Document Detail

Biological rhythms in the context of light at night (LAN).
MedLine Citation:
PMID:  12163844     Owner:  NLM     Status:  MEDLINE    
In mammals including man, the most important zeitgeber for endogenous rhythms is the environmental light/dark cycle. Mammals perceive light through the eyes and that perception is relayed to the suprachiasmatic nucleus (SCN) by means of neuronal signals. The SCN, in turn, innervates the pineal gland, resulting in the production and release of melatonin almost exclusively during night-time hours. Thus, besides object recognition, eyes serve as the sensory organ for detecting the presence or absence of light. The way that light entrains the SCN is still a matter of intense research. It has been shown, for example, that the light intensities required for affecting melatonin rhythms are much higher than the intensities needed for object identification. On the other hand, even in rodents who completely lack the "classical" photoreceptors of the retina, their endogenous rhythms still can be synchronized by normal light/dark cycles. These two observations led to the hypothesis that there must be photoreceptors, apart from the known (object-identifying) retinal photoreceptors, which are responsible for the entrainment of internal rhythms. Very recently, a number of reports showed that in fact a completely new type of retinal photoreceptor, located in ganglion cells, may be responsible for entraining the SCN. It contains a photopigment, melanopsin, which shares homologies with rhodopsin, but also is evolutionarily older. Compared to rods or cones, the melanopsin-containing neurons are rare, but evenly distributed within the retina, indicating that they serve as a global, integrating light sensor. These ganglion cells apparently project directly into the SCN. Taken together, these new developments in photo-chronobiology open new areas of research. It will be of special interest, for example, to determine how the photosensitive ganglion cells and their dendrites integrate the environmental light stimuli.
Alexander Lerchl
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Publication Detail:
Type:  Journal Article; Review    
Journal Detail:
Title:  Neuro endocrinology letters     Volume:  23 Suppl 2     ISSN:  0172-780X     ISO Abbreviation:  Neuro Endocrinol. Lett.     Publication Date:  2002 Jul 
Date Detail:
Created Date:  2002-08-06     Completed Date:  2002-09-12     Revised Date:  2004-11-17    
Medline Journal Info:
Nlm Unique ID:  8008373     Medline TA:  Neuro Endocrinol Lett     Country:  Sweden    
Other Details:
Languages:  eng     Pagination:  23-7     Citation Subset:  IM    
School of Engineering and Science, International University Bremen, Campus Ring 1, D-28759 Bremen, Germany.
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MeSH Terms
Biological Clocks / physiology*
Melatonin / physiology
Pineal Gland / physiology*
Reg. No./Substance:

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