Purification of L-glutamic acid decarboxylase from catfish brain

Advances in Reproductive Endocrinology and Neuroendocrine Research Using Catfish Models

Catfishes, belonging to the order siluriformes, represent one of the largest groups of freshwater fishes with more than 4000 species and almost 12% of teleostean population. Due to their worldwide distribution and diversity, catfishes are interesting models for ecologists and evolutionary biologists. Incidentally, catfish emerged as an excellent animal model for aquaculture research because of economic importance, availability, disease resistance, adaptability to artificial spawning, handling, culture, high fecundity, hatchability, hypoxia tolerance and their ability to acclimate to laboratory conditions. Reproductive system in catfish is orchestrated by complex network of nervous, endocrine system and environmental factors during gonadal growth as well as recrudescence. Lot of new information on the molecular mechanism of gonadal development have been obtained over several decades which are evident from significant number of scientific publications pertaining to reproductive biology and neuroendocrine research in catfish. This review aims to synthesize key findings and compile highly relevant aspects on how catfish can offer insight into fundamental mechanisms of all the areas of reproduction and its neuroendocrine regulation, from gametogenesis to spawning including seasonal reproductive cycle. In addition, the state-of-knowledge surrounding gonadal development and neuroendocrine control of gonadal sex differentiation in catfish are comprehensively summarized in comparison with other fish models.

Nutrition and metabolism of glutamate and glutamine in fish

Glutamate (Glu) and glutamine (Gln) comprise a large proportion of total amino acids (AAs) in fish in the free and protein-bound forms. Both Glu and Gln are synthesized de novo from other α-amino acids and ammonia. Although these two AAs had long been considered as nutritionally non-essential AAs for an aquatic animal, they must be included adequately in its diet to support optimal health (particularly intestinal health) and maximal growth. In research on fish nutrition, Glu has been used frequently as an isonitrogenous control on the basis of the assumption that this AA has no nutritional or physiological function. In addition, purified diets used for feeding fish generally lack glutamine. As functional AAs, Glu and Gln are major metabolic fuels for tissues of fish (including the intestine, liver, kidneys, and skeletal muscle), and play important roles not only in protein synthesis but also in glutathione synthesis and anti-oxidative reactions. The universality of Glu and Gln as abundant intracellular AAs depends on their enormous versatility in metabolism. Dietary supplementation with Glu and Gln to farmed fish can improve their growth performance, intestinal development, innate and adaptive immune responses, skeletal muscle development and fillet quality, ammonia removal, and the endocrine status. Glu (mainly as monosodium glutamate), glutamine, or AminoGut (a mixture of Glu and Gln) is a promising feed additive to reduce the use of fishmeal, while gaining the profitability of global aquaculture production. Thus, the concept of dietary requirements of fish for Glu and Gln is a paradigm shift in the nutrition of aquatic animals (including fish).

Distribution of GABA-immunoreactive neurons in the forebrain of the goldfish, Carassius auratus

The distribution of gamma-aminobutyric acid (GABA) immunoreactivity was studied in the forebrain (tel- and diencephalon) of the goldfish by means of immunocytochemistry on Vibratome sections using antibodies against GABA. Positive perikarya were detected in the olfactory bulbs and in all divisions of the telencephalon, the highest density being found along the midline. In the diencephalon, GABA-containing cell bodies were found in the hypothalamus, in particular in the preoptic and tuberal regions. The inferior lobes, the nucleus recessus lateralis, and more laterodorsal regions, such as the nucleus glomerulosus and surrounding structures, also exhibited numerous GABA-positive perikarya. Cell bodies were also noted in the thalamus, in particular in the dorsomedial, dorsolateral and ventromedial nuclei. The relative density of immunoreactive fibers was evaluated for each brain nucleus and classified into five categories. This ubiquitous distribution indicates that, as in higher vertebrates, GABA most probably represents one of the major neurotransmitters in the brain of teleosts.

