Effect of Constant Light on the Circadian Rhythm in Locomotor Activity in Intact of Eyelids-removed Rats

Abstract

According to the Aschoff's role, exposure to continuous light (LL) results in the elongation of the free-running period of the rat circadian rhythm. However, the LL may not always mean the constant intensity of the light for the suprachiasmatic nucleus, since the rat may regulate the contrast of the illumination by their eyelids which are closed during the sleep phase. In this study, the surgical removal of the eyelids under the LL caused arrhythmicity of the locomotor activity in 7 of 10 rats. The remaining 3 rats maintained the free-running rhythm after the removal of the eyelids. These results suggest that constant light may affect the free-running rhythm of the rat with or without eyelids in the different manner.