摘要:

Abstract—The characteristics of the accumulation of 14 L‐amino acids (Leu, Ileu, Val, His, Tyr, Phe, Gly, Ala, Ser, Thr, Asp, Pro, Arg and Lys) by synaptosomal fractions prepared from rat brains were studied. Distinct differences were observed in the ion requirements for the accumulation of these amino acids. The accumulation of Asp and Pro alone showed a total requirement for Na+; uptakes of the other amino acids were either maximal in Na+‐free media or only partially dependent on the presence of external Na+. With brain maturation, two types of developmental alterations could be distinguished: (1) changes in rates of influx, and (2) changes in the effects of ions. Synaptosomal fractions prepared from brains of immature rats accumulated Leu, Arg and Lys to a greater extent and Val, Tyr, Pro and Asp to a lesser extent than did the fractions prepared from brains of mature animals. The accumulation of Ser and Thr by immature fractions was partially dependent on external Na+, whereas their accumulation by adult fractions was Na+‐independent. These alterations in Na+requirements coincided with developmental changes in mutual inhibitions of amino acid tr

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb05086.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Abstract—The superfused, isolated retina of the chicken was used to investigate the mechanisms responsible for the increase in retinal transparency and the release of glutamate associated with stimuli known to elicit spreading depression (SD). We sought to distinguish between (1) mechanisms involving glutamate‐induced increase in Na+permeability and consequent uptake of extracellular material into the intracellular compartment and (2) mechanisms involving interference with operation of the Na+pump that would result in a similar uptake of extracellular materials. Tetrodotoxin (which inhibits inward movements of Na+) depressed the transparency increase caused by stimulation with glutamate but not that elicited by application of KCl. Ouabain (which inhibits the Na+pump) caused a marked increase in tissue transparency. The application of inhibitors of the aerobic metabolism, such as DNP or cyanide, or deprivation of O2had no effect on the retinal transparency; results suggesting that the energy for the Na+pump could be supplied by glycolysis. Indeed iodoacetate (which inhibits glycolysis) caused a marked change in transparency. Furthermore we found evidence for a compound in the superfusion fluid supplemented with iodoacetate that may be a reaction product of glutamate and iodoacetate. In some preparations superfusion with glucose‐free solutions caused a slowly developing increase in transparency and release of glutamate; in others the increase in transparency was more sudden and there was a larger release of glutamate. Seemingly, interference with the tissue metabolism can cause an uptake of extracellular material either by arrest of the Na+pump or by the release of glutamate, depending on the conditions of the exper

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb05087.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Abstract—Alterations in the localization and concentration of zinc in the hippocampus and in other regions of rat brain were studied during postnatal maturation. Histochemical observations indicated increasing levels of zinc in the hippocampal mossy fibre layer at about 20 days of age. Between 18 and 22 days, hippocampal levels of zinc increased by 35 per cent to reach adult levels (121 ng/mg of protein). After subcellular fractionation, more than one‐half of the hippocampal zinc was found in the first pellet (P1; 1085g– 10 min), where large boutons would be expected. Autoradiographic evidence, revealing the sequential location of positron tracks first in the granular cell layer and later in the mossy fibre layer, raises the possibility of axoplasmic transport of zinc from granule cell perikarya to their terminal boutons. Our data suggest that zinc may be involved in the maturation and function of the mossy fibre pa

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb05088.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Abstract—The incorporation of [3H]thymidine into nuclear DNA of rat brain progressively increased from birth until the 8th postnatal day and it was lowest in the adult brain. When isolated nuclei from brain cells were separated into a neuronal‐ and a glial‐rich fraction (composed of glial and neuroblast nuclei in young animals), the specific radioactivity of the DNA was higher in the glial‐rich fraction at all ages investigated. The incorporation of [3H]leucine into proteins of rat brain was considerably higher in the 8‐than in the 1‐day‐old rat. The greatest difference in the rate of protein synthesis between 8‐ and 1‐day‐old brain occurred in the nuclear proteins, especially those associated with DNA. There was an accumulation of protein and RNA in nuclei from brain cells from birth to the 8th postnatal day. The increased content of proteins occurred primarily in the fraction soluble in buffered s

