Figure 5.

Ability of opioid agonists to stimulate G protein activity in whole brain homogenates from Gα_o transgenic mice. Agonist-stimulated [³⁵S]GTPγS (0.1 nM) binding was measured in the presence of various concentrations of the opioid agonists (a) DAMGO or (b) morphine, (c) in the presence of 10 μM DAMGO plus increasing concentrations of unlabeled GTPγS, and (d) in the presence of 10 μM DAMGO, methadone, morphine, or nalbuphine in membrane homogenates from whole brain of wild-type, Gα_o +/− and Gα_o −/− mice. Nonspecific binding was evaluated in the presence of unlabeled GTPγS (10 μM). Data are plotted as agonist-stimulated [³⁵S]GTPγS binding, defined as the increase in [³⁵S]GTPγS incorporation in the presence of agonist over that of basal (measured in the absence of agonist), and represent the mean±SEM (n=2–3 performed in at least duplicate). Legend in (a) also applies to panels (b) and (c). Symbols indicate a statistical difference vs wild type (^*p<0.05, ^**p<0.01, ^***p<0.001) or Gα_o +/− (⁺p<0.05, ⁺⁺p<0.01, ⁺⁺⁺p<0.001) by Bonferroni's post-test.