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D Pleasure

Publications and source records attributed to D Pleasure.

At least 73 records · Page 4Linked to original sources
PubMed1993

Charcot-Marie-Tooth syndrome.

Charcot-Marie-Tooth syndrome (CMT) is a group of genetically determined symmetric distal polyneuropathies. The CMT loci are known to map to chromosome 1 (CMT1B), chromosome 17 (CMT1A), the X chromosome (CMTX), and two additional unknown autosomes (CMT1C and CMT2). The most prevalent form is CMT1A, an autosomal dominant demyelinative disorder caused either by a tandem duplication in band p11.2-12 of chromosome 17 (17p11.2-12) with trisomic expression of the peripheral myelin protein-22 (PMP-22) gene or, less frequently, by a missense mutation of PMP-22. Missense mutations in PMP-22 are also responsible for two forms of demyelinative polyneuropathy in mice, trembler and trembler. Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder characterized by recurrent focal neuropathy. In all families thus far studied, patients with HNPP have been found to be monosomic for a segment of chromosome 17p11.2-12. The duplication in CMT1A and deletion in HNPP map to the same region in 17p11.2-12 and are both likely to be consequences of unequal crossing over during germ cell meiosis.

Animals↗
PubMed1993

Electrophysiologic and molecular properties of cultured enteric glia.

Enteric glia, the support cells of myenteric ganglia, have been widely studied with respect to their morphology and immunohistochemical phenotype, but little is known about their functional properties. We developed a method for the amplification of enteric glia from newborn guinea pigs to further characterize these cells. Treatment with a combination of basic fibroblast growth factor and the adenylate cyclase activator, cholera toxin, permitted expansion of enteric glial cultures to confluence and serial passage for up to 8 months. The long-term cultured cells retained expression of 1) S100 protein, 2) GD3 ganglioside recognized by the monoclonal antibody LB1, and 3) the gene encoding glutamine synthetase. The electrophysiologic properties of cultured enteric glia were studied under whole-cell patch clamp conditions. Most cells expressed "delayed rectifier"-type potassium currents, and some also demonstrated tetrodotoxin-sensitive sodium currents. Other subsets of voltage-dependent potassium currents, calcium currents, and glutamate-gated currents were not demonstrable.

Animals↗
PubMed1993

Appearance of PLP mRNA in specific regions of the developing rat lumbosacral spinal cord as revealed by in situ hybridization.

The capacity of specific regions and fiber tracts of developing rat lumbosacral spinal cord to express proteolipid protein (PLP) mRNA was examined using in situ hybridization. PLP mRNA was undetectable at Day 18 postfertilization but present in the white matter by Postnatal Day 0 (P0). Initially, levels of PLP mRNA were higher in ventral than in dorsal funiculi. Hybridization signal was observed in the corticospinal tract by P10. Appearance of PLP message in gray matter lagged several days behind that in white matter. The expression of PLP mRNA in gray matter rose between P10 and P40 and the abundance of PLP transcript remained high in white matter during the same period. In the adult spinal cord some oligodendrocytes in the Lissauer tract and in the posterior commissure expressed low levels of PLP mRNA, which was undetectable in the substantia gelatinosa. Comparing the time of emergence of PLP mRNA to the histological appearance of myelination gave evidence that the message is expressed in oligodendrocytes that are not many days away from myelin formation. These results provide new information on the topographic distribution of PLP mRNA during myelination of the rat spinal cord.

Animals↗
PubMed1993

Cerebral aspartate utilization: near-equilibrium relationships in aspartate aminotransferase reaction.

