Figure 4.

H₃ receptor ligand-mediated modulation of D₂ receptor agonist binding in sheep striatal membranes. (A and C) Competition experiments of the D₂ receptor antagonist [³H] YM-09151-2 (1.4 nM) versus increasing concentrations of the D₂ receptor agonist quinpirole. In A, experiments were performed in the absence (■) or in the presence of the H₃ receptor agonists RAMH (●), immepip (○) or imetit (▼) (20 nM in all cases). In C, experiments were performed in the presence of 20 nM RAMH (●) or 20 nM RAMH plus 1 μM thioperamide (△). Data are means ± S.D. from representative experiments performed in triplicate. . (B) Displacement of 1.4 nM [³H] YM-09151-2 binding by 0.1 μM (black bars) or 1 μM (white bars) of the H3 receptor agonists RAMH, immepip or imetit or the H3 receptor antagonist thioperamide. Values are expressed as specific binding percentage respect to the specific binding in absence of H₃ receptor ligands. Data are means ± S.E.M. Significant differences were calculated by Student’s t test for unpaired samples (**: p<0.01).