No loss of synaptic proteins in the hippocampus of aged, behaviorally impaired rats.

The levels of three different synaptic proteins in the hippocampus of young (6 months of age) and aged (26-27 months of age) Long Evans rats were examined using quantitative Western blotting. An important feature to this study is that prior to the neurobiological analysis, hippocampal function was determined by assessing spatial learning ability in the Morris water maze. A subset of the aged rats was impaired on the learning task while the remaining aged cohort performed within the range of young rats. The amount of immunoreactivity for synaptophysin, synaptotagmin, and synaptosomal associated protein-25 did not differ between the young and aged rats. In addition, the aged rats with severe cognitive impairment had levels of these synaptic proteins that were similar to those of the aged rats with preserved cognitive function. This finding of no change in the levels of synaptic proteins suggests that substantial synapse loss in the hippocampal formation does not underlie cognitive decline in normal aging.