Fig. 2.

Stimulation of [³⁵S]GTPγS binding to membranes from the limbic forebrain (A) and lower midbrain (B) by the μ-opioid receptor agonist morphine in wild-type (WT) and dopamine D₃ receptor knock-out (D3KO) mice. Membranes were incubated with [³⁵S]GTPγS (50 pm) and GDP (30 μm) with morphine in the presence or absence of the selective μ-opioid receptor antagonist CTOP. The data are shown as the percentage of the basal [³⁵S]GTPγS (50 pm) binding measured in the presence of GDP (30 μm) and the absence of morphine. Eachcolumn represents the mean with SEM of three samples.