Dopamine D1-receptor immunolocalization in goldfish retina

Dopamine, a neuromodulator in the vertebrate retina, is involved in numerous functions related to light adaptation. However, unlike in mammals, localization of retinal D1-dopamine receptors in nonmammalian vertebrates has been hampered due to a lack of antisera. To address this problem, an antiserum against the 18 C-terminal amino acids of the goldfish D1 receptor (gfD1r) was generated in chicken eggs and tested in retinae of goldfish and rat, and rat caudate putamen, by using immunoblots and light microscopic immunocytochemistry. No labeling was observed in any tissue or immunoblots with preabsorbed gfD1r antiserum. Immunoblot analysis of goldfish retina revealed a single band at about 101 kDa. The patterns of gfD1r immunoreactivity (gfD1r-IR), found in rat caudate putamen and rat retina were virtually identical to that previously reported with other D1-receptor ligands and antisera. In goldfish retina, gfD1r-IR was most intense over cell bodies in the ganglion cell layer, amacrine cells in the proximal inner nuclear layer (INL), and bipolar cells in the distal INL. Weaker gfD1r-IR was observed over horizontal cell bodies and both plexiform layers. Müller cells and axons of cone photoreceptors were labeled as well. Double labeling showed that all protein kinase C-immunoreactive bipolar cells (ON type) were gfD1r-IR on the soma, axon terminal, and dendrites. All glutamate decarboxylase-immunoreactive (i.e., gamma-aminobutyric acid utilizing) amacrine cells and horizontal cells were gfD1r-IR. Retinal D1r distribution is more extensive than dopamine neuron innervation, but is consistent with physiologic estimates of dopamine function, suggestive of both wiring and volume transmission of dopamine in the retina. The gfD1r antiserum displays cross-reactivity to dopamine receptors in a mammal and a nonmammal and should prove useful in future studies of dopaminergic systems.

Dopaminergic and GABAergic retinal cell populations in mammals

A number of modern techniques now allow histologists to characterize subpopulations of retinal neurons by their neurotransmitters. The morphologies and connections of these chemically defined neurons can be analyzed precisely at both light and electron microscope levels and lead to a better understanding of retinal circuitry. The dopaminergic neurons form a loose population of special wide-field amacrine cells bearing intraretinal axons within the inner plexiform layer. One subtype, the interplexiform cell, sends an axon to the outer plexiform and outer nuclear layers. The number of interplexiform cells is variable throughout mammalian species. The GABAergic neurons form a dense and heterogeneous population of amacrine cells branching at all levels of the inner plexiform layer. The presence of GABA in horizontal cells seems to be species-dependent. Close relationships occur between dopaminergic and GABAergic cells. GABA antagonizes a number of dopaminergic actions by inhibiting both the release and synthesis of dopamine. This inhibition can be supported by GABA synapses onto dopaminergic cells, but GABA can also diffuse to its targets. Finally, GABA is also contained and synthesized in dopaminergic cells. This colocalization might be the basis of an intracellular modulation of dopamine by GABA.

Glutamate-, GABA-, and GAD-immunoreactivities co-localize in bipolar cells of tiger salamander retina

The presence of inhibitory bipolar cells in salamander retina was investigated by a comparative analysis of the distribution of glutamate- and GABA-immunoreactivities (GLU-IR; GABA-IR) using a postembedding immunocytochemical method. GLU-IR was found in virtually all photoreceptors, bipolar cells and ganglion cells, neuronal elements that transfer information vertically through the retina. GLU-IR also was found in numerous amacrine cells in the mid and proximal inner nuclear layer as well as in the cytoplasm of horizontal cells, while the nucleus of horizontal cells was either lightly labeled or not labeled at all. GLU-IR was found in the outer plexiform layer and intensely in the inner plexiform layer, in which there was no apparent sublamination. Forty-seven percent of Type IB bipolar cells in the distal inner nuclear layer and 13% of the displaced bipolar cells were GABA-IR. All bipolar cells were also GLU-IR, indicating that GABA-IR bipolar cells were a subset of GLU-IR bipolar cells rather than a separate population. About 12% of the Type IB bipolar cells were moderately GABA-IR and likely comprised a GABAergic subtype. GLU-IR levels in the presumed GABAergic bipolar cells were higher than in other purely GLU-IR bipolar cells suggesting that these GABA-IR bipolar cells are glutamatergic as well. All of the displaced bipolar cells were only lightly GABA-IR, indicating that displaced bipolar cells comprise a more homogeneous class of glutamatergic cell than orthotopic bipolar cells. GAD-IR co-localized with GABA-IR in orthotopic but not displaced bipolar cells, further supporting the idea that some orthotopic bipolar cells are GABAergic. A small proportion of bipolar cells in salamander retina contain relatively high levels of both GABA and glutamate. Co-release of these substances by bipolar cells could contribute to the "push-pull" modulation of ganglion cell responses.

