LIPIDS PRESENT IN BRAIN AND NERVOUS TISSUE 745 



following unsaturated acids are listed as being present under certain condi- 

 tions, in addition to oleic acid and hexadecenoic acid 226-229 : 



C 2 o acids A u -Eicosenoic acid 



A 11>14 -Eicosadienoic acid 

 A Bi8,u -Eicosatrienoic acid 

 A B,8,11,14 -Eicosatetraenoic acid 



C22 acids A 7 ' 10 ' 13 -Docosatrienoic acid 



A 4 * 7,10,13 -Docosatetraenoic acid 

 A 7, 10, 13 > 16 -Docosatetraenoic acid 

 A 4 - 7 ' 10 - 13 - 16 -Docosapentaenoic acid 

 A 7 - 10 ' 13> 16 > 19 -Docosapentaenoic acid 

 ^4,7, 10, 13, i6, 19-Docosahexaenoic acid 



The high proportion of unsaturated acids in the cephalin fractions in the 

 brain is of interest. Although the C 2 4-acids are the principal acids in the 

 case of cerebrosides, they are practically absent in the phospholipids. 

 Beauvallet and Manuel 230 have called attention to the high proportion of 

 arachidonic acid occurring in the phospholipids of nervous tissue; these 

 workers suggest that this acid plays a structural rather than a dynamic 

 role in this case. 



Sphingomyelin is another important phospholipid in nervous tissue. 

 According to Johnson et al., 2Z1 both white and gray matter are character- 

 ized by a relatively high concentration of sphingomyelin, together with 

 cholesterol and cerebroside. The white matter in beef brain has been 

 shown to have four times as much sphingomyelin as the gray matter. 37 

 According to Thannhauser and co-workers, 36 sphingomyelin accounts for 

 20% of the total phospholipids in the brain and for only 5 to 10% of these 

 lipids in most other organs. 



The great difference in sphingomyelin content in the brain and in the 

 peripheral nerves is evident from the studies of Schmidt, Benotti, Hersh- 

 man, and Thannhauser. 37 In the case of the rat, this compound comprised 

 5% of the total phospholipids in the brain, compared with 22% in the sci- 

 atic nerve. In the cat, sphingomyelin accounted for 24% of the brain phos- 

 pholipids while, in the sciatic nerve, it made up 46.3 of the total phos- 

 pholipid content. The variation in sphingomyelin content between the 

 brain and the spinal cord is emphasized in the studies of Carter and asso- 



226 E. Klenk, Z. physiol. Chem., 200, 51-68 (1931). 



227 E. Klenk, Z. physiol. Chem., 206, 25-40 (1932). 



228 K. Schuwirth, Z. physiol. Chem., 277, 147-158 (1943). 



229 E. Klenk and W. Bongard, Z. physiol. Chem., 291, 104-118 (1952). 



230 M. Beauvallet and S. Manuel, Compt. rend. soc. biol., 144, 1599-1602 (1950). 



231 A. C. Johnson. A. R. McNabb, and R. J. Rossiter, Biochem. J., 43, xxii (1948). 



