Neuronal Nicotinic Receptor Deficits in Alzheimer Patients with the Swedish Amyloid Precursor Protein 670/671 Mutation

The influence of β-amyloid on cholinergic neurotransmission was studied by measuring alterations in nicotinic acetylcholine receptors (nAChRs) in autopsy brain tissue from subjects carrying the Swedish amyloid precursor protein (APP) 670/671 mutation. Significant reductions in numbers of nAChRs were observed in various cortical regions of the Swedish 670/671 APP mutation family subjects (-73 to -87%) as well as in sporadic Alzheimer's disease (AD) cases (-37 to -57%) using the nicotinic agonists [ 3 H]epibatidine and [ 3 H]nicotine, which bind with high affinity to both a3 and α4 and to α4 nAChR subtypes, respectively. Saturation binding studies with [ 3 H]epibatidine revealed two binding sites in the parietal cortex of AD subjects and controls. A significant decrease in B max (-82%) for the high-affinity site was observed in APP 670/671 subjects with no change in K D compared with controls (0.018 nM APP 670/671; 0.036 nM control). The highest load of neuronal plaques (NPs) was observed in the parietal cortex of APP 670/671 brains, whereas the number of [ 3 H]nicotine binding sites was less impaired compared with other cortical brain regions. Except for a positive significant correlation between the number of [ 3 H]nicotine binding sites and number of NPs in the parietal cortex, no strict correlation was observed between nAChR deficits and the presence of NPs and neurofibrillary tangles, suggesting that these different processes may be closely related but not strictly dependent on each other.