Effect of intrathecal morphine and ketamine on substance P expression in the dorsal horn of neuropathic rats

Objective To study the effect of intrathecal morphine and ketamine on substance P(SP)immunohistochemical staining in the dorsal horn of neuropathic rats.Methods 12 wistar rats weighing 220～260 g were prepared for placing loosely constrictive ligatures around the common sciatic nerves,and intrathecal implantation of a catheter.The rats were randomly allocated into four groups(n=3):group B(vehicle,no drugs available),group C(saline 10 μL),group M(morphine 20 μg),group KM(morphine 10 μg and ketamine 25 μg).Morphine and ketamine were administrated intrathecally once a day for 7 days on the forth day after operation 7 days later,the rats were decapitated and the lumbar spinal cord were removed.SP in spinal cord were measured by immunohistochemistry.Results Immunostaining density of SP in group C decreased compared with group B(P0.05)and group KM(P0.01).SP staining density in group KM was significantly higher than that in group M(P0.01).Conclusion The antinociceptive mechanism of intrathecal morphine and ketamine was related to the increase of SP staining in lumbar spinal cord,however decrease of SP in spinal cord may mediate pain sensitivity after chronic sciatic nerve injury.