bluuebunny/crossref_metadata_2025_split huggingface dataset:
Muscimol Potentiation of Acidic Amino Acid Release from Cerebellar Synaptosomes Is Chloride Dependent
Authors: Gallo Vittorio , Aloisi Francesca , Levi Giulio 
Published: October 2006

Abstract:In previous studies we have shown that the depolarization‐induced release of preaccumulated acidic amino acids and newly synthesized glutamate from cerebellar synaptosomal preparations is potentiated by γ‐aminobutyric acid (GABA) agonists through a GABAergic presynaptic mechanism. Here we report a systematic analysis of the ionic requirements of the potentiating effect of muscimol on the high K+‐evoked release of d‐[3H]aspartate. Our studies show that: Ca2+, Na+, and Mg2+ are not required for muscimol to exert its effect; a depolarizing concentration of K+ is a necessary, but not sufficient, condition to observe the presynaptic effect in question; and a minimal Cl‐ concentration (50–70 mM) is also required. A possible model based on these findings is proposed.
Changes in Free Amino Acid Levels in Developing Human Foetal Brain Regions
Authors: Datta Salil C. , Mukherjee Kanai L. 
Published: October 2006

Abstract:The levels of free amino acids were determined in human foetal brain regions during prenatal development. Variation in the distribution of amino acids and their rate of change in five segments of the CNS at different stages of ontogeny was observed. Striking developmental changes were found in the levels of aspartic acid in medulla‐pons and spinal cord, glycine in the spinal cord, γ‐aminobutyric acid in the cerebral cortex, glutamic acid in the cerebral cortex, midbrain, and spinal cord, and taurine in the medulla‐pons and spinal cord. At a late gestational period, glutamic acid was found most abundantly over all the brain regions, whereas the level of taurine was highest at an early gestational stage but not in spinal cord.
Biochemical and Pharmacological Characteristics of Conjugated Catecholamines in the Rat Brain
Authors: Karoum F. , Chuang L.‐W. , Wyatt R. J. 
Published: October 2006

Abstract:Mass‐fragmentographic methods are described that enable the simultaneous measurement of total, free, and conjugated catecholamines in brain tissues. These methods were used to assess the distribution, kinetics, and pharmacological characteristics of total, free, and conjugated catecholamines in the hypothalamus, caudate nucleus, hippocampus, and septum. Conjugated norepi‐nephrine (NE) represents ˜20% of total NE in the hypothalamus, septum, and hippocampus, whereas the percentage is ˜ 50% in the caudate nucleus. The percentages of conjugated dopamine (DA) in these brain areas are consistently less than those of NE (˜13%). Although in the hypothalamus the steady‐state concentrations of total, free, and conjugated NE are over four times higher than those of the corresponding total, free, and conjugated DA, the turnover rates of this DA are comparable with those of the corresponding NE. Further, the ratios of conjugated NE or DA turnover rates to those of the total amines are higher than the corresponding ratios of their steady‐state concentrations. Treatments with pargyline (75 mg/kg, i.p.; rats killed 30 and 60 min later) failed to change the contents of conjugated catecholamines in the hypothalamus and the caudate nucleus significantly. Pharmacological manipulation with a number of proto‐typic drugs revealed that although the assay of conjugated catecholamines might shed additional light on the effects of drugs on central catecholamines, the assessment of total or free amines are on the whole equally informative. In conclusion, a detailed assessment of brain conjugated catecholamines is reported. The information provided, fills a gap in our knowledge that has up to now not been adequately addressed.
Regionally Selective Inhibition of Cerebral Protein Synthesis in the Rat During Hypoglycemia and Recovery
Authors: Kiessling Marika , Xie Yaxia , Kleihues Paul 
Published: October 2006

