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Identification of putative learning and memory genes in the dentate gyrus of aged rats following the Morris Water Maze

ABSTRACT: The aim of this study was to investigate whether the differences in memory decline associated with aging are a result of differences in gene expression. We first categorized age-unimpaired and age-impaired rats based on their performance in the Morris water maze, when compared to young rats. Then we isolated messenger RNA from the dentate gyrus of the hippocampus of each animal to interrogate Affymetrix RAE 230A rat genome microarrays. Supervised statistical analysis of the different groups of aged animals recognized 85 genes (p<0.005) that were significantly different in the dentate gyrus of aged rats that had learned the Morris water maze (MWM) paradigm when compared to learning impaired and a number of controls for stress, exercise and non-spatial learning. In addition, statistical analysis of the microarray data that included young and aged rats identified 1129 genes (p<0.005) that were differentially expressed between aged and young rats independent of behavior, but due to aging alone. Keywords: behavior comparison, age comparison

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE4821 | GEO | 2007/07/31

SECONDARY ACCESSION(S): PRJNA95629

REPOSITORIES: GEO

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Project description:Although immediate early genes (IEGs) such as Bdnf, Arc and Egr1, have been implicated in plasticity, the larger pathways related to memory and memory disorders are not well understood. Here, we combined statistical Affymetrix microarray and behavioral analyses to identify key genes and pathways associated with aging-related cognitive impairment. Aged rats were separated into cognitively unimpaired (AU) or impaired (AI) groups, based on their Morris water maze performance relative to young-adult (Y) animals. Hippocampal gene expression was assessed in Y, AU and AI on the fifth (last) day of maze training or 21 days posttraining, and in non-trained aged and young animals (eight groups, overall n = 78, one chip/animal). ANOVA, linear contrasts, and overrepresentation analyses identified genes and pathways that differed from Y generally with aging (in both AU and AI) or selectively with cognitive status (only in AI or AU). Plasticity pathways, including insulin/cAMP/IEG signaling, and glycogenolytic and lipogenic pathways, were selectively downregulated (5 days) in AI, whereas Notch2 (regulating oligodendrocyte differentiation) and myelination pathways were upregulated (particularly at 21 days). Downregulation with general aging occurred in signal transduction and axonal growth/transport pathways, whereas upegulation occurred in immune/inflammatory, lipid metabolism/transport (e.g., Lxr-Srebf1), and lysosomal pathways. In AU, receptor/signal transduction genes were selectively upregulated, suggesting possible compensatory mechanisms. Immunohistochemistry confirmed and extended results to the protein level. Thus, this study identified novel cognition-linked processes, suggesting a new model in which energy-intensive, plasticity/lipogenic processes and energy-generating pathways necessary for learning are coordinately downregulated during training, while myelinogenic programs that impair cognition are concurrently activated. Experiment Overall Design: Aged rats were separated into cognitively unimpaired (AU) or impaired (AI) groups, based on their Morris water maze performance relative to young-adult (Y) animals (NT, 5D, and 21D, N=10/group). Hippocampal gene expression was assessed in Y, AU and AI on the fifth (last) day of maze training or 21 days posttraining, and in non-trained aged and young animals (eight groups, overall n = 78, one chip/animal)

Project description:Background: Age-related cognitive deficits negatively affect quality of life and can presage serious neurodegenerative disorders. Despite sleep disruption’s well-recognized negative influence on cognition, and its prevalence with age, surprisingly few studies have tested sleep’s relationship to cognitive aging. Methodology: We measured sleep stages in young adult and aged F344 rats during inactive (enhanced sleep) and active (enhanced wake) periods. Animals were behaviorally characterized on the Morris water maze and gene expression profiles of their parietal cortices were taken. Principal Findings: Water maze performance was impaired, and inactive period deep sleep was decreased with age. However, increased deep sleep during the active period was most strongly correlated to maze performance. Transcriptional profiles were strongly associated with behavior and age, and were validated against prior studies. Bioinformatic analysis revealed increased translation and decreased myelin/ neuronal pathways. Conclusions: The F344 rat appears to serve as a reasonable model for some common sleep architecture and cognitive changes seen with age in humans, including the cognitively disrupting influence of active period deep sleep. Microarray analysis suggests that the processes engaged by this sleep are consistent with its function. Thus, active period deep sleep appears temporally misaligned but mechanistically intact, leading to the following: first, aged brain tissue appears capable of generating the slow waves necessary for deep sleep, albeit at a weaker intensity than in young. Second, this activity, presented during the active period, seems disruptive rather than beneficial to cognition. Third, this active period deep sleep may be a cognitively pathologic attempt to recover age-related loss of inactive period deep sleep. Finally, therapeutic strategies aimed at reducing active period deep sleep (e.g., by promoting active period wakefulness and/or inactive period deep sleep) may be highly relevant to cognitive function in the aging community. KEYWORDS: frontal cortex, rat, young or aged We implanted young and aged Fischer 344 rats (n = 6/ group) with wireless EEG, EMG and movement monitoring devices to measure sleep architecture. Animals were trained in the Morris water maze to assess cognitive function, and frontal cortices were removed for microarray analysis.sleep disruption and cognitive decline.

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Identification of putative learning and memory genes in the dentate gyrus of aged rats following the Morris Water Maze

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