摘要:

AbstractTransferrin, the iron mobilization protein, and its mRNA are normally present in oligodendrocytes. Previous reports using myelin mutants have shown both a decrease in transferrin protein and mRNA when the oligodendrocyte population is compromised. In this study the shiverer mouse mutant in which the oligodendrocyte population is numerically normal, but has both quantitatively diminished and qualitatively abnormal myelin was used. This animal model was chosen to address the question whether expression of the transferrin message and/or protein correlated more closely to the number of oligodendrocytes (normal) or the amount of myelin (abnormally low). A 1/2 to 2/3 decrease in transferrin protein occurred in all brain regions examined except for the spinal cord in the shiverer group compared to both heterozygous littermates and wild type controls. Levels of transferrin transcripts in the brain are not affected by the shiverer mutation. These results taken with previous reports from this laboratory indicate that the presence of oligodendrocytes is a requirement for normal expression of transferrin mRNA in brain but is not sufficient for normal values of the protein. The level of Tf protein correlates more closely with the amount of myelin present than it does with the numbers of oligodendrocytes present. These data are consistent with previous reports from our laboratory that transferrin accumulation by oligodendrocytes is associated with myelin production by these cells. These data further suggest transferrin mRNA may be constitutively expressed by oligodendrocytes and that the protein expression is regulated at the level of translation. © 1993 Wiley‐Liss, I

ISSN:0360-4012    

DOI:10.1002/jnr.490360502

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

年代:1993

数据来源: WILEY

摘要:

AbstractMyelin P2is a basic protein of an apparent molecular weight of 14,800. Expression of P2has been found largely in the cytosol of Schwann cells in the peripheral nervous system. Although the function of P2is unknown, its striking homology to a family of fatty acid binding proteins has led to the idea that P2may function as a fatty acid transport molecule. To investigate the DNA elements that control the expression of P2, sequences 5′ to the coding region were cloned upstream of thecatreporter gene. A series of 3′ and 5′ promoter mutants was constructed and their activity determined following transfection into secondary Schwann cells and the MT4H1 Schwann cell line. Using this strategy, we have identified a 217 bp silencer region and a 142 bp positive regulatory region. In addition, we have localized the 5′ flanking sequences in the promoter that are responsive to cAMP induction and to the transcription factor CCAAT/enhancer binding protein (C/EBP). © 1993 Wiley

ISSN:0360-4012    

DOI:10.1002/jnr.490360503

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

年代:1993

数据来源: WILEY

摘要:

AbstractInsulin‐like growth factor I (IGF‐I) and its receptor are expressed in functionally related areas of the rat brain such as the inferior olive and the cerebellar cortex. A marked decrease of IGF‐I levels in cerebellum is found when inferior olive neurons are lesioned. In addition, Purkinje cells in the cerebellar cortex depend on this growth factor to survive and differentiate in vitro. Thus, we consider it possible that IGF‐I forms part of a putative trophic circuitry encompassing the inferior olive and the cerebellar cortex and possibly other functionally connected areas. To test this hypothesis we have studied whether IGF‐I may be taken up, transported, and released from the inferior olive to the cerebellum. We have found that125I‐IGF‐I is taken up by inferior olive neurons in a receptor‐mediated process and orthogradely transported to the cerebellum. Thus, radioactivity found in the cerebellar lobe contralateral to the injection site in the inferior olive was immunoprecipitated by an anti‐IGF‐I antibody, co‐eluted with125I‐IGF‐I in an HPLC column, and co‐migrated with125I‐IGF‐I in an SDS‐urea polyacrylamide gel electrophoresis. Time‐course studies indicated that orthograde axonal transport is relatively rapid since 30 min after the injection, radiolabeled IGF‐I was already detected in the contralateral cerebellum. Furthermore, transport of IGF‐i from the inferior olive is specific since when125I‐neurotensin was injected in the inferior olive or when125I‐IGF‐I was injected in the pontine nucleus, no radiactivity was found in the contralateral cerebellum. In addition, no specific transport of125I‐IGF‐I was found in climbing fiber‐deafferented rats or when excess unlabeled IGF‐I was co‐injected with125I‐IGF‐I. We next studied whether IGF‐I is released by inferior olive neurons. We found that the release of IGF‐I from cerebellar slices of normal rats was significantly greater in response to depolarizing stimuli than that from slices obtained of climbing fiber‐deafferented animals. Indeed, in vitro release of IGF‐I in response to KCI or veratridine was almost completely abolished in the latter. These data suggest that IGF‐I is taken up by inferior olive neurons through IGF‐I receptors and transported to the cerebellum through their axons without any major modification. Moreover, the release of IGF‐I from the cerebellum after depolarization depends on the presence of climbing fiber afferents. Altogether these results indicate that the olivo‐cerebellar pathway is able to take up, orthogradely transport, and release IGF‐I. Since a similar process has been described in the visual system for basic fibroblast growth factor (bFGF), we propose that IGF‐I, bFGF, and possibly other growth factors may constitute afferent trophic signals involved i

