Long-term observation of pial microcirculatory parameters using an implanted cranial window method in the rat.

The aim of this study was to confirm whether our improved closed cranial window (CCW) method could be used for long-term microscopical observation of pial microcirculation intravitally in the rat. We investigated chronological changes in three microcirculatory parameters: permeability of blood-brain barrier, leukocyte behavior, and plasma velocities in the pial venules, immediately after implantation (control group) and at one and four weeks after implantation in different age-matched rats (implanted group). No extravasation of sodium fluorescein from pial venules was confirmed in any observation period. The number of endothelial-adhering leukocytes in the implanted group kept within the physiological range, being similar to those of the control group. The velocities of fluorescent microspheres flowing in pial venules showed no noticeable changes between the two groups. These findings suggest that our CCW method allows long-term observation of the pial microcirculation without any pathophysiological changes in the evaluated parameters up to four weeks after the implantation.