Competition uptake analysis of forebrain-derived synaptosomes. (A) Serotonin, (B) paroxetine, (C) fluoxetine, (D) cocaine, (E) citalopram, and (F) escitalopram were assessed for their ability to compete with [3H]5-HT uptake. Fluoxetine, cocaine, citalopram, and escitalopram demonstrated significantly reduced potencies in SERT M172 relative to SERT I172 synaptosomes (n = 6–8 per drug; P < 0.05, one-tailed Student t test).