2020 Volume 57 Issue 4 Pages 212-216
The cholinergic neurons originating in the basal forebrain send projections to the neocortex, hippocampus, and olfactory bulb that contribute to cognition, memory, and olfactory function, respectively. These cholinergic projections to the neocortex and the hippocampus act as vasodilator nerves similar to autonomic nerves. We have recently examined the role of cholinergic projections to the olfactory bulb in blood flow regulation. The cholinergic input to the olfactory bulb releases acetylcholine, but the amount of acetylcholine is less than half of that of the neocortex, and does not influence the regional blood flow in the olfactory bulb. In contrast, the odor-induced increase response of the olfactory bulb blood flow is potentiated by activation of nicotinic acetylcholine receptors in the brain. This indicates that cholinergic transmission enhances olfactory sensitivity in the olfactory bulb. Cholinergic dysfunction may cause the olfactory dysfunction known as an early symptom of dementia.