bluuebunny/crossref_metadata_2025_split huggingface dataset:
Uptake of Endoneurial Lipoprotein into Schwann Cells and Sensory Neurons Is Mediated by Low Density Lipoprotein Receptors and Stimulated After Axonal Injury
Authors: Rothe Thomas , Müller Hans W. 
Published: October 2006

AbstractDuring Wallerian degeneration of rat sciatic nerve, the expression of apolipoprotein E increases and apolipoprotein E‐containing endoneurial lipoproteins accumulate in the distal nerve segment. In established primary cultures dissociated from dorsal root ganglia, Schwann cells and sensory neurons internalized rhodamine‐labeled lipoproteins isolated from crushed rat sciatic nerve as well as low density lipoprotein (LDL) from human serum. The uptake of endoneurial lipoproteins could be inhibited by an excess of LDL or at low temperature (4°C). After transection of nerve fibers in dorsal root ganglia explant cultures, the uptake of lipoproteins was markedly stimulated in Schwann cells that were in close proximity to degenerating neurites. A specific monoclonal antibody directed to the bovine LDL receptor (clone C7) was shown to cross‐react with LDL receptor preparations of rat endoneurial cells. LDL receptor immunoreactivity was expressed by cell bodies and processes of cultured Schwann cells, sensory neurons, and fibroblasts from dorsal root ganglia. Incubation of Schwann cells and neurons with the LDL receptor antibody strongly inhibited the uptake of endoneurial lipoproteins. Our results provide direct evidence for the important role of the LDL receptor‐mediated pathway to internalize endoneurial lipoproteins into Schwann cells and peripheral neurons required for reuse of cholesterol and other lipids in myelin and plasma membrane biogenesis during nerve repair.
Inhibitory Modulation by Sodium Ions of the N‐Methyl‐D‐Aspartate Recognition Site in Brain Synaptic Membranes
Authors: Yoneda Yukio , Ogita Kiyokazu 
Published: October 2006

AbstractSpecific binding of radiolabeled L‐glutamic acid (Glu) was examined using rat brain synaptic membranes treated with a low concentration of Triton X‐100. The binding drastically increased in proportion to increasing concentrations of the detergent used up to 0.1%. Addition of 100 mM sodium acetate significantly potentiated the binding in membranes not treated with Triton X‐100, whereas it markedly inhibited the binding in Triton‐treated membranes. The binding in Triton‐treated membranes was inversely dependent on incubation temperature and reached a plateau within 10 min after the initiation of incubation at 2°C, whereas the time required to attain equilibrium at 30°C was <1 min. Sodium acetate invariably inhibited the binding detected at both temperatures independently of the incubation time via decreasing the affinity for the ligand. The binding was significantly displaced by agonists and antagonists for an N‐methyl‐d‐aspartate (NMDA)‐sensitive subclass of brain excitatory amino acid receptors, but not by those for the other subclasses. Inclusion of sodium acetate reduced the potencies of NMDA agonists to displace the binding without virtually affecting those of NMDA antagonists. Moreover, sodium ions inhibited the ability of Glu to potentiate the binding of N‐[3H][1‐(2‐thienyl)cyclohexyl]piperidine to open NMDA channels in Triton‐treated membranes. These results suggest that sodium ions may play an additional modulatory role in the termination process of neurotransmission mediated by excitatory amino acids via facilitating a transformation of the NMDA recognition site from a state with high affinity for agonists to a state with low affinity.
Modulation of γ‐Aminobutyric AcidA Receptor‐Operated Chloride Channels by Benzodiazepine Inverse Agonists Is Related to Genetic Differences in Ethanol Withdrawal Seizure Severity
Authors: Buck Kari J. , McQuilkin Susan J. , Harris R. Adron 
Published: October 2006

