The serotonergic system plays a significant regulatory role in osteoblast differentiation and proliferation. Serotonin (five-hydroxytryptamine or 5HT) may promote or inhibit osteoblast proliferation depending upon the serotonin receptor isoforms expressed by the cell. Classically, 5HT receptor 1B (5HTR1B) reduces osteoblast proliferation by inhibiting phosphorylation of the cAMP response element binding...