I) The chemical composition of the CNS (separated into cerebrum, cerebellum, brain stem and spinal cord) was determined in sheep during foetal and post-natal development and in adults.(2) The spinal cord differed from the remainder of the CNS in growing more after the period studied (50-day-old foetuses to 5-week-old lambs) than before it. This was largely attributable to lipid accumulation.(3) Chemical growth (accumulation of DNA, protein and lipid) proceeded linearly in spinal cord, logarithmically in cerebrum and cerebellum while in brain stem growth was described by a sigmoid function.(4) Fat-free dry matter, protein, total lipid, cholesterol and phospholipid concentrations increased progressively in all parts of the CNS but DNA concentrations changed little. In the cerebrum alone there was an increase in DNA concentration during maturation suggesting an increased cell population. Cholesterol was present predominantly in the free form but esters were detected in foetal tissues from 70 up to 120 days gestation.(5) Cerebroside, the characteristic lipid of myelin, increased in concentration soon after 85 days of gestation, up to which point very low values were recorded, the rate varying according to the region of the CNS examined. Rates of increase in total regional cerebroside content were used to identify periods of myelination and the results suggest that there are two periods of peak activity, one about 20 days before birth and the other at 10-20 days after birth.(6) The composition of lipids added during the two phases of myelination and during maturation were characteristically different. In the spinal cord, lipid analyses best reflect changes in myelin composition. DAVISON and OXBERRY, 1964, 1969; PATTERSON, TERLECKI, DONE, SWEASEY and HEBERT, 1971) there has been little detailed analytical data relating to the chemistry of normal ovine development. To varying extents, individual investigators have met this need by using appropriate healthy controls. The present neurochemical study of the developing lamb CNS sought to provide some of the required basic data, extending earlier preliminary results for the spinal cord (PATTERSON and SWEASEY, 1970) to include four anatomically defined parts of the CNS : cerebrum, cerebellum, brain stem and spinal cord. MATERIALS A N D METHODS Animals. Clun Forest or Suffolk cross ewes mated with a Dorset Horn ram were used in this study which spanned two lambing seasons. The Suffolk cross ewes were spread as evenly as possible amongst groups of Clun Forest ewes so that, at each stage of development investigated, they contributed approx. one-fifth of the Iambs or foetuses. Each group of adult ewes consisted of five Cluns and one Suffolk cross. Mating dates were recorded and foetuses were removed from the ewes by Caesarian 2027 * A significant proportion present in the esterified form. p1 J a 9
IN EARLIER neurochemical studies of diseased central nervous tissues of lambs (HOWELL,