AbstractTo determine whether genetic differences in development of ethanol dependence are related to changes in γ‐aminobutyric acidA (GABAA) receptor function, we measured 36Cl uptake by brain cortical membrane vesicles from withdrawal seizure prone and withdrawal seizure resistant (WSP/WSR) mice treated chronically with ethanol. Musci‐mol‐stimulated chloride flux was not different between WSP and WSR mice before or after ethanol treatment. Also, augmentation of muscimol action by flunitrazepam or inhibition of muscimol action by the inverse agonists Ro 15–4513 (ethyl‐ 8‐azido‐5,6‐dihydro‐5‐methyl‐6‐oxo‐4H‐imidazo[1,5a]‐ [1,4]benzodiazepine‐3‐carboxylate) and methyl‐6,7‐dime‐ thoxy‐4‐ethyl‐β‐carboIine‐3‐carboxylate (DMCM) was not different for ethanol‐naive WSP and WSR mice. However, chronic ethanol administration enhanced the inhibitory actions of DMCM and Ro 15–4513 on membranes from WSP but not WSR mice. Conversely, chronic ethanol treatment attenuated the action of flunitrazepam on membranes from WSR but not WSP mice, suggesting that the actions of benzodiazepine agonists and inverse agonists are under separate genetic control. These genetic differences in actions of DMCM and Ro 15–4513 indicate that sensitization to benzodiazepine inverse agonists produced by chronic ethanol treatment may be related to development of withdrawal seizures and suggest that differences in the GABA/benzodiazepine receptor complex represent alleles that have segregated during the selection of the WSP/WSR mice.
The Cholinergic Regulation of Intracellular Calcium in the Human Neuroblastoma, SH‐SY5Y
Authors: Murphy Nuala P. , Vaughan Peter F. T. , Ball Stephen G. , McCormack James G. 
Published: October 2006

AbstractThe regulation of intracellular calcium by cholinergic agonists was investigated in the human neuroblastoma SH‐SY5Y, loaded with fura‐2. The resting free Ca2+ concentration in this cell line was 199 ± 14 nM (mean ± SEM, n = 19). At 1 mM extracellular Ca2+, high concentrations of carbachol and acetylcholine evoked a biphasic change in intracellular Ca2+ concentration, consisting of a transient initial peak followed by a decline to a plateau that was significantly higher than the basal level. Carbachol (0.5 mM) and acetylcholine (10 μM) caused a maximal increase in the intracellular Ca2+ concentration, reaching a peak of 465 ± 52 (mean ± SEM, n = 12) and 422 ± 48 nM (mean ± SEM, n = 7), respectively, in <4 s. This initial calcium transient declined to a plateau of 268 ± 36 and 240 ± 27 nM for carbachol and acetylcholine, respectively, in ∼40 s. The plateau persisted until the agonist was displaced by the addition of antagonist. Atropine, hexahydrosiladifenidol (HHSD), pirenzepine, and methoctramine inhibited the carbachol‐evoked initial calcium transient with Ki values of 0.85 ± 0.05, 8.3 ± 1.6, 411 ± 36, and 240 ± 46 nM (mean ± SEM, n = 3), respectively, and the acetylcholine‐induced initial calcium transient with Ki values of 0.48 ± 0.18, 13.5 ± 8.5, 192 ± 32, and 414 ± 25 nM (mean ± SEM of two experiments), respectively, results suggesting that an M3 muscarinic receptor was predominantly mediating these effects. Furthermore, atropine, HHSD, and pirenzepine inhibited the plateau phase of the carbachol‐ evoked change in intracellular Ca2+ concentration with Ki values of 0.25, 1, and 861 nM, respectively, which are consistent with an M3 receptor being coupled to this effect. The plateau was abolished in the presence of EGTA, thereby converting the biphasic signal into a monophasic response. Under these conditions, the initial calcium transient or its pharmacology was not altered. However, if the cells were washed in calcium‐free buffer for 3 min, the initial peak was decreased by∼30%. The subsequent readdition of calcium caused a further increase in fura‐2 fluorescence. The influx of calcium and hence the plateau were also blocked by nickel but were insensitive to verapamil. We may conclude, therefore, on pharmacological grounds, that an M3 muscarinic receptor is coupled both to the peak response, presumably due to inositol trisphosphate mobilization of intracellular calcium, and to the plateau due to an influx of extracellular calcium.
Exogenous GM3 Ganglioside Stimulates Process Formation and Glycoprotein Release by Cultured Bovine Oligodendrocytes
Authors: Yim Sung Hye , Yavin Ephraim , Hammer Jeffrey A. , Quarles Richard H. 
Published: October 2006

