Differential RNA Metabolism in Rat Brain Cells Fractionated by Zonal Centrifugation

Combined fractionation and RNA metabolism studies were made on homologous cell types (neurons and glia) banded from rat brain cerebral cortex and hippocampus tissue at 40, 000 rev/min for 50 minutes in a Beckman Ti 14 zonal rotor loaded with a discontinuous methyl cellulose (Methocel) and sucrose density gradient. Comparisons were made on the cellular fractions recovered from animals intracisternally injected with 15 μCi tritiated cytidine (³HCR) RNA precursor one hour before sacrifice and tissue cellular filtrate preparation. Immediate³H pool-correction of extracted³HRNA from the three cellular Bands recovered made possible a mathematically valid measure of³HCR-precursor incorporation into RNA of the different cell types. Comparison of the cellular³HRNA data by analysis of variance revealed the occurrence of differential tritium labelling of RNA in the same cell types banded from different brain regions. In particular, an important advance was demonstrated by the procedures developed in these studies for the quantitative cellular assay of brain in vivo (differential) RNA metabolism.