Chromatin structure in neuronal and neuroglial cell nuclei as a function of age.

Nuclei from the cerebral cortices of animals of different ages were separated into neuronal and neuroglial populations. Nuclei from cerebellar neurons were also studied. Using the enzyme micrococcal nuclease as a probe for chromatin structure, we found that the DNA from both neuronal preparations showed a decreased susceptibility to digestion during aging, although the onset of this alteration varies. In addition, both neuronal populations showed dramatic increases in the nucleosome spacing of the chromatin. Cerebral neuronal chromatin has a repeat length (nucleosome core and linker region) of 164 base pairs at 22 days and 11 months, 186 base pairs at 24 months, and 199 base pairs at 30 months. Cerebellar neuronal chromatin has a repeat of 188 base pairs at both 22 days and 11 months, 208 base pairs at 24 months, and 243 base pairs at 30 months. Neuroglial chromatin, on the other hand, showed no change in either accessibility to nuclease or repeat length.