Effects of glutamate decarboxylase and gamma-aminobutyric acid (GABA) transporter on the bioconversion of GABA in engineered <Emphasis Type="Italic">Escherichia coli</Emphasis>

Gamma-aminobutyric acid (GABA) is a non-essential amino acid and a precursor of pyrrolidone, a monomer of nylon 4. GABA can be biosynthesized through the decarboxylation of l-glutamate by glutamate decarboxylase. In this study, the effects of glutamate decarboxylase (gadA, gadB), glutamate/GABA antiporter (gadC) and GABA aminotransferase (gabT) on GABA production were investigated in Escherichia coli. Glutamate decarboxylase was overexpressed alone or with the glutamate/GABA antiporter to enhance GABA synthesis. GABA aminotransferase, which redirects GABA into the TCA cycle, was knock-out mutated. When gadB and gadC were co-overexpressed in the gabT mutant strain, a final GABA concentration of 5.46 g/l was obtained from 10 g/l of monosodium glutamate (MSG), which corresponded to a GABA yield of 89.5%.     

Contents of several amino acids in the cerebellum, brain stem and cerebrum of the 'staggerer', 'weaver' and 'nervous' neurologically mutant mice.

The content of glutamate, GABA, aspartate, glycine and alanine was determined in the cerebellum, brain stem and cerebrum of three different mutant mice which have been named ‘staggerer’, ‘weaver’ and ‘nervous’ on the basis of neurological symptoms. In the ‘staggerer’ and ‘weaver’ mutants there is an almost complete absence of granule cells in the cerebellar cortex while in the ‘nervous’ mutant there is a loss of Purkinje cells (and to a lesser extent a loss of granule cells) in the cerebellar cortex. In the cerebellum of the ‘weaver’ mutant, the content of glutamate was signficantly lower (P < 0.025) than control values (8.77 ± 0.76 vs 12.0 ± 1.3 μmol/g tissue wet wt) and the contents of GABA and glycine were significantly greater than normal levels. In the cerebellum of the ‘staggerer’ mutant, the content of glutamate was significantly lower (6.62 ± 0.70 μmol/g) and the contents of glycine and alanine significantly higher than control values. In the cerebrum and brain stem regions of the staggerer mutant, weaver mutant and the normals the contents of the five amino acids were the same. The contents of glycine and alanine in the cerebellum, GARA and glycine in the brain stem and GABA and alanine in the cerebrum of the nervous mutants were higher than control values. The data are discussed in terms of a possible role for glutamate functioning as an excitatory transmitter when released from the cerebellar granule cells.     

Regional distribution of putative amino acid neurotransmitters in the CNS of spiders (Arachnida: Araneida)

The regional occurrence of five amino acid neurotransmitters (GABA, taurine, glycine, glutamate, aspartate) was studied in the CNS of five spider families, using a fluorescence microchromatogram method. Clear differences in transmitter distribution were obvious in relation to the phylogenetic standard of the spider families and the CNS regions investigated. For example, high relative amounts of taurine and GABA were typically confined to the protocerebral brain parts, particularly in the Araneidae and Salticidae. Remarkable amounts of glutamate were shown to exist in the lower CNS parts of the Agelenidae and, especially, the Theraphosidae.The results obtained confirm the dominant functional role of the protocerebrum in arthropods.     

Changes in the content of glutamate and GABA in the cerebellar vermis and hemispheres of the Purkinje cell degeneration (pcd) mutant

The contents of glutamate and GABA, as well as aspartate, glycine, and alanine, were examined in the cerebellar vermis and hemispheres of normal and Purkinje cell degeneration (pcd) mutant mice at 6, 9, and 12 months of age. Relative to normal values, the content of glutamate was approximately 50% lower in the vermis for the 3 age groups. In the hemispheres, the content of glutamate was also lower than control values and showed a progressive loss from 30 to 47% with age. On the other hand, in the case of GABA in the vermis, the level was 39% lower in the pcd mutant at 6 months of age but no different from control values at 12 months. However, relative to data for normal mice, the content of GABA in the hemispheres was consistently lower (20%) for all age groups. The level of aspartate was approximately 60% lower in the cerebellar vermis and 45 to 55% lower in the hemispheres of the mutant with respect to control data for all three age groups. Likewise, alanine showed a reduced content in the hemispheres (36–46%) and vermis (24%) in the mutant relative to normal values at 6, 9, and 12 months of age. On the other hand, the level of glycine was 43–64% higher in the vermis and 77–100% greater in the hemispheres of the mutant than in the control group. The higher values for glycine were observed at the two oldest ages. In conclusions, the data are consistent with the idea that glutamate and GABA are present in high concentrations in granule and Purkinje cells, respectively, and provide additional support for a transmitter function for both amino acids in the cerebellum.     