AbstractIsolated adult bovine Oligodendrocytes maintained in vitro for 10 days were treated for 1 day with 50 μg/ml of GM3 ganglioside (NeuNAcα2‐3Galβ1–4Glcβ1‐l'ceramide) in serum‐free culture medium. The treated Oligodendrocytes had significantly longer processes with more branching than control cells in the same medium without GM3. The treatment also stimulated the release of a series of 22‐ 100‐kDa, [3H]glucosamine‐labeled glycoproteins into the culture medium. Treatment of Oligodendrocytes maintained in vitro for 50 days with GM3 for 1 day resulted in a thickening of the processes and the appearance of many fine branches on existing processes as well as a similar stimulation of glycoprotein release into the medium.
Characterization and Pharmacological Responsiveness of Dopamine Release Recorded by Microdialysis in the Substantia Nigra of Conscious Rats
Authors: Santiago M. , Westerink B. H. C. 
Published: October 2006

AbstractThe extracellular concentration of dopamine (DA) and 3,4‐dihydroxyphenylacetic acid in the substantia nigra (SN) and striatum was estimated by microdialysis. The dialysate content of DA from the SN was recorded during infusion of a DA uptake blocker (nomifensine; 5 μmol/L) dissolved in the perfusion fluid. Perfusion of tetrodotoxin (1 μmol/L) produced a virtually complete disappearance of nigral and striatal DA release. Dendritic as well as terminal release of DA was inhibited for several hours when the nerve impulse flow in dopaminergic neurons was blocked by systemic administration of γ‐butyrolactonc (750 mg/kg, i.p.). The systemic administration (0.3 mg/kg, i.p.) as well as infusion (1 μmol/L) of the D2 agonist (‐)‐N‐0437 [2‐(n‐propyl‐N‐2‐thienylethylamino)‐5‐hydroxytetralin] produced a significant decrease in the release of DA in both the striatum and the SN. DA levels were recorded in the striatum both with and without addition of nomifensine to the perfusion fluid. The decrease in the striatum after (‐)‐N‐0437 was suppressed in the presence of nomifensine. Infusion (1 μmol/L) as well as systemic administration (40 mg/kg) of sulphide caused a similar increase in the release of striatal DA; this increase was, in both experiments, potentiated by nomifensine coinfusion. Sulpiride administration induced a small increase in the release of nigral DA. Infusion of (‐)‐N‐0437 or (‐)‐sulpiride into the nigra caused a moderate decrease and increase, respectively, of striatal DA level. It was possible to estimate the relative contribution of nigral and striatal au‐toreceptors to the typical changes in striatal DA release seen after peripheral administration of D2 agonists or antagonists. These results suggest that the dendritic release of DA fulfills classical release criteria.
Characterization and Partial Purification of AIM: A Plasma Protein That Induces Rat Cerebral Type 2 Astroglia from Bipotential Glial Progenitors
Authors: Levison Steven W. , McCarthy Ken D. 
Published: October 2006

