Fig. 5.

[¹²⁵I]IBNtxA competition studies. Rat brain homogenate was incubated with [¹²⁵I]IBNtxA (0.1 nM) with blockers at the indicated concentrations of the specified competitor. Nonspecific binding was determined using levallorphan (1 µM). Results are from three independent replications. Each data set was fit with both a one-site and two-site model using GraphPad Prism, and the models were compared using an extra-sum-of-squares F-test. The two-site model was preferred for each of the four drugs tested (P < 0.0001 for each).