bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impaired Synthesis of Acetylcholine by Mild Hypoxic Hypoxia or Nitrous Oxide
Authors: Gibson Gary E. , Duffy Thomas E. 
Published: October 2006

Abstract:The effect of mild hypoxic hypoxia on brain metabolism and acetylcholine synthesis was studied in awake, restrained rats. Since many studies of hypoxia are done with animals anesthetized with nitrous oxide (N2O), the effects of N2O were evaluated. N2O (70%) increased the cerebral cortical blood flow by 33% and the cortical metabolic rate of oxygen by 26%. In addition, the synthesis of acetylcholine in N2O‐anesthetized animals, measured with [U‐14C]glucose and [1‐2H2,2‐2H2]choline, decreased by 45 and 53%, respectively. Consequently, mild hypoxia was studied in unanesthetized rats. Control rats breathing 30% O2 (partial pressure of oxygen, Pao2= 120 mm Hg) were compared with rats exposed to 15% O2 (Pao2= 57 mm Hg) or 10% O2 (Pao2= 42 mm Hg). The synthesis of acetylcholine, measured with [U‐14C]glucose, was decreased by 35 and 54% with 15% O2 and 10% O2 respectively; acetylcholine synthesis, measured with [1‐2H2,2‐2H2]choline, was decreased by 50 and 68% with 15% O2 and 10% O2 respectively. Animals breathing either 15% or 10% O2 had normal cerebral metabolic rates of oxygen but had increased brain lactates and increased cortical blood flows compared with animals breathing 30% O2. These results show that even mild hypoxic hypoxia impairs acetylcholine synthesis, which in turn may account for the early symptoms of brain dysfunction associated with hypoxia.
Microvessels Isolated from Rat Brain: Localization of Astrocyte Processes by Immunohistochemical Techniques
Authors: White Fredric P. , Dutton Gary R. , Norenberg Michael D. 
Published: October 2006

Abstract:Microvascular networks were isolated from rat telencephalon by density gradient centrifugation. The vessels prepared were characterized morphologically at the light and electron microscope level and immunohistochemically by the localization of glutamine synthetase and glial fibrillary acidic protein, two proteins found almost exclusively in astrocytes. The vast majority of the vessels prepared contained more than just endothelial cells surrounded by a basement membrane. Many arterioles were found still retaining their smooth muscle cells. Pericytes were found in association with most of the venules and many of the capillaries. Astrocyte processes remained attached to most of the microvessels. These results show that vessels prepared from rat brain still maintain most of their complex intercellular contacts and must be viewed as a heterogeneous network of cells.
Glutamate as a Putative Transmitter in the Cerebellum: Stimulation by GABA of Glutamic Acid Release from Specific Pools
Authors: Levi Giulio , Gallo Vittorio 
Published: October 2006

Abstract: The aim of the present paper was to determine whether the release of glutamate from putative “glutamergic” terminals in the cerebellum is influenced by γ‐aminobutyric acid (GABA). In a group of preliminary experiments, we present biochemical evidence in favour of a neurotransmitter role of glutamate in the cerebellum: (1) endogenous glutamate was released from depolarized cerebellar synaptosomal preparations in a Ca2+‐dependent way; (2) [14C]glutamate was synthesized from [14C]glutamine in cerebellar synaptosomes, and the newly synthesized [14C]glutamate was released in a Ca2+‐dependent way; (3) the elevation of cyclic GMP elicited by depolarization of cerebellar slices in the presence of Ca2+ was partly reversed by the glutamate antagonist glutamic acid diethyl ester, which probably prevented the interaction of endogenously released glutamate with postsynaptic receptors.GABA and muscimol at low concentrations (2‐20 μM) potentiated the depolarization‐induced release of D‐[3H]aspartate (a glutamate analogue which labels the glutamate “reuptake pool”) from cerebellar synaptosomes. The effect was concentration dependent and was largely prevented by two GABA antagonists, bicuculline and picrotoxin. The stimulation of D‐[3H]aspartate release evoked by muscimol was linearly related to the logarithm of K+ concentration in the depolarizing medium. GABA did not affect the overall release of endogenous glutamate, but potentiated, in a picrotoxin‐sensitive manner, the depolarization‐evoked release of [14C]glutamate previously synthesized from [14C]glutamine. Since nerve endings are the major site of glutamate synthesis from glutamine, GABA and muscimol appear to exert their stimulatory effect at the level of “glutamergic” nerve terminals, probably after interacting with presynaptic GABA receptors. The possible functional significance of these findings is briefly discussed.
Characterization of Separated Cell Types from the Developing Rat Cerebellum: Transport of Glutamate and Aspartate by Preparations Enriched in Purkinje Cells, Granule Neurones, and Astrocytes
Authors: Gordon R. D. , Balàzs R. 
Published: October 2006