Synthesis of nylon 4 from gamma-aminobutyrate (GABA) produced by recombinant Escherichia coli

In this study, we developed recombinant Escherichia coli strains expressing Lactococcus lactis subsp. lactis Il1403 glutamate decarboxylase (GadB) for the production of GABA from glutamate monosodium salt (MSG). Syntheses of GABA from MSG were examined by employing recombinant E. coli XL1-Blue as a whole cell biocatalyst in buffer solution. By increasing the concentration of E. coli XL1-Blue expressing GadB from the OD₆₀₀ of 2–10, the concentration and conversion yield of GABA produced from 10 g/L of MSG could be increased from 4.3 to 4.8 g/L and from 70 to 78 %, respectively. Furthermore, E. coli XL1-Blue expressing GadB highly concentrated to the OD₆₀₀ of 100 produced 76.2 g/L of GABA from 200 g/L of MSG with 62.4 % of GABA yield. Finally, nylon 4 could be synthesized by the bulk polymerization using 2-pyrrolidone that was prepared from microbially synthesized GABA by the reaction with Al₂O₃ as catalyst in toluene with the yield of 96 %.     

Conidium formation and germination inNeurospora crassa: Glutamic acid metabolism

In order to assess the role of the large (200 μmol/g) pool of glutamic acid normally found in wild-typeNeurospora crassa conidia, the levels of glutamic acid and other amino acids were manipulated by employing a strain blocked in glutamate synthesis. The double mutant strainen(am)-2;am, which has a lesion in NADP-glutamate dehydrogenase (am) and is auxotrophic for glutamate, was employed in order to obtain conidia with a decreased level of glutamic acid. When cultures of this strain were grown in the presence of 50 or 20 mM glutamate as sole nitrogen source, conidia were obtained with a glutamate pool of 97 and 47 μmole/g, respectively, which represents approximately 57 and 28% of the control values obtained from a prototrophic strain. These observations are interpreted to indicate that conidiation can occur even without the accumulation of the entire pool of glutamate in the conidia. However, when conidia of this double mutant strain were incubated in a minimal medium lacking glutamate, germ tube formation was greatly delayed. Germ tube formation was normal in the presence of glutamate or alanine. During germination of conidia in minimal medium, the levels of glutamate, glutamine, aspartic acid, and γ-aminobutyric acid (GABA) were measured at different times. The results obtained support the view that glutamic acid was catabolized through the GABA pathway during the very early stages of germination.     

Metabolic routes of GABA formation in chick embryo brain

Sobue and Nakajima (1978) reported that GABA formation from putrescine is significant in chick embryo brain between days 6 and 8 of incubation. They attributed an important functional role to the putrescine-derived GABA. We found that depletion of putrescine and spermidine in chick embryos by inhibition of ornithine decarboxylase activity did not decrease the in vivo rate of GABA formation, showing that putrescine is, from a quantitative point of view, a negligible source for GABA in chick embryo brain. The changes of brain GABA levels obtained after administration of glutamate decarboxylase inhibitors and in vitro determinations of glutamate decarboxylase activity were compatible with the assumption that GABA is mainly formed by decarboxylation of l-glutamate, even during early brain development. Participation of the NAD⁺-dependent, aerobic transformation of glutamate into GABA (Seiler and Wagner, 1976) in the overall GABA production of chick embryo brain could, however, not be excluded.     

Independent Effects of γ-Aminobutyric Acid Transaminase (GABAT) on Metabolic and Sleep Homeostasis

