bluuebunny/crossref_metadata_2025_split huggingface dataset:
In vitro modulation of changes in ganglioside patterns of differentiating neurons in the presence of an anti‐GM1 antibody
Authors: Allende M. L. , Panzetta P. 
Published: January 2005

AbstractRetinal cells from 7‐day‐old chicken embryos were cultured in the presence of a polyclonal anti‐GMI antibody, at low and high density in a “sandwich cell culture”. Cells that were about 80% neurofilament positive at all times, changed their morphology and emitted processes as controls. By examining immunocytochemical expression of gangliosides, cells cultured in the presence of the antibody maintained GD3 expression longer than controls, albeit the expression of the gangliotetraosylgangliosides (GTOG) was not considerably affected. This leads to an extension of the transient period in which differentiating cells coexpressed both types of gangliosides (GD3 and GTOG). At 3–4 days in vitro the relative synthesis of GD3 was about 30% higher and that of GD1a about 40% lower than in controls, indicating a delay in the shift of the synthesis pattern. Nevertheless, the pattern of ganglioside composition resembled at 4 days in vitro.Results indicate that the anti‐GMI antibody may modulate the expression and synthesis of gangliosides without a detectable decrease in neuritogenesis. Considering that the emission of neurites occurs in coexpressing GD3 and GTOG neurons, it is suggested that neuritogenesis could be irrespective of losing the GD3 expression.
Many naturally occurring mutations of myelin proteolipid protein impair its intracellular transport
Authors: Gow A. , Friedrich V. L. , Lazzarini R. A. 
Published: January 2005

AbstractThe primary structure of the proteolipid protein (PLP) from the central nervous system (CNS) myelin of mammals is highly conserved with only three amino acid differences between the mouse, rat, dog, bovine, and human proteins. Furthermore, within a particular species no polymorphisms in the protein have been identified. Recent interest has focused on the targeting of PLP in oligodendrocytes and the role that mutant forms of this protein play in generating dysmyelinating or hypomyelinating diseases. We previously expressed the human cDNA encoding PLP in transiently transfected Cos‐7 cells and characterized the subcellular distribution of the protein in this simple heterologous system. In the current study we have used the same paradigm to examine the effect of five missense mutations in the PLP gene on processing of the encoded protein. The mutations chosen span the carboxy‐terminal half of PLP and encompass that part of the protein in which most mutations have been identified. Our results show that transport of all mutations examined was arrested in the secretory pathway at an early stage, causing the mutant proteins to accumulate in the endoplasmic reticulum. Thus, a common mechanism of protein misfolding and failure of PLP to reach the cell surface of oligodendrocytes rather than the inability of the mutant protein to perform some crucial function at the cell surface may be responsible for the diseases caused by many PLP mutations. Our results, together with those of others, prompt us to speculate that the pathobiology observed in PLP mutants may result from oligodendrocyte cell death caused by the accumulation of misfolded protein in the endoplasmic reticulum. This speculation is consistent with the observations that oligodendrocytes bearing misfolded PLP, as in the jimpy mutant, proliferate but die rapidly while oligodendrocytes from PLP deletion survive and produce a myelin‐like membrane which lacks PLP. © 1994 Wiley‐Liss, Inc.
Effects of nerve segment supernatants on cultured Schwann cell proliferation and laminin production
Authors: Zhang Q.‐L. , Lin P.‐X. , Chang Y. , Webster H. deF. 
Published: January 2005

