Age-dependence of heat-induced strand separation of DNA in situ in postmitotic cells of rat brain as revealed by acridine orange microfluorimetry.

Acridine orange microfluorimetry as well as Feulgen microfluorimetry were applied on smears of cerebral and cerebellar cortex of young (2-month-old) and old (24-27-month-old) female Wistar rats. The strand separation of DNA caused by thermal denaturation was measured between 50 degrees and 90 degrees C in the nuclei of cortical nerve cells and cerebellar granular cells. In the young nerve cell nuclei a considerable DNA-loss was observed after thermal denaturation, therefore, corresponding corrections should have been made on the heat denaturation curves. The old nerve cell nuclei of brain cortex showed a much higher heat stability than the young ones, whereas in the cerebellar granular cells the age-dependent difference was much less expressed. Our observations on chromatin in situ show the same tendency as do the findings obtained on isolated chromatin by others. The results are discussed first from a methodical point of view then the arguments are listed suggesting a possible role of interprotein cross-links in the age-dependent stabilization of the chromatin gel.