Endogenous Gamma-aminobutyric Acid Research Articles

Interaction of Gamma-Aminobutyric Acid and Ca2+ on Phenolic Compounds Bioaccumulation in Soybean Sprouts under NaCl Stress.

NaCl stress can enhance the accumulation of phenolic compounds in soybean during germination. In the present study, effects of gamma-aminobutyric acid (GABA) and Ca2+ on the biosynthesis of phenolic compounds in soybean sprouts germinated with NaCl stress were investigated. Results showed that addition of Ca2+ increased the content of total phenolics, phenolic acids, and isoflavonoids in soybean sprouts by ca. 15%, 7%, and 48%, respectively, through enhancing the activities of three key enzymes involved in the biosynthesis. On the other hand, addition of LaCl3, a calcium channel blocker, inhibited the synthesis of phenolic compounds, indicating that Ca2+ plays an important role in the synthesis of these compounds in soybean sprouts. Addition of GABA can increase the content of Ca2+ in soybean sprouts by ca. 20% and alleviate the inhibition of LaCl3 on phenolics biosynthesis in soybean sprouts. Similarly, addition of Ca2+ can reverse the inhibition of 3-mercaptopropionate, an inhibitor of endogenous GABA synthesis, on the biosynthesis of phenolic compounds in soybean sprouts under NaCl stress. To conclude, both GABA and Ca2+ can enhance the biosynthesis of phenolic compounds in soybean sprouts and there was an interaction between their effects on the promotion of phenolic compounds biosynthesis.

Exogenous Application of GABA Alleviates Alkali Damage in Alfalfa by Increasing the Activities of Antioxidant Enzymes

Alfalfa (Medicago sativa L.) is a widely grown and important forage crop. However, alkali stress is detrimental to alfalfa yield and nutritional quality. Gamma-aminobutyric acid (GABA) is a signaling molecule, it participates in and responds to metabolic regulation related to plant growth and development and stress. In this study, we clarify the effect of spraying alfalfa seedlings with GABA on the alkali tolerance of the seedlings. We determined that exogenous application of GABA at 75 mmol/L improved the resistance of alfalfa seedlings to alkali stress caused by exposure to 100 mmol/L NaHCO3, pH 8.5. Exogenous GABA significantly increased the chlorophyll content, the accumulation of soluble sugars in the plants, significantly decreased their relative electrical conductivity, malondialdehyde (MDA), superoxide anion (O2−) and hydrogen peroxide (H2O2) contents, and significantly increased the activities of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD). Exogenous GABA increased the activities of GAD and GABA-T, increased the content of glutamate and endogenous GABA, and regulated the expression of the genes MsGAD, MsGABA-T and MsGDH. In alfalfa plants that survived for a long time, compared to the control group, root length and fresh weight were significantly higher. Exogenous GABA had a positive effect on the resistance of alfalfa seedlings to alkali stress, and the effect was closely associated with GAD and GABA-T activity, glutamate content and the levels of endogenous GABA and antioxidants. This work provides a new method for the cultivation of early-stage alfalfa seedlings under low or moderate alkali stress conditions through the application of 75 mmol/L GABA.

Stimulation of GABA Receptors in the Lateral Septum Rapidly Elicits Food Intake and Mediates Natural Feeding

The increasing prevalence of obesity and eating disorders makes identifying neural substrates controlling eating and regulating body weight a priority. Recent studies have highlighted the role of the lateral septum (LS) in eating control mechanisms. The current study explored the roles of gamma-aminobutyric acid (GABA) receptors within the LS in the control of food intake. Experiments with a rat model (n ≥ 11/group) showed that LS microinjection of the GABAA receptor agonist, muscimol, and the GABAB receptor agonist, baclofen hydrochloride (baclofen), elicited intense, dose-dependent feeding. In contrast, LS pretreatment with the GABAA receptor antagonist, picrotoxin, markedly reduced the muscimol-elicited feeding, and pretreatment injections with the GABAB receptor antagonist, 2-hydroxysaclofen (2-OH saclofen), reduced the baclofen evoked response. Next, we showed that picrotoxin injection at the beginning of the dark phase of the light-dark cycle—when rats show a burst of spontaneous eating—reduced naturally occurring feeding, whereas 2-OH saclofen was ineffective. These results indicate that the activation of LS GABAA and GABAB receptors strongly stimulates feeding and suggests potential roles in feeding control neurocircuitry. In particular, our evidence indicates that endogenous LS GABA and GABAA receptors may be involved in mediating naturally occurring nocturnal feeding.

