Settlement of the barnacle Balanus improvisus: The roles of dopamine and serotonin

Figures & data

Figure 1 Settlement process of cyprid larvae ofBalanus improvisus. A, Cyprid larvae exploring the substrate by flicking their antennulae; scale bar 500 µm (ant: antennulae; ta: thoracic appendages). B, Cyprid larva in permanent attachment, after cement secretion. C, Juvenile after ecdysis; scale bar 300 µm.

Table I. The pharmacological agents tested in the present study, their reported endogenous targets in vertebrates and their respective chemical structures.

Figure 2 Effects of dopamine and serotonin on the settlement rate ofBalanus improvisus cyprids. The experiment used different concentrations of the two agents in combination with different larval age (d0, d2 and d4). Results are shown as mean settlement (%) as observed two days after the beginning of the experiment±SE. *Significantly different from controls.

Figure 3 Effects of different concentrations of dopamine receptor agonists and antagonists on the settlement rate ofB. improvisus newly hatched (day 0) cyprids. The bars represent mean settlement (%) observed 6 days after the beginning of the experiment±SD. Concentrations in which settlement is lower than 1% are not presented in the figure but listed in Table II. *P⩽0.05; **P⩽0.01; ***P⩽0.001; ****P⩽0.0001.

Figure 4 Effects of different concentrations of serotonin receptor agonists, antagonists and of the serotonin uptake inhibitor on the settlement ofB. improvisus newly hatched (day 0) cyprids. The bars represent mean settlement (%) observed 6 days after the beginning of the experiment±SD. Concentrations in which settlement was lower than 1% are not presented in the figure but listed in Table III. *P⩽0.01; **P⩽0.001; ***P⩽0.0001.

Table II. The effects of different dopamine receptor agonists and antagonists on the settlement propensity of cyprid larvae of B. improvisus.

Pharmacological agent	Molecular target in vertebrates	Concentrations tested (µM)	Inhibition of settlement (P‐values ⩽)
(±)‐SKF‐38393	D1 receptor agonist	100	Lethal
		10	0.001
		1	0.01
		0.1	0.05
		0.01	NS
		0.001	NS
S(−)‐Lisuride	D2 receptor agonist; α? and β‐adrenoceptor antagonist; D1 dopamine receptor antagonist	100	Lethal
		10	0.0001
		1	0.0001
		0.1	0.0001
		0.01	0.0001
Quinpirole (LY‐141,865)	Selective D2‐like receptor agonist, which possesses some activity at D3sites	100	Lethal
		10	0.0001
		1	0.0001
		0.1	0.0001
		0.01	NS
R(+)‐SCH‐23390	Selective D1 receptor antagonist	1	Lethal
		0.1	NS
		0.01	NS
		0.001	NS
Clozapine	Selective antagonist for D4‐ receptor. Antagonist at 5‐HT2A, 5‐HT2C, 5‐HT3, 5‐HT6, and 5‐HT7 receptors	100	Lethal
		10	Lethal
		1	0.0001
		0,1	0.0001
		0,01	NS
		0.001	NS
		0.0001	NS

Table III. The effects of different serotonin receptor agonists and antagonists and the effect of one serotonin reuptake inhibitor on the settlement propensity of cyprids of B. improvisus.

Pharmacological agent	Molecular target in vertebrates	Concentrations tested (µM)	Inhibition of settlement (P‐values ⩽)
Fluoxetine (LY‐110,140)	Selective 5‐HT uptake inhibitor	10	Lethal
		1	0.01
		0.1	NS
		0.01	NS
		0.001	NS
8‐OH‐DPAT	Selective 5‐HT1 agonist with high affinity for subtype 5‐HT1A receptor	1	Lethal
		0.1	0.01
		0.01	NS
		0.001	NS
R‐(−)‐DOI	Potent and selective 5‐HT2 receptor agonist	100	Lethal
		10	0.001
		1	0.01
		0.1	NS
		0.01	NS
		0.001	NS
WAY‐100635	Highly selective 5‐HT1A receptor antagonist	100	Lethal
		10	0.01
		1	NS
		0.1	NS
		0.01	NS
		0.001	NS
Ritanserin	Potent 5‐HT2A receptor antagonist/inverse agonist	100	Lethal
		10	Lethal
		1	0.0001
		0.1	0.001
		0.01	NS
		0.001	NS

Table IV. A comparison between the effects of dopamine and serotonin on B. amphitrite settlement vs B. improvisus settlement. Also, the table includes those pharmacological agents hitherto tested on both species.

Pharmacological agent	Physiological target	Effect on B. amphitrite cyprid larvae	Effect on B. improvisus cyprid larvae
Dopamine hydrochloride	Neurotransmitter	Induced metamorphosis without prior attachment (Kon‐Ya et al. 1995).	Significant induction of attachment and metamorphosis in 10 µM when using cyprids of age 2 and 4 days. No effect on cyprids of age 0 days.
		Inhibited attachment and metamorphosis of competent cyprids (>3 days old) (Yamamoto et al. 1996)	No induction of attachment and metamorphosis in 100 µM with any of the ages tested.
(±)‐SKF‐38393	D1 Dopamine receptor agonist.	Complete inhibition in 10 µM	Significant inhibition in 1 µM
S‐(−)‐Lisuride	D2 Dopamine receptor agonist; D1 dopamine receptor antagonist; α‐ and β‐adrenoceptor antagonist	In 0.1–1 µM attachment was inhibited but searching behaviour stimulated.	Strong settlement inhibition in 0.01–10 µM.
		Complete inhibition of both attachment and searching behaviour in 10 µM	No stimulation of cyprid searching behaviour.
5‐HT (5‐hydroxytryptamine, serotonin)	Neurotransmitter	Induced attachment and metamorphosis in young cyprids (1 day old).	Significant inhibition of day 2 and 4 larvae in 10 µM.
		No effect on 7‐day‐old cyprids	Strong but non‐significant trend toward inhibition of day 0 larvae when used in 10 µM
			Significantly inhibited settlement of cyprids of all ages in 100 µM (0, 2 and 4 days old).

Kon‐ya , K. , Miki , W. and Endo , M. 1995 . L‐tryptophan and related compounds induce larval settlement of the barnacle Balanus amphitrite Darwin. . Fisheries Science , 61 : 800 – 803 .

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Yamamoto , H. , Tachibana , A. , Kawaii , S. , Matsamura , K. and Fusetani , N. 1996 . Serotonin involvement in larval settlement of the barnacle, Balanus amphitrite. . Journal of Experimental Zoology , 275 : 339 – 345 .

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