Laser photolysis of caged Ca²⁺ in axonal varicosities between two connected MLIs evokes simultaneous pre- and postsynaptic currents. (A; left) Fluorescence picture taken with a CCD camera. (Right) Reconstruction of a pair of synaptically connected MLIs. The presynaptic cell is shown in green, and the postsynaptic cell is in magenta. The stimulated site is indicated with the arrowhead in the reconstruction. (B) Simultaneous pre- (top, green) and postsynaptic (bottom, magenta) currents recorded when photolyzing DM-nitrophen with a 100-µs laser pulse. The recordings correspond to individual traces. (C) Latency (left), τ_rise (middle), and amplitude (right) of pre- (green symbols) and post- (magenta symbols) synaptic currents recorded simultaneously in four different pairs. Open circles correspond to individual experiments, and closed circles correspond to the averages ± SD. Average ± SD values are: pre- and postsynaptic latencies: 1.6 ± 0.4 and 1.6 ± 0.2 ms, respectively; pre- and postsynaptic τ_rise: 2.8 ± 1.7 and 0.8 ± 0.2 ms, respectively (n = 3 for the presynaptic measurements caused by the difficulties in measuring the τ_rise in one of the recordings); and pre- and postsynaptic amplitudes: 24 ± 7.7 and 118.5 ± 111 pA, respectively.