Figure 5.

Pacemakers engage spinal networks innervating hindlimb extensor muscles in the neonatal rat. A, Pacemaker axonal boutons (magenta) are in close apposition to a GFP-expressing soma (green) in the deep dorsal horn following PRV-152 injection into the quadriceps muscles. Scale bar = 50 μm. B, Single 0.5 μm optical sections showing higher magnification of the boxed region in panel A, illustrating putative sites of contact between the pacemaker axon and the PRV-infected cell (arrows). Scale bar = 10 μm. C, A pacemaker axon branches extensively in the vicinity of numerous PRV-infected cells located in the deep dorsal horn. Scale bar = 20 μm. D, Higher magnification of the boxed region shown in C (single 0.5 μm optical sections) reveals multiple putative contacts between the axon of the pacemaker neuron and a GFP-expressing cell (arrows). Scale bar = 10 μm. E, Example of a pacemaker axon in close association with a PRV-infected soma in the spinal ventral horn. Scale bar = 50 μm. F, Single 0.5 μm optical sections showing higher magnification of the boxed region in E. Scale bar = 10 μm. G-J, Examples of electrophysiologically identified lamina I pacemaker neurons that were infected with PRV-152 at 52 hours following virus injection into the left quadriceps, as evidenced by the co-localization (H3, J3) of biocytin labeling (H2, J2; magenta) and GFP expression (H1, J1; green). Scale bars = 100 μm. H, J, Single optical sections (0.5 μm thickness) showing higher magnification of boxed regions in panels G and I, respectively. Scale bars = 20 μm.