The Journal of neuroscience : the official journal of the Society for Neuroscience
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We hypothesized that adenosine, acting via the A1 receptor, is a key factor in the homeostatic control of sleep. The increase in extracellular levels of adenosine during prolonged wakefulness is thought to facilitate the transition to sleep by reducing the discharge activity of wakefulness-promoting neurons in the basal forebrain. Adenosine A1 receptor control of the homeostatic regulation of sleep was tested by microdialysis perfusion of antisense oligonucleotides against the mRNA of the A1 receptor in the magnocellular cholinergic region of the basal forebrain of freely behaving rats. ⋯ Control experiments with microdialysis perfusion of nonsense (randomized antisense) oligonucleotides and with artificial CSF showed no effect during postdeprivation recovery sleep or spontaneously occurring behavioral states. Antisense to the A1 receptor suppressed A1 receptor immunoreactivity but did not show any neurotoxicity as visualized by Fluoro-Jade staining. These data support our hypothesis that adenosine, acting via the A1 receptor, in the basal forebrain is a key component in the homeostatic regulation of sleep.
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Traumatized axons possess an extremely limited ability to regenerate within the adult mammalian CNS. The myelin-derived axon outgrowth inhibitors Nogo, oligodendrocyte-myelin glycoprotein, and myelin-associated glycoprotein, all bind to an axonal Nogo-66 receptor (NgR) and at least partially account for this lack of CNS repair. Although the intrathecal application of an NgR competitive antagonist at the time of spinal cord hemisection induces significant regeneration of corticospinal axons, such immediate local therapy may not be as clinically feasible for cases of spinal cord injury. ⋯ Furthermore, delaying the initiation of systemic NEP1-40 administration for up to 1 week after cord lesions does not limit the degree of axon sprouting and functional recovery. This indicates that the regenerative capacity of transected corticospinal tract axons persists for weeks after injury. Systemic Nogo-66 receptor antagonists have therapeutic potential for subacute CNS axonal injuries such as spinal cord trauma.
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The presence of reactive astrocytes around glioma cells in the CNS suggests the possibility that these two cell types could be interacting. We addressed whether glioma cells use the astrocyte environment to modulate matrix metalloproteinase-2 (MMP-2), a proteolytic enzyme implicated in the invasiveness of glioma cells. We found that astrocytes in culture produce significant amounts of the pro-form of MMP-2 but undetectable levels of active MMP-2. ⋯ In correspondence with this biochemical cascade, the transmigration of U251N cells through Boyden invasion chambers coated with an extracellular matrix barrier was increased significantly in the presence of astrocytes, and this was inhibited by agents that disrupted the uPA-plasmin cascade. Finally, using resected human glioblastoma specimens, we found that tumor cells, but not astrocytes, expressed plasminogen in situ. We conclude that glioma cells exploit their astrocyte environment to activate MMP-2 and that this leads to the increased invasiveness of glioma cells.
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To investigate the intracellular signal transduction pathways involved in regulating the gene expression of brain-derived neurotrophic factor (BDNF) in primary afferent neurons, we examined the activation of extracellular signal-regulated protein kinase (ERK) in dorsal root ganglion (DRG) neurons after peripheral inflammation and sciatic nerve transection. Peripheral inflammation induced an increase in the phosphorylation of ERK, mainly in tyrosine kinase A-containing small-to-medium-diameter DRG neurons. The treatment of the mitogen-activated protein kinase (MAPK) kinase 1/2 inhibitor U0126 reversed the pain hypersensitivity and the increase in phosphorylated-ERK (p-ERK) and BDNF in DRG neurons induced by complete Freund's adjuvant. ⋯ The intrathecal application of nerve growth factor (NGF) induced an increase in the number of p-ERK-and BDNF-labeled cells, mainly small neurons, and the application of anti-NGF induced an increase in p-ERK and BDNF in some medium-to-large-diameter DRG neurons. The activation of MAPK in the primary afferents may occur in different populations of DRG neurons after peripheral inflammation and axotomy, respectively, through alterations in the target-derived NGF. These changes, including the changes in BDNF expression, might be involved in the pathophysiological changes in primary afferent neurons.
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Tyrosine kinase phosphorylation plays an important role in the induction of long-term potentiation (LTP). Focal adhesion kinase (FAK) is a 125 kDa nonreceptor tyrosine kinase that shows decreased phosphorylation in fyn mutant mice, and Fyn plays a critical role in LTP induction. By examining the role of FAK involved in LTP induction in dentate gyrus in vivo with medial perforant path stimulation, we found that both FAK and mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) phosphorylation were increased significantly 5 and 10 min after LTP induction, whereas cAMP-responsive element binding protein (CREB) phosphorylation was increased 40 min later. ⋯ Immunoprecipitation results revealed that tyrosine phosphorylation of NR2A and NR2B as well as the association of phosphorylated FAK with NR2A and NR2B was increased with LTP induction. These results together suggest that FAK is required, but not sufficient, for the induction of LTP in a NMDAR-independent manner and that MAPK/ERK and CREB are the downstream events of FAK activation. Further, FAK may interact with NR2A and NR2B to modulate LTP induction.