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      Glucocorticoid Generates ROS to Induce Oxidative Injury in the Hippocampus, Leading to Impairment of Cognitive Function of Rats

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          Abstract

          The present study attempted to clarify whether over-secretion of glucocorticoids in the serum caused by increased hypothalamus-pituitary-adrenal activity induces oxidative stress in the rat brain, and how the stress causes the emergence of cognitive deficits. When rats were subcutaneously injected with corticosterone, lipid hydroperoxides and protein carbonyls increased markedly in the hippocampus in association with a decrease in activity of antioxidative enzymes, such as superoxide dismutase, catalase and glutathione peroxidase. These results suggest that high-level corticosterone in the serum induces reactive oxygen species (ROS), leading to oxidative damage in the hippocampus. After administration of corticosterone to rats, glucose and superoxide levels in the serum increased markedly. Furthermore, pyramidal cell apoptosis was observed to accompany the loss of glucocorticoid receptors at the cornus ammonis 1 region of the hippocampus. Rats injected with corticosterone showed marked deficits in memory function. The present results imply that ROS generated from the glycation reaction of increased glucose levels caused by gluconeogenesis activation through glucocorticoid with proteins in the serum attack the hippocampus to induce neurodegeneration, resulting in cognitive deficits in rats.

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          Most cited references 16

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          Identification of programmed cell death in situ via specific labeling of nuclear DNA fragmentation

          Programmed cell death (PCD) plays a key role in developmental biology and in maintenance of the steady state in continuously renewing tissues. Currently, its existence is inferred mainly from gel electrophoresis of a pooled DNA extract as PCD was shown to be associated with DNA fragmentation. Based on this observation, we describe here the development of a method for the in situ visualization of PCD at the single-cell level, while preserving tissue architecture. Conventional histological sections, pretreated with protease, were nick end labeled with biotinylated poly dU, introduced by terminal deoxy- transferase, and then stained using avidin-conjugated peroxidase. The reaction is specific, only nuclei located at positions where PCD is expected are stained. The initial screening includes: small and large intestine, epidermis, lymphoid tissues, ovary, and other organs. A detailed analysis revealed that the process is initiated at the nuclear periphery, it is relatively short (1-3 h from initiation to cell elimination) and that PCD appears in tissues in clusters. The extent of tissue-PCD revealed by this method is considerably greater than apoptosis detected by nuclear morphology, and thus opens the way for a variety of studies.
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            The role of the hippocampus in feedback regulation of the hypothalamic-pituitary-adrenocortical axis.

            There is considerable, although not entirely consistent, evidence that the hippocampus inhibits most aspects of HPA activity, including basal (circadian nadir) and circadian peak secretion as well as the onset and termination of responses to stress. Although much of the evidence for these effects rests only on the measurement of corticosteroids, recent lesion and implant studies indicate that the hippocampus regulates adrenocortical activity at the hypothalamic level, via the expression and secretion of ACTH secretagogues. Such inhibition results largely from the mediation of corticosteroid feedback, although more work is required to determine whether the hippocampus supplies a tonic inhibitory input in the absence of corticosteroids. It must be noted that the hippocampus is not the only feedback site in the adrenocortical system, since removal of its input only reduces, but does not abolish, the efficacy of corticosteroid inhibition, and since other elements of the axis appear eventually to compensate for deficits in feedback regulation. The importance of other feedback sites is further suggested not only by the presence of corticosteroid receptors in other parts of the brain and pituitary, but also by the improved prediction of CRF levels by combined hypothalamic and hippocampal receptor occupancy. The likelihood of feedback mediated by nonhippocampal sites underscores the need for future work to characterize hippocampal influence on HPA activity in the absence of changes in corticosteroid secretion. However, despite the fact that the hippocampus is not the only feedback site, it is distinguished from most potential feedback sites, including the hypothalamus and pituitary, by its high content of both type I and II corticosteroid receptors. The hippocampus is therefore capable of mediating inhibition over a wide range of steroid levels. The low end of this range is represented by corticosteroid inhibition of basal (circadian nadir) HPA activity. The apparent type I receptor specificity of this inhibition and the elevation of trough corticosteroid levels after hippocampal damage support a role for hippocampal type I receptors in regulating basal HPA activity. It is possible that basal activity is controlled in part through hippocampal inhibition of vasopressin, since the inhibition of portal blood vasopressin correlates with lower levels of hippocampal receptor occupancy, and the expression of vasopressin by some CRF neurons is sensitive to very low corticosteroid levels. At the high end of the physiological range, stress-induced or circadian peak corticosteroid secretion correlates strongly with occupancy of the lower affinity hippocampal type II receptors.(ABSTRACT TRUNCATED AT 400 WORDS)
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              Cognitive impairment of rats caused by oxidative stress and aging, and its prevention by vitamin E.

              In order to verify whether brain damage caused by chronic oxidative stress induces the impairment of cognitive function, the ability of learning and memory was assessed using the water maze and the eight-arm radial maze tasks. Young rats showed significantly greater learning ability before the stress than the old and vitamin E-deficient rats. At five days after subjection to oxidative stress, the memory function of the young declined toward the level of that in the aged rats maintained under normal condition. This phenomenon is supported by the findings that the delayed-type apoptosis appeared in the CA1 region of the hippocampus of the young at five to seven days after the stress. Vitamin E supplementation to the young accelerated significantly their learning functions before the stress and prevented the deficit of memory caused by the stress. When rats were subjected to stress, thiobarbituric acid-reactive substance (TBARS), lipid hydroperoxides, and protein carbonyls were significantly increased in synaptic plasma membranes. It was found that zeta-potential of the synaptic membrane surface was remarkably decreased. These phenomena were also observed in the aged and vitamin E-deficient rats maintained under normal condition. These results suggest that oxidative damage to the rat synapse in the cerebral cortex and hippocampus during aging may contribute to the deficit of cognitive functions.
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                Author and article information

                Journal
                J Clin Biochem Nutr
                JCBN
                Journal of Clinical Biochemistry and Nutrition
                the Society for Free Radical Research Japan (Kyoto, Japan )
                0912-0009
                1880-5086
                November 2010
                29 October 2010
                : 47
                : 3
                : 224-232
                Affiliations
                [1 ]Division of Biological Chemistry, Shibaura Institute of Technology, 3-7-5 Toyosu, Kohtoh-ku, Tokyo 135-8548, Japan
                [2 ]Division of Biochemistry, Shibaura Institute of Technology, 307 Fukasaku, Minuma-ku, Saitama-shi, Saitama 337-8570, Japan
                Author notes
                *To whom correspondence should be addressed. Tel: +81-48-720-6035 Fax: +81-48-720-6011 E-mail: urano@ 123456sic.shibaura-it.ac.jp
                Article
                jcbn10-58
                10.3164/jcbn.10-58
                2966932
                21103031
                a0e6c1ee-161e-4afe-a4a1-e233c4fd52a7
                Copyright © 2010 JCBN

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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