Improved Serotonin Measurement With Fast‐Scan Cyclic Voltammetry: Analysis of Electrode Fouling by Fluoxetine in Live Brain Tissue

Fast‐scan cyclic voltammetry at carbon‐fiber microelectrodes is a method of choice for measuring 5‐hydroxytryptamine (5‐HT, serotonin) in brain tissue. The classic Jackson–Nafion Waveform method (JNW) offers high sensitivity and selectivity over interferents like dopamine and fouling agents like 5‐hydroxyindoleacetic acid (5‐HIAA). Nevertheless, in vitro evidence suggests that JNW method is susceptible to fouling by radical oxidative serotonin products and selective serotonin reuptake inhibitors (SSRIs). This fouling was mitigated by using an extended serotonin waveform (ESW) on bare electrodes. To investigate these differences, further repeated, controlled spritzes of serotonin were conducted ex vivo in brain tissue from zebrafish and mice. The ESW resisted fouling better than the JNW after superfusion with 10 μM fluoxetine, with final normalized signals of 0.84 and 0.55, respectively. Furthermore, superfusion with 100 nM fluoxetine and physiologically relevant 5‐HIAA concentrations did not degrade electrode response when using either method. The electrochemical signal from serotonin release, evoked in the substantia nigra pars reticulata of mouse brain slices, was significantly greater after fluoxetine administration as measured with the ESW compared to the JNW. These results indicate that the ESW may be more suitable for ex vivo applications when used in combination with SSRIs.