Immunochemical comparisons of vertebrate glutamic acid decarboxylase

Relational features of acetylcholine, noradrenaline, serotonin and GABA axon terminals in the stratum radiatum of adult rat hippocampus (CA1)

In a well-defined sector of adult rat hippocampus (CA1, stratum radiatum), the ultrastructural features of acetylcholine (ACh), noradrenaline (NA), serotonin (5-HT) and GABA axon terminals (varicosities) were compared by electron microscopy after immunostaining with antibodies against choline acetyltransferase, NA, 5-HT and glutamic acid decarboxylase. Approximately 100 sectional profiles of each type were analyzed for size, presence of a synaptic membrane specialization (synaptic incidence) and composition of the microenvironment. An equivalent number of immunonegative varicosity profiles selected at random from the same micrographs were similarly examined. ACh, NA and 5-HT varicosity profiles were of comparable size, and significantly smaller than GABA profiles. They exhibited a low frequency of junctional specialization, amounting to 7%, 15% and 21%, respectively, when extrapolated to the whole volume of these terminals. In contrast, GABA varicosities appeared entirely synaptic. The ACh, NA and 5-HT varicosities also differed from their GABA counterparts in being juxtaposed to a greater number of unlabeled axonal varicosities and a lower number of dendritic branches. In addition, the microenvironment of immunostained terminals showed a much lower number of dendritic spines than that of immunonegative varicosities. This latter finding was viewed as another indication that predominantly asynaptic varicosities do not maintain particular relationships with their immediate surround. It was also concluded that volume transmission represents a major mode of transmission for ACh, NA and 5-HT in adult rat hippocampus, thus contributing to the properties and functions assigned to these transmitters in this part of brain.

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.

GABAergic synapses in the brain identified with antisera to GABA and its synthesizing enzyme, glutamate decarboxylase

GABA is a known inhibitory neurotransmitter in the mammalian brain. The site of GABAergic synapses can be determined with immunocytochemical methods that localize either GABA or its synthesizing enzyme, glutamate decarboxylase (GAD). In general, GABAergic axon terminals contain pleomorphic synaptic vesicles and form symmetric synapses. However, a small number of GABAergic axon terminals in selected brain regions (spinal cord, cerebellum, superior colliculus, striatum, globus pallidus, inferior olive, and substantia nigra) form asymmetric synapses. GAD- and GABA-immunoreactive processes that contain synaptic vesicles participate in every known morphological type of chemical synapse. These include axosomatic, axodendritic, axospinous, initial segment, axoaxonic, dendrodendritic, serial, reciprocal, and ribbon synapses. Although GABAergic synapses form a heterogeneous group, they most commonly form axosomatic, axodendritic, and initial segment synapses in the brain and spinal cord. These findings provide helpful guidelines for the identification of GABAergic synapses in future studies.

Temporal disparity in pineal and retinal ontogeny

The development of photoreceptors and two putative neurotransmitter systems in the pineal organ and retina was studied during embryogenesis in the three-spined stickleback Gasterosteus aculeatus L. The investigation was performed by aid of immunocytochemistry using well characterized antisera to the retinal proteins alpha-transducin (TD alpha) and S-antigen (SA) (photoreceptor-markers), antisera against L-glutamic acid decarboxylase (GAD), gamma-aminobutyric acid (GABA), choline-O-acetyltransferase (ChAT) and with acetylcholinesterase (AChE) histochemistry (neurotransmitter-markers). It was possible to set up the following developmental time-table concerning the first appearance of positive immuno- and enzyme-reactive cells in the pineal organ and retina: I AChE-activity and TD alpha- and SA-immunoreactive cells in the pineal organ; II GAD- and GABA-immunoreactive cells in the pineal organ and retina; ChAT immunoreactivity and AChE activity in the retina; III hatching; IV SA-immunoreactive cells in the retina. The obtained results provide good evidence that while photoreceptor cells develop much earlier in the pineal organ than in the retina, neurons develop simultaneously in the pineal organ and retina.