AbstractMouse sciatic nerves were transected and 3 hr to 16 days later proximal segments were removed and homogenized. Supernatants of these segments or of normal sciatic nerves were added to Schwann cells maintained in Dulbecco's modified Eagle's medium (DMEM) + 15% fetal calf serum (FCS). After 6 days, Schwann cells were solubilized and the protein content was measured using a Bio‐Rad (Melville, NY) protein assay. Samples containing the same amounts of protein were then applied to microtiter plates and the laminin content was determined by enzymelinked immunosorbent assay (ELISA). Lysates of cultures treated with 24 hr proximal segment supernatants contained significantly higher levels of laminin than those prepared from other intervals, from distal segments, or from control nerves. Increased surface and cytoplasmic anti‐laminin immunoreactivity also was found in Schwann cells treated with 24 hr supernatants. To identify the source(s) of this effect, proximal segments removed 24 hr after transection were bisected; supernatants were prepared from each half and tested. Significant increases in laminin production were produced by supernatants from both halves. When supernatants from proximal and distal halves were compared, the latter produced significantly higher laminin levels. Electron microscopic examination of both halves showed that distal halves contained sprouting neurites and growth cones ensheathed by Schwann cells which had a basal lamina and resembled those seen during development and regeneration. Proximal halves appeared normal. Schwann cell proliferation also was compared in supernatant‐treated cultures by using a bromodeoxyuridine (BrdU) ELISA. The 24 hr and 2 day supernatants increased Schwann cell proliferation significantly; 12 hr, 4 day, and 8 day supernatants produced smaller increases. Our observations suggest that axons undergoing early regenerative changes are one of several possible sources of substance(s) in our proximal segment supernatants which increased Schwann cell proliferation and laminin production. © 1994 Wiley‐Liss, Inc.
In vivo acidosis reduces extracellular concentrations of taurine and glutamate in the rat hippocampus
Authors: Puka M. , Lehmann A. 
Published: January 2005

AbstractMicrodialysis‐perfusion of the urethane‐anesthetized rat hippocampus was performed to assess the effects of acidosis on extracellular amino acids. Perfusion with Krebs‐Ringer bicarbonate buffer at pH 6.9 produced a selective decrease in taurine. A further reduction of pH to 6.4 induced diminished glutamate levels. The CI−/HCO3− exchange inhibitor 4,4′‐diisothiocyano‐2,2′‐disulfonic acid stilbene (DIDS) did not affect interstitial taurine during perfusion, but there was a rebound increase in taurine levels upon withdrawal of the agent. In contrast, glutamate concentrations were elevated during DIDS administration, and decreased upon reperfusion with standard buffer. The reduction of extracellular taurine and glutamate concentrations caused by low pH was inhibited by DIDS. The results suggest that taurine and glutamate uptake and/or release in vivo is pH‐dependent, and that the effects of acidosis possibly are mediated by the CI−/HCO3− antiporter. The decrease in extracellular glutamate brought about by low pH may have pathophysiologic implications in conditions associated with disturbed pH homeostasis such as cerebral ischemia and spreading depression. © 1994 Wiley‐Liss, Inc.
Transcriptional regulation of myelin associated glycoprotein gene expression by cyclic AMP
Authors: Ye P. , Laszkiewicz I. , Wiggins R. C. , Konat G. W. 
Published: January 2005

AbstractThe treatment of rat glioma C6 cells with 10μ isoproterenol (Ipt) for 4 days upregulated the expression of the myelin‐associated glycoprotein (MAG) gene by approximately 55‐fold over the control value. The constant presence of Ipt in the medium was required for the maximal upregulation, as time‐restricted exposures to the drug produced only partial, or no upregulation of the gene. No difference in the MAG mRNA stability could be detected in Ipt‐treated vs untreated cells indicating that the drug upregulates the MAG gene at transcriptional level. Serum (FCS) strongly attenuated the response of the MAG gene to Ipt.The stimulatory effect of Ipt was profoundly reduced by supermine and H‐89, indicating that protein kinase A‐dependent protein phosphorylation is involved in the MAG gene activation. Within 30 min after Ipt administration, the c‐fos gene was upregulated by 10‐fold, and thereafter, its message level decreased and stabilized at approximately 3‐fold over control. In contrast, the c‐jun gene was downregulated to approximately 20% of control within 30 min after Ipt administration. Subsequently, its message level rose and fell once again within 12 h to approximately half of control, and returned to control level within 72 h.Transfection of C6 cells with progressively deleted pCAT constructs containing up to 861 bp of the MAG gene upstream region demonstrated that active core promoter of the gene is located within 138 bp upstream from the initiation start site. Additional sequences contain both activating and repressive cis‐elements. Practically no upregulation of the CAT activity could be elicited by challenging the transfected cells with Ipt, indicating that AP‐1 sites (14 within the 861 bp region) are not solely responsible for the Ipt‐induced upregulation of the MAG gene, and that the responsible cis‐elements map further upstream from the transcriptional unit. Wiley‐Liss, Inc.
Properties of osmolyte fluxes activated during regulatory volume decrease in cultured cerebellar granule neurons
Authors: Pasantes‐Morales H. , Chacón E. , Murray R. A. , Morán J. 
Published: January 2005

