G Protein-Gated Inwardly Rectifying Potassium Channel Subunit 3 Is Upregulated in Rat DRGs and Spinal Cord After Peripheral Nerve Injury

Abstract

Background: G protein-gated inwardly rectifying potassium (GIRK) channels are involved in the regulation of neuronal excitability. Four GIRK subunits (GIRK1-4) are expressed in rat dorsal root ganglia (DRGs). Recently, we have characterized the expression of GIRK1 and − 2, and both are downregulated in rat DRGs and spinal cord after a complete sciatic nerve transection (axotomy). Here, we aimed to study the neurochemical characteristics of GIRK3, and its regulation in rat DRGs and spinal cord induced by nerve injury. Methods: A sciatic nerve axotomy was performed to study the influences of injury on GIRK3 expression in DRGs and spinal cord. A dorsal root rhizotomy and a sciatic nerve crush were employed to study the axonal transport of GIRK3 protein, respectively. Immunohistochemistry analysis was employed for investigating the neurochemical characteristics of GIRK3. Results: In control DRGs, ∼ 18% of neuron profiles (NPs) were GIRK3-positive (+), and ∼ 41%, ∼ 48% and ∼ 45% of GIRK3+ NPs were CGRP+, IB4+ and NF200+, respectively. GIRK3-like immunoreactivity was observed in glabrous skin of hind paws and axons originating from DRG neurons. Fourteen days after axotomy, more than one-third of DRG NPs were GIRK3+, and among these ∼ 51% and ∼ 56% coexpressed galanin and neuropeptide Y, respectively. In control animals, a small group of interneurons found in the dorsal horn was GIRK3+. In addition, GIRK3+ processes could be observed in superficial laminae of spinal dorsal horn. After nerve injury, the intensity of GIRK3-like immunoreactivity in the superficial layers was increased. Evidence based on rhizotomy and sciatic nerve crush indicated both anterograde and retrograde transport of GIRK3. Conclusion: Our study demonstrates that GIRK3 is expressed in sensory neurons and spinal cord. GIRK3 has both anterograde and retrograde axonal transport. GIRK3 expression can be regulated by peripheral nerve injury.