| Objective: To observe the influence on the ultramicrostructure of spinal cord and the expression of Bax and Bcl-2 in spinal cord of rats under intrathecal ropivacaine intermittently with different concentration, and to investigate whether mitochondrial apoptogenesis was involved in cellular induced by ropivacaine spinal neurotoxicity and provide theoretical fundation for the application of ropivacaine in intrathecal delivery.Methods: 72 male SD rats(weighed 280±16g) were successfully implanted with microspinal catheter following the methods of Yaksh .Animals were randomly assigned to two groups: group saline(Group N,n=18) and group ropivacaine(Group R,n=54).Group R was divided into three subgroups to receive either 0.5%, 0.75%, 1% ropivacaine with 0.12ul/kg ,which were respectively signed with Group R1(n=18), Group R2(n=18), Group R3(n=18) .Each rat was administered repeatedly per 1.5h.We observed the recovery time to ambulation and measured the threshold to noxious thermal and mechanical stimuli .At 6hr,12hr,24hr after administration ,six rats of each subgroup were killed and the lumbar spinal cord was removed .1mm~3 cornu posterius medullae spinalis and nerve root with a fixative solution was randomly obtained for observing the change of ultramicrostructure under transmission electron microscope. The remains was measured the Bax and bcl-2 expression by the method of immunohistochemistry.Results: 1. The recovery time to ambulation in group R3 were slower than subgroup R1 and R2 at each time point (P<0.05) .There is no difference at each time point in every group (P>0.05) .2. Myelin ovoid, swelling in intercellular substance and karyopycnosis in nerve cells shrinkage were observed with HE stain in subgroup of R3 at ghe time point of 12hr and 24hr. The cells under electron microscopy in Group N was normal. Mild edema of themitochondria and the endoplasmic reticulum were the major histopathologic changes in Group R1 and R2 . Local degeneration of both the myelin sheaths and axons was observed at the time point of 12hr and 24hr in subgroup of R2. The histologic abnormality in R3 group is significantly. The shrinkage of nucler membrane and vacuolar mitochondria were observed at each time point of group R3. The majority of the rough endoplasmic reticulum were serious swelling. local demyelination ,degeneration or disappearance of axon and edema of intercellular substance can also be observed. The changes in group 24hr is the most serious.3. The expression of Bax and Bcl-2 in Group N is low, began to increase in the subgroups R1 and R2 at the time point of 6hr and was significant at the time point of 12hr and such increase lasted until the time point of 24hr(the timepoint that we ended the observation). During the same period, the expression of Bcl-2 was also raised ,so Bcl-2/Bax ratio has no significant difference compared with group N (P> 0.05). Bax expression in R3 group was higher than the other groups at all time points (P <0.05), but the Bcl-2 expression were lower than group R1 or R2 (P <0.05) and the Bcl-2/Bax ratio were also low than the other three groups (P<0.05).Conclusion: 1. 0.5%, 0.75% ropivacaine with 24hr intrathecal injection intermittently may cause mild edema of themitochondria and the endoplasmic reticulum in a time and dose-depended way. 1% ropivacaine with 6hr intrathecal injection intermittently can elicit spinal neurotoxicity.2. Spinal expression of Bax began to increase six hours and keep increasing until 24 hours after injection of 1% ropivacaine. Spinal neurotoxicity was correlated with Bcl-2/Bax ratio .It suggested that mitochondrial apoptosis pathway may involved in spinal neurotoxicity of ropivacaine. |
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