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Figure 4: Embryonic respiratory pacemaker neurons are sensitive to SP. (a) Schematic of an embryonic transverse slice showing location of a preBötC network pacemaker neuron monitored with calcium imaging. (b) Traces of calcium transients recorded in the cell in control conditions (top), after synaptic isolation from the other network elements (middle, cocktail) and in the presence of 0.5 μM SP (bottom). After isolation, the frequency of the cell’s ongoing rhythmic activity was significantly increased in the presence of SP. (c) Pooled data showing mean frequency (± SEM) of activity expressed by 16 pacemaker neurons in cocktail (white bar) and under the presence of SP (black bar). Asterisk: .