Lipids of the Nervous System: Changes with Age, Species Variations, Lipid Class Relationships, and Comparison of Brain to Other Organs

Abstract

Changes with age of the lipid composition of human and animal brains were investigated. Individuals of the same species were found to differ and fall into one of four groups differing in lipid content. Species differences among animals were small and fungal mycelia were similar to animals. The total amount of lipid in brain and other organs increases during differentiation (i.e. with advancing age) and then, as shown for humans, declines (after 26 years of age). The changes were defined by two forms of graphic analysis. In one, the total amount of lipid, the amount of each lipid class, or sums of various classes were plotted as a function of age. In the other, the amount of one lipid and the sums of various lipids were plotted against total lipid or sums of various lipid classes. The latter plots were used to define the interrelationships of the lipid classes and to provide information necessary to fit lines through points on lipid vs. age plots. During development, some brain lipid classes make up progressively less of the total, whereas the relative amount of other classes increases. Thus, some lipid classes substitute for others. Two general substitution groups were recognized by graphic analysis. In substitution group I, the changes with age consist of an increase of cerebroside, sulfatide, and sphingomyelin with a decrease of phosphatidyl choline and phosphatidyl ethanolamine. In group II, a decline of phosphatidyl inositol and other acidic lipids is balanced by a rise of phosphatidyl serine. Equations defining the relationship of each lipid class to total lipid of brain and other organs are presented. Equations defining the changes in the total amounts of each lipid class of human brain as a function of age are also presented.