bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of Monoamine Oxidase Selectively in Brain Monoamine Nerves Using the Bioprecursor (E‐β‐Fluoromethylene‐m‐Tyrosine (MDL 72394), a Substrate for Aromatic L‐Amino Acid Decarboxylase
Authors: Palfreyman Michael G. , McDonald Ian A. , Fozard John R. , Mely Yves , Sleight Andrew J. , Zreika Monique , Wagner Joseph , Bey Philippe , Lewis Peter J.
Published: October 2006

Abstract: (E)‐β‐Fluoromethylene‐m‐tyrosine (FMMT) is a dual‐enzyme‐activated inhibitor of monoamine oxidase (MAO). The compound is not an inhibitor per se but is decarboxylated by aromatic L‐amino acid decarboxylase (AADC) to yield a potent enzyme‐activated irreversible inhibitor of MAO, (E)‐β‐fluoromethylene‐m‐tyramine, which shows some selectivity for inhibition of MAO type A. Decarboxylation of FMMT was demonstrated in vitro using hog kidney AADC and in vivo in rats by the ability of α‐monofluoromethyldopa (MFMD), a potent inhibitor of AADC, to prevent MAO inhibition produced by FMMT. In isolated synaptosomes. FMMT was decarboxylated by AADC, and, furthermore, the compound was actively transported into these isolated nerve endings. An active transport into the CNS has also been demonstrated in vivo by performing competition experiments with leucine. To demonstrate that FMMT is preferentially decarboxylated within monoamine nerves of the CNS, the nigrostriatal 3,4‐dihydroxyphenylethylamine (dopamine) pathway of rats was unilaterally lesioned with 6‐hydroxydopamine or infused with MFMD. Under these conditions, MAO inhibition produced by orally administered FMMT in the striatum ipsilateral to the lesion or infusion was markedly attenuated. Combination of FMMT with an inhibitor of extracerebral AADC, such as carbidopa, protected peripheral organs against the MAO inhibitory effects and concomitantly enhanced MAO inhibition in the CNS. Such combinations had a greatly reduced propensity to augment the cardiovascular effects of intraduodenally administered tyramine, when compared with FMMT given alone or with clorgyline, a selective inhibitor of MAO type A. The results obtained with FMMT suggest the possibility of achieving selective inhibition of MAO within monoamine nerves of the CNS and, further, suggest that combination of FMMT with an inhibitor of extracerebral AADC will reduce the propensity of this inhibitor to produce adverse interactions with tyramine.
Subcellular Site of Action of Imipramine in Rodent Brain
Authors: Wood Martyn D. , Wyllie Michael G.
Published: October 2006

Abstract: To determine the site of action of imipramine, the subcellular distribution of [3H]imipramine in rodents was followed after both in vivo administration and in vitro incubation with tissue slices under “physiological” conditions. Total [3H]imipramine (10–1,000 nM) binding was associated with all primary fractions, but in particular with the nuclear (P1) and mitochondrial (P2) pellets and the synaptosomal (P2B) and myelin (P2A) fractions; Using an excess of imipramine to define any nonspecific interactions, a specific association was observed mainly in those fractions containing isolated nerve terminals and to a lesser extent with the purified myelin fraction. Preparation of subsynaptosomal fractions by osmotic lysis indicated that [3H]imipramine was associated with the synaptic vesicle and microsomal fractions and also with synaptosomal membranes. The degree of binding to the vesicular and microsomal fractions was increased with the length of preparation time, whereas there was an inverse relationship between the length of preparation and the amount bound to the synaptosomal membrane fraction. There was no evidence of an intrasynaptosomal accumulation of [3H]imipramine at concentrations up to 1,000 nM. [3H]2‐Nitroimipramine, a slowly dissociating imipramine derivative, was exclusively located in synaptic membrane fractions. Prior treatment of rats with a combination of 5,7‐dihydroxytryptamine and desipramine reduced 5‐hydroxytryptamine levels and the levels of [3H]imipramine associated with the synaptosomal fractions to the same extent. It is concluded that imipramine is associated with a binding site localised on 5‐hydroxytryptaminergic nerve terminals and that there is a redistribution to other sites (vesicular and microsomal) during the isolation procedure.
Dopaminergic Regulation of Cone Retinomotor Movement in Isolated Teleost Retinas: II. Modulation by γ‐Aminobutyric Acid and Serotonin
Authors: Dearry Allen , Burnside Beth
Published: October 2006

Abstract: In the accompanying paper we reported that 3,4‐dihydroxyphenylethylamine (dopamine) induced light‐adaptive retinomotor movements in teleost photoreceptors and that this effect was mediated by D2 dopamine receptors located on the photoreceptors them‐selves. In this study, we investigated the effects on cone retinomotor movement of three agents that have been reported by others to modulate retinal dopamine release: γ‐aminobutyric acid (GABA), 5‐hydroxytryptamine (5HT, serotonin), and melatonin. We report here that the GABA antagonists bicuculline and picrotoxin induced light‐adaptive cone contraction in dark‐adapted green sunfish retinas cultured in constant darkness; thus they mimic the effect of light or exogenously applied dopamine. Since their effects were blocked by either the D2 dopamine antagonist sulpiride or by Co2+, it seems likely that these agents act by enhancing retinal dopamine release. The GABA agonist muscimol produced effects opposite to those of GABA antagonists. Muscimol inhibited light‐induced cone contraction in previously darkadapted retinas and induced dark‐adaptive cone elongation in light‐adapted retinas. These results suggest that in green sunfish retinas, as has been reported for other retinas, GABA inhibits dopamine release. 5‐HT induced light‐adaptive cone contraction in dark‐adapted retinas; thus 5‐HT also mimics the effect of light or exogenously applied dopamine. The effect of 5‐HT was blocked by sulpiride, Co2+, or the 5‐HT antagonist mianserin. These results suggest that 5‐HT induces cone contraction by stimulating dopamine release. Melatonin neither inhibited dopamine‐induced cone contraction in retinas cultured in the dark nor induced cone elongation in retinas cultured in the light. Our results suggest that both GABA and 5HT (but not melatonin) affect cone retinomotor movements in green sunfish by modulating dopamine release: GABA by inhibiting and 5‐HT by stimulating dopamine release. We report in the companion paper that dopamine induced contraction in isolated cone fragments. Together these observations strongly suggest that dopamine serves as the final extracellular messenger directly inducing light‐adaptive cone retinomotor movement, and that GABA and 5‐HT affect these movements by modulating dopamine release.
Excitatory Amino Acid Neurotransmitters in the Corticostriate Pathway: Studies Using Intracerebral Microdialysis In Vivo
Authors: Young A. M. J. , Bradford H. F.
Published: October 2006