Abstract:Preparations of structurally preserved cerebellar perikarya (cells) were found to express high‐affinity transport systems for glutamate but not for certain putative transmitter substances (including monoamines, glycine and taurine) and non‐transmitter amino acids. The characteristics of the high‐affinity glutamate transport system were similar to those of other preparations of brain tissue: [3H]glutamate uptake by the cells was Na+‐dependent and was inhibited competetively by other acidic amino acids. The rank order of apparent affinities of the carrier for acidic amino acids was L‐aspartate > L‐glutamate > D‐aspartate ≫ D‐glutamate (the affinity for D‐glutamate being over two orders of magnitude lower than for the other three amino acids). Comparison of high‐affinity [3H]glutamate uptake in preparations enriched in different cell types showed that although the affinities are similar (2‐4 fiM), the rate is outstandingly high in astrocytes (Vmax 18 nmol/min per mg protein). Significantly, uptake into the putatively glutamatergic granule cells was very low. These observations were supported by autoradiographic findings which showed that the predominant sites of [3H]glutamate uptake in cerebellar cultures enriched in interneurones are the astrocytes. Furthermore, the Vmax in cultures enriched in astrocytes was as high as that in separated astrocytes. Thus, it seems that the principal cell type involved in acidic amino acid uptake in the cerebellum is the astrocyte, and this must be taken into consideration when high‐affinity uptake is used as a marker for glutamatergic transmitter systems. Furthermore, the selective cellular distribution of glutamate transport sites, together with the uneven distribution of enzymes related to glutamate metabolism observed previously, indicates that a metabolic interaction takes place between the different cell types, supporting the current hypothesis on metabolic compartmentation in the brain.
Kainate‐Enhanced Release of d‐[3H]Aspartate from Cerebral Cortex and Striatum: Reversal by Baclofen and Pentobarbital
Authors: Potashner S. J. , Gerard D. 
Published: October 2006

Abstract:A study was made of the actions of the excitant neurotoxin, kainic acid, on the uptake and the release of d‐[2,3‐3H]aspartate (d‐ASP) in slices of guinea pig cerebral neocortex and striatum. The slices took up d‐ASP, reaching concentrations of the amino acid in the tissue which were 14–23 times that in the medium. Subsequently, electrical stimulation of the slices evoked a Ca2+‐dependent release of a portion of the d‐ASP. Kainic acid (10‐5‐10‐3M) produced a dose‐dependent inhibition of d‐ASP uptake. The electrically evoked release of d‐ASP was increased 1.6–2.0 fold by 10‐5 and 10‐4M kainic acid. The kainate‐enlarged release was Ca2+‐dependent. Dihydrokainic acid, an analogue of kainic acid with little excitatory or toxic action, did not increase d‐ASP release but depressed d‐ASP uptake. Attempts were made to block the action of kainic acid with baclofen and pentobarbital, compounds which depress the electrically evoked release of l‐glutamate (l‐GLU) and l‐aspartate (l‐ASP). Baclofen (4 × 10‐6M), an antispastic drug, and pentobarbital (10‐4M), an anesthetic agent, each inhibited the electrically evoked release of d‐ASP and prevented the enhancement of the release above control levels usually produced by 10‐4M kainic acid. It is proposed that 10‐5 and 10‐4M kainic acid may enhance the synaptic release of l‐GLU and l‐ASP from neurons which use these amino acids as transmitters. This action is prevented by baclofen and pentobarbital. In view of the possibility that cell death in Huntington's disease could involve excessive depolarization of striatal and other cells by glutamate, baclofen might be effective in delaying the loss of neurons associated with this condition.
Isoguvacine Binding, Uptake, and Release: Relation to the GABA System
Authors: White W. F. , Snodgrass S. R. 
Published: October 2006

