HRH3 and Alzheimer disease: Over the past decade, preclinical studies and clinical trials identified histamine H3 receptor (H3R), a histamine receptor subtype that is predominantly expressed in neurons of the central nervous system (CNS), as a possible target for cognition-enhancing candidates that may have beneficial effects on mild-to-moderate AD (Esbenshade et al., 2006; Bonaventure et al., 2007; Mani et al., 2017).