The interaction between endogenous GABA, functional connectivity, and behavioral flexibility is critically altered with advanced age

The flexible adjustment of ongoing behavior challenges the nervous system’s dynamic control mechanisms and has shown to be specifically susceptible to age-related decline. Previous work links endogenous gamma-aminobutyric acid (GABA) with behavioral efficiency across perceptual and cognitive domains, with potentially the strongest impact on those behaviors that require a high level of dynamic control. Our analysis integrated behavior and modulation of interhemispheric phase-based connectivity during dynamic motor-state transitions with endogenous GABA concentration in adult human volunteers. We provide converging evidence for age-related differences in the preferred state of endogenous GABA concentration for more flexible behavior. We suggest that the increased interhemispheric connectivity observed in the older participants represents a compensatory neural mechanism caused by phase-entrainment in homotopic motor cortices. This mechanism appears to be most relevant in the presence of a less optimal tuning of the inhibitory tone as observed during healthy aging to uphold the required flexibility of behavioral action. Future work needs to validate the relevance of this interplay between neural connectivity and GABAergic inhibition for other domains of flexible human behavior.

Enantiomers of 4-aminopentanoic acid act as false GABAergic neurotransmitters and impact mouse behavior.

Imbalance in the metabolic pathway linking excitatory and inhibitory neurotransmission has been implicated in multiple psychiatric and neurologic disorders. Recently, we described enantiomer-specific effects of 2-methylglutamate, which is not decarboxylated to the corresponding methyl analogue of gamma-aminobutyric acid (GABA): 4-aminopentanoic acid (4APA). Here, we tested the hypothesis that 4APA also has enantiomer-specific actions in brain. Mouse cerebral synaptosome uptake (nmol/mg protein over 30min) of (R)-4APA or (S)-4APA was time and temperature dependent; however, the R enantiomer had greater uptake, reduction of endogenous GABA concentration, and release following membrane depolarization than did the S enantiomer. (S)-4APA exhibited some weak agonist (GABAA α4β3δ, GABAA α5β2γ2, and GABAB B1/B2) and antagonist (GABAA α6β2γ2) activity while (R)-4APA showed weak agonist activity only with GABAA α5β2γ2. Both 4APA enantiomers (100mg/kg IP) were detected in mouse brain 10min after injection, and by 1hr had reached concentrations that were stable over 6hr; both enantiomers were cleared rapidly from mouse serum over 6hr. Two-month-old mice had no mortality following 100-900mg/kg IP of each 4APA enantiomer but did have similar dose-dependent reduction in distance moved in a novel cage. Neither enantiomer at 30 or 100mg/kg impacted outcomes in 23 measures of well-being, activity chamber, or withdrawal from hot plate. Our results suggest that enantiomers of 4APA are active in mouse brain, and that (R)-4APA may act as a novel false neurotransmitter of GABA. Future work will focus on disease models and on possible applications as neuroimaging agents.

Development and validation of a UPLC-MS/MS method for the simultaneous determination of gamma-aminobutyric acid and glutamic acid in human plasma

