Aged dogs demonstrate both increased sensitivity to scopolamine impairment and decreased muscarinic receptor density

► Aged dogs are hypersensitive to scopolamine-induced impairment. ► Aged dogs lower muscarinic receptor density than young dogs. ► Aged dogs model the spectrum of normal aging to early Alzheimer's disease. ► Dogs may show age-related cholinergic deficits in addition to early amyloid pathology. ► Dogs model the functional effects of early pathological events in Alzheimer's disease.