The neurotransmitter serotonin (5-HT) was reported to induce metamorphosis in larval Tritia (Levantine and Bonar, 1986, American Zoologist 26: 14A), but the mode of action of 5-HT was unclear. To begin to determine whether 5-HT induced metamorphosis by binding to external chemosensory receptors or by being taken up by larvae to act internally as a neurotransmitter, Julia Couper Leo – MS degree 1995 conducted a series of pharmacological studies. Her investigations included both bath application and injection experiments. Results with various serotonergic reagents provided evidence supporting the idea that 5-HT acts as a neurotransmitter in the pathway that promotes metamorphosis (Couper and Leise, 1996). The graph (Below) shows that injection of serotonin (5HTi) induces far more larvae to metamorphose than does injection of artificial seawater (FIOi). Injections of the 5-HT agonist, α-methyl 5-HT (AMT), also induce larval metamorphosis. Results illustrated in this graph are 48 hours after injection.
Above: Injection of 5-HT and the 5-HT agonist α-methyl 5-HT induce larval metamorphosis.
