Developmental changes in the fatty acids of synaptic membrane phospholipids: effect of protein malnutrition

Parallel changes in cortical neuron biochemistry and motor function in protein-energy malnourished adult rats

While protein-energy malnutrition in the adult has been reported to induce motor abnormalities and exaggerate motor deficits caused by stroke, it is not known if alterations in mature cortical neurons contribute to the functional deficits. Therefore, we explored if PEM in adult rats provoked changes in the biochemical profile of neurons in the forelimb and hindlimb regions of the motor cortex. Fourier transform infrared spectroscopic imaging using a synchrotron generated light source revealed for the first time altered lipid composition in neurons and subcellular domains (cytosol and nuclei) in a cortical layer and region-specific manner. This change measured by the area under the curve of the δ(CH₂) band may indicate modifications in membrane fluidity. These PEM-induced biochemical changes were associated with the development of abnormalities in forelimb use and posture. The findings of this study provide a mechanism by which PEM, if not treated, could exacerbate the course of various neurological disorders and diminish treatment efficacy.

Docosahexaenoic acid partially ameliorates deficits in social behavior and ultrasonic vocalizations caused by prenatal ethanol exposure

Prenatal ethanol exposure disrupts social behavior in humans and rodents. One system particularly important for social behavior is the somatosensory system. Prenatal ethanol exposure alters the structure and function of this area. Docosahexaenoic acid (DHA), an omega 3 polyunsaturated fatty acid, is necessary for normal brain development and brains from ethanol-exposed animals are DHA deficient. Thus, we determined whether postnatal DHA supplementation ameliorated behavioral deficits induced by prenatal ethanol exposure. Timed pregnant Long-Evans rats were assigned to one of three groups: ad libitum access to an ethanol-containing liquid diet, pair fed an isocaloric isonutritive non-alcohol liquid diet, or ad libitum access to chow and water. Pups were assigned to one of two postnatal treatment groups; gavaged intragastrically once per day between postnatal day (P)11 and P20 with DHA (10 mg/kg in artificial rat milk) or artificial rat milk. A third group was left untreated. Isolation-induced ultrasonic vocalizations (iUSVs) were recorded on P14. Social behavior and play-induced USVs were tested on P28 or P42. Somatosensory performance was tested with a gap crossing test around P33 or on P42. Anxiety was tested on elevated plus maze around P35. Animals exposed to ethanol prenatally vocalized less, play fought less, and crossed a significantly shorter gap than control-treated animals. Administration of DHA ameliorated these ethanol-induced deficits such that the ethanol-exposed animals given DHA were no longer significantly different to control-treated animals. Thus, DHA administration may have therapeutic value to reverse some of ethanol's damaging effects.

Large litters rearing changes brain expression of GLUT3 and acetylcholinesterase activity in adult rats

Effects of malnutrition in the brain are more pronounced during the period of growth spurt, corresponding to the suckling in rodents. Neuronal glucose transporter GLUT3 expression and acetylcholinesterase activity were studied in the brain of adult young rats (84 days old) suckled in litters formed by 6 (control group) or 12 pups (malnourished group). In the adult rats, brain weight, blood glucose levels and GLUT3 expression were decreased in malnourished group (5%, 18%, 58%, respectively, P<0.001, Student's t test) compared to the control. Increased activity of acetylcholinesterase was found in cerebral cortex homogenates and a significant interaction (P=0.019, ANOVA two-way, Tukey's test) was found between nutritional state and homogenate fraction. In summary, malnutrition during suckling period decreased GLUT3 expression and increased acetylcholinesterase activity in the rat brain that could contribute to possible cognitive deficits and changes of brain metabolic activity.

Identification of novel mammalian phospholipids containing threonine, aspartate, and glutamate as the base moiety

In this study, we showed the occurrence of phosphatidyl-L-threonine (PThr), phosphatidyl-L-aspartate (PAsp), and phosphatidyl-L-glutamate (PGlu) in rat brain. Analyses using an HPLC-ESI-MS and an amino acid analyzer showed the presence of L-threonine, L-aspartate, and L-glutamate in the acid-hydrolysates of phospholipids from porcine cerebrum, rat cerebrum, and rat liver. Results of ESI-MS/MS analyses with neutral loss scanning and product ion scanning suggest the presence of PThr-(18:0, 18:1), PThr-(18:0, 22:6), PAsp-(18:0, 18:1), PAsp-(18:0, 22:6), PGlu-(18:0, 18:1), and PGlu-(18:0, 22:6) in rat brain. This is the first study to identify 2 novel phospholipids, PAsp and PGlu, with a carboxylate-phosphate anhydride bond, in living organisms.

