Targeted Delivery of Glycine Receptors to Peripheral Neurons as Treatment for Pain

Abstract

Neurotransmitter-gated receptors play a vital role in the regulation of nociception. In the adult CNS, the ionotropic glycine and GABA receptors are typically inhibitory and act to silence neurons by transiently permitting inward Cl− currents upon activation. However, depending on the Cl− equilibrium potential, these receptors may instead depolarize neurons. We hypothesized that targeted expression of the α1 subunit of glycine receptor (GlyR) in peripheral sensory neurons using a non-replicating herpes simplex virus (HSV)-based vector might reduce nociceptive behavior upon subsequent GlyR activation by exogenously-applied glycine. HSV-directed expression of the human α1 subunit of GlyR alone is sufficient to produce glycine-gated chloride currents in whole-cell patch clamp studies of infected mammalian cells. In cultured dorsal root ganglion neurons, expressed GlyRs are diffusely localized in the neuronal plasma membrane. In both a formalin footpad model of inflammatory pain or an osteosarcoma pain model, rats inoculated with the GlyR-expressing vector (vHGlyRα1) exhibited significantly reduced nociceptive behavior following subcutaneous injection of glycine into the footpad. This reduction in pain-related behavior was reversed following injection of the GlyR antagonist strychnine. Targeted expression of GlyRs and their modulation via mutagenesis and/or exogenous application of agonists, antagonists, and allosteric modulators offer a novel and potentially powerful method to alter neuronal activity. Here we show that selective activation of HSV-directed α1 GlyR expression in peripheral neurons eliminates pain-related behavior in two pain models, and has the potential to be used therapeutically for pain management.