A NOVEL MODEL FOR THE STUDY OF SYNOVIAL MICROCIRCULATION IN THE MOUSEKNEE-JOINT IN-VIVO

A novel model for the investigation of the microcirculation in synovia l tissue of the mouse knee joint is presented. The mouse knee joint wa s exposed on a specially designed plexiglass stage with a slight flexi on. After partial resection of the skin, the patella tendon was cut tr ansversally, which allowed for visualization of the ''Hoffa's fatty bo dy'', an intraarticular fatty tissue containing synovial cells on the interior surface of the joint. An intravital fluorescence microscope w as adjusted to observe the microcirculation of this intraarticular syn ovial tissue without opening of the joint capsula. For staining of the plasma, fluorescein isothiocyanate (FITC)-dextran was used, and for t he staining of leukocytes rhodamine 6G was used. The tissue investigat ed presents with a high-density honeycomb-like capillary network, cont aining some postcapillary venules and a few arterioles. The following parameters were assessed off-line using a computer-assisted microcircu lation analysis system: flow and diameter of arterioles and postcapill ary venules, as well as functional capillary density. Moreover, leukoc yte-endothelial cell interaction was quantified by counting the number of rolling cells and cells adhering to the endothelium in postcapilla ry venules. As an indication of endothelial leakage, macromolecular ex travasation was also assessed. To validate the model, we investigated these parameters at three time points during an observation period of 60 min. There was no change in functional capillary density, nor in ve ssel diameter after 60 min of observation. Moreover, there was neither a change in the number of rolling cells, nor in the number of cells a dhering to the endothelium nor in extravasation of FITC-dextran, thus indicating the stability of the preparation. The new model allows the quantitative analysis of the intraarticular microcirculation of the sy novial fatty tissue in vivo. It provides insight into the dynamics of synovial microcirculation and leukocyte-endothelial cell interaction i n acute or chronic joint inflammation.