O significantly potentiates acoustic emissions and enhancement rate on post-contrast MRI images, compared to MA at all measured pressures (0.39, 0.45, 0.67 MPa). Furthermore, N₂O reduces the microbubble dose to 0.02μl/kg and FUS pressures to 0.28 and 0.39 MPa for BBB disruption and enhanced viral gene delivery, respectively. Hence, N₂O potentiates microbubble oscillations, allowing reduced microbubble dose and FUS pressures and improved viral gene delivery.