COMPARISON OF CIRCADIAN OSCILLATION OF MELATONIN RELEASE IN PINEAL CELLS OF HOUSE SPARROW, PIGEON AND JAPANESE-QUAIL, USING CELL PERFUSION SYSTEMS

We compared the circadian oscillation of melatonin release from cultur ed pineal cells in Japanese quail, pigeon and house sparrow, to determ ine whether the pineal gland of these species retains the circadian os cillator function in vitro. After dissociated pineal cells have been c ultured for 4 days under 12 h:12 h light-dark (LD) cycle, they were pe rfused at a flow rate of 0.25 ml/h for 6-7 days under LD or constant d arkness (DD). Melatonin release increased during the dark period and l ow during the light period in all pineal cell cultures. Under DD condi tions, the circadian rhythm of melatonin release persisted for up to 3 -4 cycles in pigeon and house sparrow pineal cells, but the amplitude of the rhythm decreased gradually. However, in Japanese quail pineal c ell culture the circadian oscillation of melatonin release was weak or abolished under DD conditions. These results strengthen the argument that the avian pineal gland's role in circadian organization differs b etween species. The direct demonstration of species-specific differenc es in the mechanism of the circadian oscillation of melatonin release from pineal cells should provide a useful model for the analysis of th e pineal's circadian system at the cellular level.