Gamma-aminobutyric acid (GABA) and its precursor glutamic acid are important neurotransmitters. Both are also present in peripheral tissues and the circulation, where abnormal plasma concentrations have been linked to specific mental disorders. In addition to endogenous synthesis, GABA and glutamic acid can be obtained from dietary sources. An increasing number of studies suggest beneficial cardio-metabolic effects of GABA intake, and therefore GABA is being marketed as a food supplement. The need for further research into their health effects merits accurate and sensitive methods to analyze GABA and glutamic acid in plasma. To this end, an ultra-pressure liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) method was developed and validated for the quantification of GABA and glutamic acid in human plasma. Samples were prepared by a protein precipitation step and subsequent solid phase extraction using acetonitrile. Chromatographic separation was achieved on an Acquity UPLC HSS reversed phase C18 column using gradient elution. Analytes were detected using electrospray ionization and selective reaction monitoring. Standard curve concentrations for GABA ranged from 3.4 to 2500 ng/mL and for glutamic acid from 30.9 ng/mL to 22,500 ng/mL. Within- and between-day accuracy and precision were <10% in quality control samples at low, medium and high concentrations for both GABA and glutamic acid. GABA and glutamic acid were found to be stable in plasma after freeze–thaw cycles and up to 12 months of storage. The validated method was applied to human plasma from 17 volunteers. The observed concentrations ranged between 11.5 and 20.0 ng/ml and 2269 and 7625 ng/ml for respectively GABA and glutamic acid. The reported method is well suited for the measurement of plasma GABA and glutamic acid in pre-clinical or clinical studies.

Gamma-aminobutyric acid (GABA) alleviates salt damage in tomato by modulating Na+ uptake, the GAD gene, amino acid synthesis and reactive oxygen species metabolism

BackgroundSalt stress is a serious abiotic stress that caused crop growth inhibition and yield decline. Previous studies have reported on the the synthesis of gamma-aminobutyric acid (GABA) and its relationship with plant resistance under various abiotic stress. However, the relationship between exogenous GABA alleviating plant salt stress damage and ion flux, amino acid synthesis, and key enzyme expression remains largely unclear. We investigated plant growth, Na+ transportation and accumulation, reactive oxygen species (ROS) metabolism and evaluated the effect of GABA on amino acids, especially SlGADs gene expression and the endogenous GABA content of tomato (Solanum lycopersicum L.) seedlings treated with or without 5 mmol·L− 1 GABA under 175 mmol·L− 1 NaCl stress.ResultsExogenous application of GABA significantly reduced the salt damage index and increased plant height, chlorophyll content and the dry and fresh weights of tomato plants exposed to NaCl stress. GABA significantly reduced Na+ accumulation in leaves and roots by preventing Na+ influx in roots and transportation to leaves. The transcriptional expression of SlGAD1–3 genes were induced by NaCl stress especially with GABA application. Among them, SlGAD1 expression was the most sensitive and contributed the most to the increase in glutamate decarboxylase (GAD) activity induced by NaCl and GABA application; Exogenous GABA increased GAD activity and amino acid contents in tomato leaves compared with the levels under NaCl stress alone, especially the levels of endogenous GABA, proline, glutamate and eight other amino acids. These results indicated that SlGADs transcriptional expression played an important role in tomato plant resistance to NaCl stress with GABA application by enhancing GAD activity and amino acid contents. GABA significantly alleviated the active oxygen-related injury of leaves under NaCl stress by increasing the activities of antioxidant enzymes and decreasing the contents of active oxygen species and malondialdehyde.ConclusionExogenous GABA had a positive effect on the resistance of tomato seedlings to salt stress, which was closely associated with reducing Na+ flux from root to leaves, increasing amino acid content and strengthening antioxidant metabolism. Endogenous GABA content was induced by salt and exogenous GABA at both the transcriptional and metabolic levels.

Crosstalk between GABA and ALA to improve antioxidation and cell expansion of tomato seedling under cold stress