Purification and Characterization of a High-Molecular-Weight Endogenous Glutamate-Binding Inhibitor in Porcine Brain

A high-molecular-weight glutamate-binding inhibitor (HGBI) from porcine brain extract was purified to homogeneity. The results of this purification process show that glutamate receptor activity can be regulated by a high-molecular-weight protein, which inhibits [(3)H]L-glutamate binding to excitatory amino acid (EAA) receptors. The purified HGBI appears to be a protein with a molecular weight of approximately 70 kD. The purified HGBI is negatively charged, suggesting that it may contain acidic amino acids, and most likely, L-glutamate- and L-aspartate-enriched regions, responsible for its surface charge as well as for its binding to glutamate receptors. Inhibition of [(3)H]L-glutamate binding by the purified HGBI is reversible, and appears to change the binding kinetics. This endogenous ligand for glutamate receptors has unique characteristics separating it from all the other ligands found so far in the EAA receptor system. This HGBI represents a new class of modulator for the EAA receptor, thus further investigation of the function and structure of the HGBI should provide new understanding of the mechanisms of EAA-mediated neutrotransmission. Copyright 1994 S. Karger AG, Basel

The distribution of GABA-immunoreactive neurons in the brain of the silver eel (Anguilla anguilla L.)

The distribution of GABA-immunoreactivity was studied in the brain of the silver eel (Anguilla anguilla) by means of antibodies directed against GABA. Immunoreactive neuronal somata were distributed throughout the brain. Positive perikarya were detected in the internal cellular layer of the olfactory bulb, and in all divisions of the telencephalon, the highest density being observed along the midline. Numerous GABA-reactive cell bodies were found in the diencephalon, particularly in the preoptic and tuberal regions of the hypothalamus, and the dorsolateral, dorsomedial and ventromedial thalamic nuclei. In the optic tectum, the majority of GABA-positive cell bodies were located in the periventricular layer. A number of immunolabeled cell bodies were observed in different tegmental structures, notably the torus semicircularis. In the cerebellum, the Purkinje cells were either very intensely or very weakly immunoreactive. In the rhombencephalon, reactive cell bodies were observed in the eminentia granularis, the valvula cerebellaris, the octavolateral nucleus, the lobus vagus and in the vagal and glossopharyngeal motor nuclei. Intensely immunoreactive axons and terminals were observed in the external granular layer and internal cellular layer of the olfactory bulb. In the telencephalon, the highest density of reactive fibres and boutons was found in the fields of the medial wall. Many immunolabeled fibres were seen in the medial and lateral forebrain bundles. In the diencephalon, intense labelling of fibres and terminals were observed in the nuclei situated close to the midline. In the optic tectum the highest density of reactive fibres was seen in the sfgs, the layer to which the retina projects massively. Finally, in the rhombencephalon the strongest labelling of neurites was observed in the nuclei of the raphé, the nucleus octavocellularis magnocellularis and the nuclei of the IXth and Xth cranial nerves. The GABAergic system of the eel, which is well developed, appears to be generally comparable to that described in tetrapod vertebrates.

GABA and glycine in retinal amacrine cells: combined Golgi impregnation and immunocytochemistry

Golgi-impregnated amacrine cells in the all-cone lizard retina (Anolis carolinensis) were characterized on the bases of dendritic and somatic criteria. Four major cell categories, comprising 23 types were identified: three non-stratified, 13 monostratified, five bistratified, and two tristratified types. Four of the cell types comprised two to four subtypes based on stratification of their dendrites within the inner plexiform layer (IPL). Golgi impregnation strongly favoured monostratified amacrine cells with cell bodies at the proximal margin of the inner nuclear layer. The neurotransmitter content of each of the 23 amacrine cell types was examined by combined Golgi-immunocytochemistry after morphological classification. Putative neurotransmitters examined included gamma-aminobutyric acid (GABA), glycine (GLY) and aspartate (ASP). Seventeen cell types showed GABA-immunoreactivity (IR), three cell types showed GLY-IR, and four cell types showed neither GABA-IR nor GLY-IR. No cell types showed ASP-IR. Each cell type had a characteristic neurochemical signature, with the exception of one monostratified cell type that showed three different neurochemical signatures. Postembedding immunocytochemistry on conventionally processed retinas confirmed the localization of glutamic acid decarboxylase, the synthetic enzyme for GABA, to cells similar to several of the GABA-IR Golgi-stained types. Postembedding immunocytochemistry for tyrosine hydroxylase (the synthetic enzyme for catecholamines) and GABA on serial sections demonstrated colocalization of GABA and a catecholamine, probably dopamine, in a bistratified amacrine cell type. We conclude that GABA-IR amacrine cell types are more numerous and morphologically heterogeneous than GLY-IR amacrine cells. The morphological heterogeneity and, with one exception, exclusivity of GABA-IR and GLY-IR amacrine cell types indicate that both neurotransmitters play a variety and different functional roles in the lizard inner retina.

