Distribution of tenascin-C and tenascin-X, apoptotic and proliferating cells in postnatal soft-diet rat temporomandibular joint (TMJ)

We immunohistochemically examined the relationship between the distribution of extracellular matrix glycoproteins (tenascin-C and tenascin-X), apoptotic cells, and proliferating cells to determine the effect of a soft diet in the rat temporomandibular joint (TMJ) over a period of 4 weeks from 21 days of age. Using confocal laser scanning microscopy, strong expression of tenascin-C and tenascin-X was found in the soft-diet group, mainly from the proliferative layer to the cartilage layer of the condyle, and posterior and anterior regions of the disk, in contrast to that of the control group, which was fed a hard diet. The number of proliferating cells in the soft-diet group was lower than that in the control group and was especially low in the calcified zone and proliferative cell layer of the sagittal section of the TMJ. The apoptotic cells were found mainly in the endochondral ossification layer of the condyle. On day 28 in the soft-diet group, they were also highly concentrated in endochondral ossification layer of the anterior condyle beneath the disk. A few apoptotic cells were observed in the synovial membrane and the disk. These distributions reflect the process of replication in the TMJ in accordance with the feeding of a soft diet.