Remote nerve injection of mu opioid receptor adeno-associated viral vector increases antinociception of intrathecal morphine.
We have shown previously that using recombinant adeno-associated viral vector (rAAV) to up-regulate mu opioid receptors (muORs) in dorsal root ganglia (DRGs) increases the potency of subcutaneous morphine. Here we report an improved method of introducing rAAV-muOR viral vectors into DRGs. Instead of injecting the rAAV-muOR gene directly into DRGs as shown before, the vector was introduced into the sciatic nerve of rats. Changes in muOR expression and antinociceptive effects of intrathecal morphine in rAAV-muOR rats were examined. Immunocytochemical studies showed that the transduced muORs were expressed in all types (ie, small, medium, and large) of DRG neurons. The expression of muORs in DRG neurons, quantified by Western blotting, was increased by 1.7-fold 4 weeks after the sciatic nerve injection. The up-regulation persisted for more than 6 months. The effects of intrathecal morphine on paw withdrawal latencies to heat were studied in rats inflamed with complete Freund's adjuvant. Compared with rats injected with rAAV containing the enhanced green fluorescent protein gene (rAAV-EGFP), the antinociceptive potency of intrathecal morphine in rAAV-muOR rats was significantly increased, and the effective dose (ED50) for morphine was 5.4-fold lower (rAAV-muOR: ED50 = 0.84 microg, confidence interval, 0.70-0.99 microg; rAAV-EGFP: ED50 = 4.50 microg, confidence interval, 3.55-5.86 microg). With minimum tissue damage and a large persistent increase in the opioid potency, remote nerve injection of rAAV-muOR to up-regulate muORs could be a useful therapeutic strategy for the treatment of chronic pain.


CONCLUSIONS
Injection of adeno-associated viral vector containing the muOR gene into the sciatic nerve produces a significant up-regulation of muORs in DRGs for up to 6 months without producing any immune responses in the injected animals. This results in a 5.4-fold increase in the potency of intrathecal morphine.
Gu
Yanping
Y
Department of Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, Texas 77555, USA.
Xu
Ya
Y
Li
Guang-Wen
GW
Huang
Li-Yen Mae
LY
D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance / Q000235:genetics; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015316:Genetic Therapy / Q000379:methods / Q000639:trends; D005822:Genetic Vectors / Q000502:physiology*; D007278:Injections, Spinal; D008297:Male; D008845:Microinjections / Q000379:methods; D009020:Morphine / Q000494:pharmacology*; D009475:Neurons, Afferent / Q000187:drug effects / Q000378:metabolism*; D009619:Nociceptors / Q000187:drug effects / Q000378:metabolism; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D017450:Receptors, Opioid, mu / Q000096:biosynthesis / Q000235:genetics*; D012584:Sciatic Nerve / Q000166:cytology / Q000378:metabolism* / Q000601:surgery; D014161:Transduction, Genetic / Q000379:methods; D014162:Transfection / Q000379:methods*; D015854:Up-Regulation / Q000235:genetics
D000701:Analgesics, Opioid; D017450:Receptors, Opioid, mu; D009020:Morphine