Figure 4: cAMP signaling pathways. Serotonin receptors 5-HT1 and 5-HT5 interact with α i/0 G-protein inhibiting the formation of cyclic adenylate monophosphate (cAMP) by adenylate cyclase (AC), while 5-HT4, 5-HT6, and 5-HT7 activate AC by means of α S G-protein. βγ subunits of G-protein may interact in other signaling pathways, for example, modulating GIRK or calcium voltage gated channels. Representation of β-arrestin (β-arr) is made to indicate other signaling pathways. Traditional ligands to study different subtype receptors are written in the extracellular zone; note that 5-HT7 may bind the traditional ligand for 5-HT1A as well as LSD (5-HT2 ligand).