Ultrastructure of the developing fibrocartilage of the os penis of rat

Development of the fibrocartilage of the os penis of rat was studied by transmission electron microscopy. Prepubertal (0-4 weeks of development) and pubertal (4-8 weeks of development) males were examined. Effects of castration on the development of the fibrocartilage were also examined. During the first 0-4 weeks of development, cells in the primordium of the fibrocartilage became large and the cytoplasm had well-developed rough endoplasmic reticulum (rER) and many intermediate filaments. Collagen fibers increased markedly in amount in the extracellular matrix (ECM) during the period. For 4-6 weeks, when gonadal secretion of androgens increases, the cells developed into mature chondrocytes with lacunae. Collagenous bundles were pushed away from the lacunae, resulting in a characteristic appearance of this fibrocartilage. The cytoplasm of the mature chondrocytes of the fibrocartilage was characterized by many intermediate filaments, oil droplets, glycogen granules, and well-developed rER. At 6 weeks, calcification started on the cell membrane of the mature chondrocytes. At 8 weeks, a large part of the cartilage matrix was calcified. Matrix vesicles that originate from degenerated chondrocytes were found in the ECM of decalcified samples. In castrated males, cells of the primordium of the fibrocartilage ceased further development after castration. Intermediate filaments were still abundant in the cytoplasm and collagen fibers increased even after castration, but mature chondrocytes never differentiated. There were no signs of matrix vesicle formation, calcification, or cell degeneration in the fibrocartilage primordium. The developmental process of the fibrocartilage can be subdivided into two phases: collagenous matrix formation during the prepubertal period (0-4 weeks), and maturation of chondrocytes and calcification after puberty (4-8 weeks).