CHEMICAL ARCHITECTURE OF THE CENTRAL NERVOUS SYSTEM 



1803 



LIPIDS " NUCLEIC ACIDS 



P A 



1 r 



1 1 1 r 



fig. 9. Variations of lipid compo- 

 nents, nucleic acids and seven enzymes 

 in layers of Amnion's horn (rabbit). 

 The plots in .-1 are per kg of protein and 

 in B per kg dry weight. Units for cepha- 

 lins plus lecithins (C + L), cholesterol 

 ICH), sphingomyelin (S) and nucleic 

 acid phosphorus (XA-P) are moles per 

 appropriate unit weight. Units for en- 

 zymes are moles per hr. per unit weight. 

 Enzymes are (reading from the top) 

 malic dehydrogenase (MDH), fuma- 

 rase {F), lactic dehydrogenase \LDH), 

 aldolase (ALD), cholinesterase {CHE), 

 adenosinetriphosphatase (Mg ++ acti- 

 vated! (ATPase) and glutamic de- 

 hydrogenase (GDH). In order to 

 achieve convenient plots, actual values 

 in many cases have been multiplied by 

 some factor as indicated. For enzymes 

 in plot B the factors are the same as in 

 plot .1 , for lipids no factor was necessary 

 in A but, as indicated in B, the actual 

 values arc X 2. Data are taken from 

 Lowr) ft ill. 114(1) and Strominger & 

 LowT) (216) 



are quite distinct one from another. By serial section- 

 ing, layers composed essentially of dendrites, of cell 

 bodies or of mvelinated axons could be obtained for 

 analysis. The results of this study are summarized in 

 figures 8 and 9. In general composition, cell bodies 

 are limited to 4 per cent of the total cortical volume 

 while the dendrites are found in over half the total. 

 Fluid spaces are of the same order in all layers, 

 except the myelinated layer, while solids are lowest 

 in the cell body layer and highest in the two layers 

 containing myelinated fibers, due to the increased 

 lipid component. It is noteworthy that protein 

 content is relatively constant throughout all layers. 



The layer distribution of several solid components 

 and representative enzymes are shown in figure 9, 

 plotted both in terms of unit weight of protein and 

 unit dry weight. [Complete data may be obtained by 

 reference to the original reports (143, 14,6, 216)]. 

 The plots per unit weight of protein also reflect 

 the trends for a plot per unit wet weight (not shown), 

 as inspection of figure 8 would indicate. Correla- 

 tion of lipids and nucleic acids with the histological 

 picture are good, the former being high in mve- 

 linated layers and low in the cell body layer, the 

 latter showing a peak only in the cell body layer. 

 Cholesterol would appear to be a good indictor of 

 relative degree of myelination per layer (cf. table 2). 



Enzyme activities are relativerj low in the cell body- 

 layer and high in dendritic layers, although this is 

 less apparent when related to dry weight rather than 

 protein. These results, loyether with the relatively 

 larger volume of dendrites compared to cell bodies, 

 have led Lowry el a/. (146) to reaffirm Holmes" (1 1 1 ) 

 view that neural gray matter metabolism is largely 

 dendrite metabolism. 



other cortical areas. From such a general picture, 

 the more complex cortical areas can be more easily 

 understood. Similar studies of motor and visual 

 cerebral cortex and cerebellar cortex (excluding the 

 Purkinje cell layer) have now been reported by 

 Robins and collaborators (189-193), and analogous 

 studies on somatosensory and frontal cerebral cortex 

 for enzyme activity have been carried out by Pope 

 and his group (1 77-180). Some representative data for 

 motor and visual cortex are shown in figures 10 and 

 1 1 . Complete data may be obtained in the original 

 reports (191-193). 



As indicated earlier, total cell densities for the 

 respective areas are relatively constant layer by 

 layer, including the white matter, although the 

 visual cortex contains an average twice that of the 

 motor cortex. Both dry weight and cholesterol 

 increase in the deepest layers, especially for the 



