Melatonin activity rhythms in eyes and cerebral ganglia of Aplysia californica

In this study, we used a sensitive and specific radioimmunoassay to detect a substance which appears to be melatonin, an acetylation and methylation product of serotonin, in the eyes and central nervous system of the opisthobranch mollusc Aplysia californica. This identification was confirmed in the eyes by HPLC with fluorimetric detection. Melatonin activity was high in the eyes during the day and in the cerebral ganglia during the night. Only small amounts of melatonin were present at midday or midnight in the pedal ganglia. A single 1-hr exposure to light in the middle of the dark phase resulted in a sharp increase of melatonin in the eyes, whereas no such activity was detectable in cerebral and pedal ganglia. Eyes maintained in culture exhibited a diurnal rhythm of released melatonin activity over a 3-day period. These results suggest that melatonin is produced in A. californica in a rhythmic pattern different from that associated with pineal melatonin production in vertebrates.