Biochemical and biological functions of docosahexaenoic acid in the nervous system: modulation by ethanol

Docosahexaenoic acid (DHA, 22:6n-3), an n-3 fatty acid highly concentrated in the central nervous system, is essential for proper neuronal and retinal function. While a high level of DHA is generally maintained in neuronal membranes, inadequate supply of n-3 fatty acid or ethanol exposure leads to a significant loss of DHA in neuronal cells. The roles of DHA in neuronal signaling have been emerging. In this review, biological, biochemical and molecular mechanisms supporting the essential function of DHA in neuronal survival and development are described in relation to n-3 fatty acid depleting conditions.

Inhibition of phosphatidylserine biosynthesis in developing rat brain by maternal exposure to ethanol

Phosphatidylserine (PtdSer), major acidic phospholipids in neuronal membranes, participate in important cell signaling processes. The PtdSer in brain is highly enriched with docosahexaenoic acid (DHA; 22:6n-3), and the DHA status or ethanol exposure has been shown to influence the PtdSer level. This study shows that ethanol exposure during prenatal and developmental period significantly attenuates microsomal PtdSer biosynthetic activities and reduces PtdSer, particularly 18:0, 22:6-PtdSer, in developing rat brain cortices. Brain microsomes were incubated with deuterium labeled exogenous substrates in vitro and the products formed were detected by reversed phase HPLC-electrospray ionization mass spectrometry (ESI-MS). These in vitro bioassays showed that 1-stearoyl-2-docosahexaenoyl (18:0, 22:6) species is the best substrate for PtdSer synthesis from both phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn). The PtdSer biosynthetic activity of brain, especially for 18:0, 22:6-PtdSer production, was hampered significantly by maternal exposure to ethanol. PtdSer levels were consistently reduced significantly in brain cortices of the pups from ethanol-exposed dams, due mainly to the depletion of 18:0, 22:6-PtdSer. The mRNA expression of PtdSer synthase 1 (PSS1) and PtdSer synthase 2 (PSS2) was not reduced by ethanol. Similarly, the PSS1 enzyme level did not change after ethanol exposure but PSS2 could not be probed with the antibody available currently. Degradation of PtdSer by mitochondrial PtdSer decarboxylation was not enhanced but also inhibited. Taken together, attenuated PtdSer biosynthetic activities are largely responsible for the PtdSer reduction observed in developing rat brains after maternal exposure to ethanol.

Mechanisms of action of docosahexaenoic acid in the nervous system

This review describes (from both the animal and human literature) the biological consequences of losses in nervous system docosahexaenoate (DHA). It then concentrates on biological mechanisms that may serve to explain changes in brain and retinal function. Brief consideration is given to actions of DHA as a nonesterified fatty acid and as a docosanoid or other bioactive molecule. The role of DHA-phospholipids in regulating G-protein signaling is presented in the context of studies with rhodopsin. It is clear that the visual pigment responds to the degree of unsaturation of the membrane lipids. At the cell biological level, DHA is shown to have a protective role in a cell culture model of apoptosis in relation to its effects in increasing cellular phosphatidylserine (PS); also, the loss of DHA leads to a loss in PS. Thus, through its effects on PS, DHA may play an important role in the regulation of cell signaling and in cell proliferation. Finally, progress has been made recently in nuclear magnetic resonance studies to delineate differences in molecular structure and order in biomembranes due to subtle changes in the degree of phospholipid unsaturation.

Inhibition of neuronal apoptosis by docosahexaenoic acid (22:6n-3). Role of phosphatidylserine in antiapoptotic effect

Enrichment of Neuro 2A cells with docosahexaenoic acid (22:6n-3) decreased apoptotic cell death induced by serum starvation as evidenced by the reduced DNA fragmentation and caspase-3 activity. The protective effect of 22:6n-3 became evident only after at least 24 h of enrichment before serum starvation and was potentiated as a function of the enrichment period. During enrichment 22:6n-3 incorporated into phosphatidylserine (PS) steadily, resulting in a significant increase in the total PS content. Similar treatment with oleic acid (18:1n-9) neither altered PS content nor resulted in protective effect. Hindering PS accumulation by enriching cells in a serine-free medium diminished the protective effect of 22:6n-3. Membrane translocation of Raf-1 was significantly enhanced by 22:6n-3 enrichment in Neuro 2A cells. Consistently, in vitro biomolecular interaction between PS/phosphatidylethanolamine /phosphatidylcholine liposomes, and Raf-1 increased in a PS concentration-dependent manner. Collectively, enrichment of neuronal cells with 22:6n-3 increases the PS content and Raf-1 translocation, down-regulates caspase-3 activity, and prevents apoptotic cell death. Both the antiapoptotic effect of 22:6n-3 and Raf-1 translocation are sensitive to 22:6n-3 enrichment-induced PS accumulation, strongly suggesting that the protective effect of 22:6n-3 may be mediated at least in part through the promoted accumulation of PS in neuronal membranes.