Cold stress inhibits plant growth and ultimately affects yield formation. Exogenous 5- aminolevulinic acid (ALA) can improve tomato cold tolerance and promote plant growth. It significantly up-regulated glutamate decarboxylase gene (SlGAD4) expression, which was involved in gamma-aminobutyric acid (GABA) synthesis. Whether the GABA was involved in ALA-regulated tomato cold tolerance and plant growth was unclear. Thus, this study aimed to explore the effects of exogenous ALA and GABA on endogenous ALA and GABA synthesis. The roles of ALA and GABA on regulating the antioxidation and cell morphological changes related to plant growth in tomato leaves were further explored. And the internal relationship between ALA and GABA in increasing tomato cold tolerance was also determined. Results showed that cold stress increased the glutamate (Glu) and GABA contents and reduced the ALA content. The exogenous ALA- or GABA-treated plants demonstrated decreased Glu content and increased GABA or ALA contents. Exogenous ALA or GABA treatment promoted the expansion of upper epidermal (UEP) and palisade parenchymal (PA) cells and up-regulated the xyloglucan endotransglucosylase/hydrolases gene (SlXTH23) expression in tomato leaves. Exogenous ALA or GABA significantly alleviated cold-induced tomato membrane lipid peroxidation and enhanced C-repeat binding factors gene (SlCBF2) expression and superoxide dismutase (SOD), catalase (CAT), APX and GR activities. Inhibiting endogenous GABA with 3-mercaptopropionic (3-mp) dramatically decreased the size of UEP and PA cells and reduced SOD and CAT activities. It also aggravated the membrane peroxidation damage, which notably weakened the alleviated effects of exogenous ALA. Inhibiting endogenous ALA with gabaculine (gaba) partly inhibited the alleviated effects of exogenous GABA. These findings indicated that spray with exogenous ALA or GABA could increase endogenous ALA and GABA levels in tomato leaves. In addition, endogenous GABA and ALA could be mutually converted through Glu. Exogenous ALA and GABA promoted cell expansion, stimulated the antioxidant system and might enhance tomato cold tolerance via endogenous GABA signal and the C-repeat binding factor regulation pathway, thereby alleviating cold inhibited plant growth. In conclusion, GABA crosstalk with ALA improved tomato cold stress tolerance and promoted plant growth by regulating antioxidants and cell expansion.

The use of deuterium-labeled gamma-aminobutyric (D6-GABA) to study uptake, translocation, and metabolism of exogenous GABA in plants

BackgroundExogenous application of gamma-aminobutyric acid (GABA) could relieve stress symptoms caused by abiotic stresses including anoxia, heat and cold shock, drought, and salt. However, studying translocation and metabolism of exogenous GABA is challenged by the presence of endogenous GABA.ResultsHerein, we used D6-GABA in order to investigate the uptake, translocation, and the metabolism of exogenous GABA in Mexican lime (Citrus aurantifolia) seedlings using gas chromatography-mass spectrometry (GC–MS). The GC–MS analysis showed that D6-GABA could be easily distinguished from the non-labeled GABA after methyl chloroformate (MCF) derivatization. The D6-GABA was detected in the cortex (phloem), inner stem (xylem), and leaves after root drench. Girdling did not affect the translocation of D6-GABA, indicating that it is mainly translocated via the xylem. In addition, D4-labled succinic acid was detected in D6-GABA-treated plants, indicating that exogenous GABA was metabolized to succinic acid. The half-life of D6-GABA in citrus was about 1.3 h, indicating a quick conversion to succinic acid.ConclusionThe use of D6-GABA offers a valuable tool to study the translocation and metabolism of GABA in plants. D6-GABA and its metabolite (D4-succinic acid) can be easily distinguished from the endogenous GABA and succinic acid using GC–MS.

Gamma-aminobutyric acid-producing lactobacilli positively affect metabolism and depressive-like behaviour in a mouse model of metabolic syndrome

Metabolic and neuroactive metabolite production represents one of the mechanisms through which the gut microbiota can impact health. One such metabolite, gamma-aminobutyric acid (GABA), can modulate glucose homeostasis and alter behavioural patterns in the host. We previously demonstrated that oral administration of GABA-producing Lactobacillus brevis DPC6108 has the potential to increase levels of circulating insulin in healthy rats. Therefore, the objective of this study was to assess the efficacy of endogenous microbial GABA production in improving metabolic and behavioural outcomes in a mouse model of metabolic dysfunction. Diet-induced obese and metabolically dysfunctional mice received one of two GABA-producing strains, L. brevis DPC6108 or L. brevis DSM32386, daily for 12 weeks. After 8 and 10 weeks of intervention, the behavioural and metabolic profiles of the mice were respectively assessed. Intervention with both L. brevis strains attenuated several abnormalities associated with metabolic dysfunction, causing a reduction in the accumulation of mesenteric adipose tissue, increased insulin secretion following glucose challenge, improved plasma cholesterol clearance and reduced despair-like behaviour and basal corticosterone production during the forced swim test. Taken together, this exploratory dataset indicates that intervention with GABA-producing lactobacilli has the potential to improve metabolic and depressive- like behavioural abnormalities associated with metabolic syndrome in mice.

