Light-stimulated and light-inhibited bioluminescence of the euphausiid Meganyctiphanes norvegica (G. O. Sars)

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Abstract
Innocuous physiological stimuli which excite bioluminescence in Meganyctiphanes norvegica are few; one such is exposure to an appropriate light, another is chemical stimulation by 5-hydroxytryptamine. Meganyctiphanes responds to a photoflash, after some tens of seconds delay, with a bioluminescent glow lasting a few minutes. A second flash stimulus applied during this luminescent response rapidly abolishes it for tens of seconds, after which the glow returns again at full strength. Weak light of about the same colour and intensity as the animal''s own luminescence also depresses the flash-excited glow for the whole time the ambient light is present. 5-Hydroxytryptamine (5-HT), added to the sea water in which the animal swims can either excite continual luminescence or set whatever physiological controls exist into some hypersensitive state so that Meganyctiphanes becomes much more responsive to optical stimulation. The delay of onset, duration, amplitude and time course of flash-excited luminescence have been determined quantitatively, together with their dependence upon the intensity and spectral composition of the sitmulating flash. Some characteristics of the inhibition by flash and by weak continuous light have been recorded, and also the interaction of 5-HT sensitiza-tion upon light excitation and inhibition. These optical stimulus-bio-luminescent response relationships establish a well-documented excitatory stimulus which can be used to initiate luminescence at will, leaving the animal in its natural physio-chemical environment. The observations provide an experimental basis for judging some hitherto weakly based speculations about the physiological control of bioluminescence in Meganyctiphanes and suggest sensible ways to investigate this in greater detail.

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