Breakdown of the major sleep-promoting neurotransmitter, γ-aminobutyric acid (GABA), in the GABA shunt generates catabolites that may enter the tricarboxylic acid cycle, but it is unknown whether catabolic by-products of the GABA shunt actually support metabolic homeostasis. In Drosophila, the loss of the specific enzyme that degrades GABA, GABA transaminase (GABAT), increases sleep, and we show here that it also affects metabolism such that flies lacking GABAT fail to survive on carbohydrate media. Expression of GABAT in neurons or glia rescues this phenotype, indicating a general metabolic function for this enzyme in the brain. As GABA degradation produces two catabolic products, glutamate and succinic semialdehyde, we sought to determine which was responsible for the metabolic phenotype. Through genetic and pharmacological experiments, we determined that glutamate, rather than succinic semialdehyde, accounts for the metabolic phenotype of gabat mutants. This is supported by biochemical measurements of catabolites in wild-type and mutant animals. Using in vitro labeling assays, we found that inhibition of GABAT affects energetic pathways. Interestingly, we also observed that gaba mutants display a general disruption in bioenergetics as measured by altered levels of tricarboxylic acid cycle intermediates, NAD⁺/NADH, and ATP levels. Finally, we report that the effects of GABAT on sleep do not depend upon glutamate, indicating that GABAT regulates metabolic and sleep homeostasis through independent mechanisms. These data indicate a role of the GABA shunt in the development of metabolic risk and suggest that neurological disorders caused by altered glutamate or GABA may be associated with metabolic disruption.     

Overexpression of Neurospora crassa OR74A glutamate decarboxylase in Escherichia coli for efficient GABA production

This study investigated the effect of glutamate decarboxylase from Neurospora crassa OR74A on GABA production in Escherichia coli. GABA is one of the inhibitory neurotransmitters in the mammalian central nervous system, and can be used as a precursor of promising biopolymer Nylon 4. E. coli that overexpressed N. crassa glutamate decarboxylase was cultured at various pH levels and temperatures to determine optimum conditions for GABA production. When the recombinant E. coli strain was cultured at 30°C and pH 3, a final GABA concentration of 5.26 g/L was obtained from 10 g/L of monosodium glutamate (MSG), corresponding to a GABA yield of 86.23%.     

Brain GABA and glutamate levels in workers of two ant species (Hymenoptera: Formicidae): Interspecific differences and effects of queen presence/absence

Presence of amino acid neurotransmitters gamma‐aminobutyric acid (GABA) and glutamate (Glu) in ant brains was reported in very few studies. To learn more about factors influencing GABA and Glu levels in ant brains, we applied high‐performance liquid chromatography to measure levels of these compounds in single brains of workers of 2 ant species, Myrmica ruginodis (subfamily Myrmicinae) and Formica polyctena (subfamily Formicinae) taken from queenright/queenless colony fragments and tested in dyadic aggression tests consisting of an encounter with a nestmate, an alien conspecific or a small cricket. Brain glutamate levels were higher than those of GABA in both tested species. Brain GABA levels (in μmol/brain) and GABA : Glu ratio were higher in M. ruginodis (a submissive species) than in F. polyctena (a dominant, aggressive species) in spite of smaller brain weight of M. ruginodis. Brain glutamate levels (in μmol/brain) did not differ between the tested species, which implies that glutamate concentration (in μmol/mg of brain tissue) was higher in M. ruginodis. Queen absence was associated with increased worker brain GABA levels in F. polyctena, but not in M. ruginodis. No significant effects of opponent type were discovered. As GABA agonists enhance friendly social behavior in rodents, we hypothesize that elevated brain GABA levels of orphaned workers of F. polyctena facilitate the adoption of a new queen. This is the first report providing information on GABA and glutamate levels in single ant brains and documenting the effects of queen presence/absence on brain levels of amino acid neurotransmitters in workers of social Hymenoptera.     

Gamma Aminobutyric Acid (GABA) and Plant Responses to Stress

4-aminobutyrate (GABA) is a non-protein amino acid that is widely distributed throughout the biological world. In animals, GABA functions as the predominant inhibitory neurotransmitter in the central nervous system by acting through the GABA receptors. The neuromuscular system enables animals to escape from environmental stresses. Being nonmotile, plants have evolved chemical responses to mitigate stress. Mechanisms by which GABA may facilitate these responses are discussed in this review. Environmental stresses increase GABA accumulation through two different mechanisms. Stresses causing metabolic and/or mechanical disruptions, resulting in cytosolic acidification, induce an acidic pH-dependent activation of glutamate decarboxylase and GABA synthesis. Extremely marked declines in cytosolic pH occur under oxygen deprivation, which is the primary stress factor in flooded soils, and this stress induces the greatest accumulation of GABA. Other stresses, including cold, heat, salt, and mild or transient environmental factors, such as touch, wind, rain, etc. rapidly increase cellular levels of Ca²⁺. Increased cytosolic Ca²⁺ stimulates calmodulin-dependent glutamate decarboxylase activity and GABA synthesis. A review of the kinetics of GABA accumulation in plants reveals a stress-specific pattern of accumulation that is consistent with a physiological role for GABA in stress mitigation. Recent physiological and genetic evidence indicates that plants may possess GAB A-like receptors that have features in common with the animal receptors. The mechanism of action of animal GABA receptors suggests a model for rapid amplification of ion-mediated signals and GABA accumulation in response to stress. Metabolic pathways that link GABA to stress-related metabolism and plant hormones are identified. The survival value of stress-related metabolism is dependent on metabolic changes occurring before stress causes irreversible damage to plant tissue. Rapid accumulation of GABA in stressed tissue may provide a critical link in the chain of events leading from perception of environmental stresses to timely physiological responses.     

