Fig. 4.

Tetrodotoxin (TTX) applied locally to selected interganglionic connectives blocked impulse conduction and uncoupled swimmeret activity on opposite sides of the block. A, Impulses triggered by stimulation of the connectives anterior to A1 were recorded by electrodes on the connective between A5 and A6 under control conditions (compare Fig. 1), but disappeared when a TTX well was placed on the connectives between A3 and A4. This block was washed away by replacing the TTX solution with saline. B, When the TTX block was in place, the predictable phase-lag of PS bursts in ganglia anterior to the block disappeared. Solid circles show phases of A3 bursts from one preparation in each interval of A5 activity under control conditions; open circles are phases of the same A3 recorded when the TTX block was in place. In these cumulative–frequency plots, phases of the PS bursts were sorted and then plotted in ascending order. The data of A andB are from the same preparation.