Abstract
Obesity is a growing problem worldwide with a clear impact on health status. It is also a condition that negatively affects circadian rhythms. When the mouse Neotomodon alstoni is fed a regular rodent chow, some individuals develop obesity, representing an opportunity to compare the effects of spontaneous obesity upon the circadian organization in this species with that observed in other rodents with induced obesity. We report differences in the free running circadian locomotor activity rhythm and in the effects of light pulses between lean and obese mice. Also, the photo-induced expression of the c-Fos protein and vasoactive intestinal peptide (VIP) in the suprachiasmatic nucleus (SCN) were examined at circadian time (CT) 14 and 22. We show that obese mice have a larger dispersion of the period of circadian locomotor rhythm in constant darkness. Photic induced phase shifts are nearly 50% shorter at CT 14, and 50% larger at CT 22 than in lean mice. The photoinduction of VIP in the SCN at CT 22 was larger in obese mice, which may be related to the differences observed in photic phase shifting. Our work indicates that the obesity in Neotomodon has effects on the neural mechanisms that regulate the circadian system.
Highlights
Most living organisms have an internal clock that confers 24-h rhythmicity to their physiological processes
We present the differences in circadian phase shift, from lean and obese N. alstoni born in vivarium conditions and we address the mechanisms of such differences by studying the photoinduction of c-Fos synthesis in the suprachiasmatic nucleus (SCN), as observed by others [8, 23] as well as in the presence of vasoactive intestinal peptide (VIP) [33, 34]
Body weight increase in Neotomodon F1 mice In order to explore whether Neotomodon offspring had a body weight increase similar to that of the wild mice observed before [40], we followed a group of mice born
Summary
Most living organisms have an internal clock that confers 24-h rhythmicity to their physiological processes. Entrainment of the clock by external periodic signals is an evolutionary advantage, because it allows rhythms to adapt and anticipate natural periodic changes [1,2,3]. Exposure during the early subjective night causes phase delays, whereas, during the late subjective night, the exposure causes phase advances; brief light exposure during the subjective day does not alter the circadian phase [7]. These behavioral changes are usually correlated with photoinduction of the protein c-Fos in the SCN [8]
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