Effects of intrathecal butorphanol on rat′s pain threshold and changes of neuronal NMDA receptor expression in rat spinal dorsal horn following spared nerve injury of sciatic nerve

[Objective] To observe the changes of neuronal NMDA receptor expression in rat spinal dorsal horn following spared nerve injury of sciatic nerve by using immunohistochemistry method. [Methods] Fifteen healthy male Sprague-Dawley rats (200~270 g) were randomly devided into three groups(5 in each group): control group(group C1 and group C2), normal saline group(group NS). There weren′t operative procedure in group C1 rats. The rats in other two groups were was insterted intrathecally into the lumbar region(about 8 cm) according to the method of Yaksh. After 5 days, the rats in group NS were made into the spared nerve injury model (SNI). Group C2 involved exposure of the sciatic nerve and its branches without any lesion; group C2, NS were intrathecally injected 20 μL normal saline or 10 μL Butorphanol (12 μg and 24 μg) followed by 10 μL normal saline after 2 days post-surgery, respectively. Mechanical allodynia and radiogenic heat pain thresholds were measured pre-surgery and on day 1, 2 post-surgery and 30 min after intrathecally injection. 2 hours after intrathecally injection, all rats were killed, and the L5 spinal cord were dissected for determination of the expression of NMDA receptor using immunohistochemical techniques. [Result] In group C1 and group C2, there were no difference on the statistics in pain threshold (P 0.05). ②There were significant difference on the statistics in pain threshold in group NS and C1, C2 (P 0.01) on day 1,2 post-surgery, but the radiant heat stimulus paw withdrawal latency was no change in three groups compared with that in group C1, C2 (P 0.05). The number of immunoreactive soma in the superficial laminae of the L5 spinal cord was significantly incressed significantly in group NS than that in group C1 and group C2(P 0.05). ④The immunoreactive soma quantity density of NMDAR was higher in group NS than those in group C1 and C2 (P 0.05), The immunoreactive soma optical density of NMDAR was higher in SNI model group than that in control group (P 0.05). [Conclusions] Hyperpathia may be caused in the injured side limbs of rats following spared nerve injury of sciatic nerve; The expression of NMDA receptor in spinal cord is up regulated following spared nerve injury of sciatic nerve in rats and intrathecal butorphanol can restrain this change.