The pathways of nitrogen transfer from 50 microM [15N]aspartate were studied in rat brain synaptosomes and cultured primary rat astrocytes by using gas chromatography-mass spectrometry technique. Aspartate was taken up rapidly by both preparations, but the rates of transport were faster in astrocytes than in synaptosomes. In synaptosomes, 15N was incorporated predominantly into glutamate, whereas in glial cells, glutamine and other 15N-amino acids were also produced. In both preparations, the initial rate of N transfer from aspartate to glutamate was within a factor of 2-3 of that in the opposite direction. The rates of transamination were greater in synaptosomes than in astrocytes. Omission of glucose increased the formation of [15N]-glutamate in synaptosomes, but not in astrocytes. Rotenone substantially decreased the rate of transamination. There was no detectable incorporation of 15N from labeled aspartate to 6-amino-15N-labeled adenine nucleotides during 60-min incubation of synaptosomes under a variety of conditions; however, such activity could be demonstrated in glial cells. The formation of 15N-labeled adenine nucleotides was marginally increased by the presence of 1 mM aminooxyacetate, but was unaffected by pretreatment with 1 mM 5-amino-4-imidazolecarboxamide ribose. It is concluded that (1) aspartate aminotransferase is near equilibrium in both synaptosomes and astrocytes under cellular conditions, but the rates of transamination are faster in the nerve endings; (2) in the absence of glucose, use of amino acids for the purpose of energy production increases in synaptosomes, but may not do so in glial cells because the latter possess larger glycogen stores; and (3) nerve endings have a very limited capacity for salvage of the adenine nucleotides via the purine nucleotide cycle.

Adenine Nucleotides↗
PubMed1993

Brain glutamate metabolism: neuronal-astroglial relationships.

The concentration of glutamate in the brain extracellular fluid must be kept low (approximately 3 microM) in order to maximize the signal-to-noise ratio upon the release of glutamate from neurons. In addition, the nerve endings require a supply of glutamate precursors that will not cause depolarization. The major precursor to neuronal glutamate is glutamine, which is synthesized in astrocytes and converted to glutamate in neurons. However, glutamine is not the sole source. Alanine also might serve as a precursor to glutamate via transamination, although this reaction is relatively inactive in synaptosomes. Finally, the branched-chain amino acids, and in particular leucine, appear to be very important precursors to glutamate and glutamine in astrocytes. By providing alpha-NH2 groups for the synthesis of glutamine, leucine also abets the uptake into brain of neutral amino acids, which are transported in exchange for brain glutamine. In addition, the branched-chain ketoacids are readily reaminated to the cognate amino acids, in the process consuming glutamate. Intraneuronal consumption of glutamate via ketoacid reamination might serve to buffer internal [glutamate] and to modulate the releasable pool.

Animals↗
PubMed1992

Structure and expression of proteolipid protein in the peripheral nervous system.

Proteolipid protein (PLP), the major myelin protein in the central nervous system (CNS), is also made by Schwann cells (SC) in the peripheral nervous system (PNS) but is not incorporated into the SC myelin sheath. We analyzed several PLP cDNA clones isolated from a rat sciatic nerve cDNA library and found that their coding sequences were identical to PLP cDNAs previously isolated from the CNS. In addition, we have discovered an unusual form of PLP message, present in both brain and sciatic nerve RNA, that is likely formed by alternative splicing within the 3' untranslated region of the primary PLP transcript. The absence of PLP from the SC myelin sheath thus cannot be explained by an alteration in its amino acid sequence. Steady-state levels of PLP mRNA in SC cultures treated with the cAMP analogue dibutyryl cAMP (dBcAMP) were not increased, whereas dBcAMP increased steady-state levels of mRNA encoding the major myelin protein, P0. We have also shown that expression of PLP, unlike that of P0, is regulated in SC in vitro at a posttranscriptional level. Finally, the steady-state levels of P0 mRNA are much more dramatically reduced than those of PLP mRNA during Wallerian degeneration of the peripheral nerve. Thus PLP expression in the PNS is probably controlled by different molecular mechanisms from P0, and may not be part of the coordinate program of myelin gene expression. In contrast to its expression in the PNS, transcription of PLP in the CNS is coordinately regulated along with the other myelin protein genes, suggesting there may be differences in the cis-acting elements and transacting factors involved in the regulation of PLP transcription in SC and oligodendrocytes (OC). Consistent with this notion, we have found that most PLP transcripts are initiated at the more proximal of two start sites in the PNS, while in the CNS proportionally more PLP transcripts are initiated from the distal start site. We propose that the proximal site, utilized predominantly in SC, is responsible for maintenance expression of PLP and is not inducible, while the distal site is responsible for the rapid, inducible increase of PLP message during brain development.

