Spikelets of the Complex Spike Fail to Propagate
Figure 9. A. Voltage-sensitive dye fluorescence image of the axonal section containing a primary and a secondary branch in recording position. The spatial relationship with the soma is shown schematically in the lower left panel. B. Electrical (soma; black) and optical recordings of the complex spike signals from locations on the main axon before (black) and after (red) the branch point as well as the membrane potential in the primary (green) and secondary (orange) axon collaterals indicated in the schematic. Top trace (black); timing of electrical stimulation of the climbing fiber. In this experiment, the first spike reliably propagates throughout the main axon and axon collaterals. The first spikelet failed to propagate into the primary collateral, and subsequent spikelets propagated with intermediate probability. C. Summary data showing propagation probability for the initial spike (1), 1st spikelet (2), and 2nd spikelet (3) comprising complex spikes evoked with climbing fiber stimulation (n=6 cells). Propagation probability for each component of the complex spike was identical for the main axon after the axon collateral branch point and for axon collaterals.