Challenges of simultaneous measurements of brain extracellular GABA and glutamate in vivo using enzyme-coated microelectrode arrays

BackgroundAlthough GABA is the major inhibitory neurotransmitter in the CNS, quantifying in vivo GABA levels has been challenging. The ability to co-monitor both GABA and the major excitatory neurotransmitter, glutamate, would be a powerful tool in both research and clinical settings. New methodCeramic-based microelectrode arrays (MEAs) were used to quantify gamma-aminobutyric acid (GABA) by employing a dual-enzyme reaction scheme including GABase and glutamate oxidase (GluOx). Glutamate was simultaneously quantified on adjacent recording sites coated with GluOx alone. Endogenous glutamate was subtracted from the combined GABA and glutamate signal to yield a pure GABA concentration. ResultsElectrode sensitivity to GABA in conventional, stirred in vitro calibrations at pH 7.4 did not match the in vivo sensitivity due to diffusional losses. Non-stirred calibrations in agarose or stirred calibrations at pH 8.6 were used to match the in vivo GABA sensitivity. In vivo data collected in the rat brain demonstrated feasibility of the GABA/glutamate MEA including uptake of locally applied GABA, KCl-evoked GABA release and modulation of endogenous GABA with vigabatrin. Comparison with existing methodsImplantable enzyme-coated microelectrode arrays have better temporal and spatial resolution than existing off-line methods. However, interpretation of results can be complicated due to the multiple recording site and dual enzyme approach. ConclusionsThe initial in vitro and in vivo studies supported that the new MEA configuration may be a viable platform for combined GABA and glutamate measures in the CNS extending the previous reports to in vivo GABA detection. The challenges of this approach are emphasized.

Application of gamma-aminobutyric acid increased the level of phytohormones in Citrus sinensis.

In the current study, we showed that exogenous GABA supplementation increases the endogenous GABA level, several amino acids, and phytohormones in citrus plants, suggesting that GABA works in harmony with phytohormones. Gamma-aminobutyric acid (GABA) plays a key role in cytosolic regulation of pH, controlling of carbon and nitrogen metabolism, and protection against biotic and abiotic stresses. Although it is well-known that GABA is implicated in plant defense and it could act as a signaling molecule, its effect on phytohormones is not completely understood. In this study, we investigated the effect of exogenous GABA on citrus phytohormones using gas chromatography-mass spectrometry. A significant increase in endogenous GABA was observed in GABA-treated plants. The highest increase in GABA was recorded in plants treated with 10mM7days post-treatment. In addition, we observed a moderate increase in several amino acids including glycine, L-alanine, L-proline, L-asparagine, and L-glutamine. The levels of benzoic acid, cinnamic acid, salicylic acid, trans-jasmonic acid, indole acetic acid, indole propionic acid, and abscisic acid were significantly increased in GABA-treated plants compared to the control. The gene expression showed that GABA transaminase (GABA-T) and succinic semialdehyde dehydrogenase (SSADH) were induced in GABA-treated plants, indicating a conversion of GABA to succinate. In addition, the gene expression of the regulatory enzymes of the TCA cycle (malate dehydrogenase and succinic dehydrogenase) was upregulated in GABA-treated plants, indicating an induction of respiration. In agreement with the chemical analysis, the gene expression results showed that most of the genes implicated in the biosynthesis of phytohormones were also upregulated in GABA-treated plants. Our results indicated that GABA works in harmony with phytohormones and suggested that regulation of phytohormones by exogenous GABA could play a key role in reducing plant stress.

