Circadian feeding entrains anticipatory metabolic activity in piriform cortex and olfactory tubercle, but not in suprachiasmatic nucleus

Oct 5, 2014Brain research

Daily feeding schedules influence metabolism in smell-related brain areas but not in the brain’s main clock

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Abstract

Metabolic activity increased in the anterior piriform cortex, olfactory tubercle, and olfactory bulb during food anticipatory activity in nursed rabbit pups.

Food anticipatory activity (FAA) occurs 2-3 hours before scheduled feeding in animals with restricted food availability.
Rabbit pups demonstrated clear FAA when entrained to specific nursing times.
Increased metabolic activity was observed in the anterior piriform cortex, olfactory tubercle, and olfactory bulb during FAA and after feeding.
Metabolic activity in the suprachiasmatic nucleus did not show changes based on the nursing schedule.
The anterior piriform cortex and olfactory tubercle may play a significant role in integrating odor signals with the body's energy state and reward mechanisms.

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Animals maintained under conditions of food-availability restricted to a specific period of the day show molecular and physiological circadian rhythms and increase their locomotor activity 2-3h prior to the next scheduled feeding, called food anticipatory activity (FAA). Although the anatomical substrates and underlying mechanisms of the food-entrainable oscillator are not well understood, experimental evidence indicates that it involves multiple structures and systems. Using rabbit pups entrained to circadian nursing as a natural model of food restriction, we hypothesized that the anterior piriform cortex (APCx) and the olfactory tubercle (OTu) are activated during nursing-associated FAA. Two groups of litters were entrained to one of two different nursing times. At postnatal day 7, when litters showed clear FAA, pups from each litter were euthanized at nursing time, or 1, 2, 4, 8, 12, 16 or 20h later. Neural metabolic activities of the APCx, OTu, olfactory bulb (OB) and suprachiasmatic nucleus (SCN) were assessed by cytochrome oxidase histochemistry. Additionally, two fasted groups were nurse-deprived for two cycles before being euthanized at postnatal day 9. In nursed pups, metabolic activity of APCx, OTu and OB increased during FAA and after feeding, independently of the geographical time. Metabolic activity in SCN was not affected by nursing schedule. Given that APCx and OTu are in a key network position to integrate temporal odor signals with body energetic state, brain arousal and reward mechanisms, we suggest that these structures could be an important part of the conditioned oscillatory mechanism that leads to food entrainment.

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Circadian feeding entrains anticipatory metabolic activity in piriform cortex and olfactory tubercle, but not in suprachiasmatic nucleus

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