The cerebrospinal fluid (CSF) is a complex solution circulating around the brain and spinal cord. Behavior has long been known to be influenced by the content and flow of the CSF, but the underlying mechanisms are elusive. CSF-contacting neurons by their location at the interface between the CSF and the nervous system are in ideal position to sense CSF cues and to relay information to local networks. By combining electrophysiology, optogenetics and calcium imaging in vivo in zebrafish larvae, we demonstrate that neurons contacting the CSF detect local bending of the spinal cord and in turn feedback GABAergic inhibition to multiple interneurons driving locomotion and posture in the ventral spinal cord. This GABAergic feedback modulates target in a state-dependent manner, depending on the fact that the animal is at rest or actively moving at a define speed. Behaviour analysis of animals deprived of this mechano-sensory pathway reveals a differential contribution to slow and fast locomotions, as well as a role in the control of posture during active locomotion. Altogether, this body of work sheds light on the cellular and network mechanisms enabling sensorimotor integration of mechanical and chemical cues from the CSF onto motor circuits controlling locomotion and posture in the spinal cord.
Light on an ancestral sensory interface linking cerebrospinal fluid to motor circuits in vertebrates