Project 4- The cognitive functions of the prefrontal cortex (PFC) are impaired early in the aging process, and there is significant spine loss from the dendrites of aged PFC neurons. Project 4 will examine whether these age-related changes can be prevented by chronic treatment with the alpha-2A noradrenergic (NE) agonist, guanfacine. We hypothesize that guanfacine will inhibit detrimental cAMP actions in the PFC that lead to weakened connectivity in PFC networks. Electron microscopy (EM) studies of young PFC have shown that alpha-2A receptors are co-expressed wih HCN (Hyperpolarization-activated Cyclic Nucleotide-gated) channels in the spines of monkey PFC neurons, where they are ideally positioned to gate synaptic events. When the HCN channels are opened by cAMP, they weaken inputs onto the spine. Guanfacine inhibits the production of cAMP and strengthens functional connectivity. With advancing age, there is a decrease in alpha-2 receptors, evidence of excessive cAMP signaling, and increased HCN expression. We hypothesize that disinnibited cAMP actions early in the aging process weakens the functional connectivity of PFC networks, contributing to declines in PFC cognitive function. With advancing age, sustained synaptic weakness would lead to spine loss.
Aim 1 will test this hypothesis by examining ultrastructural changes in dendrites, NE axons, alpha-2A receptors, and HCN channels in the superficial layers of PFC from young, middle aged and aged monkeys. We will use dual immunoEM to visualize the distribution of these molecules, and the integrity of dendrites, with particular focus on layer I. We predict that there will be changes in neuromodulators early in the aging process (e.g. decreased NE axons and alpha-2A receptors in layer I, increased HCN channels on dendritic spines), followed by architectural decreases in dendritic spines with advancing age.
Aims 2 and 3 will examine whether chronic stimulation of alpha-2A receptors with guanfacine will reduce functional weakening of synapses and thus prevent spine loss and working memory decline in aging rats and monkeys. Preliminary results indicate that chronic guanfacine produces enduring improvements in spine density and working memory abilities. As guanfacine is available for human use, this research is directly relevant to the treatment of age-related cognitive decline. LAY SUM: The research will test whether chronic treatment with guanfacine will protect brain cells and memory in aged animals.
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