Search

GABA signaling sustains fundamental brain functions, from nervous system development to the synchronization of population activity and synaptic plasticity. Despite these pivotal features, molecular determinants underscoring the rapid and cell-autonomous replenishment of the vesicular neurotransmitter GABA and its impact on synaptic plasticity remain elusive. Here, we show that genetic disruption of the glutamine transporter Slc38a1 in mice hampers GABA synthesis, modifies synaptic vesicle morphology in GABAergic presynapses and impairs critical period plasticity. We demonstrate that Slc38a1-mediated glutamine transport regulates vesicular GABA content, induces high-frequency membrane oscillations and shapes cortical processing and plasticity. Taken together, this work shows that Slc38a1 is not merely a transporter accumulating glutamine for metabolic purposes, but a key component regulating several neuronal functions., (© The Author(s) 2019. Published by Oxford University Press.)

It is well known that traumatic or ischemic brain injury is followed by acute excitotoxicity caused by the presence of abnormally high glutamate (Glu) in brain fluids. It has recently been demonstrated that excess Glu can be eliminated from brain into blood following the intravenous administration of oxaloacetate (OxAc), which, by scavenging blood Glu, induces an enhanced and neuroprotective brain-to-blood Glu efflux. In this study, we subjected rats to intravenous OxAc administration (i.v., 12.5, 25, and 50 mg/kg, respectively), and studied its effects on somatosensory evoked cortical potentials (EPs). Against our expectation, the amplitudes of EPs did not decrease but increased in a dose- and time-dependent manner after OxAc administration. Similar effects were observed when blood Glu scavenging was enhanced by combining OxAc (12.5 mg/kgbw) with recombinant glutamate-oxaloacetate transaminase (GOT, 0.14 nmol/100 g rat). On the basis of these results, we suggest that the changes of amplitudes of the EPs involve not only a glutamatergic but also the weakening of a GABAergic component. We cannot rule out the possibility that OxAc penetrates into the brain and improves mitochondrial functions.

The beneficial effect of dietary n-3 polyunsaturated fatty acids (PUFAs) on developing hypertension has been repeatedly demonstrated. However, related changes in brain membrane composition and its cognitive correlates have remained unclear. Our study aimed at a comprehensive analysis of behavior and cerebral fatty acid concentration in hypertension after long-term PUFA-rich dietary treatment. Hypertensive and normotensive rats were provided a placebo, or one of two PUFA-enriched diets with a reduced (n-6)/(n-3) ratio for 75 weeks. Exploratory behavior and spatial learning capacity were tested. Systolic blood pressure (BP) was repeatedly measured. Finally, brain fatty acid composition was analyzed by gas chromatography. Hypertensive rats exhibited more active exploration but impaired spatial learning compared to normotensives. Both diets reduced BP, increased PUFA and monounsaturated fatty acid (MUFA) concentration, and reduced saturated fatty acid content in brain. The level of cerebral PUFAs and MUFAs was lower in hypertensive than in normotensive rats. Furthermore, BP positively, while spatial learning negatively correlated with cerebral (n-6)/(n-3) PUFA ratio. We concluded that regular n-3 PUFA consumption could prevent the development of hypertension, but reached only a very delicate improvement in spatial learning. Furthermore, we consider a potential role of metabolically generated MUFAs in the beneficial effects of PUFA supplementation.

Advanced age is associated with reduced brain levels of long-chain polyunsaturated fatty acids, arachidonic acid (AA) and docosahexaenoic acid (DHA). Memory impairment is also a common phenomenon in this age. Two-year-old, essential fatty acid-sufficient rats were fed with fish oil (11% DHA) for 1 month, and fatty acid as well as molecular composition of the major phospholipids, phosphatidylcholine and phosphatidylethanolamine (PE), was compared with that of 2-month-old rats on the same diet. DHA but not AA was significantly reduced in brains of old rats but was restored to the level of young rats when they received rat chow fortified with fish oil. This effect was pronounced with diacyl 18:0/22:6 PE species, whereas levels of 18:1/22:6 and 16:0/22:6 remained unchanged in all of the three PE subclasses. Fish oil reduced the AA in the old rat brains, diacyl and alkenylacyl 18:0/20:4 PE being most affected. Phosphatidylcholines gave less pronounced response. Six genes were up-regulated, whereas no significant changes were observed in brains of old rats receiving fish oil for 1 month. None of them except synuclein in young rat brains could be related to mental functions. Old rats on the fish-oil diet did not perform better in Morris water maze test than the control ones. A 10% increase in levels of diacyl 18:0/22:6 PE in young rat brains resulted in a significant improvement of learning capacity. The results are interpreted in terms of the roles of different phospholipid molecular species in cognitive functions coupled with differential responsiveness of the genetic machinery of neurons to n-3 polyunsaturated fatty acids.

