The basal forebrain cholinergic system connects olfaction with dementia suggesting ways of early detection and prevention of dementia

Abstract

Since olfactory impairment occurs in the very early stage of dementia, it is expected to have an application in the early detection and prevention of dementia. Animal experiments at our laboratory have shown that basal forebrain cholinergic nerves, which degenerate in Alzheimer’s disease, play a role of autonomic-like vasodilators that increase regional blood flow in the neocortex and hippocampus. The cholinergic nerve also projects to the olfactory bulb, the primary olfactory center. Recently, we reported that intravenously injecting anesthetized rats with nicotine, a nicotinic cholinergic agonist, increases the olfactory-evoked blood flow response in the olfactory bulb, suggesting a role in enhancing olfactory sensitivity. Also, in a clinical study, we found a relationship between olfaction and cognitive function, especially attention, in the elderly. In this paper, we present basic and clinical research on olfaction and cognitive function, focusing on the cholinergic system.