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.jpg): Failed to open stream: No such file or directory in C:\Inetpub\vhosts\kidney.de\httpdocs\pget.php on line 117 J+Biol+Rhythms
2016 ; 31
(3
): 223-43
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The Retina and Other Light-sensitive Ocular Clocks
#MMPMID27095816
Besharse JC
; McMahon DG
J Biol Rhythms
2016[Jun]; 31
(3
): 223-43
PMID27095816
show ga
Ocular clocks, first identified in the retina, are also found in the retinal
pigment epithelium (RPE), cornea, and ciliary body. The retina is a complex
tissue of many cell types and considerable effort has gone into determining which
cell types exhibit clock properties. Current data suggest that photoreceptors as
well as inner retinal neurons exhibit clock properties with photoreceptors
dominating in nonmammalian vertebrates and inner retinal neurons dominating in
mice. However, these differences may in part reflect the choice of circadian
output, and it is likely that clock properties are widely dispersed among many
retinal cell types. The phase of the retinal clock can be set directly by light.
In nonmammalian vertebrates, direct light sensitivity is commonplace among body
clocks, but in mice only the retina and cornea retain direct light-dependent
phase regulation. This distinguishes the retina and possibly other ocular clocks
from peripheral oscillators whose phase depends on the pace-making properties of
the hypothalamic central brain clock, the suprachiasmatic nuclei (SCN). However,
in mice, retinal circadian oscillations dampen quickly in isolation due to weak
coupling of its individual cell-autonomous oscillators, and there is no evidence
that retinal clocks are directly controlled through input from other oscillators.
Retinal circadian regulation in both mammals and nonmammalian vertebrates uses
melatonin and dopamine as dark- and light-adaptive neuromodulators, respectively,
and light can regulate circadian phase indirectly through dopamine signaling. The
melatonin/dopamine system appears to have evolved among nonmammalian vertebrates
and retained with modification in mammals. Circadian clocks in the eye are
critical for optimum visual function where they play a role fine tuning visual
sensitivity, and their disruption can affect diseases such as glaucoma or retinal
degeneration syndromes.
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