Document Detail

Roles of PACAP-containing retinal ganglion cells in circadian timing.
MedLine Citation:
PMID:  16939776     Owner:  NLM     Status:  MEDLINE    
The brain's biological clock located in the suprachiasmatic nucleus (SCN) generates circadian rhythms in physiology and behavior. The clock-driven rhythms need daily adjustment (entrainment) to be synchronized with the astronomical day of 24 h. The most important stimulus for entrainment of the clock is the light-dark (LD) cycle. In this review functional elements of the light entrainment pathway will be considered with special focus on the neurotransmitter pituitary adenylate cyclase-activating polypeptide (PACAP), which is found exclusively in the monosynaptic neuronal pathway mediating light information to the SCN, the retinohypothalamic tract (RHT). The retinal ganglion cells of the RHT are intrinsically photosensitive due to the expression of melanopsin and seem to constitute a non-image forming photosensitive system in the mammalian eye regulating circadian timing, masking behavior, light-regulated melatonin secretion, and the pupillary light reflex. Evidence from in vitro and in vivo studies and studies of mice lacking PACAP and the specific PACAP receptor (PAC1) indicate that PACAP and glutamate are neurotransmitters in the RHT which in a clock and concentration-dependent manner interact during light entrainment of the clock.
Jens Hannibal
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Review    
Journal Detail:
Title:  International review of cytology     Volume:  251     ISSN:  0074-7696     ISO Abbreviation:  Int. Rev. Cytol.     Publication Date:  2006  
Date Detail:
Created Date:  2006-08-30     Completed Date:  2006-10-18     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  2985180R     Medline TA:  Int Rev Cytol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1-39     Citation Subset:  IM    
Department of Clinical Biochemistry, Bispebjerg Hospital, University of Copenhagen, Denmark.
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MeSH Terms
Biological Clocks / genetics,  physiology*
Circadian Rhythm / physiology*
Glutamic Acid / metabolism
Neural Pathways / anatomy & histology,  physiology
Pituitary Adenylate Cyclase-Activating Polypeptide / genetics,  metabolism*
Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I / genetics,  metabolism
Retinal Ganglion Cells / metabolism*
Rod Opsins / metabolism
Signal Transduction / physiology
Suprachiasmatic Nucleus / cytology,  metabolism
Reg. No./Substance:
0/Pituitary Adenylate Cyclase-Activating Polypeptide; 0/Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I; 0/Rod Opsins; 0/melanopsin; 56-86-0/Glutamic Acid

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