AbstractEfflux pathways for amino acids, K, and CI activated during regulatory volume decrease (RVD) were characterized in cultured cerebellar granule neurons exposed to hyposmotic conditions. Results of this study favor diffusion pores (presumably channels) over energy‐dependent transporters as the mechanisms responsible for the efflux of these osmolytes. The selectivity of osmolyte pathways activated by RVD was assessed by increasing the extracellular concentrations of cations, anions, and amino acids to such an extent that upon opening of the pathway, a permeable compound will enter the cell and block RVD by reducing the efflux of water carried by the exit of intracellular osmolytes. The cationic pathway was found selective for K (and Rb), whereas the anionic pathway was rather unselective being permeable to CI, nitrate, iodine, benzoate, thiocyanate, and sulfate but impermeable to gluconate. Glutamate and aspartate as K but not as Na salts were permeable through the anion channel. RVD was slightly inhibited by quinidine but otherwise was insensitive to known K channel blockers. RVD was inhibited by 4,4′‐ diisothiocyanostilbene‐2‐2′‐disulfonic acid (DIDS), niflumic acid, and dipridamole. Gramicidin did not affect cell volume in isosmotic conditions but greatly accelerated RVD, suggesting that cell permeability to CI is low in isosmotic conditions but increase markedly during RVD making K permeability the rate limit of the process. The permeability pathway for amino acids activated during RVD was permeable to short chain α‐ and β‐amino acids, but excluded glutamine and basic amino acids. Wiley‐Liss, Inc.
Met5‐enkephalin is localized within axon terminals in the subfornical organ: Vascular contacts and interactions with neurons containing gamma‐aminobutyric acid
Authors: Pickel V. M. , Chan J. 
Published: January 2005

AbstractMet5‐enkephalin inhibits sodium and water excretion and antagonzes the central actions of angiotensin II in subfornical organ of rat brain. We examined the ultrastructural basis for enkephalin modulation in this circumventricular region. Additionally, we examined the possibility that there might be cellular sites for functional interactions involving Met5‐enkephalin and gamma‐aminobutyric acid (GABA), a known inhibitory transmitter throughout the central nervous system. Met5‐enkephalin and GABA were indentified in single coronal sections through the subfornical organ using immunoperoxidase and silver‐enhanced immunogold labeling methods, repectively, Enkephalin‐like immunoreactivity was most prominently localized within axon terminals. These were distributed primarily in the central, highly vascular, regions of the subfornical organ. Enkephalinlabeled terminals were apposed to the basement membranes of fenestrated capillaries and also formed symmetric, inhibitory type synapses with neurons. In terminals associated with either blood vessels or neurons, the enkephalin immunoreactivity was enriched in large (80–150nm) dense core vesicles. The immunoreactive vesicles were usually located within portions of the axon in close proximity to astrocytic processes. In contrast, smaller vesicles in the same terminals were more often aggregated near the basement membrane of the capillaries and the active zone of the synape. The targets of enkephalin‐immunoreactive terminals were either unlabeled or GABA‐labeled dendrites of local neurons. Enkephalin was also co‐localized with GABA in perikarya and in axons terminals. Terminals containing only GABA were far more abundant than those containing enkephalin or enkephalin and GABA. GABA‐immunoreactive terminals formed symmetric synapses on unlabeled dendrites some of which also received convergent input from terminals containing enkephalin. Additionally, the enkephalin‐immunoreactive terminals were closely apposed to GABA‐labeled and unlabedled terminals. These results suggest sites for nonsynaptic release of Met5‐enkephalin from dense core vesicles in contact with astrocyes near blood vessels and synaptic complexes in the rat subfornical organ. Moreover, the observed dual localization and pre‐and postsynaptic associations between neurons containing Met5‐enkephalin and GABA indicate that inhibitory effects of opioids in the subfornical organ may be mediated or potentiated by GABA. Wiley‐Liss, Inc.
Isolation and characterization of a soluble lactose‐binding lectin from postnatal chicken retina
Authors: Castagna L. F. , Landa C. A. 
Published: January 2005