Abstract The concentration of extracellular excitatory amino acids in the striatum of conscious, unrestrained rats was measured using intracerebral microdialysis, during chemical stimulation of the striatum in intact and hemidecorticate animals. Chemical stimulation of the striatum with tityustoxin (0.1 μM) evoked a rise in dialysate concentration of glutamate (to 383% of basal) and aspartate (to 156% of basal), accompanied by a drop in glutamine (to 55% of basal). These changes showed significant attenuation after treatment with L‐proline (1 mM) or 2‐chloroadenosine (15 μM). Unilateral degeneration of the corticostriate pathway, produced by frontal hemidecortication, caused a reduction in both basal and stimulated levels of glutamate in the lesioned side, whereas no effect was observed in the intact side. Similarly, basal and stimulated levels of glutamine were unchanged in the intact side, but were increased in the lesioned side. These results provide in vivo evidence for glutamate and possibly aspartate being neurotransmitters in the corticostriate pathway. In addition they lend support to previous studies in vitro, which implicated glutamine as the principal precursor for neurotransmitter glutamate.
Specific Insulin‐Mediated Regulation of Glutamine Synthetase in Cultured Chick Astroglial Cells
Authors: Tholey G. , Sena A. H. , Ledig M.
Published: October 2006

Abstract The expression of glutamine synthetase (GS; L‐glutamate ammonia ligase; EC 6.3.1.2) in primary cultures of chick astroglial cells and neurons grown in a chemically defined medium, with and without insulin added, was investigated. An inhibitory effect of insulin toward GS activity, and specific to chick astroglial cells, was observed. Neurons in culture were not sensitive to the hormone effect. Modulation of the activating effect of hydrocortisone onglial GS by insulin was also observed. The data suggest that insulin contributes to the regulation of the metabolism of amino acid neurotransmitters via its effect on GS.
Identity Between Cytoplasmic and Membrane‐Bound S‐100 Proteins Purified from Bovine and Rat Brain
Authors: Donato Rosario , Prestagiovanni Bruno , Zelano Giovanni
Published: October 2006

Abstract: Cytoplasmic and membrane‐bound S‐100 proteins were purified to homogeneity from bovine and rat brain. Cytoplasmic and membrane‐bound S‐100 from single species are identical by immunological, electrophoretic, spectrophotometric, and functional criteria. Cytoplasmic and membrane‐bound S‐100 from bovine brain consists of nearly equal amounts of S‐100a and S‐100b, whereas cytoplasmic and membrane‐bound S‐100 from rat brain consists mostly of S‐100b. The functional role of membrane‐bound S‐100 remains to be elucidated.
Amino Acid Neurotransmitters in the CNS: Properties of Diaminobutyric Acid Transport
Authors: Erecińska Maria , Troeger Melody B. , Alston Theodore A.
Published: October 2006

Abstract: Uptake of L‐2,4‐diaminobutyric acid (DABA), a positively charged analogue of γ‐aminobutyric acid (GABA), by a synaptosomal fraction isolated from rat brain occurred with a Km of 54 ± 12 μM and a Vmax of 1.3 ± 0.2 nmol/min/mg protein. The transport of DABA was inhibited competitively by GABA whereas that of GABA was affected in the same manner by addition of DABA. The maximal accumulation of DABA ([DABA]i/[DABA]e) was observed to increase as the second power of the transmembrane electrical potential ([K+]i/[K+]e) and the first power of the sodium ion concentration gradient. These findings indicate that DABA is transported on the GABA carrier with a net charge of + 2, where one charge is provided by the cotransported Na+ and the second is contributed by the amino acid itself. Since uptake of GABA, an electroneutral molecule, is accompanied by transfer of two sodium ions, the results obtained with DABA suggest that one of the sodium binding sites on the GABA transporter is in proximity to the amino acid binding site.
Veratridine‐Stimulated Release of Amine Conjugates from Centrifugal Fibers in the Limulus Peripheral Visual System
Authors: Battelle B‐A. , Evans J. A.
Published: October 2006

Abstract: Centrifugal fibers that originate in the brain and project to the Limulus peripheral visual system synthesize and store octopamine and conjugates of octopamine and tyramine. In a previous study we showed that depolarization, induced by elevating extracellular K+, stimulated a preferential release of octopamine from these fibers. Here we show that veratridine‐induced depolarization stimulates a rapid, transient release of octopamine and a delayed, sustained release of amine conjugates. Veratridine‐stimulated release of both octopamine and amine conjugates depends on the influx of extracellular Ca2+ and is blocked by tetrodotoxin or the absence of extracellular Na+. The depolarization‐stimulated release of amine conjugates raises the possibility that these molecules serve as intercellular messengers in the Limulus peripheral visual system.
A Rapid Method for Purification of Myelin Basic Protein
Authors: Bellini Tiziana , Rippa Mario , Matteuzzi Maurizio , Dallocchio Franco
Published: October 2006