Animals↗
PubMed1992

Platelet-derived growth factor and regulation of Schwann cell proliferation in vivo.

To examine the role of platelet-derived growth factor (PDGF) in the in vivo regulation of Schwann cell proliferation, steady-state levels of mRNAs encoding PDGF A and B chains, and PDGF alpha and beta receptors were measured in immature and adult rat sciatic nerves and in cultured rat Schwann cells. PDGF B chain and PDGF beta receptor mRNAs are present in immature rat sciatic nerves and to a lesser extent in adult rat nerves. Short-term cultures of neonatal rat Schwann cells express PDGF beta receptor mRNA, but not PDGF B chain mRNA, and are stimulated to synthesize DNA by addition of PDGF BB to the medium. These data indicate that PDGF BB is a developmentally regulated paracrine growth factor for rat Schwann cells. Very long-term cultures of rat Schwann cells, which have lost normal dependence on exogenous growth factors, express PDGF B chain mRNA as well as mRNAs encoding the PDGF alpha and beta receptors, suggesting that, under these circumstances, PDGF BB also act as an autocrine growth factor. PDGF A chain mRNA is present in both immature and adult rat sciatic nerves and is expressed by primary and secondary cultures of rat Schwann cells as well. However, because the abundance of PDGF alpha receptor mRNA is very low in rat Schwann cells, PDGF AA is not likely to be a significant autocrine growth factor for rat Schwann cells.

Animals↗
PubMed1992

Expression of genes encoding receptors for IgG (FcRIII) and for C3b/C4b (Crry) in rat sciatic nerve during development and Wallerian degeneration.

Northern blots were used to examine the expression of genes encoding receptors for IgG (FcRIII) and for C3b/C4b (Crry) in rat sciatic nerve during development and Wallerian degeneration. Steady state levels of FcRIII (1.4 kb) and Crry (1.9 and 2.1 kb) mRNAs were higher in adult rat nerves than in 6 day and 21 day postnatal rat nerves, indicating that the expression of these receptors is developmentally regulated. The FcRIII and Crry cDNA probes also hybridized with total RNA from 3 day old rat Schwann cells and from adult rat peritoneal macrophages. The size of the FcRIII mRNA expressed by cultured Schwann cells (1.6 kb) differed from that expressed by peritoneal macrophages (1.4 kb); the two may be splice variants of one transcript or products of related genes. Peritoneal macrophages contained approximately 100 times higher FcRIII mRNA levels than Schwann cells. In contrast, steady state levels of both 1.9 and 2.1 kb Crry mRNAs were similar in cultured Schwann cells and macrophages. Nerve transection induced a generalized increase in the level of sciatic FcRIII mRNA (1.4 kb) 3 days post-surgery, whereas the level of Crry mRNA was increased only in the nerve segment immediately to the cut. The increase of FcRIII mRNA that occurred in Wallerian degeneration was most likely due to infiltration of macrophages, as FcRIII mRNA-positive macrophages were demonstrated in the degenerating nerves by in situ hybridization. FcRIII mRNA-positive macrophages were not found in normal nerve. The functions of FcRIII and Crry in peripheral nerves are uncertain, but they may be of significance in phagocytosis, antibody-dependent cellular cytotoxicity, and in local immune regulation.

Aging↗
PubMed1992

Expression of platelet-derived growth factor (PDGF) and PDGF receptor genes in the developing rat brain.

