The long-term goal of this research is to develop gene therapy for chronic pain. Opiates have remained to be the drugs of choice for treating patients with severe pain. The side effects of opiates, including respiratory depression, tolerance and dependence, have often limited their use. The focus of this grant is to design viral vectors that allow for efficient and stable delivery of wild type or mutant mu opioid receptor (muOR) genes to sensory neurons. We hypothesize that appropriate muOR gene delivery and expression in dorsal root ganglion (DRG) neurons will lower the doses of mu-opioids required for analgesia and reduce tolerance, thus decreasing the side effects of opioids. To test this hypothesis, we will (1) deliver the wild type or mutant mu OR gene into sensory neurons using an adeno- associated virus (AAV) vector, (2) evaluate the effects of mu- opioids on pain behaviors in inflamed rats injected with recombinant AAV-mediated muOR transgene (rAAV-muOR), (3) evaluate the effects of mu-opioid in tolerant rats that receive injections of rAAV-muOR and (4) evaluate the effects of mu-opioids on membrane conductance and receptor trafficking in rAAV-muOR- transduced DRG neurons isolated from non tolerant and tolerant rats. The experiments will be performed on rats treated with complete Freund's adjuvant (CFA) and on DRG neurons isolated from those rats. Pain behaviors will be monitored by paw withdrawal latencies, membrane currents will be measured with perforated patch electrodes and receptor trafficking will be examined with immunofluorescence staining and receptor binding assays. These experiments will establish the feasibility of a genetic approach to pain treatment. If successful, the study will provide clinicians with a new tool to treat patients with severe pain and provide researchers a model for studying the role of opioid receptor regulation in the development of opioid tolerance.
