Faculty Collaboration Database

Dim nighttime illumination interacts with parametric effects of bright light to increase the stability of circadian rhythm bifurcation in hamsters. Chronobiol Int 2011 Jul;28(6):488-96

Date

07/30/2011

Pubmed ID

21797777

DOI

10.3109/07420528.2011.591952

Scopus ID

2-s2.0-79960981588 (requires institutional sign-in at Scopus site)   9 Citations

Abstract

The endogenous circadian pacemaker of mammals is synchronized to the environmental day by the ambient cycle of relative light and dark. The present studies assessed the actions of light in a novel circadian entrainment paradigm where activity rhythms are bifurcated following exposure to a 24-h light:dark:light:dark (LDLD) cycle. Bifurcated entrainment under LDLD reflects the temporal dissociation of component oscillators that comprise the circadian system and is facilitated when daily scotophases are dimly lit rather than completely dark. Although bifurcation can be stably maintained in LDLD, it is quickly reversed under constant conditions. Here the authors examine whether dim scotophase illumination acts to maintain bifurcated entrainment under LDLD through potential interactions with the parametric actions of bright light during the two daily photophases. In three experiments, wheel-running rhythms of Syrian hamsters were bifurcated under LDLD with dimly lit scotophases, and after several weeks, dim scotophase illumination was either retained or extinguished. Additionally, "full" and "skeleton" photophases were employed under LDLD cycles with dimly lit or completely dark scotophases to distinguish parametric from nonparametric effects of bright light. Rhythm bifurcation was more stable in full versus skeleton LDLD cycles. Dim light facilitated the maintenance of bifurcated entrainment under full LDLD cycles but did not prevent the loss of rhythm bifurcation in skeleton LDLD cycles. These studies indicate that parametric actions of bright light maintain the bifurcated entrainment state; that dim scotophase illumination increases the stability of the bifurcated state; and that dim light interacts with the parametric effects of bright light to increase the stability of rhythm bifurcation under full LDLD cycles. A further understanding of the novel actions of dim light may lead to new strategies for understanding, preventing, and treating chronobiological disturbances.

Author List

Evans JA, Elliott JA, Gorman MR

Author

Jennifer A. Evans PhD Assistant Professor in the Biomedical Sciences department at Marquette University

MESH terms used to index this publication - Major topics in bold

Animals
Behavior, Animal
Biological Clocks
Circadian Rhythm
Cricetinae
Darkness
Light
Lighting
Mesocricetus
Motor Activity
Photic Stimulation
Time Factors