Daily rhythm of melanopsin-expressing cells in the mouse retina

🎖️ Top 10% JournalJun 30, 2009Frontiers in cellular neuroscience

Daily activity pattern of light-sensitive cells in the mouse eye

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Circadian Biology on OpenScience ↗PubMed ↗DOI ↗

Abstract

A daily oscillation in the number of melanopsin-expressing retinal ganglion cells was observed, with the highest count occurring one hour before lights on.

The highest number of immunopositive cells was detected just before the light period, while the lowest count occurred four hours later.
Melanopsin-expressing retinal ganglion cells may 'turn on' and 'off' in response to the day/night cycle.
Daily variations in these cells were noted even during early postnatal development when other photoreceptor systems are not yet functional.
Two subpopulations of melanopsin-expressing cells (M1 and M2) exhibited different patterns of daily oscillations throughout the light/dark cycle.
No defined rhythm of melanopsin-expressing cells was detected in mice maintained in constant darkness for six days, suggesting light dependency.

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In addition to some other functions, melanopsin-expressing retinal ganglion cells (RGCs) constitute the principal mediators of the circadian photoentrainment, a process by which the suprachiasmatic nucleus (the central clock of mammals), adjusts daily to the external day/night cycle. In the present study these RGCs were immunohistochemically labelled using a specific polyclonal antiserum raised against mouse melanopsin. A daily oscillation in the number of immunostained cells was detected in mice kept under a light / dark (LD) cycle. One hour before the lights were on (i.e., the end of the night period) the highest number of immunopositive cells was detected while the lowest was seen 4 h later (i.e., within the first hours of the light period). This finding suggests that some of the melanopsin-expressing RGCs "turn on" and "off" during the day/night cycle. We have also detected that these daily variations already occur in the early postnatal development, when the rod/cone photoreceptor system is not yet functional. Two main melanopsin-expressing cell subpopulations could be found within the retina: M1 cells showed robust dendritic arborization within the OFF sublamina of the inner plexiform layer (IPL), whilst M2 cells had fine dendritic processes within the ON sublamina of the IPL. These two cell subpopulations also showed different daily oscillations throughout the LD cycle. In order to find out whether or not the melanopsin rhythm was endogenous, other mice were maintained in constant darkness for 6 days. Under these conditions, no defined rhythm was detected, which suggests that the daily oscillation detected either is light-dependent or is gradually lost under constant conditions. This is the first study to analyze immunohistochemically the daily oscillation of the number of melanopsin-expressing cells in the mouse retina.

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