Day-night changes in melatonin levels in different organs of the cricket (Gryllus bimaculatus)

Day-night levels of melatonin (N-acetyl-5-methoxytryptamine) were determined in different organs of adult female crickets (Gryllus bimaculatus) exposed to a 12/12 light/dark cycle, using reversed-phase high performance liquid chromatography coupled with fluorometric detection. Melatonin levels in the compound eye, brain, and palp were significantly higher during the dark period than during the light period, suggesting that a diurnal rhythm of melatonin levels exists in these organs of crickets, with a peak during the dark period. Conversely, melatonin levels were significantly higher during the light period than the dark period in the cercus, ovipositor, antenna, hind-leg and ovary. No significant day-night difference was found in the fore- and mid-legs, Malpighian tube, and digestive tube. Thus, these organs may have different melatonin-metabolizing systems compared to those found in the compound eye, brain, and palp. Differences in the phasing of the melatonin rhythm in various organs of the cricket suggest possible differences in melatonin function in these organs.