Rats were fed from conception till adulthood either with normal rat chow with a linoleic (LA) to linolenic acid (LNA) ratio of 8.2:1 or a rat chow supplemented with a mixture of perilla and soy bean oil giving a ratio of LA to LNA of 4.7:1. Fat content of the feed was 5%. Fatty acid and molecular species composition of ethanolamine phosphoglyceride was determined. Effect of this diet on gene expression was also studied. There was an accumulation of docosahexaenoic (DHA) and arachidonic acids (AA) in brains of the experimental animals. Changes in the ratio sn-1 saturated, sn-2 docosahexaenoic to sn-1 monounsaturated, sn-2 docosahexaenoic were observed. Twenty genes were found overexpressed in response to the 4.7:1 mixture diet and four were found down-regulated compared to normal rat chow. Among them were the genes related to energy household, lipid metabolism and respiration. The degree of up-regulation exceeded that observed with perilla with a ratio of LA to LNA 8.2:1 [Proc. Natl. Acad. Sci. U. S. A. 99 (2002) 2619]. It was concluded that brain sensitively reacts to the fatty acid composition of the diet. It was suggested that alteration in membrane architecture and function coupled with alterations in gene expression profiles may contribute to the observed beneficial impact of n-3 type polyunsaturated fatty acids on cognitive functions.

Rats were fed either a high linolenic acid (perilla oil) or high eicosapentaenoic + docosahexaenoic acid (fish oil) diet (8%), and the fatty acid and molecular species composition of ethanolamine phosphoglycerides was determined. Gene expression pattern resulting from the feeding of n-3 fatty acids also was studied. Perilla oil feeding, in contrast to fish oil feeding, was not reflected in total fatty acid composition of ethanolamine phosphoglycerides. Levels of the alkenylacyl subclass of ethanolamine phosphoglycerides increased in response to feeding. Similarly, levels of diacyl phosphatidylethanolamine molecular species containing docosahexaenoic acid (18:0/22:6) were higher in perilla-fed or fish oil-fed rat brains whereas those in ethanolamine plasmalogens remained unchanged. Because plasmalogen levels in the brains of rats fed a n-3 fatty acid-enriched diet increased, it is plausible, however, that docosahexaenoic acid taken up from the food or formed from linolenic acid was deposited in this phospholipid subclass. Using cDNA microarrays, 55 genes were found to be overexpressed and 47 were suppressed relative to controls by both dietary regimens. The altered genes included those controlling synaptic plasticity, cytosceleton and membrane association, signal transduction, ion channel formation, energy metabolism, and regulatory proteins. This effect seems to be independent of the chain length of fatty acids, but the n-3 structure appears to be important. Because n-3 polyunsaturated fatty acids have been shown to play an important role in maintaining normal mental functions and docosahexaenoic acid-containing ethanolamine phosphoglyceride (18:0/22:6) molecular species accumulated in response to n-3 fatty acid feeding, a casual relationship between the two events can be surmised.

In a Hungarian family with triosephosphate isomerase (TPI; D-glyceraldehyde-3-phosphate keto-isomerase, EC 5.3.1.1) deficiency, two germ-line identical, but phenotypically differing compound heterozygote brothers (one of them with neurological disorder) have been identified with the same very low (<5%) TPI activity and 20- or 40-fold higher erythrocyte dihydroxyacetone phosphate levels as compared with normal controls. Our present studies with purified TPI and hemolysates revealed the binding of TPI, and the binding of human wild-type and mutant TPIs in hemolysate, to the red cell membrane, and the interference of binding with other hemolysate proteins. The binding of the mutant TPI is enhanced as compared with the wild-type enzyme. The increased binding is influenced by both the altered structure of the mutant and the changes in the red cell membrane. Compared with binding of glyceraldehyde-3-phosphate dehydrogenase, the isomerase binding is much less sensitive to ionic strength or blocking of the N-terminal tail of the band-3 transmembrane protein. The binding of TPIs to the membrane decreases the isomerase activity, resulting in extremely high dihydroxyacetone phosphate levels in deficient cells. In cell-free brain extract, tubulin copolymerizes with TPI and with other cytosolic proteins forming highly decorated microtubules as shown by immunoblot analysis with anti-TPI antibody and by electron microscopic images. The efficacy order of TPI binding to microtubules is propositus > brother without neurological disorder > normal control. This distinct microcompartmentation of mutant proteins may be relevant in the development of the neurodegenerative process in TPI deficiency and in other, more common neurological diseases.