AbstractRegional cerebral protein synthesis was investigated in anesthetized, mechanically ventilated rats during progressive insulin‐induced hypoglycemia and the recovery period following glucose infusion. Polysome profiles from precomatose animals with slow wave/polyspike EEG revealed a slight reduction of polyribosomes and a concurrent increase in monoribosomes, but autoradiographs showed a pattern of l‐[3‐3H]tyrosine incorporation indistinguishable from that of control rats. During the initial 30 min of insulin‐induced isoelectric EEG (“coma”), autoradiographs showed a selective inhibition of protein synthesis in neurons and glial cells of the hippocampus and cerebral cortex, i.e., regions with high susceptibility for the development of hypoglycemic brain damage. Basal ganglia were less affected and areas with low vulnerability (hypothalamus, brainstem, and cerebellum) exhibited a normal pattern of amino acid incorporation. Using a flooding dose of l‐[1‐14C]valine (7.5 mmol/kg; 15 μCi/mmol), the rate of incorporation in cerebral cortex and cerebellum was found to be reduced to 2% and 80% of control values, respectively. Inhibition of protein synthesis was paralleled by a breakdown of polyribosomes and a concomitant increase in ribosomal subunits, indicating a block in peptide chain initiation. After 90 min of isoelectric EEG all brain structures with the exception of hypothalamus and area postrema showed an almost complete lack of amino acid incorporation. Glucose infusion after a 30‐min period of hypoglycemic coma led to a partial restoration of cortical and hippocampal protein synthesis. Within 70–90 min of recovery, l‐[1‐14C]valine incorporation into neocortical and cerebellar proteins amounted to 47% and 125% of fasted controls. The very specialized patterns of regional impairment of cerebral protein synthesis during progressive hypoglycemia may reflect a selective vulnerability of some neuronal cell populations to hypoglycemic cell injury. Alternatively, the striking resistance of hypothalamus, brainstem, and cerebellum may be due to a more efficient glucose uptake at very low blood glucose levels.
DNA Changes in Spinal Cords of Rats with Experimental Allergic Encephalomyelitis
Authors: Smith Marion Edmonds , Somera F. Paul , Saldivar Robert , Massacesi Luca , Trotter Jacqueline 
Published: October 2006

AbstractDNA levels were measured in the spinal cords of Lewis rats during the development of and recovery from experimental allergic encephalomyelitis (EAE). Spinal cord DNA was first increased 11 days after immunizing the rats with guinea pig myelin and rose to levels four times that of the Freund's adjuvant controls at day 14, then subsided after day 22. Spinal cord DNA was still 150% of control levels 60 days after immunization. These DNA changes were compared with fluctuations in spinal cord acid proteinase in the same animals. Acid proteinase activity in EAE spinal cord increased later than the rise in DNA and attained a level of 170% of control at days 15–17, then subsided. Spinal cord DNA was higher in rats immunized with whole myelin than in those administered equivalent amounts of purified myelin basic protein. Furthermore DNA was higher in spinal cords of rats immunized with a larger dose of myelin (1.0 mg) than with a lower amount (0.5 mg). Various protease inhibitors including pepstatin, nitrophenyl p‐guanidino benzoate, polylysine, and dipropionyl rhein, previously shown to protect Lewis rats against EAE, suppressed the increase of DNA in the spinal cord. Measurement of DNA increases in the spinal cord of EAE animals provides a convenient reproducible measurement of the severity of inflammation in the CNS and provides an objective criterion for assessment of the efficacy of various agents screened as possible therapeutic treatment for multiple sclerosis.
Neurochemical and Histochemical Characterization of Neurotoxic Effects of 1‐Methyl‐4‐Phenyl‐1,2,3,6‐Tetrahydropyridine on Brain Catecholamine Neurones in the Mouse
Authors: Hallman H. , Lange L. , Olson L. , Strömberg I. , Jonsson G. 
Published: October 2006

Abstract:Systemic administration of 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) caused a rapid and long‐lasting reduction of both 3,4‐dihydroxyphenylalanine (dopamine, DA) and noradrenaline (NA) in mouse brain, as observed histo‐ and neurochemically. The depleting effects were more pronounced after repeated MPTP administration and the most marked reductions were observed after 2 × 50 mg MPTP/kg s.c., when DA in striatum and NA in frontal cortex were reduced by > 90% 1 week after MPTP. Mice with such catecholamine depletions were markedly sedated and almost completely immobilized. The behavioural syndrome after MPTP resembled that seen after reserpine, a monoamine‐depleting drug. MPTP also caused a long‐lasting reduction of catecholamine uptake in striatal DA and cortical NA nerve terminals and reduced tyrosine hydroxylase activity in these regions. There was no evidence that MPTP caused any marked DA and NA cell body death. MPTP given acutely transiently elevated serotonin levels. The results are compatible with a neurotoxic action of MPTP on both DA and NA nerve terminals. The nigro‐striatal DA and the locus coeruleus NA neurone systems appeared to be most susceptible. Synthesis and utilization of residual striatal DA and cortical NA were increased, as often observed in partially denervated monoamine‐innervated brain regions. Both DA and NA showed a gradual recovery, which took months to become complete and may have been related to a regrowth of catecholamine nerve terminals.
Effects of Guanyl Nucleotides on [3H]Flunitrazepam Binding to Rat Hippocampal Synaptic Membranes: Equilibrium Binding and Dissociation Kinetics
Authors: Fung S.‐C. , Fillenz M. 
Published: October 2006

