摘要:

AbstractCultures of oligodendrocyte precursor cells can be grown from brain hemispheres of newborn rats. These cells, also called O‐2A progenitor cells, can differentiate in vitro into oligodendrocytes or type 2 astrocytes. Basic FGF and PDGF are known to stimulate their proliferation and delay their differentiation. Lack or excess of retinoic acid (RA) has been known for a long time to alter brain development suggesting that this compound is involved in normal brain development. Here we report that RA partially inhibits both the proliferation and the differentiation of oligodendrocyte precursor cells. It also down‐regulates the mitogenic effect of bFGF on these cells while keeping them in an immature stage. RA is more effective than bFGF in inhibiting myelin basic protein mRNA expression in these cells, and like bFGF, it preserves their bipotential character. RA nuclear receptors RAR‐α and their transcripts are expressed in oligodendrocyte precursor cells as seen by Western blot, Northern blot and in situ hybridization. The expression of RAR‐α transcripts is stimulated transiently by RA alone or associated to bFGF. The expression of RAR‐β transcripts is not constitutive and is induced by RA alone or associated to bFGF and to a lesser extent by bFGF alone. These results suggest that retinoids participate in the control of the development of glial cells of the oligodendrocyte lineage. © 1994 Wi

ISSN:0360-4012    

DOI:10.1002/jnr.490390602

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractAdult dorsal root ganglion (DRG) cells are capable of neurite outgrowth in vivo and in vitro after axotomy. We have investigated, in cultured adult rat DRG cells, the relative influence of nerve growth factor (NGF) or a prior peripheral nerve lesion on the capacity of these neurons to produce neurites. Since there is evidence suggesting that the growth‐associated protein GAP‐43 may play a crucial role in axon elongation during development and regeneration, we have also compared the effect of these treatments on GAP‐43 mRNA expression. NGF increased the early neurite outgrowth in a subpopulation of DRG cells. This effect was substantially less, however, than that resulting from preaxotomy, which initiated an early and profuse neurite outgrowth in almost all cells. No difference in the expression of GAP‐43 mRNA was found between neurons grown in the presence or absence of NGF over 1 week of culture, in spite of the increased growth produced by NGF. In contrast, cultures of neurons that had been preaxotomized showed substantial increase in GAP‐43 mRNA and NGF had, as expected, a significant effect on substance P mRNA levels. Two forms of growth may be present in adult DRG neurons: an NGF‐independent, peripheral nerve injury‐provoked growth associated with substantial GAP‐43 upregulation, and an NGF‐dependent growth that may underlie branching or sprouting of NGF‐sensitive neurons, but which is not associated with increased levels of GAP‐43 mRNA.

ISSN:0360-4012    

DOI:10.1002/jnr.490390603

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe expression of GABABreceptors in cultured mouse cerebellar granule cells was investigated in binding experiments using [3H](S, R)‐baclofen as well as in functional assessment of the ability of (R)‐baclofen to interact with depolarization (15–40 mM KCI) coupled changes in intracellular Ca2+homeostasis and neurotransmitter release. In the latter case a possible functional coupling between GABAAand GABABreceptors was investigated. The binding studies showed that the granule cells express specific binding sites for (R)‐baclofen. The number of binding sites could be increased by exposure of the cells to the GABAAreceptor agonist THIP (4,5,6,7‐tetrahy‐droisoxazolo[5,4‐c]pyridin‐3‐ol) during the culture period. Pretreatment of the neurons with pertussis toxin showed that the GABABreceptors are coupled to G‐proteins. This coupling was, however, less pronounced when the cells had been cultured in the presence of THIP. When45Ca2+uptake was measured or the intracellular Ca2+concentration ([Ca2+]i) determined using the fluorescent Ca2+chelator Fluo‐3 it could be demonstrated that culturing the neurons in THIP influences intracellular Ca2+homeostasis. Moreover, this homeostasis was found to be functionally coupled to the GABABreceptors as (R)‐baclofen inhibited depolarization‐induced increases in45Ca2+uptake and [Ca2+]i. (R)‐Baclofen also inhibited K+‐induced transmitter release from the neurons as monitored by the use of [3H]D‐aspartate which labels the neurotransmitter pool of glutamate. Using the selective GABAAreceptor agonist isoguvacine it could be demonstrated that the GABABreceptors are functionally coupled to GABAAreceptors in the neurons leading to a disinhibitory action of GABABreceptor a

