HCN4 subunit expression in fast-spiking interneurons of the rat spinal cord and hippocampus

► HCN4 channel expression in selected fast-spiking spinal interneuron populations. ► HCN4 channels expressed in most fast-spiking hippocampal interneurons. ► HCN4 channels rarely expressed in regular- or gap-firing interneurons. ► HCN channelopathies now implicated in neurodegenerative diseases and chronic pain.