Temporal expression of clock genes in central and peripheral tissues of spotted munia under varying light conditions: Evidence for circadian regulation of daily physiology in a non-photoperiodic circannual songbird species

Spotted munia exhibited rhythmic activity patterns under a 12-hour light-dark cycle but became arrhythmic under continuous light.

• Both core clock and clock-controlled genes demonstrated significant 24-hour rhythms in hypothalamus, retina, liver, and gut under a 12-hour light-dark cycle, except for the Clock gene in the liver.
• Exposure to an aberrant light-dark cycle (3.5L:3.5D) or continuous light resulted in arrhythmic transcriptional oscillation of all eight genes in the hypothalamus, with some exceptions.
• In the retina, all genes showed arrhythmic expression under continuous light, while some maintained rhythmicity under the aberrant light-dark cycle.
• Bmal1, Per2, Cry1, Rorα, and Rev-erbα mRNA expressions were rhythmic in the gut under both the aberrant cycle and continuous light, contrasting with the liver's response.
• These findings indicate a variable relationship between internal circadian clocks and the external light environment, suggesting weak coupling of circadian rhythms between central and peripheral tissues.

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