Left: Column: 100 μm i.d. X 5.1 cm, 1.7 μm BEH C18 bonded. Temperature: 70 °C. Flow rate: 4 μL/min. Mobile phase: pH 4.0 aqueous buffer containing 100 mM sodium acetate, 0.15 mM disodium EDTA, and 10.0 mM SOS, mixed with 4% (v/v) acetonitrile, electrochemical detection. 1. aCSF, 2. 500 pM 5-HT, 3. Representative baseline microdialysate collected from the hippocampus in a serotonin transporter deficient mouse (SERT−/−) at 3 μL/min, 4. Baseline microdialysate at 1 μL/min. Right: Column: 100 μm i.d. × 5.5 cm length, Flow rate: 3.7 μL/min, remainder of conditions same as above. Top trace, 200 pM 5-HT standard in aCSF; middle trace, representative hippocampal microdialysate sample from a wildtype SERT+/+ mouse; bottom trace, aCSF.