The cannabinoid type 2 (CB2) receptor plays an important role in neuroinflammatory and neurodegenerative diseases such as multiple sclerosis, amyotrophic lateral sclerosis, and Alzheimer's disease and is therefore a very promising target for therapeutic approaches as well as for imaging. Based on the literature, we identified one 4‐oxoquinoline derivative (designated KD2) as the lead structure. It was synthesized, radiolabeled and evaluated as a potential imaging tracer for CB2. [11C]KD2 was obtained in 99% radiochemical purity. Moderate blood–brain barrier (BBB) passage was predicted for KD2 from an in vitro transport assay with P‐glycoprotein‐transfected Madin Darby canine kidney cells. No efflux of KD2 by P‐glycoprotein was detected. In vitro autoradiography of rat and mouse spleen slices demonstrated that [11C]KD2 exhibits high specific binding towards CB2. High spleen uptake of [11C]KD2 was observed in dynamic positron emission tomography (PET) studies with Wistar rats and its specificity was confirmed by displacement study with a selective CB2 agonist, GW405833. A pilot autoradiography study with post‐mortem spinal cord slices from amyotrophic lateral sclerosis (ALS) patients with [11C]KD2 suggested the presence of CB2 receptors under disease conditions. Specificity of [11C]KD2 binding could also be demonstrated on these human tissues. In conclusion, [11C]KD2 shows good in vitro and in vivo properties as a potential PET tracer for CB2.
Imaging the density of metabotropic glutamate receptor 5 (mGluR5) in brain by positron emission tomography (PET) is of interest in relation to several brain disorders. We have recently introduced [18F]PSS232, an F‐18‐labeled analog of the mGluR5‐targeting [11C]ABP688. Quantitative PET requires kinetic modeling with an input function (IF) or an appropriate reference tissue model. We aimed at minimizing invasiveness of IF recording in rat and employing this protocol for mGluR5 quantitative PET with [18F]PSS232. We further aimed at defining models of low complexity for quantitative PET with [18F]PSS232. The IF was recorded in an arterio‐venous shunt applied by minimally invasive cannulation. PET data were analyzed with a modified two‐tissue compartment model including a single variable for radiometabolite correction in brain. We further evaluated a simple reference tissue model. Receptor‐dependent accumulation was similar to [11C]ABP688 at lower unspecific accumulation of unchanged [18F]PSS232, in agreement with its higher plasma protein binding and lower lipophilicity. The minimally invasive protocol revealed similar results as the invasive shunt method and parameters calculated with the modified two‐tissue compartment model were similar to those calculated with the standard model. The simple area under the curve ratios agreed with the Logan reference method. [18F]PSS232 is a promising radioligand for mGluR5 quantification.
The mechanistic link of ketosis to neuroprotection under certain pathological conditions continues to be explored. We investigated whether chronic ketosis induced by ketogenic diet results in the partitioning of ketone bodies toward oxidative metabolism in brain. We hypothesized that diet‐induced ketosis results in increased shunting of ketone bodies toward citric acid cycle and amino acids with decreased carbon shunting from glucose. Rats were fed standard (STD) or ketogenic (KG) diets for 3.5 weeks and then infused with [U‐13C]glucose or [U‐13C]acetoacetate tracers. Concentrations and 13C‐labeling pattern of citric acid cycle intermediates and amino acids were analyzed from brain homogenates using stable isotopomer mass spectrometry analysis. The contribution of [U‐13C]glucose to acetyl‐CoA and amino acids decreased by ~ 30% in the KG group versus STD, whereas [U‐13C]acetoacetate contributions were more than two‐fold higher. The concentration of GABA remained constant across groups; however, the 13C labeling of GABA was markedly increased in the KG group infused with [U‐13C]acetoacetate compared to STD. This study reveals that there is a significant contribution of ketone bodies to oxidative metabolism and GABA in diet‐induced ketosis. We propose that this represents a fundamental mechanism of neuroprotection under pathological conditions.
