IntroductionThere have been only a few morphological studies on the cervical loop (CL) of the enamel organ. It was originally reported on the basis of light microscopic observations that the CL of the rat incisor was difficult to discriminate into the four cell layers, i.e., the inner enamel epithelium, the stellate reticulum, the stratum intermedium and the outer enamel epithelium [1]. Later, however, it was shown by WARSHAWSKY et al. [2] that in the CL of the rat incisor, both the inner and outer enamel epithelia consisted of multilayers.Previous electron microscopic studies have focused mainly on the morphological changes occurring in the process of inner enamel epithelial differentiation into secretory ameloblasts [3][4][5][6][7][8][9][10][11]. Only a few investigations have been made on the outer enamel epithelium using electron microscopy; PANNESE [12] [16] all briefly reported the fine structure of the outer enamel epithelium. These studies showed that the outer enamel epithelium is lined by an outer basal lamina, and that the cells in the outer enamel epithelium have microvilli on their lateral membranes and are connected with adjacent cells by desmosomes. However, no ultrastructural details of the outer enamel epithelium have yet been clarified. It was also shown by DECKER[3] that lipid granules are often seen within cells, while details of their distrubution in the CL have not been revealed. The author therefore studied these various points in detail using the growing end of the rat incisor, and observed, mainly by electron microscopy, the fine structure of the outer enamel epithelium in the CL during the process of tooth formation.

Degenerating chondrocytes are often localized in the lower hypertrophic and calcifying zone of rat epiphyseal cartilage. The ability of these degenerating chondrocytes to synthesize and secrete sulfated proteoglycans was investigated using the light microscopic radiosulfate labeling method and the high-iron diamine-thiocarbohydrazide-silver proteinate (HID-TCH-SP) method for sulfated complex carbohydrates at the ultrastructural level. At 30 min following intraperitoneal (IP) injection of 35SO4, only intracellular autoradiographic labeling was observed, whereas both intracellular and extracellular radiosulfate labeling was seen at 1 h postinjection. A giadual increase in intracellular and extracellular labeling was seen at 3, 12 and 24h following IP injection of 35SO4. In ultrastructural cytochemical preparations, HID-TCH-SP weakly to moderately stained the chondrocyte Golgi vacuoles or immature and intermediate secretory granules but did not stain Golgi saccules. Mature secretory granules and extracellular matrix granules demonstrated strong staining. These results therefore indicate that proteoglycans are sulfated in the degenerating chondrocyte Golgi vacuoles, packaged in the secretory granules and then released into the extracellular matrix to form matrix granules.

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