Effects Of Mecobalamin On Spinal Neuronal Apoptosis And Pain Following Sciatic Nerve Ligation In Rats

Objective The objective of this study was to determine whether sciatic nerve ligation induces spinal neuronal apoptosis and to observe the effects of mecobalamin on spinal neuronal apoptosis and pain after sciatic nerve ligation in rats.Methods Sixty-six healthy adult male wistar rats weighing 230-250g were anesthetized with ethyl urethane (6ml/kg) and subjected to ligate sciatic nerve. Animals were randomly divided into three groups: model group (n=30), mecobalamin-treated group (n=30) and sham-operated control group (n=6). Pain behaviors were recorded by using the von Frey test at -1 day, 6 hours, 1, 3, 7 and 14 days after surgery . Pathologic methods were used to evaluate the degree of spinal injury. The expression levels and distribution of TNF-α and IL-6 were detected by immunohistochemical technique respectively. Apoptosis of spinal neuron was observed by TdT-mediated dUTP-biotin nick end labelling (TUNEL).Results The pathologic lesion of spinal cord was significantly attenuated in mecobalamin-treated group compared with that in model group. In model group, the expression of TNF-α, which quickly up-regulated after injury and reach the maximum on day 1 after injury, was positive in non-injuryed spinal cord tissue; IL-6 was first detected in spinal cord on day 1 after injury, thereafter, reaching the peak on day 3 after injury(P<0.01) . The levels of TNF-α and IL-6 in spinal cord tissue were obviously higher in model group than those in mecobalamin-treated group at the corresponding time points(P<0.05); In contrast to in control group, the expressions of TNF-α and IL-6 were significantly increased in mecobalamin-treated group and model group at the corresponding time points (P<0.05). In model group, a small quantity of labeled apoptosis cells were detected on 6 hours and day 1 after sciatic nerve ligation and the number of apoptosis cells reached the peak on day 3 after injury, the apoptosis cells content remained elevated on day 3 and returned to baseline levels again by day 14 after crush; The level of apoptosis cells in spinal cord tissue in mecobalamin-treated group was markedly reduced than that in model group and there existed significant difference between mecobalamin-treated group and model group(P<0.01). Behavior Test: Compared to control group, there were mechanical hyperalgesia and allodynia in mecobalamin-treated group and model group, and the differences were significant (P<0.01); and there also was significant different between mecobalamin-treated group and model group(P<0.01).Conclusions Sciatic nerve ligation can lead to spinal neuronal apoptosis, and is associated with the development and maintenance of neuropathic pain. Mecobalamin can effectively inhibit spinal neuronal apoptosis in dorsal horn of rats and prominently relieve pain, and the mechanism maybe have relate to suppression of the overexpression of TNF-α and IL-6 in spine cord .