Abstract: A rapid procedure for purification of myelin basic protein has been developed. White matter is delipidated with 2‐butanol, and the residue is extracted at pH 7.5 and 8.5. Myelin basic protein is solubilized by extraction in acetate buffer, pH 4.5. The entire procedure requires less than 4 h, and gives homogeneous protein essentially free of protease activity. This procedure can be scaled down to process milligram amounts of white matter; thus it can be very useful for purification of myelin basic protein from very limited amounts of human white matter obtained during surgery.
Rat 3‐Hydroxyanthranilic Acid Oxygenase: Purification from the Liver and Immunocytochemical Localization in the Brain
Authors: Okuno Etsuo , Kohler Christer , Schwarcz Robert
Published: October 2006

Abstract:3‐Hydroxyanthranilic acid oxygenase (3HAO; EC 1.13.11.6). the biosynthetic enzyme of the endogenous excitotoxin quinolinic acid, was purified to homogeneity from rat liver and partially purified from rat brain. The pure enzyme is a single subunit protein with a molecular weight of 37–38.000. Kinetic analyses of both pure liver and partially purified brain 3HAO revealed an identicalKmof 3 μMfor the substrate 3‐hydroxyanthranilic acid. Evidence for the identity of liver and brain 3HAO was further provided by physicochemical (electrophoretic behavior, heat sensitivity) and biochemical (pH dependency, activation by Fe2+) means. Antibodies were produced against the pure liver enzyme and the identity of liver and brain 3HAO substantiated immunologically in immunotitration and Ouchterlony double‐diffusion experiments. Immuhohistochemical studies using purified anti‐rat 3HAO antibodies were performed on tissue sections of perfused brains and demonstrated a preferential staining of astroglial cells. Notably, the cellular localization of 3HAO in the brain appears to be in part distinct from that of quinolinic acid phosphoribosyltransferase, the catabolic enzyme of quinolinic acid. Pure rat 3HAO and its antibodies can be expected to constitute useful tools for the further elucidation of the brain's quinolinic acid system.
Free Amino Acid Content of Astroglial Cell Clones Derived from 8‐Day Postnatal Mouse Cerebella
Authors: Cambier Danièle , Pessac Bernard
Published: October 2006

Abstract: We have measured the free amino acid content of three distinct astroglial cell clones derived from permanent lines obtained after “spontaneous immortalization” of 8‐day postnatal mouse cerebellar cultures; these clones show characteristics similar to the Golgi Bergmann glia cells, the fibrous astrocytes, and the velate protoplasmic astrocytes, i.e., the three main types of cerebellar astrocytes. The relative concentrations of amino acids that are thought to act as neurotransmitters were compared in confluent cultures of the different astroglial clones. The most striking result was a high concentration of glycine (20% of free amino acids), even in astroglial cells cultured in a glycine‐free medium, a finding suggesting that glycine is synthesized by the astroglial clones. Furthermore, no γ‐aminobutyric acid (GABA) was detected. In contrast, a “neuron‐like” clone derived from the same cerebellar culture contained GABA, whereas its glycine content was much lower than that of the astroglial clones. The present results, together with our previous finding of glycine synthesis in an astrocytic clone derived from 14‐day postnatal mouse cerebella transformed by simian virus 40, indicate that a high glycine content may be characteristic of many cerebellar astroglial types.
Characterization of the Dihydropyridine Binding Sites of Rat Neocortical Synaptosomes and Microvessels
Authors: Dooley David J. , Mahlmann Horst , Brenner Otto , Osswald Hartmut
Published: October 2006

Abstract: The dihydropyridine binding sites associated with rat neocortical synaptosomes and microvessels were compared using an in vitro [3H]PN 200–110 [(+)‐[methyl‐3H]‐isopropyl 4‐(2,1,3‐benzoxadiazol‐4‐yl)‐1,4‐dihydro‐2,6‐di‐methyl‐5‐methoxycarbonylpyridine‐3‐carboxylate] binding assay. Saturation experiments yielded similar KD values (∼70 pM) and Bmax values (∼400 fmol/mg of protein) for the two membrane preparations. Interaction experiments with [3H]PN 200–110 and various calcium‐modulating substances provided further evidence for the practically identical nature of the synaptosomal and microvascular dihydropyridine binding sites. These findings predict that lipophilic dihydropyridines, simultaneously occupying the two central binding sites, have the dual effect of altering neuronal function and local blood flow.
Acetylcholine Content in Rat Brain Is Elevated by Status Epilepticus Induced by Lithium and Pilocarpine
Authors: Jope Richard S. , Simonato Michele , Lally Kathleen
Published: October 2006

Abstract: The effects of status epilepticus on the concentration, synthesis, release, and subcellular localization of acetylcholine, the concentration of choline, and the activity of acetylcholinesterase in rat brain regions were studied. Generalized convulsive status epilepticus was induced by the administration of pilocarpine to lithium‐treated rats. The concentration of acetylcholine in the cortex, hippocampus, and striatum decreased prior to the onset of spike activity or status epilepticus. Once status epilepticus began, the concentration of acetylcholine increased over time in the cortex and hippocampus, reaching peak levels that were 461% and 304% of control levels, respectively, after 2 h of seizures. Such high in vivo levels of acetylcholine had not been reported previously following any treatment. During status epilepticus, the concentration of acetylcholine in the striatum returned to control levels after the initial depression, but did not accumulate to high levels as it did in the other two regions. The in vivo cortical efflux of acetylcholine was also increased during the seizures. Choline levels were increased by status epilepticus in all three brain regions. Inhibition of seizures by pretreatment with atropine blocked the increases of acetylcholine and choline. Synaptosomes prepared from the cortex and from the hippocampus of rats with status epilepticus had elevated concentrations of acetylcholine: in the hippocampus the acetylcholine was principally in the cytoplasmic fraction, whereas in the cortex the acetylcholine was elevated in both the cytoplasmic and the vesicular fractions. The extra acetylcholine was in a releasable compartment, since increased K+ in the media or ouabain increased the release of acetylcholine from cortical slices to a greater extent in tissue from seized rats than from controls. The activity of acetylcholinesterase was not reduced by status epilepticus. These findings demonstrate that status epilepticus induced by lithium and pilocarpine alters the regulation of acetylcholine synthesis.
A Single Nucleotide Difference in the Gene for Myelin Proteolipid Protein Defines the Jimpy Mutation in Mouse
Authors: Nave †Klaus‐Armin , E. Bloom, Floyd , J. Milner Robert
Published: October 2006