Gamma-Aminobutyric Acid (GABA) Modulates Nitrate Concentrations and Metabolism in the Leaves of Pakchoi (Brassica campestris ssp. chinensis Makino) Treated with a Nitrogen-Rich Solution

Pakchoi plants were grown in 32 mM NO3− nutrient solution with or without 2.5 mM γ-aminobutyric acid (GABA) to investigate metabolite changes, gene and protein expression levels, and the activities of key enzymes related to nitrate metabolism in the leaves over a period of 0–12 days. High-nitrogen treatment enhanced plant growth and the NO3−, NO2−, NH4+, Gln, and Glu contents in the leaves; promoted the gene and protein expression of nitrate reductase (NR) and glutamate decarboxylase (GAD); and increased the activities of NR, nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), and GAD. The endogenous GABA concentration in the leaves was enhanced in parallel with the increase in GAD activity. The GABA-treated leaves displayed the greatest increases in the gene and protein expression levels of NR and GAD and in the activities of NR, NiR, GS, GOGAT, and GAD. In addition, accelerated rates of nitrate reduction and assimilation were detected, and these changes occurred concurrently with the observed increases in gene or protein expression and enzyme activity. As a result, the concentrations of NH4+, Gln, Glu, and endogenous GABA were significantly elevated, and the NO3− and NO2− contents were significantly decreased, in GABA-treated leaves compared with plants exposed to nitrogen-rich conditions. Our results reveal a potential positive that GABA may act as a nitrogen source to improve the plant growth and the most prominent effect of decreasing nitrate contents by accelerating NO3− reduction and assimilation. Exogenous GABA plays an important role in reducing the NO3− content of leaves, and thereby improves the ability to harvest leafy vegetables containing higher levels of endogenous GABA.

Aluminum-Activated Malate Transporters Can Facilitate GABA Transport.

Plant aluminum-activated malate transporters (ALMTs) are currently classified as anion channels; they are also known to be regulated by diverse signals, leading to a range of physiological responses. Gamma-aminobutyric acid (GABA) regulation of anion flux through ALMT proteins requires a specific amino acid motif in ALMTs that shares similarity with a GABA binding site in mammalian GABAA receptors. Here, we explore why TaALMT1 activation leads to a negative correlation between malate efflux and endogenous GABA concentrations ([GABA]i) in both wheat (Triticum aestivum) root tips and in heterologous expression systems. We show that TaALMT1 activation reduces [GABA]i because TaALMT1 facilitates GABA efflux but GABA does not complex Al3+ TaALMT1 also leads to GABA transport into cells, demonstrated by a yeast complementation assay and via 14C-GABA uptake into TaALMT1-expressing Xenopus laevis oocytes; this was found to be a general feature of all ALMTs we examined. Mutation of the GABA motif (TaALMT1F213C) prevented both GABA influx and efflux, and resulted in no correlation between malate efflux and [GABA]i We conclude that ALMTs are likely to act as both GABA and anion transporters in planta. GABA and malate appear to interact with ALMTs in a complex manner to regulate each other's transport, suggestive of a role for ALMTs in communicating metabolic status.

Exogenous GABA stimulates endogenous GABA and phenolic acid contents in tomato plants under salt stress

Gamma aminobutyric acid (GABA) is a non protein amino acid found in various organisms including plants. In recent years, the signal role of GABA in the stress response has of special interest. However, the effects of exogenous GABA on phenolic compounds which have special roles as antioxidants are not well known. In this study, the effects of exogenous GABA on endogenous GABA and phenolic contents were analyzed in tomato plants under salt stress. Tomato plants were grown in a growth chamber under controlled conditions and NaCl and GABA were applied in Hoagland solution. Qualitative and quantitative analysis of GABA and phenolic compounds (Benzoic, caffeic, chlorogenic, gallic, hydroxybenzoic, syringic, rosmarinic, p-coumaric, sinapic, t-cinnamic, t-ferulic acids, catechin, epicatechin, hesperidin and quercetin) were measured by HPLC. Differences were found in chlorogenic acid, coumaric acid and gallic acid among the phenolic substances. We found a significant increase in gallic acid and coumaric acid contents under 200 mM NaCl and GABA applications. Exogenous GABA treatment caused a slight increase in endogenous GABA content. The increase in GABA content under GABA+salt treatments were higher than that of single salt and GABA applications. According to our results we can suggest that exogenous GABA could enhance the stress response by enhancing some phenolic substances and GABA content under salt stress.

