Figure 5. Functional comparison of axonal varicosities supplied by the same axon.

A-D: Example. Axonal fragment with two varicosities (denoted 1 and 2 in A; Alexa 594 fluorescence; increased brightness in the middle of varicosity 1 implies that its size in the Z direction exceeds the axon diameter 2-3-fold) showed Ca²⁺ transients in response to evoked action currents (B, average of 10 line scans). Application of L-AP4 reduced ΔF/F in varicosity 1 but not in varicosity 2 (C; quantitative results are shown in D with black traces, control; red trace, L-AP4).

E: Shuffled control (Monte Carlo) test for similarity between varicosities supplied by the same axon. Cumulative distributions are shown; the black line indicates the distribution of the absolute difference between two randomly selected varicosities (shuffled control, sample size = 500); the red line indicates the distribution of the absolute difference between two varicosities on the same axon (experimental sample sizes are indicated). The difference in the effect of L-AP4 on neighboring varicosities was distributed the same way as the difference between any two varicosities randomly drawn from the sample (left panel). In contrast, the effects of CgTx and AgTx among neighbors showed much greater similarity than among randomly selected pairs of varicosities (p < 0.001 and p < 0.01, respectively, Kolmogorov - Smirnov test), implying that the presynaptic axon largely determines whether N-type or P-type channels are expressed.