Whilst there are conflicting data about the histamine content in the brain of AD patients, one recent study using a highly selective H3R ligand had shown the level of H3R expression to be unaltered in the late stages of human AD compared to age matched controls, as well as in TASTPM mice (a mouse model of AD) compared with wild type mice [6], [16]. This evidence concerns the gene HRH3 and Alzheimer disease.