Accumulation of docosahexaenoic acid in phosphatidylserine is selectively inhibited by chronic ethanol exposure in C-6 glioma cells

Neuronal membranes are highly enriched with docosahexaenoic acid (22:6n-3), and its content can be altered by ethanol consumption. We have previously reported that the 22:6n-3 status in membrane affects the biosynthesis of phosphatidylserine (PS), a phospholipid class which contains an exceptionally high proportion of 22:6n-3. The aim of the present study is to investigate the effect of chronic ethanol exposure on PS accumulation in relation to the 22:6n-3 status. C-6 glioma cells were enriched with 25 microM 22:6n-3 for 48 h and the PS accumulation was first evaluated in comparison to nonenriched cells as well as cells enriched with arachidonic acid (20:4n-6). Electrospray liquid chromatography-mass spectrometry analysis revealed that cells treated with 22:6n-3 showed significantly higher accumulation of PS in comparison to nonenriched or 20:4n-6-enriched cells, primarily due to an increase of 1-stearoyl-2-docosahexaenoyl-glycerophosphoserine (18:0,22:6-PS). Chronic ethanol exposure selectively affected the accumulation of PS in 22:6n-3-enriched cells. After cells were exposed to 20 or 50 mM ethanol for 4 wk, accumulation of 18:0,22:6-PS upon 22:6n-3 supplementation was significantly lower, resulting in a drastic reduction of total PS. Concomitantly, ethanol-treated cells showed lower incorporation of serine in comparison to control cells. From these data, it was concluded that supplementation of cells with 22:6n-3 promotes the accumulation of PS and chronic ethanol treatment diminishes this effect at least in part through impaired serine incorporation processes. Attenuated accumulation of 22:6n-3 in PS and the reduction of PS thus may have significant implications in pathophysiological effects of ethanol, especially in tissues with abundant 22:6n-3.

Maturation of the spontaneous transmitter release by regenerated nerve endings in vitamin E-deficient rats

In order to verify the importance of the protection against lipid peroxidation in presynaptic differentiation and maturation, the reappearance and maturation of the spontaneous transmitter release during the extensor digitorum longus muscle reinnervation following a lesion of the sciatic nerve were studied in normal and vitamin E-deficient rats. The study was carried out by intracellular recordings in order to observe the miniature end plate potentials in the reinnervated end plates. In control and vitamin E-deficient rats the first signs of muscle innervation reappeared simultaneously, but in the latter the spontaneous transmitter release mechanism matured more slowly; furthermore, in the long-term, very low mepp frequencies continued to occur. The data suggest a slowing of the transmitter release mechanism maturation and a protracted rearrangement of innervation in the deficient rats.

Postnatal development of thiamine metabolism in rat brain

The activities of thiamine diphosphatase (TDPase), thiamine triphosphatase (TTPase), and thiamine pyrophosphokinase and the contents of thiamine and its phosphate esters were determined in rat brain cortex, cerebellum, and liver from birth to adulthood. Microsomal TTPase activity in the cerebral cortex and cerebellum increased from birth to 3 weeks, whereas that in the liver did not change during postnatal development. Microsomal TDPase activity in the cerebral cortex showed a transient increase at 1-2 weeks, but that in the cerebellum did not change during development. In contrast to the activity of the brain enzyme, that of liver microsomal TDPase increased stepwise after birth. Thiamine pyrophosphokinase activity in the cerebellum increased from birth to 3 weeks and then decreased, whereas that in the cerebral cortex and liver showed less change during development. TDP and thiamine monophosphate (TMP) levels increased after birth and plateaued at 3 weeks whereas TTP and thiamine levels showed little change during development in the cerebral cortex and cerebellum. The contents of thiamine and its phosphate esters in the liver showed more complicated changes during development. It is concluded that thiamine metabolism in the brain changes during postnatal development in a different way from that in the liver and that the development of thiamine metabolism differs among brain regions.

