Pain-related mediators underlie incision-induced mechanical nociception in the dorsal root ganglia

Approximately 50-70% of patients experience incision-induced mechanical nociception after surgery. However, the mechanism underlying incision-induced mechanical nociception is still unclear. Interleukin-10 and brain-derived neurotrophic factor are important pain mediators, but whether interleukin-10 and brain-derived neurotrophic factor are involved in incision-induced mechanical nociception remains uncertain. In this study, forty rats were divided randomly into the incision surgery (n = 32) and sham surgery (n = 8) groups. Plantar incision on the central part of left hind paw was performed under anesthesia in rats from the surgery group. Rats in the sham surgery group received anesthesia, but not an incision. Von Frey test results showed that, compared with the sham surgery group, incision surgery decreased the withdrawal threshold of rats at 0.5, 3, 6 and 24 hours after incision. Immunofluorescence staining in the dorsal root ganglia of the spinal cord (L3-5) showed that interleukin-10 and brain-derived neurotrophic factor were expressed mainly on small- and medium-sized neurons (diameter < 20 μm and 20-40 μm) and satellite cells in the dorsal root ganglia of the spinal cord (L3-5) in the sham surgery group. By contrast, in the surgery group, high expression of interleukin-10 and brain-derived neurotrophic factor appeared in large-sized neurons (diameter > 40 μm) at 6 and 24 hours after incision surgery, which corresponded to the decreased mechanical withdrawal threshold of rats in the surgery group. These experimental findings suggest that expression pattern shift of interleukin-10 and brain-derived neurotrophic factor induced by incision surgery in dorsal root ganglia of rats was closely involved in lowering the threshold to mechanical stimulus in the hind paw following incision surgery. Pain-related mediators induced by incision surgery in dorsal root ganglia of rats possibly underlie mechanical nociception in ipsilateral hind paws.