To determine whether nitric oxide (NO) might repress or promote metamorphosis, Stephan Froggett – MS degree 1997 conducted a series of pharmacological investigations using nitrergic reagents. Bath application of NO-donors to competent larvae elicited no responses, as did most NOS inhibitors. However, when injected into larvae, several NOS inhibitors induced metamorphosis, suggesting that NO functions to inhibit metamorphosis during the larval stage (Froggett and Leise, 1999). An example of his data is below. In this experiment, N-methyl-L-arginine acetate (L-NMMA), a potent NOS inhibitor, induced significantly more larvae to metamorphose, within 24 hours of injection, than did injection of filtered artificial seawater (iFIO). 5-HT and injected 5-HT (i5-HT) were additional controls in this experiment. Steve’s experiments demonstrated a physiological role for NO in molluscan larvae, but did not locate the nitrergic neurons. Supported in part by NSF grant IBN-9604516.
Above: Injection of the NOS inhibitor L-NMMA triggers metamorphosis in competent larvae of Tritia obsoleta.
