Analysis of paired-pulse ratio of the excitatory transmission from the TS to DVC neurons. A, above, IR-DIC photomicrographs indicating the location of the patch recording pipette (p) and the stimulation electrode in the DVC. Left, recording from a dm-cNTS (NTS) neuron; right, recording from a DMX neuron (designated as "cell 1"). Bottom, confocal microscopic images of a dm-cNTS neuron that is visualized with injected Alexa Fluor 488 (left) and two DMX neurons (cell 1, visualized with Alexa Fluor 488 and shown in green; cell 2, with Alexa Fluor 568 and shown in red). B, sample traces of the EPSC waveform evoked by TS stimulation. Gray traces show the eight overlaid traces of consecutive responses and the red traces show their average. Left, responses of the dm-cNTS neuron shown in (A); right, responses of adjacent DMX neurons shown in A (cell 1 and cell 2). The values on the bottom show the PPR calculated for these three neurons. C, a histogram showing the distribution of PPR of the DMX and dm-cNTS neurons. Bars in light red show the PPR for dm-cNTS neurons (n = 35) and those in light blue show the PPR for DMX neurons (n = 120). Note a trough of the histogram around PPR = 0.6, which is the threshold used to classify the DMX neurons into type I (PPR > 0.6) and type II (PPR < 0.6). All dm-cNTS neurons showed PPR < 0.6. Curves in red, blue and green show the best-fit Gaussian distributions representing the histogram peaks for dm-cNTS, type II DMX and type I DMX neurons, respectively. D, schematic drawings of the distribution and localization of the soma of recorded neurons (33 dm-cNTS, red triangles; 56 type I DMX, green circles; 52 type II DMX, blue circles) and the tip of stimulus electrodes (black crosses, for DMX neuron responses; red crosses, for dm-cNTS neuron responses), plotted on three representative coronal slices (from top to bottom, rostral to caudal).