Microamperometric analysis of 5 HT release in raphe slice culture. A. Amperometric trace from an EGFP-expressing varicosity during an active episode. Spike-like events of varying sizes are visible. Note that the noise level looks exaggerated at this time scale due to low frequency baseline variability. B. Examples of amperometric spikes of various quantal sizes which were detected at 5 HTergic varicosities. C. Quantal size distribution of release events at 5 HTergic varicosities and cell bodies. At somata, several large release events, outside of the main population, were observed.