ISSN:0360-4012    

DOI:10.1002/jnr.490360504

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

年代:1993

数据来源: WILEY

摘要:

AbstractCranin is a 120 kDa integral membrane glycoprotein which binds laminin under conditions of physiologic ionic strength in a calcium‐dependent manner. Here, binding of cranin to laminin has been characterized using both ligand‐blotting assays and laminin affinity bead assays. Binding was specifically inhibited by anti‐laminin antibodies against the A chain terminal domain G, but not by several other region‐specific antibodies. Dextran sulfate, fucoidin, and sulfatide were potent inhibitors of binding (50% inhibition at 0.03, 0.5, and 1.7 μg/ml, respectively); heparin was a weaker inhibitor (50% inhibition ∼5 μg/ml), and mannan and chondroitin sulfate were not inhibitory at 100 μ/ml. Binding was not inhibited by lactose or the A chain peptide PA22‐2. The mobility of the broad, fuzzy cranin band was shifted after digestion with neuraminidase, N‐glycanase, and O‐glycanase, though none of these treatments decreased band heterogeneity nor destroyed the ability to bind laminin. Cranin bound to Jacalin lectin, which recognizes the Galβ1‐3GalNAc linkage expressed in certain classes of mucins. These findings indicate that cranin binds at or near the high affinity sulfatide‐binding site previously mapped to the E3 domain of laminin, which is known to exhibit bioactivity for neural cells. In view of the extremely low abundance of cranin in brain membranes (∼0.005%), its avid laminin‐binding activity is remarkable, and strongly suggests that cranin may play a physiologic role in regulating specific neural cell interacti

ISSN:0360-4012    

DOI:10.1002/jnr.490360505

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

年代:1993

数据来源: WILEY

摘要:

AbstractEpidermal growth factor (EFG) induced short neurites in two different strains of PC12 cells. The length of the EGF‐induced neurites was markedly increased in the presence of the protein kinase inhibitor K252a, which is known to inhibit differentiation induced by nerve growth factor (NGF). EGF‐induced differentiation of PC12 required RNA synthesis and activity of the ras proto‐oncogene product. EGF increased the levels of three neurofilament proteins and the mRNA level of two late response genes (SCG10 and 63) known to be induced by NGF. Together, EGF and K252a caused a greater increase in these mRNAs than did either agent alone. K252a did not alter the extent of EGF‐induced autophosphorylation of the EGF receptor, but it did decrease the extent of receptor phosphorylation in the absence of added EGF. Thus, the ability of the EGF receptor to trigger neuronal differentiation may depend on the state of its phosphorylation at serine and/or threonine residues. Two other strains of PC12 did not extend neurites when exposed to EGF, even when K252a was also present. Thus the differentiating effect of EGF on PC12 is PC12 strain‐specific. © 1993 Wiley

