Echinodermata) Does Not Share a Common Nervous Control in All Species Y

Echinodermata) Does Not Share a Common Nervous Control in All Species Y

The Journal of Experimental Biology 205, 799–806 (2002) 799 Printed in Great Britain © The Company of Biologists Limited 2002 JEB3797 Luminescence in ophiuroids (Echinodermata) does not share a common nervous control in all species Y. Dewael* and J. Mallefet Laboratory of Animal Physiology, Catholic University of Louvain, Bâtiment Carnoy, 5 Place Croix du Sud, B-1348 Louvain-la-Neuve, Belgium *e-mail: [email protected] Accepted 2 January 2002 Summary Study of the control mechanisms of light emission species. Only A. filiformis emits light in response to in invertebrates shows the involvement of several acetylcholine. In this species, the involvement of both neurotransmitters. In ophiuroids, only one species muscarinic and nicotinic receptors is proposed, since (Amphipholis squamata) has so far been characterized for atropine and tubocurarine (at 10–3 mol l–1) inhibited 99 % luminescence control, which seems to be cholinergic, and 71 %, respectively, of the light emitted. Study of the with an influence of several excitatory and inhibitory subtypes of cholinergic receptors involved in photogenesis neuromodulators (amino acids, catecholamines, revealed that several subtypes of muscarinic receptors neuropeptides S1 and S2, purines). The aim of this work is might be involved. It was also clearly shown that to investigate the nature of control mechanisms of light ophiuroids did not share a common mechanism of nervous emission in three luminous ophiuroid species, A. filiformis, control of luminescence in all species. O. aranea and O. californica, in order to see whether or not they share common mechanisms. Luminescence Key words: echinoderm, ophiuroid, bioluminescence, nervous induced by general depolarisation of tissues using KCl control, acetylcholine, muscarinic receptor, nicotinic receptor, (200 mmol l–1) shows different patterns, according to Amphiura filiformis, Ophiopsila aranea, Ophiopsila californica. Introduction The ability of living organisms to produce light seems to (Amphiura filiformis, Ophiopsila aranea and O. californica) have originated independently several times, perhaps 30 or and hence to find out whether they share common signalling more, in evolution (Hastings, 1983). This is reflected in pathways, leading to light emission. the diversity of its phylogenetic distribution, biology, A. filiformis (O. F. Müller 1776) is a rapidly growing chemistry and control mechanisms. Studies of the nervous suspension feeder brittlestar frequently found on sub-tidal control of light emission have shown the involvement of bottoms off the coasts of Europe and of the Mediterranean Sea. several neuromediators, including adrenaline (Protista, This burrowing ophiuroid is a dominant species in the benthic Cnidaria, Chordata), acetylcholine (Ctenophora, Annelida, shelf ecosystem, especially in the northeastern part of the Echinodermata) and 5-hydroxytryptamine (Arthropoda) (for North Atlantic region (Josefson, 1995). It has been shown that a review, see Mallefet, 1999). In echinoderms, control arms of this species represent an important food source for mechanisms of bioluminescence have been almost flatfishes (Duineveld and Van Noort, 1986). Although it has a exclusively studied in the small ophiuroid Amphipholis high predatory rate, A. filiformis has a surprisingly long life squamata. In this species, it has been shown that span (up to 25 years) according to Muus (1981). This can be photogenesis is under nervous cholinergic control (De explained by its ability to rapidly regenerate chopped arms Bremaeker et al., 1996) and that some neuromediators (amino (Wilkie, 1978; Bowner and Keegan, 1983) (J. Mallefet, acids, catecholamines, neuropeptides SALMFamide S1 and unpublished results). S2, purines) were able to modulate light emission positively Despite numerous eco-ethological investigations on A. or negatively (De Bremaeker et al., 1999a,b,c). Furthermore, filiformis (see Josefson, 1995; Loo et al., 1996; Sköld and it was shown that calcium was required for light emission Rosenberg, 1996; Nilsson and Sköld 1996; Rosenberg and triggered by potassium chloride (KCl) and by acetylcholine Selander, 2000) nearly nothing is known about its capability (ACh), either in isolated arms or in dissociated photocytes to produce light. Emson and Herring (1985) reported the first (Mallefet et al., 1994, 1998). data on A. filiformis bioluminescence: light emission is blue The aim of this work was to investigate nervous control in colour, it appears to be intracellular and the luminous mechanisms of luminescence in three other ophiuroid species cells, called photocytes, are restricted to the arm spines. No 800 Y. Dewael and J. Mallefet physiological data are available concerning the control of light