AbstractStudies on glial cultures have demonstrated that fetal bovine serum contains a factor that induces bipotential glial precursors known as oligodendrocyte‐type 2 astrocyte (O‐2A) progenitors to become type 2 astroglia rather than oligodendroglia. The goal of this research project was to characterize and purify this factor, which we refer to as the astroglia‐inducing molecule (AIM). Using cultures enriched in O‐2A progenitors, we determined that AIM is present in human and bovine sera and that fetal bovine serum qualified as the best serum for purifying AIM. AIM is heat and trypsin labile and may be a plasma glycoprotein. A 240‐fold enriched AIM preparation was produced by applying an ammonium sulfate precipitate of fetal bovine serum to heparin and then lentil lectin‐agarose, followed by gel nitration chromatog‐ raphy. In crude preparations, AIM activity migrated at 50 kDa by gel nitration. With enrichment, activity was seen at several molecular masses, all of which were approximate multiples of 50 kDa. Treatment with 6 M guanidine hydrochloride generated an AIM with a molecular mass between 12 and 18 kDa, a result suggesting that AIM aggregates. On a preparative isoelectric focusing gel, AIM activity most frequently migrated between pH values of 3 and 4; however, proteins with isoelectric points of >9 or at 6 also had activity in several experiments. These data suggest that either multiple AIMs exist or that a single AIM exists that associates with other proteins. Immunofluorescence for ganglioside GD3 and glial fibrillary acidic protein confirmed that AIM preparations induce type 2 astroglia from O‐2A progenitors and suggests that AIM has little effect on type 1 astroglia. Because none of the known growth factors that have been tested to date mimics its effects, AIM may be a novel differentiation factor.
The Differential Role of Protein Kinase C Isozyme in the Rapid Induction of Neurofilament Phosphorylation by Nerve Growth Factor and Phorbol Esters in PC12 Cells
Authors: Clark Edwin A. , Lee Virginia M.‐Y. 
Published: October 2006

AbstractWe examined the short‐term regulation of the phosphorylation of the mid‐sized neurofilament subunit (NF‐M) by kinases which were activated in rat pheochromocytoma (PC12) cells by nerve growth factor (NGF) and/or 12‐O‐tet‐radecanoylphorbol 13‐acetate (TPA). We found that NGF and TPA, alone or in combination, increased (a) the incorporation of [32P]Pi into NF‐M and (b) the rate of conversion of NF‐M from a poorly phosphorylated to a more highly phosphorylated form. This was not due to increased synthesis of NF‐M, because NGF alone did not increase NF‐M synthesis and TPA alone or TPA and NGF together inhibited the synthesis of NF‐M. Further, an increase in calcium/phospholipid‐dependent kinase (PKC) activity resulting from the treatment of PC12 cells with NGF and TPA was observed concomitant with the increased phosphorylation of NF‐M. This PKC activity was determined to be derived from the PKCα and PKCβ isozyme. Finally, when PC12 cells were rendered PKC‐deficient by treatment with 1 μM TPA for 24 h, NGF maintained the ability to induce an increase in NF‐M phosphorylation, though not to the level attained in cells which were not PKC‐deficient. These data suggest (hat NGF with or without TPA stimulates NF‐M phosphorylation as a result of a complex series of events which include PKC‐in‐dependent and PKC‐dependent pathways.
Degradation of Mitochondrial Phospholipids During Experimental Cerebral Ischemia in Rats
Authors: Nakahara Ichiro , Kikuchi Haruhiko , Taki Waro , Nishi Syogo , Kito Makoto , Yonekawa Yasuhiro , Goto Yasunobu , Ogata Nobuyoshi 
Published: October 2006