Gamma-aminobutyric acid- and glutamic acid decarboxylase-immunoreactive neurons in the retina of different vertebrates

The localization of gamma-aminobutyric acid (GABA)- and L-glutamate 1 carboxy-lyase (GAD)-immunoreactive neurons was compared in the skate, frog, pigeon, chicken, rabbit, and man. Horizontal cells show both GABA and GAD immunoreactivity in the skate, frog, and bird. Certain amacrine cells show GABA and GAD immunoreactivity in all species. The distribution of GABA- and GAD-immunoreactive cell bodies and cell processes was very similar, if not identical, in the skate and man. In the other species, cell populations with GAD immunoreactivity also showed GABA immunoreactivity. However, in the bird, frog, and rabbit, the GABA-immunoreactive amacrine cells were at least twice as numerous as the GAD-immunoreactive cells. In birds, the distributions of the GAD and GABA immunoreactivities were different in the sublayers of the inner plexiform layer. The reason for the difference is currently unknown. GABA-immunoreactive bipolar-like cells were seen in the frog.

GABA and GAD-like immunoreactivity in the primate retina

GABA immunoreactivity was studied and compared with GAD immunoreactivity in the retinae of baboon, cynomolgus monkey and man. The central and peripheral parts of the retinae were investigated separately in cynomolgus monkey and in man. The same kinds of structures were stained with both antisera. Cells with a position corresponding to amacrine cells were stained, as well as processes in the inner plexiform layer and some cells in the ganglion cell layer. The outer plexiform layer and some cells with the position and configuration of horizontal cells also appeared immunoreactive. Staining was also observed in bipolar-like cells, in man most clearly when using the GABA antiserum in sections from the central parts of the retina. It is possible that horizontal cells, as well as bipolar-like cells, may play a previously unsuspected role in GABAergic transmission in the primate retina.

Time course of the reduction of GABA terminals in a model of focal epilepsy: a glutamic acid decarboxylase immunocytochemical study

Immunocytochemical localization of glutamic acid decarboxylase (GAD), the synthesizing enzyme for the neurotransmitter gamma-aminobutyric acid (GABA), has been used to study the time course of the decrease in putative GABAergic synaptic terminals that occurs in an alumina gel-induced model of focal epilepsy. Monkeys were studied at progressive intervals following unilateral application of alumina gel to sensorimotor cerebral cortex, and were categorized into 3 different experimental groups depending upon their clinical status. These groups respectively exhibited: (1) no abnormal bioelectrical (EEG and ECoG) activity; (2) abnormal bioelectrical activity, but no clinical seizures; and (3) both abnormal bioelectrical activity and clinical seizures. Normal and sham-operated monkeys were also studied. The amounts of GAD-positive terminal-like structures were determined on control and experimental sides of motor cortex (layer V) of all specimens with an image analysis system. This quantitative study revealed that monkeys from the 3 experimental groups showed reductions of GAD-positive terminals on the experimental cortical side, with greater losses occurring at progressively longer times following alumina gel implants. Statistical tests showed that there were no significant cortical side differences for the normal and sham groups, but that cortical side variations were significantly different for each of the 3 experimental groups. Conventional electron microscopy of an early experimental stage revealed degenerating axon terminals in layer V of motor cortex, as well as phagocytosis of degenerating material and astrogliosis. Similar findings were obtained from a chronically epileptic specimen, except that degenerating terminals were observed less often and fibrous astrocytic scarring was more prevalent, especially surrounding the somata of pyramidal neurons. The main conclusion drawn from the results of this investigation is that significant decreases of GAD-positive terminals occur prior to the onset of clinical seizures, and this is consistent with a causal role for a loss of GABAergic innervation in the development of seizure activity in this primate model of focal epilepsy.

An improved method of toluidine blue counterstaining of neurons in immunocytochemical preparations

Immunocytochemical methods can identify individual neurons and processes made immunoreactive by virtue of the antigens they contain. However, frequently it is also useful to visualize surrounding nonimmunoreactive cells, but immunocytochemical procedures often interfere with the quality of subsequent counterstaining. This report describes an improved method of counterstaining immunocytochemical specimens with either aged (at least 1 year) or concentrated solutions of toluidine blue. This technique combines well with immunocytochemical preparations of at least two antigens, i.e., choline acetyltransferase and glutamic acid decarboxylase, to delineate nonimmunoreactive somata. Additionally, a method of photographing these color preparations is described that, by the use of an appropriate filter, allows one to illustrate sections essentially with and without blue counterstain in black and white photomicrographs.

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)

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.