ISSN:0360-4012    

DOI:10.1002/jnr.490360506

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe mechanisms involved in the development of morphine tolerance and dependence are still unknown. Recently much attention has been directed toward the changes in post receptor events. Opiate receptors, like other hormone and neurotransmitter receptors, have been shown to mediate their effects through guanine nucleotide binding proteins (G‐proteins). This, in turn, may cause alterations in intracellular events, one of which is transcription of specific genes. We investigated the changes in the levels of mRNA of proenkephalin (PPE) and prodynorphin (DYN) and the stimulatory G protein alpha subunit (Gαs) in adult morphine tolerant rats. Chronic morphine treatment induced reciprocal alterations in the levels of opioid peptide mRNA and Gαsin discrete brain regions. In striatum, PPE mRNA decreased by 49% (P<.01) and in hypothalamus. DYN mRNA showed a decrease of 21% (P<.01). In contrast, GαsmRNA increased 20% (P<.01) in striatum and 97% (P<.01), in hypothalamus. In hippocampus the changes were reversed: PPE mRNA increased (55%,P<.05) and GαsmRNA decreased (33%,P<.01). Frontal cortex exhibited a samll decrease in PPE (11.5%,P<.05) without any change on Gαsor DYN mRNA levels. These reciprocal alterations suggest an apposing mode of regulation of Gαsand PPE/DYN gene expression in morphine tolerant animals. © 1993 Wiley

ISSN:0360-4012    

DOI:10.1002/jnr.490360507

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe neurotoxic effect of glutamate in cultured mouse mesencephalic dopaminergic neurons was investigated. Neuron‐rich cell cultures were prepared from 13–14‐day‐old fetal mouse ventral mesencephalic tissue. Cultures were exposed to glutamate for 10 min and evaluated for glutamate neurotoxicity (GNT) 18–24 hr later by tyrosine hydroxylase (TH) immunostaining, microtubule associated protein‐2 (MAP2)immunostaining, and radiolabeled dopamine uptake assay.In glutamate‐exposed cultures, the number of TH‐positive neurons and the level of dopamine uptake were reduced to 40% (35–45%) and 50% (47–52%), respectively, of control cultures. The number of MAP2‐positive neurons was also reduced to 47%, indicating that the GNT was not restricted or selective to dopaminergic neurons.It is concluded that GNT was mediated by the N‐methyl‐D‐aspartic acid (NMDA) receptor from the following observations: (1) GNT was completely blocked by MK‐801, an NMDA receptor antagonist; (2) NMDA itself was as toxic as glutamate; (3) 6‐cyano‐7‐nitroquinoxaline‐2, 3‐dione (CNQX), an antagonist of the α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid/kainate (AMPA/KA) receptor, did not block GNT; (4) kainate did not show neurotoxicity at a low concentration; and 5) two modulators of the NMDA receptor, 7‐chlorokynurenic acid and magnesium, were effective in blocking GNT.Protective effects of phorbol myristate acetate, a tumor promoter, and gangliosides (GM1and GT1bon GNT were also demonstrated. Possible interactions between GNT and several protein kinase cascades were also investigated. Forskolin, an activator of adenyl cyclase and protein kinase A, showed some protective effect on GNT. But okadaic acid, an inhibitor of phosphatases, and genistein, a tyrosine kinase inhibitor, did not show any protective effect.These results suggest that (1) glutamate is capable of causing neuronal death in the substantia nigra; (2) GNT on dopaminergic neurons is mainly mediated by the NMDA receptor under the conditions of our study; (3) protein kinase C translocation is a key mechanism of GNT; and (4) there is an interplay of a signal transduction sys