GABA- and glycine-immunoreactive neurons in the spinal cord of the carp, Cyprinus carpio

gamma-Aminobutyric acid (GABA) and glycine are the two main inhibitory transmitter amino acids in the central nervous system of vertebrates. The distribution of cells containing GABA and glycine in the carp spinal cord was examined by using specific antisera raised against the two amino acids conjugated to bovine serum albumin. The immunoreaction on serial paraffin sections was visualized by a streptavidin-biotin method. Both antisera gave highly specific labelings of cells. At least three types of GABA-immunoreactive cells were found. They were small cells in the dorsal grey matter, various sized cells in the central and ventral grey, and some ependymal cells contacting the central canal. In addition, very small cells and neuropil structures in the dorsal horn were strongly immunoreactive to the GABA serum. Certain cells in the ventral horn have moderate numbers of labelled synaptic boutons on the perikarya, but very few GABA-labelled terminals were found on putative motoneurons. The immunoreactive ependymal cells appeared to have a ventrolaterally directed axon. The glycine antiserum labelled small and intermediate cells in the dorsal grey, large, elongated cells in the median region, and varying sized cells in the ventral grey. The numbers and density of immunoreactive cells and neuropil structures in the ventral horn were fewer and lower than in GABA-stained sections. The median large cells had a thick ventrolateral process. The ventral intermediate cells were often found near putative motoneurons. Labelled synaptic boutons were present on most ventral cells including putative motoneurons and interneurons. Abundant distribution of cells immunoreactive to both antisera suggest important roles of both GABA and glycine as neurotransmitters for controlling swimming movements in teleosts.

Pancreatic antigenic complex p64 69: involvement in regulation of insulin secretion and relation to glutamic acid decarboxylase

The role of pancreatic beta-cell antigenic structures in modulation of insulin secretion in vitro was recently demonstrated by others. Here we report generation of a monoclonal antibody (mAB) ICA-1 to non-species specific beta-cell antigen(s) 64, 67 and 69 kDa. The mAB inhibits glucose stimulated insulin secretion in islet cell cultures. The ability of mAB ICA-1 to immunoprecipitate active glutamic acid decarboxylase from high speed supernatants of pancreatic and brain crude extracts was demonstrated. The 64, 67 and 69 kDa antigenic material was affinity purified from pancreatic islet cell high speed supernatants, active glutamic acid decarboxylase was found in the material. Immunoaffinity purification with mAB ICA-1 of GAD-like pancreatic beta-cell antigenic material has provided evidence of possible involvement of glutamic acid decarboxylase in modulation of insulin secretion.

Glycine-receptor immunoreactivity in retinal bipolar cells is postsynaptic to glycinergic and GABAergic amacrine cell synapses

Glycinergic innervation of the synaptic terminals of mixed rod-cone bipolar cells in the goldfish retina was investigated by electron microscopical immunocytochemistry with presynaptic and postsynaptic markers for glycinergic neurons: a monoclonal antibody (mAb 7A) against the 93 kDa subunit of the strychnine-sensitive glycine receptor and polyclonal antisera against a glycine/BSA conjugate. Conventional "glycinergic" synaptic contacts, made by amacrine cell processes, accounted for 7-10% of the input to the bipolar cell terminals, whether determined by glycine receptor immunoreactivity (GlyR-IR) or glycine-IR. In addition to the conventional synapses, the large bipolar cell terminals in the proximal inner plexiform layer (type Mb) gave rise to spinules (spine-like protrusions) that invaginated into presynaptic amacrine cell processes. Although 85% of the spinules were GlyR-IR, no spinules were postsynaptic to glycine-IR processes; yet 86% of the spinules were postsynaptic to GAD-IR processes, suggesting that the GlyR-IR spinules were postsynaptic to GABAergic terminals. Furthermore, a single amacrine cell process could make two synapses with an Mb terminal: a GlyR-IR contact onto a spinule and a conventional synapse that was not GlyR-IR. We suggest that glycinergic innervation of bipolar cell terminals involves conventional glycinergic synapses as well as an unconventional situation in which GABA and glycine may interact in as yet undetermined manner, perhaps by potentiation.

