γ-aminobutyric acid measurement in the human brain at 7 T: Short echo-time or Mescher–Garwood editing

The purposes of the current study were to introduce a Mescher–Garwood (MEGA) semi-adiabatic spin-echo full-intensity localization (MEGA-sSPECIAL) sequence with macromolecule (MM) subtraction and to compare the test–retest reproducibility of γ-aminobutyric acid (GABA) measurements at 7 T using the sSPECIAL and MEGA-sSPECIAL sequences. The MEGA-sSPECIAL editing scheme using asymmetric adiabatic and highly selective Gaussian pulses was used to compare its GABA measurement reproducibility with that of short echo-time (TE) sSPECIAL. Proton magnetic resonance spectra were acquired in the motor cortex (M1) and medial prefrontal cortex (mPFC) using the sSPECIAL (TR/TE = 4000/16 ms) and MEGA-sSPECIAL sequences (TR/TE = 4000/80 ms). The metabolites were quantified using LCModel with unsuppressed water spectra. The concentrations are reported in institutional units. The test–retest reproducibility was evaluated by scanning each subject twice. Between-session reproducibility was assessed using coefficients of variation (CVs), Pearson's r correlation coefficients, and intraclass correlation coefficients (ICCs). Intersequence agreement was evaluated using Pearson's r correlation coefficients and Bland–Altman plots. Regarding GABA measurements by sSPECIAL, the GABA concentrations were 0.92 ± 0.31 (IU) in the M1 and 1.56 ± 0.49 (IU) in the mPFC. This demonstrated strong between-session correlation across both regions (r = 0.81, p < 0.01; ICC = 0.82). The CVs between the two scans were 21.8% in the M1 and 10.2% in the mPFC. On the other hand, the GABA measurements by MEGA-sSPECIAL were 0.52 ± 0.04 (IU) in the M1 and 1.04 ± 0.24 (IU) in the mPFC. MEGA-sSPECIAL demonstrated strong between-session correlation across the two regions (r = 0.98, p < 0.001; ICC = 0.98) and lower CVs than sSPECIAL, providing 4.1% in the M1 and 5.8% in the mPFC. The MEGA-editing method showed better reproducibility of GABA measurements in both brain regions compared with the short-TE sSPECIAL method. Thus it is a more sensitive method with which to detect small changes in areas with low GABA concentrations. In GABA-rich brain regions, GABA measurements can be achieved reproducibly using both methods.     

Reproducibility of prefrontal γ-aminobutyric acid measurements with J-edited spectroscopy

γ‐Aminobutyric acid (GABA) is the chief inhibitory neurotransmitter of the human brain, and GABA‐ergic dysfunction has been implicated in a variety of neuropsychiatric disorders. Recent MRS techniques have allowed the quantification of GABA concentrations in vivo, and could therefore provide biologically relevant information. Few reports have formally characterized the reproducibility of these techniques, and differences in field strength, acquisition and processing parameters may result in large differences in measured GABA values. Here, we used a J‐edited, single‐voxel spectroscopy method of measurement of GABA + macromolecules (GABA + ) in the anterior cingulate cortex (ACC) and right frontal white matter (rFWM) at 3 T. We measured the coefficient of variation within subjects (CVw) and intra‐class correlation coefficients on two repeated scans obtained from 10 healthy volunteers with processing procedures developed in‐house for the quantification of GABA + and other major metabolites. In addition, by segmenting the spectroscopic voxel into cerebrospinal fluid, gray matter and white matter, and employing a linear regression technique to extrapolate metabolite values to pure gray and white matter, we determined metabolite differences between gray and white matter in ACC and rFWM. CVw values for GABA + /creatine, GABA + /H₂O, GABA + , creatine, partially co‐edited glutamate + glutamine (Glx)/creatine, partially co‐edited Glx and N‐acetylaspartic acid (NAA)/creatine were all below 12% in both ACC and rFWM. After extrapolation to pure gray and pure white matter, CVw values for all metabolites were below 16%. We found metabolite ratios between gray and white matter for GABA + /creatine, GABA + , creatine, partially co‐edited Glx and NAA/creatine to be 0.88 ± 0.21 (standard deviation), 1.52 ± 0.32, 1.77 ± 0.4, 2.69 ± 0.74 and 0.70 ± 0.05, respectively. This study validates a reproducible method for the quantification of brain metabolites, and provides information on gray/white matter differences that may be important in the interpretation of results in clinical populations. Published in 2011 by John Wiley & Sons, Ltd.     

