Observation of the blood-brain barrier function and vasomotor response in rat microcirculation using intravital fluorescence microscopy.

The blood-brain barrier function and the vasomotor response in rat microcirculation was studied using a closed cranial window technique and an intravital fluorescence microscope with an attempt to reduce both the light intensity and the amount of 2% Na(+)-fluorescein to as little as possible. The light intensities in the focus were less than or equal to 2.5 mW/cm2, and with the low-light TV camera we were able to reduce the total amount of the dye to less than or equal to 0.7 ml during 6-h experiments. Observing the brain surface every 30 min showed that the barrier function remained intact for up to 6.0 h following the first iv administration of the dye. This study has reconfirmed that the pial vessels have physiological vasomotor responses (e.g., CO2 reactivity). The osmotic barrier disruption started at a small venule 10 min after the start of superfusion with mannitol (1000 mOsm/liter). In conclusion, the microscope system and the small animal model used in this study were useful in studying the blood-brain barrier function and the vasomotor response simultaneously under various experimental conditions.