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Recognition of familiar food activates feeding via an endocrine serotonin signal in Caenorhabditis elegans

eLife digest

Many species, including our own, show a preference for familiar foods over novel ones. This behavior probably evolved to reduce the risk of consuming items that turn out to be poisonous, but the mechanisms that underlie a preference for familiar foods are largely unknown.

The nematode worm, C. elegans, is a useful organism in which to study such processes. Having only around 1000 cells and a simple anatomy, C. elegans is an attractive model system for studying molecular biology, and was the first multicellular organism to have its genome fully sequenced.

C. elegans feeds on bacteria, which it detects using a pair of sensory cells called ADF neurons, which sense extrinsic cues. When the ADF neurons detect bacteria, they release the transmitter serotonin. Serotonin stimulates the worm to consume the bacteria by pumping them into the pharynx, its feeding organ, and then transporting them to its intestine after crushing them.

Now, Song et al. have demonstrated that C. elegans consumes familiar bacteria more rapidly than it does novel ones, and have identified the molecular mechanism behind this behavior. They found that familiar bacteria stimulated the release of serotonin from the ADF cells: this activated SER-7 receptors on a specific type of motor neuron in the pharynx and this, in turn, triggered the worms' feeding response. Novel bacteria, on the other hand, failed to either activate ADF or to trigger feeding. Moreover, when Song et al. offered the worms familiar bacteria in medium that had previously contained novel bacteria, the residual traces of the novel bacteria stopped the worms from responding to familiar food.

Further research is needed to determine whether the mechanisms that underpin the more active consumption of familiar food by C. elegans can also explain the preference for familiar foods shown by other species. A better understanding of the mechanisms by which different foods elicit feeding could also offer important insights into factors that contribute to obesity.

DOI: http://dx.doi.org/10.7554/eLife.00329.002