The "Other" Circadian System: Food as a Zeitgeber

Abstract

It is not surprising that limiting food access to a particular time of day has profound effects on the behavior and physiology of animals. It has been clear for some time that pre-meal behavioral activation, a rise in core temperature, elevated serum corticosterone, and an increase in duodenal disaccharidases are under circadian control and that the observed circadian properties are not abolished by lesions of the suprachiasmatic nucleus (SCN), but the search for the locus of a separate food-entrainable oscillator (FEO) has not been successful. The cloning of circadian clock genes and the discovery that these genes are expressed in many central nervous system structures outside the SCN and in peripheral tissues have led to new strategies for investigating potential loci of an FEO. Recent findings concerning the entrainment of clock gene expression in the central nervous system and in peripheral tissues by periodic food access are presented, and the implications of these findings for a better understanding of a circadian system that entrains to meals, rather than to light, are discussed.

Interactions between endocrine and circadian systems

“…The timing of food intake is an important entrainment signal for peripheral clocks, best characterized in, but not limited to, the liver and adipose clocks (Stephan 2002). Anticipatory behavior just before scheduled feeding (food anticipatory activity (FAA)) is seen in animals with restricted access to food.…”

Energy-responsive timekeeping

“…In normal animals, light-driven diurnal behaviour can be easily overcome by alterations in energy supply, such as during restricted feeding schedules (RFS) (Mistlberger 1994;Stephan 2002). During RFS, food is only available to animals during set periods that typically occur outside of their normal feeding period (such as during the day for nocturnal rodents).…”

“…Under RFS numerous physiological and metabolic functions become entrained to the availability of food, e.g., locomotor activity, body temperature, insulin and corticosterone release. Strong support for the existence of a foodentrainable timing system is the circadian pattern of food anticipatory activity (FAA) rhythms that emerge in intact and SCN-ablated animals maintained on RFS (Krieger 1972;Stephan and Zucker 1972;Boulos and Terman 1980;Mistlberger 1994;Stephan 2002). Further, feeding-related anticipation is not dictated simply by a threshold of energy depletion, as such behaviours are not observed in fasted animals with no prior RFS conditioning, nor during the first few days of RFS.…”

“…Further, feeding-related anticipation is not dictated simply by a threshold of energy depletion, as such behaviours are not observed in fasted animals with no prior RFS conditioning, nor during the first few days of RFS. This implies the existence of other foodentrainable oscillators (FEO), located outside of the SCN, capable of coordinating behaviour and physiology with daily feeding schedules (Mistlberger 1994;Stephan 2002). Once established by RFS, the FEO appear to be robust, as anticipatory activity can continue for several cycles after RFS is stopped and animals are subsequently fasted or returned to ad libitum feeding (Davidson et al 2001b).…”

Does feeding time affect fish welfare?

“…When subjected to scheduled-feeding, most animals display an increase in locomotor activity in anticipation of the forthcoming meal, and this can occur several hours before mealtime. This is known as food anticipatory activity (FAA) (Mistlberger 1994) and has been reported in a wide variety of animals, from bees to mammals (Stephan 2002) and also in fish López-Olmeda and Sánchez-Vázquez 2010). To the authors knowledge, the first evidence of FAA in fish was observed in the bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides), which displayed pre-feeding activity consisting of increases in swimming activity 1-3 h before the scheduled mealtime (Davis 1963).…”