Abstract:Isoguvacine (1,2,3,6‐tetrahydropyridine‐4‐car‐boxylic acid) is a GABA (γ‐aminobutyric acid) agonist with limited conformational flexibility. In these studies we investigated the binding, uptake, and release of [3H] isoguvacine by use of tissue preparations of rat CNS, comparing the results with similar studies of [3H]GABA. The results from these investigations indicate that isoguvacine binds to membrane preparations of rat forebrain with pharmacological characteristics similar to the post‐synaptic GABA recognition site; that it is transported into synaptosomal preparations by an uptake system similar to the high‐affinity GABA uptake system; and that recently accumulated isoguvacine is released in a Ca2+‐dependent manner and by heteroexchange with external GABA. The ability of isoguvacine and γ‐hydroxybutyric acid to decrease the K+‐stimulated Ca2+‐dependent release process was also investigated. The results indicate that isoguvacine interactions have many of the biochemical features of GABA synaptic function, isoguvacine being, however, less potent than GABA.
Interaction of N‐(2‐Nitro‐4‐Azidophenyl)‐Serotonin with Two Types of Monoamine Oxidase in Rat Brain
Authors: Chen Shiuan , Shih Jean C. , Xu Qin‐Ping 
Published: October 2006

AbstractThe effects of N‐(2‐nitro‐4‐azidophenyl) serotonin (NAP‐5‐HT) on types A and B monoamine oxidase (MAO) in rat brain cortex were studied. In the dark this compound acted as a competitive inhibitor for both types A and B MAO (K1 values of 0.19 μM and 0.21 μM for types A and B MAO, respectively). Upon photolysis, NAP‐5‐HT became an irreversible inhibitor for only type B MAO. A 50% inhibition was obtained by irradiation of the enzyme in the presence of 35 nM NAP‐5‐HT. Furthermore the inhibition of type B MAO could be protected by including its substrate phenylethylamine during the irradiation. Under the same photolytic conditions photodependent inhibition of type A MAO by NAP‐5‐HT was not clearly observed. These results provide further evidence that there is a fundamental difference in the active site of the two types of MAO in brain. NAP‐5‐HT may be a useful photoaffinity probe for characterizing the active site of type B MAO.
Effect of Age on Human Brain Serotonin (S‐1) Binding Sites
Authors: Marcusson Jan , Oreland Lars , Winblad Bengt 
Published: October 2006

AbstractThe effect of age on the binding of [3H]5‐hydroxytryptamine ([3H]5‐HT, serotonin) to postmortem human frontal cortex, hippocampus, and putamen from individuals between the ages of 19 and 100 years was studied. One high‐affinity binding site was observed in adult brains, with a mean KD of 3.7 nM and 3.2 nM for frontal cortex and hippocampus, respectively, and 9.2 nM for putamen. Decreased binding capacities (Bmax) with age were detected in frontal cortex and hippocampus. In putamen a decrease in affinity was noted. Postmortem storage did not significantly contribute to the age‐related changes. No significant sex differences were detected. [3H]5‐HT binding was also studied in brains from human neonates. The specific binding was 1.5–3 times lower than in adult frontal cortex and putamen, and Scatchard analysis suggested more than one binding site. In infant hippocampus a single binding site was observed and except for a premature individual, the binding capacity approximated adult values.
Bradykinin Receptor‐Mediated Cyclic GMP Formation in a Nerve Cell Population (Murine Neuroblastoma Clone N1E‐115)
Authors: Snider R. Michael , Richelson Elliott 
Published: October 2006

