The histological localization of DNA in rabbit medullary neurons

The nuclei of unfixed isolated rabbit neurons cleared on incubation with DNAse (10 mg/ml), but not RNAse (10 mg/ml). The nuclei stained for DNA with eight chromosomal or nuclear stains more intensely than the cytoplasm, and less intensely after treatment with DNAse (10 mg/ml). On the other hand, when the whole tissue was embedded and sectioned, DNA did not appear to be stained in the nucleus; the nucleolus and the cytoplasm were more heavily stained than the nucleoplasm. Possible explanations for this apparent anomaly are considered. It was concluded that DNA diffused out of the nucleus during embedding and sectioning, and that the colouration of the nucleolus and cytoplasm with the eight staining systems used was due to other nucleotides present.