Fig. 1. Pain rating utilizing the weighted scores technique for 60 min following peripheral injection of saline, formalin, or zymosan subcutaneously in the left hind plantar paw. Lower scores represent fewer spontaneous pain behaviors. Negative time represented baseline behaviors for 15 min prior to injection. Time zero represented 5 min after injection to allow the animals to recover from anesthesia. The graph shows the average ± SEM pain rating for each group for 2 min out every 5 min.

Fig. 2. Time course for mechanical allodynia in the insulted hindpaw following subcutaneous saline, formalin, zymosan, or L5 spinal nerve transection. Plotted are the average ± SEM responses to 30 stimulations with a 12 g von Frey filament.

Fig. 3. Ipsilateral (B,D) and contralateral (A,C) L5 spinal sections with OX-42 labelling activated microglia. Seven days following L5 spinal nerve transection (A,B) there was focal dorsal and ventral horn microglial activation which was confined to the ipsilateral side while at 1 h post zymosan injection (C,D) there was mild microglial activation across both the ipsilateral and contralateral spinal cord (bar=500 μm).

Fig. 4. Ipsilateral dorsal and ventral horn OX-42 immunoreactivity was intense at seven days following L5 spinal nerve transection (A), very mild at 6 h following saline (B), very mild at 1 h following formalin (C), and moderate at 6 h following zymosan (D). OX-42 IR following saline, zymosan, or formlin peripheral injection was similar on both ipsilateral and contralateral sides. Bar=500 μm.

Fig. 5. Ipsilateral dorsal horn GFAP immunoreactivity was moderate with many condensed astrocytes at seven days following L5 spinal nerve transection (A), very mild at 6 h following saline (B), and mild with several less ramified astrocytes at both 1 h following formalin (C), and 6 h following zymosan (D). Bar=100 μm.

Fig. 6. IL-1β immunoreactivity (red–brown) co-labeled to the neuronal marker NeuN (blue–grey) in both the dorsal (A) and ventral horn (B–D) of the spinal cord at 1 h following peripheral hindpaw formalin injection. IL-1β did not co-label with every neuron. (A) and (B) bar=100 μm, (C) bar=50 μm, (D) bar=25 μm.

Fig. 7. Ipsilateral dorsal and ventral horn exhibited mild reticular and neuronal IL-1β immunoreactivity at seven days following L5 spinal nerve transection (A), normal reticular and neuronal staining at 6 h following saline (B), and mild reticular staining with moderate neuronal staining at both 1 h following formalin (C), and 6 h following zymosan (D). IL-1β immunoreactivity did not require microglial activation and the contralateral side exhibited similar morphology as the ipsilateral side in all injury models. Bar=500 μm.

Table 1. Tactile sensitivity, spinal glial response, and spinal IL-1β immunoreactivity following L5 spinal nerve transection or peripheral injection of 200 μl saline

Table 2. Tactile sensitivity, spinal glial response, and spinal IL-1β immunoreactivity following peripheral injection of 50 μl formaline

Table 3. Tactile sensitivity, spinal glial response, and spinal IL-1β immunoreactivity following peripheral injection of 200 μl zymosan