Changes in the expression of neuromedin U receptor 2 in spinal dorsal horn in a rat model of bone cancer pain

Objective To investigate the changes in the expression of neuromedin U receptor 2 (NMUR2) in spinal dorsal horn in a rat model of bone cancer pain (BCP).Methods Thirty-two female Sprague-Dawley rats,weighing 150-180 g,were randomly divided into 2 groups (n =16 each):sham operation group (group S) and BCP group.BCP was induced by inoculating Walker 256 mammary gland carcinoma cells (1 × 105) into the medullary cavity of left tibia.Heat-killed Walker 256 cells (1 × 105) were injected into the medullary cavity of left tibia in S group.Eight rats were chosen from each group and the paw withdrawal threshold (PWT) to yon Frey filaments was measured at 1 day before operation (baseline) and 1,3,6,9,12 and 15 days after operation.Bone destruction was shown by X-ray at 15 days after operation.At 1 day before operation and 15 days after operation,4 rats in each were chosen and sacrificed,and L4,5 segments of the spinal cord were removed for measurement of the expression of NMUR2 mRNA (by real-time PCR) and protein (using Western blot analysis) in the spinal dorsal horn.Results Compared with S group,the PWT was significantly decreased at day 6-15 after operation and the expression of NMUR2 mRNA and protein in the spinal dorsal horn was up-regulated at 15 days after operation in BCP group (P ＜ 0.05 or 0.01).Compared with the baseline value,the PWT was significantly decreased at day 6-15 after operation and the expression of NMUR2 mRNA and protein in the spinal dorsal horn was up-regulated at 15 days after operation in BCP group (P ＜ 0.05 or 0.01).X-ray showed defect of bone trabecula and cortical bone destruction in BCP group.Conclusion The expression of spinal NMUR2 is up-regulated in rats with BCP and this change may be involved in the development and maintenance of BCP. Key words: Bone neoplasms ;  Pain ;  Receptors, neurotransmitter;  Spinal cord