This link has been bookmarked by 3 people . It was first bookmarked on 28 Sep 2008, by Gerhard Stoltz.
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09 Oct 08
This study shows that inhibiting neurogenesis has strikingly different consequences in two distinct regions of the brain. In the olfactory bulb, it leads to significant shrinkage but apparently does not alter smell-related behaviour. In the hippocampus, t
brain neuro neurogenesis memory stem_cell olfaction aging science_is_a_method
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strong evidence that the continuous generation of new neurons is critical for brain function, and that the newly-generated cells perform two distinct roles which are critical for tissue maintenance in the olfactory system and for the formation of two distinct forms of memory.
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Newborn neurons generated in the SVZ migrate along a pathway called the rostral migratory stream to populate the olfactory bulb
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Cre-mediated recombination, which allowed them to label neural stem cells for long periods of time. It also labelled the neurons generated from them, as they inherit the stem cell during cell division. The method involved engineering mutant mice in which the gene encoding Cre recombinase is under the control of a stretch of regulatory DNA which normally activates a gene called nestin in neural stem cells. These animals were then mated with several other mutant strains, each enginnered to possess a "reporter" gene encoding a fluorescent protein. In this system, the activity of Cre recombinase is induced by a drug called tamixifen. Thus, when the offspring of the mutant mice strains are treated with this compound, Cre causes reshuffling of the genes, so that the reporters are activated only in the neural stem cells.
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The researchers then investigated what would happen in the olfactory bulb if they aborted the supply of new neurons from the SVZ. To do so, they used the same genetic approach to eliminate the newborn cells. In this case though, the first strain of mutants was crossed with another whose cells contained the gene encoding diptheria toxin unde the control of regulatory DNA which normally switches on a gene during the early stages of neuronal differentiation. When tamixifen is administered in the offspring produced from this mating, Cre activation in causes the toxin to be synthesized as soon as differentiation begins, and the newborn cells are killed.
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because the new method labelled cells for far longer than previous ones, this study provides more details.
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while neurogenesis was necessary to maintain the structure of the olfactory bulb, it was not in this case required for olfactory function. This is at odds with earlier findings, and so will need to be confirmed further with more tests of olfactory behaviour.
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the number of cells in the dentate remained constant for up to 6 months. (By contrast, the hippocampi of the control animals increased in size.) But it did have dramatic effects on spatial memory and associative learning - the mutant mice were unable to learn their way around a maze, and did not exhibit fear behaviour
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28 Sep 08
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Using an elegant new strategy for engineering strains of mutant mice, Itaro Imayoshi and his colleagues now provide strong evidence that the continuous generation of new neurons is critical for brain function, and that the newly-generated cells perform two distinct roles which are critical for tissue maintenance in the olfactory system and for the formation of two distinct forms of memory.
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This study shows that inhibiting neurogenesis has strikingly different consequences in two distinct regions of the brain. In the olfactory bulb, it leads to significant shrinkage but apparently does not alter smell-related behaviour. In the hippocampus, the effect on structure is not so marked, but it is clear that newly-generated neurons are necessary for the processes of learning and memory. The role of new cells in memory formation is, however, still unclear.
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27 Sep 08
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