The sensation of hunger after a period of fasting and of satiety after eating is crucial to behavioral regulation of food intake, but the biological mechanisms regulating these sensations are incompletely understood. We studied the behavioral and physiological adaptations to fasting in the vinegar fly (Drosophila melanogaster). Here we show that both male and female flies increased their rate of food intake transiently in the post-fasted state. Although the basal feeding rate was higher in females than males, the magnitude of the post-fasting feeding response was the same in both sexes. Flies returned to a stable baseline feeding rate within 12 h after return to food for males and 24 h for females. This modulation in feeding was accompanied by a significant increase in the size of the crop organ of the digestive system, suggesting that fasted flies responded both by increasing their food intake and storing reserve food in their crop. Flies demonstrated increased behavioral attraction to an attractive odor when food-deprived. Expression profiling of head, body, and chemosensory tissues by microarray analysis revealed 415 genes regulated by fasting after 24 h and 723 genes after 48 h, with downregulated genes outnumbering upregulated genes in each tissue and fasting time point. These transcriptional changes showed rich temporal dynamics and affected genes across multiple functional gene ontology categories. These observations suggest that a coordinated transcriptional response to internal physiological state may regulate both ingestive behaviors and chemosensory perception of food.
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