Dynamic and interacting profiles of *NO and O2 in rat hippocampal slices

Center for Neurosciences and Cell Biology, University of Coimbra, 3000 Coimbra, Portugal.
Free Radical Biology and Medicine (Impact Factor: 5.74). 04/2010; 48(8):1044-50. DOI: 10.1016/j.freeradbiomed.2010.01.024
Source: PubMed


Nitric oxide (*NO) is a ubiquitous signaling molecule that participates in the neuromolecular phenomena associated with memory formation. In the hippocampus, neuronal *NO production is coupled to the activation of the NMDA-type of glutamate receptor. Although *NO-mediated signaling has been associated with soluble guanylate cyclase activation, cytochrome oxidase is also a target for this gaseous free radical, for which *NO competes with O(2). Here we show, for the first time in a model preserving tissue cytoarchitecture (rat hippocampal slices) and at a physiological O(2) concentration, that endogenous NMDA-evoked *NO production inhibits tissue O(2) consumption for submicromolar concentrations. The simultaneous real-time recordings reveal a direct correlation between the profiles of *NO and O(2) in the CA1 subregion of the hippocampal slice. These results, obtained in a system close to in vivo models, strongly support the current paradigm for O(2) and *NO interplay in the regulation of cellular respiration.

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    • "The NO-inhibited respiration lowers the steepness of intracellular O 2 gradients and allows O 2 to diffuse further along its gradient, extending the space of adequate tissue oxygenation away from the blood vessel. Endogenous NO production has been shown to inhibits tissue O 2 consumption in hippocampal slices at physiological O 2 concentration, strongly supporting the current paradigm for O 2 and NO interplay in the regulation of cellular respiration (Ledo et al., 2010). "
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    ABSTRACT: Taking into account the importance of aerobic metabolism in brain, the aim of the present work was to evaluate mitochondrial function in cerebral cortex and hippocampus in a model of sustained hypobaric hypoxia (5000 m simulated altitude) during a short (1 mo) and a long (7 mo) term period, in order to precise the mechanisms involved in hypoxia acclimatization. Hippocampal mitochondria from rats exposed to short-term hypobaric hypoxia showed lower respiratory rates than controls in both states 4 (45%) and 3 (41%), and increased NO production (1.3 fold) as well as eNOS and nNOS expression associated to mitochondrial membranes, whereas mitochondrial membrane potential decreased (7%). No significant changes were observed in cortical mitochondria after 1 mo hypobaric hypoxia in any of the mitochondrial functionality parameters evaluated. After 7 mo hypobaric hypoxia, oxygen consumption was unchanged as compared with control animals both in hippocampal and cortical mitochondria, but mitochondrial membrane potential decreased by 16% and 8% in hippocampus and cortex respectively. Also, long-term hypobaric hypoxia induced an increase in hippocampal NO production (0.7 fold) and in eNOS expression. A clear tendency to decrease in H2O2 production was observed in both tissues. Results suggest that after exposure to hypobaric hypoxia, hippocampal mitochondria display different responses than cortical mitochondria. Also, the mechanisms responsible for acclimatization to hypoxia would be time-dependent, according to the physiological functions of the brain studied areas. Nitric oxide metabolism and membrane potential changes would be involved as self-protective mechanisms in high altitude environment.
    Brain Research 12/2014; 1598. DOI:10.1016/j.brainres.2014.12.018 · 2.84 Impact Factor
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    • "By using this methodological approach we were able to show that NMDA-evoked •NO concentration dynamics is heterogeneous along the trisynaptic loop in the rat hippocampus [57]. We also provided evidence that the AMPAr in addition to the NMDAr could contribute to the fine tuning of glutamate-dependent •NO production [58] and that NMDA-evoked •NO production inhibits tissue O2 consumption for submicromolar concentrations [59]. "
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    ABSTRACT: During the last decades nitric oxide ((•)NO) has emerged as a critical physiological signaling molecule in mammalian tissues, notably in the brain. (•)NO may modify the activity of regulatory proteins via direct reaction with the heme moiety, or indirectly, via S-nitrosylation of thiol groups or nitration of tyrosine residues. However, a conceptual understanding of how (•)NO bioactivity is carried out in biological systems is hampered by the lack of knowledge on its dynamics in vivo. Key questions still lacking concrete and definitive answers include those related with quantitative issues of its concentration dynamics and diffusion, summarized in the how much, how long, and how far trilogy. For instance, a major problem is the lack of knowledge of what constitutes a physiological (•)NO concentration and what constitutes a pathological one and how is (•)NO concentration regulated. The ambient (•)NO concentration reflects the balance between the rate of synthesis and the rate of breakdown. Much has been learnt about the mechanism of (•)NO synthesis, but the inactivation pathways of (•)NO has been almost completely ignored. We have recently addressed these issues in vivo on basis of microelectrode technology that allows a fine-tuned spatial and temporal measurement (•)NO concentration dynamics in the brain.
    International Journal of Cell Biology 06/2012; 2012(4):391914. DOI:10.1155/2012/391914
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    • "While more data is needed to better address this question, perfusing slices with a 20% O2 solution might be closer to physiological conditions and is unlikely to induce cell death (D'Agostino et al., 2007). In a recent study, Ledo et al. (2010) simultaneously measured NO and O2 levels 200 μm deep into the slice using an aCSF solution bubbled with 95% O2–5% CO2; under these conditions O2 levels were around 57.3 ± 38.2 μM. To our knowledge the outcome of 20% O2 levels on NO availability at different depths of the brain slice has not been explored and would need further consideration, given the steep O2 gradient from the surface of the slice to deeper layers (∼200 μm) (Ledo et al., 2005). "
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    Frontiers in Neuroenergetics 08/2010; 2. DOI:10.3389/fnene.2010.00016
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