ISSN:0360-4012    

DOI:10.1002/jnr.490390604

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractGABAAagonist‐induced formation of low‐affinity GABAAreceptors in cultured cerebellar granule cells was studied in the presence or absence of α‐difluoromethylornithine (DFMO), a blocker of polyamine formation. High‐ and low‐affinity GABAAreceptors were monitored by Scatchard analysis of [3H]GABA binding to membranes from cells cultured for either 4 or 10 days in the presence or absence of the GABA agonist 4,5,6,7‐tetrahydroisoxazolo[5,4‐c]pyridin‐3‐ol (THIP). Cultures grown for 4 days were exposed to THIP and DFMO for an additional period of 6 hr (acute exposure), whereas cultures grown for 10 days were exposed to the same agents during the entire culture period (chronic exposure). Regardless of the culture period or drug exposure protocol, control cells expressed only a high‐affinity (KD7 nM) binding site for GABA, whereas the cultures treated with THIP for either 6 hr or 10 days exhibited an additional low‐affinity binding site (KD∼ 500 nM). Chronic exposure to DFMO prevented the THIP induction of low‐affinity GABAAreceptors, whereas acute exposure to DFMO had no effect on the ability of THIP to induce low‐affinity GABAAreceptors. Measurements of the intracellular polyamine concentration demonstrated a slight decrease in the putrescine level in the granule cells exposed to DFMO or THIP + DFMO for 6 hr. In contrast, granule cells chronically (10 days) exposed to DFMO or THIP + DFMO were depleted of putrescine and spermidine. Hence, the ability of THIP to induce low‐affinity GABAAreceptors was prevented by the simultaneous depletion of the cellular content of putrescine and spermidine, whereas inhibition of ornithine decarboxylase and of putrescine formation was not sufficient to prevent THIP‐induced receptor f

ISSN:0360-4012    

DOI:10.1002/jnr.490390605

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe effect of lindane (γ‐hexachlorocyclohexane) on [35S]t‐butylbicyclophosphorothionate ([35S]TBPS) binding and GABA‐stimulated36Cl−influx was investigated in cultured cerebral cortical neurons. In addition, the cytotoxic action of lindane as well as a protection by GABA and flunitrazepam were studied together with the ability of lindane to increase the intracellular concentration of free Ca2+. Lindane was found to be toxic to the neurons, an effect that could be completely prevented by the simultaneous presence of GABA (0.1 μM) and flunitrazepam (100 μM) and reduced by GABA alone. An interaction with the GABA receptor‐gated chloride channel was demonstrated by an inhibitory action of lindane on [35S]TBPS binding (IC50188 ± 51 nM) and on GABA‐stimulated36Cl−influx in the neurons. Lindane only marginally increased the intracellular Ca2+concentration in the neurons. It is concluded that the cytotoxic action of lindane is mediated through interaction with GABA receptors in a manner essentially independent of changes in intracellular Ca2+homeostasis. © 19

ISSN:0360-4012    

DOI:10.1002/jnr.490390606

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe microtubule‐associated protein τ is hyperphosphorylated in the paired helical filaments (PHFs) of Alzheimer's disease. Immunological and direct chemical studies have identified Ser396and Ser404as two of the phosphorylated sites. Previously, we have demonstrated, using synthetic τ peptides containing phosphorylated Ser396, that this site is recognized by the monoclonal antibody PHF‐1. The present sudy extends this observation by showing that PHF‐1 recognizes τ peptides containing either individually phosphorylated Ser396or Ser404, but that there is a>10‐fold increase in the sensitivity of detection of τ peptides by PHF‐1 when both serines are phosphorylated. The recognition of singly or doubly phosphorylated Ser396and Ser404in τ by PHF‐1 can also be demonstrated in Chinese hamster ovary cells transfected with full‐length wild‐type τ constructs or mutant constructs with Ala substituted for Ser396or Ser404. We conclude that the PHF‐1 epitope contains both phosphorylated Ser396and Ser404.

