[The mechanism of transition from notochordal nucleus to fibrocartilagenous nucleus of the disc in the young monkey--an electron microscopic study].
Invasion of the fibrocartilage tissue into the notochordal nucleus is recognized in the monkey disc. From this viewpoint, monkey disc would be a suitable experimental model to clarify the developmental process of the human disc. In this report three problems are investigated microscopically and electron-microscopically using the discs of the young monkeys. The first one is about the mechanism of transition from the notochordal nucleus to the fibrocartilagenous nucleus in the disc. The second one is about significance of the degenerative findings which are observed in the discs of young subjects. The third one is about the function of the remnant of the notochordal cell. The results are as follows: 1) Chondrocytes with extended halo first invade the notochordal nucleus from the surrounding fibrocartilagenous tissue in which chondrocytes are moderately proliferating. Then the substance of the halo is freed as numerous pieces into the matrix producing the island-like tissues. Fibrogenesis seems to begin both in numerous island-like tissues and in extended halo of the chondrocytes. 2) The stage of formation of granular debris which is observed microscopically in the disc of the young subject seems to correspond to the first stage of invasion of fibrocartilage tissue into notochordal nucleus. 3) The remnant of notochordal cell takes part in synthesis of mucopolysaccharide in the notochordal nucleus which is gradually reducing its size by invasion of fibrocartilage until notochordal cell undergoes complete necrosis. According to this experiment there is no possibility of inflow of proteoglycan from the annulus into the notochordal nucleus.
D000818:Animals; D002356:Cartilage / Q000648:ultrastructure*; D005260:Female; D007403:Intervertebral Disc / Q000254:growth & development / Q000473:pathology / Q000648:ultrastructure*; D008252:Macaca fascicularis; D008297:Male; D008854:Microscopy, Electron