PARALLEL SUPPRESSION OF RETINAL AND PINEAL MELATONIN SYNTHESIS BY RETINALLY MEDIATED LIGHT

WE have recently shown that light, over a narrow range of low intensit ies suppresses the activity of the enkephalin-immunoreactive amacrine cells of the chicken retina. In this paper, we show that over the same range of low light intensities the rate of melatonin synthesis in bot h the retina and the pineal of the chicken is suppressed. We further s how that the effects of light on the pineal at these low intensities a re mediated by the retina and not by direct actions on the pineal. Com bined with our evidence that dopaminergic pathways within the retina a re involved in controlling the state of activity of the pineal, these results suggest, but do not prove, that the change in state of a micro circuit within the retina involving the photoreceptors, dopaminergic a macrine cells and enkephalin-immunoreactive amacrine cells may be caus ally related to changes in the state of the pineal.