Abstract:The effects of guanyl nucleotides on the binding of [3H]flunitrazepam to rat hippocampal synaptic membranes were studied. In equilibrium binding studies, γ‐amino‐n‐butyric acid (GABA) increased and GTP decreased the binding affinity of [3H]flunitrazepam; GTP also caused a decrease in binding capacity. The effect, however, is variable. In studies of the dissociation kinetics of [3H]flunitrazepam using diazepam and the antagonist Ro 15–1788 as the displacers, there was evidence of two dissociation rate constants. GTP increased both the fast and slow‐dissociation rate constants and increased the ratio of the slow‐dissociation binding state. The effect of GTP was mimickled by its nonhydrolyzable analogue 5′‐guanylylimidodiphosphate but not by ATP and occurred when diazepam, but not when Ro 15–1788, was used as the displacer. GABA antagonized the effect of GTP on the dissociation of [3H]flunitrazepam. The nature of the benzodiazepine recepter, its actions, and the possible role of cyclic AMP as a second messenger are discussed.
Dopamine Autoreceptor Stimulation Increases Protein Carboxyl Methylation in Striatal Slices
Authors: Wolf Marina E. , Roth Robert H. 
Published: October 2006

Abstract:We have investigated the possibility that protein carboxyl methylation is involved in coupling dopamine autoreceptor stimulation to intracellular events such as inhibition of dopamine synthesis or release. The dopamine agonists apomorphine and TL‐99 were found to stimulate methyl ester formation in striatal slices preloaded with [3H]methionine. The stimulatory effects of apomorphine were dose‐dependent, were not due to changes in [3H]methionine uptake or S‐[3H]‐adenosyl‐methionine formation, and were blocked by the stereospecific dopamine antagonist (+)‐butaclamol. Stimulation of methyl ester formation by dopamine agonists is readily observed only when slices are prepared from rats pretreated with reserpine to deplete endogenous brain catecholamines. This suggests that in slices prepared from normal rats endogenous dopamine (DA) released during slice preparation and incubation masks the effects produced by exogenously administered dopamine agonists on protein carboxyl methylase (PCM) activity. Additional experiments suggested that the effects of apomorphine were mediated via an interaction with DA autoreceptors rather than with postsynaptic DA receptors. Destruction of monoamine neurons and their associated autoreceptors by injecting 6‐hydroxydopamine into the area of the medial forebrain bundle abolished the stimulatory effects of apomorphine on methyl ester formation in striatal slices. Furthermore the putative selective DA autoreceptor agonist EMD 23 448 was also found to stimulate methyl ester formation in striatal slices. These findings, discussed in terms of calcium‐dependent functions, support the hypothesis that PCM may be a key component in the biochemical transduction of DA autoreceptor stimulation.
Reversible Dihydropyridine Isothiocyanate Binding to Brain Calcium Channels
Authors: Greenberg David A. , Cooper Edward C. , Carpenter Celia L. 
Published: October 2006

Abstract:Voltage‐dependent calcium channels from ileal smooth muscle can be affinity‐labeled with a [3H]dihydropyridine isothiocyanate radioligand. We examined the binding of this agent to brain membranes, to compare the properties of calcium channel drug binding sites in brain with those previously described in ileum. In brain, the [3H]dihydropyridine isothiocyanate labels sites that correspond in number and pharmacologic characteristics to binding sites for the classic calcium entry blocker, [3H]nitrendipine. However, in contrast to the covalent nature of dihydropyridine isothiocyanate binding in ileum, brain calcium channels are labeled reversibly. This difference in binding properties may reflect structural variations in voltage‐dependent calcium channels in different tissues.
A Monoclonal Antibody to Rabbit Brain GABA Transaminase
Authors: Edwardson J. Michael , Phillips Nicholas I. , Kirby Neil , Fowler Leslie J. 
Published: October 2006

