摘要:

Abstract:We have identified the chicken equivalent of growth‐associated protein GAP‐43 in a detergent‐resistant membrane skeleton from cultures of chick neurones and embryonic chick brain. Antisera to the membrane skeleton protein, the 3D5 antigen, precipitate the translation product of chick GAP‐43 cDNA, and the 3D5 antigen is also detected by antisera against synthetic peptides from the known amino acid sequence of rat GAP‐43. The chick protein and the rat GAP‐43 are biochemically similar proteins that both serve as major targets of phosphorylation by endogenous protein kinase C. The detergent‐resistant complex in which GAP‐43 is found also contains actin ˜5% of the total protein) and a neurone‐specific cell surface glycoprotein. We suggest that the membrane skeleton of neurones may be a primary site o

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb02312.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:The phorbol ester 12‐O‐tetradecanoylphorbol 13‐acetate (TPA) was found to stimulate phospholipase D activity in cultured primary astrocytes. Both the hydrolysis and the transphosphatidylation reaction catalyzed by phospholipase D were studied in cells labeled with [3H]glycerol. Phosphatidic acid (PA) synthesis was increased after addition of 100 nMTPA. When ethanol was present in the cell culture medium, phosphatidylethanol (Peth), a product of phospholipase D‐catalyzed transphosphatidylation, was formed. The half‐maximum effective concentrations (EC50) of TPA were 25 nMfor PA increase as well as for Peth formation. The formation of Peth in ethanol‐treated cells was accompanied by an inhibition of the TPA‐induced increase in labeled PA. Increasing ethanol concentrations led to an increase in [3H]Peth and a decrease in [3H]PA. A protein kinase C inhibitor, 1‐(5‐isoquinolinesulfonyl)‐2‐methylpiperazine (H7), inhibited both the synthesis of PA and the formation of Peth observed after TPA addition to the astrocytes. Dioctanoylglycerol (100 μM) stimulated the formation of Peth in the presence of ethanol. In addition to the induction of Peth formation in astrocytes, TPA induced Peth formation in ethanol‐treated neurons. The present results indicate that phospholipase D activity is stimulated by TPA in cultured primary brain cells. Modulation of phospholipase D activity by protein kinase C is a mechanism that may be important in sign

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb02313.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:The 1‐methyl‐4‐phenylpyridinium species (MPP+) is the four‐electron oxidation product of 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) and is widely assumed to be the actual neurotoxic species responsible for the MPTP‐induced destruction of dopaminergic neurons. MPTP is oxidized by the enzyme monoamine oxidase‐B to a dihydropyridinium intermediate which is oxidized further to MPP+, an effective inhibitor of the oxidation of the Complex I substrates glutamate/malate in isolated mitochondrial preparations. In the present study, the tetraphenylboron anion (TPB) greatly potentiated the inhibitory effects of MPP+and other selected pyridinium species on glutamate/malate respiration in isolated mouse liver mitochondria. At 10 μMTPB, the potentiation ranged from approximately 50‐fold to greater than 1,000‐fold for the several pyridinium species tested. In other experiments, TPB greatly enhanced the accumulation of [3H]MPP+by isolated mitochondrial preparations. This facilitation by TPB of MPP+accumulation into mitochondria explains, at least in part, the potentiation by TPB of the above‐mentioned inhibition of mitochondrial respiration. Moreover, TPB addition increased the amount of lactate formed during the incubation of mouse neostriatal tissue slices with MPTP and other tetrahydropyridines. The administration of TPB also potentiated the dopaminergic neurotoxicity of MPTP in male Swiss‐Webster mice. All of these observations, taken together, are consistent with the premise that the inhibitory effect of MPP+on mitochondrial respiration within dopaminergic neurons is the ultimate mechanism to expl

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb02314.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:We have solubilized, affinity‐purified, and functionally reconstituted the γ‐aminobutyric acid/benzodiazepine (GABA/BDZ) receptor from rat brain into natural brain lipid liposomes. The detergent, 3‐[(3‐cholamidopropyl)‐dimethylammonio] 1‐propanesulphonate, was employed for the isolation of the receptor in the presence of a whole rat brain lipid extract supplemented with cholesteryl hemisuccinate. The soluble and reconstituted protein showed a homogeneous [3H]flunitrazepam binding population and the allosteric modulation of this binding site by GABA, by the pyrazolopyridine, cartazolate, and by the depressant barbiturate, pentobarbital. The purified GABA/BDZ receptor when incorporated into liposomes has been visualized by electron microscopy and reveals rosette structures, 8–9 nm in diameter, which appear to have a central pore. Sodium dodecyl sulphate‐polyacrylamide gel electrophoresis of the reconstituted GABA/BDZ receptor reveals three major protein bands of 41, 52–56, and 59–62 kDa, the latter two of which appear as doublets. Functional receptor reconstitution is demonstrated by the measurement of GABA‐stimulated36Cl‐flux into the purified GABA/BDZ receptor incorporated liposomes and its modulation by the BDZs, barbiturate