AbstractA clone of murine neuroblastoma (N1E‐115) was shown to have functional receptors for the nonapeptide bradykinin. These receptors mediated a large, rapid (about 1 min to peak) and calcium‐dependent increase in cyclic GMP. The median effective concentration (EC50) averaged 1.4 nM. In addition, this event was inhibited by quinacrine, 5,8,11,14‐eicosatetraynoic acid, and nordi‐hydroguaiaretic acid, suggesting involvement of phospholipase A2 with subsequent formation of lipoxygenase metabolites of arachidonic acid. [3H]Bradykinin binding to intact cells, investigated under conditions nearly identical to those used in the cyclic GMP assay, yielded binding sites with KDs of 0.83 pM, 1.0 nM, and 4.9 nM with respective Bmax values of 12, 160, and 250 fmol/106 cells. Apparently, the cyclic GMP response was associated with the binding site in which the KD= 1.0 nM. Peptide analogs of bradykinin stimulated cyclic GMP with EC50s nearly identical to their respective KDs determined in binding assays with [3H]bradykinin, thus providing evidence for receptor specificity of this response. This finding of a biochemical response of bradykinin promises to make N1E‐115 cells a convenient model system for study of neuronal bradykinin receptors.
Kinetics of the Mechanism of Action of Monoamine Oxidase in the Regulation of Na+, K+‐ATPase Activity in Rat Brain
Authors: Mayanil C. S. K. , Baquer N. Z. 
Published: October 2006

Abstract:Kinetic studies on the action of monoamine oxidase (MAO) in the regulation of Na+,K+‐ATPase were performed using 3‐methoxy‐4‐hydroxybenzaldehyde (MHB), which is an analogue of 3‐methoxy‐4‐hydroxyphenylacetylaldehyde (product of MAO‐catalysed reaction with dopamine as substrate). It was observed that at 2.6 μM MHB, the activation of Na+,K+‐ATPase may be the result of the removal of the inhibitory Ca2+, thereby increasing the Vmax. Double‐reciprocal plots of Pi versus MHB showed that Ca2+ counteracted the effect of the aldehyde not by changing the Km, but be decreasing the Vmax of the Na+,K+‐ATPase stimulation. The removal of 3′,5′‐cyclic AMP‐dependent protein kinase from the microsomes by sodium dodecyl sulphate treatment abolished the activation and/or inhibition of the Na+,K+‐ATPase by aldehyde; it can therefore be inferred that 3′,5′‐cyclic AMP‐dependent protein kinase is involved in the regulation of Na+,K+‐ATPase.
Characterization of Glutamate Uptake into Synaptic Vesicles
Authors: Naito Shigetaka , Ueda Tetsufumi 
Published: October 2006

Abstract:Recent evidence indicates that L‐glutamate is taken up into synaptic vesicles in an ATP‐dependent manner, supporting the notion that synaptic vesicles may be involved in glutamate synaptic transmission. In this study, we further characterized the ATP‐dependent vesicular uptake of glutamate. Evidence is provided that a Mg‐ATPase, not Ca‐ATPase, is responsible for the ATP hydrolysis coupled to the glutamate uptake. The ATP‐dependent glutamate uptake was inhibited by agents known to dissipate the electrochemical proton gradient across the membrane of chromaffin granules. Hence, it is suggested that the vesicular uptake of glutamate is driven by electrochemical proton gradients generated by the Mg‐ATPase. Of particular interest is the finding that the ATP‐dependent glutamate uptake is markedly stimulated by chloride over a physiologically relevant, millimolar concentration range, suggesting an important role of intranerve terminal chloride in the accumulation of glutamate in synaptic vesicles. The vesicular glutamate translocator is highly specific for L‐glutamate, and failed to interact with aspartate, its related agents, and most of the glutamate analogs tested. It is proposed that this vesicular translocator plays a crucial role in determining the fate of glutamate as a neurotransmitter.
Simultaneous Determination of 5‐Hydroxytryptophan and 3,4‐Dihydroxyphenylalanine in Rat Brain by HPLC with Electrochemical Detection Following Electrical Stimulation of the Dorsal Raphe Nucleus
Authors: Duda N. J. , Moore K. E. 
Published: October 2006