Improvement of gamma-amino butyric acid production by an overexpression of glutamate decarboxylase from Pyrococcus horikoshii in Escherichia coli

In this study, the effect of glutamate decarboxylase from Pyrococcus horikoshii on gamma-aminobutyric acid (GABA) production was investigated in Escherichia coli for the first time. E. coli with overexpressed P. horikoshii glutamate decarboxylase was cultured at various pH levels and temperatures to determine the optimum conditions for GABA production. The highest final GABA concentration, 5.07 g/L, was obtained from 10 g/L of monosodium glutamate (MSG) with a GABA yield of 83% at 30°C and pH 3.5. When P. horikoshii glutamate decarboxylase was introduced into a GABA aminotransferase knock-out E. coli XBT strains, 5.69 g/L of GABA was produced with a GABA yield of 93%.     

Metabolic fate of glutamate and evaluation of flux through the 4-aminobutyrate (GABA) shunt in Aspergillus niger

Accumulation of GABA and a concurrent block in the Krebs cycle suggest a functional GABA bypass in the acidogenic Aspergillus niger. Apart from the demonstration of enzyme machinery required, a direct measurement of flux through this glutamate decarboxylation loop was attempted. The distribution of carbon from glucose and glutamate was studied using A. niger mycelia grown on different media. The uptake and incorporation of (14)C label into organic acids and amino acids was followed by paper chromatography. Flow of label from glucose into citrate, glutamate and GABA increased in cells harvested at later stages of acidogenic growth. Very little citrate was derived from glutamate while ten times more label reached GABA from labeled glutamate. Radioactivity from L-[U-(14)C]glutamate and not from L-[1-(14)C]glutamate was recovered in GABA. This demonstrated that alpha-decarboxylation of L-glutamate was the source of GABA. Unless grown on GABA, A. niger mycelia did not take up externally supplied GABA. A direct measure of GABA shunt flux was thus not feasible. Therefore a combination of metabolite balance technique and the kinetic approach was applied to evaluate flux from glutamate to succinate in normal and acidogenic A. niger. The flux relative to TCA cycle was estimated by using uptake rate for radiolabeled glutamate, rate of accumulation of certain metabolites and the reactions of GABA metabolism. The analysis indicated that GABA shunt is operative in A. niger and its operation is enhanced during acidogenic growth of the fungus. This is the first report of an estimation of the flux through GABA shunt in a fungus.     

Molecular characterization and physico-chemical analysis of a new giant embryo mutant allele (ge t) in rice (Oryza sativa L.)

The rice embryo is rich in lipid and protein bodies, bioactive chemicals such as dietary fiber, phytic acids, vitamin B and E, and gamma aminobutyric acid (GABA) than the endosperm. In this paper, we report a new giant embryo mutant,ge ^t, induced from somaclonal variation derived by anther culture in rice. Sequence analysis of Cytochrome P450 of the get mutant revealed thatge ^t is a new allele of theGE gene with a single point mutation with substitution of amino acid, W³⁹⁵ to L³⁹⁵. The weight of thege ^t mutant embryo was 3.7 times higher than normal embryo. Tocopherol and mineral content were also higher than the previously reported giant embryo rice variety, Keunnun. These results indicated that this new giant embryo rice (ge ^t) offers a promising source of genetic material in improving nutritional quality of rice especially tocopherol, essential minerals, and GABA.     