AbstractWe investigated the presence of endogenous lectins in postnatal chicken retinal tissue assaying the hemagglutinating activity of crude soluble extracts of the tissue that was homogenized in a buffer supplemented with different sugars. Lactose was the most effective sugar to extract an hemagglutinating activity. Using similar extraction conditions, other sugars, such as glucose, N‐acetylglucosamine, mannose, fucose, glucuronic and sialic acid, were ineffective to extract any significant hemagglutinating activity. The lectin was purified by affinity chromatography on lactosyl‐Sepharose. SDS‐PAGE and isoelectric focusing analyses showed that it has a subunit molecular weight of 16 kDa and a pl about 4.5. The retinal lectin crossreacted immunologically with a rabbit antiserum raised against a lectin purified from adult chicken liver, which is a CLL‐I (Beyer et al.: J Biol Chem 255:4236–4239, 1980) or C‐16 (Sakakura et al.: J Biol Chem 265:21573–21579, 1990) form of chicken endogenous soluble lactose‐binding lectins. Gel filtration studies showed that the oligomeric structure of the retinal lectin is dependent on the ionic strength of the elution buffer. The lectin hemagglutinating activity and the amount of lectin protein reached their highest levels at late developmental stages of the retinal tissue, suggesting that retinal lectin might have a functional role during terminal differentiation of retinal cells. Wiley‐Liss, Inc.
Abnormal phosphorylation of tau proteins associated with bovine brain microtubules: Activation by excess ATP and tyrosine dephosphorylation
Authors: Lu Q. , Kanumury R. , Wood J. G. 
Published: January 2005

AbstractPhosphorylation of tau protein has been suggested as a major mechanism regulating its functions. In assembled brain microtubules, tau is phosphorylated, but additional phosphorylation can be induced in vitro. Supply of excess ATP alone was sufficient to reduce migration of tau on SDS gels, diminish Tau‐1 immunostaining, and induce the expression of epitopes recognized by the PHF‐1 antibody, suggesting that Alzheimer‐type phosphorylation may have occurred. Okadaic acid had no further effect. However, treatment with tyrosine kinase inhibitors modifies the phosphorylation profiles of tau proteins. Most evidently, migration of the largest tau isoform was further retarded on SDS gels and PHF‐1 immunostaining was enhanced. The profound effect of tyrosine kinase inhibitors on tau phosphorylation was also demonstrated in living cells following microinjection of cultured hippocampal neurons. Identification of proline‐directed protein kinases and their regulatory factors associated with assembled microtubules indicated the presence of multiple phosphorylation pathways in microtubules. Our results are consistent with the hypothesis that sequential phosphorylation of tau proteins is at least partially mediated through tyrosine phosphorylation/dephosphorylation mechanisms. Wiley‐Liss, Inc.
Heat shock alters Alzheimer's β amyloid precursor protein expression in human endothelial cells
Authors: Ciallella J. R. , Rangnekar V. V. , McGillis J. P. 
Published: January 2005

AbstractOne of the pathological lesions in Alzheimer's disease (AD) is the amyloid or senile plaque. The plaque core is predominantly made up of amyloid beta peptide (Aβ), a 42–43 amino acid peptide derived from amyloid precursor protein (APP). APP is a membrane bound glycoprotein which is expressed ubiquitously is many cells. Although normal or pathological functions for APP are not well understood, several observations suggest that APP may play a role in cellular stress and inflammation at the endothelial cell/vascular barrier. APP is found in platelets and endothelial cells, it can inhibit a blood coagulation factor, and secreted APP can be neuroprotective. Changes in expression of APP during cellular stress or inflammation may contribute to pathological deposition of Aβ. In the present studies, expression of APP in human endothelial cells was examined following heat shock. In human umbilical vein endothelial cells (HUVECs) exposed to 42°C for 30 min, there was a five‐to eight‐fold increase in APP mRNA levels which peaked at 4 hr. The increase in APP mRNA was followed by an increase in APP protein immunoreactivity in the cytoplasm in a perinuclear Golgi‐like region, and in discrete granular cytoplasmic structures. Immunoblot analysis of APP in the cell media found a transient increase in APP which peaked at 1 hr after heat shock. These results suggest that cellular stress induces the secretion of APP from endothelial cells followed by a subsequent increase in APP mRNA and protein synthesis. The upregulation of APP mRNA and protein supports a cellular stress role for APP. Wiley‐Liss, Inc.
Tacrine alters the secretion of the beta‐amyloid precursor protein in cell lines
Authors: Lahiri D. K. , Lewis S. , Farlow M. R. 
Published: January 2005