Astrocytes have recently become a major center of interest in neurochemistry with the discoveries on their major role in brain energy metabolism. An interesting way to probe this glial contribution is given by in vivo13C NMR spectroscopy coupled with the infusion labeled glial‐specific substrate, such as acetate. In this study, we infused alpha‐chloralose anesthetized rats with [2‐13C]acetate and followed the dynamics of the fractional enrichment (FE) in the positions C4 and C3 of glutamate and glutamine with high sensitivity, using 1H‐[13C] magnetic resonance spectroscopy (MRS) at 14.1T. Applying a two‐compartment mathematical model to the measured time courses yielded a glial tricarboxylic acid (TCA) cycle rate (Vg) of 0.27 ± 0.02 μmol/g/min and a glutamatergic neurotransmission rate (VNT) of 0.15 ± 0.01 μmol/g/min. Glial oxidative ATP metabolism thus accounts for 38% of total oxidative metabolism measured by NMR. Pyruvate carboxylase (VPC) was 0.09 ± 0.01 μmol/g/min, corresponding to 37% of the glial glutamine synthesis rate. The glial and neuronal transmitochondrial fluxes (Vxg and Vxn) were of the same order of magnitude as the respective TCA cycle fluxes. In addition, we estimated a glial glutamate pool size of 0.6 ± 0.1 μmol/g. The effect of spectral data quality on the fluxes estimates was analyzed by Monte Carlo simulations.
As reported previously, in the lithium–pilocarpine model of temporal lobe epilepsy (TLE), carisbamate (CRS) produces strong neuroprotection, leads to milder absence‐like seizures, and prevents behavioral impairments in a subpopulation of rats. To understand the metabolic basis of these effects, here we injected 90 mg/kg CRS or vehicle twice daily for 7 days starting 1 h after status epilepticus (SE) induction in rats. Two months later, we injected [1‐13C]glucose and [1,2‐13C]acetate followed by head microwave fixation after 15 min. 13C incorporation into metabolites was analyzed using 13C magnetic resonance spectroscopy. We found that SE reduced neuronal mitochondrial metabolism in the absence but not in the presence of CRS. Reduction in glutamate level was prevented by CRS and aspartate levels were similar to controls only in rats displaying absence‐like seizures after treatment [CRS‐absence‐like epilepsy (ALE)]. Glutamine levels in CRS‐ALE rats were higher compared to controls in hippocampal formation and limbic structures while unchanged in rats displaying motor spontaneous recurrent seizures after treatment (CRS‐TLE). Astrocytic mitochondrial metabolism was reduced in CRS‐TLE, and either enhanced or unaffected in CRS‐ALE rats, which did not affect the transfer of glutamine from astrocytes to neurons. In conclusion, CRS prevents reduction in neuronal mitochondrial metabolism but its effect on astrocytes is likely key in determining outcome of treatment in this model.
(R)‐3‐[2,6‐cis‐Di(4‐methoxyphenethyl)piperidin‐1‐yl]propane‐1,2‐diol (GZ‐793A) inhibits methamphetamine‐evoked dopamine release from striatal slices and methamphetamine self‐administration in rats. GZ‐793A potently and selectively inhibits dopamine uptake at the vesicular monoamine transporter‐2 (VMAT2). This study determined GZ‐793A's ability to evoke [3H]dopamine release and inhibit methamphetamine‐evoked [3H]dopamine release from isolated striatal synaptic vesicles. Results show GZ‐793A concentration‐dependent [3H]dopamine release; nonlinear regression revealed a two‐site model of interaction with VMAT2 (High‐ and Low‐EC50 = 15.5 nM and 29.3 μM, respectively). Tetrabenazine and reserpine completely inhibited GZ‐793A‐evoked [3H]dopamine release, however, only at the High‐affinity site. Low concentrations of GZ‐793A that interact with the extravesicular dopamine uptake site and the High‐affinity intravesicular DA release site also inhibited methamphetamine‐evoked [3H]dopamine release from synaptic vesicles. A rightward shift in the methamphetamine concentration‐response was evident with increasing concentrations of GZ‐793A, and the Schild regression slope was 0.49 ± 0.08, consistent with surmountable allosteric inhibition. These results support a hypothetical model of GZ‐793A interaction at more than one site on the VMAT2 protein, which explains its potent inhibition of dopamine uptake, dopamine release via a High‐affinity tetrabenazine‐ and reserpine‐sensitive site, dopamine release via a Low‐affinity tetrabenazine‐ and reserpine‐insensitive site, and a low‐affinity interaction with the dihydrotetrabenazine binding site on VMAT2. GZ‐793A inhibition of the effects of methamphetamine supports its potential as a therapeutic agent for the treatment of methamphetamine abuse.
