This is an interesting study in PLoS One examining the involvement of melatonin in the retina, particularly in the survival of retinal neurons through aging studies in CH3-f+/+ mice, a melatonin proficient mouse strain. As expected, certain physiological measures (a and b waves) are lost during aging, and in particular, the daily circadian rhythms of those measures. However, the authors, Kenkichi Baba, Francesca Mazzoni, Sharon Owino, Susana Contreras-Alcantara, Enrica Strettoi and Gianluca Tosini did something really interesting and added exogenous melatonin to their assay and concluded that responsiveness of exogenous melatonin is also reduced during aging.
I’ve watched the development of the circadian rhythm research starting with Joe Takahashi‘s work discovering CLOCK in the mammalian SCN back in 1994. Since then there has been an explosion of circadian rhythm biology work including an I suppose, unsurprising amount of research in the retina proper.
This paper by Anamika Sengupta, Kenkichi Baba, Francesca Mazzoni, Nikita V. Pozdeyev, Enrica Strettoi, P. Michael Iuvone, and Gianluca Tosini describes the localization of type 1 melatonin receptors in the mouse retina that has interesting potential implications for additional circadian mechanisms in the retina.