A decrease in the number of GABAergic somata is associated with the preferential loss of GABAergic terminals at epileptic foci

Previous studies have indicated that a loss of GABAergic terminals occurs at epileptic foci. The present study was undertaken to investigate if this loss is associated with a loss of GABAergic neuronal somata. Seven juvenile monkeys (M. mulatta) received alumina gel injections to the pre-central gyrus of the left cerebral hemisphere to produce epileptic foci. Four of these monkeys were chosen for further quantitative study. One was sacrificed prior to seizure onset ('pre-seizure'), one had seizures for 3 days ('acute'), and two had a seizure record of one month ('chronic'). Sections of tissue from the epileptic cortex and from the contralateral, non-epileptic cortex were processed for glutamate decarboxylase (GAD) immunocytochemistry at the light microscopic level. Quantitative analysis revealed that a loss of GAD-positive neuronal somata ranging from 24 to 52% occurred at epileptic foci for all monkeys. This decrease was significant (P less than 0.01) for the two chronic monkeys. There was also a slight decrease in GAD-positive neurons 1 cm distal to the focus ('parafocus') in the chronic monkeys, but not in the acute or pre-seizure animals. In addition, small GAD-positive somata (50-150 micron2) were more severely decreased in number at epileptic foci than larger ones (200-250 micron2). As an experimental control, an additional monkey was given a surgical lesion in area 4 of one cerebral hemisphere. It did not display seizure activity prior to sacrifice and did not show a loss of GAD-positive neurons proximal to the control lesions. The results of this study indicate that a loss of GABAergic neuronal somata is associated with a loss of GABAergic terminals at epileptic foci, and that this loss may be more specific for the small GABAergic neurons.

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.

Neuropeptides and gamma-aminobutyric acid in the vestibular nuclei of the rat: an immunohistochemical analysis. I. Distribution

The distribution of substance P, Leu-enkephalin and gamma-aminobutyric acid (GABA) containing structures in the rat vestibular nuclei were investigated by means of an indirect immunofluorescent method using specific antisera to substance P, Leu-enkephalin and glutamic acid decarboxylase (GAD), respectively. Numerous positive neurons and fibers containing these three substances were found in the medial vestibular nucleus. Most of them were situated in the caudal part of the nucleus and those in the rostral part were concentrated dorsally. In the descending vestibular nucleus, a large number of substance P, Leu-enkephalin and GAD containing neurons were evenly distributed among longitudinally directing fiber bundles. A number of positive fibers with these substances were also observed. The lateral vestibular nucleus contained numerous coarse GAD-immunoreactive fibers surrounding Deiters' neurons, while substance P-immunoreactive and Leu-enkephalin-immunoreactive fibers were rather poorly distributed in this nucleus as well as in the superior vestibular nucleus.

Immunocytochemical localization of glutamic acid decarboxylase in the dorsal lateral vestibular nucleus: evidence for an intrinsic and extrinsic GABAergic innervation

Immunocytochemical methods were used to localize the gamma-aminobutyric acid (GABA) synthesizing enzyme glutamic acid decarboxylase (GAD) in normal and partially deafferented dorsal lateral vestibular nucleus (dLVN) of the rat. Normal dLVN exhibited more intense staining than the ventral part of the nucleus (vLVN), and this was mainly due to more numerous GAD+ axon terminals surrounding dLVN somata and within neuropil. Small GAD+ somata were also present. Electron microscopy suggested the existence of two types of GAD+ synaptic terminals. The major type conformed to descriptions of Purkinje cell terminals, whereas the minor type did not. Ablation of the anterior cerebellar vermis resulted in a 73% reduction in the number of GAD+ terminals, the percentage decrease being greater around neuronal somata (83%) than within neuropil (70%). The presence of GAD+ somata within the nucleus and the persistence of some GAD+ terminals after extensive lesions of the Purkinje cell afferents suggest that both extrinsic and intrinsic GABAergic neurons may contribute to information processing within the dLVN.

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.

Morphological diversity of immunocytochemically identified GABA neurons in the monkey sensory-motor cortex

