The turnover of phosphatidyl choline in rat cerebral cortex membranes in vivo

Lapetina, Eduardo G.; Lunt, George G.; Robertis, E. De

doi:10.1002/neu.480010305

Cited by 20 publications

(5 citation statements)

References 20 publications

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“…More recently, Friede and Samorajski (21) and Webster (54) have done careful morphological investigations which suggest that growth of the myelin sheath occurs at the region of the outer mesaxon. Biochemical studies of lecithin metabolism in brain (28,31,50) and tissue culture (27) have indicated that myelin metabolism of this component does not cease in the adult. The studies.…”

Section: Discussionmentioning

confidence: 99%

Incorporation of newly formed lecithin into peripheral nerve myelin.

Gould¹,

Dawson²

1976

The Journal of Cell Biology

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Radioactive choline was used to study the metabolism and movement of choline-containing phospholipids in peripheral nerve myelin of adult mice. Incorporation at various times after intraperitoneal injection was measured in serial segments of sciatic nerve as well as in myelin isolated from those segments. At no time (1 h to 35 days) could a proximal-distal difference in the extent of labeling be demonstrated. This finding suggests that incorporation of precursor choline phospholipids into nerve membranes is a local event, with little contribution from the neuronal perikaryon via axoplasmic transport.Autoradiographic investigations were undertaken to elucidate the pattern of movement of radioactive choline-labeled phospholipids, predominantly lecithin, into the myelin sheaths of the sciatic nerve. A sequence of autoradiographs was prepared from animals sacrificed between 20 min and 35 days after a microinjection of precursor directly into the nerve. Analysis of these autoradiograms revealed that labeling is initially concentrated in the Schwann cell cytoplasm. Later, the label moves first into the outer regions of the myelin sheaths and is eventually distributed evenly throughout the inner and outer layers of the sheath. At no time is there a build-up of label in the axon.The rate of uptake of precursor and subsequent redistribution of lecithin into the myelin were also examined in frog sciatic nerve (18~ Both uptake and redistribution processes were considerably slower in the cold-blooded animal.Various metabolic studies ( 15, 57) have shown that the sequence of events responsible for the dynamic turnover of membrane phospholipid (and protein) components includes synthesis in the endoplasmic reticulum and subsequent translocation to a variety of other membrane structures. Many recent reports have supported the contention that a turnover of myelin phospholipids occurs in the brain of adult animals (e.g. 9, 28, 29, 50). Miller and Dawson (34), employing subcellular fractionation of brain, have shown that most phospholipid biosynthesis including that of phosphatiylcholine takes place in "microsomes," with no activities detectable in isolated mitochondria or myelin. In addition, these authors (35) were unable to detect any component in brain cytoplasm which could

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Section: Discussionmentioning

confidence: 99%

Incorporation of newly formed lecithin into peripheral nerve myelin.

Gould¹,

Dawson²

1976

The Journal of Cell Biology

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“…The radioactivity recovered from the supernate as phosphorylcholine, choline, or acetylcholine plus that solubilized from the pellet by chloroform-methanol accounted for 92% of the total radioactivity present in the homogenate . Previous data in a variety of neural tissues indicate that most of the choline present in the phospholipid pathway after briefexposure to [''H]choline is in the form of phosphorylcholine or phosphatidylcholine (10,20,46,48). That this was the case for the rabbit retina was confirmed in retinas where a chloroformmethanol extract of the pellet was prepared according to Folch et al (28) and analyzed by thin-layer chromatography on silica gel in 95 :36:6 chloroform : methanol :water according to Flower and Blackwell (27) .…”

Section: Chemical Analysismentioning

confidence: 99%

Autoradiographic identification of acetylcholine in the rabbit retina.

