ULTRASTRUCTURE OF FELINE ARTICULAR-CARTILAGE IN THE POSTNATAL-PERIOD

Articular cartilage was investigated in five cats of both sexes, aged 1, 21 and 43 days, and in two adult cats aged 5 years. Samples for tra nsmission electron microscopy were collected from femoral heads and pr ocessed using conventional techniques. The object of the investigation s was cellular structures and intercellular matrix of the superficial, middle and deep layers, but not those of transition cells and the tid e-mark region. In the superficial layer of the samples collected from 1-, 21- and 43-day old kittens, chondrocytes were found mostly in pair s sharing a common laf una surrounded with well formed pericellular ma trix. Reticular-type nucleoli were usually present in nuclei, and scar ce: small mitochondria dilated GER (granular endoplasmic reticulum) ci sternae and transport vacuoles were observed in cytoplasm. Towards the middle layer, cell membranes of chondrocytes contacted the intercellu lar matrix. The surface of the articular cartilage was covered by a co ntinuous and well formed chondrosynovial membrane. Areas with various appearances can be distinguished in the cartilages of adult cats. Cont inuous chondrosynovial membrane covered a thick layer of intercellular matrix with scarce chondrocytes in undamaged areas, while other areas showed signs of various degrees of damage. No differences in the stru cture of the middle layer were found among the various age groups. Ova l or spherical chondrocytes contain large nuclei and cytoplasm contain s numerous GER cisternae, mitochondria, Golgi's complex, numerous smoo th vesicles, sporadic lysosomes and rare centrioles and lipid droplets . Pericellular matrix had almost disappeared and cell membrane contact ed closely the intercellular matrix. The deep layer of the articular c artilage of 1-, 21- and 43-day-old kittens contained lacunae harbourin g either single chondrocytes or pairs thereof arranged perpendicularly to the surface. The spindle-shaped cells were smaller and contained a lesser amount of organelles than their counterparts in the middle and the surface layers. The pattern of the intercellular matrix was simil ar to that of the middle layer. In addition to intact chondrocytes wit h a normal structure of cytoplasm and nucleus, the deep layer of the a dult cartilage contained degenerated cells with large lipid droplets, glycogen deposits, disintegrated mitochondria and pyknotic nuclei.