HTR4 and Alzheimer disease: There is a connection between different serotonin receptor subtypes, especially on 5-HT1AR, 5-HT4R, and 5-HT6R and emerging AD therapies (Sabbagh, 2009; Mangialasche et al., 2010; Herrmann et al., 2011) and other degenerative disorders connected to an impaired cholinergic function (Esbenshade et al., 2008; Sander et al., 2008; Gemkow et al., 2009).