GABAergic neurons have been identified in monkey sensory-motor cerebral cortex by light microscopic, immunocytochemical localization of the GABA synthesizing enzyme, glutamic acid decarboxylase (GAD). All GAD-positive neurons are non-pyramidal cells. Their somata are present in all layers and are evenly distributed across layers II-VI of the motor cortex (area 4), but are found in greater concentrations in layers II, IV and VI of all areas of first somatic sensory cortex (SI; areas 3a, 3b and 1-2). GAD-positive puncta (putative axon terminals) are present throughout the sensory-motor cortex, and they are found immediately adjacent to the somata, dendrites and presumptive axon initial segments of GAD-negative pyramidal cells. In addition, they are observed in close approximation to the somata of both large and small GAD-positive neurons. In area 4, the density of puncta is highest in the superficial cortical layers (layers I-III) and gradually declines throughout the deeper layers. In SI, the highest densities of puncta are present in layer IV, while moderately high densities are found in layers I-III and VI. In areas 3a and 3b, the puncta in layers IV and VI are particularly numerous and form foci that exhibit greater density than adjacent regions. GAD-positive neurons with large somata, 15-33 micron in diameter, are present in layers IIIB-VI of all areas. Such cells have many primary dendrites that radiate in all directions. In addition they have axons that ascend either from the superficial aspect of the somata or from primary dendrites, and that exhibit horizontal collateral branches. These neurons closely resemble the large basket cells (Marin-Padilla, 1969; Jones, 1975), and they may give rise to many of the GAD-positive endings surrounding the somata and proximal dendrites of pyramidal cells in layers III-VI. In addition, small GAD-positive somata are present in all layers, but they are most numerous in layers II and IIIA of all areas and in layer IV of SI. The somata and proximal dendrites of these cells vary from a multipolar shape with small, beaded dendrites, found primarily in layer IV, to bitufted and multipolar shapes with larger, smooth dendrites. The diversity of somal sizes and locations, the variety of dendritic patterns, and the different distributions of GAD-positive puncta, all combine to suggest that several different morphological classes of intrinsic neurons comprise the GABA neurons of monkey cerebral cortex.

Synaptic organization of immunocytochemically identified GABA neurons in the monkey sensory-motor cortex

Neurons in the monkey somatic sensory and motor cortex were labelled immunocytochemically for the GABA synthesizing enzyme, glutamic acid decarboxylase (GAD), and examined with the electron microscope. The somata and dendrites of many large GAD-positive neurons of layers III-VI receive numerous asymmetric synapses from unlabelled terminals and symmetric synapses from GAD-positive terminals. Comparisons with light and electron microscopic studies of Golgi-impregnated neurons suggest that the large labelled neurons are basket cells. Small GAD-positive neurons generally receive few synapses on their somata and dendrites, and probably conform to several morphological types. GAD-positive axons from symmetric synapses on many neuronal elements including the somata, dendrites and initial segments of pyramidal cells, and the somata and dendrites of non-pyramidal cells. Synapses between GAD-positive terminals and GAD-positive cell bodies and dendrites are common in all layers. Many GAD-positive terminals in layers III-VI arise from myelinated axons. Some of the axons form pericellular terminal nests on pyramidal cell somata and are interpreted as originating from basket cells while other GAD-positive myelinated axons synapse with the somata and dendrites of non-pyramidal cells. These findings suggest either that the sites of basket cell terminations are more heterogeneous than previously believed or that there are other classes of GAD-positive neurons with myelinated axons. Unmyelinated GAD-positive axons synapse with the initial segments of pyramidal cell axons or form en passant synapses with dendritic spines and small dendritic shafts and are interpreted as arising from the population of small GAD-positive neurons which appears to include several morphological types.

Immunocytochemical localization of L-glutamate decarboxylase, gamma-aminobutyric acid transaminase, cysteine sulfinic acid decarboxylase, aspartate aminotransferase and somatostatin in rat retina

The regional distribution and cellular location of GABA-synthesizing enzyme, L-glutamate decarboxylase (GAD), GABA degrading enzyme, GABA-transaminase (GABA-T), taurine synthesizing enzyme, cysteine sulfinic acid decarboxylase (CSAD), aspartate and glutamate converting enzyme, aspartate aminotransferase (AAT), and somatostatin have been visualized in the rat retina by immunocytochemical methods. GAD immunoreactivity was found to be concentrated in the inner plexiform layer. A moderate to weak staining of GAD was found in the inner nuclear layer. The distribution of GABA-T immunoreactivity was similar to that of GAD with the exception that a weak to moderate staining of GABA-T was also observed in the outer plexiform layer. CSAD immunoreactivity was seen in every layer with the heaviest staining in the inner plexiform layer, and moderate staining in the inner and outer nuclear layers and ganglion cell layer. AAT immunoreactivity was mostly concentrated in the outer nuclear layer; there was weak staining in the inner nuclear layer and inner and outer plexiform layer. Dense somatostatin staining was seen in the inner plexiform layer and moderate staining was present in the inner nuclear layer, outer plexiform layer and ganglion cell layer. These findings suggest that in rat retina, GABA-containing cells occur in some types of amacrine cells only, while taurine and somatostatin appear in both amacrine and horizontal cells. AAT immunoreactivity was primarily associated with the photoreceptor cells suggesting that AAT may be used as a marker for aspartergic/glutamergic cells and their endings in the central nervous system.