The operation of the γ-aminobutyrate bypath of the tricarboxylic acid cycle in brain tissue in vitro

1. Cerebral-cortex slices prelabelled with gamma-amino[1-(14)C]butyrate (GABA) were incubated in a glucose-saline medium. After the initial rapid uptake there was no appreciable re-entry of (14)C into the GABA pool, either from the medium or from labelled metabolites formed in the tissue. The kinetic constants of GABA metabolism were determined by computer simulation of the experimental results by using mathematical procedures. The GABA flux was estimated to be 0.03mumol per min/g, or about 8% of the total flux through the tricarboxylic acid cycle. It was found that the assumption of compartmentation did not greatly affect the estimates of the GABA flux. 2. The time-course of incorporation of (14)C into amino acids associated with the tricarboxylic acid cycle was followed with [1-(14)C]GABA and [U-(14)C]-glucose as labelled substrates. The results were consistent with the utilization of GABA via succinate. This was confirmed by determining the position of (14)C in the carbon skeletons of aspartate and glutamate formed after the oxidation of [1-(14)C]GABA. These results also indicated that under the experimental conditions the reversal of reactions catalysed by alpha-oxoglutarate dehydrogenase and glutamate decarboxylase respectively was negligible. The conversion of [(14)C]GABA into gamma-hydroxybutyrate was probably also of minor importance, but decarboxylation of oxaloacetate did occur at a relatively slow rate. 3. When [1-(14)C]GABA was the labelled substrate there was evidence of a metabolic compartmentation of glutamate since, even before the peak of the incorporation of (14)C into glutamate had been reached, the glutamine/glutamate specific-radioactivity ratio was greater than unity. When [U-(14)C]glucose was oxidized this ratio was less than unity. The heterogeneity of the glutamate pool was indicated also by the relatively high specific radioactivity of GABA, which was comparable with that of aspartate during the whole incubation time (40min). The rates of equilibration of labelled amino acids between slice and medium gave evidence that the permeability properties of the glutamate compartments labelled as a result of oxidation of [1-(14)C]GABA were different from those labelled by the metabolism of [(14)C]glucose. The results showed therefore that in brain tissue incubated under the conditions used, the organization underlying metabolic compartmentation was preserved. The observed concentration ratios of amino acids between tissue and medium were also similar to those obtaining in vivo. These ratios decreased in the order: GABA>acidic acids>neutral amino acids>glutamine. 4. The approximate pool sizes of the amino acids in the different metabolic compartments were calculated. The glutamate content of the pool responsible for most of the labelling of glutamine during oxidation of [1-(14)C]GABA was estimated to be not more than 30% of the total tissue glutamate. The GABA content of the ;transmitter pool' was estimated to be 25-30% of the total GABA in the tissue. The structural correlates of metabolic compartmentation were considered.     

Systematic Analysis of γ-Aminobutyric Acid (GABA) Metabolism and Function in the Social Amoeba Dictyostelium discoideum

While GABA has been suggested to regulate spore encapsulation in the social amoeba Dictyostelium discoideum, the metabolic profile and other potential functions of GABA during development remain unclear. In this study, we investigated the homeostasis of GABA metabolism by disrupting genes related to GABA metabolism and signaling. Extracellular levels of GABA are tightly regulated during early development, and GABA is generated by the glutamate decarboxylase, GadB, during growth and in early development. However, overexpression of the prespore-specific homologue, GadA, in the presence of GadB reduces production of extracellular GABA. Perturbation of extracellular GABA levels delays the process of aggregation. Cytosolic GABA is degraded by the GABA transaminase, GabT, in the mitochondria. Disruption of a putative vesicular GABA transporter (vGAT) homologue DdvGAT reduces secreted GABA. We identified the GABA_B receptor-like family member GrlB as the major GABA receptor during early development, and either disruption or overexpression of GrlB delays aggregation. This delay is likely the result of an abolished pre-starvation response and late expression of several “early” developmental genes. Distinct genes are employed for GABA generation during sporulation. During sporulation, GadA alone is required for generating GABA and DdvGAT is likely responsible for GABA secretion. GrlE but not GrlB is the GABA receptor during late development.     

Decreased levels of free d-aspartic acid in the forebrain of serine racemase (Srr) knock-out mice

d-Serine, an endogenous co-agonist of the N-methyl-d-aspartate (NMDA) receptor is synthesized from l-serine by serine racemase (SRR). A previous study of Srr knockout (Srr-KO) mice showed that levels of d-serine in forebrain regions, such as frontal cortex, hippocampus, and striatum, but not cerebellum, of mutant mice are significantly lower than those of wild-type (WT) mice, suggesting that SRR is responsible for d-serine production in the forebrain. In this study, we attempted to determine whether SRR affects the level of other amino acids in brain tissue. We found that tissue levels of d-aspartic acid in the forebrains (frontal cortex, hippocampus and striatum) of Srr-KO mice were significantly lower than in WT mice, whereas levels of d-aspartic acid in the cerebellum were not altered. Levels of d-alanine, l-alanine, l-aspartic acid, taurine, asparagine, arginine, threonine, γ-amino butyric acid (GABA) and methionine, remained the same in frontal cortex, hippocampus, striatum and cerebellum of WT and mutant mice. Furthermore, no differences in d-aspartate oxidase (DDO) activity were detected in the forebrains of WT and Srr-KO mice. These results suggest that SRR and/or d-serine may be involved in the production of d-aspartic acid in mouse forebrains, although further detailed studies will be necessary to confirm this finding.     

