HISTONES AND DNA INCREASE SYNCHRONOUSLY IN NEURONS DURING EARLY POSTNATAL-DEVELOPMENT OF THE RAT FOREBRAIN CORTEX

Cytophotometric measurements reveal that a temporally coordinate accumulation of histones and DNA occurs in rat cortex neurons between the last gestational day and the end of the third postnatal week. A rapid rise of both constituents around birth is followed by a more protracted synthesis. This leads to adult histone and DNA levels of approximately 3.3 arbitrary units as compared with 2 arbitrary units found in neuronal precursor cells at all foetal stages and in reference diploid nuclei from glia and liver. A secondary DNA increase in the fourth postnatal week, previously suspected on the basis of cytofluorometric measurements using the Schifftype stain BAO (bis-[4-aminophenyl]-1,3,4-oxadiazole), is not substantiated by the present work. This derives from the finding that alternative cytophotometric DNA measurements (ultraviolet absorption scanning) and autoradiographs of neuronal nuclei following repeated injections of [3H]thymidine into the lateral ventricles during the relevant period give no evidence of a further DNA increase after the third postnatal week. Neither does the accumulation of histones (measured by sulfaflavine cytofluorometry) continue beyond day 21. This leads us to conclude that DNA and histone syntheses cease at the end of the third week. Electrophoretic analyses of the histones show that the relative histone composition changes only slightly during neuronal development. Apart from an increase in the ratio of the histones H1o:H1 around birth no developmental alterations in histone composition are detectable. © 1979 Springer-Verlag.