文摘
The G-protein activations induced by κ-opioid receptor agonists, (−)U50,488H, U69,593 and TRK-820 in the mouse lower midbrain, striatum and limbic forebrain were determined by monitoring guanosine-5′-o-(3-[35S]thio)triphosphate ([35S]GTPγS) binding. All κ-opioid receptor agonists produced approximately 40, 20 and 10 % increases of [35S]GTPγS binding over baseline in the lower midbrain, striatum and limbic forebrain, respectively. The increases of [35S]GTPγS binding induced by κ-opioid receptor agonists were completely reversed by the selective κ-opioid receptor antagonist, norbinaltorphimine (norBNI), in all brain regions. The intrinsic activities of κ-opioid receptor agonists for G-protein activation in brain regions observed in the present study are not correlated with densities of κ-opioid receptor binding sites from previous reports. The present results suggest that the catalytic efficiency of κ-opioid receptor-G-protein coupling may be variable in different brain regions.