Masland¹,

Mills²

1979

The Journal of Cell Biology

280

144

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Retinas pulse-labeled by a 15-min exposure to 0.3 ,uM [3H]choline were incubated for a subsequent hour under chase conditions designed either to retain newly synthesized acetylcholine within synapses or to promote its release. At the end of this time the two groups of retinas were found to contain equal amounts of radioactivity in the phospholipid pathway, but only the retinas incubated under the acetylcholine-protecting conditions contained [3H]acetylcholine. Freeze-dried, vacuum-embedded tissue from each retina was autoradiographed on dry emulsion . All retinas showed silver grains over the photoreceptor cells and faint labeling of all ganglion cells. In the retinas that contained [3H]acetylcholine, silver grains also accumulated densely over a few cells with the position of amacrine cells, over a subset of the cells of the ganglion cell layer, and in two bands over the inner plexiform layer.Fixation of the retina with aqueous osmium tetroxide retained only the radioactive compounds located in the photoreceptor and ganglion cells. Sections from freeze-dried tissue lost their water-soluble choline metabolites when exposed to water, and autoradiography of such sections again revealed radioactivity primarily in the photoreceptor and ganglion cells. Radioactive compounds extracted from the sections were found to faithfully reflect those present in the tissue before processing; analysis of the compounds eluted from sections microdissected along the outer plexiform layer showed [3H]acetylcholine to have been synthesized only by cells of the inner retina.Taken together, these results indicate that the photoreceptors and ganglion cells are distinguished by a rapid synthesis of choline-containing phospholipids, while acetylcholine synthesis is restricted to a few cells at both margins of the inner plexiform layer. They imply that the only neurons to release acetylcholine within the rabbit retina are a small group of probable amacrine cells. J. CELL BIOLOGY

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“…Although brain lipids may be labeled in vivo by many types of precursors, the information gained is influenced by the choice of precursors. The use of choline (10,11) or ethanolamine (12,13) as precursors is restricted to comparisons of subclasses of the respective phosphoglycerides. Acetate and glucose ( 14,15) are incorporated not only into all lipid classes but also into all moieties of the lipid molecules.…”

Section: Introductionmentioning

confidence: 99%

Incorporation of [1‐¹⁴C]‐oleic acid into neutral glycerides and phosphoglycerides of mouse brain

Yau

Sun

1973

Lipids

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The incorporation of [1‐14C]‐oleic acid into the neutral glycerides and phosphoglycerides of adult mouse brain was examined between 1 and 80 min after intracerebral injection. Radioactivity of the free oleic acid in brain decreased rapidly with a half‐life of ca. 5 min. The specific radioactivity of the phosphatidic acids was highest at 1 min after injection. This was followed by the diacylglycerols and triacylglycerols which attained a maximum specific radioactivity at 3 and 20 min after injection, respectively. Specific radioactivities of the neutral glycerides were higher than the phosphoglycerides. A larger proportion of the radioactivity in the diacylglycerols was transferred to the phosphoglycerides than to the triacylglycerols. Among the phosphoglycerides, radioactivity was actively incorporated into the inositol phosphoglycerides. The specific radioactivity of the inositol phosphoglycerides was higher than the diacylsn‐glycero‐3‐phosphorylcholines, and the kinetics of incorporation of radioactivity into these lipids was also different. A water soluble material was found which showed maximum specific radioactivity at 6–10 min after injection. The properties of this water soluble material suggested that it may be an intermediate involved in the acyl group metabolism of phosphoglycerides in brain.

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The turnover of phosphatidyl choline in rat cerebral cortex membranes in vivo

Cited by 20 publications

References 20 publications

Incorporation of newly formed lecithin into peripheral nerve myelin.

Incorporation of newly formed lecithin into peripheral nerve myelin.

Autoradiographic identification of acetylcholine in the rabbit retina.

Incorporation of [1‐¹⁴C]‐oleic acid into neutral glycerides and phosphoglycerides of mouse brain

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The turnover of phosphatidyl choline in rat cerebral cortex membranes in vivo

Cited by 20 publications

References 20 publications

Incorporation of newly formed lecithin into peripheral nerve myelin.

Incorporation of newly formed lecithin into peripheral nerve myelin.

Autoradiographic identification of acetylcholine in the rabbit retina.

Incorporation of [1‐14C]‐oleic acid into neutral glycerides and phosphoglycerides of mouse brain

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Incorporation of [1‐¹⁴C]‐oleic acid into neutral glycerides and phosphoglycerides of mouse brain