Tonic inhibition in spinal ventral horn interneurons mediated by α5 subunit-containing GABAA receptors

GABAA receptors mediate synaptic and tonic inhibition in many neurons of the central nervous system. These receptors can be constructed from a range of different subunits deriving from seven identified families. Among these subunits, α5 has been shown to mediate GABAergic tonic inhibitory currents in neurons from supraspinal nuclei. Likewise, immunohistochemical and in situ hybridization studies have shown the presence of the α5 subunit in spinal cord neurons, though almost nothing is known about its function. In the present report, using slices of the adult turtle spinal cord as a model system we have recorded a tonic inhibitory current in ventral horn interneurons (VHIs) and determined the functional contribution of the α5 subunit-containing GABAA receptors to this current. Patch clamp studies show that the GABAergic tonic inhibitory current in VHIs is not affected by the application of antagonists of the α4/6 subunit-containing GABAA receptors, but is sensitive to L-655708, an antagonist of the GABAA receptors containing α5 subunits. Last, by using RT-PCR and immunohistochemistry we confirmed the expression of the α5 subunit in the turtle spinal cord. Together, these results suggest that GABAA receptors containing the α5 subunit mediate the tonic inhibitory currents observed in VHIs.

► We recorded a GABAergic tonic inhibitory current in turtle spinal cord interneurons. ► Turtle spinal cord interneurons express the α5 subunit of GABAA receptors. ► Tonic inhibition in interneurons is sensitive to antagonists of α5 subunit-containing receptors. ► α5 Subunit-containing GABAA receptors mediate tonic inhibition in spinal cord interneurons.