AbstractThe characteristic features of Alzheimer's disease (AD) include a high density of β‐amyloid‐containing plaques in the cerebral cortex and the loss of basal forebrain cholinergic neurons. Amyloid β‐protein (Aβ, Mr. ∼4.5 kDa) is derived from a family of large (Mr. ∼110–140 kDa) β‐amyloid precursor proteins (APP) which are integral membrane glycoproteins consisting of a large extracytoplasmic domain, a transmembrane domain, and a short cytoplasmic tail. Secreted derivatives of APP lacking the cytoplasmic tail, transmembrane domain, and a small portion of the extracellular domain are generated by the proteolytic processing of full length APP by a family of proteolytic enzymes known as APP secretases. Using cell cultures, we investigated the possibility that APP processing can be regulated by a centrally active cholinesterase inhibitor, tacrine, which has recently been shown to improve memory and cognitive functions in patients with AD. We analyzed the level of APP in glial, fibroblast, pheochromocytoma (PC12), and neuroblastoma cells by immunoblotting cell lysates and conditioned media. Normal levels of secretion of soluble APP derivatives by cells into conditioned media were severely inhibited by treating cells with tacrine. A similar decrease after treatment with tacrine was observed when neuroblastoma and PC12 cells were pretreated with either growth factors, phorbol ester, or retinoic acid. To determine whether the effect of tacrine on APP levels was specific or a more general phenomenon affecting other proteins, we measured the level of heat shock protein‐70 (HSP‐70) and another secretory protein, protease nexin‐1 (PN‐1). Tacrine treatment did not alter the level of HSP‐70 in cell extracts and tacrine affected mildly the secretion of PN‐1. Thus, the processing of HSP and PN‐1, unlike APP, was not severely affected by treating cells with tacrine. Our results suggest that tacrine may inhibit an acetylcholinesterase‐associated proteolytic activity involved in the secretion of APP, which results in less secretion of soluble APP into the conditioned media from tacrine treated cells. These results demonstrate that tacrine regulates APP secretion in cell cultures and suggest the possibility that tacrine therapy of Alzheimer's disease may, in the longer term, have effects on the process of Aβ deposition. Wiley‐Liss, Inc.
Extracellular ATP‐induced currents in astrocytes: Involvement of a cation channel
Authors: Walz W. , Gimpl G. , Ohlemeyer C. , Kettenmann H. 
Published: January 2005

AbstractWhole‐cell currents were measured with the perforated patch clamp technique in cultured rat astrocytes to analyze the underlying ionic mechanism for a P2‐purinoceptor‐mediated depolarization. ATP (100 μM) induced an inward current with a mean amplitude of 130 pA and an EC50 of 17 μM. The response desensitized during a 1 min application. Replacement of extracellular Na+ with NMDG or K+ abolished the ATP‐evoked inward current. Replacement of Na+ with choline, however, resulted in an ATP‐evoked response of one‐third the amplitude in normal solution. This is indicative of a cation rather than Na+ channel. However, due to difficulties in voltage‐clamping these gap junction‐coupled cells at voltages different from the membrane resting potential, the current reversal potential could not be determined. Measurements with K+‐sensitive microelectrodes showed that 100 μM ATP lowered the intracellular K+ concentration. Replacement of extracellular Ca2+ or Cl− did not alter the ATP‐induced inward currents. Fura‐2 imaging experiments revealed a transient rise of the intracellular Ca2+ concentration during ATP application. Removal of extracellular Ca2+ did not influence the peak response; it did, however, shorten the time course. These results and previous observations that the permeability changes are caused by a P2× receptor are indicative of an ATP‐sensitive cation conductance. In addition, cytoplasmic Ca2+ is increased by mobilization from intracellular stores, and by additional influx across the cell membrane. Extracellular ATP released by neurons could evoke K+ release from astrocytes as well as be a mediator for cation changes that signal cell activation processes when released by damaged cells. © 1994 Wiley‐Liss, Inc.