Serotonin (5-HT) and catecholamines (CA) antagonistic food-related behaviors in C. elegans

Abstract

Despite the intermodulation between serotonergic and adrenergic signals is crucial throughout the animal kingdom, the molecular and cellular mechanisms underlying this interrelation are poorly understood. We here use C. elegans as a model to get insights into the neural circuits linking 5-TH and CA. When food-deprived worms encounter food, 5-HT is released to slow-down their locomotion and to stimulate pharyngeal pumping.In contrast, exogenous Tyramine (TA) and Octopamine (OA), invertebrate counterparts for adrenaline and noradrenaline, stimulate locomotion and decreases pharyngeal pumping. We found that tdc-1 mutants (unable to synthesize TA and OA) are hypersensitive to 5-HT-mediated paralysis, suggesting that TA and OA acts antagonistically to 5-HT. We also identify the TA (TYRA-3) and OA (SER-3 and SER-6) receptors involved in this antagonism. Moreover, our calcium imaging recordings showed that the peak of activity of serotoninergic neurons upon encountering food is significantly higher in tdc-1 null mutant background. Taken together these results suggest that TA and OA counteract serotoninergic signaling by driving opposing behaviors and by inhibiting 5-HT release. Our final aim is to decipher the neural circuit and the molecules involved in the reciprocal modulation between CA and 5-HT in C. elegans. Given the conservation in molecular components of these pathways, our studies are likely significant to understand this interrelation in other animals.