ISSN:0360-4012    

DOI:10.1002/jnr.490360508

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn this study we used as glial cell models, early and late passage C‐6 glial cells, 2B clone, and advanced passages of glial cells derived from aged mouse cerebral hemispheres (MACH) to examine responsiveness to opioids. We have previously reported that early passage C‐6 glial cells, 2B clone, are bipotential and can be geared toward oligodendrocyte or astrocytic expression, whereas late passage C‐6 glial cells are astrocytic. In addition, MACH cultures have been previously characterized and consist of astrocytes type 1 and 2, some oligodendrocytes, and few glial precursors. In this study, early passage (17–20) and late passage (106–108) C‐6 glial cells or MACH cells of passages 16–19 were grown from plating time until harvesting, day 7 or 8, in DMEM + 10% FBS in the presence or absence of opioid peptides, Leu‐enkephalin (10−8to 10−10M) or its synthetic analog, dalargin (Tyr‐D‐Ala‐Gly‐Phe‐Leu‐Arg; 10−8to 10−10M). We examined for the activities of glutamine synthetase (GS) and cyclic nucleotide phosphohydrolase (CNP), enzyme markers for astrocytes and oligodendrocytes, respectively. We found that CNP activity was markedly increased in the early passage following opioid treatment, indicative of a shift to oligodendrocytic expression. In the late passage cells, already committed to astrocytic expression, opioid treatment enhanced GS activity suggesting that astrocytes respond to opioids. GS activity was markedly increased in MACH cultures grown in the presence of opioids with no changes in CNP. Thus, type 1 astrocytes, the predominant glial type in MACH cultures, responded to opioids. We conclude from these findings derived from two different glial models that regulation of astrocytes by microenvironmental signals appears to be maintained

ISSN:0360-4012    

DOI:10.1002/jnr.490360509

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

年代:1993

数据来源: WILEY

摘要:

AbstractNADPH‐diaphorase histochemistry has been applied for the localization of nitric oxide synthase during the postnatal development of the mouse cerebellum. Staining for NADPH‐diaphorase during the first week after birth was confined to some but not all laminae of the immature cerebellum: NADPH‐diaphorase activity was located in the molecular/Purkinje cell layer and in inner parts of the internal granular layer. The external granular layer and the developing white matter were essentially unstained. Expression was earliest and very strong in parallel fibers and in the internal granule layer of the ventral part of the pyramis and the dorsal part of the uvula. Staining in the Purkinje cell layer was observed throughout the cerebellum. The presence of formazan deposits within Purkinje cells was verified by colocalization with calbindin D‐28k immunoreactivity. The distribution of NADPH‐diaphorase activity changed into the adult pattern between 8 and 12 days of age: Within the molecular layer, basket cells and their processes became strongly stained. Reaction product within Purkinje cells gradually disappeared. Likewise, strongly stained parallel fibers were no longer detectable. These results suggest that nitric oxide is involved in different processes in cerebellar development. © 1993 Wiley

ISSN:0360-4012    

DOI:10.1002/jnr.490360510

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

年代:1993

数据来源: WILEY

摘要:

AbstractDirect brain injections of the N‐methyl‐D‐aspartate receptor agonist quinolinic acid (QA) trigger an excitotoxic cascade characterized by rapid neuronal death and glial/immune cell activation. The present study compared the timing of immediate early gene (IEG; c‐fos, c‐jun, jun‐B, and zif/268) induction with the response of neuronal ranscripts during the first 24 hr of a QA lesion within the rodent striatum. Following QA exposure, IEG mRNA induction periods extended from 30 min to 24 hr. Several characteristics of this prolonged transcriptional response suggest that separate cell populations (neuronal vs. glial) originate individual IEG phases during the first day of the lesion. The first IEG phase was rapid and peaked at 60 min. This initial IEG phase, likely neuronal in origin, was dominated by robust increases in the expression of c‐fos, jun‐B, and zif/268 mRNAs in contrast to small increases in c‐jun expression. A second, delayed IEG phase was initiated after the first hour and extended to 24 hr. This IEG phase was more intense and continued beyond the period of neuronal survival as detected by the loss of neurotransmitter‐specific mRNAs (preprotachykinin, preproenkephalin, and glutamic acid decarboxylase). During this phase, c‐jun mRNA levels coordinately increased with c‐fos. Interestingly, the transcriptional peak of the delayed IEG phase occurred between 4 and 12 hr, the time which corresponded to the rapid decline of neuronal transcripts. The temporal association of a delayed phase of IEG induction, possibly originating in nonneuronal cells, with neuronal death during the acute phases of the excitotoxic cascade suggest a link between glial IEG activation and the spreading cascade of neuronal damage characteristic of excitatory amino acid receptor overstimulation.

ISSN:0360-4012    

DOI:10.1002/jnr.490360511

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

年代:1993

数据来源: WILEY