Immunobiological specificity of antibodies against glutamate and γ-aminobutyric acid

Experiments on C57Bl/6 mice showed that chronic epileptization of the brain (pharmacological pentylenetetrazole kindling) is accompanied by induction of autoantibodies against glutamate and GABA. Immunohistochemical similarity of antibodies against glutamate and GABA was demonstrated. Study on the model of pentylenetetrazoleinduced acute generalized epileptiform activity showed high immunobiological specificity of intraperitoneally injected antibodies against GABA and glutamate: antiepileptic effect of antiglutamate antibodies and proepileptic effect of antibodies against GABA. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 143, No. 5, pp. 572–575, May, 2007     

Identification of N-carboxyethyl γ-aminobutyric acid in bovine brain and human cerebrospinal fluid

The di-carboxylated derivative of spermidine, N-carboxyethyl γ-aminobutyric acid (CEGABA) has been identified in bovine brain and human cerebrospinal fluid by HPLC. This discovery strongly suggests the existence of a metabolic pathway connecting polyamines and GABA via putreanine and CEGABA through progressive oxidative deamination of the amino terminal groups in spermidine.     

Interaction of ivermectin with γ-aminobutyric acid receptors in Trichinella spiralis muscle larvae

The value of the γ-aminobutyric acid (GABA) receptor of nematodes as a target for ivermectin's mode of action remains unclear. Using binding assays, we examined extracts from Trichinella spiralis muscle larvae for the presence of [³H]-ivermectin and [³H]-GABA binding sites. Tissue preparations displayed affinity binding sites for [³H]-ivermectin with a dissociation constant (K _d) of 83 nM and a receptor density (B_max) of 145 fmol/mg protein. We also identified a specific [³H]-GABA binding activity with a K _d of 1.2 μM and a B_max of 4.78 pmol/mg protein. In competition studies, ivermectin was found to be a competitive inhibitor of specific [³H]-GABA binding activity with an inhibition constant (K _i) of 3.39 nM, suggesting that GABA receptors could be implicated in the mechanism of action of ivermectin in nematodes. Received: 7 August 1998 / Accepted: 22 September 1998     

Activation of subconductance states by γ-aminobutyric acid and its analogs in chick cerebral neurons

The action of -aminobutyric acid (GABA) and the GABA_A-receptor agonists muscimol, isoguvacine and 4,5,6,7-tetrahydroisoxazolo [5,4–c]pyridin-3-ol (THIP) were studied at the single-channel level in outside-out membrane patches from cultured chick cerebral neurons. All agonists activated channels with multiple-conductance states. The main-state conductance activated by all agonists had a value around 26 pS in symmetrical TRIS/Cl solutions. Subconductance states of around 13 pS and 18 pS were seen with application of each agonist. Muscimol and isoguvacine tended preferentially to activate subconductance states. Gating by all agonists was complex. Open-time distributions for main-state activity gated by GABA, isoguvacine and THIP were best described by the sum of two exponential curves with similar time constants. Muscimol-gated activity was best described by the sum of three exponentials indicating the presence of an additional longer open state. These results indicate that certain GABA_A-receptor agonists are capable of preferentially activating subconductance states.     

Comparison of seven modelling algorithms for γ-aminobutyric acid–edited proton magnetic resonance spectroscopy

Edited MRS sequences are widely used for studying γ-aminobutyric acid (GABA) in the human brain. Several algorithms are available for modelling these data, deriving metabolite concentration estimates through peak fitting or a linear combination of basis spectra. The present study compares seven such algorithms, using data obtained in a large multisite study. GABA-edited (GABA+, TE = 68 ms MEGA-PRESS) data from 222 subjects at 20 sites were processed via a standardised pipeline, before modelling with FSL-MRS, Gannet, AMARES, QUEST, LCModel, Osprey and Tarquin, using standardised vendor-specific basis sets (for GE, Philips and Siemens) where appropriate. After referencing metabolite estimates (to water or creatine), systematic differences in scale were observed between datasets acquired on different vendors' hardware, presenting across algorithms. Scale differences across algorithms were also observed. Using the correlation between metabolite estimates and voxel tissue fraction as a benchmark, most algorithms were found to be similarly effective in detecting differences in GABA+. An interclass correlation across all algorithms showed single-rater consistency for GABA+ estimates of around 0.38, indicating moderate agreement. Upon inclusion of a basis set component explicitly modelling the macromolecule signal underlying the observed 3.0 ppm GABA peaks, single-rater consistency improved to 0.44. Correlation between discrete pairs of algorithms varied, and was concerningly weak in some cases. Our findings highlight the need for consensus on appropriate modelling parameters across different algorithms, and for detailed reporting of the parameters adopted in individual studies to ensure reproducibility and meaningful comparison of outcomes between different studies.     