Carp (Cyprinus carpio L.) whole brain was used to investigate the thermal acclimation changes under normoxic conditions of three-subclasses (alkenylacyl-, alkylacyl- and diacyl-subclasses) of choline glycerophospholipids (CGP), ethanolamine glycerophospholipids (EGP) and inositol glycerophospholipids (IGP) as well as their acyl chain profiles and molecular species composition. The alkenylacyl subclass of CGP and IGP and the alkylacyl subclass of CGP and EGP varied significantly during summer (25 degrees C) acclimation compared to winter (5 degrees C). The levels of alkenylacyl and alkylacyl-CGP, alkylacyl-EGP and alkenylacyl-IGP were 17.3-, 3.7-, 3.5- and 1.3-fold higher in the summer, respectively, while the alkenylacyl EGP was moderately lower. The levels of diacyl subclasses from CGP and IGP were considerably lower in the summer to compensate for the higher proportion of alkenylacyl and alkylacyl subclasses. Significant changes of ether phospholipids and the reorganization of the molecular species composition of all lipid subclasses may be associated with the "fine tuning" of the physical properties of the cellular membranes in carp brain due to temperature acclimation. The overall acyl chain profile of the three subclasses of carp brain phospholipids showed differences in composition depending upon the subclass of the individual phospholipid. Generally the polyunsaturated fatty acid (PUFA) chain composition increased relative to monounsaturated fatty acid (MUFA) and saturated fatty acids (SFA) during winter acclimation. Docosahexaenoic acid (DHA) was richer in the winter compared to summer. However, no DHA was found in ether-containing species of IGP from either winter or summer, except for 2% in alkylacyl-IGP during the summer. The above observations suggest that the content of ether phospholipids (alkenylacyl and alkylacyl) as well as the reorganization of the molecular species composition of all phospholipids may serve to maintain a functional fluid-crystalline state to preserve the signaling functions in carp brain.

Fluorescence anisotropy parameter of [p-(6-phenyl)-1,3,5-hexatrienyl]phenyl-propionic acid (DPH-PA) and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) embedded in synaptic plasma membranes prepared from brains of cold (5 degrees C) and warm (22 degrees C) adapted fish (Cyprinus carpio L.), rat (Rattus norvegicus) and bird (Branta canadensis), was studied. Fatty acid composition of total lipids as well as molecular species composition of diacyl phosphatidylcholines and phosphatidylethanolamines was also determined. The amount of long-chain polyunsaturated fatty acids decreased with increasing body temperature. There was a near-complete compensation of membrane structural order for environmental/body temperature over the evolutionary scale as seen by DPH-PA. Using TMA-DPH, the compensation was partial with rat and bird. Since DPH-PA and TMA-DPH differ in their charges, it is proposed, that the former reported membrane regions rich in cationic or zwitterionic (neutral) phospholipids and the latter, membrane regions rich in negatively charged phospholipids in the synaptic plasma membranes. Many different molecular species (20-25) of diacyl phosphatidylcholines and diacyl phosphatidylethanolamines were identified. The level of 16:0/22:6 phosphatidylcholine decreased while disaturated phosphatidylcholines increased with increase of environmental/body temperature from the fish through the bird. Level of 1-monoenoic, 2-polyenoic phosphatidylethanolamines also decreased with an increase in environmental/body temperature. Experiments using vesicles made of mixed synthetic phosphatidylcholine vesicles (16:0/16:0, 16:0/18:1, 16:0/22:6 in various proportions) showed that increase in disaturated phosphatidylcholine species does not explain the observed complete adjustment of membrane structural order in synaptic plasma membranes. Change in level of 1-monoenoic, 2-polyenoic phosphatidylethanolamines might be one of the factors involved in controlling the biophysical properties of the membrane according to the temperature.

