The ultrastructural changes of mitochondria in the ovarian oocytes from Graafian follicles, the ovulated tubal ova, and the various stages of preimplantation rabbit embryos have been observed with an electron microscope. From the ovarian oocytes to the 4-cell stage, mitochondria showed oval and round forms with a few cristae arranged concentrically and peripherally at the inner membrane. In 8-cell and 16-cell stages, mitochondria tended to change their forms to be elongated, and their sizes, and the outer membrane of the mitochondria had a tendency to become rough and irregular although there were few changes in the inner structure. In morula, some mitochondria began to show several transverse cristae proceeding into the matrix. Mitochondria rapidly increased in number at the late blastocyst stage. Matrix of mitochondria with transverse cristae found in the morula and in blastocyst stages was less dense than that of the earlier stages. The authors believe that the morphological changes of mitochondria during early embryonal development indicate the level of enzymatic activity at which this organelle is engaged in energy metabolism.
Animal ; Cell Membrane/ultrastructure ; Embryo/ultrastructure* ; Embryo Implantation ; Female ; Microscopy, Electron ; Mitochondria/ultrastructure* ; Organoids/ultrastructure ; Ovum/ultrastructure ; Rabbits