Abstract:HPLC coupled with electrochemical detection was used to make concurrent measurements of the rate of accumulation of 5‐hydroxytryptophan and 3,4‐dihydroxyphenylalanine in selected brain regions (striatum, nucleus accumbens, septum, medial periventricular hypothalamus) and thoracic spinal cords of rats treated with NSD 1015, an inhibitor of aromatic‐L‐amino‐acid decarboxylase. 5‐Hydroxytryptophan and 3,4‐dihydroxyphenylalanine accumulated in all brain regions 30 min after the intravenous infusion of various doses of NSD 1015; there were no significant differences in the responses to 12.5, 25, 50, and 100 mg/kg. After the intravenous administration of 25 mg/kg NSD 1015 the concentrations of 5‐hydroxytryptophan and 3,4‐dihydroxyphenylalanine increased linearly with time in all brain regions for at least 30 min. Electrical stimulation of 5‐hydroxytryptamine neurons in the dorsal raphe nucleus for 30 min at 5 or 10 Hz increased 5‐hydroxytryptophan accumulation in all brain regions but not in the spinal cord. Unexpectedly, this stimulation also increased the accumulation of 3,4‐dihydroxyphenylalanine in the hypothalamus and spinal cord. These results suggest that 5‐hydroxytryptophan accumulation following the administration of NSD 1015 is a valid index of 5‐hydroxytryptamine neuronal activity in the brain.
Hydrophobic Regions in Myelin Proteins Characterized Through Analysis of “Hydropathic”Profiles
Authors: Weise Michael J. 
Published: October 2006

Abstract:Computer‐generated “hydropathic’ profiles were constructed for graphic comparison of the amino acid sequences for P2 protein, 18.5 kilodalton (kDa) myelin basic protein (BP), and myelin proteolipid protein (PLP). Profiles were also obtained for cytochrome b5, a membrane protein known to be capable of reversible association with lipid bilayers and of a size comparable to that of the myelin BPs. Analysis of the PLP sequence produced profiles generally compatible with the suggestions that PLP has three transbilayer and two bilayer intercalating segments. Profiles for P2 and 18.5 kDa BP were found to contain hydrophilic segments separated by relatively short hydrophobic regions. Whereas hydropathic indices in hydrophobic regions of P2, 18.5 kDa BP, and PLP fall in the value ranges recently reported for cores of globular proteins and intrabilayer domains of membrane proteins, hydrophobic sections of P2 and 18.5 kDa BP have hydropathic indices similar to those in the hydrophobic core (transprotein) regions of globular proteins. None of them are comparable to the region of cytochrome b5 known to anchor that protein in its membrane or to the segments of PLP sequence proposed as intrabilayer domains. This comparison suggests that neither BP has structural characteristics compatible with insertion into the hydrocarbon core of the myelin lipid bilayer, a conclusion that is consistent with a recently published study that identified the bilayer penetrating proteins of myelin with a hydrophobic probe. The above findings suggest an enhancement for some details of myelin architecture and a cautious approach to interpreting data for BP intercalation into bilayers.
Free and Conjugated Amines in Human Lumbar Cerebrospinal Fluid
Authors: Tyce Gertrude M. , Rorie Duane K. , Byer David E. , Danielson David R. 
Published: October 2006

