Figure 5.

The SP-induced slow depolarization brings a subset of non-pacemaker neurons to an NMDA-dependent bursting level. A, Blocking just non-NMDARs with 20 μm CNQX is enough to block population respiratory rhythm (top trace). Whereas most of non-pacemaker neurons lose their bursting activity, some respiratory neurons exhibit subthreshold oscillations (bottom trace) that are able to produce CPP-sensitive bursts of action potentials during the SP-induced slow depolarization. B, Same non-pacemaker neuron as A in an expanded time scale showing subthreshold oscillations before (left) and bursts of action potentials (second panel from left) during the SP-induced slow depolarization. Negative DC current (arrow) was applied to bring the membrane potential to the original level (third panel from left). Note that subthreshold oscillations have the same amplitude. After application of 10 μm CPP to block NMDARs, both burst activity and subthreshold oscillations are blocked, whereas depolarization persists (right). C, Application of SP in the presence of 10 μm CPP produces excitation of the respiratory network (top trace) accompanied with depolarization of a respiratory neuron (bottom trace). D, Quantification of the membrane depolarization produced for SP alone and in the presence of 10 μm CPP. Note that there is no difference between the depolarization induced by SP under both conditions.