Adaptation to short photoperiods augments circadian food anticipatory activity in Siberian hamsters

Mar 27, 2014Hormones and behavior

Short daylight increases food-related daily activity in Siberian hamsters

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Abstract

Male Siberian hamsters (Phodopus sungorus) exhibited greater and more persistent food anticipatory activity (FAA) in short photoperiods (9h light/day) compared to long photoperiods (15h light/day).

All hamsters showed increases in FAA during a timed-feeding schedule, regardless of photoperiod.
In short photoperiods, FAA emerged more rapidly than in long photoperiods.
During probe trials after food deprivation, FAA was greater in both magnitude and persistence in hamsters from short photoperiods.
Gonadectomy in long photoperiods did not produce FAA patterns similar to those observed in short photoperiods.
The findings suggest that the effects of photoperiod on FAA may not be mediated by gonadal hormones.

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This article is part of a Special Issue "Energy Balance". Both the light-dark cycle and the timing of food intake can entrain circadian rhythms. Entrainment to food is mediated by a food entrainable circadian oscillator (FEO) that is formally and mechanistically separable from the hypothalamic light-entrainable oscillator. This experiment examined whether seasonal changes in day length affect the function of the FEO in male Siberian hamsters (Phodopus sungorus). Hamsters housed in long (LD; 15 h light/day) or short (SD; 9h light/day) photoperiods were subjected to a timed-feeding schedule for 10 days, during which food was available only during a 5h interval of the light phase. Running wheel activity occurring within a 3h window immediately prior to actual or anticipated food delivery was operationally-defined as food anticipatory activity (FAA). After the timed-feeding interval, hamsters were fed ad libitum, and FAA was assessed 2 and 7 days later via probe trials of total food deprivation. During timed-feeding, all hamsters exhibited increases FAA, but FAA emerged more rapidly in SD; in probe trials, FAA was greater in magnitude and persistence in SD. Gonadectomy in LD did not induce the SD-like FAA phenotype, indicating that withdrawal of gonadal hormones is not sufficient to mediate the effects of photoperiod on FAA. Entrainment of the circadian system to light markedly affects the functional output of the FEO via gonadal hormone-independent mechanisms. Rapid emergence and persistent expression of FAA in SD may reflect a seasonal adaptation that directs behavior toward sources of nutrition with high temporal precision at times of year when food is scarce.

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Adaptation to short photoperiods augments circadian food anticipatory activity in Siberian hamsters

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