In this study, we have evaluated cerebral atrophy, neurometabolite homeostasis, and neural energetics in 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridin (MPTP) model of Parkinson's disease. In addition, the efficacy of acute l ‐DOPA treatment for the reversal of altered metabolic functions was also evaluated. Cerebral atrophy and neurochemical profile were monitored in vivo using MRI and 1H MR Spectroscopy. Cerebral energetics was studied by 1H‐[13C]‐NMR spectroscopy in conjunction with infusion of 13C labeled [1,6‐13C2]glucose or [2‐13C]acetate. MPTP treatment led to reduction in paw grip strength and increased level of GABA and myo‐inositol in striatum and olfactory bulb. 13C Labeling of glutamate‐C4 (1.93 ± 0.24 vs. 1.48 ± 0.06 μmol/g), GABA‐C2 (0.24 ± 0.04 vs. 0.18 ± 0.02 μmol/g) and glutamaine‐C4 (0.26 ± 0.04 vs. 0.20 ± 0.04 μmol/g) from [1,6‐13C2]glucose was found to be decreased with MPTP exposure in striatum as well as in other brain regions. However, glutamine‐C4 labeling from [2‐13C]acetate was found to be increased in the striatum of the MPTP‐treated mice. Acute l ‐DOPA treatment failed to normalize the increased ventricular size and level of metabolites but recovered the paw grip strength and 13C labeling of amino acids from [1,6‐13C2]glucose and [2‐13C]acetate in MPTP‐treated mice. These data indicate that brain energy metabolism is impaired in Parkinson's disease and acute l ‐DOPA therapy could temporarily recover the cerebral metabolism.
Our study was aimed at investigating whether complement, a complex of soluble and membrane‐associated serum proteins, could, in addition to its well‐documented post‐synaptic activity, also pre‐synaptically affect the release of classic neurotransmitters in central nervous system (CNS). Complement (dilution 1 : 10 to 1 : 10000) elicited the release of preloaded [3H]‐d ‐aspartate ([3H]d ‐ASP) and endogenous glutamate from mouse cortical synaptosomes in a dilution‐dependent manner. It also evoked [3H]d ‐ASP release from mouse hippocampal, cerebellar, and spinal cord synaptosomes, as well as from rat and human cortical nerve endings, but left unaltered the release of GABA, [3H]noradrenaline or [3H]acetylcholine. Lowering external Na+ (from 140 to 40 mM) or Ca2+ (from 1.2 to 0.1 mM) ions prevented the 1 : 300 complement‐evoked [3H]d ‐ASP release from mouse cortical synaptosomes. Complement‐induced releasing effect was unaltered in synaptosomes entrapped with the Ca2+ ions chelator 1,2‐bis‐(2‐aminophenoxy) ethane‐N,N,N’,N’, tetra‐acetic acid or with pertussis toxin. Nifedipine,/ω‐conotoxin GVIA/ω‐conotoxin MVIIC mixture as well as the vesicular ATPase blocker bafilomycin A1 were also inefficacious. The excitatory amino acid transporter blocker DL‐threo‐ß‐benzyloxyaspartic acid, on the contrary, reduced the complement‐evoked releasing effect in a concentration‐dependent manner. We concluded that complement‐induced releasing activity is restricted to glutamatergic nerve endings, where it was accounted for by carrier‐mediated release. Our observations afford new insights into the molecular events accounting for immune and CNS crosstalk.
