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Article
New neurons in the dentate gyrus are involved in the expression of enhanced long-term memory following environmental enrichment.
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Year: 2005

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Abstract

Although thousands of new neurons are continuously produced in the dentate gyrus of rodents each day, the function of these newborn cells remains unclear. An increasing number of reports have provided correlational evidence that adult hippocampal neurogenesis is involved in learning and memory. Exposure of animals to an enriched environment leads to improvement of performance in several learning tasks and enhances neurogenesis specifically in the hippocampus. These data raise the question of whether new neurons participate in memory improvement induced by enrichment. To address this issue, we have examined whether the increase in the number of surviving adult-generated cells following environmental enrichment contributes to improved memory function. To this end, neurogenesis was substantially reduced throughout the environmental enrichment period using the antimitotic agent methylazoxymethanol acetate (MAM). Recognition memory performance of MAM-treated enriched rats was evaluated in a novel object recognition task and compared with that of naive and nontreated enriched rats. Injections of 5-bromo-2'-deoxyuridine were used to label dividing cells, together with double immunofluorescent labelling using glial or neuronal cell-specific markers. We found that enrichment led to improved long-term recognition memory and increased hippocampal neurogenesis, and that MAM treatment during environmental enrichment completely prevented both the increase in neurogenesis and enrichment-induced long-term memory improvement. These results establish that newborn cells in the dentate gyrus contribute to the expression of the promnesic effects of behavioural enrichment, and they provide further support for the idea that adult-generated neurons participate in modulating memory function


Article
Environmental enrichment inhibits spontaneous apoptosis, prevents seizures and is neuroprotective.
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Year: 1999

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Abstract

The mammalian brain has a high degree of plasticity, with dentate granule cell neurogenesis(1) and glial(2,3) proliferation stimulated by an enriched environment combining both complex inanimate and social stimulation. Moreover, rodents exposed to an enriched environment both before and after a cerebral insult show improved cognitive performance(1,4). One of the most robust associations of environmental enrichment is improved learning and memory in the Morris water maze, a spatial task that mainly involves the hippocampus(5). Furthermore, clinical evidence showing an association between higher educational attainment and reduced risk of Alzheimer(6) and Parkinson-related dementia(7) indicates that a stimulating environment has positive effects on cerebral health that may provide some resilience to cerebral insults. Here we show that in addition to its effects on neurogenesis, an enriched environment reduces spontaneous apoptotic cell death in the rat hippocampus by 45%. Moreover, these environmental conditions protect against kainate-induced seizures and excitotoxic injury. The enriched environment induces expression of glial-derived neurotrophic factor and brain-derived neurotrophic factor and increases phosphorylation of the transcription factor cyclic-AMP response element binding protein, indicating that the; influence of the environment on spontaneous apoptosis and cerebral resistance to insults may be mediated through transcription factor activation and induction of growth factor expression

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