Effect of stimulation protocol, electrode position and stimulus intensity on the PPR values. A, left, schematic representation of the location of the two DMX neurons in which the EPSCs were evoked by stimulation at 1-mA intensity, which was delivered by the stimulating electrode placed on the TS. This electrode was never moved and the stimulation intensity was never changed during the recording of either DMX neuron. Right, IR-DIC images showing that two DMX neurons were located close to each other and the stimulation electrode on the TS was not moved. B, EPSC waveforms recorded from a type I (left) and type II (right) DMX neuron. Overlaid consecutive responses and the average trace (n = 8) in response to paired stimuli (arrowheads) at an interstimulus interval of 100 ms. Values on the bottom indicate the PPR. These results indicate that the distinct types of short-term plasticity in the DMX neurons do not depend on the intensity and site of stimulation. C, superimposed EPSC traces recorded from a type I DMX neuron (top), a type II DMX neuron (middle) and a dm-cNTS neuron (NTS; bottom) evoked by distinct stimulation intensities. EPSC1 and EPSC2 amplitudes gradually increased and reached the maximal amplitude. D, relationship between stimulus intensity and PPR (a) and normalized EPSC1 amplitude (b) that was measured in type I DMX (n = 4), type II DMX (n = 5) and dm-cNTS neurons (n = 4). Note that, despite marked increases in EPSC1 amplitude upon increasing stimulation intensity, the classification of neurons according to the PPR value was essentially unaffected, especially beyond the stimulus intensity that yielded 50%-EPSC1 amplitudes (50%-stimulus intensity).