HRH3 and Alzheimer disease: Interestingly, several H3R antagonists have in earlier preclinical studies been designated as talented candidates for AD and were suggested to be of possible novel therapeutics due to their capability to interact with H3 auto- and hetero-receptors, modulating the synthesis and release of numerous brain neurotransmitters critical for cognition, including histamine, dopamine, and acetylcholine (Brioni et al., 2011; Sadek and Stark, 2015; Sadek et al., 2016b).