Blood-brain barrier preservation in the in vitro isolated guinea pig brain preparation

The morphofunctional preservation of the blood-brain barrier (BBB) was evaluated in the isolated guinea pig brain maintained in vitro by arterial perfusion. Electron microscopy evaluation after 5 hr in vitro demonstrated that cerebral capillaries and BBB specializations in this preparation retain features compatible with structural integrity. BBB-impermeable and -permeable atropine derivatives arterially perfused to antagonize carbachol-induced fast oscillatory activity confirmed the functional preservation of the BBB in vitro. To study BBB function further, changes in extracellular K⁺ concentration during arterial perfusion of a high-K⁺ solution were measured with K⁺-sensitive electrodes positioned in the cortex and, as control, at the brain venous outlet, where the solution perfused through the brain arterial system was collected. After 5 hr in vitro, the [K⁺]_o values measured during high-K⁺ perfusion in the piriform and entorhinal cortices were 5.02±0.17 mM (mean±SE) and 5.2±0.21 mM, respectively (n = 6). Coperfusion of the high-K⁺ solution with the Na⁺/K⁺ pump blocker ouabain (10μM;n=4) induced consistently spreading depression preceded by a rise in [K⁺]_o. Finally, sporadic, isolated spots of extravasation of the fluorescent marker fluorescein isothiocyanate (FITC)-dextran preferentially circumscribed to deep cortical layers was observed in brains perfused with FITC-dextran after 5 hr in vitro. The study demonstrates that the in vitro isolated guinea pig brain is viable for studying cerebrovascular interactions and BBB permeability of compounds active in the central nervous system.