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb05089.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Abstract—Total ornithine decarboxylase (ODC) (EC 4.1.1.17) activity per rat brain was elevated markedly from 14 days after conception to 12 days postnatum. ODC activity in the brainstem was very low and changed little during postnatal development. Activity in the cerebral hemispheres declined from a high level at birth to the low adult level by 8 days postnatum. Conversely activity in the cerebellum increased markedly from 3 days until 11 days postnatum, then suddenly decreased. Hence, the periods of greatest ODC activity paralleled those of maximal cell proliferation in each brain region. During perinatal brain development ODC activity changed considerably; it declined at about one day prior to term, and then increased rapidly to its highest level of activity at 4 h postnatum. Premature birth by caesarian section or lack of maternal care and nutrition did not affect this early postnatal response. The postnatal burst in ODC activity appears to be unique for brain tissue, since this response did not occur in heart, skeletal muscle or liver.Data from studies in which portions of fractions characterized by high or low enzymatic activity, respectively, were mixed or in which the supernatant enzyme fraction was dialysed are not consistent with the presence of direct inhibitors or activators of the enzyme. In addition, administration of cycloheximide to newborn rats abolished the 4‐h postnatal burst in ODC activity. Our results suggest that the increase in ODC activity reflects enzyme synthesisde n

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb05090.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Abstract—Cerebroside in the brain is highly localized in myelin and has a relatively slow turnover rate. The aim of this study was to evaluate the true cerebroside biosynthetic activity under conditions in which the degradation and reutilization of brain lipids were as small as possible. The 3‐week‐old mice were decapitated at 0·5, 1, 2·5, 5 and 15 min after the intraperitoneal injection of labelled acetate and the incorporation of radioactivity into each lipid class was examined. Even at 0·5 min, a considerable amount of radioactivity was found in simple lipids, especially in the free fatty acid fraction, and in the course of time the radioactivity of complex lipids increased. On the other hand, the incorporation of radioactivity into cerebrosides was extremely small throughout the experimental period. Results indicated that the low radioactivity of cerebroside might be due to its high content of long‐chain fatty acids which were weakly labelled. The radioactivity of the sphingosine moiety was also low. In short, one of the rate‐limiting steps of cerebroside synthesis in brain might exist in long‐chain fatty acid and sphingosine synthesis. In addition, the incorporation curves of each component of cerebroside were compared with each other and the difference of the incorporation pattern of non‐hydroxy fatty acids of cereb

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb05091.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

AbstractThe activities ofd‐glycerate dehydrogenase, 3‐phosphoglycerate dehydrogenase and lactate dehydrogenase have been measured in high‐speed supernatant fractions from different regions of the cat CNS. Onlyd‐glycerate dehydrogenase showed any significant regional variation in levels of activity, and this regional distribution correlated well with the regional distribution of glycine. In view of the previous finding that glycine inhibitsd‐glycerate dehydrogenase of rat cortex in a non‐competitive manner suggesting endproduct inhibition (Uhrand Sneddon, 1971) this correlation is considered additional evidence to suggest thatd‐glycerate may be an important source of glyci

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb05092.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

AbstractThe subcellular distributions of potassium, sodium, magnesium, calcium and chloride have been determined for rabbit cerebral cortex. After homogenization and differential centrifugation, the following percentages of ions were associated with the particulate fraction (nuclear, mitochondrial, synaptic vesicles, and microsomal): (a) 19% of the total potassium; (b) 22% of the total sodium; (c) 77% of the total calcium; (d) 69% of the total magnesium; and (e) less than 2% of the total chloride. However, the sum of the potassium and sodium content in each of the particulate fractions was greater than the sum of the calcium and magnesium content. After hypo‐osmotic shock of the crude mitochondrial fraction (MT), more sodium than potassium (μmol/g wet wt.) was associated with the mitochondrial (M1) and synaptic vesicle (M2) fractions. The molar ratio of sodium to potassium was 1·4 forM1and 4·5 forM2. The association of22Na+with the particulate fractions was further studied by the method of equilibrium dialysis. The data from both types of experiments indicate that a large fraction of the sodium in cortical tissue appears to be in a bound s

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb05093.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Abstract—ECS markedly increased tryptophan and 5‐hydroxyindoleacetic acid levels in brain. Brain serotonin and plasma tryptophan levels were unaffec

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb05094.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Abstract—In order to determine whether or not various histological elements of the nervous system may differ in their relative content of hexosaminidase A and B (O'Brien, Okada, Chenand Fillerup, 1970) and in the‘acid’and‘neutral’forms of β‐galactosidase (Ho and O'Brien, 1971), these isoenzymes were determined separately in the layers of human cerebellum. The proportion of the heat‐stable hexosaminidase B was greater in the granular layer than in the molecular layer or underlying white matter. The activity of the‘neutral’form of β‐galactosidase was very low compared to the‘acid’type, but its

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1972.tb05095.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY