Properties of subependymal cerebrospinal fluid contacting neurones in the dorsal vagal complex of the mouse brainstem

Abstract

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 chemoor 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 chemoor 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 A. Orts-Del'Immagine and N. Wanaverbecq contributed equally to the work.

Morphology, Distribution and Phenotype of Polycystin Kidney Disease 2-like 1-Positive Cerebrospinal Fluid Contacting Neurons in The Brainstem of Adult Mice

“…More recently, the presence of PKD2L1 was reported in medullospinal S-CSF-cNs [12], [16]. Our data confirm that PKD2L1 is a reliable marker for these cells, and we demonstrated here that PKD2L1 is exclusively expressed on the soma and the dendrite of S-CSF-cNs with an apparent strong level of expression on the bud and none on the axon-like process.…”

Investigation of spinal cerebrospinal fluid-contacting neurons expressing PKD2L1: evidence for a conserved system from fish to primates

“…The peculiar location of CSF-cNs in contact with the CSF strongly suggests a role for PKD2L1 as a sensor of CSF composition, pH and/or osmolarity (Huang et al, 2006; Orts-Del'Immagine et al, 2012) since the channel is activated upon acidification (Ishimaru et al, 2006; Inada et al, 2008; Orts-Del'Immagine et al, 2012), alkalinization (Shimizu et al, 2011; Orts-Del'Immagine et al, 2012) or hypo-osmotic variations (Shimizu et al, 2009; Orts-Del'Immagine et al, 2012). …”

Central Nervous System Control of Gastrointestinal Motility and Secretion and Modulation of Gastrointestinal Functions

“…Additionally, the brainstem area containing the dorsal vagal complex (DVC, i.e., DMV, NTS, and area postrema) is essentially a circumventricular organ, lying ventral to the fourth ventricle and is highly vascularized with fenestrated capillaries (111, 171). An additional layer of neurons, termed subependymal cerebrospinal containing neurons (CSF-cNs) are positioned, strategically, between the CSF and neuronal parenchyma and potentially integrate CSF signaling with autonomic homeostatic signaling (361). Indeed, we have demonstrated previously that brainstem neurons can be excited following peripheral administration of the GI neurohormone, cholecystokinin (CCK) even after surgical removal of vagal afferent input to the brainstem (31) implying that the activity of central vagal neurons, including DMV neurons, may be modulated directly by circulating factors.…”