Quantification of the blood‐brain barrier solute permeability and brain tissue transport by multiphoton microscopy

Abstract

To quantify the blood‐brain barrier (BBB) solute permeability (P) and effective diffusion coefficients in brain tissue (Deff) in vivo, we used laser scanning multiphoton microscopy with 800~850nm excitation wavelength to determine P and Deff in the rat brain tissue 200–400 μm below the pia mater. Sodium fluorescein, or FITC‐dextrans, or Alexa Fluor 488‐IgG in 1% BSA mammalian Ringer was injected into the rat (SD, 250–300g) cerebral circulation via the ipsilateral carotid artery by a syringe pump at a constant rate of ~3 ml/min. P and Deff were determined from the rate of tissue solute accumulation and the radial concentration gradients around individual microvessels in the brain tissue. The mean P was 19.6, 7.4, 1.9, 1.4, 1.3 and 0.58 × 10−7cm/s, respectively, for sodium fluorescein (MW 376Da), dextran‐4k, ‐20k, ‐40k, ‐70k, and IgG (MW ~160kDa). These P values were not significantly different from those of rat pial microvessels for the same sized solutes except small solute sodium fluorescein, suggesting that pial microvessels at the brain surface can be a good model for studying the BBB transport of relatively large solutes. The mean Deff/Dfree was 0.46, 0.19, 0.12, 0.12, 0.11, 0.12 for sodium fluorescein, dextran‐4k, ‐20k, ‐40k, ‐70k, and IgG, respectively. Quantification of BBB permeability and brain tissue transport is important in developing better drug delivery strategies. Supported by NIH SC1CA153325–01.