Dynamics of ultrastructural changes in sciatic nerve traction injury in an experiment

Background. The need to improve approaches to the diagnosis and treatment of combat trauma victims is extremely urgent, given the significant number of patients with severe polystructural injuries, including peripheral nerve trauma. Such injuries are often accompanied by a high level of complications and disability, which requires the creation of new and optimization of existing methods of providing medical care. Traction injuries of the peripheral nerve caused by stretching often lead to unsatisfactory functional outcomes. Studying the functional and structural changes that affect the likelihood and quality of recovery after such injuries is of utmost importance, because valid model of nerve traction injury will allow studying the effect of regenerative therapy. The purpose was to compare ultrastructural cell characteristics and changes in sciatic nerve traction injury in an experiment. Materials and methods. After general anesthesia in aseptic conditions, surgical approach to sciatic nerve in white outbreed male rats (250 ± 50 g) and sciatic nerve stretching was performed using a specially designed device. The animals were divided into groups depending on the observation period: 15 days after injury (n = 10), 30 days (n = 10), 60 days (n = 10) and the control group (sham-operated) (n = 6). All of them underwent a surgical procedure to isolate the sciatic nerve after causing traction injury for its further analysis and were removed from experiment by injection of lethal dose of anesthetics. The sciatic nerve tissue was examined at the ultrastructural level using electron microscopy to assess morpho-functional compensatory-adaptive reactions. Results. On day 15, the nerve fiber density in the proximal segment of the sciatic nerve was 177 (168; 194), and in the distal segment — 175 (152; 203), which was statistically significantly lower compared to the control group (287 (276; 292)), by 1.6 times for both segments. The myelin sheath to axial cylinder ratio was 0.389 (0.345; 0.515) in the proximal segment and 0.435 (0.360; 0.494) in the distal segment, which was statistically significantly higher than the value of the control group (0.292 (0.262; 0.320)), by 1.3 and 1.5 times, respectively. On the 30th day, in the proximal part of the sciatic nerve of the animals, the nerve fiber density was 258 (248; 274), and in the distal part — 243 (236; 269) that was statistically insignificant compared to the control group. On day 60 of the study, a statistically significant decrease in the myelin sheath to axial cylinder ratio was recorded in the proximal segment to 0.257 (0.190; 0.335) and in the distal one — to 0.292 (0.250; 0.356), which is 1.5 times lower than on day 15 for both segments. Conclusions. In case of traction nerve injury, structural changes and disruption of order in the proximal and distal segments of the sciatic nerve are observed, which depend on the time after injury. In the early stages, there were cell swelling, reduction of intercellular spaces, axoplasmic lightening of myelinated axons, and loss of part of the cytoskeleton (microtubules and neurofilaments). The morphogenesis of peripheral nerve injury requires further research to develop effective treatment strategies, including regenerative therapy.