Using ephaptic coupling to estimate the synaptic cleft resistivity of the calyx of Held synapse
Fig 3
Relation between the calyceal AP and the prespike.
(A) An example of a train of presynaptic APs (vpre) elicited by afferent stimulation and the postsynaptic voltage-clamp recording (ipost). A large EPSC is elicited by the first AP, which rapidly depresses during the train. Stimulation artefacts were blanked. The first AP (blue dot) and the last AP (green dot) are shown on an expanded scale in B. Horizontal scale bar: 50 ms. Vertical scale bar: 90 mV, 1.5 nA. (B) The left and right column show the first and last AP of the train, respectively. From top to bottom: the AP recorded in CC from the calyx of Held, its inverted first (-AP’) and second derivative (-AP”), and postsynaptic voltage clamp recording showing the accompanying prespike (ipost). Vertical scale bars (from top to bottom panels): 40 mV, 0.3 kV/s, 2.5 MV/s2, 0.2 nA. Horizontal: 0.5 ms. (C) Relation between the delay between the first negative and positive peak of the prespike and the first two peaks in the first (blue, circle) and second (black, triangle) derivative of the presynaptic AP of the first AP-prespike pair in the train. Dashed line is the identity line. (D) Relation between the amplitude of the first negative and positive peak of the prespike and the first two peaks in the first (blue, circle) and second (black, triangle) derivative of the presynaptic AP of all AP-prespike pairs from an example train. The red lines indicate the linear regression lines. Note how the regression line crosses closer to the origin for the second derivative than for the first derivative. (E) Comparison for each train of Pearson’s r for the regression lines. (F) Comparison of the absolute deviation at 0 V/s (AP’) versus 0 V/s2 (AP”). (G) Cumulative distribution of the regression slope. Paired T-tests: ** p<0.01, *** p<0.001.