Morphine Induces Differential Activation and Cellular Localization of Protein Kinases in the Mouse Periaqueductal Gray

Abstract

Morphine is a commonly used potent opioid analgesic with very high propensity for tolerance development. The analgesic and tolerance properties of opioids are partially regulated by the midbrain ventrolateral periaqueductal gray (vlPAG). Here, we investigate the intracellular kinase activation and localization patterns in the mouse vlPAG following acute and chronic morphine treatment. Wild‐type mice were treated with morphine (10 mg/kg, i.p.) or saline in a chronic or acute administration paradigm. We performed fluorescence immunohistochemistry to map the localization and activation of extracellular signal‐regulated kinase 1/2 (ERK 1/2), protein kinase‐C (PKC), and protein kinase‐A (PKA). We observed significantly greater activated ERK 1/2 in the vlPAG chronic morphine‐treated animals. We also visualized the co‐localization of ERK 1/2 with the endosomal marker Eea1. We note that phosphorylated PKC tends to localize to the plasma membrane in the vlPAG following chronic morphine treatment and interacts with the μ‐opioid receptor. Further, we observed that although PKA activation is increased following chronic morphine treatment, there is a significant reduction in nuclear translocation of this kinase. Additionally, we examined the cell‐type specificity of kinase activation by co‐localizing these kinases to GAD67 and VGluT neurons that project from the PAG downstream to the Rostral Ventromedial Medulla. Taken together, this study demonstrates a differential activation and localization of ERK 1/2, PKC and PKA, and opens avenues to explore the role of chronic morphine treatment on G‐protein signaling and kinase nuclear transport.Support or Funding InformationThis research is supported by the Department of Biology at Utah State UniversityThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.