Stimulations emission of A. filiformis. Stimulations were performed by injection of drugs onto arm O. aranea (Forbes 1843) inhabits the encrusting coralline segments. Light emission was measured with a FB12 Berthold algae zone (coralligene) in the Mediterranean Sea. Some luminometer linked to a PC-type computer. For each morphological studies described the luminescence sites as experimental protocol, one arm segment was treated with the originating from glandular cells located on lateral and ventral control stimulus (200 mmol l–1 KCl or 10–3 mol l–1 ACh), plates, and in some spines of the arms, next to the disc while the other preparations were stimulated with the tested (Mangold, 1907; Reichensperger, 1908; Trojan, 1909). Later, drug. Harvey (1952) mentioned a yellowish green fluorescence at the sites of luminescence. The exact nature of luminous cells Drugs remains unknown. Mallefet and Dubuisson (1995) described The following drugs were used in this study: acetylcholine the KCl-induced luminescence as a series of flashes whose chloride (Sigma), adenosine (Sigma), adenosine 5′- maximal intensity increases as a function of KCl concentration. triphosphate (ATP; Sigma), L-adrenaline (Fluka), 4- O. californica (Clarck 1921) is a sand-dwelling ophiuroid aminobutyric acid (GABA; Aldrich), 2-aminoethylsulfonic found along the Californian coast. Previous work has shown acid (taurine; Fluka), atropine (Sigma), carbamylcholine that luminescence is used as an aposematic signal (Basch, (carbachol; Janssen Chimica), 4-diphenylacetoxy-N-methyl 1988) and that photocytes, of nervous origin, are located in the peperidine (4-DAMP methiodide; ICN), 1,1-dimethyl-4- arms. Light emission seems to be under nervous control phenyl piperazium iodide (DMPP; ICN) eserine (Sigma), L- (Brehm, 1977; Brehm and Morin, 1977) and requires the glutamic acid hydrochloride (glutamate; Sigma), glycine presence of calcium (Brehm, 1977). hydrochloride (Sigma), hexamethonium dichloride (RBI), These ophiuroid species were chosen for this comparative hydroxylamine hydrochloride (Sigma), 5-hydroxytryptamine study since they belong to two different families (Amphiuridae (5-HT; Sigma), 5-hydroxytyramine hydrochloride (dopamine; for A. filiformis, Ophiocomidae for O. aranea and O. Sigma), McN-A-343 (RBI), L-noradrenaline hydrochloride californica) and they live in two different types of habitat (in (Fluka), pirenzepine dihydrochloride (RBI), SALMFamide 1 mud or sand for A. filiformis and O. californica, in coralligene and SALMFamide 2 (provided by M. Thorndyke’s for O. aranea). Our results show that control mechanisms of laboratory), sodium nitroprusside (Sigma), tubocurarine light emission differ from species to species; a cholinergic chloride (Janssen Chimica). All solutions were diluted in system appears to be involved in light emission of A. filiformis, ASW. The concentrations used ranged from 10–6 to but the nature of luminous control in Ophiopsila sp. remains 10–3 mol l–1. These rather high concentrations are commonly undetermined. used in echinoderms because of the heavy calcification of the ophiuroid arms, which impairs adsorption and penetration to the photocytes. Materials and methods Animals Statistics Specimens of A. filiformis were collected at the Kristineberg Statistical analyses (ANOVA) were performed using SAS Marine Station (Fiskebäckskil, Sweden) by mechanical grab at (Statistic Analysis System). 25–40 m depth. Animals were then kept in circulating natural sea water. Specimens of O. aranea were collected at the Photogenesis characterization ARAGO biological station (CNRS) of Banyuls-sur-Mer Different parameters were used in order to characterize the (France) by scuba diving at a depth of 20–25 m and specimens photogenesis. (1) Lmax, the maximum level of light emission of O. californica were collected in the same way at the Marine expressed as a percentage of the control; (2) LT, latency time, Sciences Institute of the University of California (Santa- the time between stimulation and the beginning of the light Barbara). All these animals were transported to our laboratory emission; (3) TLmax, the time between onset of light production in Belgium in aerated natural sea water and then kept in and maximum light emission. aquaria filled with recirculating natural and artificial sea water (ASW) at 12 °C. Food was provided to ophiuroids once a week. Results Pattern of light emission Experiments on arm segments Using KCl (200 mmol l–1) to depolarise cells, it was possible After anaesthesia of the animals by immersion in 3.5 % to record light emission of arm segments isolated from A. MgCl2 in ASW, arms were isolated from the disc and divided filiformis (Fig. 1A), O. aranea (Fig. 1B) and O. californica into segments of 8 articles (Ophiopsila) or 20 articles (Fig. 1C). Isolated discs never emitted light when

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