Differential Effects of Oxycodone, Hydrocodone, and Morphine on Activation Levels of Signaling Molecules
Abstract
Opioids alter the responses of D2-like dopamine receptors (D2DRs), known to be involved in the pathology of addiction and other mental illnesses. Importantly, our recent results demonstrated that various opioids differentially modulate the behavioral responses of D2DRs. To examine the effect of various opioids on striatal activation levels of Akt and ERK1/2, as well as the signaling responses of D2DRs following opioid exposure. Mice were pre-treated with 20 mg/kg morphine, hydrocodone, oxycodone, or saline for 6 days. Twenty-four hours later, mice were injected with vehicle or a D2/D3 receptor agonist, quinpirole. Thirty minutes later, dorsal striatum was collected and analyzed using Western blot. In morphine-pretreated animals, baseline Akt activation level was unchanged, but was reduced in response to quinpirole. In contrast, baseline Akt activation levels were reduced in mice pretreated with hydrocodone and oxycodone, but were unchanged in response to quinpirole. In mice pretreated with all opioids, baseline ERK2 activation levels were unchanged and increased in response to quinpirole. However, quinpirole-induced ERK2 activation was significantly higher than drug naïve animals only in the morphine-pretreated mice. Various op...Continue Reading
References
Activation of microtubule-associated protein kinase (Erk) and p70 S6 kinase by D2 dopamine receptors
IRS2-Akt pathway in midbrain dopamine neurons regulates behavioral and cellular responses to opiates
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