Effects of exogenous gamma-aminobutyric acid on α-amylase activity in the aleurone of barley seeds

Gamma-aminobutyric acid (GABA), a nonprotein amino acid, often accumulates in plants exposed to certain environmental stimuli. Previous studies indicated that a closed relationship existed between endogenous GABA and seed germination. However, there are few studies on the effect of exogenous GABA on seed germination. The objective of this study was to explore whether exogenous GABA affected α-amylase activity which the activation is an important stage in seed germination. The level of endogenous GABA in barley seeds rose gradually during germination, suggesting that endogenous GABA was involved in germination. We measured starch degradation under application of various concentration GABA and found that GABA promoted seed starch degradation with a dose-responsive effect. The relationship between GABA and α-amylase activity was investigated by treating barley aleurone with exogenous GABA. The result showed that α-amylase activity began to rise after about 24 h and reached a peak at 48 h. Molecular evidence suggested that GABA increased α-amylase gene expression. We explore the possible roles played by GABA in signal transduction.

GABAA receptor: a unique modulator of excitability, Ca2+ signaling, and catecholamine release of rat chromaffin cells.

The role of gamma-aminobutyric acid (GABA) in adrenal medulla chromaffin cell (CC) function is just beginning to unfold. GABA is stored in catecholamine (CA)-containing dense core granules and is presumably released together with CA, ATP, and opioids in response to physiological stimuli, playing an autocrine-paracrine role on CCs. The reported paradoxical "dual action" of GABAA-R activation (enhancement of CA secretion and inhibition of synaptically evoked CA release) is only one aspect of GABA's multifaceted actions. In this review, we discuss recent physiological experiments on rat CCs in situ which suggest that GABA regulation of CC function may depend on the physiological context: During non-stressful conditions, GABAA-R activation by endogenous GABA tonically inhibits acetylcholine release from splanchnic nerve terminals and decreases spontaneous Ca2+ fluctuations in CCs, preventing unwanted CA secretion. During intense stress, splanchnic nerve terminals release acetylcholine, which depolarizes CCs and allows the Ca2+ influx that triggers the release of CA and GABA. With time, CA secretion declines, due to voltage-independent inhibition of Ca2+channels and desensitization of cholinergic nicotinic receptors. Nonetheless, acute activation of GABAA-R is depolarizing in about 50% of CCs, and thus GABA, acting as an autocrine/paracrine mediator, could help to maintain CA exocytosis under stress. GABAA-R activation is not excitatory in about half of CCs' population because it hyperpolarizes them or elicits no response. This percentage possibly varies, depending on functional demands, since GABAA-R-mediated actions are determined by the intracellular chloride concentration ([Cl-] i ) and therefore on the activity of cation-chloride co transporters, which is functionally regulated. These findings underscore a potential importance of a novel and complex GABA-mediated regulation of CC function and of CA secretion.

Segregation of Acetylcholine and GABA in the Rat Superior Cervical Ganglia: Functional Correlation.

Sympathetic neurons have the capability to segregate their neurotransmitters (NTs) and co-transmitters to separate varicosities of single axons; furthermore, in culture, these neurons can even segregate classical transmitters. In vivo sympathetic neurons employ acetylcholine (ACh) and other classical NTs such as gamma aminobutyric acid (GABA). Herein, we explore whether these neurons in vivo segregate these classical NTs in the superior cervical ganglia of the rat. We determined the topographical distribution of GABAergic varicosities, somatic GABAA receptor, as well as the regional distribution of the segregation of ACh and GABA. We evaluated possible regional differences in efficacy of ganglionic synaptic transmission, in the sensitivity of GABAA receptor to GABA and to the competitive antagonist picrotoxin (PTX). We found that sympathetic preganglionic neurons in vivo do segregate ACh and GABA. GABAergic varicosities and GABAA receptor expression showed a rostro-caudal gradient along ganglia; in contrast, segregation exhibited a caudo-rostral gradient. These uneven regional distributions in expression of GABA, GABAA receptors, and level of segregation correlate with stronger synaptic transmission found in the caudal region. Accordingly, GABAA receptors of rostral region showed larger sensitivity to GABA and PTX. These results suggest the presence of different types of GABAA receptors in each region that result in a different regional levels of endogenous GABA inhibition. Finally, we discuss a possible correlation of these different levels of GABA modulation and the function of the target organs innervated by rostral and caudal ganglionic neurons.

