In:
Visual Neuroscience, Cambridge University Press (CUP), Vol. 16, No. 5 ( 1999-09), p. 909-918
Abstract:
Vertebrate retinal photoreceptors periodically
shed membrane from their outer segment distal tips; this material is phagocytosed and degraded by the retinal pigmented
epithelium. Both a circadian oscillator and the daily light–dark cycle affect disk shedding, and the effects of both may
be mediated by melatonin. To clarify melatonin's role in this process, we asked whether endogenous melatonin
is required for rhythmic disk shedding in mouse retina. We analyzed disk shedding in two mouse strains: C3H, which
produce melatonin in retina and pineal under the control of circadian oscillators, and C57BL/6, which do not produce
melatonin. In cyclic light, both strains exhibited a robust cycle of disk phagosome content in the pigmented epithelium.
Peak shedding occurred just after dawn, and trough levels occurred during the middle of the dark phase. In constant
darkness, mice exhibited circadian rhythms of locomotor activity, the characteristics of which were similar between
strains. Both strains also exhibited rhythmic disk shedding in constant darkness, although amplitudes of the rhythms
were damped. Exogenous melatonin delivered once per day failed to reestablish high-amplitude cyclic shedding in
mice held in constant darkness. Our results show that, while disk shedding in cyclic light is robustly rhythmic,
neither rhythmic production of melatonin nor the circadian oscillator responsible for rhythmic locomotor activity
is sufficient to drive high-amplitude rhythmic shedding in constant darkness. More importantly, melatonin is required
neither for cyclic changes in the rate of disk shedding in cyclic light, nor for the circadian rhythm of disk shedding
in constant darkness.
Type of Medium:
Online Resource
ISSN:
0952-5238
,
1469-8714
DOI:
10.1017/S0952523899165106
Language:
English
Publisher:
Cambridge University Press (CUP)
Publication Date:
1999
detail.hit.zdb_id:
1489922-X
SSG:
12
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