Figure 4.

In vivo imaging of cerebral microcirculation in anesthetized rats equipped with a closed cranial window shows that local and transient blood flow reductions through cerebral capillaries provide conditions compatible with neisserial adhesion. A tracer dose of FITC-dextran was used to label the vascular network. Erythrocytes were labeled with FITC and injected into the animal. (A) Confocal microscope view through the cranial window of the superficial vascular network (10x lens) and a capillary network at a depth of ∼200 μm below the pia mater (20x lens) in the region corresponding to the inset in the left panel. The arrow points to a passing erythrocyte. (B) Example of tracking of erythrocytes using the Quia image treatment software to determine blood velocity in capillaries. Panels show the object detection and tracking at two successive time points separated by 400 ms. The arrow indicates flow direction. (C) Computed blood velocities in portions of two typical capillaries represented as a function of the position along the capillary (μ corresponds to the average velocity). (D) Blood velocities in a portion of capillary with temporary reduction in flow velocity (red line). (E) Blood velocities in another capillary exhibiting average low flow (63 μm/s) with a temporary further reduction in flow velocity (blue line). (F) Further analysis of the two periods of time where blood flow is reduced as described in D and E. Shear stress values were calculated from erythrocyte velocities and plotted as a function of time. The dotted line identifies shear stress levels compatible with neisserial adhesion (<0.5 dynes/cm²).