Exogenous GABA application transiently improves the tolerance to root hypoxia on a sensitive genotype of Prunus rootstock

Prunus species are considered to be moderately sensitive to root hypoxia, but with some degree of tolerance to oxygen deficiency. In a previous work on a set of commercial Prunus rootstocks we identified the plum-based rootstock ‘Mariana 2624’ and the cherry-based rootstock ‘Mazzard F12/1’ as the most tolerant and sensitive genotypes, respectively, to root hypoxia by waterlogging. We then sequenced, for both genotypes, the root transcriptome responsive to hypoxic conditions. The early differentially expressed genes included a transcript with high homology to a root-specific Glutamate decarboxylase of Arabidopsis, AtGAD1. A homology search of the peach genome detected four putative GAD sequences. They exhibited a very high identity in their deduced amino acid sequences except in the C-terminal region, where the calmodulin binding domain is located. In addition, these GAD isoforms showed organ-specific expression and different transcriptional responses to root hypoxia stress. GAD is the enzyme responsible for the synthesis of gamma aminobutyric acid (GABA), an amino acid that reaches high levels during stresses. We assessed the effect of exogenous GABA application on molecular, physiological, biochemical and metabolic parameters in ‘Mariana 2624’ and ‘Mazzard F12/1’. The root hypoxia-tolerant genotype was unaffected by GABA supplementation. In contrast, exogenous GABA triggered transient but substantive changes in the root hypoxia-sensitive genotype under waterlogging. This effect was associated with changes in the mRNA levels of some GAD isoforms, an improvement in photosynthetic parameters, a higher CO2 assimilation rate and stomatal conductance, a smaller loss of chlorophyll content, lower levels of H2O2 and increased levels of endogenous GABA. We discuss GABA’s wide spectrum of biological actions and its effect on root hypoxia-sensitive Prunus species’ adaptive response to oxygen deficiency.

Retinal development impairment and degenerative alterations in adult rats subjected to post-natal malnutrition

BackgroundThe early stages of central nervous system (CNS) development are extremely important. Key events such as neurogenesis, gliogenesis, synaptogenesis, and ontogenesis occur. Malnutrition promotes alterations in CNS development, including the retinal development. During retinal development, malnutrition can induce a delay in some important events, such as neurotransmitter expression and neurogenesis. Methodology/Principal findingsPostpartum Wistar rats were fed either a commercial diet or a multideficient diet. Pups were breastfed by these rats, and from PND21 were kept with the same diet until PND45. We investigated the effects of malnutrition on adult retinal tissue with regard to (1) endogenous gamma-amino butyric acid (GABA) release induced by excitatory amino acids (EAAs) and (2) the expression of cellular markers related to degenerative events, such as reactive gliosis, microglial activation, cell proliferation and cell death. Endogenous GABA release induced by EAAs was higher in the retina of malnourished rats. The Müller cell population was reduced and displayed alterations in their phenotype profile compatible with reactive gliosis. The expression of glutamine synthetase and markers of cellular proliferation were higher in the retina of malnourished rats. Additionally, retinal dysplasia-like structures were present, indicating disturbance in the cell cycle machinery. Conclusion/SignificanceThe current study provides evidence that the adult retina shows degenerative processes induced by long-term malnutrition during the postnatal development. These findings have high clinical significance with regard to the identification of possible targets for interventions in malnourished patients.