Abstract:A monoclonal antibody of class IgG (subclass IgG1) has been prepared to rabbit brain GABA transaminase (GABA‐T). This antibody reveals a single band of molecular weight 52,000 on a nitrocellulose filter blotted with purified GABA‐T. On a filter blotted with unfractionated rabbit brain supernatant a major band of molecular weight 58,000 is revealed. An immunoaffinity column was prepared by coupling proteins from ascites fluid containing anti‐rabbit GABA‐T antibody to Bio‐Rad Affi‐Gel 15. This column bound purified GABA‐T and extracted from unfractionated rabbit brain supernatant a protein of molecular weight 58,000, which was almost homogeneous and which had GABA‐T enzyme activity. Using immunoaffinity chromatography, therefore, a high degree of purification of GABA‐T may be achieved in a single step. Further, this technique may preserve an authentic form of the enzyme that is lost during the conventional purification procedure. The antibody inhibits GABA‐T enzyme activity, up to a maximum of 35%.
Methylation of Chromosomal Proteins in Neuronal and Glial Nuclei Purified from Cerebral Hemispheres of Rat During Postnatal Development
Authors: Serra I. , Avola R. , Lombardo B. , Kamiyama M. , Hashim G. A. , Giuffrida A. M. 
Published: October 2006

Abstract:The process of methylation of chromosomal proteins [histones and nonhistone proteins (NHP)] in neuronal and glial cell nuclei obtained from cerebral hemispheres of rats at 1, 10, and 30 days of age was investigated. Purified neuronal and glial nuclei were incubated in the presence of S‐adensyl[methyl‐3H]methi‐onine. Histone and NHPs were extracted and fractionated by polyacrylamide gel electrophoresis. The results obtained indicate remarkable differences in the process of methylation of histones and NHPs between neuronal and glial nuclei, especially during the first period of postnatal development. In both nuclear populations the histone fraction H3 was labeled to a greater degree than the other fractions and showed the major changes during postnatal development. The densitometric and radioactive patterns of NHPs show considerable changes in the two nuclear populations at the various ages examined. The main difference between neuronal and glial nuclei consists in the intense methylation of proteins with a molecular weight of approximately 100,000, which are present in neuronal nuclei and virtually absent in glial ones. The results obtained may be correlated with the different chromatin structures of neuronal and glial nuclei and with the patterns of maturation and differentiation of neuronal and glial cells during postnatal development.
Uptake and Anterograde Axonal Transport of Aleuria Lectin in Retinal Ganglion Cells of the Rabbit
Authors: Ohlson C. , Nilsson E. , Karlsson J.‐O. 
Published: October 2006

Abstract:A fucose‐specific lectin from Aleuria aurantia was used to study the dynamics of neuronal membrane glycoproteins. Albino rabbits received vitreal injections of affinity‐purified 125I‐Aleuria lectin. The radioactive probe was internalized by adsorptive endocytosis into retinal ganglion cells, and transported intact down to the nerve terminals in the contralateral geniculate bodies and superior colliculi. We found that the radiolabeled lectin was transported with at least two distinct rates (I, $205 mm/day; II, $45 mm/day) corresponding to the two rapid phases of anterograde transport of endogenous polypeptides described earlier in this system. This is the first evidence that an exogenous macromolecule may be transported along the axon at more than one velocity.
Binding Sites for l‐[3H]Glutamate on Hippocampal Synaptic Membranes: Three Populations Differentially Affected by Chloride and Calcium Ions
Authors: Nadler J. Victor , Wang Andrew , Werling Linda L. 
Published: October 2006

Abstract:The effects of Cl− and Ca2+ were studied on the specific binding of l‐[3H]glutamate to multiple sites on rat hippocampal synaptic membranes. Quisqualate (5 μM) or dl‐2‐amino‐4‐phosphonobutyrate (2‐APB) (300 μM) was used to discriminate two previously identified classes of binding sites. Saturation isotherms and displacement curves constructed under different ionic conditions suggested that the effects of Cl− and Ca2+ could best be explained by postulating the existence of three major binding site populations in this preparation rather than two. The binding of l‐glutamate to Glu A sites exhibits an absolute dependence on Cl−, and Ca2+ markedly increases the maximum density of these sites. Glu A sites bind quisqualate and 2‐APB with relatively high affinity. Cl− (47 μM) more than doubles the maximum density of Glu B sites, but Ca2+ appears to have no effect. Glu B sites can be discriminated from the other classes by their relatively low affinity for quisqualate and 2‐APB. There is reason to think that the Glu B population is heterogeneous. The novel Glu C population can be virtually selectively labeled by exposing 2‐APB‐sensitive binding sites to radioligand in Tris‐HOAc buffer with Ca2+. Binding of l‐[3H]glutamate to these sites is enhanced by both Cl− and Ca2+, but requires neither ion. Ca2+ appears to increase both the affinity of Glu C sites for l‐glutamate and their maximum binding site density. In the presence of Ca2+ and Cl−, Glu C sites bind the radioligand with micromolar affinity (KD > 2 μM) and high capacity (Bmax > 160 pmol/mg protein). The structural specificity of these binding sites closely resembles that of Glu A sites, but these sites bind excitants with about an order of magnitude lower affinity. The Glu C binding sites exhibit characteristics compatible with a synaptic receptor function in the hippocampal formation.
Blockade of Receptor‐Mediated Cyclic GMP Formation by Hydroxyeicosatetraenoic Acid
Authors: McKinney Michael 
Published: October 2006