Ethanol is a known neuromodulatory agent with reported actions at a range of neurotransmitter receptors. Here, we measured the effect of alcohol on metabolism of [3‐13C]pyruvate in the adult Guinea pig brain cortical tissue slice and compared the outcomes to those from a library of ligands active in the GABAergic system as well as studying the metabolic fate of [1,2‐13C]ethanol. Analyses of metabolic profile clusters suggest that the significant reductions in metabolism induced by ethanol (10, 30 and 60 mM) are via action at neurotransmitter receptors, particularly α4β3δ receptors, whereas very low concentrations of ethanol may produce metabolic responses owing to release of GABA via GABA transporter 1 (GAT1) and the subsequent interaction of this GABA with local α5‐ or α1‐containing GABA(A)R. There was no measureable metabolism of [1,2‐13C]ethanol with no significant incorporation of 13C from [1,2‐13C]ethanol into any measured metabolite above natural abundance, although there were measurable effects on total metabolite sizes similar to those seen with unlabelled ethanol.
Most ingested ethanol is metabolized in the liver to acetaldehyde and then to acetate, which can be oxidized by the brain. This project assessed whether chronic exposure to alcohol can increase cerebral oxidation of acetate. Through metabolism, acetate may contribute to long‐term adaptation to drinking. Two groups of adult male Sprague–Dawley rats were studied, one treated with ethanol vapor and the other given room air. After 3 weeks the rats received an intravenous infusion of [2‐13C]ethanol via a lateral tail vein for 2 h. As the liver converts ethanol to [2‐13C]acetate, some of the acetate enters the brain. Through oxidation the 13C is incorporated into the metabolic intermediate α‐ketoglutarate, which is converted to glutamate (Glu), glutamine (Gln), and GABA. These were observed by magnetic resonance spectroscopy and found to be 13C‐labeled primarily through the consumption of ethanol‐derived acetate. Brain Gln, Glu, and, GABA 13C enrichments, normalized to 13C‐acetate enrichments in the plasma, were higher in the chronically treated rats than in the ethanol‐naïve rats, suggesting increased cerebral uptake and oxidation of circulating acetate. Chronic ethanol exposure increased incorporation of systemically derived acetate into brain Gln, Glu, and GABA, key neurochemicals linked to brain energy metabolism and neurotransmission.
Drugs acting at the serotonin‐2C (5‐HT2C) receptor subtype have shown promise as therapeutics in multiple syndromes including obesity, depression, and Parkinson's disease. While it is established that 5‐HT2C receptor stimulation inhibits DA release, the neural circuits and the localization of the relevant 5‐HT2C receptors remain unknown. This study used dual‐probe in vivo microdialysis to investigate the relative contributions of 5‐HT2C receptors localized in the rat substantia nigra (SN) and caudate‐putamen (CP) in the control of nigrostriatal DA release. Systemic administration (3.0 mg/kg) of the 5‐HT2C receptor selective agonist Ro 60‐0175 [(αS)‐6‐Chloro‐5‐fluoro‐α‐methyl‐1H‐indole‐1‐ethanamine fumarate] decreased, whereas intrastriatal infusions of the selective 5‐HT2C antagonist SB 242084 [6‐Chloro‐2,3‐dihydro‐5‐methyl‐N‐[6‐[(2‐methyl‐3‐pyridinyl)oxy]‐3‐pyridinyl]‐1H‐indole‐1‐carboxyamide; 1.0 μM] increased, basal DA in the CP. Depending on the site within the SN pars reticulata (SNpr), infusions of SB 242084 had more modest but significant effects. Moreover, infusions of the GABA‐A receptor agonist muscimol (10 μM) into the SNpr completely reversed the increases in striatal DA release produced by intrastriatal infusions of SB 242084. These findings suggest a role for 5‐HT2C receptors regulating striatal DA release that is highly localized. 5‐HT2C receptors localized in the striatum may represent a primary site of action that is mediated by the actions on GABAergic activity in the SN.
