Figure 5.

Effect of histamine H₃ receptor activation on the stimulatory action of the A_2A receptor agonist CGS-21680 on depolarization-evoked [³H]-GABA release from rat globus pallidus synaptosomes. The experimental protocol was as described in the legend to Figure 4. Where required, drugs under test were present for 5 min (CGS-21680 and immepip) or 10 min (clobenpropit) before and during the second depolarizing stimulus. (A) Effect of the H₃ receptor agonist immepip (100 nM) or the antagonist/inverse agonist clobenpropit (3 μM) alone on depolarization-evoked [³H]-GABA release. Values are means ± SEM from three experiments. NS, no statistically different from control release (no drugs added), ANOVA and Dunnett’s post hoc test. (B) Inhibition by immepip (100 nM) of the effect of the A_2A receptor agonist CGS-21680 (3 nM). Values are means ± SEM from three experiments. The statistical analysis was performed with ANOVA and Dunnett’s test. (C) Effect of different concentrations of immepip. To allow for the variability between experiments, values were expressed as percentage of control release. Values are means ± SEM from the combined data from five experiments with three to five determinations for each concentration of immepip. (D) Blockade by clobenpropit (3 μM) of the effect of immepip (100 nM). Values are means ± SEM from four experiments. The statistical analysis was performed with ANOVA and Tukey’s post hoc test.