Histologic and molecular characterization of dissected membranes and adjacent tissues (a) Histologic cross-sections illustrating the plane of dissection. Left image: cross-section through an entire monosodium urate (MSU) crystal inflamed pouch wall, showing membrane (short red arrow) and the overlying cutaneous soft tissue (long black arrow). Original magnification: 100×. Center image: cutaneous soft tissue of the air pouch wall after removal of the membrane by the dissection method outlined in Figure 2. Original magnification: 100×. Right image: normal dorsal skin. It is nearly identical in appearance to the cutaneous parts shown in part b, which are left after dissection of the membrane. Original magnification: 100×. (b) Tissues that will probably contaminate the dissected membrane if they are not avoided during the final steps of the dissection. Left image: tissue from the nuchal cape-like structure to which the most rostral parts of the membrane are often attached. Original magnification: 200×. Center image: tissue obtained from the paraspinal ridges from which the base of the membrane arises (for the macroscopic appearance see the tissue marked with the arrow in Figure 2k). Original magnification: 200×. Right image: dissected membrane obtained from an air pouch injected with MSU crystals (2 mg in 1 ml phosphate-buffered saline). It consists mostly of fibroblasts and inflammatory cells. Blood vessels can also be found but are not abundant. Original magnification: 100×. (c) Partitioning of selected mRNAs between pouch membrane and the overlying cutaneous soft tissues. Membranes (n = 4) were dissected from the soft tissues 9 hours after injecting MSU crystals into the air pouches. RNA was extracted from dissected membranes or the soft tissues and analyzed separately by quantitative PCR. Results were normalized to GAPDH and the data obtained from membrane RNA arbitrarily assigned the value 1.