Abstract
Under normal light–dark conditions, nocturnal rodents consume most of their food during the dark period. Diets high in fat and sugar, however, may affect the day–night feeding rhythm resulting in a higher light phase intake. In vitro and in vivo studies showed that nutrients affect clock-gene expression. We therefore hypothesized that overconsuming fat and sugar alters clock-gene expression in brain structures important for feeding behavior. We determined the effects of a free-choice high-fat high-sugar (fcHFHS) diet on clock-gene expression in rat brain areas related to feeding and reward and compared them with chow-fed rats. Consuming a fcHFHS diet for 6 weeks disrupted day–night differences in Per2 mRNA expression in the nucleus accumbens (NAc) and lateral hypothalamus but not in the suprachiasmatic nucleus, habenula, and ventral tegmental area. Furthermore, short-term sugar drinking, but not fat feeding, upregulates Per2 mRNA expression in the NAc. The disruptions in day–night differences in NAc Per2 gene expression were not accompanied by altered day–night differences in the mRNA expression of peptides related to food intake. We conclude that the fcHFHS diet and acute sugar drinking affect Per2 gene expression in areas involved in food reward; however, this is not sufficient to alter the day–night pattern of food intake.
Highlights
The suprachiasmatic nucleus (SCN) controls the circadian (24-h period) rhythms in behavior and physiology [1, 2]
In free-choice high-fat high-sugar (fcHFHS)-fed rats, this day–night difference was absent in the nucleus accumbens (NAc) and lateral hypothalamus (LH); i.e., no significant difference between day and night in animals fed the fcHFHS diet (Figure 1A)
We measured day–night expression of Vglut2 in all areas, orexin in the LH and pre-pro-enkephalin in NAc to investigate whether the observed changes in Per2 were reflected in feedingregulating genes
Summary
The suprachiasmatic nucleus (SCN) controls the circadian (24-h period) rhythms in behavior and physiology [1, 2]. We previously reported changes in the molecular clock properties of the lateral habenula (LHb) in fcHFHS diet-exposed mice, an area involved in reward-related behavior, whereas clock proteins in the arcuate nucleus, an important area for homeostatic feeding, were unchanged [9]. It remains, to be determined whether molecular clock-gene expression in food-related reward circuitry, such as striatum and lateral hypothalamus (LH), are affected by a diet high in fat and sugar and if these effects are involved in disruption of the day/night feeding rhythm. We evaluated the acute effects of sugar intake on Per gene expression in the nucleus accumbens (NAc) of rats
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