The Role of L-dopa in the Nervous System of Sea a a Putative Inhibitory Transmitter in Tentac

nerve al. 19 These substa neuroa dopam signifi anemo Puta by Da Dopa) and R Metridium senile tentacles have also been shown to accumulate L-Dopa (Carlberg and Elofsson, 1987; Carlberg, 1990). Here we re-investigate the actions of dopamine on the sea anemones Actinia equina, Urticina felina and Calliactis parasitica, and also consider whether the dopamine precursor L-Dopa and the dopamine metabolite 3,4,5-trihydroxyphenylalanine (5-OH-Dopa) could be neurotransmitters. Although dopamine, L-Dopa and 5-OHDopa have not been identified in Actinia equina, they are known to occur in two closely related species, Urticina felina and Bolocera tueidae (Carlberg and Rosengren, 1985). The physiological actions of dopamine described in this paper are compared with those of a neuropeptide, Antho-RWamide II (Glu-Gly-Leu-Arg-Trp-NH2), that causes contraction of isolated sphincter muscle cells (McFarlane et al. 1991) and thus may be a neurotransmitter. Antho-RWamide II was ry act L-Dop d from itive t al. 19 gically eptides primit