Adsorption of charged substrates and products on an enzyme reactor prepared by glutaraldehyde coupling on alkylamine derivatives of Ti(IV)-coated porous silica beads

Ti(IV) coating of porous silica beads, followed by derivatization with 1,6-diaminohexane and activation with glutaraldehyde was tested for the immobilization of glutamate decarboxylase (l-glutamate 1-carboxylyase, EC 4.1.1.15). The enzyme column prepared with the immobilized glutamate decarboxylase was designed for the preparation of 1 μmol γ-[¹³N]aminobutyric acid, a new tracer for positron emission tomography. Preliminary results, indicating high immobilization yields of active enzyme with good long term stabilities, led to a more detailed investigation of the Ti(IV) coating. When a column, containing about 1 g of enzyme-loaded beads was used for the synthesis of γ-[¹³N]aminobutyric acid (GABA) from l-[¹³N]glutamate, most of the¹³N activity remained adsorbed onto the column. The elution patterns of l-glutamate and GABA from columns of glutamate decarboxylase, immobilized on Ti(IV) coated silica beads, were investigated by using an h.p.l.c. u.v. detector. Different treatments of the Ti(IV) coated supports were tested to improve the desorption kinetics of GABA and l-glutamate. None of these methods gave a satisfactory improvement of the elution patterns of GABA and l-glutamate. The results indicate that the Ti(IV) coated silica beads have a large adsorption capacity, even though the enzyme is covalently linked. The described immobilization method is not recommended for enzymes having charged substrates or products and in which a small amount of substrate has to be applied onto a reactor containing a large amount of Ti(IV) coated support. The method can be applied when the enzyme reactor is operated in steady state conditions with continuous supply of substrate.     

A Rhizobium meliloti mutant, lacking a functional γ-aminobutyrate (GABA) bypass, is defective in glutamate catabolism and symbiotic nitrogen fixation

Abstract A Rhizobium meliloti mutant, CMF1 2:38, was isolated which was specifically defective in the degradation of glutamate as sole carbon and nitrogen source. Biochemical analysis of CMF1 2:38 revealed a reduction in succinic semialdehyde dehydrogenase (SSDH) activity, the third enzyme of the γ-aminobutyrate (GABA) bypass. Evidence is presented which suggests that the Tn 5-induced mutation in CMF1 2:38 exists in a regulatory gene governing the expression of both NAD and NADP-linked SSDH activity. CMF1 2:38 nodulated alfalfa plants, but was reduced in its nitrogen fixation activity and biomass accumulating ability relative to the wild-type strain. The results presented in this study indicate that the GABA bypass is a major mechanism of glutamate degradation in R. meliloti CMF1 and that glutamate catabolism via this pathway may play an important role in the symbiotic nitrogen fixation process.     

GABA and glutamate immunoreactivity in tentacles of the sea anemone Phymactis papillosa (LESSON 1830)

Sea anemones have a structurally simple nervous system that controls behaviors like feeding, locomotion, aggression, and defense. Specific chemical and tactile stimuli are transduced by ectodermal sensory cells and transmitted via a neural network to cnidocytes and epithelio‐muscular cells, but the nature of the neurotransmitters operating in these processes is still under discussion. Previous studies demonstrated an important role of peptidergic transmission in cnidarians, but during the last decade the contribution of conventional neurotransmitters became increasingly evident. Here, we used immunohistochemistry on light and electron microscopical preparations to investigate the localization of glutamate and GABA in tentacle cross‐sections of the sea anemone Phymactis papillosa. Our results demonstrate strong glutamate immunoreactivity in the nerve plexus, while GABA labeling was most prominent in the underlying epithelio‐muscular layer. Immunoreactivity for both molecules was also found in glandular epithelial cells, and putative sensory cells were GABA positive. Under electron microscopy, both glutamate and GABA immunogold labeling was found in putative neural processes within the neural plexus. These data support a function of glutamate and GABA as signaling molecules in the nervous system of sea anemones. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.