Serotonergic neuron ADF modulates avoidance behaviors by inhibiting sensory neurons in C-elegans

Serotonin plays an essential role in both the invertebrate and vertebrate nervous systems. ADF, an amphid neuron with dual ciliated sensory endings, is considered to be the only serotonergic sensory neuron in the hermaphroditic Caenorhabditis elegans. This neuron is known to be involved in a range of behaviors including pharyngeal pumping, dauer formation, sensory transduction, and memory. However, whether ADF neuron is directly activated by environmental cues and how it processes these information remains unknown. In this study, we found that ADF neuron responds reliably to noxious stimuli such as repulsive odors, copper, sodium dodecyl sulfonate (SDS), and mechanical perturbation. This response is mediated by cell-autonomous and non-cell autonomous mechanisms. Furthermore, we show that ADF can modulate avoidance behaviors by inhibiting ASH, an amphid neuron with single ciliated ending. This work greatly furthers our understanding of 5-HT's contributions to sensory information perception, processing, and the resulting behavioral responses.