Octopaminergic neurons innervate the tracheal supply: a pulse of octopamine releases nitric oxide, which activates the flash reaction by allowing penetration of oxygen ( Trimmer et al., 2001). In fireflies, regulation of oxygen supply to the light organ also seems to be the key regulator of bioluminescence. Serotonergic neurons innervate muscular sphincters that regulate the access of haemolymph to the light organ, thus serotonin regulates the flow of oxygenated haemolymph to the light organ, modulating the bioluminescence reaction ( Kronstrom et al., 2007). In northern krill, serotonin is the primary regulatory biogenic amine ( Fregin and Wiese, 2002 Kronstrom et al., 2007). Administration of the octopamine antagonists phentolamine or mianserin results in very high bioluminescence output levels, similar to the effect of anaesthetics, but only mianserin acts directly on the light organ. Exposure to elevated levels of octopamine via feeding, injection or bathing of the isolated light organ indicates that it is involved in the regulation of repression. Using these methods, dopamine, serotonin and tyramine do not affect bioluminescence output. Candidate biogenic amines were introduced by several methods: feeding prey items injected with test solution, injecting the whole larva, injecting a ligated section containing the light organ or bathing the isolated light organ in test solution. Blocking of neural signals from the central nervous system through ligation leads to uncontrolled release of bioluminescence but light is emitted at relatively low levels compared with under anaesthesia. The effect of the anaesthetic, carbon dioxide, on the isolated light organ from the present study indicates that the repression is at least partially mediated at the light organ itself rather than less directly through the central nervous system. The existing model for the neural regulation of bioluminescence in Arachnocampa, based on use of anaesthetics and ligations, is that bioluminescence is actively repressed during the non-glowing phase and the repression is partially released during the bioluminescence phase. Bioluminescence is modulated through the night although light levels change quite slowly compared with the flashing of the better-known fireflies (Coleoptera). ![]() The light organ is derived from cells of the Malpighian tubules, representing a bioluminescence system that is unique to the genus. ![]() The glowworm Arachnocampa flava is a carnivorous fly larva (Diptera) that uses light to attract prey into its web.
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