Cognitive decline is associated with reduced surface GluR1 expression in the hippocampus of aged rats

Individual differences in cognitive aging exist in humans and in rodent populations, yet the underlying mechanisms remain largely unclear. Activity-dependent delivery of GluR1-containing AMPA receptor (AMPARs) plays an essential role in hippocampal synaptic plasticity, learning and memory. We hypothesize that alterations of surface GluR1 expression in the hippocampus might correlate with age-related cognitive decline. To test this hypothesis, the present study evaluated the cognitive function of young adult and aged rats using Morris water maze. After the behavioral test, the surface expression of GluR1 protein in hippocampal CA1 region of rats was determined using Western blotting. The results showed that the surface expression of GluR1 in the hippocampus of aged rats that are cognitively impaired was much lower than that of young adults and aged rats with preserved cognitive abilities. The phosphorylation levels of GluR1 at Ser845 and Ser831 sites, which promote the synaptic delivery of GluR1, were also selectively decreased in the hippocampus of aged-impaired rats. Correlation analysis reveals that greater decrease in surface GluR1 expression was associated with worse behavioral performance. These results suggest that reduced surface GluR1 expression may contribute to cognitive decline that occurs in normal aging, and different pattern of surface GluR1 expression might be responsible for the individual differences in cognitive aging.