ISSN:0360-4012    

DOI:10.1002/jnr.490390607

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractDelta opioid receptor (DOR) mRNA levels were studied in mice rendered tolerant to [D‐Ala2]deltorphin II by 4 days of repeated intracerebroventricular administration (10μg, [tid]). ED50determinations on day 5 revealed a 10‐fold loss in [D‐Ala2]deltorphin II potency with the tail‐flick test. Utilization of a microdissection technique followed by quantitative solution hybridization of RNA extracts from mouse brain revealed mean levels of DOR mRNA ranging from 3.9 pg/μg RNA in the caudate‐putamen to 0.4 pg/μg RNA in the cerebellum. DOR mRNA levels were not different when RNA extracts from tolerant and nontolerant mice were compared. These data suggest that altered DOR mRNA levels are not one of the adaptive changes that occur with delta opioid ([D‐Ala2]deltorphin II) tolerance. © 1994

ISSN:0360-4012    

DOI:10.1002/jnr.490390608

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe gene for glial fibrillary acidic protein (GFAP) was compared for CpG sites that are potential locations of methylated cytosine (mC). GFAP sequences in the 5′‐upstream promoter and in exon 1 of rat, mouse, and human showed extensive similarity in the locations of CpG sites in the promoter and in exon 1, implying conservation. The methylation ofmC at 9 CpG sites in the promoter and 10 sites in exon 1 was analyzed in F344 male rats by a quantitative application of ligation‐mediated polymerase chain reaction (LMPCR). CpG sites with varyingmC in different tissues were found in the GFAP promoter and in a CpG island in exon 1. In the brain, the promoter had about 40% lessmC than in testis and liver. The degree of methylation varied strikingly between adjacent sites within and between tissues. Testis GFAP exon 1 had a gradient ofmC from 5′ to 3′ across the exon that was absent in liver, brain, and cultured neurons and astrocytes. Among brain regions, the hippocampus had 10–40% lessmC at 12 CpG sites than in hypothalamus; the other sites (7/19) showed smaller differences between these brain regions. In DNA from primary cultures, astrocytes has slightly lessmC than neurons at all sites. Because neuron‐rich hippocampal subregions and primary neuron cultures had less methylation than nonneural tissues, we hypothesize that neuroectodermal derivatives tend to be less methylated, whether or not GFAP is expressed. Four domains of methylated CpG sites are proposed on the basis of tissue and cell‐type distribution: (I) a constitutively methylated domain in the mid‐upstream promoter; (II) a testis‐specific gradient of methylation in exon 1; (III) a hypomethylated domain found in neuroectodermal derivatives; and (IV) subsets of sites in the promoter and in exon 1 that have the least methylation in astrocytes, and therefore may be astrocytespecific domains. ©

ISSN:0360-4012    

DOI:10.1002/jnr.490390609

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe glial fibrillary acidic protein (GFAP) is an intermediate filament protein, specific of the cytoskeleton of astrocytes in the central nervous system. In the present work, as a preliminary step to the study of glial‐specific gene expression, we cloned the rat GFAP gene, and we report the sequence of 1.9 kb of the 5′ flanking region, exon 1, and the majority of the first intron. By digestion with methylation‐sensitive restriction enzymes followed by Southern blot analysis, the methylation status of various CpG sites was examined in this genomic segment. We tested whether structural modification of the GFAP gene, such as DNA methylation, could be related to its tissue‐specific transcriptional activity. Therefore, we compared a GFAP‐expressing cell population (primary culture of astroglial cells), a mixed population of GFAP‐expressing and ‐nonexpressing cells (adult rat cerebral hemispheres), and a GFAP‐nonexpressing tissue (liver). In the 5′ flanking region we identified a CpG site at position −1176 whose level of methylation is inversely correlated to GFAP expression. In primary cultured astrocytes, 75% of the GFAP gene alleles were demethylated at this site, while the corresponding value obtained for the cerebral hemispheres was 45%, and for liver only 9%. On the basis of the sequence data, a CpG‐rich region (putative CpG island) was identified extending from −38 to + 347 and overlapping 80% of the first exon.HhaI andHpaII sites located in the putative CpG island showed a relatively high level of methylation in all the cell populations examined, and did not show any clear correlation with the level of GFAP gene expression or with the methylation status of the −1176 site. Further in vivo developmental studies and in vitro differentiation studies are necessary to better understand the functional differences of the various methylatable CpG sites in the 5′ end of the GFAP g

ISSN:0360-4012    

DOI:10.1002/jnr.490390610

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

ISSN:0360-4012    

DOI:10.1002/jnr.490390611

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY