Functional consequences of locus coeruleus degeneration in Alzheimer's disease.

Alzheimer's disease (AD) is the most common cause of cognitive impairment in older patients, and its prevalence is expected to soar in coming decades. Neuropathologically, AD is characterized by beta-amyloid-containing plaques, tau-containing neurofibrillary tangles, and cholinergic neuronal loss. In addition to the hallmark of memory loss, the disease is associated with other neuropsychiatric and behavioral abnormalities, including psychosis, aggression, and depression. Although cholinergic cell loss is clearly an important attribute of the pathological process, another well-described yet underappreciated early feature of AD pathogenesis is degeneration of the locus coeruleus (LC), which serves as the main source of norepinephrine (NE) supplying various cortical and subcortical areas that are affected in AD. The purpose of this review is to explore the extent to which LC loss contributes to AD neuropathology and cognitive deficits.