l8o2 



IIANDlii ii >K OF I'HYSIOLOGY ^ NEl'ROI'HVSK >l .< ICY III 



ensues (i), a situation which rapidly leads to ir- 

 reversible damage. 



Bv contrast, the brain contains a relatively high 

 concentration of tree amino acids, and total amino 

 acids (free and combined) account for about 40 per 

 cent of the total dry weight ( 1 53 ) . Some 70 per cent 

 of the amino nitrogen fraction is composed of glutamic 

 and aspartic acids and their derivatives (12, 218-220, 

 247). This group, in particular glutamic acid (230) 

 and glutamine (231), is present in brain in higher 

 concentrations than in any other organ (219, 241), 

 and is associated with metabolic systems specific 

 to neural tissues (187, 218, 220). Gamma-amino- 

 butyric acid, which is uniquely present in mammals 

 in central nervous system gray matter areas, is of 

 particular interest in this regard (188). These findings 

 have suggested important roles for this group of 

 amino acids in the structural and metabolic economy 

 of the neuron (154, 188, 226-228, 241, 247). 



DYNAMIC STATE OF STRUCTURAL COMPONENTS. The 



original concepts of the chemical structure of brain 

 as a static framework have now been abandoned in 

 the light of better understanding of the blood-brain 

 barrier factor and as the result of studies by isotopic 

 tracer techniques. Turnover of structural components 

 (i.e. metabolic repair, degradation and replacement), 

 which is characteristic of most bodily tissues, is also 

 active among brain proteins, lipids and nucleic 

 acids. With P* 2 as the tracer, rapid turnover of 

 nucleotide phosphorus (47, 215), of phosphatide 

 phosphorus, especially the inositides (6), and of 

 phosphoprotein phosphorus (98) can be demon- 

 strated. Tracer studies with C M , 1 [*, N' 5 and s 

 labeling of compounds show active turnover of lipid 

 and protein constituents (28, 244). Cerebral protein 

 turnover, as judged by incorporation of labeled 

 amino acids, appears to be comparable to turnover of 

 liver proteins (244), whereas most cerebral lipids are 

 probably less active in this respect than lipids in 

 other body tissues (28). 



I he lunctional significance of this dynamic state of 

 cerebral constituents remains to be fully explored. 

 The suggested roles for neural lipids of cellular 

 membranes as receptors (25) and in cation transport 

 17 ; 11 i.i\ be pertinenl here. Evidence for the partici- 

 pation of neural proteins in the actions of biologically 

 ,, !i- e amines 1 jo), as sources of endogenous ammonia 

 1 |u, 2 ;-'i, and in amino group interchanges with free 

 imino acid poof (232) would also appear to be 

 in. \ 1 lose association of changes in cytoplasmic 

 inn leit .11 ids with the fun* tional state of neurons has 

 l .ecu recognized (87, 113, 157), but what such changes 



COMPOSITION 

 100 



MOL LAC RAO. PYR 



OR. ALV 



16 12 32 4 20 16 % CORTE X (I250>i) 



TERM DEHOR. DENDRITES AXONS MYELINATED 



AR80RIZ MYEL F CELLS AXONS 



fig. 8. Chemical composition and histological composition 

 of Amnions horn (rabbit). The layers (from left to right) are 

 molrcularis (MOL.), lacunosum (LAC), radiata [RAD. — 

 pure dendrites), pyramidalis (PVR. — cell bodies), oriens (OR.) 

 and alveus (ALV. — myelinated fibers). Data are adapted 

 from Lowry el al • i )i> 



may mean in metabolic terms is still not clear. 

 Although much of the necessary data which would 

 permit an understanding of these phenomena is 

 lacking, it is important to recognize that the majority 

 of cerebral structural components are in a dynamic 

 slate and that this fact must certainly have important 

 implications in terms of cerebral function. 



Mil rochemical Data 



From the foregoing a general picture of the chemical 

 constitution and structure of the central nervous 

 system and for the most part of its major gray and 

 white subdivisions can be obtained. Because of the 

 lack of uniformity or homogeneity within these 

 divisions, the question arises as to what the pattern 

 of distribution of components is within the sub- 

 divisions or layers of various areas and what, if any, 

 are the differences between neurons and glia in these 

 areas Information regarding white matter is scarce, 

 but the studies of Lowry (143, 146, 2l6), Rollins 



( 1 89—1 93 1 and Pope (177 t8o), and their respective 



collaborators, have provided considerable data on 

 various cortical areas and Subadjacent white matter. 



vmmon's horn. Lowry et al. (14b) chose to study, 

 with the aid ol mil rochemical methods, the consti- 

 tution of Amnion's horn, a cortical area in which the 

 various elements comprising cortical gray matter 



