Characterization of the physiological role of CSF-contacting neurons in mammalian CNS. – MotAct-CSF

This proposal aims at elucidating the physiological, molecular and anatomical properties of cerebrospinal fluid-contacting neurons (CSF-cNs) in the mammalian central nervous system. CSF-cNs are a unique neuronal population, conserved from lower vertebrates to primates, lining the central canal (CC) at all medullospinal levels and are characterized by selective expression of the Polycystin Kidney Disease 2-Like 1 channel (PKD2L1). These neurons are highly polarized cells with a dendrite projecting to the CC and forming a large protrusion in contact with the CSF, while their axons appear to extend in the parenchyma along the longitudinal axis of the ventral spinal cord. CSF-cNs are strategically positioned to monitor CSF composition and sense mechanical deformation of the spine, thus possible functions in providing sensory information about the physiological and/or postural state of the organism have been hypothesized.

In recent studies, we conducted pioneering characterization of the physiology and anatomy of mouse medullar CSF-cNs, demonstrating expression of functional ionotropic receptors and spontaneous PKD2L1 channel activity capable of regulating CSF-cNs excitability. We also described that CSF-cNs positioning around the CC varies at different segmental levels, suggesting potential differences in physiological properties, circuitry and function along the rostro-caudal axis of CNS. However, to date, the role of CSF-cNs in the central nervous system remains unknown.
By combining electrophysiological, calcium imaging, molecular and viral tracing techniques, we propose to determine for the first time in mammals the molecular profile, cellular and connectivity properties of CSF-cNs at different medullospinal levels according to the following specific aims:

AIM 1 - Physiology and synaptic integration of CSF-cNs along the central canal
A. CSF-cNs electrophysiological properties and calcium homeostasis
B. Region specific transcriptomic on isolated medullospinal CSF-cNs
C. Identification of CSF-cNs input/output relationships and modulation of their activity
AIM 2 - Characterization of CSF-cNs input-output connectivity
A. Identification of CSF-cNs projection patterns and pre-synaptic terminals
B. Mapping CSF-cNs circuits
C. Identification of CSF-cNs pre- and post-synaptic partners

The proposed studies will advance our current understanding of CSF-cNs biology to fully characterize their molecular and cellular properties. Moreover, we will determine both anatomically and functionally the specific neuronal networks CSF-cNs are inserted in. Altogether, these data will be a necessary step to define the function of CSF-cNs in the mammalian central nervous system.