Figure 2. Excitable properties of the preBötC network in slice preparations without spontaneous rhythm at 3 mm K⁺.

A, [K⁺]_o was lowered from 9 to 3 mm, which silenced the respiratory rhythm in 3 out of 17 slices and hyperpolarized the baseline voltage of −60 mV in this preBötC neuron (V_M, upper trace) by 8 mV. Bilateral XII output is shown in the middle and lower traces. B, in the same slice as A, single unilateral AMPA stimulation in the right preBötC depolarized the preBötC neuron (V_M, the voltage axis was truncated for display) but did not evoke XII output unless three or more pulses were applied (see Methods). Tonic XII discharge occurred in the side ipsilateral to the AMPA injection when 20–25 AMPA pulses were applied in rapid succession. C, the amplitude of the evoked XII output in arbitrary units (a.u.) plotted versus the number of successive AMPA pulses from B. XII area and half-width measurements yielded commensurate plots (not shown). D, the number of cycles of XII_evoked plotted versus number of AMPA pulses from B (left y-axis, open circles) and the frequency of XII_evoked (right y-axis, filled circles). E, the latency Δt_evoked in seconds of XII_evoked plotted versus number of AMPA pulses from B.