Dietary fat in experimental nephrotic syndrome: beneficial effects of fish oil on serum lipids and, indirectly, on the kidney

Three isocaloric diets with different fat composition were fed to rats for seven weeks after the production of nephrotic syndrome by adriamycin. The effects of feeding 3% and 14% fish oil were compared with those of feeding beef fat. At the fourth week of feeding the levels of triglycerides and cholesterol were lower in both fish oil fed groups. At the seventh week these levels, and the LDL cholesterol, were lower only in the 14% fish oil group. In rats fed beef fat, but not in those fed fish oil, there was a striking positive correlation of the four-week serum triglycerides and cholesterol with the seven-week serum creatinine level and with the degree of glomerular hyalinosis and endothelial swelling. The favorable effects of fish oil feeding on serum lipids may have a protective effect on the development of glomerular damage.

Effect of ganglioside-GM1 on the order of phosphatidylcholine-cholesterol multilamellar liposomes. A fluorescence polarization study

The effect(s) of bovine brain ganglioside-GM1 on the order of phosphatidylcholine-cholesterol membranes were studied using steady-state fluorescence polarization (FPZ) techniques with 1,6-diphenyl-1,3,5-hexatriene (DPH) as the membrane probe. In the absence of cholesterol, GM1 (30 mol%) increases both membrane order and the phase transition temperature of dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) membranes. However, in the presence of cholesterol (0.3 or 0.5, cholesterol/phospholipid molar ratio), GM1 significantly decreases steady-state anisotropy (rs) at temperatures above the Tm for the particular phospholipid. This effect may, in part relate to a dilution of membrane cholesterol and is shared by bovine brain sphingomyelin (SM). GM1 (30 mol%) increases the order of 1-palmityl-2-oleyl-PC (POPC) membranes. However, in the presence of cholesterol (0.3 molar ratio) GM1 neither increases or decreases order. Thus, in cholesterol containing artificial membranes, the effect of GM1 depends on the phosphatidylcholine (PC) fatty acid composition and may not be evident from the effect of GM1 on pure PC membranes.

Beneficial effects of polyunsaturated fatty acids in partially nephrectomized rats

Evening primrose oil, safflower oil, and salmon oil, all with high polyunsaturated fatty acid content, were fed to partially nephrectomized rats; the effects were compared to those of feeding beef tallow. All three oils had favorable effects on progression of renal failure, salmon oil on kidney histology as well. The changes induced in platelet production of thromboxane A2, and in the renal production of various eicosanoids may explain the protective role of these oils.

Membranes, methylation and lithium responsive psychoses

Data are presented showing that the erythrocyte ghost membranes of lithium-responsive and non-responsive schizophrenic-like patients are different from control membranes. In both groups of patients there was a significant decrement of phosphatidylcholine (PC) which was largely compensated for by an increase in sphingomyelin. The decrement in PC may in part be associated with a decrease in phospholipid methylation which converts phosphatidylethanolmine (PE) to PC. Interestingly, in the lithium-responsive but not the non-responsive patients, lithium stimulates methylation activity. This stimulation may affect a variety of membrane functions, e.g. adenyl cyclase activity, which would be involved in lithium's therapeutic actions.

Determination of ethanol partition coefficients to the interior and the surface of dipalmityl-phosphatidylcholine liposomes using deuterium nuclear magnetic resonance spectroscopy

The binding of ethanol-d6 to dipalmityl-phosphatidylcholine liposomes (DPPC) can be separated into two processes, namely, ethanol in the bilayer and on the surface of the bilayer. For the deuterons of the methylene group, the T2 of both bound states is shorter than the respective preexchange lifetime (tau beta) and therefore the amount of ethanol bound to both sites can be determined from the decrease in the methylene intensity resonance in the presence of DPPC. For the methyl resonance, however, only the T2 of deuterons on ethanol bound to the surface is less than its tau beta and the amount of surface bound ethanol-d6 can be determined. Subtraction yields the amount of ethanol bound within the bilayer. The partition coefficient for internally bound ethanol remains constant from 0 to 3.5 m ethanol. Surface binding is, however, highly cooperative.

