Monitoring Blood-Brain Barrier Opening in Rats with a Preclinical Focused Ultrasound System

Summary

This study describes a combined magnetic resonance imaging (MRI) and low-intensity pulsed focused ultrasound (FUS) protocol, utilizing living rats with jugular vein catheterization to monitor blood-brain barrier (BBB) opening.

Abstract

The brain has a highly selective semipermeable blood barrier, termed the blood-brain barrier (BBB), which prevents the delivery of therapeutic macromolecular agents to the brain. The integration of MR-guided low-intensity pulsed focused ultrasound (FUS) with microbubble pre-injection is a promising technique for non-invasive and non-toxic BBB modulation. MRI can offer superior soft-tissue contrast and various quantitative assessments, such as vascular permeability, perfusion, and the spatial-temporal distribution of MRI contrast agents. Notably, contrast-enhanced MRI techniques with gadolinium-based MR contrast agents have been shown to be the gold standard for detecting BBB openings. This study outlines a comprehensive methodology involving MRI protocols and animal procedures for monitoring BBB opening in a rat model. The rat model provides the added benefit of jugular vein catheter utilization, which facilitates rapid medication administration. A stereotactic-guided preclinical FUS transducer facilitates the refinement and streamlining of animal procedures and MRI protocols. The resulting methods are characterized by reproducibility and simplicity, eliminating the need for specialized surgical expertise. This research endeavors to contribute to the optimization of preclinical procedures with rat models and encourage further investigation into the modulation of the BBB to enhance therapeutic interventions in neurological disorders.

Introduction

The BBB regulates the movement of ions, molecules, and cells between the blood vessels and brain tissues¹. This function allows the maintenance of neuronal function and health while preventing the delivery of therapeutic macromolecular agents to the brain tissues. The limited permeability of the BBB can result in decreasing the efficacy and effectiveness of treatments for brain tumors and neurodegenerative diseases, such as Parkinson's disease, amyotrophic lateral sclerosis, and Alzheimer's disease². Hence, various approaches, such as convection-enhanced delivery, direct intracranial injections, osmotic disruptio....

Protocol

All animal experiments in this study were approved by the University of California, San Francisco (UCSF) Institutional Animal Care and Use Committee (IACUC). Male Sprague-Dawley rats (200-250 g) were used in this study. Rats were housed and cared for according to the National Institutes of Health Office of Animal Care and Use Guidelines in mice and rats. The details of the reagents and the equipment used are listed in the Table of Materials.

1. Animal preparation

Discussion

A protocol and animal procedure using a rat model of jugular vein catheterization for BBB opening studies has been developed. While numerous preclinical protocols exist, this protocol incorporates a commercially available FUS system and a rat model, minimizing animal preparation procedures and thereby ensuring experimental reproducibility.

In this protocol, microbubble selection was based on its stability and room temperature storage. Other commercial microbubbles may be considered as alternat.......

Materials

Name	Company	Catalog Number	Comments
1 mL syringe	BD plastipak
20 mL, Sodium Chloride 0.9%	Hospira, Inc	00409-7101-67
3 mL syringe	BD plastipak
5 mL syringe	BD plastipak
Blunt Needle, 21 G	SAI infusion technologies	B21-50
Catheter connector, 21 G	SAI infusion technologies	CC-25-25
Catheter lock solution	SAI infusion technologies	Sku # HGS-10	(500 µ/mL) Glycerol
Evans Blue	Sigma aldrich	E2129-10g
ExAblate Neuro	Insightec Inc., Israel
Gadavist	Bayer	2068062
GE  isoflurane Vaporizer	GE Healthcare
IPS-12RS Syringe Pump	Inovenso	IPS-12
isoflurane USP	Vet one	501017
Lumason microbbuble	Bracco Diagnostics Inc	SKJ709700
Male Sprague-Dawley rats (200–250 g)	Charles River Laboratories
Needle, 18 G	BD Precisionglide
Phosphate-buffered saline	Mediatech	21-030-CVR
Polyethylene Tubing	BD Intramedic
preclinical 3T cryogen-free Bruker Biospin scanner	Bruker	Biospec3T
Rat with jugular vein catheterization	Charles River Laboratories
RK-50  focused ultrasound transducer	FUS Instruments	Tx-50-1000-0
RK-50 benchtop focused ultrasound system	FUS Instruments
Sonic Concepts	Sonic Concepts Inc., WA, USA
vented dispensing pin	B Braun	4550560