Chemical heterogeneity in cerebellar Purkinje cells: existence and coexistence of glutamic acid decarboxylase-like and motilin-like immunoreactivities

Purkinje neurons of the cerebellar cortex from a chemically and morphologically heterogeneous population containing some members that have gamma-aminobutyric acid (GABA), others that have immunoreactivity for motilin, and a small number that have both. The remaining 30-40% of all Purkinje cells have neither of these two neuroactive substances, leaving possibilities for other transmitter candidates. The evidence was compiled from double-staining immunocytochemical procedures performed on single sections of the cerebellum and brain stem in rat, mouse, and monkey. Two polyclonal antibodies were applied in succession, one directed against the midregion and COOH terminus of the 22-amino acid polypeptide motilin and the other against glutamic acid decarboxylase (glutamate decarboxylase; L-glutamate 1-carboxy-lyase, EC 4.1.1.15), the rate-limiting enzyme in the synthesis of the neurotransmitter GABA. The staining combinations employed the immunoperoxidase method, with different chromogens for distinguishing the motilin-like immunoreactivity from glutamic acid decarboxylase immunoreactivity by different colors, or the immunoperoxidase method for one antiserum and immunofluorescence for the other. The locations of both motilin and GABA cell types were mapped. The recognition of motilin in Purkinje cells calls for experimental definition of the role of this substance in the cerebellum and for reevaluation of the roles of Purkinje cells and of GABA in cerebellar function. The significant motilin representation in the flocculus, paraflocculus, and vermis suggests that it may be the Purkinje cell mediative chemical in the vestibular parts of the cerebellum. However, the presence of GABA as well in the same regions indicates that the chemical preference may be at least bimodal.

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.

Autoradiographic localization of benzodiazepine receptors in immunocytochemically identified gamma-aminobutyrergic synapses

Benzodiazepine receptors can be visualized in regions of synaptic contact by electron microscopic autoradiography using [3H]flunitrazepam as a photoaffinity label in fresh brain tissue. Perfusion fixation of the tissue prior to photoaffinity labeling left the ligand binding characteristics and the light and electron microscopic distribution of benzodiazepine receptors unaltered. Therefore, the immunocytochemical localization of a neuronal marker in fixed tissue could be combined with photoaffinity labeling in order to identify the types of synapses containing benzodiazepine receptors. By using antiserum to glutamate decarboxylase, a marker of gamma-aminobutyrergic neurons, one-third of the photolabeled benzodiazepine receptors were found to be associated with immunocytochemically stained nerve endings. Thus, these synapses are the site of at lest some benzodiazepine receptors. The enhancement of gamma-aminobutyrergic synaptic transmission by benzodiazepines, shown electrophysiologically, appears to be a primary mechanism of action of this group of drugs.

Purification and characterization of clathrin from bovine brain

Clathrin has been purified to electrophoretic homogeneity by initial extraction of clathrin from purified coated vesicle fraction, followed by column chromatographies with gel filtration, DEAE-cellulose, and hydroxylapatite and finally by preparative sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Antibody specific to clathrin has also been obtained. Two forms of native clathrin, fast and slow components, have been prepared to about 95% purity by hydroxylapatite column chromatography. Both fast and slow components are believed to represent two different aggregates of clathrin subunit because they comigrate in agarose electrophoresis, pH 7.4, and also migrate as clathrin subunit on SDS-PAGE with a molecular weight of 175,000. Furthermore, both components cross-react with antibody against purified clathrin and compete for antibody binding site with labeled fast component. The fast component can also be converted to the slow component. In addition to clathrin, two proteins of about 38,000 and 35,000 M.W. that consistently copurified with native clathrin are probably also intrinsic to coated vesicle.

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.

Abnormal protein patterns in multiple sclerosis

Sera from patients with multiple sclerosis (MS) and those obtained from normal subjects are indistinguishable by regular 5% or 7% polyacrylamide gel electrophoresis. However, 11 out of 15 MS sera examined by gradient polyacrylamide gel electrophoresis showed three distinct protein bands. None of the sera obtained from 10 normal subjects showed the characteristic protein patterns when they were examined by gradient gel electrophoresis. Similar results were obtained with de-albumin serum samples or with serum proteins precipitable at 50% ammonium sulfate saturation. These three proteins have now been purified to homogeneity by preparative gradient gel electrophoresis. Molecular weights of these proteins were estimated from gradient gel electrophoresis as 398,000, 363,000 and 302,000 daltons, respectively.

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.