A comparison of the structural orders of membranes of a mixed brain-cell population isolated from Cyprinus carpio L. acclimated to either summer (23-25 degrees C) or winter (5 degrees C) revealed a high degree of compensation (80%) for temperature, as assayed by electron spin resonance spectroscopy. The cells rapidly forget their thermal history and adjust the physical properties of the membranes when shifted to the other extreme of temperature either in vivo or in vitro. Phospholipids separated from both types of animals exhibit only around 10% compensation. Arachidonic and docosahexaenoic acids are the major polyunsaturated fatty acids in the brains, but the fatty acid composition of the brain total phospholipids does not vary with adaptation to temperature. Separation of phosphatidylcholines and phosphatidylethanolamines into molecular species revealed a 2- to 3-fold accumulation of 18:1/22:6, 18:1/20:4, and 18:1/18:1 species in the latter; 18:0/22:6 showed an opposite tendency. Molecular species composition of phosphatidylcholines did not vary with the temperature. The same trends of changes were seen with brains of freshwater fish from subtropical (Catla catla L.) or boreal (Acerina cernua) regions. It is concluded that the gross amount of docosahexaenoic acid (22:6) plays only a minor role in adjusting the membrane physical properties to temperature. Factors other than lipids might be involved in the adaptation processes. Due to their specific molecular architecture, molecules such as 18:1/22:6, 18:1/20:4, or 18:1/18:1 phosphatidylethanolamine might prevent the contraction of membranes in the cold and may provide an environment for some other components involved in the temperature regulation of physical properties of nerve cell membranes.

Thirteen diagnosed schizophrenics and 11 normal controls were studied with a method using the PETT III positron emission tomograph (PET) and fluorodeoxyglucose labeled with fluorine 18. Each subject also had a computed tomographic (CT) scan. For each subject, two brain levels, one through the basal ganglia and one through the semioval center, were analyzed for the mean regional metabolic glucose rate. Specifically, relationships between frontal and posterior regions were evaluated. The CT scans of matching levels were superimposed on the functional PET images to provide anatomic criteria for region of interest selection. While no whole-slice metabolic differences were apparent between groups, schizophrenics had significantly lower activity in the frontal lobes, relative to posterior regions. The medicated and drug-free groups did not differ from one another in these regards. Trait v state dependency of the phenomenon was analyzed, and several technological limitations were considered.

The specific binding of [3H]ethylketocyclazocine to frog brain membrane preparation was enhanced in the presence of sodium ions administered as NaCl, both at 0 degree C and at room temperature. The optimal NaCl concentration was 25 mM at 0 degree C and 50 mM at 24 degrees C. MgCl2 inhibited the [3H]ethylketocyclazocine binding. Two binding sites (high and low affinity) were established with [3H]ethylketocyclazocine as ligand by equilibrium binding studies. Addition of NaCl increased the Bmax of the low-affinity site more than that of the high-affinity site at both temperatures. Affinities were higher at 0 degree C than at 24 degrees C. The KD values were not significantly influenced by sodium ions. The dissimilarities between the rat and frog brain opioid receptors in [3H]ethylketocyclazocine binding are attributed to the different lipid composition of the two membranes.

Abstract The effect of temperature on fluidity, fatty acid and molecular species composition of liver and brain phospholipids in fish adapted or exposed to extreme temperatures was investigated. Membranes from cold-adapted fish were more fluid than those from warm-adapted fish. Ability to control membrane fluidity according to temperature appears in early ontogenesis and is first evident in swim-up fry of carp. Red blood cells as well as neurons of adult carp can continuously adjust the fluidity of their external membranes to changing temperatures. Segregation of choline and ethanolamine phosphoglycerides from livers of fish adapted to a cold/warm environment showed an accumulation of molecular species containing a monoenic fatty acid in position sn-1 and a polyenic fatty acid in position sn-2 of the molecule in cold conditions. Model experiments using mixtures of synthetic 18:1/22:6 phoshatidylethanolamines and 16:0/18:1 phosphatidylcholines demonstrated the involvement of these molecular species in rendering the membranes less packed (more fluid) during adaptation to reduced temperatures. [ABSTRACT FROM AUTHOR]