Article Figures & Data
Figures
- Figure 1.
A–E, Spike propagation delay in simulation (A, B) and in the LG network (C–E). A, Current pulses of 20 nA/100 μs were injected (S) to initiate a paired spike that was recorded at various propagation distances (Ep). B, Paired current injection (S) into a presynaptic neuron connected to a postsynaptic neuron with gap junctions of either 50 or 25 nS in conductance. The SIs of paired spikes in presynaptic and postsynaptic axons (SIpre and SIpost) were measured. C, The LG neurons on the left side of ganglia (from LLG1 to LLG6) couple with septal junctions. Six pairs of LG neurons (from LLG1, RLG1 to LLG6, RLG6) are each connected with commissural junctions. Two biphasic pulses (0.8–3 V, 0.1 ms of duration) on an LG axon (S1 or S2) initiated the paired spikes. Recordings were made by microelectrodes (R1, R2, R3, Rpre, and Rpost) located near each side of septum. Ligations were made on the connectives of LG neurons in the fifth ganglia (RLG5, LLG5) and the sixth ganglia (RLG6, LLG6) for the measurements of commissural transmission. D, Paired spikes recorded in precommissural and postcommissural axons (Rpre and Rpost) for SI measurements. E, The ratio of SIpost/SIpre is plotted against SIpre to illustrate the change in SIs after commissural transmissions.
- Figure 2.
Spike reverberates in a junction-coupled network. A, Evoked paired spikes (middle axon) transmitted through high- (g = 5 μS) but not low- (g = 1.05 μS) conductance gap junctions. B, The second spike of evoked paired spikes transmitted through a synapse 5 mm away from initiation site, but not through the synapse at the spike initiation site. C, Asymmetric paired spike transmission and spike collision led to spike reverberation in a three-cell loop (N1, N2, and N3). D, Transmission failure of paired spikes (indicated by dashed circle) initiated spike oscillation. Directions of spike propagation are indicated by arrows. E, Recordings of oscillatory LG spikes in the second, third, and fourth abdominal ganglia induced by paired-pulse stimuli. LLG4 represents the LG neuron on the left side of the fourth ganglion. F, The SIs of paired-spike-induced oscillations plotted against the estimated time for an isolated spike to propagate through a network consisting of 2, 4, 6, 8, 10, 12, and 14 neurons.
- Figure 3.
Initiation of paired-spike-induced oscillations in the LG network. A, Illustration of the initially evoked paired spikes (indicated by dashed polygon), the direction of spike reverberation (indicated by arrows), and the sequence of propagation (marked by numbers) during the early phase of oscillation. Failure of spike transmission is indicated by the dashed circle. B, Summary of the propagation delay and failure of spike transmission of paired spikes of short SI. Propagation delay of the second spike led to spike transmission from LLG3 to RLG3 (indicated by dashed arrow). C, The spike reverberated in the oscillator center formed by LLG3, RLG3, RLG4, and LLG4 (indicated by dashed arrows). Multiple spikes generated by the oscillator center were transmitted via septal junctions to the LG neurons outside this center (indicated by solid arrows).
- Figure 4.
Termination of paired-spike-induced oscillations in the LG network. A, Spike failed to transmit (dashed circle) through the junction during the late phase of oscillation. B, An inserted extra spike (indicated by dashed rectangle) causing the failure of spike transmission (dashed circle) terminated oscillation. Bottom panels summarize the directions of spike propagation in the oscillator centers (indicated by gray dashed arrows) before the termination of oscillations. The propagations of the inserted spike are indicated by a solid black arrow.
- Figure 5.
Irregular multiple spikes by the blockade of GABAergic inhibition. A, Multiple spikes in RLG6 and LLG6 were produced by the repetitive excitatory inputs from the interneurons in the sixth ganglion that are excited by the initial single shock on LLG4 in the presence of picrotoxin (100 μm). B, The directions of spike propagation are indicated by arrows, and propagation sequences are marked by numbers. C, In Ca2+-free crayfish saline containing picrotoxin (100 μm), only a single spike without multiple spikes was evoked. D, Typical paired-spike-induced spike reverberation is obtained in Ca2+-free crayfish saline without picrotoxin.
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