[A quantitative study of Ag-positive nucleolar segments revealed by silver staining in the interphase nuclei of trophoblast cells from the rat placental connective zone].

A cytomorphological study was made of silver stained nucleoli in interphasic nuclei of trophoblast cells from the rat placenta connective zone, in addition to calculation of Ag-positive spherules in the nucleoli. The prevalent number of Ag-positive nucleolar spherules in the nuclei was 6, corresponding to the number of nucleolar organizers (NOR's) in the diploid chromosome complement of the rat. The mean number of Ag-positive spherules in the nucleoli progressively increase in the course of polyploidization from 2c to 32c; variability of the spherule number also increasing. The mean area of nucleoli is found to increase in proportion to the ploidy degree. A high correlation is found between the number of Ag-positive spherules and the area of nucleoli in the nucleus (r = 0.78). This appropriateness is exhibited at all the ploidy levels. The number of Ag-spherules and the area of nucleoli are found to depend slightly on the number of nucleoli. The possibility to use the number of Ag-positive spherules as a criterion of the activity of the NOR in interphasic nuclei is discussed.