A Circadian Clock in the Inner Retina Regulated by Dopamine

Abstract

Methods: : mPer2^Luc knockin mice (C57BL/6J background) were backcrossed with C3H rd mice to produce mPer2^Luc mice that were heterozygous for the rd gene and were genetically capable of producing melatonin. Retinas from these mice were isolated, cultured and assayed for circadian rhythms of the transgenic PER2::LUC reporter by luminescence. Drugs were applied to retinal explant cultures either 3 hr or 12 hr after the 2^nd peak of PER2 expression rhythms in vitro, and then left in the cultures.

Results: : PER2::LUC retinal rhythms were routinely measured from whole-mount retinal explants for 10 days and for up to 30 days with media changes. Imaging of vertical retinal slices demonstrated that the rhythmic luminescence signal was concentrated in the inner nuclear layer. Persistence of rhythms in C57BL/6J mouse retinas that lack melatonin synthesis and during blockade of melatonin receptors with luzindole (5 µM; N=6) demonstrated that retinal PER2::LUC rhythms generation does not require communication via melatonin. In contrast, dopamine, acting mainly through D1 receptors, reset the phase of retinal PER2::LUC rhythms.

Keywords: circadian rhythms • dopamine • melatonin