Several studies have reported that the noradrenergic (NA) and the serotoninergic (5-HT) systems are affected in Alzheimer's Disease (AD). Since these systems appear to play a role in many diverse functions such as memory, learning and attention, it would be important to study degenerative changes in these systems that may be associated with AD. To date, little work has been done to study the role of the presynaptic uptake system for norepinephrine (NE) and serotonin (5-HT) in neurodegenerative diseases. A measure of the changes in the density of uptake sites for NE and 5-HT could provide specific information regarding the integrity of these neuronal systems in AD. Our hypotheses are that the density of uptake sites for NE and 5-HT will be decreased in the cell body areas, given previous reports of decreased cell counts in the locus coeruleus (LC) and dorsal raphe nucleus (DR). We also expect to find a loss of presynaptic sites for NE and 5-HT in the terminal field areas given reports of synaptic pathology in AD. In this proposal, we will investigate whether uptake sites for NE and 5-HT are altered in the LC, DR, cortex (CTX) and hippocampus (HIP) in AD by selective radiolabelling of uptake sites for NE (with 3H-nisoxetine) and 5-HT (with 3H- cyanoimipramine) in tissue sections from different brain regions using the technique of quantitative autoradiography. This technique offers several advantages over previously used methods in that it provides a quantitative measure of the density of uptake sites as well as a detailed anatomical map of the location of these sites. Neuropathological characterization of AD involves the formation of neurofibrillary tangles (NFT) and amyloid plaques (AP) which are thought to contribute to neuronal degeneration in the CTX and HIP in AD and reports of significant synaptic loss suggest that the presynaptic terminal system may play an important role in the pathological events that occur in AD. In this proposal, we will investigate whether NFT, AP and synaptophysin (SYP) (a presynaptic terminal protein) share the same anatomical localization as the NE and 5-HT presynaptic uptake sites that are undergoing degeneration in the cell body and terminal field areas. For these studies, brain sections adjacent to those used for the quantitative autoradiographic analysis of NE and 5-HT uptake sites will be used. These sections will be labelled immunohistochemically using monoclonal antibodies specific for tau proteins to determine the relative abundance of NFT, antibodies for beta-amyloid or A4 peptide to study AP formation and SY38 to study SYP immunoreactivity. The results of this study should provide a quantitative measure of the regional distribution and integrity of the NE and 5-HT systems in AD, as well as determine whether the pathological formation of tangles and plaques and synaptic decline in AD can be associated with losses in the NA and/or 5-HT presynaptic systems within the same brain regions.
