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Figure 4. Autoradiograph of a coronal section through the squamo-mandibular joint of a rat, 24 hrs after an intraperitional injection of 3H-thymidine to label cells synthesizing DNA. Most of the labeled cells are located within the proliferative zone. It is the mesenchymal stem cells of the PZ that differentiate into the chondroblasts of the cartilage layer under the influence of function. Counting both labeled and unlabeled cells in a ’representative’ field to obtain a labeling index is a laborious procedure, and, in young animals, it is also sometimes difficult to distinguish the boundaries between different cellular layers. SJS, superior joint space; D, interarticular disc; AZ, articular zone; PZ, proliferative zone; CC condylar cartilage. Hematoxylin stain. Original magnification, 350x. Scale bar not available.
