DNA and RNA and the cytoarchitecture of human frontal cortex.

Abstract

AbstractDNA and RNA were studied in the layers of human prefrontal cortex by quantitative microchemical analyses on microtome‐prepared serial frozen sections. Eleven cortical specimens from six autopsy brains were assayed. The mean total number of cells per mm3 of fresh cortex was estimated from DNA values. The number in layer I (61,000) was falsely high because of the inclusion of cells from the pia mater. From a plateau of 82,000‐86,000 in layers II, IIIa and IIIb, the number of cells rose to 91,000 and 113,000 in layers IIIc and IV, respectively. The mean number was slightly lower in layer V, then gradually rose through layer VI to 127,000 cells in white matter. Per unit dry weight, DNA and cells varied much less than per unit volume; values averaged 14 per cent higher in layers II and IV than in neighbouring layers and in white matter were 20 per cent lower than in layer I.Intracortical patterns of RNA and RNA/cell reflected chiefly the distribution of neuronal cell bodies. Per unit fresh volume, RNA roughly paralleled DNA in layers I‐V; through layer VI and into white matter RNA declined as DNA rose, reflecting the decline in neurons and increasing predominance of glial cells of lower RNA content. Per unit dry weight, RNA rose 50 per cent from layer I to layer II; a plateau of high values extended through layers II‐V, then RNA declined rapidly through layer VI to a level in white matter that was 28 per cent of the value in layer II. Mean RNA/cell in cortex was 9‐8 pg, with a maximum in layer IIIb (11.4 pg); in subcortical white matter it was 5.3 pg.