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: The present study was initiated 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-five healthy male Sprague-Dawley rats (200-270g) were randomly devided into five groups(n=5,in each group): control group(group C1 and group C2),normal saline group(group NS), butorphanol 12μg group(group B1), butorphanol 24μg group(group B2).There weren't operative procedure in group C1 rats.The rats in other four groups were anesthetized with 10% Chlroral Hydrate and a microapinal catheterwas insterted intrathecally into the lumbar region(about 8cm) according to the method of Yaksh. After 5 days, group C2 involved exposure of the sciatic nerve and its branches without any lesion;the rats in group NS,group Bland group B2 received a lesion of two of the three terminal branchesof the sciatic nerve(tibial and common peroneal nerves) leaving the remaining sural nerve intact (the spared nerve injury model,SNI).group C2,group NS,groupB1 and group B2 were intrathecally injected 2014 normal saline or 10μl butorphanol(12μg and 24μg) followed by 10μl 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: (1) In group C1 and group C2,there were no difference on the statistics in pain threshold (P>0. 05 ) ; (2) There were significant difference on the statistics in pain threshold in group NS,B1,B2 as comparede with that in group 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 comparede with that in group C1,C2 (P>0. 05 ) ; (3) In group B2,there was significant difference on the statistics in pain threshold 30min post-injection when compared to pre-injection levels (P <0. 01), the radiant heat stimulus paw withdrawal latency was also noticeable prolonged (P<0. 05); (4) 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). The number of immunoreactive soma in group B1and B2 becreased significantly compared with that in group NS,and there was also difference between group B1 and B2 (P<0. 05);(5) The immunoreactive soma quantity density of NMDAR was higher in group NS than those in group C1 and C2(P<0. 05),but the quantity density in group B1and B2 were lower than that in the group NS,and between group Bland 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: (1) Hyperpathia may be caused in the injured side limbs of rats following spared nerve injury of sciatic nerve; (2) Intrathecal butorphanol (24μg) can lessen hyperalgia of neuropathic pain and the dosage was correlation with the effect ; (3) 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.