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb02315.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:A set of cDNA clones encoding a protein highly homologous to the mammalian middle‐size class of neurofilaments (NF‐M) was characterized. The amino acid similarity between theTorpedoand rat NF‐M approaches 90% in the amino‐terminal “rod‐like”domain and is significantly lower in the carboxy‐terminal tail. TheTorpedoprotein contains 13 tandem repeats of a unique six amino acid core, containing a Lys‐Ser‐Lys putative phosphorylation site. Surprisingly, the 3’untranslated region contains stretches of 80‐90% nucleic acid homology with the mammalian, but not with the chicken sequences. This homology is greater than much of the coding region, suggesting that the 3’untranslated region of the message has an important functional role, perhaps governing RNA stability or localization. ThisTorpedoNF‐M mRNA is expressed specifically in the electric lobe and was not detected in other tissues, including brain and spinal cord. A polyclonal antibody generated against a fusion protein synthesized inE. colidetects a 150‐kDa protein in the electric lobe and organ, as well as a small amount of material in the brain. Cytochemical studies reveal immunoreactivity in electromotor neuron axons and terminals. Specific expression of neurofilament genes in subsets of central neurons may be important in determining the morphology and functional characteristics

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb02316.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:Excitatory amino acids stimulated inositol phospholipid hydrolysis in primary cultures of astrocytes, as reflected by an increased formation of [3H]inositol monophosphate ([3H]InsP) in the presence of 10 mMLi+. Quisqualate was the most potent activator of inositol phospholipid hydrolysis, followed by glutamate and ibotenate. Kainate exhibited low activity, whereasN‐methyl‐D‐aspartate (NMDA) andα‐amino‐3‐hydroxy‐5‐methylisoxazolepropionate (AMPA) were inactive. The increase in [3H]InsP formation induced by glutamate was potentiated after 12‐h exposure to the proliferative agent epidermal growth factor (EGF), suggesting that activation of the mitotic cycle leads to an enhanced coupling of glutamate recognition sites with phospholipase C. To study how glutamate receptors are involved in regulating cell proliferation, we have measured [methyl‐3H]thymidine incorporation in cultured astrocytes. Excitatory amino acids reduced thymidine incorporation with a pharmacological profile similar to that observed for the stimulation of inositol phospholipid hydrolysis. Quisqualate acted as a potent antiproliferative agent, both under basal conditions and in cells stimulated to proliferate by addition of EGF or phorbol 12‐tetradecanoate 13‐acetate. Glutamate and ibotenate reduced [methyl‐3H]‐thymidine incorporation at high concentrations, whereas kainate, AMPA, and NMDA were virtually inactive. The action of quisqualate on both inositol phospholipid hydrolysis and thymidine incorporation was attenuated by 2‐amino‐4‐phosphonobutyrate, which acted as a weak agonist/competitive antagonist. Other excitatory amino acid receptor antagonists were not effective. Inhibition of [methyl‐3H]thymidine incorporation by quisqualate required a lag time of about 4 h and, in cells synchronized to proliferate, occurred when the drug was added during the transition between G0and G1, but not during the S phase of the mitotic cycle. This suggests that an inducible factor may be involved in the antiproliferative effect of excitatory amino acids. Accordingly, activation of quisqualate receptors led to a rapid and transient increase in mRNA levels of the early inducible gene, c‐fos.These results suggest that activation of a specific class of “quisqualate‐preferring”excitatory amino acid receptors reduces pro

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb02317.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:The incorporation and redistribution of [1‐14C]arachidonic acid in SK‐N‐BE human neuroblastoma cell phospholipids were investigated. By continuous labelling in serum‐enriched medium, a rapid radioactivity incorporation into phosphatidylcholine (PtdCho), phosphatidylinositol, and phosphatidylserine was observed; initially, phosphatidylethanolamine (PtdEtn) was poorly labelled, but at later stages it displayed the highest level of arachidonic acid incorporation, in comparison with other phospholipid classes. Labelling of triacylglycerols was also observed. When cells were pulse‐labelled with [1‐14C]arachidonic acid and then reincubated in label‐free medium, a decrease of the radioactivity in triacylglycerols was observed initially, paralleled by an increase of phospholipid labelling; thereafter, arachidonic acid redistribution was consistent with a net decrease of the radioactivity associated with PtdCho acid‐stable forms (i.e., diacyl plus alkylacyl forms), concomitantly with a net labelling increase of both acid‐stable PtdEtn and alkenylacyl‐PtdEtn. Data indicate the following: (a) neuroblastoma cells incorporate arachidonic acid into phospholipids through complex kinetics involving transfer of the fatty acid from acid‐stable PtdCho to both alkenylacyl‐PtdEtn and acid‐stable PtdEtn; and (b) triacylglycerols act as storage molecules for arachidonic acid which is subsequently incorporated into phospholipids. The possibility that arachidonic acid transfer to PtdEtn subclasses is driven by distinc

