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 effect of intrathecal Butorphanol on rat's pain threshold and changes of nervronal NMDA receptor expression in rat spinal dorsal horn following spared nerve injury of sciatic nerve by using immunohistochemistry method. [Methods] Twenty healthy male Sprague-Dawley rats (200~270 g) were randomly devided into four groups (n =5,in each group): control group (group C), normal saline group (group NS), Butorphanol 12 μg group (group B1), Butorphanol 24 μg group (group B2). A microapinal catheter was insterted intrathecally into the lumbar region (about 8 cm) according to the method of Yaksh. After 5 days, group C involved exposure of the sciatic nerve and its branches without any lesion. the other groups were made to the spared nerve injury model (SNI).group C, group NS, groupB1 and group B2 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. 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] 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 C (P 0.05). The number of immunoreactive soma in group B1 and B2 increased significantly compared with that in group NS, and there was also difference between group B1 and B2 (P 0.05). The immunoreactive soma quantity density of NMDAR was higher in group NS than those in group C (P0.05), but the quantity density in group B1and B2 were lower than that in the group NS, and between group B1 and B2 the quantity density was also different (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] Intrathecal Butorphanol (24 μg) can lessen hyperalgia of neuropathic pain and the dosage was correlation with the effect. 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.