Acute ischemic stroke is a complex disease with huge interindividual evolution variability that makes challenging the prediction of an adverse outcome. Our aim was to study the association of bloodstream signatures to early neurological outcome after stroke, by combining a subpooling of samples strategy with protein array discovery approach. Plasma samples from 36 acute stroke patients (< 4.5 h from onset) were equally pooled within outcome groups: worsening, stability, and improvement (n = 3 pools of four patients each, for each outcome group). These nine pools were screened using a 177 antibodies library, and 35 proteins were found altered regarding outcome classification (p < 0.1). Processes of inflammation, immune response, coagulation, and apoptosis were regulated by these proteins. Ten representative candidates, mainly cytokines and chemokines, were assayed for replication in individual baseline plasma samples from 80 new stroke patients: β‐defensin2, MIP‐3b, plasminogen activator inhibitor 1 active, β‐cell‐attracting chemokine 1, Exodus‐2, interleukin‐4 receptor (IL‐4R), IL‐12p40, leukemia inhibitor factor, MIP‐1b, and tumor necrosis factor‐related weak inducer of apoptosis. Multivariate logistic regression analysis showed β‐defensin 2 (ORadj 4.87 [1.13–20.91] p = 0.033) and IL‐4R (ORadj 3.52 [1.03–12.08] p = 0.045) as independent predictors of worsening at 24 h after adjustment by clinical variables. Both biomarkers improve the prediction by 19% as compared to clinical information, suggesting a potential role for risk stratification in acute thrombolyzed stroke patients.
3,4‐Methylenedioxymethamphetamine (MDMA, ecstasy) use may have long‐term neurotoxic effects. In this study, positron emission tomography with the tracer alpha‐[11C]methyl‐l ‐tryptophan (11C‐AMT) was used to compare human brain serotonin (5‐HT) synthesis capacity in 17 currently drug‐free MDMA polydrug users with that in 18 healthy matched controls. Gender differences and associations between regional 11C‐AMT trapping and characteristics of MDMA use were also examined. MDMA polydrug users exhibited lower normalized 11C‐AMT trapping in pre‐frontal, orbitofrontal, and parietal regions, relative to controls. These differences were more widespread in males than in females. Increased normalized 11C‐AMT trapping in MDMA users was also observed, mainly in the brainstem and in frontal and temporal areas. Normalized 11C‐AMT trapping in the brainstem and pre‐frontal regions correlated positively and negatively, respectively, with greater lifetime accumulated MDMA use, longer durations of MDMA use, and shorter time elapsed since the last MDMA use. Although the possibility of pre‐existing 5‐HT alterations pre‐disposing people to use MDMA cannot be ruled out, regionally decreased 5‐HT synthesis capacity in the forebrain could be interpreted as neurotoxicity of MDMA on distal (frontal) brain regions. On the other hand, increased 5‐HT synthesis capacity in the raphe and adjacent areas could be due to compensatory mechanisms.
This study investigates the effects of ethanol on neuronal and astroglial metabolism using 1H‐[13C]‐NMR spectroscopy in conjunction with infusion of [1,6‐13C2]/[1‐13C]glucose or [2‐13C]acetate, respectively. A three‐compartment metabolic model was fitted to the 13C turnover of GluC3, GluC4, GABAC2, GABAC3, AspC3, and GlnC4 from [1,6‐13C2]glucose to determine the rates of tricarboxylic acid (TCA) and neurotransmitter cycle associated with glutamatergic and GABAergic neurons. The ratio of neurotransmitter cycle to TCA cycle fluxes for glutamatergic and GABAegic neurons was obtained from the steady‐state [2‐13C]acetate experiment and used as constraints during the metabolic model fitting. 1H MRS measurement suggests that depletion of ethanol from cerebral cortex follows zero order kinetics with rate 0.18 ± 0.04 μmol/g/min. Acute exposure of ethanol reduces the level of glutamate and aspartate in cortical region. GlnC4 labeling was found to be unchanged from a 15 min infusion of [2‐13C]acetate suggesting that acute ethanol exposure does not affect astroglial metabolism in naive mice. Rates of TCA and neurotransmitter cycle associated with glutamatergic and GABAergic neurons were found to be significantly reduced in cortical and subcortical regions. Acute exposure of ethanol perturbs the level of neurometabolites and decreases the excitatory and inhibitory activity differentially across the regions of brain.
