Role of interleukin-12 in spinal cord in maintenance of arthritic pain in rats

Objective To evaluate the role of interleukin-12 (IL-12) in the spinal cord in the maintenance of arthritic pain (AP) in rats. Methods Adult male Sprague-Dawley rats, aged 6-8 weeks, weighing 200-300 g, were randomly divided into 4 groups using a random number table: control group (group C, n= 6); AP group (n= 9); phosphate buffer solution (PBS) group (n= 6); IL-12 antibody group (n= 6). AP was induced by injecting 50 μl of complete Freund's adjuvant into the ankle joint cavity of the left hindpaw of rats anesthetized with isoflurane.Goat anti-rat IL-12 antibody 1.50 μg (20 μl) was intrathecally injected on 9 days after establishment of the model in group IL-12 antibody, while 0.01 mol/L PBS (20 μl) was administered in group PBS.The mechanical paw withdrawal threshold to von Frey filament stimulation (MWT) was measured before establishment of the model (baseline) and on 9 and 10 days after establishment of the model.The rats were sacrificed after the last measurement of pain threshold, and the L4-6 segments of the spinal cord were obtained for detection of IL-12 expression in the spinal dorsal horn (by immunofluorescence), and the co-expression of IL-12 and glial fibrillary acidic protein (an astrocyte marker) was examined simultaneously in group AP. Results Compared with group C, the MWT was significantly decreased, and the expression of IL-12 was up-regulated on 9 and 10 days after establishment of the model in AP, PBS and IL-12 antibody groups.Compared with group AP, the MWT was significantly increased at 10 days after establishment of the model, and the expression of IL-12 was down-regulated in group IL-12 antibody, and no significant change was found in the MWT at 10 days after establishment of the model and expression of IL-12 in group PBS.IL-12 was co-expressed with glial fibrillary acidic protein in group AP. Conclusion IL-12 in the spinal cord is involved in the maintenance of AP in rats. Key words: Spinal cord; Interleukin-12; Arthritis; Pain