We have previously shown that, in the myelin‐deficient jimpy mutant mouse, 74 nucleotides are absent from the mRNA for proteolipid protein (PLP) as a result of aberrant RNA processing. To define the exact site of the jimpy mutation, we have analyzed the PLP gene obtained from a jimpy mouse genomic library. We find that the nucleotide sequence that is absent from jimpy PLP mRNA is fully preserved in the jimpy PLP gene. The missing segment corresponds to a separate exon, equivalent to exon 5 of the human PLP gene. The nucleotide sequence at the 3’end of intron 4 in the jimpy PLP gene contains a single point mutation. A base change A → G in the 3’acceptor splice site has altered a position that is 100% conserved in all published splice acceptor sequences. We conclude that the primary genetic defect of the jimpy mouse is a single base change in the PLP gene disabling an invariant recognition sequence of RNA splicing.
Ionic Mechanisms Implicated in the Stimulation of Cerebellar Cyclic GMP Levels by N‐Methyl‐D‐Aspartate
Authors: Carter C. J. , Scatton F. Noel B.
Published: October 2006

Abstract: N‐Methyl‐D‐aspartate (NMDA) increases cyclic GMP levels in immature rat cerebellar slices incubated in magnesium‐containing Krebs buffer in vitro. This effect is blocked by 2‐amino‐5‐phosphonovalerate and by D‐α‐aminoadipate, but not by glutamic acid diethyl ester or 7–0‐glutamylaminomethylsulfonic acid, indicating specific involvement of the NMDA receptor. The response produced by NMDA is abolished by removal of calcium from the medium, proportional to the concentration of extracellular calcium, and blocked by a number of inorganic (Ni2+, Co2+, Cd2+, La3+, Mn2+) calcium antagonists. The responses to NMDA are not blocked by barium or strontium and persist when these ions are substituted for calcium in the incubation medium. The effects of NMDA are blocked by, but are not particularly sensitive to, the organic voltage‐dependent calcium channel antagonists. Nifedipine (10 μM) produces partial inhibition of the effects of NMDA, which are also antagonized by high (>200 μM) concentrations of diltiazem and verapamil. The effects of NMDA are tetrodotoxin insensitive but are abolished by omission of sodium from the medium and inhibited by a tetrodotoxin‐insensitive sodium channel blocker, Zn2+. The results suggest that calcium channel opening is a consequence of NMDA receptor activation in this model. However, the sodium dependence of the response argues against the use of receptor‐operated calcium channels, whereas the weak activity of the organic voltage‐sensitive calcium channel antagonists argues either against the use of voltage‐dependent calcium channels, or that those implicated in the effects of NMDA are insensitive to these agents. The combined sodium and calcium dependence of the response, and the apparent lack of involvement of either receptor‐operated or voltage‐dependent calcium channels, might alternatively reflect the use of sodium‐dependent calcium influx, initially triggered by NMDA‐induced sodium entry.
Effect of Exogenous Gangliosides on Amino Acid Uptake and Na+,K+‐ATPase Activity in Superior Cervical and Nodose Ganglia of Rats
Authors: Nagata Yutaka , Ando Masato , Iwata Mitsuyoshi , Hara Atsushi , Taketomi Tamotsu
Published: October 2006

Abstract: The effects of some gangliosides on active uptake of nonmetabolizable a‐aminoisobutyric acid (AIB) and Na+,K+‐ATPase and Ca2+,Mg2+‐ATPase activities in superior cervical ganglia (SCO) and nodose ganglia (NG) excised from adult rats were examined during aerobic incubation at 37°C for 2 h. In NG, amino acid uptake was greatly acceler‐a.ed with addition of galactosyl‐N‐acetylgalactosaminyl‐[N‐acetylneuraminyl]‐galactosylglucosyl ceramide (GM1) (85%) and also with N‐acetylgalactosaminyl‐[N‐acetylneuraminyl]‐galactosylglucosyl ceramide (GM2) or [N‐acetylneuraminyl]‐galactosyl‐N‐acetylgalactosaminyl‐[N‐acetylneuraminyl]‐galactosylglucosyl ceramide (GD1a) (43% each) compared with a nonaddition control at a 5 nM concentration. Under identical conditions, Na+,K+‐ATPase activity was strongly stimulated with GM1 (180%) and GD1a (93%), whereas Ca,Mg2+‐ATPase activity showed no change. In SCG, on the other hand, AIB uptake was apparently inhibited (‐27%) by addition of GM1, with a slight decrease in Na+,K+‐ATPase but no change in Ca2+,Mg2+‐ATPase activity in the tissue. Both asialo‐GM1, in which W‐acetylneuraminic acid is deficient, and Forssman glycolipid, which is not present in nervous tissue, failed to produce any significant increase in both SCG and NG not only in amino acid uptake, but also in Na+,K+‐ATPase activity. A kinetic study of active AIB uptake showed that GM1 ganglioside produced an increase in Km with no change in Vmax in SCG, whereas it caused a decrease in Km with a slight increase in Vmax in NG. Treatment of NG and SCG with neuraminidase from Vibrio cholerae, an enzyme that split off sialic acid from polysialoganglioside, leaving GM1 intact, caused little inhibition of the amino acid uptake. GM1‐evoked amino acid uptake increase in NG and decrease in SCG seem both to be independent of the effect of nerve growth factor (NGF). Glia maturation factor (GMF)‐induced AIB uptake was further increased by GM1 application in NG. These results suggest that exogenous brain gangliosides may modulate membrane transport of amino acid by processes somewhat different from those of NGF or GMF, with or without affecting the activity of a transport enzyme, Na+,K+‐ATPase.
Time Course of Adaptations in Dopamine Biosynthesis, Metabolism, and Release Following Nigrostriatal Lesions: Implications for Behavioral Recovery from Brain Injury
Authors: Altar C. Anthony , Marien Marc R. , Marshall John F.
Published: October 2006

