Figure 4

Prevention of nerve injury-induced expression of c-Fos protein in the spinal cord by pre-injury administration of morphine. A,B: Only a few c-Fos-positive neurons were found the spinal dorsal horn of control sham-operated mice. C: At 7 days following peripheral nerve injury, numerous c-Fos-positive cells were observed in most dorsal horn laminas of ipsilateral side of the spinal cord. D: Some c-Fos-positive cells were also observed in the contralateral side. E,F: Pre-injury administration of 10 mg/kg of s.c. morphine prevented the injury-induced expression of c-Fos in the spinal dorsal horn. G: Histogram of the number of c-Fos positive cells in ipsi- and contralateral sides of sham-operated (sham), nerve-injured (NI) and pre-injury morphine treated (Pre-morp) mice from three animals of each treatment group taking three sections from each animal. * p < 0.05 indicates statistically significant difference compared between the ipsilateral sides of sham and nerve-injured mice. # p < 0.05 indicates significant compared between the ipsilateral sides of the nerve-injured and pre-injury morphine treated mice. Scale bar represents 100 μm for all images.