One key issue in understanding the function of the retinal clock is to localize which cells types are capable of circadian oscillation. Until very recently the vast majority of the experimental evidence suggested that, as observed in non-mammalian vertebrates, circadian clock functions in the retina were localized to the classical photoreceptors cells, rods ands cones). Such a view has been recently challenged by a series of studies suggesting that the inner layer neurons may also contain circadian clocks and by the demonstration that retina lacking photoreceptors still expresses circadian rhythms in several retinal function. Studies in my laboratory are now underway to develop new culture methods to isolate and culture different type of retinal neurons (photoreceptor, amacrine and ganglion cells) to address this important question, and to identify the mechanisms (neural and humoral) that are responsible for the communication of the information among the different cells. In contrast to the SCN (the master circadian pacemaker in the brain) the retina is a complete circadian system where photoreception and pacemaker functions and physiological output are present in the same tissue and most likely in the same cells (photoreceptors), and therefore such an organ represents an ideal experimental model to understand the mechanisms of circadian rhythms generation, entrainment outputs control and biological significance.
Research Key Words : circadian rhythms, melatonin, retina, dopamine, melanopsin