Figure 2.

VSI and C2 made synaptic connections in both pedal ganglia. A, A drawing made from confocal images of VSI (red) labeled by Neurobiotin tracer (Vector Laboratories). Locations of C2 (green) and the follower neurons (FNs) (orange and blue) in the pedal ganglia are also shown. The VSI axon projects ipsilaterally through the posterior portion of the cerebral–pedal connective and then continues through the pedal–pedal connective (PdN6). The axon of C2 projects contralaterally toward the pedal ganglion as previously published (Getting et al., 1980). Bi, The VSI action potentials were recorded in PdN6 and evoked one-for-one EPSPs in FNs in the right and left pedal ganglia. Simultaneous intracellular recordings from right VSI, right VFN, and left VFN and extracellular recording from PdN6 are shown. Each sweep was triggered by a VSI action potential; three sweeps were superimposed. Bii, C2 spikes were recorded in PdN6 and C2 evoked summated EPSPs in FNs of both pedal ganglia. Overlaid traces were triggered by the first stimulus current pulse (7 nA, 20 ms) injected into C2 to evoke a train of action potentials (10 Hz). The EPSPs facilitated greatly and had a slow time course, making it difficult to distinguish individual EPSPs. Ci, C2 caused delayed excitation of VSI. Simultaneous intracellular recordings from left C2 and right VSI and extracellular en passant recording from PdN6 are shown. C2 was stimulated by injecting repetitive square current pulses (7 nA, 20 ms) at 10 Hz for 4 s, which induced a burst of action potentials in VSI. Cii, The C2-evoked action potentials in VSI were antidromic. Overlaid traces of VSI action potentials and corresponding PdN6 impulses evoked by C2 are shown. The traces were triggered by the peak of VSI action potentials. The nerve impulse preceded the somatic action potential in each trace, suggesting that these action potentials propagated antidromically from the distal pedal ganglion.