Why Deprivation Makes Food Taste Better?

Abstract

The phenomenon of food tasting better after deprivation is conserved across many species. In C. elegans, an enhanced slowing response is ob- served when encountering food after 30 minutes of food deprivation (Sawin et al., 2000). This response is mediated by a large increase in serotonin (5-HT) release from the NSM and ADF neurons (Iwanir et al., 2016; Rhoades et al, 2019). We found that this slowing response and the activity of serotonergic neurons upon food exposure are further enhanced in tyramine (TA)-deficient mutants. TA levels decrease during fasting, and C. elegans reduces its locomotion rate after prolonged fasting (>30 minutes). This reduction in locomotion can be counteracted by the addition of exogenous TA, highlighting the role of TA in regulating movement. In contrast, serotonin (5-HT) decreases locomotion, indicating an antagonistic relationship between 5-HT and TA. We found that tyramine exerts an inhibitory effect on the NSM neuron by activating the tyramine GPCR receptors SER-2 and TYRA-2 Downregulation of tyramine during food deprivation leads to the disinhibition of serotonergic signaling and increased NSM activity upon re-encountering food. This disinhibition provides molecular and neural insights into the enhanced slowing response, enabling the worm to efficiently exploit a new food source. The antagonistic crosstalk between TA and 5-HT illustrates how the nervous system controls discrete behavioral state transitions during foraging. This mechanism may explain why food is perceived as more rewarding or appealing in states of hunger, offering a neural basis for the enhanced sensory experience of food after deprivation.