Structure and function of L-glutamate decarboxylase

Membrane bound L-glutamate decarboxylase (GAD) has been solubilized and partially purified from hog brain. The solubilized GAD appears to exist in two forms, alpha and beta, differing in their size and electrophoretic mobility. The alpha form has similar mobility as that of the soluble GAD in 7.5% and 5-25% gradient polyacrylamide gel electrophoresis suggesting that they are similar in size and charge. In addition, gene encoding for mouse brain GAD has been cloned and characterized. Mouse brain GAD cDNA consists of two DNA fragments with 1.6 and 1.0 Kb. The 1.6 and 1.0 Kb fragments contain 1657 and 974 bP, respectively. The significance of multiple forms of GAD is also discussed.

The mismatch problem for GABAergic amacrine cells in goldfish retina: resolution and other issues

GABAergic neurons in the vertebrate retina have received intensive study. Yet there are several notable examples of a "mismatch" among the cytochemical markers used to identify GABAergic neurons. The mismatch between [3H]GABA uptake autoradiography and all other indicators of GABAergic neurons as they pertain to amacrine cells in goldfish retina is examined in this overview. The discrepancies can be accounted for largely by barriers to diffusion presented by significant GABA uptake sinks at the inner and outer margins of the retina and by the differential subcellular distribution of the various markers for GABAergic neurons. Also, conditions producing a redistribution of [3H]-GABA and endogenous GABA stores within the retina are described and discussed.

GABA as a potential transmitter in lizard photoreceptors: immunocytochemical and biochemical evidence

The retina of the desert night lizard, Xantusia vigilis, was examined for immunoreactivity to antibodies against gamma-aminobutyric acid and L-glutamate decarboxylase. At the electron microscopic level it was found that a distinct population of the photoreceptor cells was immunoreactive to both antibodies. Computer-assisted reconstruction of serial sections positively identified the immunoreactive receptors as cones. These cones constituted 15% of the photoreceptors in the retinal sections, and they were morphologically distinct. The mean diameter of the labeled cone synaptic pedicles was 5.8 micron whereas that of the unlabeled pedicles was 7.9 micron, a statistically significant difference. L-glutamate decarboxylase was extracted from the lizard brain, positively identified radiometrically, and shown by immunodiffusion to crossreact with the antibody used for localization. The authors suggest that the immunoreactive cones synthesize and accumulate gamma-aminobutyric acid. Whether or not it is used by those cones as a neurotransmitter should be tested directly.

GABAergic input to the synaptic terminals of mb1 bipolar cells in the goldfish retina

An EM-autoradiographical/immunocytochemical technique was used to study amacrine cell synapses onto mb1 bipolar cell terminals in goldfish retina. Tissue was double labeled for [3H]GABA uptake and glutamate decarboxylase (GAD) immunolocalization. Nearly 90% of the amacrine cell synaptic processes onto both proximal and distal halves of mb1 terminals were labeled with either [3H]GABA or GAD-immunoreactivity (IR). Proximal half: 73% of the amacrine synapses were labeled with [3H]GABA uptake and 82% with GAD-IR; 88% of [3H]GABA labeled contacts were double labeled. Distal half: 17% of the amacrine synapses were labeled with [3H]GABA uptake and 67% with GAD-IR; 63% of [3H]GABA labeled contacts were double labeled. After consideration of the possible sources of [3H]GABA labeled synapses onto mb1 terminals, we concluded that the synaptic terminals of pyriform Ab amacrine cells double label for [3H]GABA and GAD-IR despite our previous report that Ab cell bodies do not stain for anti-catfish brain GAD antiserum. We suggest that Ab cells contain isoenzymes of GAD which differ in subcellular distribution, thereby accounting for the differential staining of the cell bodies and dendrites obtained with the GAD antiserum we used.

Brain L-glutamate decarboxylase: purification and subunit structure

Glutamate decarboxylase (GDCase; L-glutamate-1-carboxy-lyase, EC 4.1.1.15) was purified from whole rat brain approximately equal to 1300-fold to apparent homogeneity with a specific activity of 2.4 units per mg of protein by a combination of column chromatographies on DEAE-cellulose, hydroxylapatite, and gel filtration, and preparative nondenaturing polyacrylamide gel electrophoresis. The purified preparation contained a single protein band that comigrated with GDCase activity in three diverse analyses: nondenaturing regular (5%) and gradient (3.6-25%) polyacrylamide gel electrophoresis and isoelectric focusing at pH 4-7. The native molecular mass was calculated to be 120 +/- 10 kDa from gradient polyacrylamide gel electrophoresis and 110 +/- 10 kDa from gel filtration. Under the treatment with NaDodSO4 and 2-mercaptoethanol, GDCase dissociated into two subunits of 40 +/- 2 and 80 +/- 4 kDa, as estimated from NaDodSO4 gel electrophoresis. However, only a 40-kDa subunit was detected when GDCase was treated with 4 M urea plus NaDodSO4 and 2-mercaptoethanol, suggesting that the 80-kDa subunit is the dimer of the 40-kDa subunit. In immunoblotting, polyclonal antibodies against GDCase reacted with both 40- and 80-kDa subunits, while monoclonal antibody reacted with only 80-kDa subunits. The isoelectric point of the native enzyme was 5.4. The Km for glutamate was 1.59 X 10(-3) M. In addition to L-glutamate, cysteine sulfinic acid was also decarboxylated at approximately equal to 10% of the rate of glutamate. The pH optimum was fairly broad, with a maximum at approximately equal to 7.3. The enzyme was strongly inhibited by carbonyl-trapping agents, sulfhydryl reagents, thiol compounds, and beta-methylene-DL-aspartate.

