Inhibition of phosphodiesterase4's in culture or in vivo overcomes inhibition of regeneration by MAG and myelin.
Item
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Title
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Inhibition of phosphodiesterase4's in culture or in vivo overcomes inhibition of regeneration by MAG and myelin.
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Identifier
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AAI3083695
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identifier
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3083695
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Creator
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Nikulina, Elena.
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Contributor
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Adviser: Marie T. Filbin
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Date
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2003
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Neuroscience | Biology, Molecular
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Abstract
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Axons of the adult mammalian central nervous system (CNS) do not regenerate after injury. Previously, we showed that elevation of cAMP, either via db-cAMP or by priming neurons with BDNF prior to exposure to myelin, blocks inhibition of axonal regeneration by myelin associated glycoprotein (MAG) and myelin. Here, we assess the effects of elevating cAMP in neurons using rolipram, a specific inhibitor of phosphodiesterase4's (PDE4) (the enzymes that hydrolyze cAMP) on the ability of the neurons to grow in the presence of MAG and myelin. First, rolipram was added directly to the media of neurons growing on MAG, which partially overcame the inhibition by MAG. However, prior incubation of neurons with rolipram before exposure to MAG or myelin resulted in a complete block of inhibition by MAG and myelin. Second, we administered rolipram subcutaneously to animals prior to isolation of neurons used in the neurite outgrowth assay. We report here that after continuous, subcutaneous delivery of rolipram for one day with osmotic minipumps, DRG neurons were not inhibited by MAG or myelin when grown in culture, this block of inhibition was abrogated by inhibitors of protein kinase A (PKA) and transcription. After two days of rolipram treatment, growth of DRG neurons, both in presence and absence of inhibitors, was improved. This improved growth was PKA-independent and transcription-independent. This study reveals the potential therapeutic value of specific inhibitors of PDE4 in encouraging axonal regeneration after injury.;Additionally, we report that downregulation of PDE4 activity can account for the elevation of CAMP levels in the course of priming neurons with BDNF. Total PDE activity in neurons decreases sharply after addition of BDNF. This decrease in PDE activity, specifically PDE4s, is ERK-dependent. Subsequent elevation of CAMP levels is dependent on activation of ERK. To our knowledge, this is the first time that ERK-dependent inactivation of PDE4 activity and subsequent elevation of CAMP levels have been demonstrated in primary neuronal cultures in response to BDNF.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
