In group A, the DM fibers were in fusiform shape and funiculose; the cellular nucleus had consistent contours; and no infiltration of connective tissue could be detected in the muscular bundles. However, from groups B–G, the muscular fibers were gradually more crescent-shaped or irregular; they showed misalignment and disarray; and marked infiltration of connective tissue was observed in the muscle bundles (Fig. 4.1). Gradually progressive atrophy of the DM over time was found in groups B–G (Fig. 4.2). The sectional areas of the DM fibers in groups A–G were 7265.86 ± 114.36, 5156.31 ± 310.42, 5398.47 ± 453.08, 4146.49 ± 284.06, 3067.40 ± 130.91, 2123.56 ± 235.66, and 1675.98 ± 322.09 μm², respectively. The sectional areas of muscle fibers in groups E, F, and G were significantly lower (P < 0.05) than that in control group A, but there was no significant difference between groups B, C, and D, and group A.

In group A, DM cells were well-arranged and well-distributed with consistent contours and size, and normal intermediate junctions were observed, with the distance between muscular cells being much smaller than that in abnormal specimens. A few collagen fibers and elastic fibers could be seen in the matrix. Organelles such as the mitochondria and endocytoplasmic reticulum, myofilaments and dense bodies were well-organized in the smooth muscle cells. By contrast, in groups B–G, the atonic bladders showed abnormalities in the ultrastructure of detrusor cells that were gradually aggravated over time, such as inconsistent contours, misalignment and disarray; wide separation between muscular cells; abundant collagen fibers and irregular dense structures between individual cells; obviously widened rough endoplasmic reticulum (ER) and mitochondrial edema (Fig. 4.3).