Oscillators entrained by food and the emergence of anticipatory timing behaviors

Abstract

Circadian rhythms are adjusted to the external environment by the light–dark cycle via the suprachiasmatic nucleus, and to the internal environment of the body by multiple cues that derive from feeding/fasting. These cues determine the timing of sleep/wake cycles and all the activities associated with these states. We suggest that numerous sources of temporal information, including hormonal cues such as corticoids, insulin, and ghrelin, as well as conditioned learned responses determined by the temporal relationships between photic and feeding/fasting signals, can determine the timing of regularly recurring circadian responses. We further propose that these temporal signals can act additively to modulate the pattern of daily activity. Based on such reasoning, we describe the rationale and methodology for separating the influences of these diverse sources of temporal information. The evidence indicates that there are individual differences in sensitivity to internal and external signals that vary over circadian time, time since the previous meal, time until the next meal, or with duration of food deprivation. All of these cues are integrated in sites and circuits modulating physiology and behavior. Individuals detect changes in internal and external signals, interpret those changes as “hunger,” and adjust their physiological responses and activity levels accordingly.

Increased Sensitivity of the Circadian System to Temporal Changes in the Feeding Regime of Spontaneously Hypertensive Rats - A Potential Role for Bmal2 in the Liver

“…Nevertheless, based on the published data, it is plausible to speculate that brain active mediators such as ghrelin and/or orexin may play a role in FAA. Their involvement in the mediation of FAA has previously been suggested because their deficiency resulted in decreased FAA in mice (reviewed by [41]). Interestingly, ghrelin plasma levels [42] as well as orexinergic activity in the brain [43] were found to be elevated in SHR compared with controls.…”

Food anticipation depends on oscillators and memories in both body and brain

“…The circadian rhythm of adrenal corticoid secretion is a well studied example of control by oscillators both centrally in the SCN and peripherally in the adrenal (summarized in [63]). The SCN activates rhythmic release of corticotrophin-releasing hormone from the paraventricular nucleus (PVN) that evokes circadian adrenocorticotropin hormone (ACTH) release from hypophyseal adrenocorticotrophs [64].…”

A Significant Role of the Truncated Ghrelin Receptor GHS-R1b in Ghrelin-induced Signaling in Neurons

“…Ghrelin is an orexigenic hormone, an internal signal for the animal to engage in food-directed behavior (1,2). It is produced by stomach oxyntic cells, which provide plasma levels that fluctuate diurnally with a peak in the day and trough at night.…”

“…It is produced by stomach oxyntic cells, which provide plasma levels that fluctuate diurnally with a peak in the day and trough at night. Notably, oxyntic cells qualify as food-entrained oscillators, and ghrelin plasma levels increase during anticipated mealtimes and decrease after meals (1). These and other less well characterized central neuronal functions of ghrelin depend on its ability to cross the blood-brain barrier by still unclear mechanisms and reaching ghrelin receptors localized in specific brain areas, such as the hypothalamus, hippocampus, amygdala, mesencephalic dopaminergic regions, and striatum (2)(3)(4).…”