The influence of nutritional disorder on the lipid composition of the central nervous system

I n recent years there has been growing interest in the effects of malnutrition on the developing brain (Dobbing, 1967;Coursin, 1967).The proposition that undernutrition may be associated with impaired intellectual function is quite clearly a topic of considerable medical and social interest.From an economic standpoint nutritional disorder is also of importance, for failure to thrive in some farm animals can also be related to permanent damage to the developing ccntral nervous systcm.I n adults, damage to the central nervous system may result in demyelination, while, in developing animals, incomplete or faulty myelination may be produced by disease or nutritional disorder.Some indication of the nature and extent of such effects can be obtained from a knowledge of the metabolism of neural lipids and from an examination of changes in the lipid composition of brain and spinal cord, for more than half the total brain lipid is localized within the myelin sheath.Myelin is particularly rich in lipid containing cholesterol, cerebrosides and phospholipids together with protein-the last accounting for about a quarter of the dry weight of myelin.T h e lipid and protein are firmly associated in fixed proportions within myelin and there are only small differences in its composition even between species (Cuzner, Davison & Gregson, I 965).Experiments using isotopic precursors indicate that the myelin sheath is one of the most metabolically stable structures in the body.Radioactive isotopes incorporated into the myelin of growing animals indicate little change in its constituents in more than a year (Davison, 1964).I n addition, lipid biosynthesis is most active during the period of myelination and in the nervous system of adult animals the rate of synthesis of myelin lipid is slow, It has therefore been suggested (Davison & Dobbing, 1966) that the period of myelination may be regarded as a vulnerable period in development, for restrictions at this time could reduce the supply of suitable substrates and, by inhibiting lipid biosynthesis, interfere with the process of myelination.It would be expected that deprivation of the mature nervous system would have little effect.