ACETYLCHOLINE AND SEROTONIN INDUCE LARVAL
METAMORPHOSIS OF THE JAPANESE SHORT-NECK CLAM RUDITAPES PHILIPPINARUM
P.M. Urrutia, K. Okamoto, N. Fusetani-2004
Journal of Shellfish Research, 23(1): 93-100
Abstract:
The effects of neuroactive compounds on larval
metamorphosis of the Japanese short-neck clam Ruditapes philippinarum (Heterodonta,
Veneridae) were investigated by exposing pediveligers to acetylcholine,
serotonin, epinephrine, norepinephrine, dopamine,
t.-3,4-dihydroxyphenylalanine (c-DOPA), carbamylcholine, and succinylcholine
at concentrations of 1, 10, and 100 µM. Larval metamorphosis with 100 rM serotonin was 80.7%, and that with 10 µM and 100 µM acetylcholine was 92.9% and 70.6%,
respectively. No significant differences were observed in the induction
activities of epinephrine (35.1-36.1%), L-norepinephrine (2.1-20.3%), r-DOPA
(6.4-15.8%), and nontreated groups (0-5.6%). Dopamine showed no inducing
activity. Treatment with 100 RM carbamylcholine induced 37.6% of
metamorphosis in 23-day-old larvae. Larval metamorphosis rate increased
significantly with exposure time when treated with acetylcholine,
carbamylcholine, and serotonin. Low postlarval survivorship after treatments
might not be related to toxicity of chemicals but due to an energy
deficiency after an accelerated completion of metamorphosis in
neurochemically stimulated larvae. The effectiveness of inducer drugs was
observed to be age-dependent. Nineteen-day-old larvae reacted less than
23-day-old ones from the same cohort. Larvae of R. philippinarum responded
differently to neurotransmitters from bivalves of the subclass Pterimorphia
(i.e., Ostreidae, Pectinidae, Mytilidae) which are more sensitive to
catecholamines and L-DOPA. This difference suggests that the mechanisms
triggering metamorphosis may differ among bivalve groups.
(Laboratory of Aquatic Natural Products Chemistry, Department of Aquatic
Biosciences, Graduate School of Agricultural and Life Sciences, The
University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan, e-mail of N.
Fusetani: anobu@mail.ecc.u-tokyo.ac.jp)