Food odors trigger an endocrine response that affects food ingestion and metabolism
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Food odors stimulate appetite and innate food-seeking behavior in hungry animals. The smell of food also induces salivation and release of gastric acid and insulin. Conversely, sustained odor exposure may induce satiation. We demonstrate novel effects of food odors on food ingestion, metabolism and endocrine signaling in Drosophila melanogaster. Acute exposure to attractive vinegar odor triggers a rapid and transient increase in circulating glucose, and a rapid upregulation of genes encoding the glucagon-like hormone adipokinetic hormone (AKH), four insulin-like peptides (DILPs) and some target genes in peripheral tissues. Sustained exposure to food odors, however, decreases food intake. Hunger-induced strengthening of synaptic signaling from olfactory sensory neurons (OSNs) to brain neurons increases food-seeking behavior, and conversely fed flies display reduced food odor sensitivity and feeding. We show that increasing the strength of OSN signaling chronically by genetic manipulation of local peptide neuromodulation reduces feeding, elevates carbohydrates and diminishes lipids. Furthermore, constitutively strengthened odor sensitivity altered gene transcripts for AKH, DILPs and some of their targets. Thus, we show that food odor can induce a transient anticipatory endocrine response, and that boosted sensitivity to this odor affects food intake, as well as metabolism and hormonal signaling.
KeywordsInsulin-like peptides Adipokinetic hormone Neuropeptides Olfactory sensory neurons Feeding Drosophila melanogaster
We thank E. Rulifson (Stanford, CA), K. Yu (Daejeon, Korea), J. H. Park (Knoxville, TN), Ping Shen (Athens, GA) and Bloomington Drosophila Stock Center (BDSC), Bloomington, IN for providing fly stocks. We are grateful to J. A. Veenstra (Bordeaux, France) and Mark Brown (Athens, GA) for providing antisera. Drs Heinrich Dircksen and Jonas Bengtsson (both Stockholm) kindly read and commented on an earlier version of the manuscript. Funding was from the Swedish Research Council (VR) and Karl Trygger Foundation (both to D.R.N.).
Conflict of interest
The authors declare that there was no conflict of interest.
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