The in vivo incorporation of linolenic acid into neuronal and glial cells and myelin

Abstract— Neurons, astrocytes, oligodendrocytes, and myelin were prepared from 21-day-old rat brain at various times after intracerebral injection of [1-¹⁴C]linolenate. Comparisons of phospholipid specific radioactivity demonstrated that the oligodendrocytes were much more active than neuronal, astroglial, or myelin fractions. This is consistent with the concept that the oligodendrocyte is responsible for synthesis of the relatively large mass of myelin sheath. Initially the phosphatidylcholine fraction was more active than the phosphatidylethanolamine fraction, but during the 36 h after injection the former decreased in radioactivity while the latter fraction showed an increase. Fatty acid elongation occurred rapidly. Within 2h after injection, 2/3 of the label had been converted to elongated products (20:4. 20:5, 22:5 and 22:6). All three cell types apparently contained the enzymes necessary to incorporate, elongate, and desaturate linolenic acid and this occurred at similar rates in each cell type. No direct precursor-product relationship was found between the lipids of oligodendrocytes and myelin. There was, however, a lag in the appearance of elongated fatty acids in the phosphoglycerides of myelin. indicating that the polyunsaturated fatty acids in myelin were synthesized elsewhere and transported into the myelin sheath.     

THE INCORPORATION OF [1-14C]LINOLENATE INTO LIPIDS OF DEVELOPING RAT BRAIN DURING ESSENTIAL FATTY ACID DEPRIVATION

Abstract— Twenty-one-day old essential fatty acid (EFA) deprived rats incorporated about twice the radioactivity from [1-¹⁴C]linolenate into brain lipid fractions as did controls. At 5 min after injection, 2/3 of the radioactivity was associated with the less polar lipid fraction of both control and EFA deprived animals. By 30 min after injection, 70% of the radioactivity was in the phospholipid fraction. This value increased to 90% at later time points.
The specific activity of brain phospholipids from EFA deprived rats was always greater than that of controls. This held true for the individual phosphatide fractions also. In general, phosphatidylcholine (PC) was labeled most rapidly. With increasing time intervals, radioactivity was transferred to phospha-tidylethanolamine (PE) and phosphatidylserine + phosphatidylinositol (PS + PI).
The transfer of fatty acid radioactivity into phospholipid and the distribution of radioactivity among individual phosphatides did not appear to be affected by the dietary state. However, the total amount of radioactivity incorporated was related to the amount initially retained by brain after injection. Our data suggest that one or more components of the less polar lipid fraction may act as a 'trap' or reservoir for fatty acids which are required for phospholipid synthesis.     

Four-Hour Urease Test for Distinguishing Between Klebsiella and Enterobacter

Infections with Klebsiella and Enterobacter have increased among hospitalized patients. To study such infections, relatively simple but precise methods are needed for clinical laboratories to identify the two genera accurately. Moreover, a rapid identification is essential for assisting with the therapy of the patients. For this purpose, a new 4-hr urease test was developed so that colonies could be tested directly from blood-agar plates which have been inoculated with clinical material and allowed to incubate overnight. This 4-hr test was positive with 98.5% of 202 Klebsiella species and negative with 80 Enterobacter species. As a single criterion for distinguishing between the two major genera, the new 4-hr urease test was just as accurate as a motility test (99% of the 282 isolates were accurately identified with either). The 4-hr urease test represents a simple, rapid, and reliable technique which is ideally suited for use in clinical microbiology laboratories.     

CHANGES IN PHOSPHOGLYCERIDE FATTY ACIDS OF RAT BRAIN INDUCED BY LINOLEIC AND LINOLENIC ACIDS AFTER PRE- AND POST-NATAL FAT DEPRIVATION

Abstract— Pregnant rats were maintained on a fat-free diet, starting at 10–12 days after impregnation and the offspring continued on the diet during a developmental period of 120 days. Brain fatty acids showed decreases in the level of (n-3) and (n-6) fatty acids of brain phophoglycerides, except for 22:5 (n-6) which increased. These changes preceded an increase in the (n-9) fatty acids (20:3 and 22:3). Supplementation with either linoleic or linolenic acid for 10 or 30 days after induction of the deficiency state caused an increase in the (n-6) and (n-3) fatty acids respectively, to control levels. The level of 22:5 (n-6) was increased additionally by linoleic supplementation while linolenic refeeding to deficient animals decreased 22:5 (n-6) to near control levels. The anomalous results obtained on 22:5 (n-6) with 18:3 (n-3) supplementation is attributed to competitive inhibition of linoleate desaturation by linolenate. Linoleic and linolenic acid were equally effective in reducing the elevated levels of the (n-9) fatty acids toward control levels, although control levels with either fatty acid was not reached after 30 days supplementation. The increase of the (n-6) and (n-3) fatty acids to normal values precedes the decrease of (n-9) fatty acids following supplementation of linoleic or linolenic acid to fat-deficient rats. No change in fatty acid composition in control animals between 30 and 120 days was observed. In fat deficient as well as supplemented animals the total saturated, monounsaturated and polyunsatur-ated fatty acid composition was constant as was the unsaturation index.     

Acetate-1-14C incorporation into polyunsaturated fatty acids of phospholipids of developing chick brain

The incorporation of acetate-1-(14)C into the polyunsaturated fatty acids of glycerophosphatides of chick embryonic brain has been studied. After the injection of acetate-1-(14)C into the yolk sac, differences were found in the degree of labeling of the major fatty acids of the omega3 and omega6 series. Arachidonic acid (20:4omega6) showed a high degree of radioactivity while docosahexaenoic acid (22:6omega3) was poorly labeled, at a period of brain development when both fatty acids were being actively deposited. Evidence is presented to indicate that the low activity in docosahexaenoic acid is not explicable on the basis of either a low or high rate of turnover of this polyenoic acid. Similar results were obtained whether the rapid early or slower late stage of brain development was examined. It is suggested that the elongation of omega3 and omega6 series acids may be under the control of different regulatory mechanisms.     

Esterases of developing human brain

Abstract The free and bound nonspecific esterases occurring in, respectively, the saline and triton X-100 extracts of adult and developing human brain were studied by starch gel electrophoresis (zymograms). Zymograms of the free esterase fraction visualized with NA as substrate were qualitatively similar at 5-12 days of age to the electrophoretic patterns observed in adult material. In both adult and developing brain, zymograms of bound esterase resembled those of the free enzyme, the major difference being the presence in the former of a slow, broad, anodic zone of diethyl-p-nitrophenyl phosphate-inhibited enzyme. Esterases characteristic of adult white matter and having preferential affinity for alpha-naphthylpropionate, alpha-naphthyl butyrate and alpha-naphthyl valerate were not identified in infant brain until about 4 months postnatal age. A far-moving, anodic enzyme was distinctly evident in zymograms of brains of less than 1 month of age. This enzyme hydrolysed NP, NB, and NV more actively than alpha-naphthyl acetate. It was present in the adult brain but, in contrast to the infant, was no longer electrophoretically-separable from another enzyme which had greater affinity for NA and had previously been designated the A₁₀ band. Quantitative assays demonstrated that the bound esterase increased in cerebral and cerebellar cortex during development. In contrast, the proportion of free to bound esterase showed little change in white matter. Acetylcholinesterase and butyrylcholinesterase zymograms became identical to adult patterns from 1 to 4 months of age. Thiolacetic acid esterase was present at 38 weeks gestation. Some functional and anatomical correlations were attempted in explanation of the biochemical observations.