Uptake of gamma-aminobutyric acid by catfish brain

Using homogenates of catfish whole-brain in an isotonic medium, we observed an accumulation of [3H]GABA that was temperature-sensitive and was dependent on the presence of sodium ions, the optimum concentration of which was 75 mM. A kinetic analysis showed that the [3H]GABA uptake mechanism became saturated with increasing GABA concentrations. A high-affinity system, only, was evident whose Km was calculated as 12 microM. Four structural analogues of GABA were found to be competitive inhibitors of uptake, and Ki values were determined. Nipecotic acid (Ki = 1.8 microM) and guvacine (Ki = 3.9 microM) were the most potent compounds, however 2,4-diaminobutyric acid (Ki = 8.9 microM) and beta-alanine (Ki = 55 microM) also had an effect. The characteristics of the uptake mechanism in catfish brain that we have studied are similar to those reported for uptake by mammalian brain except that in the latter, both a high- and a low-affinity transport processes are present. Our data, taken together with what is already known, strongly suggest that the biochemistry of the GABA system in lower vertebrates does not differ significantly from that in mammals.

Production and characterization of polyclonal and monoclonal antibodies to rat brain L-glutamate decarboxylase

Specific monoclonal and polyclonal antibodies to rat brain glutamate decarboxylase (GAD) were produced and characterized. Polyclonal antibodies against GAD were raised in rabbits by injecting a total of 70-210 micrograms of purified GAD i.m. The specificity of anti-GAD serum was established from a variety of tests including Ouchterlony immunodiffusion, immunoelectrophoresis, immunoprecipitation, dot immunoassay, ELISA tests and Western immunoblottings. In immunodiffusion and immunoelectrophoresis tests using partially purified GAD preparations and anti-GAD serum a single, sharp precipitin line corresponding to GAD activity was obtained. Quantitative immunoprecipitation of GAD activity was achieved using anti-GAD IgG and Staphylococcus aureus. Specificity of the antiserum was further indicated from a dot immunoassay and ELISA tests in which the intensity of the reaction product was proportional to the amount of GAD protein present. In the Western immunoblotting experiments using partially purified GAD preparations only two protein bands corresponding to the position of the two subunits of GAD were stained by anti-GAD IgG, further supporting the specificity of polyclonal antibodies against GAD. In addition to polyclonal antibodies, several specific GAD-antibodies-producing clones were also obtained by the hybridoma technique. The specificity of monoclonal antibodies against GAD were established from the following criteria: positive on ELISA test using homogeneous GAD as antigen; formation of GAD--anti-GAD IgG complex as indicated from gel filtration chromatography and sodium dodecyl sulfate polyacrylamide gel electrophoresis; and specific recognition of GAD subunit in a partially purified GAD preparation in Western immunoblotting test. Monoclonal antibodies were further characterized by immunohistochemical localization of known GABAergic neurons and their processes in the cerebellum and retina.

Phylogenesis of brain glutamic acid decarboxylase from vertebrates: immunochemical studies

