Effects of fixation and demineralization on the intensity of autoradiographic labelling over the periodontal ligament of the mouse incisor after administration of [3H]-proline

Abstract

The effect of different histological procedures on the autoradiographic grain count over the periodontal ligament was studied quantitatively in autoradiographs made eight hours after administration of [3H]-proline. The lower jaws of 9 mice were fixed in Bouin's fixative, in 10 per cent formalin or in Carnoy's fluid and were demineralized either in EDTA or in a mixture of formic acid and sodium citrate. With Bouin's fixative, higher grain densitites were obtained than with formalin or Carnoy's fluid. Liquid scintillation counting revealed that in formalin traces of non-dialyzable tritiated substances were present. A greater loss of non-dialyzable radioactivity occurred during the demineralization of the jaws fixed in Carnoy's fluid particularly when this was performed in a formic acid and sodium citrate mixture. For the latter mandibles, autoradiography revealed a low grain density over the periodontal ligament while the relative shrinkage of the tissue appeared to be high. Biochemical analysis of the dialysates of the formic acid and sodium citrate mixtures from these mandibles showed that part of the radioactivity lost was bound to collagen.