Figure 2.

The dorsal ramus is a primary source of sympathetic sprouts in the DRG early after SNL. A: Composite whole mount DRG picture 3 days after (ventral ramus) spinal nerve ligation: showing extensive TH-fiber sprouting onto the surface of the DRG. Many of the sprouting fibers originate in the dorsal ramus onto the dorsal surface of the DRG. Scale bar 500 μm. B. Magnification of the boxed region in A, showing TH-positive fibers coursing from the dorsal ramus towards the DRG. Scale bar 100 μm. C. Whole mount image from another DRG on POD3, in the region on the edge of the DRG near the spinal nerve. TH-positive fibers are shown on the surface of the DRG originating primarily from the dorsal ramus. Scale bar 100 μm. At higher magnification (panel D; scale bar 20 μm), fibers surrounding individual neurons can be observed (* symbols), as previously described in sectioned DRG. Arrows indicate varicosities and growth cone-like structures. E. Image from more distal region of the same DRG on POD3, showing TH-positive fibers in the region of the dorsal ramus. Scale bar 100 μm. At higher magnification (F; scale bar 20 μm) examples of bifurcating or branching fibers can be observed (arrows). G. Schematic showing the proposed origin of sympathetic sprouts in the dorsal ramus after ventral ramus ligation (SNL). Neuron color scheme is as in Fig. 1. The dotted line represents a newly sprouted sympathetic fiber entering the DRG as a collateral from an intact sympathetic axon in the dorsal ramus. Wavy lines indicate fibers in the ventral ramus that have been severed by the SNL.