Brain high-speed supernatants from various lower and higher vertebrates were subjected to sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, electroblot on nitrocellulose membranes, and immunolabelling using an anti-glutamic acid decarboxylase (anti-GAD) antiserum prepared from rat antigen. Rat brain extracts showed two distinct immunolabelled bands (MW 59,000 and 62,000 daltons). The molecular weight of the native enzyme was 120,000 daltons. The immunoblot pattern was not affected by a 3-h incubation of the homogenate. In the substantia nigra, the decrease in the immunolabelling of both bands corresponded very closely to the decrease of GAD activity following lesioning of the striato-nigral pathway. Moreover, experiments with preadsorbed antiserum showed that both subunits have common antigenic determinants. The immunolabelling was consistently more intense over the lightest band. The autoradiography of immunoprecipitated rat brain GAD, iodinated prior to electrophoresis, revealed two radiolabelled bands corresponding to the two immunolabelled ones. Their radioactivity was found in a one-to-five ratio which closely paralleled their respective immunolabelling intensity. Thus, the two subunits recognized by the antiserum are not present in stoichiometric proportions in the rat brain high-speed supernatant. These findings suggest the existence of two homodimeric GAD with common antigenic determinants which are present in different amounts. Immunoprecipitation curves of brain GAD from rat, mouse, rabbit, monkey, human, quail, frog, and trout were similar, with a less than 10-fold maximum shift in affinity for GAD. GAD immunoblots from the various higher vertebrates showed a pattern similar to that obtained in rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of histidine decarboxylase from mouse kidney

Histidine decarboxylase was purified 800-fold from the kidneys of thyroxine-treated mice. The purification procedure included precipitation of protein from a crude supernatant after heating it to 55 degrees C at pH 5.5, fractionation with (NH4)2SO4, phosphocellulose column chromatography, chromatofocusing, DEAE-Sepharose column chromatography, gel filtration on Sephacryl S-300 and preparative polyacrylamide-gel electrophoresis. The native enzyme had an estimated Mr of 113 000. The protein was analysed in SDS/10%-polyacrylamide gels and formed a single band corresponding to a subunit Mr of 55 000, indicating that it is a dimer. Three forms of the enzyme were resolved on isoelectrofocusing gels, with pI 5.3, 5.5 and 5.7.

Comparative distribution of 3H-GABA uptake and GAD immunoreactivity in goldfish retinal amacrine cells: a double-label analysis

The comparative distribution of 3H-GABA uptake and glutamic acid decarboxylase immunoreactivity (GAD-IR) in amacrine cells of goldfish retina was studied simultaneously by using a combined autoradiographic/immunocytochemical technique in order to determine the degree of colocalization of these two markers of GABAergic neurons; 3H-GABA was taken up most intensely by large pyriform Ab amacrine cells (3% of inner nuclear layer (INL) somata), and less intensely by smaller, polyform amacrine cells (12% of INL somata), cell bodies in the ganglion cell layer (one-half as common as Ab cells), and cell bodies in the inner plexiform layer (very rare). GAD-IR was observed in 25% of amacrine cells in the INL, the vast majority of which were polyform in shape, and cell bodies in the ganglion cell layer. Twice as many cells were labeled for GAD-IR as for 3H-GABA uptake. Of the cells that took up 3H-GABA, colocalization of 3H-GABA uptake and GAD-IR was observed in 90% of the polyform amacrine cells, 80% of the cells in the ganglion cell layer, and none of the pyriform Ab amacrine cells or cells in the inner plexiform layer. We suggest that the polyform cells compose the major population of GABAergic amacrine cells in the goldfish retina, rather than the pyriform Ab cells. GABAergic displaced amacrine cells or ganglion cells are also indicated by our data. The implications of these data with regard to the physiology of the goldfish retina are discussed as well.

Purification of L-glutamate decarboxylase from rabbit brain and preparation of a monospecific antiserum

L-Glutamate decarboxylase (GAD), the enzyme responsible for the biosynthesis of gamma-aminobutyric acid, has been purified from rabbit brain and used for the production of a monospecific rabbit antiserum. The enzyme was purified approximately 500-fold by a combination of ion exchange, hydrophobic, hydroxyapatite, and gel filtration column chromatography, and preparative polyacrylamide gel electrophoresis. The preparation thus obtained was injected into a rabbit, producing a polyspecific antiserum. This first antiserum was used for the preparation of an immunoprecipitate containing GAD; injections of the immunoprecipitate into a second rabbit led to the production of a second, monospecific anti-GAD serum. The specificity of the antiserum for GAD has been demonstrated by enzyme precipitation, immunodiffusion, line immunoelectrophoresis, gel filtration chromatography of GAD/anti-GAD immune complexes, and immunocytochemistry in the rat cerebellum.