Abstract:Significant amounts of acid‐hydrolyzable conjugates of 3,4‐dihydroxyphenylethylamine, norepinephrine, and 5‐hydroxytryptamine were detected in lumbar CSF from 22 awake unpremedicated healthy individuals. In the CSF samples, the amounts of conjugated amines almost always exceeded the amounts of free amines, but were less than the amounts of the acid metabolites 3,4‐dihydroxyphenylacetic acid, homovanillic acid, and 5‐hydroxyindoleacetic acid.
Taurine Stimulation of Isolated Hamster Brain Na+, K+‐ATPase: Activation Kinetics and Chemical Specificity
Authors: Hastings David F. , Welty Joseph D. , Rohani Farrokh 
Published: October 2006

Abstract:Epileptic foci are associated with locally reduced taurine (2‐aminoethanesulfonic acid) concentration and Na+, K+‐ATPase (EC 3.6.1.3) specific activity. Topically applied and intraperitoneally administered taurine can prevent the development and/or spread of foci in many animal models. Taurine has been implicated as a possible cytosolic modulator of monovalent ion distribution, cytosolic “free” calcium activity, and neuronal excitability. Taurine may act in part by modulating Na+, K+‐ATPase activity of neuronal and glial cells. We characterized the requirements for in vitro modulation of Na+, K+‐ATPase by taurine. Normal whole brain homogenate Na+, K+‐ATPase activity is 5.1 ± 0.4 (4) μmol Pi± h−1± mg−1 Lowry protein. Partial purification of the plasma membrane fraction to remove cytosolic proteins and extrinsic proteins and to uncouple cholinergic receptors yields a membrane‐bound Na+, K+‐ATPase activity of 204.6 ± 5.8 (4) mol Pi± h−1± mg−1 Lowry protein. Taurine activates the Na+, K+‐ATPase at all levels of purification. The concentration dependence of activation follows normal saturation kinetics (K1/2= 39 mM taurine, activation maximum =+87%). The activation exhibits chemical specificity among the taurine analogues and metabolites: taurine = isethionic acid > hypotaurine > no activation =β‐alanine = methionine = choline = leucine. Taurine can act as an endogenous activator/modulator of Na+, K+‐ATPase. Its action is mediated by a membrane‐bound protein.
Cerebrospinal Fluid Glucose: Turnover and Metabolism
Authors: Hochwald Gerald M. , Magee Jill , Ferguson Vicki 
Published: October 2006

Abstract:The turnover of cerebrospinal fluid (CSF) glucose was studied in cats during steady‐state perfusion. In all experiments, the perfusion fluid contained either tracer [14C]glucose alone or tracer glucose along with 4.45 mM unlabeled glucose. In some studies, serum glucose was lowered with insulin. The concentration of glucose and [14C]glucose in the effluent fluid was measured, and the distribution of 14C between glucose and lactate was determined by chromatography. From these values, the extraction of glucose and the metabolism of glucose to lactate were calculated. From the decrease in the specific activity of glucose in the perfusion fluid, the influx of glucose from serum was also determined. During steadystate perfusion, 71% of the radioactivity was recovered in the effluent fluid: 50% in the form of glucose, 6% in the form of lactate, and 15% in forms that were not identified. Thus, 50% of the perfusion fluid glucose was cleared, of which 29% was extracted and 21% metabolized. The influx of glucose was proportional to the serum glucose when the latter was about 2.5 mM or 10.0 mM. During perfusion with tracer glucose only, the concentration of glucose in the effluent fluid was 25% that of serum. The transport of glucose from serum was independent of the glucose concentration gradient between serum and perfusion fluid. However, when perfusion fluid glucose concentration was greater than that of serum, transport was inhibited. These studies suggest that in maintaining CSF glucose at a lower concentration than serum glucose, with equal amounts of glucose entering and leaving the CSF, 50% of CSF glucose concentration cleared is replaced by 25% of serum glucose concentration.