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb02318.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:The relationships between the concentration of serotonin (5‐HT) and related metabolites in human blood and CSF have been studies. Plasma tryptophan (TP), 5‐HT, 5‐hydroxyindoleacetic acid (5‐HIAA), and indoleacetic acid (IAA), whole‐blood 5‐HT, and CSF TP, 5‐HT, 5‐HIAA, IAA, homovanillic acid, and 3‐methoxy‐4‐hydroxyphenylethylene glycol were determined in 35 unmedicated outpatients who underwent minor surgical operations and had no history of psychiatric or neurological illnesses. Significant correlations were found between the serotoninergic parameters analyzed in blood and CSF. Plasma free 5‐HT correlated significantly with CSF 5‐HT (r= 0.411,p<0.02), and plasma 5‐HIAA correlated with the CSF 5‐HIAA/5‐HT ratio (r= 0.508,p<0.004). The concentration of 5‐HIAA in CSF correlated with the plasma 5‐HIAA/5‐HT ratio (r= 0.405,p<0.026) (which can be taken as an index of monoamine oxidase type A activity in peripheral tissues) and with the platelet 5‐HT/plasma 5‐HT ratio (r= 0.375,p<0.05). The concentrations of IAA in CSF and plasma were strongly correlated (r= 0.899,p<0.001). The significance of these results and their relationship to the use of “in vivo”measures of 5‐HT and related metabolites in plasma and platelets as an index of serotoninergi

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb02319.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:Aromatic L‐amino acid decarboxylase (AAAD) activity of rat retina increases when animals are placed in a lighted environment from the dark. The increase of activity can be inhibited by administering the selective dopamine D1 receptor agonist SKF 38393, but not the selective D2 agonist quinpirole, or apomorphine. Conversely, in the dark, enzyme activity can be enhanced by administering the selective D1 antagonist SCH 23390 or haloperidol, but not the selective D2 antagonist (–)‐sulpiride. Furthermore, in animals exposed to room light for 3 h, the D1 agonist SKF 38393 reduced retinal AAAD activity, and this effect was prevented by prior administration of SCH 23390. In contrast, quinpirole had little or no effect when administered to animals in the light. Kinetic analysis indicated that the apparentVmaxfor the enzyme increases with little change in the apparentKmfor the substrate 3,4‐dihydroxyphenylalanine or the cofactor pyridoxal‐5′‐phosphate. We suggest that dopamine released in the dark tonically occupies D1 receptors and suppresses AAAD activity. When the room light is turned on, D1 receptors are vacated and selective D1 agonists can either prevent the rise of AAAD or reverse light‐enhance

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb02320.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:We report here on the binding properties of [3H]hemicholinium‐3, a selective inhibitor of the high‐affinity choline uptake process, to human brain membranes. Under the assay conditions described, the binding of [3H]hemicholinium‐3 exhibited a dependency of physiological conditions on pH, temperature, and NaCl concentrations. Striatal binding proved to be specific, to a single site, saturable, and reversible, with an apparentKDof 10 nMand aBmaxof 82 fmol/mg of protein. [3H]Hemicholinium‐3 specific binding exhibited a pharmacological profile and an ionic dependency suggestive of physiologically relevant interactions and comparable with those reported for the high‐affinity choline uptake. Moreover, specific [3H]hemicholinium‐3 binding exhibited an uneven regional distribution: striatum ≫ nucleus basalis>spinal cord ≫ midbrain = cerebellum ≧ hippocampus>neocortex = anterior thalamus>posterior thalamus ⋙ white matter. This distribution closely corresponds to the reported activity of both enzymatic cholinergic presynaptic markers and high‐affinity choline uptake in mammalian brain. There are no significant differences between these results and those previously found in the rat brain using this radioligand. Our results demonstrate, for the first time, the presence of [3H]hemicholinium‐3 binding sites in human brain and strongly support the proposal that this radioligand binds to the carrier site mediating the high‐affinity choline uptake process on cholinergic neurons. Thus, [3H]hemicholinium‐3 binding may be used in postmortem human brain as a selective and quantifiable marker of the presyn

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb02321.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY