Fig. 2. Response of the same neuron as in  figure 1 to increasing doses of  N -methyl-d-aspartate (NMDA) at 0 and 1 minimum alveolar concentration (MAC) sevoflurane (  A ). The  horizontal bars indicate the picoejection duration. Maximal dose rates are given. (  Bottom insets ) Time-expanded views of the neuronal rate-meter recording (100 ms/bin) for 1 MAC sevoflurane before picoejection (  B ) and during picoejection of NMDA (  C ,  arrows ). The simultaneously recorded time-averaged phrenic neurogram (PNG, in arbitrary units [a.u.],  top ) identifies the neuron as inspiratory. The neuronal raw activity (N.A.,  middle trace ) is originally recorded as a train of action potential spikes. A time–amplitude window is used to discriminate the larger amplitude inspiratory activity from the lower amplitude expiratory phase activity for the rate-meter recordings (  bottom trace ) and cycle-triggered histogram analysis (not shown).