Document Detail

Photoperiodism in hamsters: abrupt versus gradual changes in day length differentially entrain morning and evening circadian oscillators.
MedLine Citation:
PMID:  9090566     Owner:  NLM     Status:  MEDLINE    
In studies of photoperiodism, animals typically are transferred abruptly from a long (e.g., 16 h light per day [16L]) to a short (8L) photoperiod, and circadian oscillators that regulate pineal melatonin secretion are presumed to reentrain rapidly to the new photocycle. Among rats and Siberian hamsters, however, reentrainment rates vary depending on whether additional darkness is added to morning or evening, and a subset of hamsters (nonresponders) fails ever to reentrain normally to short photoperiods. The authors assessed whether several short-day responses occurred at different rates when darkness was extended into morning versus evening hours and the effectiveness of abrupt versus gradual shortening in day lengths (DLs). Entrainment patterns of photoresponsive hamsters also were compared to those of photononresponsive hamsters. Responsive hamsters transferred on a single day from 16L to 8L underwent more rapid gonadal regression, weight loss, decreases in follicle-stimulating hormone titers, and expansion of nocturnal locomotor activity when darkness was added to morning versus evening. When the dark phase was extended gradually by 8 h over 16 weeks, short-day responses occurred at the same rate whether darkness was appended to morning or evening or was added symmetrically. Darkness added to evening promoted more rapid short-day responses when it was added gradually rather than abruptly, despite the fact that average DLs were significantly shorter for the latter group. Among nonresponders, morning extensions of darkness transiently increased activity duration, whereas evening extensions did not. Gradual and abrupt decreases in DL differentially affect entrainment of evening and morning circadian oscillators. The authors argue for the incorporation of simulated natural photoperiods in studies of photoperiodism.
M R Gorman; D A Freeman; I Zucker
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Journal of biological rhythms     Volume:  12     ISSN:  0748-7304     ISO Abbreviation:  J. Biol. Rhythms     Publication Date:  1997 Apr 
Date Detail:
Created Date:  1997-06-09     Completed Date:  1997-06-09     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  8700115     Medline TA:  J Biol Rhythms     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  122-35     Citation Subset:  IM    
Department of Psychology, University of California, Berkeley 94720, USA.
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MeSH Terms
Circadian Rhythm*
Motor Activity / physiology
Organ Size / radiation effects
Phodopus / physiology*
Testis / anatomy & histology
Time Factors
Grant Support

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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