The 5-hydroxytryptamine receptor (HTR3) family are members of the superfamily of ligand-gated ion channels (LGICs). Five receptors (HTR3A-E) form a heteropentamer. Binding of the neurotransmitter 5-hydroxytryptamine (5HT, serotonin) to the HTR3 complex opens the channel, which in turn, leads to an excitatory response in neurons and is permeable to sodium, potassium, and calcium ions (Miyake et al. 1995, Davies et al. 1999, Niesler et al. 2007).