Abstract: Alterations in neostriatal dopamine metabolism, release, and biosynthesis were determined 3, 5, or 18 days following partial, unilateral destruction of the rat nigrostriatal dopamine projection. Concentrations of dopamine and each of its metabolites, 3,4‐dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 3‐methoxytyra‐mine (3‐MT) were markedly decreased in the lesioned stri‐ata at 3, 5, or 18 days postoperation. The decline in striatal high‐affinity [3H]dopamine uptake closely matched the depletion of dopamine at 3 and 18 days postoperation. However, neither DOPAC, HVA, nor 3‐MT concentrations were decreased to as great an extent as dopamine at any time following lesions that depleted the dopamine innervation of the striatum by >80%. In these more severely lesioned animals, dopamine metabolism, estimated from the ratio of DOPAC or HVA to dopamine, was increased two‐ to fourfold in the injured hemisphere compared with the intact hemisphere. Dopamine release, estimated by the ratio of 3‐MT to dopamine, was more increased, by five‐ to sixfold. Importantly, the HVA/dopamine, DOPAC/dopamine, and 3‐MT/dopamine ratios did not differ between 3 and 18 days postlesioning. The rate of in vivo dopamine biosynthesis, as estimated by striatal DOPA accumulation following 3,4‐dihydroxyphenylalanine (DOPA) decarboxylase inhibition with NSD 1015, was increased by 2.6‐ to 2.7‐fold in the surviving dopamine terminals but again equally at 3 and 18 days postoperation. Thus, maximal increases in dopamine metabolism, release, and biosynthesis occur rapidly within neostriatal terminals that survive a lesion. This mobilization of dopaminergic function could contribute to the recovery from the behavioral deficits of partial denervation by increasing the availability of dopamine to neostriatal dopamine receptors. However, these presynaptic compensations are not sufficient to account for the protracted (at least 3‐week) time course of sensorimotor recovery that has been observed following partial nigrostriatal lesion.
Dissociation of the Stellate Morphology from Intracellular Cyclic AMP Levels in Cultured Rat Brain Astroglial Cells: Effects of Ganglioside GMl and Lysophosphatidylserine
Authors: Facci Laura , Skaper Stephen D. , Levin David L. , Varon Silvio
Published: October 2006

Abstract: Secondary microcultures of newborn rat cerebrum astroglial (AG) cells, maintained in a serum‐free, chemically defined medium, were treated with various agents known to elevate intracellular cyclic AMP (cAMP) levels. Earlier studies had shown these drugs to induce a process‐bearing (stellate) morphology in the AG cells, a response that was antagonized by the presence of gangliosides. One millimolar dibutyryl cyclic AMP (dBcAMP), 10 μM forskolin, 12 nM cholera toxin, and 30 μM isoproterenol all raised intracellular cAMP levels, from basal values of 3 pmol/106 cells to 30–30,000 pmol/106 cells, depending on the agent tested. dBcAMP caused the greatest elevation, and forskolin the least. The timing and/or the level of the AMP response did not precisely correlate with those of the stella‐tion response. Values of ED50 with the four agents, as determined for the cAMP response, were always higher than stellation ED50 values in all treatments, and ED50 did not correlate with the maximal levels of cyclic AMP induced by the four agents. The capacity of ganglioside GMl to block the stellation response to the four agents was not accompanied by a similar capacity to block the cAMP responses. Lysophosphatidylserine (lysoPS) had the capacity to induce AG cell stellation as well, without altering the basal level of cAMP. Both lysoPS and gangliosides, therefore, may act directly on the cellular machinery underlying the stellation response without involving changes in intracellular AMP.
Active Site Studies on a Narrow‐Specificity Thyroliberin‐Hydrolysing Pyroglutamate Aminopeptidase Purified from Synaptosomal Membrane of Guinea‐Pig Brain
Authors: O'Connor Brendan , O'Cuinn Gerard
Published: October 2006

Abstract: The effect of protein‐modifying reagents on the activity of a purified preparation of a thyroliberin‐hydrolysing pyroglutamate aminopeptidase, solubilised from synaptosomal membranes of guinea‐pig brain by treatment with papain, was investigated. The results indicated that tyrosine, histidine, arginine, and possibly lysine residues were necessary for expression of catalytic activity and that these tyrosine, histidine, and arginine residues were probably located at the active site of the enzyme. Cysteine, serine, glutamate, and aspartate residues were not involved in the expression of catalytic activity.
The Acute Effect of Ammonium Acetate on Levels of Amino Acids in the Intact and Decorticated Rat Neostriatum
Authors: Engelsen Bernt A. , Fosse Viggo M. , Fonnum Frode
Published: October 2006

Abstract: Unilateral frontal cortex ablations were performed in rats so that the glutamate terminals in the ipsilateral rostral neostriatum were removed. At 1 or 7 days later, intraperitoneal injections of ammonium acetate induced different changes in amino acid concentrations in the intact and deafferentated neostriatum. After 1 day, the level of glutamate decreased only in the intact side, whereas that of glutamine increased and that of aspartate decreased to the same extent on both sides following ammonia injection. After 7 days, the glutamate level decreased more in the intact than the decorticated side in both nonconvulsing and convulsing rats. The concentration of alanine increased most in the intact neostriatum, whereas glutamine levels increased and aspartate levels decreased to the same extent on both sides in nonconvulsing and convulsing rats. The results indicate that ammonia has a more pronounced effect on neuronal than glial glutamate pools.
Control of the Amount of a 34K Ca2+‐Dependent Membrane Binding Protein (Calelectrin)
Authors: Saitoh Tsunao , Miret Odile
Published: October 2006

