Fig. 3.

Ca²⁺ imaging of a serotonin biosensor cell closely apposed to an isolated Presynaptic Cell (such as in Fig. 2). The Presynaptic Cell (Pre) and the biosensor cell (5HT-Bio) were both loaded with the Ca²⁺-sensitive dye, Fura 2. Depolarizing the Presynaptic Cell with 50 mM KCl (bar below traces) generated a robust signal in the Presynaptic Cell due to Ca²⁺ influx. This was followed after a brief latency by a 5-HT biosensor cell response, indicating depolarization-evoked release of 5-HT from the Presynaptic Cell. KCl had no direct effect on the biosensor cell. Signals were only observed when the biosensor cell was pressed against the Presynaptic Cell. Modified from [29].