HIPPOCAMPAL SYNAPTIC STRUCTURE--PHYSIOLOGY DURING AGING

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This is a proposal for a competitive continuation of a project on basic membrane and synaptic mechanisms of brain aging that has been ongoing for over 15 years. The past periods in this project have found two main electrophysiological alterations in rat hippocampal CAl neurons with aging: 1) impaired synaptic frequency potentiation (facilitation); and 2) an increase in voltage-gated Ca2+ influx. These results and others have contributed to the general Ca2+ hypothesis of brain aging and dementia. In the most recent period, the single channel patch clamp configuration was adapted for brain aging studies and identified an increase in the membrane density of available L-type Ca2+ channels as a potential molecular basis for the changes with aging seen at the cellular level. Here, the specific hypothesis that the increase in L-type Ca2+ channels is a key mechanism in both impaired function (synaptic potentiation or spike generation) and neuronal vulnerability to death of aged mammalian neurons will be tested. Studies will be conducted in rat hippocampal slices and long-term hippocampal cultures in which L-type Ca2+ channels are enriched. Effects of repetitive synaptic activation on the magnitude and topography of Ca2+ transients in hippocampal slice neurons of adult and aged rats will be studied, using a rapid UV-compatible confocal laser scanning microscope for Ca2+ imaging simultaneously with intracellular electrophysiological recording. Multiple specific channel blockers and kinase modulators will be used to define critical Ca2+ entry pathways. These studies will determine whether postsynaptic Ca2+ transients, particularly through L-channels, can modulate neuronal short-term synaptic plasticity and contribute to changes in aged brain neurons. In parallel studies of cell cultures, the role of time-dependent ion channel changes in cell death will be tested, by investigating differences in vulnerability to excitotoxicity in cells with different complements of L-type channels. Single channel recording, Ca2+ imaging, pharmacologic blockade and kinase modulation will be used to define Ca2+ sources critical for necrosis and apoptosis.