HRH3 and Alzheimer disease: Another approach to thetherapy of Alzheimer’s disease is to inhibit the presynapticactivity of the muscarinic M2R expressed on the cholinergicneurons, in regions involved in learning and memory processes.18,19 As previously mentioned, the histamine H3R exerts modulatoryeffects on the cholinergic system, and H3R antagonist increasesACh release.