Abstract: A 34,000‐Da Ca2+‐dependent membrane binding protein (34K) was purified from the electric organ of Torpedo marmorata. Specific antibodies to this protein were raised in rabbits, and radioimmunoassay was used to test the presence of 34K in different tissues of Torpedo as well as in other species. In Torpedo, not only the electric organ, but also the muscle, the spleen, and the liver contained 34K antigenicity. Blood was the only tissue in which 34K antigenicity could not be detected. A 34,000‐Da protein (Mr 32,000–36,000) that bound to Torpedo acetylcholine receptor (AChR)‐rich membrane in a Ca2+‐dependent manner and cross‐reacted with anti‐(Torpedo 34K) antibody was found in chicken muscle, rat muscle, marine mollusk (Aplysia) central ganglia, and rat and human brain. The concentration of 34K seems to be controlled during development. Chicken 34K antigenicity reached a peak on embryonic day 18, declined, and finally gained its maximal value after synaptic maturation. The AChR concentration in chicken legs also changed in the course of muscle development, although it showed a peak on embryonic day 12 and then declined rapidly. In rat diaphragm, both AChRs and 34K were concentrated in the subsynaptic region. Transection of the phrenic nerve induced the synthesis of AChRs in postsynaptic muscle fibers. This operation did not increase the amount of 34K in the diaphragm. On the contrary, it reduced 34K content to the extrasynaptic level. Taken together, these results support the idea that 34K is an important structural constituent of mature synapses, an observation suggesting the involvement of this protein in the function of the mature synapse.
Stimulation of Inositol Phosphate Production by Neurotensin in Neuroblastoma N1E115 Cells: Implication of GTP‐Binding Proteins and Relationship with the Cyclic GMP Response
Authors: Amar Shimon , Kitabgi Patrick , Vincent Jean‐Pierre
Published: October 2006

Abstract: The association of neurotensin to its receptor in differentiated neuroblastoma N1E115 cells led to a fast and transitory increase of the intracellular concentration in inositol trisphosphate and inositol bisphosphate, followed by a slower and more stable increase in inositol monophosphate. The action of inositol 1,4,5‐trisphosphate on digitonin‐permeabilized N1E115 cells resulted in a stimulation of cyclic GMP levels that mimicked that induced by neurotensin. Therefore, the cyclic GMP stimulation is probably a consequence of the initial inositol trisphosphate formation triggered by neurotensin. Fluoroaluminate ions and pertussis toxin had the capacity to modulate positively and negatively, respectively, the formation of inositol trisphosphate induced by neurotensin, indicating that GTP‐binding proteins are involved in the regulation of inositol phosphate levels by neurotensin receptors.
Relationships Among ATP Synthesis, K+ Gradients, and Neurotransmitter Amino Acid Levels in Isolated Rat Brain Synaptosomes
Authors: Dagani Fiorenzo , Erecinska Maria
Published: October 2006

Correlations were made among ATP synthesis, transmembrane K+ gradients, and leakage of three amino acid neurotransmitters, γ‐aminobutyric acid (GABA), aspartate, and glutamate, in rat brain synaptosomes incubated under normoxic and respiration‐limited conditions. Even under normoxic conditions, a substantial proportion of total ATP synthesis (8%) was provided by glycolysis. Limitation of respiration by ∼30% through addition of amobarbital (Amytal) caused a twofold decrease in the cre‐atine phosphate/creatine ([CrP]/[Cr]) ratio, and consequently the [ATP]/[ADP] ratio, and a threefold increase in lactate production. There was a detectable decrease in intracellular [K+] and small rises in external GABA, aspartate, and glutamate concentrations. More severe limitations in ATP synthesis caused larger declines in the [CrP]/[Cr] ratio and progressive leakage of K+ and neurotransmitter amino acids. A comparison of ΔGATP and ΔGNa,k showed the former to be larger by 6 kcal, which indicates that the plasma membrane Na+/K+ pump operates at far from equilibrium. Under respiration‐limited conditions, even when total ATP synthesis decreased by ∼80% and [ATP] declined to <0.4 mM ΔGATP was still larger than ΔGNa,k. It is suggested that during hypoxia and ischemia, the activity of the plasma membrane Na+/K+ pump in brain becomes limited by [ATP], which falls below the Am value for the low‐affinity regulatory site on the enzyme. This failure of the pump and consequent collapse of the ion gradients may contribute to the leakage of neurotransmitter amino acids that occurs in these pathological states.
Influence of Dietary Choline Availability and Neuronal Demand on Acetylcholine Synthesis by Rat Brain
Authors: Wecker Lynn
Published: October 2006

Abstract: The main objective of this study was to test the hypothesis that the chronic administration of choline supplements a bound pool of choline from which free choline can be mobilized and used to support acetylcholine synthesis when the demand for precursor is increased. For these experiments, brain slices from rats fed diets containing different amounts of choline were incubated in a choline‐free buffer and acetylcholine synthesis was measured under resting conditions and in the presence of K+‐induced increases in acetylcholine synthesis and release. Rats fed the choline‐supplemented diet had circulating choline levels that were 52% greater than the controls, and striatal and cerebral cortical slices from this group produced significantly more free choline during the incubation than slices from the controls. However, the synthesis and release of acetylcholine by these tissues did not differ from those by controls, during either resting or K+‐evoked conditions. In contrast, acetylcholine synthesis and release by striatal and hippocampal slices from choline‐deficient rats, animals that had circulating choline levels that were 80% of control values, decreased significantly; the production of free choline by these tissues was also depressed. Results indicate that, despite an increased production of free choline by brain slices from choline‐supplemented rats, the synthesis of acetylcholine was unaltered, even in the presence of an increased neuronal demand. In contrast, the choline‐deficient diet led to a decreased release of free choline from bound stores and an impaired ability of brain to synthesize acetylcholine.
Cyclic AMP Analogues Potentiate k‐Opiate and Attenuate α2‐Adrenoceptor Agonist Effects on Intrasynaptosomal Free Calcium
Authors: Adamson Peter , Brammer Michael J. , Campbell Iain C.
Published: October 2006