Preparation of γ-aminopropyltriethoxysilane cross-linked poly(aspartic acid) superabsorbent hydrogels without organic solvent

Poly(aspartic acid) (PASP) hydrogel is a type of biodegradable and biocompatible polymer with high water absorbing ability. Traditionally, the production of PASP hydrogel is expensive, complex, environmentally unfriendly, and consumes a large amount of organic solvents, e.g. dimethylformamide or dimethylsulfoxide. This study introduces a one-step synthesis of PASP resin, in which the organic phase was replaced by distilled water and γ-aminopropyltriethoxysilane was used as the cross-linker. Absorbent ability and characteristics were determined by swelling ratio, FTIR, ¹³C SSNMR, and SEM. In vitro cytotoxicity evaluation and animal skin irritation tests showed the hydrogel has body-friendly properties. Preparing PASP hydrogel in aqueous solution is promising and finds its use in many applications.     

Analgesic effect of intrathecally γ-aminobutyric acid transporter-1 inhibitor NO-711 administrating on neuropathic pain in rats

Neuregulin-1 (NRG1) participates in numerous neurodevelopmental processes and plasticity of the brain. Despite this, little is known about its role in Alzheimer's disease (AD). Amyloid β (Aβ) peptide is generally believed to play a critical role in the pathogenesis of AD. The present study examined the effect of synthetic Aβ_1-42 peptides on long-term potentiation (LTP) in the CA1 region of mice hippocampal slices, a cellular model of learning and memory. We found that application of a test dose of Aβ_1-42 (200 nM) significantly inhibited the development of LTP without affecting basal synaptic transmission. Pretreatment with NRG1 effectively prevented Aβ_1-42-induced impairment of LTP, an effect that was dose-dependent. This LTP-restoring action of NRG1 was almost completely abolished by blocking ErbB4, a key NRG1 receptor, suggesting that NRG1 acts through ErbB4 to exert its protective action on LTP. The present study thus provides the first demonstration that NRG1/ErbB4 protects against Aβ-induced hippocampal LTP impairment, suggesting that NRG1 may be a promising candidate for the treatment of early-stage AD.     

Analgesic effect of intrathecally γ-aminobutyric acid transporter-1 inhibitor NO-711 administrating on neuropathic pain in rats

To investigate the analgesic effect of intrathecally administered γ-aminobutyric acid (GABA) transporter-1 inhibitor NO-711 on the sciatic nerve chronic constriction injury (CCI) rats. 5 days after intrathecal catheter placement, neuropathic pain model was established by CCI of sciatic nerve on rats. Withdrawal thresholds for mechanical allodynia and latency for thermal hyperalgesia were measured in all animals. All rats operated upon for CCI displayed decreased withdrawal thresholds for mechanical allodynia and latency for thermal hyperalgesia, which has significant difference compared with sham groups. After intrathecal NO-711 administration, withdrawal thresholds and latency were significantly increased on CCI rats compared with control group after 1 day. The results show that GABA transporter-1 inhibitor could effectively develop analgesic effect in sciatic nerve CCI rats’ model.     

The effect of stereoisomers of cycloserine on the formation and transformation of free γ-aminobutyric acid in brain tissue

Summary A study was made of the effect produced by the stereoisomers of cycloserine on decarboxylization of glutamic acid and transamination of -aminobutyric acid with -ketoglutaric acid in the homogenates of the rat brain at pH 7.5. As revealed. D.L-cycloserine in a concentration of 10^–3 M depressed the first process by 40% and the second one by 45%. In the same conditions D-cycloserine depressed glutamic acid decarboxylation by 9%; it somewhat activated -aminobutyric acid transamination. A discussion is presented on the possible effect of cycloserine isomers on the content of free -aminobutyric acid in the brain (in vivo) following the administration of isoniazid in large doses.(Presented by Active Member AMN SSSR V. V. Zakusov) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 54, No. 10, pp. 67–69, October, 1962     

Immunoelectron microscopic study of γ-aminobutyric acid inputs to identified thalamocortical projection neurons in the anterior thalamus of the rat