Steady-state levels of rat central nervous system (CNS) platelet-derived growth factor (PDGF) A- and B-chain mRNAs were measured by a polymerase chain reaction method employing a synthetic gene internal standard, and the rates of transcription of PDGF A- and B-chain genes in CNS were estimated by a nuclear runoff assay. The abundance of PDGF B-chain mRNA was an order of magnitude below that of PDGF A-chain mRNA, while the rate of PDGF B-chain transcription was only slightly below that for the PDGF A-chain gene, indicating that the half-life of PDGF B-chain in CNS is shorter than that of PDGF A-chain mRNA. No developmental alterations in expression of the PDGF A- and B-chain genes were detected. By contrast, Northern blots showed that steady-state levels of mRNAs encoding the two PDGF receptor proteins, alpha and beta, were markedly higher in embryonic day 15 and postnatal day 6 rat brains than in later life. These results suggest that the actions of PDGF on the brain in vivo are regulated not at the level of PDGF A and B-chain gene expression, but rather by changes in the level of expression of PDGF alpha- and beta-receptor genes.

Aging↗
PubMed1992

Peripheral nervous system (PNS) expression of mRNAs encoding myelin proteins and Fc gamma RIII during experimental allergic neuritis.

Experimental allergic neuritis (EAN) was induced in Lewis rats by injection of 'SP26', a peptide homologous to amino acids 53-78 of bovine myelin P2 protein, in complete Freund's adjuvant. The rats developed signs of EAN which began on day 14, were maximal on day 18, and had subsided by day 30. RNA content of cauda equina and sciatic nerves increased more than 2-fold at the height of EAN. Expression of myelin P0 and P1 mRNAs did not fall during EAN, nor rise during recovery. Fc gamma R mRNA, which encodes Fc gamma RIII, an immunoglobulin-binding protein mediating activation of natural killer cells and macrophages by immune complexes, was transiently, but markedly induced in scattered endoneural cells, presumably macrophages, in cauda equina and sciatic nerves during the period of increasing weakness.

Amino Acid Isomerases↗
PubMed1991

Differential expression of bcl2 protooncogene in neuroblastoma and other human tumor cell lines of neural origin.

The bcl2 protooncogene was originally discovered because of its involvement in t(14;18) chromosomal translocations frequently found in non-Hodgkin's lymphomas. The expression of this gene is reported to be highly tissue specific, with bcl2 mRNAs being readily detectable only in hematolymphoid tissues and brain. To explore the possible involvement of bcl2 in neural tumors, we surveyed a variety of tumor cell lines for the presence of the p26-BCL2 protein by immunoprecipitation and immunoblotting methods. Very high levels of BCL2 protein were found in three of nine neuroblastoma (NB) cell lines examined; these levels of p26-BCL2 were comparable to lymphoma cell lines that contain a t(14;18). Despite the impressive relative amounts of BCL2 protein, however, no structural alterations or changes in the methylation status of bcl2 genes were detected in these NB cell lines by conventional Southern blotting. Of the other NB cell lines surveyed, three contained intermediate levels of BCL2 and another three cell lines had little or no detectable BCL2 protein, raising the possibility that determination of relative levels of BCL2 protein may help to segregate neuroblastomas into groups with different biological and clinical characteristics. BCL2 protein levels were not influenced by induction of neuronal differentiation with nerve growth factor in two of the two cell lines examined [SH-SY5Y (high BCL2); GICAN (low BCL2)] and did not correlate with N-MYC gene amplification or expression of nerve growth factor receptors. NB cell lines that contained little or no detectable BCL2 protein, however, tended to contain significant proportions of flat epithelioid cells, whereas bcl2-expressing cell lines were composed primarily of neuronal-like cells, suggesting that expression of this protooncogene correlates with the differentiation characteristics of these tumor cell lines. In addition to NBs, lower levels of BCL2 protein were also found in a variety of other neural crest-derived tumors and tumor cell lines, including some neuroepitheliomas, Ewing's sarcomas, neurofibromas, and melanomas. With regard to tumors of central nervous system origin, bcl2 expression was absent from most medulloblastomas but was detected at moderate to low levels in a retinoblastoma and some glioblastoma multiforme cell lines. Taken together, these findings imply that bcl2 protooncogene expression is differentially regulated within the various lineages of cells that give rise to the nervous system.

Blotting, Southern↗
PubMed1991

Characterization of two neuroblastoma cell lines expressing recombinant nerve growth factor receptors.