Altered composition of polyunsaturated fatty acyl groups in phosphoglycerides of Down's syndrome fetal brain

We have observed recently that in vitro lipoperoxidation is enhanced in Down's syndrome brain homogenates of prenatal age. As this may relate to the composition of polyunsaturated acyl groups (PUFA) in phospholipids, we have examined the PUFA of ethanolamine and serine phosphoglycerides (EPG and SPG), which are particularly rich in PUFA, in the same series of cerebral cortex specimens of Down's syndrome and age-matched control fetuses. Although the total percentages of PUFA in the two phosphoglycerides were not altered, compared with controls the ratio of PUFA of the (n-3) series to those of the (n-6) series was very significantly elevated in Down's syndrome, from 0.32 to 0.55 in EPG and from 0.60 to 0.97 in SPG. In particular, docosahexaenoyl, 22:6(n-3), groups were uniformly increased in Down's syndrome compared with controls by 54% and 33% in EPG and SPG, respectively, while arachidonoyl, 20:4(n-6), groups were decreased by 16% and 30%, respectively. Similar changes occur during normal development, but the (n-3) to (n-6) ratio of PUFA in these phosphoglycerides of Down's syndrome at the fifth month of gestation resembled that of normal human cerebral grey matter at term. However, other developmental indices related to PUFA composition were not significantly affected. It seems therefore that in the developing Down's syndrome brain there may be a distortion of the normal transformations of essential fatty acids and of their incorporation into phosphoglycerides. The disproportion between docosahexaenoyl and arachidonoyl groups in membrane phosphoglycerides during prenatal development in Down's syndrome may also result in disturbances of the proper functioning, and the ontogenetic integration, of membrane enzymes and transport processes.

Lipids of nervous tissue: composition and metabolism

As indicated in the Introduction, the many significant developments in the recent past in our knowledge of the lipids of the nervous system have been collated in this article. That there is a sustained interest in this field is evident from the rather long bibliography which is itself selective. Obviously, it is not possible to summarize a review in which the chemistry, distribution and metabolism of a great variety of lipids have been discussed. However, from the progress of research, some general conclusions may be drawn. The period of discovery of new lipids in the nervous system appears to be over. All the major lipid components have been discovered and a great deal is now known about their structure and metabolism. Analytical data on the lipid composition of the CNS are available for a number of species and such data on the major areas of the brain are also at hand but information on the various subregions is meagre. Such investigations may yet provide clues to the role of lipids in brain function. Compared to CNS, information on PNS is less adequate. Further research on PNS would be worthwhile as it is amenable for experimental manipulation and complex mechanisms such as myelination can be investigated in this tissue. There are reports correlating lipid constituents with the increased complexity in the organization of the nervous system during evolution. This line of investigation may prove useful. The basic aim of research on the lipids of the nervous tissue is to unravel their functional significance. Most of the hydrophobic moieties of the nervous tissue lipids are comprised of very long chain, highly unsaturated and in some cases hydroxylated residues, and recent studies have shown that each lipid class contains characteristic molecular species. Their contribution to the properties of neural membranes such as excitability remains to be elucidated. Similarly, a large proportion of the phospholipid molecules in the myelin membrane are ethanolamine plasmalogens and their importance in this membrane is not known. It is firmly established that phosphatidylinositol and possibly polyphosphoinositides are involved with events at the synapse during impulse propagation, but their precise role in molecular terms is not clear. Gangliosides, with their structural complexity and amphipathic nature, have been implicated in a number of biological events which include cellular recognition and acting as adjuncts at receptor sites. More recently, growth promoting and neuritogenic functions have been ascribed to gangliosides. These interesting properties of gangliosides wIll undoubtedly attract greater attention in the future.(ABSTRACT TRUNCATED AT 400 WORDS)

Chronic effects of perchloroethylene on the composition of lipid and acyl groups in cerebral cortex and hippocampus of the gerbil

Continuous exposure of Mongolian gerbils to perchloroethylene (PCE) (120 ppm) for 12 months in an inhalation chamber caused no changes in body or brain weights. The protein content, the concentration of lipid phosphorus or cholesterol were unaltered in the cerebral cortex and hippocampus. However, a small change in the fatty acid pattern of phospholipid was observed. In the phosphatidylethanolamine of cerebral cortex and hippocampus a decrease was found among the long-chain, linolenic acid-derived, fatty acids. The ratio 22:4 (N-6)/22:5 (N-3) was increased, indicating a shift towards the corresponding linoleic acid-derived 22-carbon fatty acids. The observed changes among poly-unsaturated fatty acids are similar to those appearing after peroxidation and either protein or essential fatty acid malnutrition. However, an attractive explanation for the changes is that they represent a response to the fluidizing properties of PCE.

