In our earlier pre-experiments, the female rats had a lower infection rates and mortality than male rats. In order to ensure the consistency of the spinal cord injury model, we use the same sex rats and female SD rats were selected. The present study demonstrates that the anatomical recovery of injured area of the spinal cord made possibly by the x-ray treatment. However, the SCI rats exhibited no differences between the x-ray treatment group and sham-operated group at each point of observation (6 and 14Â weeks after SCI) in the physiological observations, the BBB scores, and the SEP testing in our study. We suppose that the injuries of the rats may have been excessive, and subsequent histological examination also confirmed this conclusion. Neural axon is the basic function unit of spinal cord. In our study, the NF count of irradiation groups increased significantly than that of the sham groups, but the total quantity might not be enough, and all the experimental animals exhibit serious movement dysfunction so there are no differences among each group in the BBB scores and the SEP testing.
As we know, NF, MBP, and GFAP are classic histological indicators of the spinal cord. In our study, the NF staining count in the x-ray treatment group (including the 10- and 20-Gy group) was significantly increased relative to the sham-operated group at 6 and 14Â weeks after SCI. No statistical significance was shown between the two radiation groups at each observation point. The results indicated that the irradiation treatment might promote the regeneration of the spinal cord central nervous system (CNS). In the sham-operated group, the NF count was increased notably at 14Â weeks relative to that at 6Â weeks, which showed that the spinal cord CNS has a self-repair mechanism after SCI. This process lasted at least 14Â weeks. X-ray irradiation likely sped up the process and promoted the regeneration and rehabilitation of the spinal cord CNS to a certain extent. In this study, there was no significant difference between the 10- and the 20-Gy group. The experimental results were slightly different from those of Kalderon [1, 2, 4]. In the meantime, the neuromotor function and SEP inspection results showed no difference between sham-operated and x-ray treatment groups, which suggested that the quantity change did not match the qualitative change. Of course, the detection time was also not long enough [10, 11].
Myelin is a necessary structure of the CNS cells, and it might play a role in preventing the regeneration of nerves. Further research showed that the myelin-related protein Nogo-A could inhibit the regeneration of axons in vitro and in vivo [12, 13]. Our study showed that the MBP count at 14Â weeks after SCI was increased significantly relative to that at 6Â weeks in the sham-operated group. On the contrary, it was decreased in the x-ray treatment groups (both the 10- and 20-Gy groups) as time went on. Meanwhile, we found that the MBP count of the sham-operated group was significantly reduced relative to the x-ray treatment group at 6Â weeks after SCI, and it increased at 14Â weeks after SCI. This result showed that myelin experienced a decrease first and then increased after SCI in rats. This outcome also indicated that the injury and repair of the spinal cord were existed together, being injured first and then repairing it. The myelin count was significantly reduced in the irradiation group at week 14 after SCI, which showed that ionizing radiation also has long-term effects on the spinal CNS; the duration of this effect needs further research. In addition, we found that irradiation might promote the regeneration of the spinal cord in rats, which cannot be explained by the myelin theory only. We found that when the myelin count in the irradiation group was significantly increased at 6Â weeks after SCI, Nogo-A did not concurrently increase. Possible inferences included the structure of the CNS tissue in early SCI, producing a sharp decay stage, while x-ray irradiation delayed the process and changed the tissue microenvironment, which was beneficial to the regeneration and rehabilitation of the CNS.
The GFAP monoclonal antibody could clearly indicate the normal and reactive astrocytes and the reticular structure of the spinal cord. The observed astrogliosis ultimately became an astrocyte glial scar. In our study, the glial scar gradually increased as time went on, while the irradiation group decreased relative to the sham-operated group during the same period (P??0.05). This result showed that x-ray irradiation reduced the glial scar hyperplasia of CNS to a certain extent.
Nogo-A was highly expressed in the CNS oligodendrocytes and myelin. This result showed that the Nogo protein inhibits axonal regeneration in vivo and in vitro [12, 13]. However, in our study, the expression of the Nogo protein exhibited no significant difference between the irradiated group and the sham-operated group, which showed that x-ray irradiation plays a multifaceted and complex role in CNS regeneration.