AbstractChanges in content of brain mitochondrial phospholipids were examined in rats after 30 and 60 min of decapitation ischemia compared with controls, to explore the degradation of the mitochondrial membrane and its relation to dysfunction of mitochondria. Activities of respiratory functions and respiratory enzymes (cytochrome c oxidase; F0F1‐ATPase) decreased significantly during ischemia. Considerable decreases in cardiolipin and phosphatidylinositol content were observed after 60 min, and other phospholipids showed similar but nonsignificant decreases in content. The amount of polyunsaturated fatty acid chains, such as arachidonic and docosahexaenoic acids, was reduced in each phospholipid, in some cases significantly, after 30 and 60 min of ischemia in time‐dependent manners. Degradation of mitochondrial phospholipids during ischemia associated with the deterioration of mitochondrial respiratory functions suggested the significance of such changes in phospholipid content in disintegration of cellular energy metabolism during cerebral ischemia.
Ventral Horn Neuropeptides Modulate the Release of Noradrenaline from Tissue Slices of Rat Brainstem and Ventral Thoracic Spinal Cord
Authors: Fone Kevin C. F. , Johnson Janel V. , Putland Anthony P. , Bennett Geoffrey W. 
Published: October 2006

AbstractThe release of endogenous noradrenaline (NA) from slices of adult rat brainstem and ventral thoracic spinal cord was investigated using a fixed‐volume incubation technique and HPLC with electrochemical detection. Incubation with potassium (15–50 mM) produced a dose‐related increase in basal NA release that was calcium dependent The potassium‐evoked release of NA from spinal cord or brainstem slices was potentiated according to dose by preincubation with either (a) the selective α2‐adrenoceptor antagonist idazoxan (10−6‐10−4M) or (b) the thyrotrophin‐releasing hormone (TRH) analogue RX 77368 (pGlu‐His‐3,3′‐dimethyl ProNH2; 10−5 and 10−4M). Incubation of spinal cord slices with the NA uptake inhibitor maprotiline (1 μM) enhanced the effect of idazoxan but inhibited that of RX 77368. The effects of RX 77368 and potassium alone (15 mM) on NA release from both spinal cord and brainstem slices were reduced to basal levels with tetrodotoxin (10−7M). Similarly, preincubation of spinal cord, but not brainstem, slices with the insect neuropeptide proctolin (10−4M) significantly attenuated the potassium‐or RX 77368‐induced release of NA, whereas substance P (3 × 10−5 and 1 × 10−4M) had no effect on either tissue. These results suggest that changes in NA release in the spinal cord and brainstem may mediate some of the actions of neuropeptides in ventral spinal cord, although the peptides may not be acting directly on the noradrenergic nerve terminals in these tissues.
Processing of Proenkephalin in Adrenal Chromaffin Cells
Authors: Wilson Steven P. 
Published: October 2006

AbstractThe processing of proenkephalin was studied using [35S]methionine pulse‐chase techniques in primary cultures of bovine adrenal medullary chromaffin cells. Following radiolabeling, proenkephalin‐derived peptides were extracted from the cells and separated by reverse‐phase HPLC. Fractions containing proenkephalin fragments were digested with trypsin and carboxypeptidase B to liberate Met‐enkephalin sequences and subjected to a second HPLC step to demonstrate association of radiolabel with Met‐enkephalin. Processing of proenkephalin is complete within 2 h of synthesis, suggesting completion at or soon after incorporation into storage vesicles. Pretreatment of the cells with nicotine, histamine, or vasoactive intestinal peptide to enhance the rate of proenkephalin synthesis failed to alter the time course of processing and had minimal effects on the distribution of products formed. Addition of tetrabenazine, an inhibitor of catecholamine uptake into chromaffin vesicles, during radio‐labeling and a 6‐h chase period caused enhanced proenkephalin processing. These results suggest that the full range of proenkephalin fragments normally found in the adrenal medulla (up to 23.3 kDa) represents final processing products of the tissue and that termination of processing may depend on the co‐storage of catecholamines.
Determination of Acetylcholine Release in the Striatum of Anesthetized Rats Using In Vivo Microdialysis and a Radioimmunoassay
Authors: Kawashima Koichiro , Hayakawa Toru , Kashima Yuko , Suzuki Takeshi , Fujimoto Kazuko , Oohata Hisayo 
Published: October 2006

