Firing properties of Renshaw cells defined by Chrna2 are modulated by hyperpolarizing and small conductance ion currents I_h and I_SK

Abstract

Renshaw cells in the spinal cord ventral horn regulate motoneuron output through recurrent inhibition. Renshaw cells can be identified in vitro using anatomical and cellular criteria; however, their functional role in locomotion remains poorly defined because of the difficulty of functionally isolating Renshaw cells from surrounding motor circuits. Here we aimed to investigate whether the cholinergic nicotinic receptor alpha2 (Chrna2) can be used to identify Renshaw cells (RCs(α2)) in the mouse spinal cord. Immunohistochemistry and electrophysiological characterization of passive and active RCs(α2) properties confirmed that neurons genetically marked by the Chrna2-Cre mouse line together with a fluorescent reporter mouse line are Renshaw cells. Whole-cell patch-clamp recordings revealed that RCs(α2) constitute an electrophysiologically stereotyped population with a resting membrane potential of -50.5 ± 0.4 mV and an input resistance of 233.1 ± 11 MΩ. We identified a ZD7288-sensitive hyperpolarization-activated cation current (Ih) in all RCs(α2), contributing to membrane repolarization but not to the resting membrane potential in neonatal mice. Additionally, we found RCs(α2) to express small calcium-activated potassium currents (I(SK)) that, when blocked by apamin, resulted in a complete attenuation of the afterhyperpolarisation potential, increasing cellular firing frequency. We conclude that RCs(α2) can be genetically targeted through their selective Chrna2 expression and that they display currents known to modulate rebound excitation and firing frequency. The genetic identification of Renshaw cells and their electrophysiological profile is required for genetic and pharmacological manipulation as well as computational simulations with the aim to understand their functional role.

Decoding the organization of spinal circuits that control locomotion

“…However, spinal neurons come in many types, and new molecular markers 149,150 for the different populations of inhibitory and excitatory neurons are needed to probe the functional groups of pattern- and rhythm-generating neurons. This need may be met by performing RNA sequencing with high sensitivity for individual cells or for a population of cells 151 in the spinal cord together with the use of intersectional strategies that spatially narrow the cell populations that are targeted 152 .…”

Effects of chronic spinal cord injury on relationships among ion channel and receptor mRNAs in mouse lumbar spinal cord

“…Finally, one of the most striking expression changes we detected was the almost complete loss of CHRNA2 expression, known to encode the nicotinic receptor alpha-2 subunit, in MNslices. CHRNA2 is selectively expressed in Renshaw cells of the ventral spinal cord (Perry et al, 2015), where they receive cholinergic input from alpha motor neurons as part of the recurrent inhibitory feedback circuit of motor neuron excitability (Moore et al, 2015). Loss of this connection between alpha motor neurons and Renshaw cells, which ultimately feed back to inhibit motor neurons, could be a novel mechanism involved in spasticity following SCI as well as other motor neuron diseases such as ALS (Wootz et al, 2013).…”

Characterization of Dmrt3-Derived Neurons Suggest a Role within Locomotor Circuits

“…Electrophysiology. Whole-cell patch-clamp electrophysiology recordings from transverse, lumbar spinal cord slices of Dmrt3 Cre ;tdT neonates (thickness: 300 m) were done as previously described (Lamotte d'Incamps and Ascher, 2008;Perry et al, 2015). One or at the most two cells were used per slice.…”