DAY-NIGHT CHANGES IN MELATONIN LEVELS IN DIFFERENT ORGANS OF THE CRICKET (GRYLLUS-BIMACULATUS)

Day-night levels of melatonin (N-acetyl-5-methoxytryptamine) were de t ermined in different organs of adult female crickets (Gryllus bimacula tus) exposed to a 12/12 light/dark cycle, using reversed-phase high pe rformance liquid chromatography coupled with fluorometric detection. M elatonin levels in the compound eye, brain, and palp were significantl y higher during the dark period than during the light period, suggesti ng that a diurnal rhythm of melatonin levels exists in these organs of crickets, with a peak during the dark period. Conversely, melatonin l evels were significantly higher during the light period than the dark period in the cercus, ovipositor, antenna, hind-leg and ovary. No sign ificant day-night difference was found in the fore- and mid-legs, Malp ighian tube, and digestive tube. Thus, these organs may have different melatonin-metabolizing systems compared to those found in the compoun d eye, brain, and palp. Differences in the phasing of the melatonin rh ythm in various organs of the cricket suggest possible differences in melatonin function in these organs.