AbstractA vertical‐type in vivo microdialysis probe and a sensitive, specific radioimmunoassay (RIA) were used to study the mechanism of acetylcholine (ACh) release in the striatum of anesthetized rats. Without the use of physostigmine, a cholincsterase inhibitor, our RIA could still detect the amount of ACh present in the perfusate (5.6 ± 0.6 fmol/min, n = 16). Tetrodotoxin (1 μM) produced a significant decrease in the amount of ACh collected in the perfusate, suggesting that basal ACh determined under the present experimental conditions was related to cholinergic neural activity. Atropine (0.1–1 μM) applied topically via the dialysis probe did not affect the amount of ACh recovered in the perfusate in the absence of physostigmine. Addition of physostigmine (10 μM) to the perfusion fluid produced about a 100‐fold increase in the amount of ACh collected. In the presence of physostig mine, topical administration of atropine and pirenzepine (0.01–1 μM) through a dialysis probe produced a further three‐to fourfold increase in ACh output, whereas a slight increase was produced by AF‐DX 116 at the highest concentration (1 μM). These results indicate that presynaptic modulation of ACh release in the striatum does not occur under basal conditions, and that presynaptic M, muscarinic receptors are involved in the modulation of ACh release when the ACh concentration is raised under certain conditions.
Regional Heterogeneity of L‐Glutamate and L‐Aspartate High‐Affinity Uptake Systems in the Rat CNS
Authors: Fletcher Elizabeth J. , Johnston Graham A. R. 
Published: October 2006

AbstractThe high‐affinity uptake of L‐[3H]glutamate and L‐[3H]aspartate into synaptosomes prepared from rat cerebral cortical, hippocampal, and cerebellar tissue was reduced by a number of structural analogues of L‐glutamate and L‐aspartate. thero‐3‐Hydroxy‐L‐aspartic acid was a more potent inhibitor of L‐glutamate uptake than of L‐aspartate uptake in the cerebral cortex, but not in the hippocampus or cerebellum. A similar pattern of selectivity was observed for cis‐l‐aminocyclobutane‐1,3‐dicarboxylic acid. Dihydrokainate was also more potent against L‐glutamate than against L‐aspartate in the cerebral cortex, but in the hippocampus, it was more potent against L‐aspartate than against L‐glutamate. By contrast, L‐α‐aminoadipate was significantly more potent in the cerebellum than in the cerebral cortex and hippocampus as an antagonist of both L‐glutamate and L‐aspartate. These results support other evidence that there is regional heterogeneity in acidic amino acid uptake sites and that the amino acids L‐glutamate and L‐aspartate may be taken up by a number of transport systems with overlapping substrate specificity but different inhibitor profiles.
Stereospecificity of High‐and Low‐Affinity Transport of Choline Analogues into Rat Cortical Synaptosomes
Authors: Ferguson S. S. G. , Diksic M. , Collier B. 
Published: October 2006

AbstractThe present experiments used methylcholines to examine the stereoselectivity of choline transport into rat synaptosomes. R(+)‐α‐methylcholine and S(+)‐β‐methylcholine were significantly better inhibitors of the high‐affinity choline transport system than were their enantiomers. Although both enantiomers of α‐and of β‐methylcholine inhibited [3H]choline transport, only R(+)‐α‐methylcholine and S(+)‐β‐methylcholine could be transported by the high‐affinity choline uptake mechanism. Therefore, we conclude that the chiral requirements for recognition of and for transport by the high‐affinity transporter are dearly different. In addition to high‐affinity choline transport, Na+‐independent low‐affinity transport was measured. This process transported R(+)‐α‐methylcholine, but not S(‐)‐α‐methylcholine; however, it showed no stereoselectivity for the enantiomers of β‐methylcholine. Thus, high‐and low‐affinity choline transport mechanisms exhibit distinct differences in their substrate selectivities. We suggest that the stereoselective properties of choline transport might present a unique opportunity to study choline uptake and metabolism.