UMMS Affiliation

Department of Neurology; Department of Neurobiology

Date

10-11-2011

Document Type

Article

Medical Subject Headings

Animals; Circadian Rhythm; Cricetinae; Gene Expression; Male; Mesocricetus; Period Circadian Proteins; Photic Stimulation; Photoperiod; RNA, Messenger; Suprachiasmatic Nucleus

Disciplines

Neuroscience and Neurobiology

Abstract

The circadian clock in the mammalian hypothalamic suprachiasmatic nucleus (SCN) is entrained by the ambient light/dark cycle, which differentially acts to cause the clock to advance or delay. Light-induced changes in the rhythmic expression of SCN clock genes are believed to be a critical step in this process, but how the two entrainment modalities--advances vs. delays--engage the molecular clockwork remains incompletely understood. We investigated molecular substrates of photic entrainment of the clock in the SCN by stably entraining hamsters to T cycles (non-24-h light/dark cycles) consisting of a single 1-h light pulse repeated as either a short (23.33-h) or a long (24.67-h) cycle; under these conditions, the light pulse of the short cycle acts as "dawn," whereas that of the long cycle acts as "dusk." Analyses of the expression of the photoinducible and rhythmic clock genes Period 1 and 2 (Per1 and Per2) in the SCN revealed fundamental differences under these two entrainment modes. Light at dawn advanced the clock, advancing the onset of the Per1 mRNA rhythm and acutely increasing mRNA transcription, whereas light at dusk delayed the clock, delaying the offset of the Per2 mRNA rhythm and tonically increasing mRNA stability. The results suggest that the underlying molecular mechanisms of circadian entrainment differ with morning (advancing) or evening (delaying) light exposure, and such differences may reflect how entrainment takes place in nocturnal animals under natural conditions.

Comments

Citation: Proc Natl Acad Sci U S A. 2011 Oct 11;108(41):17219-24. Epub 2011 Oct 3. Link to article on publisher's site

Publisher PDF posted as allowed by the publisher's author rights policy at http://www.pnas.org/site/misc/authorfaq.shtml.

Related Resources

Link to Article in PubMed