The broad, long-term objectives of this proposal are to evaluate the extent to which the changes in cholinergic receptor function that have been described in Alzheimer's disease can be mimicked in an animal model, to use the model to examine the mechanisms underlying adaptive changes, and to characterize the resulting alterations in cholinergic pharmacology. The hypothesis to be tested is that lesioning cholinergic inputs to the hippocampus causes changes in cholinergic receptors and function similar to those in Alzheimer's disease. This will be tested in an animal model in which about 50% of hippocampal cholinergic neurons have been lesioned with the neurotoxin ethylcholine mustard aziridinium (AF64A). Specific aims are: 1) Examine whether the function of presynaptic cholinergic autoreceptors which modulate acetylcholine release from the surviving cholinergic neurons is altered in hippocampal slices from AF64A treated rats; 2) Examine whether the function of one population of postsynaptic cholinergic receptors, those which modulate norepinephrine release, is altered by lesion of cholinergic neurons; 3) Determine whether muscarinic receptor numbers and affinities are altered in lesioned animals, and whether changes in muscarinic receptor function result from uncoupling from G-proteins; 4) Determine whether receptor changes can be prevented by chronic administration of cholinergic agonists from the time of lesioning. These findings will provide important information which will aid in developing new drug treatments for Alzheimer's disease. The experimental design compares several functional aspects of muscarinic and nicotinic cholinergic receptors in hippocampus of normal and AF64A-lesioned rats, to determine whether these functions are altered by the cholinergic lesion in the same way as in Alzheimer's disease. The methods to be used are: 1) constructing dose-response curves for modulation of the stimulation evoked release of radioabelled acetylcholine and norepinephrine from hippocampal slices by muscarinic and nicotinic agonists, and determining whether these curves are shifted in AF64A-treated rats; 2) measuring binding of radiolabelled ligands to muscarinic and nicotinic receptors in hippocampus; 3) assessing coupling of muscarinic receptors to G-proteins using radioreceptor assays; and 4) measuring the shift in the dose response curve for modulation of acetylcholine and norepinephrine release when receptors are uncoupled with N-ethylmaleimide.