There is increasing evidence linking neuroinflammation to many neurological disorders including Alzheimer's disease (AD); however, its exact contribution to disease manifestation and/or progression is poorly understood. Therefore, there is a need to investigate neuroinflammation in both health and disease. Here, we investigate cognitive decline, neuroinflammatory and other pathophysiological changes in the APPswe×PS1Δe9 transgenic mouse model of AD. Transgenic (TG) mice were compared to C57BL/6 wild type (WT) mice at 6, 12 and 18 months of age. Neuroinflammation was investigated by [18F]DPA‐714 positron emission tomography and myo‐inositol levels using 1H magnetic resonance spectroscopy (MRS) in vivo. Neuronal and cellular dysfunction was investigated by looking at N‐acetylaspartate (NAA), choline‐containing compounds, taurine and glutamate also using MRS. Cognitive decline was first observed at 12 m of age in the TG mice as assessed by working memory tests . A significant increase in [18F]DPA‐714 uptake was seen in the hippocampus and cortex of 18 m‐old TG mice when compared to age‐matched WT mice and 6 m‐old TG mice. No overall effect of gene was seen on metabolite levels; however, a significant reduction in NAA was observed in 18 m‐old TG mice when compared to WT. In addition, age resulted in a decrease in glutamate and an increase in choline levels. Therefore, we can conclude that increased neuroinflammation and cognitive decline are observed in TG animals, whereas NAA alterations occurring with age are exacerbated in the TG mice. These results support the role of neuroinflammation and metabolite alteration in AD and in ageing.
Benefits on cognition from docosahexaenoic acid (DHA, 22 : 6 n‐3) intake are absent in humans carrying apolipoprotein E ε4 allele (APOE4), the most important genetic risk factor for Alzheimer's disease (AD). To test the hypothesis that carrying APOE4 impairs DHA distribution, we evaluated plasma and brain fatty acid profiles and uptake of [14C]‐DHA using in situ cerebral perfusion through the blood–brain barrier in 4‐ and 13‐month‐old male and female APOE‐targeted replacement mice (APOE2, APOE3, and APOE4), fed with a DHA‐depleted diet. Cortical and plasma DHA were 9% lower and 34% higher in APOE4 compared to APOE2 mice, respectively. Brain uptake of [14C]‐DHA was 24% lower in APOE4 versus APOE2 mice. A significant relationship was established between DHA and apoE concentrations in the cortex of mice (r2 = 0.21) and AD patients (r2 = 0.32). Altogether, our results suggest that lower brain uptake of DHA in APOE4 than in APOE2 mice may limit the accumulation of DHA in cerebral tissues. These data provide a mechanistic explanation for the lack of benefit of DHA in APOE4 carriers on cognitive function and the risk of AD.
Kiss1, a neuropeptide predominantly expressed in the habenula, modulates the serotonin (5‐HT) system to decrease odorant cue [alarm substance (AS)]‐evoked fear behaviour in the zebrafish. The purpose of this study was to assess the interaction of Kiss1 with the 5‐HT system as well as to determine the involvement of the 5‐HT receptor subtypes in AS‐evoked fear. We utilized 0. 28 mg/kg WAY 100635 (WAY), a selective 5‐HT1A receptor antagonist, to observe the effects of Kiss1 administration on AS‐evoked fear. We found WAY significantly inhibited the anxiolytic effects of Kiss1 (p <0.001) with an exception of freezing behaviour. Based on this, we utilized 92.79 mg/kg methysergide, a 5‐HT1 and 5‐HT2 receptor antagonist, and found that methysergide significantly blocked the anxiolytic effects of Kiss1 in the presence of the AS (p <0.001). From this, we conclude that Kiss1 modulates AS‐evoked fear responses mediated by the 5‐HT1A and 5‐HT2 receptors.
