Analysis of the changes in the morphology and staining density characteristics of cartilagenous cell nuclei from Triturus cristatus during aging and regeneration.

The modifications in the morphology and staining intensity of cell nuclei reflect their physiologic and functional state. In order to appreciate the variations in the metabolic activity of hind limb chondrocytes from Triturus cristatus during aging and regeneration, we have studied the nuclear size and shape, the DNA concentration, and the distribution and degree of condensation of the chromatin. This study was carried out using scanning cytophotometry on semithin 1 micrometer sections, Feulgen-stained for DNA, which is the major nuclear component. During aging, the nuclei decrease in size, becoming irregular in shape. The concentration of DNA increases and the chromatin distribution becomes more heterogeneous with an increase in condensed chromatin and a subsequent decrease in the diffuse chromatin fraction. During regeneration, however, these modifications are reversed whatever the age of the animal, but even more noticeably when the animal is old. The changes that occur in the chromatin fractions defined according to their state of condensation are discussed from a functional point of view.