Synaptic substrates of age-dependent memory deficits

Though aging itself is the biggest risk factor for Alzheimer’s disease (AD), many aged persons with memory problems do not ultimately suffer from AD. In such persons, pathology that would merit AD diagnosis is ab-sent, despite the overlapping cognitive symptomatology. The principal goal of this research program is to mod-el such “normal” age-related cognitive heterogeneity in rats and then use high-resolution techniques to reveal the synaptic and dendritic substrates of age-associated decline in forms of memory that require the hippocam-pus. As the primary output of the hippocampus, region CA1 has been a primary target of such investigation by us and others. Indeed, past studies have revealed that while major age-related synapse and neuron loss are ab-sent in CA1, more subtle aging-linked changes collude to modify neuronal activity patterns and behavioral plas-ticity. Importantly, such alterations are present in only a subset of aged rats, with others the same chronologi-cal age showing young adult-like acquisition on Morris Water Maze (MWM) learning and trace eyeblink condi-tioning (TEBC). Such cognitive heterogeneity among aged rats, then, provides an important opportunity to re-veal both the substrates of age-related memory decline as well as the substrates of memory preservation. The experiments proposed in this renewal application will continue to reveal the synaptic and dendritic substrates of age-related cognitive heterogeneity, but do so by building on our past findings with conceptual and technical complexity. Specifically, in Aim 1, we will behaviorally characterize young adult and aged F344xBN F1 hybrid rats with MWM learning and TEBC and then probe synaptic Ca2+ signaling with 2-photon laser scanning (2PLSM) Ca2+ imaging and 2-photon glutamate (2Pglutamate) uncaging onto spines in discrete microdomains of individual basal, oblique, and tuft dendrites. Following this high-resolution functional probing, Aims 2 and 3 will use immunogold field emission