Effect of dexmedetomidine on spinal neuronal nitricoxide synthase and substance P mRNA expression in rat model of incisional pain

Objective To investigate the analgesic effect of dexmedetomidine on rat model of incisional pain and the expression of neuronal nitricoxide synthase (nNOS) and substance P (SP) in the spinal cord.Methods Twenty-four adult male Wistar rats weighing 250-300 g were randomly divided into four groups with six rats in each groups:group S was sham operation group,group O was operation control group,group D1 received 30 μg/kg dexmedetomidine,and group D2 received 50 μg/kg dexmedetomidine. All groups were given corresponding drugs 10 min pre-operation. The rats received longitudinal incision in the left hindpaw to establish pain model. The cumulative pain score (CPS) and paw withdrawal threshold (PWT) were measured in each group to evaluate the pain magnitude. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to examine nNOS and SP expression in the spinal cord.Results The CPS in group O and D1 were significantly increased and MWT were significantly decreased after operation compared with those before operation (P0.05). The CPS in group O was significantly higher and the MWT was significantly lower than those of the other 3 groups after operation (P0.05). The CPS in group D2 was significantly lower and MWT was significantly higher than those of group D1 after operation (P0.05),and there was no significant difference between D2 and group S. The expression of nNOS and SP mRNA was significantly higher than that of the other 3 groups (P0.05),and that of group D1 was significantly higher than that of group D2 and S (P0.05).Conclusion Dexmedetomidine has an obvious analgesic effect on incisional pain in rats and the effect increases with the dose of Dexmedetomidine. The analgesic effect Dexmedetomidine is possibly related to the decrease of nNOS and SP mRNA in the spinal cord.