“…Serotonin is widely distributed in both the animal and the plant kingdoms [Pennati et al, 2001], and occurs in mammalian [Shuey et al, 1990;Wu et al, 1999] and other vertebrate and invertebrate embryos [Manukhin et al, 1981;Emanuelsson et al, 1988]. Serotonin is synthesized by embryonic stem cells [Walther, 1999], and 5-HT is likely to play a role in egg maturation [Buznikov et al, 1993], mitogen-induced vascular remodeling [Fanburg and Lee, 1997], neural crest migration [Moiseiwitsch and Lauder, 1995], control of cleavage and cell division rates, patterning of cytoskeletal structures [Emanuelsson et al, 1988;Lee et al, 1991], blastomere adhesion, gastrulation movements [Hamalainen and Kohonen, 1989;Colas et al, 1999a, b], control of gap-junctional communication [Moore and Burt, 1995;Rorig and Sutor, 1996], craniofacial patterning [Lauder and Zimmerman, 1988;Shuey et al, 1992Shuey et al, , 1993, and the specifi cation of neuronal identity and connectivity in the developing nervous system [Lauder et al, 1981[Lauder et al, , 1983.…”