Extrinsic and intrinsic nervous control of bioluminescence in ophiuroids (Echinodermata)

A diversity of organisms is endowed with the ability to emit light; this phenomenon is called bioluminescence and occurs mainly in marine organisms. Among echinoderms, some ophiuroid species (Echinodermata, Ophiuroidea) do possess this amazing capability of light production and are used as a study model in our laboratory. The present work investigates nervous control mechanisms of light emission at different levels such as extrinsic and intrinsic controls in three ophiuroid species: Amphiura filiformis, Ophiopsila aranea and Ophiopsila californica. Results were obtained by mean of different techniques such as pharmacology, immunohistochemistry, microspectrofluorometry measurements and patch-clamp. It appears from this study that nervous control of luminescence in ophiuroids presents a high diversity at all levels (e.g. neurotransmitters, second messengers, ion channels). Two new neurotransmitters have been identified as being inductors of light production in A. filiformis (tryptamine/octopamine) and O. californica (tryptamine) but up to now, all potential transmitters tested have failed to trigger luminescence in O. aranea. Some common features have however been highlighted between the studied species as to say the Ca2+ dependence of light emission and the cAMP pathway involvement. Moreover, the hypothesis of an indirect nervous control has been suggested for the three studied species. Therefore, a model can be presented in which neurotransmitters or electrical synapses, depending on the species, could act on the relay cell which would in turn activate the luminous cell (= photocyte) and induce photogenesis.