Specific lysis of GABAergic synaptosomes by an antiserum to glutamate decarboxylase

An antiserum to pure glutamate decarboxylase (GAD) when incubated with rat cortical synaptosomes in the presence of complement caused release of 33-53% of lactate dehydrogenase (LDH) and 22-41% of total GAD. In addition most of the gamma-aminobutyrate (GABA) present was released. Anti-GAD antiserum alone, or complement alone, were without action. The antiserum plus complement had no effect on noradrenaline or choline uptake, and did not release choline acetylase (ChAT). Anti-ChAT serum plus complement released 30-37% of ChAT and 10-13% of LDH. It prevented choline uptake. This serum did not produce GAD release or prevent GABA, choline or noradrenaline uptake. When cortical synaptosomes were exposed to both antisera plus complement, their actions were strictly additive. The data indicate specific lysis of GABAergic and cholinergic synaptosomal sub-populations.

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.

Chandelier cells in rat visual cortex

Golgi-impregnated chandelier cells in rat visual cortex have been examined by both light and electron microscopy. All of the chandelier cells impregnated have their cell bodies within layer II/III and although they occur throughout area 17, there are increased numbers at the area 17/18a border and to a lesser extent at the area 17/18 border. Most of the chandelier cells are bitufted neurons, with groups of dendrites extending from the upper and lower poles of an elongate cell body, but some cells have a more multipolar configuration. The perikaryal cytoplasm is rich in rough endoplasmic reticulum and both the cell body and the sparsely spinous dendrites receive axon terminals forming symmetric and asymmetric synapses. The axons of these neurons arise from either the lower pole of the cell body or the base of one of the dendrites in the lower tuft, and the axons form laterally spread plexuses which terminate in vertical strings of boutons. The boutons in each string synapse with axon initial segments of layer II/III pyramidal cells, the uppermost bouton in each string being 7 to 14 micrometers distant from the pyramidal cell body. Some layer II/III pyramidal cells seem to receive boutons from more than one chandelier cell, others from a single chandelier cell, and still other appear to receive no chandelier cell terminals. The axon terminals of the chandelier cells are irregular in shape, contain pleomorphic synaptic vesicles, and form symmetric synapses. Evidence is presented to show that axon terminals exhibiting the same morphological features and site of synaptic termination as those of the chandelier cells contain glutamic acid decarboxylase (GAD), the enzyme which synthesizes GABA. Hence the chandelier cells are probably GABAergic, inhibitory neurons. Other GAD-positive axon terminals synapse with the cell bodies, axon hillocks, and proximal portions of the axon initial segments of the layer II/III pyramidal cells, and these terminals are probably derived from the smooth and sparsely spinous stellate cells.

Ultrastructure of GABA-neurons in cultures of rat neostriatum

The subcellular distribution of glutamate decarboxylase (GAD) was revealed by electron microscopic immunocytochemistry in primary cultures of the rat neostriatum. Immunoreactivity was restricted to a small nerve cell type with rich amounts of free ribosomes and an indented nucleus. Glial cells were non-reactive. The results indicate that GABA-synthesizing neurons are viable in culture conditions and suggest that neostriatal GABA-neurons are small cells with simple ultrastructure since larger cells did not possess immunoreactivity.

Immunocytochemical localization of glutamic acid decarboxylase in monkey striate cortex

Neuronal cell bodies and synaptic terminals positive for glutamic acid decarboxylase, the enzyme responsible for synthesizing gamma-amino butyric acid, have been located by immunocytochemical staining in all layers of the macaque monkey cortex. In layers II and III the staining pattern of periodic dots is identical with that seen in sections stained for cytochrome oxidase. The rows of dots run parallel with the ocular dominance columns, suggesting that the labelled neurones are preferentially related to each eye.

Demonstration of enkephalin-, substance P- and glutamate decarboxylase-like immunoreactivity in cultured cells derived from newborn rat neostriatum

The presence of cells exhibiting leucine-enkephalin-, substance P- and glutamate decarboxylase-like immunoreactivity was demonstrated in dissociated cultures from newborn rat neostriatum. The size and shape of the enkephalin-immunoreactive cells varied, but they were generally larger than substance P- and glutamate decarboxylase-immunoreactive cells, which formed relatively uniform cell populations. Cells of apparently non-neuronal origin did not show any immunoreactivity. It is unlikely that enkephalin is present in the same cells that contain substance P or glutamate decarboxylase because of morphological differences between these cells. The possible coexistence of substance P and glutamate decarboxylase in the same cells however, could not be excluded. The results of this study confirm that the cell bodies of neurons containing three possible neurotransmitters are located in the neostriatum.

