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121.
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Robin I. M. Dunbar 《Evolutionary anthropology》1998,6(5):178-190
Conventional wisdom over the past 160 years in the cognitive and neurosciences has assumed that brains evolved to process factual information about the world. Most attention has therefore been focused on such features as pattern recognition, color vision, and speech perception. By extension, it was assumed that brains evolved to deal with essentially ecological problem-solving tasks. © 1998 Wiley-Liss, Inc. 相似文献
123.
Robert M. Clancy Steven B. Abramson Chuck Kohne John Rediske 《Journal of cellular physiology》1997,172(2):183-191
Nitric oxide (NO) has been implicated in both cartilage degradation and cell survival. Importantly, NO has been shown, in a cell-type-dependent manner, to directly cause cell death or indirectly promote cell death by compromising the ability of cells to detoxify intra- or extracellular oxidants. In this study we examined the role of NO in the survival of bovine chondrocytes exposed to catabolic cytokines (interleukin-1 (IL-1); tumor necrosis factor [TNF]) with or without the addition of an exogenous oxidant stress (e.g., H2O2, HOOCl, etc.). The exposure of chondrocytes to a mixture of IL-1 and TNF (IL-1/TNF) results in the release of NO but did not alter cell viability. However, there was evidence of NO-dependent oxidative responses in the IL-1/TNF group, as we observed an increased level of intracellular oxidants as well as the appearance of a 55 kD nitrated protein which reflects the formation of peroxynitrite. We next analyzed viability with H2O2. The LD50 for IL-1/TNF-treated cells was 0.1 mM (vs. 1 mM for control). The enhanced sensitivity was completely reversed when cells were incubated with the NO synthase inhibitor 1-n5-1-iminoethylornithine (NIO). To test whether cell death was caused by compromising the ability of cells to detoxify extracellular oxidants, we examined the hexose monophosphate shunt (HMPS) response in cells given H2O2. Treatment of control cells with H2O2 resulted in a fourfold increase in HMPS activity. In contrast, IL-1/TNF cells exhibited no increase in HMPS activity. The attenuation of stimulated HMPS activity was reversed by the coaddition of NIO. Thus, these data indicate that (1) endogenous NO mediates cytokine-dependent susceptibility to oxidant injury and (2) this effect is in part due to impaired activation of the HMPS. In inflamed joints replete with cytokines and oxidants, NO may contribute to chondrocyte death and progressive joint destruction. J. Cell. Physiol. 172:183–191, 1997. © 1997 Wiley-Liss, Inc. 相似文献
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M. Dunbar C. Onuora S. Morgan F. E. Stone T. M. Huckaba I. R. Davenport 《Journal of fish biology》2017,90(3):1031-1036
Follicle cell processes (FCP) are identified in two species of carcharhinid shark (Selachii) but are absent in the little skate Leucoraja erinacea (Batoidea). This suggests that FCPs are either a unique structure that evolved in selachians or were lost by the batoids after their divergence, some 280 mya . The presence of FCPs in the selachians would be consistent with the evolution of large oocytes in this group of animals. 相似文献
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127.
Purpose The low-density lipoprotein receptor (LDLr) mediates the uptake of LDL particles enriched with cholesterol, into several
tissues. In contrast to other tissues, the brain is thought to obtain cholesterol solely by de novo synthesis, yet certain
brain regions such as the brainstem are highly enriched with the LDLr. The goal of the present study was to assess the role
of the LDLr in maintaining cholesterol concentrations in the brainstem of wildtype and LDLr knockout (LDLr−/−) mice. Cholesterol
concentrations were also measured in the cortex, which served as a reference point, due to the lower expression of the LDLr,
as compared to the brainstem. Methods LDLr−/− and wildtype mice consumed an AIN-93G diet ad libitum until 7 weeks of age. After microwaving, the cortex and anterior
brain stem were isolated for cholesterol analysis. Cholesterol was extracted into chloroform/methanol, derivatized in trimethylsilyl
chloride and measured by gas chromatography/mass spectrometry. Results Concentrations of cholesterol in the brainstem did not differ statistically between LDLr−/− (18.8 ± 1.6 mg/g wet weight brain)
and wildtype (19.1 ± 2.0). Cortical cholesterol concentrations also did not differ statistically between LDLr−/− (11.0 ± 0.4 mg/g
wet weight brain) and wildtype (11.1 ± 0.2) mice. Conclusion The LDLr is not necessary for maintaining cholesterol concentrations in the cortex or brainstem, suggesting that other mechanisms
are sufficient to maintain brain cholesterol concentrations. 相似文献
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Chuck T. Chen Zhen Liu Melissa Ouellet Frédéric Calon Richard P. Bazinet 《Prostaglandins, leukotrienes, and essential fatty acids》2009,80(2-3):157-163
Analyses of brain phospholipid fatty acid profiles reveal a selective deficiency and enrichment in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), respectively. In order to account for this difference in brain fatty acid levels, we hypothesized that EPA is more rapidly β-oxidized upon its entry into the brain. Wild-type C57BL/6 mice were perfused with either 14C-EPA or 14C-DHA via in situ cerebral perfusion for 40 s, followed by a bicarbonate buffer to wash out the residual radiolabeled polyunsaturated fatty acid (PUFA) in the capillaries. 14C-PUFA-perfused brains were extracted for chemical analyses of neutral lipid and phospholipid fatty acids. Based on the radioactivity in aqueous, total lipid, neutral lipid and phospholipid fractions, volume of distribution (VD, μl/g) was calculated. The VD between 14C-EPA- and 14C-DHA-perfused samples was not statistically different for total lipid, neutral lipids or total phospholipids. However, the VD of 14C-EPA in the aqueous fraction was 2.5 times higher than that of 14C-DHA (p=0.025), suggesting a more extensive β-oxidation than DHA. Furthermore, radiolabeled palmitoleic acid, a fatty acid that can be synthesized de novo, was detected in brain phospholipids from 14C-EPA but not from 14C-DHA-perfused mice suggesting that β-oxidation products of EPA were recycled into endogenous fatty acid biosynthetic pathways. These findings suggest that low levels of EPA in brain phospholipids compared to DHA may be the result of its rapid β-oxidation upon uptake by the brain. 相似文献
130.
R. I. M. Dunbar A. H. Korstjens and J. Lehmann British Academy Centenary Research Project 《Biological reviews of the Cambridge Philosophical Society》2009,84(3):413-429
Conventional approaches to population biology emphasise the roles of climatic conditions, nutrient flow and predation as constraints on population dynamics. We argue here that this focus has obscured the role of time as a crucial constraint on species' abilities to survive in some habitats. Time constraints may be particularly intrusive both for species that live in intensely bonded groups (where the need to devote time to social interaction may ultimately limit the size of group that a species can maintain in a particular habitat) and for taxa that face constraints on the length of the active day. We use a linear programming approach that allows us to specify both how time allocations to different activities are influenced by local environmental and climatic variables and how these in turn limit group size and population density. The linear programming approach identifies the realizable niche space within which a species can maintain coherent groups that are larger than the minimum viable group size (or density). This approach thus allow us to understand better why a given taxon can survive in some habitats but not others, as well as the demographic stress that a population may face. In addition, they also allow us to evaluate the implications of both past and future climate change for a taxon's ability to cope with particular habitats. 相似文献