| The goal of the present studies was to describe the interactions between biological clocks---both seasonal and circadian---and food intake in Siberian hamsters. The first study indicated that short day lengths attenuate the orexigenic potency of ghrelin and reduce ghrelin-induced excitation of NPY neurons in the arcuate nucleus of the hypothalamus. The second study presents data demonstrating that photoperiod influences circadian entrainment to timed food availability and presents the first observation of food entrainment in this species. The third study indicates that food entrainment is enhanced in juvenile Siberian hamsters compared to adult hamsters, but early-life exposure to timed food availability does not provide greater enhancement of food entrainment than later-life exposure. Data presented in a fourth study suggest that food entrainment may occur in Siberian hamsters rendered arrhythmic by a disruptive phase shift, but in contrast with other models of arrhythmia, food anticipatory activity was not potentiated. A fifth study indicates that both food and light may contribute to circadian rhythms observed in measures of innate and adaptive immunity. Furthermore, asynchronous food and light cues may have a deleterious effect on immune function. Together, these data support a model of separate, but not independent, food- and light-entrainable oscillators that selectively contribute to rhythmicity in physiology and behavior. |
