Cytophotometric evidence of non-S-phase extra-DNA in human neuronal nuclei

After Feulgen staining with acriflavine-Schiff, the DNa content of glial and neuronal nuclei from various sites of the human CNS (pre- and post-central gyrus, cerebellar cortex and spinal cord) were determined by fluorescence cytophotometry. The specimens were obtained from twelve adult human autopsy cases. Glial cell nuclei always revealed a biomodal DNA distribution pattern with a large 2c and a smaller 4c peak. The 4c peak was most prominent in the cerebellum. A few 8c glial nuclei were found. Neuronal cell nuclei disclosed DNA histograms with hyperdiploid means in the range 2.2-2.5c (1.8-2.9c for the individual populations). Tetraploid 4c DNA values were not observed, neither in Purkinje cells, nor in pyramidal cells. In eleven out of a total of forty-four slides the higher DNA means of neuronal nuclei were found to be statistically significant (P greater than 0.05) when compared with a population of 2c hepatocytes on the same slide. The results indicate the existence of some 'extra DNA' in human neuronal cell nuclei, the biological significance of which has still to be elucidated. It is however, suggested that it may play an important role in the functional activity of the CNS.