THE BIOCHEMICAL changes in brain lipids during early development have been divided into four periods (MCILWAIN, 1959). The first stage is characterized by an increase in the number of cells. In man, this period is largely complete within the first two-thirds of the gestation period. In this phase, the brain appears electrically silent (CRAIN, 1952;HILL, 1955). The second phase is histologically characterized by growth of cells, axons and dendrites and, in man, continues until parturition. In this period electrical activity can be detected from the cortex (HILL, 1955). The third stage is characterized by myelination and, in addition, co-ordination of muscular movements begins (HEALD, 1960). In man this phase occupies the first 210 days after birth. The fourth stage includes the period characterized by further myelination and the establishment of the adult pattern of cortical and subcortical activity.Biochemically, these phases are all characterized by an increasing oxygen consumption (HIMWICH, 1951) and in intermediate metabolism the glycolytic pathway is modified towards a more aerobic one with more and more predominance of the heart type (H4) of the five lactate dehydrogenase isoenzymes (GERHARDT, OVLISEN, CLAUSEN and ANDERSEN, 1964). As the metabolic processes, and thereby also the electrical activity of brain tissue, are intimately related to the membrane structures of the cells (MCILWAIN, 1963), the foetal development of the structural lipids and proteolipids is intimately related not only to the first, but also to the second phase in foetal development. It is, therefore, the aim of this study to give some data about the internal changes in the extractable lipids during the gestation period. MATERIALS A N D M E T H O D SFoetal material. Twenty-one foetuses were used. They were obtained by legal abortions through the Perinatal Research Laboratory from different obstetric departments in Copenhagen. The ages of the foetuses were evaluated by means of the crown-rump length and/or the foot length as described by TROLLE (1948). Furthermore, brains from two infants were used.Biochemical methods. The brain was taken out by opening the skull along the fontanels followed by sectioning just below the medulla oblongata. Samples were taken out for estimation of total lipid, total extractable protein and, finally, for thin-layer chromatography and Sephadex filtration of the polar lipids. The wet weight of all samples was determined. The lipids were extracted with ch1oroform:methanol (2:l v/v) as described by FOLCH, ASCOLI, LEES, MEATH and LEBARON (1951) and the total lipid was measured by weighting after evaporation of the extraction fluid.Thin-layer chromatography. The polar lipids were separated by thin-layer chromatography on Kiesel Gel as described by STAHL (1956) using the ascending system. The chromatography was
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