AbstractReceptor‐mediated cyclic GMP formation in N1E‐115 murine neuroblastoma cells appears to involve oxidative metabolism of arachidonic acid. Evidence in support of this includes the blockade of this response by lipoxygenase inhibitors, e.g., eicosatetraynoic acid (ETYA) or other metabolic perturbants, e.g., methylene blue. It was recently discovered that the lipoxygenase products 15‐hydroxyeicosatetraenoic (15‐HETE) acid and 12‐HETE, like ETYA, were inhibitors of M1 muscarinic receptor‐mediated cyclic GMP formation. In the present report, the effects of monoHETEs are explored in more detail, particularly with regard to the function of the muscarinic receptor. Like 12‐HETE and 15‐HETE (IC50= 13 and 11 μM, respectively), 5‐HETE inhibited the cyclic GMP response to the muscarinic receptor (IC50= 10 μM). All three of these monoHETEs were shown also to be inhibitors of the cyclic GMP responses to receptors stimulated by carbachol, histamine, thrombin, neurotensin, and bradykinin. 15‐HETE was shown to inhibit the muscarinic receptor‐mediated response in a complex manner (apparent noncompetitive and uncompetitive components; IC50= 18 and 2 μM, respectively). 15‐HETE did not inhibit either the M1 muscarinic receptor‐stimulated release of [3H]inositol phosphates from cellular phospholipids or the M2 muscarinic receptor‐mediated inhibition of hormone (prostaglandin E1)‐induced AMP formation. It seemed possible that the monoHETEs could enter into biochemical pathways for arachidonate in N1E‐115 cells. [3H]Arachidonate and the three [3H]‐monoHETEs all rapidly labeled the membrane lipids of intact NIE‐115 cells, with each [3H]eicosanoid producing a unique labeling profile. [3H] 15‐HETE labeling was noteworthy in that 85% of the label found in the phospholipids was in phosphatidylinositol (PI; t1/2 to steady state = 3 min). Exogenous 15‐HETE inhibited the labeling of PI by [3H]‐arachidonate (IC50= 28 μM) and elevated unesterified [3H]‐arachidonate levels. Thus, the mechanism of blockade of receptor‐mediated cyclic GMP responses by monoHETEs is likely to be more complex than the simple inhibition of cytosolic mechanisms, e.g., generation of a putative second messenger by lipoxygenase, and may involve also alterations of membrane function accompanying the redistribution of esterified arachidonate.
Ion Dependence of Neurotransmitter Uptake: Inhibitory Effects of Ion Substitutes
Authors: Shank Richard P. , Schneider Craig R. , Tighe Joseph J. 
Published: October 2006

AbstractSeveral ions commonly used as substitutes for Na+ or Cl‐ were found to inhibit directly the high‐affinity uptake of norepinephrine, dopamine, serotonin, and γ‐aminobutyric acid, but not glutamate or glutamine. When Na+ was partially replaced by any of several different cations or sucrose the uptake of all neurotransmitters studied except that of serotonin was reduced more than could be accounted for by just the inhibitory effect of the cation substitute. In contrast, when Cl was partially replaced by any of several anions only the uptake of dopamine was reduced more than could be accounted for by the inhibitory effect of the anion substitute. These results suggest that for most neurotransmitters the electrochemical potential for Na+, but not for Cl, contributes to the uptake driving force. When either Na+ or Cl was totally replaced by an ion substitute or by sucrose the high‐affinity uptake was virtually abolished, an exception being that glutamate uptake was not affected when isethionate was substituted for Cl. The lack of uptake in the absence of either Na+ or Cl may reflect a specific role for these ions in either increasing the affinity between the substrate and the carrier, or facilitating the translocation process. Alternatively, the transport carriers may undergo a nonspecific conformational change to an inactive form in the absence of Na+ or Cl. A partial substitution of Na+ with Li+ or sucrose differentially affected the kinetics of uptake in that replacement with Li+, but not sucrose, usually resulted in a marked increase in the Km values. The results of this study emphasize the importance of taking into consideration the effects of ions used as substitutes in experiments undertaken to elucidate the roles of Na+ and Cl in the high‐affinity uptake of monoamine and amino acid neurotransmitters.