The gamma-aminobutyric acid system in rabbit retina: localization by immunocytochemistry and autoradiography

The localization of gamma-aminobutyric acid (GABA) neurons in the rabbit retina has been studied by immunocytochemical localization of the GABA-synthesizing enzyme L-glutamate decarboxylase (L-glutamate I-carboxy-lyase, EC 4.1.1.15) and by [3H]GABA uptake autoradiography. When Triton X-100 was included in immunocytochemical incubations with a modified protein A-peroxidase-antiperoxidase method, reaction product was found in four broad, evenly spaced laminae within the inner plexiform layer. In the absence of the detergent, these laminae were seen to be composed of small, punctate deposits. When colchicine was injected intravitreally before glutamate decarboxylase staining, cell bodies with the characteristic shape and location of amacrine cells were found to be immunochemically labeled. Intravitreally administered [3H]GABA produced a diffuse labeling of the inner plexiform layer and a dense labeling of certain amacrine cell bodies in the inner nuclear layer. Both immunocytochemical and autoradiographic results support the notion that certain, if not all, amacrine cells use GABA as their neurotransmitter.

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.

Immunocytochemical localization of gamma-aminobutyric acid transaminase at cellular and ultrastructural levels

gamma-Aminobutyric acid transaminase (GABA-Tase; 4-aminobutyrate:2-oxaglutarate aminotransferase, EC 2.6.1.19) immunoreactivity in the rat's cerebellum was studied by light and electron microscopy with indirect immunofluorescence and peroxidase-antiperoxidase methods. Evidence is presented for neuronal and neuroglial compartments of GABA-Tase. Labeled neurons included stellate, basket, Purkinje, and Golgi cells of the cortex and a few large neurons in the deep nuclei. Labeled neuroglia included those surrounding Purkinje cells, their radial fibers in the molecular layer, and astrocytes in the granular layer and deep nuclei. No evidence for sagittal microzonation was found. At the ultrastructural level, GABA-Tase immunoreactive sites were localized to cell surface membranes, intracellular organelles, and the cytoplasmic matrix. GABA-Tase immunoreactivity at synapses could be localized precisely to pre- and postsynaptic membranes in gamma-aminobutyric acid (GABA)-containing as well as non-GABA-containing neurons. Specific label was absent from tissues treated with normal rabbit preimmune sera. GABA-Tase labeling was more intense in tissues from animals anesthetized with ether than with barbiturates and after formaldehyde fixation without glutaraldehyde. Increased GABA-Tase immunoreactivity was observed on treatment with colchicine, GABA with oxamic acid, GABA, harmaline, norepinephrine and glutamate, or diazepam (in order of decreasing effectiveness). Serotonin produced no detectable change, and apomorphine and muscimol decreased the immunoreactivity.

Gamma-aminobutyric acid pathways in the cerebellum studied by retrograde and anterograde transport of glutamic acid decarboxylase antibody after in vivo injections

Injections of characterized antibody against glutamic acid decarboxylase (GAD), the enzyme responsible for the synthesis of gamma-aminobutyric acid (GABA), were made into the cerebellum. Small cortical injections of anti-GAD antibody produced labeled stellate, basket, Purkinje, and Golgi cells and their processes at the injection site. Anterograde transport of GAD antigen-antibody complexes in Purkinje cell axons caused intense labelling of terminals in deep cerebellar and several vestibular nuclei. Small groups of mossy fiber rosettes labeled and produced retrograde labeling and GAD immunoreactivity in a small number of pleomorphic neurons in the deep cerebellar nuclei. Injections into the dentate nucleus produced retrograde labeling in Purkinje cell bodies and anterograde label in a small number of mossy fiber rosettes. All projections conformed to previously reported topographic distributions of corticonuclear and nucleocortical cerebellar pathways. These findings confirm the GABA content of most Purkinje cell-deep nuclei connections and provide new evidence for a GABA component in part of the nucleocortical pathway in the cerebellum. Immunocytochemical controls for specificity were conducted by injections of preimmune rabbit serum as a substitute for GAD antibody. Only nonspecific labeling was obtained in these cases. Colchicine caused a cumulative enhancement of GAD immunoreactivity in all cases. The present studies indicate that the method of in vivo antibody injections can be utilized to study chemically specific connections in nervous tissue.

Sialogluciduria in lysosomal diseases: quantitative and qualitative analysis of urinary low molecular sialoglucides from patients with mucopolysaccharidosis and with mucolipidosis

Low molecular sialoglucides were isolated from the urines of normal human male and two patients with lysosomal disease (mucopolysaccharidosis type II and a new type of mucolipidosis) by charcoal adsorption method. Urinary sialoglucides were fractionated into two fractions (SG-1 and SG-2) by Sephadex G-25 gel filtration and considerable increase in excretion of SG-1 was observed in the patients with lysosomal diseases: two- to three-fold increase in mucopolysaccharidosis type II and seven- to eight-fold increase in mucolipidosis. SG-1 was further fractionated into 18 to 19 fractions by Sephadex G-50 gel filtration and ion exchange chromatography. Comparison of the amounts and the chemical compositions of these fractions suggested that the increase in SG-1 was dependent upon the increase in excretion of low molecular sialoglucides rich in mannose and N-acetylglucosamine.

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.