 We have carried out a semi-quantitative ultrastructural study to determine the characteristics and distribution of γ-aminobutyric acid (GABA)-containing constituents of the anterodorsal (AD) and anteroventral (AV) thalamic nuclei in adult rats. We used a polyclonal antibody to GABA and a postembedding immunogold detection method in animals in which the cortical projection neurons of these nuclei had been labelled by retrograde transport of cholera toxin/horseradish peroxidase (HRP) injected into the retrosplenial granular cortex. Two types of GABA-immunopositive structures were identified, with gold particle densities 4–40 times higher than the highest densities over blood-vessel lumens and areas of empty resin: (1) an apparently homogeneous population of axon terminals with Gray type-2 (symmetric) synaptic contacts corresponding to F-axon terminals; and (2) small–medium sized myelinated axons scattered individually or in small groups within the neuropil which may be their parent axons. These axons and terminals may originate from the ipsilateral thalamic reticular nucleus; others may arise from the basal forebrain or brainstem. The GABA-immunopositive terminals comprised approximately 16% of all axon terminal profiles in AD and 12% in AV, a significant difference. However, because the immunoreactive axon terminals in AD were significantly larger than those in AV (1.09±0.47 μm² vs 0.90±0.43 μm²) and would therefore be encountered more frequently, it is not possible to conclude that the GABAergic innervation of AD is heavier than that of AV. The GABA-positive terminals established synaptic contacts with cell bodies and dendrites of all sizes (some of which were HRP-labelled) with the following frequency distribution (AD/AV, no significant difference): somata 5%/7%; large dendrites (≥1.5 μm) 14%/9%; medium dendrites (1.00–1.49 μm) 35%/45% and small dendrites (<1 μm) 46%/40%. Despite evidence from previous studies, we found no evidence in this study for the presence of GABAergic interneurons or for GABA-containing projection neurons in AD or AV. Received: 4 March 1998 / Accepted: 15 January 1999     

A molecular scheme for the reaction between γ-aminobutyric acid and the most abundant chloride channel on crayfish deep extensor abdominal muscle

Single-channel measurements were performed with the aim of constructing a detailed molecular scheme for the reaction between -aminobutyric acid (GABA) and a chloride channel of crayfish deep extensor abdominal muscle (DEAM). GABA was applied in pulses to outside-out patches of muscle membrane, and, based on the dose-response of the peak currents and of their rise times, a linear model with five binding steps has been proposed. Evaluation of the single-channel kinetics indicated at least three open states. Two of them originate most probably from the fully liganded receptor state and are grouped in mixed bursts due to their different life times. The third one appears independently, outside the bursts, and originates from a lower liganded receptor state. Simulations of the dose-responses and the open time distributions with this model led to a set of rate constants which generated relatively optimal fits.     

CDR3δ -grafted γ9δ2T cells mediate effective antitumor reactivity

Adoptive cell-transfer therapy (ACT) has been reported to suppress growing tumors and to overcome tumor escape in animal models. As a candidate ACT effector, γ9δ2T cells can be activated and expanded in vitro and in vivo and display strong antitumor activity against colorectal, lung, prostate, ovarian and renal cell carcinomas. However, it is difficult to obtain a large enough number of γδT cells to meet the need for immunotherapy that can overcome the cancer patients' immune suppressive tumor microenvironment. In previous studies, our lab confirmed that γ9δ2T cells recognized tumor cells via the CDR3δ region of the γδ-T-cell receptor (TCR). We constructed full-length human peripheral blood mononuclear cell (PBMC)-derived γ9 and δ2 chains in which the CDR3 region was replaced by an ovarian epithelial carcinoma (OEC)-derived CDR3. We transferred the CDR3δ-grafted γ9δ2TCR into peripheral blood lymphocytes (PBLs) to develop genetically modified γ9δ2T cells. In vitro studies have shown that these CDR3δ-grafted γ9δ2T cells can produce cytokines after stimulation with tumor cell extracts and exhibit cytotoxicity towards tumor cells, including human OEC and cervical adenocarcinoma. CDR3δ-grafted γ9δ2T cells adoptively transferred into nude mice bearing a human OEC cell line demonstrated significant antitumor effects. These results indicate that CDR3δ-grafted γ9δ2T cells might be candidates for clinical tumor immunotherapy.     

Complex involvement of nitric oxide and cGMP at N-methyl-d-aspartic acid receptors regulating γ-[H]aminobutyric acid release from striatal slices

Whilst the depolarization of postsynaptic N-methyl-d-aspartic acid (NMDA) receptors leads to an influx of Ca²⁺ and subsequent synthesis of nitric oxide (NO), we examined roles for NO at striatal NMDA receptors regulating transmitter release. In superfused rat striatal slices, NMDA-evoked release of γ-[³H]aminobutyric acid ([³H]GABA) was investigated in the presence of nitrergic drugs. NMDA-induced release of [³H]GABA was attenuated by d-2-aminophosphonopentanoate, tetrodotoxin and omission of Ca²⁺. l-Arginine enhanced NMDA-evoked release of [³H]GABA, but exogenous NO donors were ineffective. Inhibitors of NO synthase (N^G-nitro- and N^G-amino-l-arginine) and guanylate cyclase (LY83583) elevated release. Since NMDA-evoked release of [³H]GABA was partially tetrodotoxin-sensitive, nitrergic-linked NMDA receptors regulating the release are both pre- and extrasynaptic. Thus not only does NO arise from multiple sites, and involve NMDA receptors with their redox site insensitive to exogenous NO donors, but the NMDA receptors are under the influence of nitrergic and cGMP-linked negative feedback mechanisms.