Vertebrate locomotion relies on precisely timed output of motor neurons. Spinal cord circuits are known to autonomously produce locomotor rhythms following sensory stimulation or descending commands from the brain. In a changing environment, it is necessary to modulate CPG activity with external and internal sensory information. CSF-contacting neurons (CSF-cNs) project a ciliary tuft into the central canal of the spinal cord and make projections throughout the motor column. Consequently, these cells have been hypothesized to act as an internal sensory cell detecting cues from the CSF that modulate locomotor activity. We previously showed that CSF-cNs modulate locomotion in zebrafish larva. Here, we demonstrate that CSF-cNs detect curvature of the spinal cord during active and passive locomotion. However, the sensory mechanisms underlying CSF-cN function remain elusive. We have developed a transgenic line to label differentiated CSF-cNs in zebrafish. In order to identify novel candidate receptors underlying their sensory function, we isolated CSF-cNs by FACS enabling us to proceed to a transcriptome analysis. After identifying candidate molecules, we will disrupt their function and assess defects on CSF-cN activity in vivo and on innate locomotion. All together, this project will characterize the role of sensory information carried by the CSF and relayed to spinal circuits. In the future, our effort in zebrafish will be ported to mammalian studies.