Abstract: The intrasynaptosomal free calcium concentration ([Ca2+]i) was measured in quin2‐loaded synaptosomes prepared from rat cerebral cortex. Membrane‐permeant cyclic adenosine‐3′,5′‐monophosphate (cAMP) analogues [8‐bromo‐cyclic adenosine‐3′,5′‐monophosphate (8‐Br‐cAMP) and dibutyryl‐cyclic adenosine‐3′,5′‐monophosphate (db‐cAMP)] increased [Ca2+]i in a dose‐dependent manner; The maximal increases were ˜50% for 8‐Br‐cAMP and 35% for db‐cAMP and occurred at ˜10 μM with both analogues. Clonidine (1 μM) alone reduced [Ca2+]i by 26.5%; db‐cAMP and 8‐Br‐cAMP attenuated this reduction to 14.2 and 8.2%, respectively. In contrast, the reduction (19.9%) in [Ca2+]i induced by the preferential k‐opiate agonist dynorphin A(1–13) was not attenuated by the cAMP analogues; in fact, db‐cAMP and 8‐Br‐cAMP potentiated the effect of dynorphin A(1–13) (1 μM), producing decreases in [Ca2+]i of 33.6 and 29.6%, respectively. We conclude that although aradrenergic and k‐opiate receptors both reduce [Ca2+]i, the α2‐adrenoceptor‐mediated response and the k‐opiate receptor‐mediated response involve different effector mechanisms. It appears that pre‐synaptic α2‐adrenoceptor agonist effects are linked to reductions in adenylate cyclase activity and cAMP production and a resultant increase in Ca2+ sequestration, Ca2+‐channel blockade, or both. On the other hand, the k‐opiate‐mediated effects possibly involve an increase in cAMP production and a blockade of Ca2+ entry.
Regulation of Myelin P0 Glycoprotein Synthesis in Cultured Rat Schwann Cells and Continuous Rat PNS Cell Lines
Authors: Kreider Barbara , Zeller Nancy , Lazzarini Robert , Shuman Sandra , Pleasure David
Published: October 2006

Abstract: We studied the effects of agents that raise intracellular cyclic AMP on synthesis of myelin components by cultured neonatal rat sciatic nerve Schwann cells and by continuous PNS cell lines derived from the fusion of neonatal rat sciatic nerve Schwann cells with rat RN22 Schwannoma. Treatment with N6,2′‐O‐dibutyryl cyclic AMP (dibutyryl cyclic AMP) caused a fourfold increase in Schwann cell incorporation of 35SO4 into sulfogalactosylceramide (sulfatide), and elicited a 10‐ to 20‐fold increase in such incorporation by the continuous PNS cell lines; a similar effect on PNS cell line sulfatide radiolabelling was obtained with forskolin. Cultured Schwann cells expressed barely detectable levels of myelin P0 glycoprotein (P0) mRNA and myelin basic protein (MBP) mRNA. Treatment of the Schwann cells with axolemmal fragments or with dibutyrylcyclic AMP did not elicit a detectable increase in the levels of these mRNAs. The PNS cell lines constitutively expressed much higher levels of P0 mRNA than did the Schwann cells, and synthesized immunochemically demonstrable P0 glycoprotein, but did not express MBP. Treatment of the PNS cell lines with dibutyryl cyclic AMP markedly reduced expression of P0 mRNA and also diminished immunoreactive P0 glycoprotein. These PNS cell lines should prove useful for further studies of the control of Schwann cell differentiation.
Angiotensin II‐Like Material Extracted from the Rat Brain Is Distinct from Authentic Angiotensin II
Authors: Pohl M. , Carayon A. , Cesselin F. , Hamon M.
Published: October 2006

Abstract: Specific radioimmunoassay and radioreceptor assay for angiotensin II (A II) were used for the possible identification of this peptide in the rat brain. An A II‐like material (A II‐LM) was detected with both assays applied to acidic extracts of various brain structures. The regional distribution of A II‐LM was uneven, but absolute levels (in A II equivalents) could not be accurately determined, as they were highly dependent on the assay used. Partial purification of A II‐LM by Sep‐Pak C 18 chromatography and affinity chromatography using anti‐A II antibodies bound to Ultrogel gave a compound coeluting with authentic A II in reverse‐phase HPLC. However, gel filtration through Sephadex G‐25 and TSK Spherogel 3000 SW as well as anion exchange HPLC demonstrated that A II‐LM did not correspond to authentic A II. Partial characterization of A II‐LM indicated that this compound was probably a peptide with an apparent molecular weight of 5,000–7,000 (instead of 1,046 for A II) and more polar but less positively charged than A II. Whether A II‐LM is, in fact, the endogenous ligand of A II binding sites in brain remains an interesting hypothesis for further investigations.
Recovery from Edema and of Protein Synthesis Differs Between the Cortex and Caudate Following Transient Focal Cerebral Ischemia in Rats
Authors: Abe Koji , Araki Tsutomu , Kogure Kyuya
Published: October 2006

