Antagonist radiotracers have shown only a low sensitivity for detecting competition from high-efficacy agonists at opioid receptors (ORs) in vivo. We report that [(11)C]PEO binds with high affinity to mu and kappa-opioid receptors, is a full agonist, and concentrates in brain regions of rats with a high density of the mu-OR after intravenous injection. Blocking studies with mu and kappa-OR selective compounds demonstrated that the binding of [(11)C]PEO is saturable and selective to the mu-OR in rat brain.
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Antagonist radiotracers have shown only a low sensitivity for detecting competition from high-efficacy agonists at opioid receptors (ORs) in vivo. We report that [(11)C]PEO binds with high affinity to mu and kappa-opioid receptors, is a full agonist, and concentrates in brain regions of rats with a high density of the mu-OR after intravenous injection. Blocking studies with mu and kappa-OR selective compounds demonstrated that the binding of [(11)C]PEO is saturable and selective to the mu-OR in...
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