Figure 1. Presynaptic signals under control conditions.

Sample traces of presynaptic compound action potentials (cAPs), fibre volleys (FVs) and Ca²⁺ transients ([Ca²⁺]_pre,t) in response to a train of four stimuli at an interpulse interval of 30 ms under control conditions. A, cAPs measured with the VSD RH 414. In addition to the rapid change of membrane potential that corresponds to the presynaptic action potential, the VSD signal also contains a slow component. B, corresponding presynaptic FVs measured by extracellular field recording. C, [Ca²⁺]_pre,t, measured separately with the Ca²⁺ indicator furaptra. D, summary data for cAP, FV (n = 12) and [Ca²⁺]_pre,t (n = 18). The responses to each stimulus within the train were normalized to the mean of the last three. There was no significant difference in the amplitudes of FV and [Ca²⁺]_pre,t between stimuli. Amplitude and half-width of the uncorrected cAP in response to the first stimulus were larger than to the rest of the stimuli. This was most probably due to the artifact of the slow component.