Ruan GX, Allen GC, Yamazaki S, McMahon DG. An autonomous circadian clock in the inner mouse retina regulated by dopamine and GABA.
PLoS Biol 2009;
6:e249. [PMID:
18959477 PMCID:
PMC2567003 DOI:
10.1371/journal.pbio.0060249]
[Citation(s) in RCA: 118] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2008] [Accepted: 09/05/2008] [Indexed: 11/20/2022] Open
Abstract
The influence of the mammalian retinal circadian clock on retinal physiology and function is widely recognized, yet the cellular elements and neural regulation of retinal circadian pacemaking remain unclear due to the challenge of long-term culture of adult mammalian retina and the lack of an ideal experimental measure of the retinal circadian clock. In the current study, we developed a protocol for long-term culture of intact mouse retinas, which allows retinal circadian rhythms to be monitored in real time as luminescence rhythms from a PERIOD2::LUCIFERASE (PER2::LUC) clock gene reporter. With this in vitro assay, we studied the characteristics and location within the retina of circadian PER2::LUC rhythms, the influence of major retinal neurotransmitters, and the resetting of the retinal circadian clock by light. Retinal PER2::LUC rhythms were routinely measured from whole-mount retinal explants for 10 d and for up to 30 d. Imaging of vertical retinal slices demonstrated that the rhythmic luminescence signals were concentrated in the inner nuclear layer. Interruption of cell communication via the major neurotransmitter systems of photoreceptors and ganglion cells (melatonin and glutamate) and the inner nuclear layer (dopamine, acetylcholine, GABA, glycine, and glutamate) did not disrupt generation of retinal circadian PER2::LUC rhythms, nor did interruption of intercellular communication through sodium-dependent action potentials or connexin 36 (cx36)-containing gap junctions, indicating that PER2::LUC rhythms generation in the inner nuclear layer is likely cell autonomous. However, dopamine, acting through D1 receptors, and GABA, acting through membrane hyperpolarization and casein kinase, set the phase and amplitude of retinal PER2::LUC rhythms, respectively. Light pulses reset the phase of the in vitro retinal oscillator and dopamine D1 receptor antagonists attenuated these phase shifts. Thus, dopamine and GABA act at the molecular level of PER proteins to play key roles in the organization of the retinal circadian clock.
The circadian clock in the mammalian retina regulates many retinal functions, and its output modulates the central circadian clock in the brain. Details about the cellular location and neural regulation of the mammalian retinal circadian clock remain unclear, however, largely due to the difficulty of maintaining long-term culture of adult mammalian retina and the lack of an ideal experimental measure of the retinal clock. We have circumvented these limitations by developing a protocol for long-term culture of intact mouse retinas to monitor circadian rhythms of clock gene expression in real time. Using this protocol, we have localized expression of molecular retinal circadian rhythms to the inner nuclear layer. We find molecular retinal rhythms generation is independent of many forms of signaling from photoreceptors and ganglion cells, or major forms of neural communication within the inner nuclear layer, and have characterized light-induced resetting of the retinal clock. Retinal dopamine and GABA, although not necessary for the generation of molecular retinal rhythms, were revealed to regulate the phase and amplitude of retinal molecular rhythms, respectively, with dopamine participating in light-induced resetting. Our data indicate that dopamine and GABA play prominent roles in the organization of the retinal circadian clock.
Long-term culture of mouse retinas reveals a circadian clock in the inner retina that can be reset by light and is regulated by the neurotransmitters dopamine and GABA.
Collapse