Dim nighttime illumination alters photoperiodic responses of hamsters through the intergeniculate leaflet and other photic pathways. Neuroscience 2012 Jan 27;202:300-8
Date
12/14/2011Pubmed ID
22155265Pubmed Central ID
PMC3578228DOI
10.1016/j.neuroscience.2011.11.037Scopus ID
2-s2.0-84856214203 (requires institutional sign-in at Scopus site) 12 CitationsAbstract
In mammals, light entrains the central pacemaker within the suprachiasmatic nucleus (SCN) through both a direct neuronal projection from the retina and an indirect projection from the intergeniculate leaflet (IGL) of the thalamus. Although light comparable in intensity to moonlight is minimally effective at resetting the phase of the circadian clock, dimly lit and completely dark nights are nevertheless perceived differentially by the circadian system, even when nighttime illumination is below putative thresholds for phase resetting. Under a variety of experimental paradigms, dim nighttime illumination exerts effects that may be characterized as enhancing the plasticity of circadian entrainment. For example, relative to completely dark nights, dimly lit nights accelerate development of photoperiodic responses of Siberian hamsters transferred from summer to winter day lengths. Here we assess the neural pathways underlying this response by testing whether IGL lesions eliminate the effects of dim nighttime illumination under short day lengths. Consistent with previous work, dimly lit nights facilitated the expansion of activity duration under short day lengths. Ablation of the IGL, moreover, did not influence photoperiodic responses in animals held under completely dark nights. However, among animals that were provided dimly lit nights, IGL lesions prevented the short-day typical expansion of activity duration as well as the seasonally appropriate gonadal regression and reduction in body weight. Thus, the present data indicate that the IGL plays a central role in mediating the facilitative effects of dim nighttime illumination under short day lengths, but in the absence of the IGL, dim light at night influences photoperiodic responses through residual photic pathways.
Author List
Evans JA, Carter SN, Freeman DA, Gorman MRAuthor
Jennifer A. Evans PhD Assistant Professor in the Biomedical Sciences department at Marquette UniversityMESH terms used to index this publication - Major topics in bold
AnimalsBiological Clocks
Circadian Rhythm
Cricetinae
Darkness
Data Interpretation, Statistical
Geniculate Bodies
Lighting
Male
Motor Activity
Phodopus
Photoperiod
Visual Pathways