In earlier studies, a 75,000-dalton glycoprotein (gp75) has been identified as a component of both low- and high-affinity nerve growth factor (NGF) receptors (NGFRs). Using an amphoteric expression vector, we have introduced the cDNA encoding the human gp75 into two neuroblastoma cell lines. SHEP is a human neuroblastoma cell line that lacks most neuronal characteristics and does not express NGFRs. The transformant line SHEP/NGFR expressed a single affinity class of NGF binding sites, did not display NGF-induced up-regulation of fos oncogene expression, and did not efficiently internalize NGF. LAN5 is a neuroblastoma cell line with neuronal characteristics, including expression of neurofilament and display of short neurites. This cell line expresses a small number of high-affinity NGFRs but no detectable low-affinity sites. The transformant line LAN5/NGFR expressed both high- and low-affinity NGFRs, displayed NGF-induced up-regulation of fos oncogene, and efficiently internalized NGF. The number of high-affinity NGF binding sites was nearly the same for LAN5 and LAN5/NGFR, a finding suggesting that there is a limiting number of some separately coded factor or subunit that is required for high-affinity NGFRs. Because NGF induction of fos oncogene expression correlated with expression of high-affinity NGFRs, the putative second factor may also limit NGF responsiveness.

Binding Sites↗
PubMed1991

Nerve growth factor receptor expression in peripheral and central neuroectodermal tumors, other pediatric brain tumors, and during development of the adrenal gland.

Nerve growth factor (NGF) is important to the survival, development, and differentiation of neurons. Its action is mediated by a specific cell surface transmembrane glycoprotein, nerve growth factor receptor (NGFR). In this study, NGFR expression by human fetal and adult adrenal medullary tissue, peripheral nervous system (PNS) neuroectodermal tumors (neuroblastoma, ganglioneuroblastoma, ganglioneuroma), pediatric primitive neuroectodermal tumors (PNETs) of the central nervous system (CNS), and CNS gliomas was examined by an immunohistochemical technique. Sixty-nine tumors in total were probed in this manner. Nerve growth factor receptor immunoreactivity was confined to nerve fibers and clusters of primitive-appearing cells in the fetal adrenal, and to nerve fibers and ganglion cells of the adult adrenal medulla; adrenal chromaffin cells were negative. In PNS neuroectodermal tumors, there was NGFR expression in tumor cells of 6 of 11 neuroblastomas and 6 of 6 ganglioneuroblastomas or ganglioneuromas. Thirteen of thirty-five CNS PNETs showed NGFR positivity. In most CNS PNETs, NGFR was restricted to scattered single or small groups of cells, but two tumors with astroglial differentiation showed much more extensive immunoreactivity. Most astrocytomas (11 of 14) and all ependymomas (3 of 3) were intensely NGFR positive.

Adolescent↗
PubMed1990

Glutathione turnover in cultured astrocytes: studies with [15N]glutamate.

The incorporation of [15N]glutamic acid into glutathione was studied in primary cultures of astrocytes. Turnover of the intracellular glutathione pool was rapid, attaining a steady state value of 30.0 atom% excess in 180 min. The intracellular glutathione concentration was high (20-40 nmol/mg protein) and the tripeptide was released rapidly into the incubation medium. Although labeling of glutathione (atom% excess) with [15N]glutamate occurred rapidly, little accumulation of 15N in glutathione was noted during the incubation compared with 15N in aspartate, glutamine, and alanine. Glutathione turnover was stimulated by incubating the astrocytes with diethylmaleate, an electrophile that caused a partial depletion of the glutathione pool(s). Diethylmaleate treatment also was associated with significant reductions of intraastrocytic glutamate, glycine, and cysteine, i.e., the constituents of glutathione. Glutathione synthesis could be stimulated by supplementing the steady-state incubation medium with 0.05 mM L-cysteine, such treatment again partially depleting intraastrocytic glutamate and causing significant reductions of 15N labeling of both alanine and glutamine, suggesting that glutamate had been diverted from the synthesis of these amino acids and toward the formation of glutathione. The current study underscores both the intensity of glutathione turnover in astrocytes and the relationship of this turnover to the metabolism of glutamate and other amino acids.

Amino Acids↗