Journal of molecular neuroscience : MN
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Neutral endopeptidase (EC3.4.24.11, NEP, enkephalinase) is a zinc-metalloendopeptidase, cleaving a variety of substrates like enkephalins, substance P, and bradykinin. In the brain, NEP is a key enzyme in the degradation of enkephalins. Pharmacological inhibition of NEP-activity causes analgesia resulting from enhanced extracellular enkephalin concentrations. ⋯ Similarly, the nitric oxide synthase inhibitor L-NAME reduced writhing in NEP-knockouts. These results indicate that genetic elimination of NEP, in contrast to pharmacological inhibition, leads to bradykinin-induced hyperalgesia instead of enkephalin-mediated analgesia. Nitric oxide (NO) is suggested to be involved in this process.
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Adenosine monophosphate-activated protein kinase (AMPK) is a member of metabolite-sensing kinase family that plays important roles in responses of muscle cells to metabolic stress. AMPK is a heterotrimer of a catalytic alpha subunit (alpha1 or alpha2), and beta (beta1 or beta2) and gamma (gamma1 or gamma2) subunits. Because the brain has a high metabolic rate and is sensitive to changes in the supply of glucose and oxygen, we investigated the expression of AMPK in rat embryonic and adult brain and its role in modifying neuronal survival under conditions of cellular stress. ⋯ The AMPK-activating agent AICAR protected hippocampal neurons against death induced by glucose deprivation, chemical hypoxia, and exposure to glutamate and amyloid beta-peptide. Suppression of levels of the AMPK alpha1 and alpha2 subunits using antisense technology resulted in enhanced neuronal death following glucose deprivation, and abolished the neuroprotective effect of AICAR. These findings suggest that AMPK can protect neurons against metabolic and excitotoxic insults relevant to the pathogenesis of several different neurodegenerative conditions.
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Zellweger syndrome is the prototypic human peroxisomal biogenesis disorder that results in abnormal neuronal migration in the central nervous system and severe neurologic dysfunction. A murine model for this disorder was previously developed by targeted deletion of the PEX2 peroxisomal gene. By labeling neuronal precursor cells in vivo with a mitotic marker, we can demonstrate a delay in neuronal migration in the cerebral cortex of homozygous PEX2 mutant mice. ⋯ Docosahexaenoic acid levels (DHA; 22:6n-3) were found to be reduced in the brain of mutant mice but were normal in visceral organs at birth. All tissues examined in postnatal mutant mice had reduced DHA. The combined use of morphologic and biochemical analyses in these mice will be essential to elucidate the pathogenesis of this complex peroxisomal disease.
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Comparative Study
Immunolocalization of tenascin-C in human type II fiber atrophy.
Tenascin-C is a multifunctional extracellular matrix glycoprotein with stimulatory and anti-adhesive or inhibitory properties for axon growth. Its location and discontinuous expression are restricted in innervated muscle tissues. Tenascin-C accumulated interstitially among human denervated muscle fibers and close to normal-sized fibers. ⋯ Around atrophic type II muscle fibers. 3. Around small-caliber myofibers with centrally located nuclei. These results indicate that tenascin-C immunoreactivity: (1) is detectable around early denervated and reinnervated muscle fibers and, therefore, (2) may reflect in part the molecularly ongoing process of denervation and reinnervation in human type II fiber atrophy.
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To study the role of the protein B-50/GAP-43 in NGF-induced neurite outgrowth, a number of stable PC12 subclones with either very low or considerably enhanced expression levels of the protein were selected. Cell bodies of subclones with suppressed B-50 expression (-B2, -B5, or -B12) possessed a relative small spherical shape and, on NGF-treatment for 7 d, developed processes that were virtually devoid of branches and that mostly bore short or blunt-ended growth cones. ⋯ Confocal microscopy with immunofluorescence for B-50 and F-actin revealed that in neurites and growth cones of the B-50-deficient subclone -B2, no detectable B-50 and reduced amounts of filamentous F-actin were present, whereas in overexpressing +B3 cells, cell membranes, neurites, and complex growth cones were intensively stained for B-50 and exhibited numerous spikes, in which B-50 was strikingly colocalized with F-actin. These data suggest that, under normal conditions of neuritogenesis, the expression level of B-50 in PC12 cells is decisive for the complexity of neurites and growth cones.