Neurons in contact with the cerebrospinal fluid (CSF) are found around the medullo-spinal central canal (CC) in adult mice. These neurons (CSF-cNs), located within or below the ependymal cell layer known as the stem cell niche, present a characteristic morphology with a dendrite projecting to the CC and ending with a protrusion. They are GABAergic, characterized by an immature neuronal phenotype and selectively express PKD2L1, a channel member of the TRP channel superfamily with properties of sensory receptor.
Using immunohistological techniques in mice, we characterize a new population of PKD2L1 positive cells that is observed around embryonic day 16 (E16), is present distant from the CC in a zone enriched with astrocytes and ependymal fibers of the ventro-medial spinal cord and medulla. With development, their number appears stable although smaller than that of CSF-cNs and they progressively become more distant from the CC with the reorganization of the CC region. These neurons share both functional and phenotypical properties with CSF-cNs, but they appear subdivided in two groups. One, present along the midline, has a bipolar morphology and extend a long dendrite along ependymal fibers and towards the CC. The second group, localized in more ventro-lateral regions, has a multipolar morphology and no apparent projection to the CC
Altogether, we describe a novel population of PKD2L1+ neurons distant from the CC but with properties similar to CSF-cNs that might serve to sense modification in the composition of either CSF or interstitial liquid, a function that will need to be confirmed.
Multiple steps characterise ventricular layer attrition to form the ependymal cell lining of the adult mouse spinal cord central canal