The positron emission tomography (PET) ligand 11C‐labeled Pittsburgh compound B (PIB) is used to image β‐amyloid (Aβ) deposits in the brains of living subjects with the intent of detecting early stages of Alzheimer's disease (AD). However, deposits of human‐sequence Aβ in amyloid precursor protein transgenic mice and non‐human primates bind very little PIB. The high stoichiometry of PIB:Aβ binding in human AD suggests that the PIB‐binding site may represent a particularly pathogenic entity and/or report local pathologic conditions. In this study, 3H‐PIB was employed to track purification of the PIB‐binding site in > 90% yield from frontal cortical tissue of autopsy‐diagnosed AD subjects. The purified PIB‐binding site comprises a distinct, highly insoluble subfraction of the Aβ in AD brain with low buoyant density because of the sodium dodecyl sulfate‐resistant association with a limited subset of brain proteins and lipids with physical properties similar to lipid rafts and to a ganglioside:Aβ complex in AD and Down syndrome brain. Both the protein and lipid components are required for PIB binding. Elucidation of human‐specific biological components and pathways will be important in guiding improvement of the animal models for AD and in identifying new potential therapeutic avenues.
Energy metabolism supports both inhibitory and excitatory neurotransmission processes. This study investigated the specific contribution of astrocytic metabolism to γ‐aminobutyric acid (GABA) synthesis and inhibitory GABAergic neurotransmission that remained to be ilucidated in vivo. Therefore, we measured 13C incorporation into brain metabolites by dynamic 13C nuclear magnetic resonance spectroscopy at 14.1 T in rats under α‐chloralose anaesthesia during infusion of [1,6‐13C]glucose. The enhanced sensitivity at 14.1 T allowed to quantify incorporation of 13C into the three aliphatic carbons of GABA non‐invasively. Metabolic fluxes were determined with a mathematical model of brain metabolism comprising glial, glutamatergic and GABAergic compartments. GABA synthesis rate was 0.11 ± 0.01 μmol/g/min. GABA‐glutamine cycle was 0.053 ± 0.003 μmol/g/min and accounted for 22 ± 1% of total neurotransmitter cycling between neurons and glia. Cerebral glucose oxidation was 0.47 ± 0.02 μmol/g/min, of which 35 ± 1% and 7 ± 1% was diverted to the glutamatergic and GABAergic tricarboxylic acid cycles, respectively. The remaining fraction of glucose oxidation was in glia, where 12 ± 1% of the TCA cycle flux was dedicated to oxidation of GABA. 16 ± 2% of glutamine synthesis was provided to GABAergic neurons. We conclude that substantial metabolic activity occurs in GABAergic neurons and that glial metabolism supports both glutamatergic and GABAergic neurons in the living rat brain.
Multiple sclerosis (MS) is considered an autoimmune demyelinating disease of the CNS and myelin‐derived glycolipids are one of the targets of this autoimmune attack. In this study, we examined for the first time the plasma distribution of sulfatide isoforms. Sulfatides with long‐chain (C24 : 0 or C24 : 1) and short‐chain (C16 : 0 or C18 : 0) fatty acids were quantified in plasma of relapsing–remitting MS patients by ultra‐high‐performance liquid chromatography tandem mass spectrometry. We found that C18 : 0 and C24 : 1 sulfatide plasma levels positively correlated with the Expanded Disability Status Scale. C16/C18 : 0 and C16/C24 : 0 ratios also correlated with the age and the time since last relapse. Healthy women showed higher levels of C16 : 0 sulfatide than healthy men; however, this gender difference disappeared in MS patients. Our data underline the potential use of sulfatides as biomarkers in relapsing–remitting MS and points to a possible association with the higher susceptibility of women to develop MS.
下载免费PDF全文