Labeling of pVIIIn and RS neurons. RS neurons (green) and pVIIIn (orange) were labeled with Oregon Green 488 and DiI, respectively. A, Two adjacent 80 μm sections were superimposed where axons and lateral dendrites of bilateral M-cells (green) and right pVIIIn (orange) were labeled. Four fascicles of pVIIIn (asterisks) were observed to project medially to where lateral dendrites of the M-series neurons likely exist (compare Fig. 3). The first bundle projected to the vicinity of the distal region of the M-cell lateral dendrite. The second and fourth bundles appeared to project into r5 and r6, respectively (also see C). Another bundle descending along the lateral edge of the brain was labeled. The dashed line indicates the midline. B, Higher-magnification image of the inset in A. The pVIIIn afferents appeared to contact the distal part of the M-cell lateral dendrite (arrowheads). C, Eight serial sections were superimposed, including two dorsal sections shown in A. Somata of dorsal RS neurons in r4–r6 were labeled. Rostral is up. Scale bars, 200 μm.