Abstract
BackgroundTemporal restriction of food availability entrains circadian behavioral and physiological rhythms in mammals by resetting peripheral oscillators. This entrainment underlies the activity of a timing system, different from the suprachiasmatic nuclei (SCN), known as the food entrainable oscillator (FEO). So far, the precise anatomical location of the FEO is unknown. The expression of this oscillator is associated with an enhanced arousal prior to the food presentation that is called food anticipatory activity (FAA). We have focused on the study of the role played by the liver as a probable component of the FEO. The aim of this work was to identify metabolic and structural adaptations in the liver during the expression of the FEO, as revealed by histochemical assessment of hepatic glycogen and triacylglycerol contents, morphometry, and ultrastructure in rats under restricted feeding schedules (RFS).ResultsRFS promoted a decrease in the liver/body weight ratio prior to food access, a reduction of hepatic water content, an increase in cross-sectional area of the hepatocytes, a moderate reduction in glycogen content, and a striking decrease in triacylglyceride levels. Although these adaptation effects were also observed when the animal displayed FAA, they were reversed upon feeding. Mitochondria observed by electron microscopy showed a notorious opacity in the hepatocytes from rats during FAA (11:00 h). Twenty four hour fasting rats did not show any of the modifications observed in the animals expressing the FEO.ConclusionsOur results demonstrate that FEO expression is associated with modified liver handling of glycogen and triacylglycerides accompanied by morphometric and ultrastructural adaptations in the hepatocytes. Because the cellular changes detected in the liver cannot be attributed to a simple alternation between feeding and fasting conditions, they also strengthen the notion that RFS promotes a rheostatic adjustment in liver physiology during FEO expression.
Highlights
Temporal restriction of food availability entrains circadian behavioral and physiological rhythms in mammals by resetting peripheral oscillators
The restricted feeding schedule (RFS) increases locomotive activity and arousal during the hours immediately before food access, generating a condition known as food anticipatory activity (FAA) [9]
The anatomical location of the food entrainable oscillator (FEO) is unknown, but the physiology of this oscillator is thought to involve the bidirectional communication between specific, energy-sensitive brain areas and nutrient-handling, peripheral organs, especially the liver [8,9,11]
Summary
Temporal restriction of food availability entrains circadian behavioral and physiological rhythms in mammals by resetting peripheral oscillators This entrainment underlies the activity of a timing system, different from the suprachiasmatic nuclei (SCN), known as the food entrainable oscillator (FEO). The precise anatomical location of the FEO is unknown The expression of this oscillator is associated with an enhanced arousal prior to the food presentation that is called food anticipatory activity (FAA). The vertebrate circadian system results from the coordinated action of a light-entrained rhythmicity, and the circadian system is no longer entrained by light but primarily by the effects of the scheduling of meal-feeding [6,7] Central to this adaptation is the expression of a food-entrainable oscillator (FEO) that controls, next to the SCN, the 24-h rhythms of behavioral, physiological, and metabolic activities [8]. The anatomical location of the FEO is unknown, but the physiology of this oscillator is thought to involve the bidirectional communication between specific, energy-sensitive brain areas and nutrient-handling, peripheral organs, especially the liver [8,9,11]
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