Two forms of rat brain glutamic acid decarboxylase differ in their dependence on free pyridoxal phosphate

There are two forms of glutamate decarboxylase (GAD) found in the rat brain. One form (form A) does not require exogenous pyridoxal-5'-phosphate (PLP) for activity whereas another form (form B) requires exogenous PLP for activity. These two forms differ greatly in temperature sensitivity, inactivation, and reactivation by the removal and readdition of PLP, electrophoretic mobility, and regional distribution. For instance, forms A and B are inactivated to an extent of 91% and 10%, respectively, by the treatment at 45 degrees C for 30 min; form A is greatly inactivated (77%) by the removal of PLP by aminooxyacetic acid and the readdition of PLP, whereas form B is only slightly inactivated (7%). Forms A and B can be clearly separated by 5% polyacrylamide gel electrophoresis in which form A migrates faster than form B. In all 10 brain regions studied, form A is present in smaller amounts than form B. This difference is greatest in the superior colliculus (the ratio of B to A is about 5), while in the locus coeruleus and cerebellum, forms A and B are present in nearly equal proportion. Forms A and B are similar with respect to relative abundance in hypotonic, isotonic, and hypertonic preparations, inhibition of catalytic activity by a carbonyl-trapping agent, immunochemical properties, and chromatographic patterns in a variety of systems. The significance of forms A and B and PLP in the regulation of gamma-amino-butyric acid (GABA) level is also discussed.

Non-correspondence of [3H]GABA uptake and GAD localization in goldfish amacrine cells

Ultrastructural analysis of the inner synaptic layer of goldfish retina, using a double-label technique, showed that [3H]GABA uptake and glutamic acid decarboxylase (GAD)-immunoreactivity (IR) occurred in different neuronal processes in most cases. Many [3H]GABA-accumulating processes were found surrounding GAD-IR processes, though not necessarily in a postsynaptic relationship. Co-localization of [3H]GABA uptake and GAD-IR occurred only when one GAD-IR process was juxtaposed to another GAD-IR process. This study suggests that [3H]GABA uptake may be a poor marker for GABA releasing neurons.

The gamma-aminobutyric acid receptor in catfish brain

When the binding of [3H]gamma-aminobutyric acid (GABA) to its receptor in catfish synaptic membranes was studied, a high affinity (Kd = 8.4 nM) and a low affinity (Kd = 65 nM) binding component was observed. Muscimol, thiomuscimol, tetrahydroisoxazole-5,4-c-pyridin-3-ol, imidazole acetic acid and bicuculline each competitively inhibited both high affinity and low affinity [3H]GABA binding. The potency of these inhibitors was similar to that reported for the GABA receptor from mammalian brain. It is concluded that the GABA receptor from catfish brain has very similar properties to the receptor from mammalian central nervous system and consequently has not undergone any obvious evolutionary changes.

Purification and characterization of cysteic acid and cysteine sulfinic acid decarboxylase and L-glutamate decarboxylase from bovine brain

L-Cysteic and cysteine sulfinic acids decarboxylase (CADCase/CSADCase) and L-glutamic acid decarboxylase (GADCase), the synthetic enzymes for taurine and gamma-aminobutyric acid, respectively, have been purified to homogeneity from bovine brain. Although CADCase/CSADCase and GADCase copurified through various column procedures, these two enzymes can be clearly separated by a hydroxyapatite column. The purification procedures involve ammonium sulfate fractionation, column chromatographies on Sephadex G-200, hydroxyapatite, DEAE-cellulose, and preparative polyacrylamide gel electrophoresis. The Km values for CADCase/CSADCase are 0.22 and 0.18 mM with L-cysteic and cysteine sulfinic acids as substrates, respectively. CADCase/CSADCase cannot use L-glutamate as substrate. GADCase can use L-glutamate, L-cysteic, and cysteine sulfinic acid as substrates with Km values of 1.6, 5.4, and 5.2 mM, respectively. Antibodies against CADCase/CSADCase do not crossreact with GADCase preparations and vice versa. It is concluded that CADCase/CSADCase and GADCase are two distinct enzyme entities and they are responsible for the biosynthesis of taurine and gamma-aminobutyric acid, respectively.

Glutamic acid decarboxylase in sea lamprey (Petromyzon marinus): characterization, localization, and developmental changes

We have carried out assays for glutamic acid decarboxylase (GAD) in homogenates of brain and spinal cord from larval and adult sea lamprey (Petromyzon marinus). The enzyme had similar characteristics in both stages. Optimal pH was 6.8; optimal temperature was 27-30 degrees C; Km at 27 degrees C was 5 mM. GAD activity was distributed uniformly along the length of the spinal cord. Specific activities for the larval cord and brain were 26 and 63 nm CO2/mg protein/h, respectively. The specific activities for the adult cord and brain were 29 and 236 nm CO2/mg protein/h, respectively. Thus, the activity of cord homogenates did not change significantly between larval and adult stages, but that of the brain increased about fourfold.