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Electrophysiological properties of the ‘bud’ in spinal neurons in contact with the CSF

Neurons in contact with the Cerebro-Spinal Fluid (CSF, CSF-cNs) have been observed around the central canal of the spinal cord in all vertebrate species studied so far. They present a characteristic and conserved morphology with a soma sitting under the ependymal cells laying the central canal and they project a thick dendrite terminated by a large protrusion or ‘bud’ (2-3 µm diameter) bathing in the CSF. Our group has largely contributed in a better understanding of this unique neuronal population in mammals. We have demonstrated that they are inserted in a neuronal network, mainly GABAergic, and that they express selectively an isoform of the ‘Transient Receptor Potential (TRP)’ channel: the TRPP3 or Polycystin Kidney Disease 2-like 1 (PKD2L1) channel. This channel, spontaneously active at the level of the unitary current, is modulated by variations in the extracellular medium composition (pH and osmolarity) and in turn PKD2L1 modulates CSF-cNS excitability (see supplementary documents).
Considering the localization of the ‘bud’ in contact with the CSF, one would suggest that this structure plays a key role in the detection and integration of circulating signals within the CSF notably thanks to the activity of the PKD2L1 channel for which a function as chemoreceptor has been proposed. To date the properties and role of the ‘bud’ is unknown and no information is available regarding the presence and nature of ionic channels at this level.
During the proposed Master training, we will conduct on spinal cord acute slices, electrophysiological recordings on the ‘bud’ using the patch-clamp technique to determine its properties and the presence of functional ionic channels. We will also carry out simultaneous patch-clamp recordings from the soma and the ‘bud’ to analyse potential crosstalk between these two cellular compartments. Finally, we will combine electrophysiological recordings with calcium imaging to analyse the calcium signalling at the level of the ‘bud’, of the soma and the functional relationships between these two regions.
Taking together, the expected results will represent the first functional characterisation of the ‘bud’ and the demonstration of its effect on CSF-cNs physiology.

Experimental procedures:
• Patch-clamp recordings on acute spinal cord slices.
Calcium imaging using epifluorescence approaches and/or multiphotonic imaging

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