Fig. 5. Retrograde labeling of NTS nuclei from tracer injections dorsal to the facial nucleus.

FG and FB were injected immediately dorsal to the facial nucleus with the FG injection located at the caudal end of the nucleus and FB located ~ 400 μm more rostrally (case 8051). Respiratory activity (inspiratory units, see inset) was recorded at the FG injection site but not observed at the FB site. Sections in A–D progress from caudal to rostral with A ~ 400 μm caudal and D ~ 900 μm rostral to obex. In contrast to the pattern of labeling following injections ventral to the facial nucleus (Fig. 4), there was only light retrograde labeling of most caudal NTS nuclei. An exception to this light labeling was the considerable FG labeling of cells in the central NTS nucleus (SolCe in D), particularly due to involvement of the AmbC by the FG injection (Cunningham and Sawchenko, 2000). Additionally, moderately dense retrograde labeling of the intermediate NTS nucleus (SolIM) was seen after the FG, but many fewer neurons after the FB injection. Significant FG and FB labeling of cells in the dorsal reticular formation is also evident in C and D, likely representing premotor neurons to the facial nucleus (Travers and Norgren, 1983). EMG in inset shows inspiratory motor activity. ECG activity was manually reduced on the EMG trace to facilitate visualization of the respiratory cycle.