Abnormalities of neurotransmitter enzymes in Huntington's chorea

The activities of L-glutamate decarboxylase (GAD), GABA-transaminase (GABA-T), choline acetyltransferase (CAT), and cysteic and cysteinesulfinic acids decarboxylase (CAD/CSAD) in putamen and frontal cortex in both Huntington's chorea and normal tissues were measured. The greatest difference between Huntington's and normal tissues occurred in putamen, in which the apparent CSAD activity was reduced by 85%, while no difference was observed in frontal cortex. GAD, CAD, and CAT activities were also reduced in putamen by 65%, 63%, and 42%, respectively (P less than 0.05). Slight reduction in the enzyme activities was also observed in frontal cortex. However, these reductions appeared to be statistically insignificant (P greater than 0.05 in all cases). GABA-T showed little difference in both putamen and frontal cortex in Huntington's chorea and normal tissues. GAD and GABA-T from Huntington's tissues were indistinguishable from those obtained from normal tissues by double diffusion test and by microcomplement fixation test, which is capable of distinguishing proteins with a single amino acid substitution. Furthermore, the similarity of the complement fixation curves for GAD from Huntington's and normal tissues suggests that the decrease in GAD activity is probably due to the reduction in the number of GAD molecules, presumably through the loss of neurons, and not due to the inhibition or inactivation of GAD activity by toxic substances which might be present in Huntington's chorea.

Tissue and regional distribution of cysteic acid decarboxylase. A new assay method

A sensitive and rapid assay method method for cysteic acid decarboxylase was develped which combined the selectivity of ion exchange resin (a complete retention of the substrate, cysteic acid, and exclusion of the product, taurine) with the speed of a vacuum filtration. The synthesis and purification of 35S-labeled cysteic acid were described. The validity of the assay was established by the identification of the reaction product as taurine. With this new method, the decarboxylase activity was measured in discrete regions of bovine brain. Putamen had the highest activity, 172 pmol taurine formed/min/mg protein (100%), followed by caudate nucleus, 90%; cerebral cortex, 82%; hypothalamus, 81%; cerebellar cortex, 79%; cerebellar peduncle, 59%; thalamus, 42%; brain stem, 25%; pons, 10%; and corpus callosum, 3%. The decarboxylase activity in various mouse tissues was also determined as follows: liver, 403; brain, 145; kidney, 143; spinal cord, 59; lung, 21; and spleen, 10 pmol taurine formed/min/mg. No activity could be detected in skeleton muscle and heart, suggesting a different biosynthetic pathway for taurine synthesis in these tissues. The advantages and disadvantages of the new assay method are also discussed.

L-Glutamate decarboxylase

Much progress has been made in recent years regarding enzymological aspects of mammalian brain GAD, such as its purification and characterization, but some uncertainty still remains concerning its molecular weight and forms, and its subunit structure. The availability of antibodies to this enzyme has allowed immunocytochemical studies which have provided important information on the intrinsic organization of GABA-ergic neurones in the CNS, particularly in the cerebellum and nigrostriatal pathway. With the increased understanding of the enzymology of GAD and the distribution of central GABA-ergic neurones, it is becoming feasible to study the regulatory biochemistry of GAD in terms of control and adaptive mechanisms at the cellular level. In our own laboratory, as well as in others, initial approaches have already begun. Obviously, cellular regulation of this phenotypic enzyme is an important issue for the understanding of GABA-ergic neurones and their functions.

Distribution and tissue specificity of 4-aminobutyrate-2-oxoglutarate aminotransferase

A rapid and specific method for assaying 4-aminobutyrate-2-oxoglutarate aminotransferase was developed. The method was based on the selectivity of ion exchange resin and the speed of vacuum filtration. With this new method, the aminotransferase activity in various tissues has been determined as follows: brain, 10.2; spinal cord, 11.8; liver, 5.7; kidney, 4.6; heart, 0.5; lung, 0.4 nmol glutamate formed/min/mg. No activity could be detected in muscle preparations. When the aminotransferases were tested with the antibody against the purified 4-aminobutyrate aminotransferase from brain, no difference could be detected among brain, spinal cord, and kidney preparations as judged from the results of immunodiffusion, inhibition of enzyme activity by antibody, and microcomplement fixation. It is concluded that 4-aminobutyrate aminotransferases from various tissues of the mouse are probably identical or closely related.