Properties of subependymal cerebrospinal fluid contacting neurones in the dorsal vagal complex of the mouse brainstem
Authors: Orts‐Del'Immagine Adeline , Wanaverbecq Nicolas , Tardivel Catherine , Tillement Vanessa , Dallaporta Michel , Trouslard Jérôme 
Published: May 2012

Key points
The brainstem is a major site of integration for autonomic information from neurones, blood and cerebrospinal fluid (CSF). Signals exchange from the CSF is limited by the ependymocytes forming the brain cavities. However neurones contacting the CSF (CSF‐cNs) are thought to integrate those signals.
Using immunohistochemical and electrophysiological approaches, we characterise in the brainstem, subependymal CSF‐cNs projecting a process ending in the central canal with a protrusion and expressing a ‘transient receptor potential’ (TRP) channel subtype suggested to act as chemo‐ or mechanoreceptors: the polycystin kidney disease 2‐like 1 channels (PKD2L1).
CSF‐cNs receive exclusively inhibitory synaptic inputs and express functional channels presenting all properties of PKD2L1: cationic non‐selective, large conductance and modulated by extracellular pH and osmolarity.
Because medullar CSF‐cNs are strategically positioned between CSF and neuronal parenchyma, we hypothesise that they could play a role in the regulation of homeostasis by integrating CSF signals.
Abstract  Cerebrospinal fluid (CSF) contacting neurones have been observed in various brain regions such as the hypothalamus, the dorsal nucleus of the raphe and around the central canal (cc) of the spinal cord but their functional role remains unclear. At the level of the spinal cord, subependymal cerebrospinal fluid contacting neurones (S‐CSF‐cNs) present a peculiar morphology with a soma close to the ependymal layer, a process projecting towards the cc and ending with a bud and a cilium. These neurones were recently shown to express polycystin kidney disease 2‐like 1 (PKD2L1 or TRPP3) channels that are members of the polycystin subtype of the transient receptor potential (TRP) channel superfamily and that have been proposed as either chemo‐ or mechanoreceptors in several tissues. Using immunohistological techniques and whole‐cell electrophysiological recordings in brain slices obtained from PKD2L1:EGFP transgenic adult mice, we looked for and determined the functional properties of S‐CSF‐cNs in the dorsal vagal complex (DVC), a hindbrain structure controlling autonomic functions such as blood pressure, energy balance and food intake. Here, we demonstrate that S‐CSF‐cNs received GABAergic and/or glycinergic synaptic entries and were also characterised by the presence of non‐selective cationic channels of large conductance that could be detected even under whole‐cell configuration. The channel activity was not affected by Psalmopoeus cambridgei toxin 1, a blocker of acid sensing ion channels (ASICs), but was blocked by amiloride and by a strong extracellular acidification. In contrast, extracellular alkalinisation and hypo‐osmotic shocks increased channel activity. Based on these properties, we suggest that the single‐channel activity recorded in medullar S‐CSF‐cNs is carried by PKD2L1 channels. Our study therefore reinforces the idea that PKD2L1 is a marker of S‐CSF‐cNs and points toward a role for S‐CSF‐cNs in the detection of circulating signals and of modifications in the extracellular environment.