title: Pulsed ultrasound expands the extracellular and perivascular spaces of the brain.
abstract: Diffusion within the extracellular and perivascular spaces of the brain plays an important role in biological processes, therapeutic delivery, and clearance mechanisms within the central nervous system. Recently, ultrasound has been used to enhance the dispersion of locally administered molecules and particles within the brain, but ultrasound-mediated effects on the brain parenchyma remain poorly understood. We combined an electron microscopy-based ultrastructural analysis with high-resolution tracking of non-adhesive nanoparticles in order to probe changes in the extracellular and perivascular spaces of the brain following a non-destructive pulsed ultrasound regimen known to alter diffusivity in other tissues. Freshly obtained rat brain neocortical slices underwent sham treatment or pulsed, low intensity ultrasound for 5min at 1MHz. Transmission electron microscopy revealed intact cells and blood vessels and evidence of enlarged spaces, particularly adjacent to blood vessels, in ultrasound-treated brain slices. Additionally, ultrasound significantly increased the diffusion rate of 100nm, 200nm, and 500nm nanoparticles that were injected into the brain slices, while 2000nm particles were unaffected. In ultrasound-treated slices, 91.6% of the 100nm particles, 20.7% of the 200nm particles, 13.8% of the 500nm particles, and 0% of the 2000nm particles exhibited diffusive motion. Thus, pulsed ultrasound can have meaningful structural effects on the brain extracellular and perivascular spaces without evidence of tissue disruption.
authors.affiliation: Department of Neurosurgery, University of Maryland School of Medicine, 22 S Greene St Suite 12D, Baltimore, MD 21201, USA; Marlene and Stewart Greenebaum Cancer Center, University of Maryland School of Medicine, 22 S Greene St, Baltimore, MD 21201, USA.
authors.forename: David S
authors.initials: DS
authors.lastname: Hersh
authors.affiliation: Department of Diagnostic Radiology and Nuclear Medicine, University of Maryland School of Medicine, 419 W Redwood St Suite 110, Baltimore, MD 21201, USA.
authors.forename: Ben A
authors.initials: BA
authors.lastname: Nguyen
authors.affiliation: Department of Neurosurgery, University of Maryland School of Medicine, 22 S Greene St Suite 12D, Baltimore, MD 21201, USA; Marlene and Stewart Greenebaum Cancer Center, University of Maryland School of Medicine, 22 S Greene St, Baltimore, MD 21201, USA.
authors.forename: Jimena G
authors.initials: JG
authors.lastname: Dancy
authors.affiliation: Department of Neurosurgery, University of Maryland School of Medicine, 22 S Greene St Suite 12D, Baltimore, MD 21201, USA; Marlene and Stewart Greenebaum Cancer Center, University of Maryland School of Medicine, 22 S Greene St, Baltimore, MD 21201, USA.
authors.forename: Arjun R
authors.initials: AR
authors.lastname: Adapa
authors.affiliation: Marlene and Stewart Greenebaum Cancer Center, University of Maryland School of Medicine, 22 S Greene St, Baltimore, MD 21201, USA; Department of Surgery, University of Maryland School of Medicine, 22 S Greene St, Baltimore, MD 21201, USA; Center for Vascular and Inflammatory Diseases, University of Maryland School of Medicine, UMB BioPark, One Room 210, 800 West Baltimore Street Baltimore, MD 21201, USA.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Winkles
authors.affiliation: Department of Neurosurgery, University of Maryland School of Medicine, 22 S Greene St Suite 12D, Baltimore, MD 21201, USA; Marlene and Stewart Greenebaum Cancer Center, University of Maryland School of Medicine, 22 S Greene St, Baltimore, MD 21201, USA.
authors.forename: Graeme F
authors.initials: GF
authors.lastname: Woodworth
authors.affiliation: Department of Neurosurgery, University of Maryland School of Medicine, 22 S Greene St Suite 12D, Baltimore, MD 21201, USA; Marlene and Stewart Greenebaum Cancer Center, University of Maryland School of Medicine, 22 S Greene St, Baltimore, MD 21201, USA; Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, 20 Penn Street, HSFII Room 520, Baltimore, MD 21201, USA; Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, 111 S. Penn St. Suite 104, Baltimore, MD 21201, USA. Electronic address: akim@smail.umaryland.edu.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Kim
authors.affiliation: Marlene and Stewart Greenebaum Cancer Center, University of Maryland School of Medicine, 22 S Greene St, Baltimore, MD 21201, USA; Department of Diagnostic Radiology and Nuclear Medicine, University of Maryland School of Medicine, 419 W Redwood St Suite 110, Baltimore, MD 21201, USA. Electronic address: VFrenkel@som.umaryland.edu.
authors.forename: Victor
authors.initials: V
authors.lastname: Frenkel
mesh_terms: D000818:Animals; D004058:Diffusion; D005110:Extracellular Space / Q000378:metabolism / Q000528:radiation effects*; D053758:Nanoparticles / Q000008:administration & dosage; D019579:Neocortex / Q000098:blood supply / Q000378:metabolism / Q000528:radiation effects* / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D000069453:Ultrasonic Waves
keywords: Diffusion; Extracellular space; Nanoparticle; Ultrasound