The effects of aging on N-methyl-d-aspartate receptor subunits in the synaptic membrane and relationships to long-term spatial memory

X. Zhao, R. Rosenke, D. Kronemann, B. Brim, S. R. Das, A. W. Dunah, K. R. Magnusson

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    80 Scopus citations

    Abstract

    There are declines in the protein expression of the NR2B (mouse ε2) and NR1 (mouse ζ1) subunits of the N-methyl-d-aspartate (NMDA) receptor in the cerebral cortex and hippocampus during aging in C57BL/6 mice. This study was designed to determine if there is a greater effect of aging on subunit expression and a stronger relationship between long-term spatial memory and subunit expression within the synaptic membrane than in the cell as a whole. Male, C57BL/6JNIA mice (4, 11 and 26 months old) were tested for long-term spatial memory in the Morris water maze. Frontal cortex, including prefrontal regions, and hippocampus were homogenized and fractionated into light and synaptosomal membrane fractions. Western blots were used to analyze protein expression of NR2B and NR1 subunits of the NMDA receptor. Old mice performed significantly worse than other ages in the spatial task. In the frontal cortex, the protein levels of the NR2B subunit showed a greater decline with aging in the synaptic membrane fraction than in the whole homogenate, while in the hippocampus a similar age-related decline was observed in both fractions. There were no significant effects of aging on the expression of the NR1 subunit. Within the middle-aged mouse group, higher expression of both NR2B and NR1 subunits in the synaptic membrane of the hippocampus was associated with better memory. In the aged mice, however, higher expression of both subunits was associated with poorer memory. These results indicate that aging could be altering the localization of the NR2B subunit to the synaptic membrane within the frontal cortex. The correlational results suggest that NMDA receptor functions, receptor subunit composition, and/or the environment in which the receptor interacted in the hippocampus were not the same in the old animals as in younger mice and this may have contributed to memory declines during aging.

    Original languageEnglish (US)
    Pages (from-to)933-945
    Number of pages13
    JournalNeuroscience
    Volume162
    Issue number4
    DOIs
    StatePublished - Sep 15 2009

    Bibliographical note

    Funding Information:
    This work was supported by NIH grant AG16322 to K.R.M. We would also like to thank David G. Standaert for his advice on the subfractionation protocol.

    Keywords

    • NR1
    • NR2B
    • hippocampus
    • learning
    • prefrontal cortex
    • spatial

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