CHANGES OCCURRING IN THE CHEMICAL COMPOSITION OF THE CENTRAL NERVOUS SYSTEM DURING FOETAL AND POST-NATAL DEVELOPMENT OF THE SHEEP

(1) 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.     

THE CHANGES IN CHEMICAL COMPOSITION DURING DEVELOPMENT OF THE BOVINE NUCHAL LIGAMENT

Whole bovine nuchal ligaments, or portions thereof (in the case of commercially valuable animals), were obtained from 45 animals (28 fetal and 17 postnatal) ranging in age from 110 days of gestation to 10 yr. Insoluble elastin was quantitatively prepared from the fresh ligaments by extraction with hot alkali and by a combination of multiple extractions with alkaline buffer and then repeated autoclaving. When adult samples were examined, the yields of insoluble residue by these two methods were very similar, but with young fetal samples the second method gave significantly higher values, because of incomplete purification of the elastin residue. The changes in the concentration of collagen, alkali-insoluble elastin, and DNA have been examined. DNA concentration, and, thus, cell population density, fell progressively during the fetal period of development, to reach a steady value soon after birth. Collagen appeared in appreciable quantities before elastin, but its concentration was rapidly halved at about the time of birth. Insoluble elastin concentration was low until the end of the 7th fetal month, at which time it began to rise rapidly. The rate of increase in elastin concentration remained high throughout the next 10–12 wk, by which time the adult value had been reached. Quantitative studies, on the basis of the whole ligament, showed that the total cell content rises to a maximum at birth, but falls soon after to a level about half that at birth. Total collagen production and elastin deposition continue at a steady, maximal rate over the interval from 235 days of gestation to the end of the 1st postnatal month. It is concluded that the immediate postnatal period would be the most favorable phase in which to attempt the isolation of the soluble precursor elastin.     

CHEMICAL CHANGES IN LESPEDEZA ASSOCIATED WITH INDUCED POLYPLOIDY

Hanson , C. H. (U.S.D.A., Beltsville, Md.), W. A. Cope and R. M. Brinkley . Chemical changes in Lespedeza associated with induced polyploidy. Amer. Jour. Bot. 46(1): 36-39. 1959.— Changes in the quantities of 5 chemical constituents which were associated with induced polyploidy were studied using leaves of the following polyploids: Autotetraploids—Lespedeza cuneata, L. latissima, L. stipulacea, and L. striata; amphidiploids—L. hedysaroides × L. cuneata and L. latissima × L. cuneata. L. stipulacea and L. striata were annuals with low concentrations of tannin; the other species were perennials and high in tannin content. The polyploids were generally lower in crude protein, P₂O₅, and CaO, and higher in K₂O and total tannin. The greatest and most significant shift was in total tannin. Induced polyploids of Lespedeza did not appear promising as forage plants.     

BIOCHEMICAL CHANGES IN RAT BRAIN ASSOCIATED WITH THE DEVELOPMENT OF THE BLOOD-BRAIN BARRIER

—Subcellular fractions from brains of 5, 10, 13, 16, 21, 30 day-old and adult rats were prepared. Protein content and various enzyme activities were assayed in all fractions and brain homogenates. γ-Glutamyl transpeptidase activity and 5′-nucleotidase were very low at 5 days of life but steadily increased, reaching adult concentrations at about 30 days after birth. Alkaline phosphatase, instead slowly decreased with maturation, while monoamine oxidase after an initial decrease, increased rapidly to adult levels. The relation between the appearance of enzymatic activity in brain and the blood-brain barrier function is discussed.     

CHANGES IN THE PROTEIN COMPOSITION OF MOUSE BRAIN MYELIN DURING DEVELOPMENT

Abstract— Myelin was isolated from the brains of mice at various ages by a procedure involving a final purification on a continuous CsCl gradient. Myelin protein accumulated throughout development, increasing from 0.25 mg of protein/brain at 8 days of postnatal age to 3.5 mg of protein/brain at 300 days, although the rate of accumulation was greatest at about 21 days of age. Quantitative studies of the protein composition of these samples were carried out, utilizing discontinuous polyacrylamide gel electrophoresis in buffers containing sodium lauryl sulphate. Mouse brain myelin, contained (in order of increasing molecular weight) two basic proteins, an uncharacterized doublet, proteolipid protein, and a group of high molecular weight proteins. There were marked changes in the quantitative distribution of these proteins with increasing postnatal age. The basic protein fraction of total myelin protein increased from about 18 per cent at 8 days to 30 per cent at 300 days of age. Proteolipid protein increased even more dramatically, from 7 to 27 per cent in the same time interval. These chemical studies were correlated with ultrastructural investigations, both of the developing myelin sheath in situ and the isolated myelin obtained from mice of various ages. A hypothesis, relating the observed changes in protein composition of myelin during development to its mode of formation, is developed. Another subcellular fraction, separated from myelin, by virtue of its greater density in a CsCl gradient, was also studied. It was a vesicular, membranous fraction present at a level of 0.35 mg of protein/brain at all ages and was related to myelin in terms of protein composition.     

PHENOLIC COMPOUNDS ASSOCIATED WITH DEVELOPMENT IN THE LIVERWORT MARCHANTIA POLYMORPHA

Extracts of Marchantia polymorpha contain substances which, in vitro, strongly inhibit or enhance indoleacetic acid oxidation by both horseradish peroxidase and an IAA oxidase enzyme from M. polymorpha. The extracts can be partially freed of such activity by dialysis, passage through a column of polyvinylpyrrolidone powder, or extraction with an anion exchange resin. Chromatographic separation of the extract revealed the presence of four as yet unidentified phenolic compounds. Two inhibited and two enhanced IAA oxidase activity. Inhibitory activity was not destroyed by horseradish peroxidase in the absence of IAA. The level of these compounds in various regions of thallus was measured. Inhibitors were present throughout the tissue, with some localization in the basal and apical areas; there was an acropetal gradient of increasing cofactor concentration.     

林窗中植物竞争强度随林窗发育的变化

 通过野外移植外来种尾叶桉(Eucalyptus urophylla)、大叶相思(Acacia auriculaef ormis)和本地种荷木(Schima superba) 3种幼苗,挖沟排除根竞争和砍树创造林窗排除地上竞争的实验,来测定林窗形成后植物地下竞争和地上竞争强度的变化以及这些竞争对3种幼苗生长的影响。在林窗内,尾叶桉、大叶相思和荷木受到的地下竞争强度和地上竞争强度均呈现出随林窗年龄的增长而逐渐增大的趋势。外来种尾叶桉和大叶相思受到的地上竞争强度大于本地种荷木受到的地上竞争强度,而荷木受到的地下竞争强度大于两种外来种受到的地下竞争强度。在只有地下竞争和地上竞争时,这3种幼苗的相对生长速率均小于没有竞争时,这反映了地下竞争和地上竞争对3种幼苗的生长有抑制性影响,而且这种影响在本地种和外来种间存在差异。