Quantitative comparison of methods for widespread delivery of small molecules across the blood-brain barrier

Achieving widespread delivery of pharmacological agents beyond the blood-brain barrier (BBB) remains a formidable challenge in preclinical and clinical research. Here we quantitatively evaluate and compare three strategies for brain-wide delivery that employ transient BBB disruption or infusion via the cerebrospinal fluid (CSF) in rats. Using molecular magnetic resonance imaging (MRI) techniques, we find that the three techniques produce spatially differentiated labeling patterns, with the most homogeneous delivery produced either using chemically mediated or unfocused ultrasound-based BBB manipulation methods. Contrast enhancement distributions are similar following chemical and ultrasound procedures, but differ notably from the results of intra-CSF infusion. Delivery efficiency using the two BBB disruption methods also correlates inversely with a marker of tight junction density, suggesting that common factors determine susceptibility to these techniques. Our study thus documents the spatial variation of BBB properties across the brain while offering guidance about brain-wide application of molecular technologies in neuroscience and neuromedicine. Parallel characterization of three techniques for brain-wide delivery of a BBB-impermeable molecule indicates comparative strengths and weaknesses of each method, while suggesting mechanistic contributions to delivery efficiency.