↵Competition curves of the D₁R antagonist [³H]SCH 23390 (2 nm) binding versus increasing concentrations of the D₁R agonist SKF 38393 were performed in the absence or the presence of 2 nm of the H₃R agonist RAMH using striatal membranes from control rats treated or not with 30 μm cocaine for 30 min, rats acutely treated with cocaine, or cocaine self-administered rats. K_D1 and K_D2 are, respectively, the equilibrium dissociation constants of SKF 38393 binding to D₁R and were determined by fitting binding data to Equation 3. Parameters are mean ± SEM (n = 3). For each group, significant differences with respect to control were calculated by an unpaired Student's t test (*p < 0.05, **p < 0.01).