Abstract: Postischemic recovery from brain edema and of protein synthesis was examined following 1 h of middle cerebral artery (MCA) occlusion in rats. Recovery from brain edema and of protein synthesis showed a good correlation until 7 days after reperfusion in each area (cerebral cortex or lateral caudate) in the occluded MCA side. However, regional differences in the above types of recovery in the cortex and in the lateral caudate were found for the first time in this experiment. A profound inhibition of protein synthesis and formation of brain edema began sooner in the lateral caudate than in the cortex and continued long after reperfusion. Grades of cerebral blood flow during ischemia and the early period of reperfusion were almost the same in the two regions. Therefore, the regional differences in the above recoveries may not be due to the difference in the blood flow during ischemia and reperfusion, but may be partly attributable to the imbalance of excitatory and inhibitory innervation in the above two areas of the brain, may be due to a distinctive response to ischemic stress, and may be caused also by the potentiative effect of free arachidonate on the excitotoxic mechanism.
Dissociation Kinetics of [3H]Paroxetine Binding to Rat Brain Consistent with a Single‐Site Model of the Antidepressant Binding/5‐Hydroxytryptamine Uptake Site
Authors: Marcusson Jan , Eriksson Kristina
Published: October 2006

Abstract: The effects of 5‐hydroxytryptamine (5‐HT) and 5‐HT uptake inhibitors on the dissociation of [3H]paroxetine from rat brain membrane binding sites have been investigated. The dissociation induced by 5‐HT (100 μM), paroxetine (0.15 μM), clomipramine (1 μM), citalopram (1 μM), imipramine (1 μM), or norzimeldine (1 μM) was consistent with first‐order dissociation kinetics with half‐life values of dissociation (t1/2) between 130 and 140 min. The dissociation induced by the combination of 5‐HT (100 μM) with either citalopram (1 μM) or imipramine (1 μM) was not different from that initiated by either agent alone. These dissociation data, which are at variance with previous data on the 5‐HT transporter labeled with [3H]imipramine, support a single‐site model of the antidepressant binding/5‐HT uptake site.
Characterization of Dopamine and β‐Adrenergic Receptors Linked to Cyclic AMP Formation in Intact Cells of the Clone D384 Derived from a Human Astrocytoma
Authors: Balmforth Anthony J. , Yasunari Kenichi , Vaughan Peter F. T. , Ball Stephen G.
Published: October 2006

Abstract: 3,4‐Dihydroxyphenylethylamine (dopamine) and β‐adrenergic receptor agonists and antagonists were assessed for their effects on cyclic AMP accumulation in human astrocytoma derived clone D384 cells. Dopamine, SKP 38393, and 2‐amino‐6,7‐dihydroxy‐l,2,3,4‐tetrahydronaphthalene increased cyclic AMP content with Ka values of 2.0, 0.2, and 1.6 μM. The D1‐selective antagonists SCH 23390 (Ki, 1.2 nM) and SKF 83566 (Ki, 0.8 nM) were over 5,000‐fold more potent than the D2‐selective antagonist domperidone (Ki, 6.7 μM) at inhibiting dopamine stimulation of cyclic AMP formation. SCH 23388 (Ki, 560 nM; the S‐enantiomer of SCH 23390) was 400‐fold less potent than SCH 23390. Isopren‐aline, adrenaline, salbutamol, and noradrenaline increased cyclic AMP content with Ka values of 0.13, 0.12, 0.22, and 7.60 μM. The β2‐selective antagonist ICI 118,551 (Ki, 0.8 nM) was almost 8,000‐fold more potent than the β,‐selective antagonist practolol (Ki, 5.9 μM) at inhibiting isoprenaline stimulated cyclic AMP accumulation. These results demonstrate that D384 cells express D1‐dopamine and β2‐adren‐ergic receptors linked to adenylate cyclase. Furthermore, the dopamine receptor expressed by D384 cells exhibits a pharmacological profile typical of a mammalian striatal D1‐re‐ceptor and therefore the use of this clone represents another approach to studying central D1‐receptors.
Chronic Intracerebroventricular Infusion of Insulin Failed to Alter Brain Insulin‐Binding Sites, Food Intake, and Body Weight
Authors: Manin M. , Balage M. , Larue‐Achagiotis C. , Grizard J.
Published: October 2006

Abstract: The present study was performed to explore the role of exogenous insulin in CSF in the control of energy balance in the rat. For this purpose, adult male Sprague‐Dawley rats carrying an indwelling cannula in the right lateral cerebral ventricle were infused for a maximum of 10 days with insulin (Actrapid) at various rates (starting at 0, 45, 85, 170, and 600 ng/day) or anti‐insulin antibody (IgG fraction; diluted 1:10 wt/vol) with an osmotic minipump. All those treatments did not modify the growing rates; neither total daily food intake nor the circadian rhythm of food intake was further modified. The chronic insulin infusion starting at 600 ng/day resulted in a chronic significant increase in CSF insulin levels without changing the plasma insulin level. It failed to alter specific insulin binding sites to Triton X‐100 solubilized microsomal membranes from various brain areas (cerebral cortex, olfactory bulbs, and lateral and medial hypothalami) at the end of the 5‐or 10‐day period of insulin infusion. Purification of insulin receptors on a wheat germ agglutinin did not reveal any further effect of insulin. From these results, it seems unlikely that the input to the brain insulin‐effector systems could arise from CSF insulin.
High Ammonia Levels in Brain Induce Tubulin in Cerebrum but Not in Cerebellum
Authors: Miñana Maria‐Dolores , Felipo Vicente , Wallace Ruth , Grisolía Santiago
Published: October 2006

Abstract: Ingestion of large amounts of ammonium increases markedly the content of tubulin in brain. The effect on tubulin induction of ammonium ingestion for up to 100 days was investigated. Brain tubulin content showed a rapid initial increase (28%) at 2 days and reached 50% after 100 days on the diet. To discern if ammonia, the increase in urea synthesis, or both was responsible for tubulin induction, rats were maintained at several levels of uremia (by administering diets containing 0 to 80% protein) or in hyperammonemia (by urease treatment). Only ammonium administration in the diet and urease injection induced tubulin in brain. Tubulin was quantified in three different brain regions. There was a regional selectivity of tubulin induction by ammonia in rat brain. Whereas the cerebellum remained unaltered, the pa‐leencephalon showed the highest increase, and the cerebral cortex exhibited only a modest increase.