Developmental changes in synaptic membrane fluidity: a comparison of 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-[4-(trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH)

Cortical synaptic plasma membranes were prepared from rats 3, 7, 10, 14, 21, 28 and 120 days of age. Developmental changes in the fluidity of these membranes were assessed using fluorescence polarization techniques. 1,6-Diphenyl-1,3,5-hexatriene (DPH), a probe of the membrane interior, showed a marked developmental increase in polarization, suggesting a developmental decrease in fluidity. The magnitude of the change from day 3 to the adult was the equivalent of lowering the temperature 7 degrees C. The developmental change in DPH polarization was maintained in liposomes (multilamellar vesicles) prepared from membrane total lipid extracts. In contrast to DPH, 1-[4-(trimethylamino)phenyl]6-phenyl-1,3,5-hexatriene (TMA-DPH), a probe of the membrane surface reported no significant developmental effect on polarization for intact membranes; however, TMA-DPH did report a significant increase in polarization for the total lipid extract liposomes. For the intact membranes, both cis- and trans-parinarate, fluorescent probes of the mid-region of the acyl chains, reported significant developmental increases in polarization. The role of gangliosides in the developmental regulation of fluidity was examined. Gangliosides did not appear to play a role in the developmental changes, but they do have a significant effect (increased polarization) on the membrane surface as reported by TMA-DPH. Fluorescence lifetime and heterogeneity analyses were performed for DPH. There was a small but significant increase in probe lifetime during development. Thus, polarization measurements alone underestimated the increases in membrane order. In an attempt to amplify the differences in membrane organization between the developing and adult membranes, we examined the effects of the membrane perturbant ethanol, on DPH polarization at the different ages. No developmental effect on the ethanol-induced fluidization of synaptic membranes was observed.

Membrane abnormalities in the psychoses and affective disorders

Erythrocyte ghost phospholipid data were collected on 67 psychotic and/or manic patients and compared to a group of 35 age and sex matched controls. Patients meeting DSM-III criteria for schizophreniform disorder or schizophrenia but not mania showed a small but significant decrease in membrane phosphatidylcholine (PC). In 53 of the patients data were available on lithium transport across red cell membranes. Patients in the upper quartile of the PC distribution showed a significant (-47%) decrease in the 24 h in vitro lithium ratio as compared to patients in the lower PC quartile. This difference was due to an increase in Na-Li+ counterflow activity in the upper PC quartile and not to a change in passive lithium leak. These data illustrate one example of a possible relationship between membrane composition and a membrane function, counterflow activity, which has been associated with the underlying mechanism(s) of lithium action.

Developmental changes in synaptic membrane lipid composition and fluidity

Synaptic membrane enriched fractions were prepared from 7 and 14 day and adult cortical nerve endings. (a) The levels of synaptic membrane phosphatidylcholine decrease 19% during development while the levels of ethanolamine phosphoglycerides increase 21%. (b) On day 7, desmosterol accounts for 33% of the total membrane sterols. With maturity, the desmosterol disappears and the molar sterol/lipid P ratio increases 56%. (c) The fatty acid composition of the membranes change during development. 16:0 decreases 36% while 18:1 increases 49%. 16:1, a minor component of adult membranes, is found in significant quantities in pup membranes. 22:6 (n-3) increases 34% during development while 22:5 (n-6) decreases 59%. (d) The microviscosity of synaptic membranes, as measured by the fluorescence depolarization technique, increases during development. This effect is observed in both intact membranes and bilayers prepared from lipid extracts of the membrane.

Developmental regulation of phospholipid methylation in rat brain synaptosomes

Phospholipid methylation was studied in cortical synaptosomes prepared from 7 and 14 day and adult rat brain. Using varying concentrations of [3H] S-adenosylmethionine, Km and Vmax values were determined for the formation of [3H] phosphatidylmonomethylethanolamine (PME), [3H] phosphatidyl-dimethylethanolamine and [3H] phosphatidylcholine (PC). At 25 degree C, the Km values for the formation of all three products, significantly decreased with development. Increasing the temperature to 37 degree C increased the Km values in the 14 day and adult but not the 7 day preparation. The Vmax values at 25 degree C were highest at 7 and 14 days, depending on the product and then decreased in the adult. At 37 degree C, the Vmax values were highest in the 14 day preparation. The overall results are discussed in terms of the developmentally regulated decrease in both synaptic membrane PC and membrane fluidity.