A non‐invasive method for measuring solute permeability of rat pial microvessels

Abstract

To quantify the permeability of rat pial microvessels, we measured the apparent microvessel permeability (P) to various sized solutes. Rats (SD, 250–300g) were anesthetized with sodium pentobarbital given subcutaneously and kept warm on a heating pad. The pial microcirculation was observed by a high numerical aperture objective lens (20X, NA=0.75) through a section of frontopariental bones (~ 5 mm × 5mm) thinned with a high-speed micro-grinder (revised method from Easton et al., J Physiol 503.3:–623, 1997). The surface of the brain was constantly superfused with 37 degrees Celsius artificial cerebrospinal fluid at the rate of ~1 ml/min through a dripping tube attached to the side of the brain. Sodium fluorescein (MW 376) with concentration 0.5 mg/ml in 1% BSA mammalian Ringer, or FITC-dextran 4K or FITC-dextran 10K with concentration 1 mg/ml, was introduced separately into the cerebral circulation via the ipsilateral carotid artery by a syringe pump at a constant rate of 3–5 ml/min. P was determined using a quantitative fluorescence imaging and analyzing system (Intracellular Imaging Inc., Cincinnati, OH). Psodiumfluoresscein = 3.2 (±1.4SD, n = 10) × 10−6cm/s, PFITC−Dextran4K= 0.91 (±0.53SD, n = 10) × 10−6cm/s, and PFITC−Dextran10K= 0.45 (±0.32SD, n = 6) × 10−6cm/s. These values were a order of magnitude lower than those for mesenteric microvessels (Fu and Shen, Microvasc. Res. 68(1): –62, 2004). Supported in part by NSF, NIH and CUNY.