CHEMICAL ARCHITECTURE OF THE CENTRAL NERVOUS SYSTEM 



1807 



GENERAL COMPOSITION 

 1 — 1 r - 



FRACTIONAL COMPOSITION 



mmmm 



(39) 



60 



1 — 1 1 — 1 1 ; 1 1 1 1 1 



% 20 40 60 80 100 



BB LIPID VZ1 PROTEIN E3 H 



2 



CYTOLOGICAL 



CYTOCHEMICAL 



A. NUCLEUS 



1. NUCLEOLUS I 



2. ASSOC. CHROMATIN 



NUCLEOLAR CAPS| 



I I. NUCLEI 



CHROMOCENTER 



J 



NUCLEOLI 

 NUCLEOPLASM 

 DEBRIS (cell 



MEMBRANES, 

 MYELIN SHEATH) 



SATTELLITE (SEXI 

 3 NUCLEOPLASM I 

 P ERIKAR YON I 



I- NISSL BODIES I II 



ENDOPLASM. RETld 

 GRANULES . 



2. MITOCHONDRIA ,111. MITOCHONDRIA 

 CRISTAE 

 MATRIX 



3. AGRAN RETICULUM IV. 



4. FIBRILLAR NET I lipio 



5. LIPID, PIGMENT I AQUEOUS 



I 



MICROSOMES 



PARTICULATE 

 SUPERNATANT 



PARTICULATE 

 SUPERNATANT 



SUPERNATANT 



fig. 12. The genera] and fractional cytological and cytochemicaJ composition of the neuron. 

 Percentages of water in the various cell fractions are per unit mass of the respective fraction. The 

 values of protein for each fraction (given in parentheses) are as percentages of the total solids per 

 unit mass of the respective fraction. Sec text lor discussion. 1 References: 15-17, 30-32, 51, 52, 57, 

 58, 61, 108, 109, 113, 143, 157, 159, 160, 169-173, 205, 206, 235, 243.) 



to mediate there the formation of perikaryal protein 

 (113). There is both support (89) and contrary 

 evidence (87, 121) regarding this concept. 



Fia<t 1 until Composition 



From a cytological standpoint the nucleus and 

 perikaryal cytoplasm are composed oi a number of 

 different elements which have been recently con- 

 firmed by electron microscopy together with deline- 

 ation of their finer structure (61, 170, 172, 173, 243). 

 These are summarized in figure 12, based on tin- 

 descriptions of Hyden (113) and Palay (172, 173). 

 With the introduction of centrifugal fractionation of 

 cell constituents by Bensley & Hoerr (20) and its 

 amplification by Claude (41), the biochemist has 

 been provided with a means of studying some of the 

 same cellular elements in isolation. Fractions obtained 

 in this wav are also summarized in figure 12. Such 

 studies have been carried out primarily on liver cells 

 and have provided a wealth of data (109, 205, 206). 

 Unlike the liver, which is relatively homogeneous, 

 the central nervous system does not lend itself so well 

 to this type of study since the fractions obtained 

 include elements from all cell types present. 



Several such studies have been carried out, pro- 

 viding a general idea of the chemical organization of 

 cell components, which probably applies in general 

 to the neuron (2-5, 28, 33, 34, 39, 48a, 83, 90, 102, 



HO, 156, 186, 195, 235, 243). A composite summary 

 of these results is presented in table 6. Since the data 

 ate composites, they may not represent absolute 

 values for the various fractions; but the general 

 relationships indicated are probably representative 

 of the actual situation. 



There are some significant but not unexpected 

 differences in composition. Virtually all the DNA is 

 in the nuclear fraction, whereas the RXA is primarily 

 associated with the microsomal fraction (equivalent 

 to the Nissl bodies). By electron microscopy the Nissl 

 bodies have been shown to be composed of a vesicular 

 membrane (endoplasmic reticulum) surrounded by 

 clusters of small granules about 10 to 30 mp in 

 diameter (173). When these two components are 

 separated by ultracentrifugation, at least 80 per cent 

 of the RNA content is found with the granules (2, 

 171, 224), suggesting that they are essentially pure 

 ribonucleic acid and ribonucleoprotein. It is of 

 interest that this same microsomal fraction contains 

 the bulk of cellular phosphatides which, in contrast 

 to the RNA, appear to be primarily associated with 

 the membraneous element. 8 



3 Mitochondria from liver have been similarly fractionated 

 into the particulate matter (cristae) and fluid matrix (108). 

 The cristae appear to carry the oxidative enzymes bound to 

 the membranes, while the matrix contains soluble enzymes 

 such as dehydrogenases, potassium and other solutes (108, 

 160, 169). Lehninger et al. 1 1371 have succeeded in chemically 



