Figure 6.

Interaction among alternative sources of repetitive firing. A, Left, Spontaneous activity of singlets and short bursts recorded from the soma of a DRG neuron ∼6 min after 4-AP application. This cell exhibited both oscillations and DAPs only after 4-AP superfusion. Some of the spikes were generated in the soma by oscillations and DAPs (unmarked spikes), whereas others (arrowheads) invaded the soma after generation elsewhere. Spikes are truncated. Right, Hyperpolarization abolished oscillations, DAPs, and resultant soma spikes, leaving only invading spikes. These were generated in a tonic pattern with multiplets. After additional hyperpolarization, the ISI within a multiplet was gradually decreased, and the number of impulses increased; however, intermultiplet interval was unaffected.B, Tonic spontaneous activity in the absence of oscillations and DAPs, indicating that the firing was generated outside the soma. A 100 ms (left) or 200 ms (right) suprathreshold depolarizing pulse applied via the recording micropipette (asterisks) generated a burst of soma spikes and then abolished firing for several seconds, too long to be accounted for by spike collision. The spike burst apparently silenced electrogenesis at the axonal pacemaker site.